Zoo 115: Introductory Ecology Course Outline (2016/17) PDF

ZOO 115: INTRODUCTORY ECOLOGY COURSE DISTRIBUTION (2016/17) Weeks Contents Lecturer Introduction of the course. 1 The organism and the environment Prof. Ugwumba 41/2 Biotic and abiotic factors of the environment Dr. Oni Population and production ecology 1o, 2 o, 3 o Production 1 /2 Continuous Assessment Test All Staff Trophic levels 41/2 Food chains and food webs Dr. Sowunmi Population growth 2 Impact of man on the environment Prof. Ugwumba 1 /2 Continuous Assessment Test All Staff DEFINITION OF ECOLOGY ❑ Ecology: It is basically, the study of relationships between organisms and their environment ❑ Ecology can be one of two types: Autecology is the study of the ecology involving one species Synecology is the study of ecology involving more than one species or a group of species ❑ In any ecological study, there are: Biotic (living) component and Abiotic (non-living) component of the environment DEFINITION OF ORGANISM An organism is a living thing at some point in time, that can respond to stimuli, grow, reproduce and it is capable of regulating and maintaining constant internal conditions of it’s body in a process known as homeostasis i.e. it is capable of maintaining a constant internal environment. TYPES OF ORGANISMS Organisms can be: Plants (multicellular, photosynthetic, and they have tissue differentiation) Animals (multicellular, non-photosynthetic, nutrition is holozoic, and they have tissue differentiation) Fungi (multinucleate mycelial plants, non-photosynthetic, nutrition is absorptive; have little or no tissue differentiation Protists or Protoctists (unicellular or acellular plants and animals, they are photosynthetic, their nutrition is also holozoic and absorptive) Bacteria (unicellular with no organelles, nutrition is absorptive) Viruses (made of a strand of DNA or RNA (i.e. nuclei acid) inside a protein coat; they cannot grow or reproduce outside their hosts cells and so they are obligatory) Organisms are important components of Ecology DEFINITION OF ENVIRONMENT An environment is the sum total of the assemblage of all the external factors affecting an organism. These factors of the environment may be: Biotic factors i.e. living Abiotc factors i.e. non-living TYPES OF ENVIRONMENTS There are different types of environments: Aquatic Terrestrial Aboreal Internal AQUATIC ENVIRONMENT This is an environment that is abound with water. The aquatic environment covers most of the earth’s surface Types of Aquatic environment: 1. Marine Environment where the salinity is very high, about an average of 35‰ e.g. oceans and seas It covers about 70% of the earth’s surface and contains about 98% of the earth’s waters. An example is Atlantic Ocean that washes the Nigerian coast Types of Aquatic Environment Cont. 2. Freshwater Environment where salinity is very low, it can be less than 1‰ Freshwater can be: Lotic i.e. fast moving/flowing like fivers and streams e.g. River Niger, Ogunpa River Lentic i.e. Slow moving or ‘standing’ water like lakes and reservoirs e.g. Kainji Lake, Awba Reservoir (in UI) Wetlands which are areas not usually covered by water but are saturated with water. They are mostly freshwater and are often used to plant crops during the dry season 3. Brackishwater Environment where salinity is in-between freshwater and marine environments. It is where freshwater and marine water meet. Salinity can be as high 35 ‰ at the peak of the dry season or at the peak of influx of marine water; Salinity can also be as low as 1‰ or less at the peak of the rainy saeson Examples of brackishwater are lagoons and estuaries e.g. Laogos Lagoon, Niger Delta Types of Aquatic Environment Cont. 4. Sub-aquatic Environment which is underground water The major problem that organisms face in the aquatic environment is hydration and so aquatic organism have adaptations to prevent hydration e.g scales of fisf TERRESTRIAL ENVIRONMENT This environment is on dry land. It is the habitat of man and it is the part of the environment that is most affected by man. Types of Terrestrial Environment: In this part of the world, terrestrial Environment are: 1. Forests made of mainly trees. The tropical rainforest is the richest in the world because it supports a variety of ecosystems as found in southern Nigeria 2. Savannah largely made of grasses with shrubs and scattered tree as found in northern Nigeria 3. Desert which are mainly sandy, dry and hot e.g Sahara Desert 4. Mountains which stretches above the surrounding in a particular area The majors problem organisms face is desiccation and so the have adaptations to prevent drying-up e.g shell of animals, hard barks of plants Aboreal Environment which is in the atmosphere and tree canopies and it home for flying and creeping and climbing plants and animals e.g birds, insects, bats, epiphytes Most aboreal animal are capable of flight Internal Environment which is within organisms e.g body fluids e.g. blood, tissue fluids like cerebrospinal fluid, synovial fluids etc. The environment has been adversely affected by anthropogenic activities which has not only degraded the environment but has wiped out many species over time. Presently, many species are threatened with extinction e.g apes DEPARTMENT OF ZOOLOGY, UNIVERSITY OF IBADAN, IBADAN. ZOO 115: INTRODUCTORY ECOLOGY LECTURER: DR. ADEOLA A. ONI SCHEDULED OUTLINE Week 2 & 3: Biotic and Abiotic factors; Week 4: Population Ecology; Week 5: Production: 1o, 2o and 3o Production THE ECOSYSTEM: BIOTIC AND ABIOTIC FACTORS Ecosystems are made up of two basic components: – biotic (from grk. “biotikos” which means “pertaining to life”) living e.g. producers such as plants, algae etc and consumers such as grasshoppers, goats, lions, humans; detritivores such as dung beetles, and decomposers such as bacteria and fungi etc); – and abiotic (i.e. not pertaining to life or the non-living components e.g. temperature, rainfall, light intensity, pH, salinity, and the physical environment such as water, soil, air etc) components – Both biotic and abiotic factors interact with each other to form a stable system. THE ECOSYSTEM: LEVELS OF COMPLEXITY LEVELS OF COMPLEXITY WITHIN THE ECOSYSTEM: ORGANISMS (made up of individual organisms be it unicellular (e.g. Paramecium) and multicellular organisms (e.g. grasshopper such as Zonocerus variegatus). POPULATION (group of organisms of the same species - [organisms that can interbreed to produce viable offspring] that are found in a particular geographical area at a particular time). COMMUNITY (group of varied populations found living within the same area). THE ECOSYSTEM: LEVELS OF COMPLEXITY LEVELS OF COMPLEXITY WITHIN THE ECOSYSTEM (CONT.): ECOSYSTEMS (a geographic area where all organisms - [flora, fauna and microbes], the environment and weather conditions work or interact together to form a stable system). They are responsible for the cycling of nutrients and allowing energy to flow from the sun to the biotic components. BIOME (a type of ecosystem characterized by a large land area or major ecological community with distinct climate or environmental conditions, and peculiar flora and fauna suited or adapted to such areas) Examples of biomes include the tropical rainforest, temperate forest, desert, tundra, savanna etc. BIOSPHERE (the parts of the earth where life exists, which are the atmosphere [air], the land [lithosphere], and the water [hydrosphere] BIOTIC FACTORS: GROUPING ACCORDING TO THEIR TROPHIC / FEEDING RELATIONSHIPS: Autotrophs (“self-feeders”) – Photo-autotrophs: Producers such as plants, algae, etc. They utilize energy from sunlight, carbon dioxide and water and light- capturing pigments such as chlorophyll to synthesize their own food (glucose) with oxygen and water given off as by- products (Photosynthesis). – Chemo-autotrophs: Organisms that transform inorganic chemicals into energy sources that they use for their survival, growth and reproduction. This include certain bacteria such as sulphur bacteria e.g. Sulfolobus found at the bottom of deep oceans obtains its food/energy requirements via the oxidation of elemental sulphur. BIOTIC FACTORS: GROUPING ACCORDING TO THEIR TROPHIC / FEEDING RELATIONSHIPS: Autotrophs (“self-feeders”) – Other examples of Chemoautotrophs: Methanogens e.g. Methanobacterium (i.e. bacteria found in cattle dung and anaerobic sludge during sewage treatment); utilize molecular hydrogen (H2) produced during bacterial and eukaryotic carbohydrate fermentation as their primary energy source. – Other examples include nitrogen fixing bacteria or nitrifiers e.g. Nitrosomonas and Nitrobacter which get their energy requirements from the oxidation of inorganic nitrogen compounds. Heterotrophs (“other-feeders") – They obtain their own food/energy requirements from producers and organisms that feed on them (consumers) or from dead and decaying plants and animals (detritivores and decomposers). BIOTIC FACTORS: GROUPING Heterotrophs (cont.) – Consumers: obtain their food (energy and protein requirements) by grazing on plants or feeding on other animals or both, or on dead and decaying flora and fauna. Consumers are sub-divided into macro and micro consumers. 1o consumers (Herbivores such as goats, sheep, grasshoppers) feed on producers 2o consumers (Carnivores such as lions, leopards, lizards) those that feed on 1o Macro- consumers consumers (all types 3o consumers (Omnivores such as humans); 2nd level carnivores are carnivores of animals) that feed on other carnivores e.g. snakes feeding on lizards); feed on secondary consumers Detritivores (dung beetles, housefly; act by ingestion of food, digestion / breakdown and finally nutrient absorption. By their feeding activities, they break down dead and decaying plant and animal matter into smaller bits to increase the surface area for more efficient action by the decomposers). Decomposers (bacteria and fungi; they act by release of enzymes for external breakdown or digestion followed by absorption of nutrients). Detritivores and Micro- decomposers in the process also convert the organic material contained in dead consumers or decaying matter into inorganic nutrients. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Introduction to biotic relationships: the ecological niche Within the ecosystem, each organism has a place where it lives (habitat), has ways of obtaining its food (nutrition) and is involved in interactions with other organisms. The ecological niche of an organism includes the habitat of an organism, nutrition (how it obtains its food) and the relationships it is involved in with other organisms within the ecosystem. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Consider a typical example of a lion found on savanna grasslands. It obtains its food by feeding on other animals such as the antelope, the deer etc. It is involved in predator-prey interactions, thus we can conclude that its role in the ecosystem is as a predator. Thus, the ecological niche of an organism in simple terms is the role it plays in the ecosystem. When two organisms have the same ecological niche, overlap of ecological niches will occur leading to competition for resources such as food, space, mates etc. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Competition – Competition results when there is an overlap in the ecological niches of organisms. Organisms may compete for food, space, water, mates etc. Competition is of two types: – Interspecific competition: This is competition between two or more organisms of different species. For example, competition between a hyena, a jackal and a vulture for the carcass of a dead animal (Fig. 1). – Intraspecific competition: This is competition between two or more organisms of the same species. It could be for food, space or even mates., e.g. competition between two male peacocks for a female for the purpose of mating. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Inter-specific competition Fig. 1: Hyena, jackal and vultures competing for a carcass Photo credit: www.alamy.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Apart from competition, other examples of biotic interactions include: – Intraspecific associations between organisms of the same species such as mating, parent-offspring behavior (parental care), aggression etc. (Figs. 2-4). – Predator-prey interactions (Figs. 5-8) and; – Symbiotic relationships (Figs. 9-16) Predator-prey interactions: This kind of interaction involves two organisms, the predator which kills and eats another organism known as the prey. Examples of such interactions include: – Sea stars (Asterias sp.) and Mussels (Mytilus sp.). – The Cheetah (Acinonyx jubatus) preying on the gazelle (Gazella dorcas) BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Intra-specific associations Fig 2a: A peacock showing its brightly colored feathers to attract a peahen for mating; peacocks often jostle for the attention of the female for mating. Photo credit: www.differencebetween.net BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Intra-specific associations Fig 2b: A male Frigate bird (Fegrata sp.) displaying its vibrant red throat sacs to attract a female for mating; the male forces air into its throat sacs to resemble a balloon to woo a female for mating. Photo credit: https://www.huffpost.com/entry/weird-animal-courtship-displays_n_4761381 BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Intraspecific interactions: Parental care Figs. 3a and 3b: Parental care in rats and chimpanzees Photo credit: www.arstechnica.com and www.pinterest.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Intra-specific interactions: Aggression Fig. 4: Aggression in chickens Photo credit: www.cs-tf.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Predator-prey interactions Figs. 5a and 5b: Sea star eating mussels BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Predator-prey interactions Fig. 6: A Boomslang snake preying upon a Bullfrog Photo credit: https://theconversation.com/ BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Predator-prey interactions Fig. 7: Cheetah (Acinonyx jubatus) attacking a gazelle (Gazella dorcas). Photo credit: www.sites.google.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Predator-prey interactions Fig. 8: Lions (Panthera leo) hunting down a Buffalo Photo credit: www.pinterest.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Symbiotic relationships: This refers to a close relationship between two organisms in which at least one of them benefits. There are three types of symbiotic relationships: – Mutualism – Parasitism – Commensalism BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Mutualism (+, +): Mutualistic relationships are obligatory relationships in which both organisms benefit and both organisms cannot do without the other, i.e. the benefit of one is necessary for the other organism to survive. A typical example is the relationship between an alga and a fungus forming what is known as a lichen. The alga synthesizes food for the lichen complex, while the fungus absorbs water several times its weight to be used by both the alga and the fungus. It also provides protection for the alga. Example the lichen Verrucarria. Another example is the association between bacteria such as Rhizobium and the root nodules of leguminous plants such as peas. Rhizobium is a type of heterotrophic nitrogen fixing bacterium that helps to convert (fix) nitrogen from the atmosphere into ammonia in the form of ammonium nitrate that is used by the plant in exchange for carbohydrates as an energy source, as well as shelter. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Fig. 9: Example of Mutualism between fungi and algae (lichens) Photo credit: www.sarburchill.com and www.en.wkipedia.org BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Fig. 10: Example of Mutualism between nitrogen fixing bacteria and the root nodules of leguminous plants Photo credit: www.phys.com; www.microbewiki.kenyon.edu BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Proto-cooperation (+, +): This is a type of mutualism in which both organisms benefit but both organisms can do without each other. The two organisms benefit but the association is not necessary for their survival. Examples include cattle egrets and cattle:- the egrets feed on the ticks and lice on the skin of the cattle. The birds benefit in getting food (insects from the cattle’s body), while the cattle benefits in having their body free of the parasitic insects. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Proto-cooperation (Other examples):- The crocodile bird, Pluvianus aegyptius enters the mouth of the crocodile to feed on parasitic leeches. The bird benefits in getting its food while the crocodile benefits in getting rid of the parasitic leeches. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Photo credit: www.twitter.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Parasitism (+, -): A parasitic relationship is one in which one member, the parasite benefits while the other member known as the host is harmed. It differs from predator-prey interactions (which is also illustrated by +, -) in that the parasite does not usually kill the host. Exceptions are facultative parasites which do not depend on their host for survival and may kill their hosts. Except in the case of facultative parasites, the parasite-host relationship is obligatory (obligatory parasites), in that the parasite needs the host for its survival unlike predators where if one prey is not available, they can feed on another. Examples include the malaria parasite Plasmodium falciparum and the human host; the liver fluke Fasciola hepatica in sheep (Ovis sp.) BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Parasitism Plasmodium parasite within the host Fig. 12: Mosquitoes transmit the malaria parasite, Plasmodium sp. when a mosquito bites a person. Plasmodium is an example of an endoparasite. Photo credit: www.pinterest.com BIOTIC FACTORS: INTERACTIONS Parasitism AMONG ORGANISMS Fig. 13: Liver fluke in sheep. The sheep gets infected when it eats vegetation with infected snails that contain the parasite. Photo credit: www.farmhealthonline.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Parasitism Fig. 14: Tapeworm, Taenia solium in man. Man gets infected from eating improperly cooked infected meat from cattle. The cattle gets infected when it grazes on vegetation containing the larvae. Photo credit: Manual on meat inspection for developing countries and www. slideshare.net BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Commensalism (+, 0): This is a relationship in which one organism benefits, while the other neither gains or loses from the relationship, i.e. it is not affected by the relationship. Examples include the association between epiphytes (i.e. climbing or creeping plants and their host trees). The trees provide support and shade to the epiphytes. The trees on the other hand neither benefit nor are they harmed in the process. Another example is the association between the barnacle and the humpback whale. Adult barnacles require a substrate for attachment. The whale’s body provides a suitable site for attachment. The whale does not benefit nor is it harmed by the association. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Commensalism Fig. 15a: Epiphytes growing on a tree trunk Photo credit: www.alamy.com BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Commensalism Fig. 15b: Epiphytes growing on a tree trunk along the road by the main building of Department of Zoology, University of Ibadan. BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Commensalism Fig. 16: Barnacles attached to the back of the humpback whale. Photo credit: www.haikudeck.com Symbiotic relationships project by Troy Rogier BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Other types of biotic interactions: Amensalism (-, 0): This is a relationship in which one species A inflicts harm or restricts or affects the success of another species B; but A is neither positively nor negatively affected by the presence of the species B. A good example is seen in some plants e.g. the black Walnut Tree (Juglans nigra) which produces compounds (juglone) in its roots that inhibit the growth of other trees and shrubs nearby. The walnut tree neither benefits nor is it harmed by the presence of the other trees or shrubs (0); while the other trees and shrubs have their growth adversely affected as a result of the poisonous substance, juglone from the walnut tree(-). BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Other types of biotic interactions: Amensalism (-, 0): Another example is seen in the elephants (Loxodonta africana) or in humans trampling on smaller organisms such as insects or trampling on the vegetation (grasses). The insects or vegetation are adversely affected by the trampling of the elephants or humans(-); while the elephants or humans neither benefit nor are they harmed by the presence of the insects or grasses (0). BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Amensalism Fig. 17: The black Walnut Tree (Juglans nigra) produces compounds in its roots that inhibit the growth of other trees and shrubs nearby Other plants are adversely affected (-), while the walnut tree neither benefits nor is it harmed by the presence of the other plants(0). Picture credit: www.bio.miami.edu BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Amensalism in the black Walnut tree: -/0 or +/0? Two additional views The black walnut may receive a benefit in terms of their competitive relationship with larger plants, but there is no significant benefit from the damage caused to smaller plants of low abundance, such as mosses, ferns, and other low-growing vegetation. (World of Biology Research Article) Amensalism is a symbiotic relationship between two interacting species in which one organism restricts the growth of other individual without being affected. It’s a biological association of -/0 types. The common process of growth inhibition is the secretion of a special chemical compound by one living organism as a part of its normal metabolic process that acts detrimental to other. Although, this type of interaction is listed as 0/- types but in a symbiotic amensalism relationship the interaction is listed as +/- type as the first species which is secreting the chemical and inhibiting the other species is able to restrict competition for resources. Thus, it gains its survival. Principles of Ecology – Sehgal et al. Most references maintain it’s a -/0 relationship, [allelopathy]; others say it depends on if it’s a large plant or not (view 2), while some insist it s a +/0 relationship (view 3), What s your take? BIOTIC FACTORS: INTERACTIONS Amensalism: AMONG ORGANISMS Fig. 18: Algal bloom from over enrichment of nitrates and phosphates in a lake leads to oxygen depletion and results in the death of fish and other aquatic organisms in a lake. The fish are adversely affected (-) by the presence of the bloom of algae but the algae is neither benefiting nor gaining (0) from the presence of the fish in the lake. Picture credit: www.ecns.cn BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Other examples include cattle trampling on vegetation, or the production of Penicillin, a toxic substance produced by the fungus, Penicillium notatum which prevents the growth of bacteria. The growth of the bacteria is adversely affected (-); while the fungus neither benefits nor is it harmed (0). Other examples of Amensalism include: The blooming of algae on lakes which causes them to use up all the available oxygen in the water leading to the death of fish and other aquatic organisms. The other organisms such as the fish are harmed (-); while the algae neither benefit nor are harmed in the process (0) BIOTIC FACTORS: INTERACTIONS AMONG ORGANISMS Neutralism (0,0): This is a type of interaction in which both species interact but one does not affect the other. It mainly describes associations in which the fitness of one organism has absolutely no effect on the fitness of the others. It describes interactions that are negligible or insignificant. Example: fish (Rainbow trout) in a lake and vegetation e.g. flowers dandelions growing at the fringes of the water body, they may interact, e.g. the fish swims close by them but neither affects the fitness of the other. Another example are two species of birds, Phalacrocorax spp. found together in a particular season at a particular location but which feed on different species of fish so there is no competition. The presence of one does not affect the fitness of the other and vice versa. Obligatory Proto-cooperation (Non-obligatory association) Fig. 19: Edited Schematic representation of the interaction among organisms Diagram credit: www.geo.libretexts.org WEEK 3: ABIOTIC FACTORS INTRODUCTION TO THE ABIOTIC FACTORS Examples of some important abiotic factors peculiar to aquatic ecosystems: o Salinity o Density o Transparency/turbidity o Dissolved oxygen o Currents Examples of some important abiotic factors in both terrestrial and aquatic ecosystems: o Rainfall o Temperature o pH o Winds o Light o Pressure INTRODUCTION TO THE ABIOTIC FACTORS Why are these abiotic factors important? Apart from biotic conditions (e.g. food, mates etc), for an organism to thrive/flourish in a particular area, there must be an ideal range of abiotic factors (e.g. temperature, pH); water etc. Where the prevailing conditions are unsuitable, populations will decline ultimately resulting in extinctions on either a local (i.e. loss of a particular species from an area) or global (worldwide) scale. This implies that the type of flora, fauna and microbes (diversity), where they are found within a particular area (distribution) and how many there are (abundance) of an organism within a particular area is governed by the presence of a suitable range of abiotic factors. INTRODUCTION TO THE ABIOTIC FACTORS Tolerance range: Regardless of the abiotic factor be it temperature, pH, soil moisture content etc., each species has a range of physical conditions under which it can survive. This is known as the tolerance range and for each abiotic factor, each species has a specific tolerance range. As conditions approach the upper and lower limits of the tolerance range, the population undergoes stress, while outside these extremes they die. At some point within the lower and upper limits of the tolerance range is the optimum range at which point population growth is maximum and the conditions most ideal (Fig.20). THE ABIOTIC FACTORS Tolerance range High Optimum Range; population is highest within this Population range size Population Population reduces reduces Outside upper Outside lower limit limit death death occurs occurs Low Lower limit of tolerance Upper limit of tolerance range; stress and low Abiotic range; stress and low population numbers factor population numbers Fig. 20: Graph showing tolerance and optimum ranges of a population to an abiotic factor e.g. temperature, salinity etc. INTRODUCTION TO THE ABIOTIC FACTORS Influence of abiotic factors on the diversity, distribution and abundance of organisms Why are some plants found in some places and not in others? Why do some plants show a patchy distribution? Why do some animals thrive in certain places and are absent in others? The reason: – First every organism has a tolerance range to each abiotic factor, outside of which it cannot survive. (Fig. 20). – These abiotic factors show variations at the local and global level and thus they determine what kind of plant, animal or microbes will be found within a particular area (diversity), where they will be found within an area (distribution) and their abundance (density). THE ABIOTIC FACTORS Example 1: The bacterium Sulfolobus is a chemoautotroph found thriving in hot acidic soils at a pH range of 1-3 and a temperature range of 55-95oC. Optimum pH and temperatures vary within this range depending on the species of Sulfolobus. These bacteria known as thermophiles are found in hot volcanic springs and hot springs at the bottom of deep oceans where they utilize elemental sulphur as energy sources. It also explains why they are found in hot acidic soils, at the bottom of deep oceans and nowhere else. Note that although the deep sea environment is characterized by high pressure and low temperature, the vicinity of hydrothermal vents located on the ocean floor is characterized by extremely high temperatures which enable organisms such as this bacterium, Sulfolobus to thrive there. THE ABIOTIC FACTORS Example 2: Plants such as Cacti can tolerate little or no water conditions and thus can withstand long periods of drought. This explains why they thrive well in hot deserts that experience little rainfall. Example 3: The hermit crab, Clibanarius africanus is a euryhaline organism that is found in brackish water such as lagoons where the salinity fluctuates widely due to the mixing action of fresh and saline water. The hermit crab is euryhaline in that it can tolerate a wide range of salinities. On the other hand, the lancelet, Branchiostoma nigeriense is a stenohaline organism that is only found during periods of high salinity, i.e. it can only tolerate a narrow range of salinity. THE ABIOTIC FACTORS Example 4: The distribution of the marsh marigold, Caltha palustris is determined by the soil moisture content coupled with high nitrate content of the soil. Example 5: Influence of temperature and altitude on a plant Larix hyalli showed that this plant was limited to high altitude montane regions with subsequently reduced (colder) temperatures. Experiments showed that when this plant was transplanted outside its native habitat in places with higher temperature and lower altitude, the plant was damaged and could not thrive under such conditions. THE ABIOTIC FACTORS It is important to note that while the abiotic factors determine where an organism will be found and how many of it will be found in a particular area; biotic factors such as food supply, competition, absence or presence of predators, parasites etc. will determine its success or otherwise within that habitat. It is also important to note that several abiotic factors may operate simultaneously to determine the distribution and abundance of a species. For example, the case of pH and temperature in determining the distribution and abundance of Sulfolobus. THE ABIOTIC FACTORS Thus, the flourishing of a species within an area in terms of where it can be found (its habitat), and its population size (density) is a result of ideal abiotic and biotic conditions which allows that species to thrive in an area. Unsuitable conditions may result in population declines or even extinction on a local or global scale. It is also important to note the inter-relatedness between some of these abiotic factors. For example, soil moisture levels will fluctuate depending on precipitation (rainfall); High temperatures will favor evaporation of water in brackish and marine aquatic environments resulting in increased salinity; currents will increase with precipitation levels etc. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS This section deals with different abiotic factors, their significance and determination. pH: – This is a measure of the acidity and/or alkalinity of a medium such as soil and / or water. – It is inversely proportional to the concentration of hydrogen ions in solution, i.e. as the concentration of hydrogen ions in solution increases (increased acidity), there is a corresponding drop in the pH value. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Importance of pH: – Plant and animal cells require enzymes for their metabolic or biological processes. – pH is important to biological processes because plant (and animal) enzymes perform best under a specific pH range. – In the case of plants for example, the pH of the surrounding soil and water absorbed by the roots will be incorporated into the plant. If its pH is outside the ideal range, the enzymes will not operate correctly, and the plant fitness will decrease. Fig. 21: Influence of pH on enzymatic activity Image credit: www.pmgbiology.com The above example illustrates the influence of pH on three digestive enzymes found in humans and other animals: pepsin produced in the stomach acts on proteins to break it into smaller peptides; amylase found in saliva and breaks down starch into sugars and lipase, another important digestive enzyme that breaks down fats. All these enzymes require an optimum pH to function, above and below this optimum pH, the activity of the enzyme is affected, ultimately affecting the fitness and survival of the organism. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Measurement of pH using a pH meter: Soil pH - Using a hand trowel, obtain soil samples from around the Department. The pH meter is first calibrated according to the manufacturer’s instructions using salts of specific pH: 4, 7 and 14 usually supplied in a kit along with the instrument and used in calibrating it. After calibration, a specified quantity of soil is weighed (e.g. 5g) and dissolved in 50 mL of distilled water in a clean 100 mL beaker (i.e. ratio 1:10 soil to water). Alternative ratios of 1:1, 1:5 of soil to water may also be used. The mixture is stirred with a stirring rod and allowed to settle for half an hour. The probe of the pH meter is then inserted into the soil-water mixture and the pH recorded after a stable measurement is reached. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Water pH – Take a known volume of water (e.g. 50 mL of the water sample whose pH is to be determined) into a clean 100 mL beaker. Calibrate the pH according to the manufacturer’s instructions. pH of known standards can be determined using salts supplied with the manufacturer’s instructions. Insert the probe of the pH meter into the water sample and record the pH after a stable measurement is reached. Measurement of pH using pH indicator papers: In the absence of a pH meter, pH indicator papers can be used by simply dipping an indicator paper in the soil or water solution and matching the color with the appropriate match on the pH color chart. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Temperature: Temperature is determined using mercury-in-glass thermometers. The thermometer is inserted in the medium to be measured (soil, water or air and temperature is recorded in oC or oF. A minimum and maximum thermometer is a U-shaped mercury-in-glass thermometer used to record the lowest and highest temperature within a period of time, usually daily. Mercury free minimum and maximum thermometers are also used for the same purpose. For deep water temperature measurements, a special type of thermometer known as a reversing thermometer is used. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Fig. 22: A reversing thermometer for deep water temperature measurements Photo credit: www.slideplayer.com ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Aquatic abiotic factors (Salinity): Significance: This is a measure of dissolved salts in water, particularly the chlorides, which constitute the major salts in sea water. Sudden changes in salinity may pose problems for some brackish water organisms, while it does not pose problems for most marine organisms. Measurement of salinity: It can be determined using a salinometer and/or a conductivity meter. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Salinity can also be determined alternatively using titrimetric methods. A known volume of water is titrated with silver nitrate solution using potassium chromate as indicator. The volume of silver nitrate required to change the color of the water from yellow to red is taken as a measure of the salinity value of the water. Aquatic abiotic factors (Transparency): Significance: Transparency is important in the aquatic environment because it determines the depth to which light can penetrate ultimately influencing the distribution of photosynthetic organisms. Transparency falls during the rainy season due to increased run-off which carries salt and debris into surface water as well as increased current flows which agitates the sediments thus reducing the transparency. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS It increases during the dry season enabling light to penetrate deeper in the clearer waters due to less run-off and decreased current flows. Transparency measurements: Transparency is measured using a Secchi disc. The disc is lowered into the water until it just disappears from view and the measurement noted with the aid of a meter rule. It is then raised again until it reappears again and the second measurement is also noted. The average of the two measurements is taken as a measurement of the transparency of the water body. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Aquatic abiotic factors (Dissolved oxygen) Significance: Dissolved oxygen is essential for the respiration of most aquatic organisms. Oxygen solubility in water is 10-20 times less than that of air which makes obtaining oxygen requirements somewhat challenging for aquatic organisms hence the evolution of various adaptations to maximize oxygen uptake in water. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Oxygen enters into water via diffusion from air and as a by-product of photosynthesis and its concentration in water is thus directly proportional to the number of photosynthesizing plants mainly phytoplankton. Winds also aid oxygen diffusion from the air as it helps to expose more of the water surface to air thus promoting faster diffusion of oxygen from the air into the water. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Measurement of dissolved oxygen: Dissolved oxygen can be determined in water via the use of dissolved oxygen meters (DO meters). The DO meter is calibrated according to the manufacturers’ instructions and the probes inserted into the sample to be measured and the reading taken. Dissolved oxygen can also be determined using the Winkler’s titrimetric method. Other dissolved gases: Carbon dioxide Carbon dioxide dissolves in water to form carbonic acid which in turn combines with other alkalis in the water to form carbonates and bicarbonates. Carbon dioxide can be measured in water using titrimetric methods involving the titration with sodium hydroxide solution using phenophthalein as indicator. It can also be determined using an instrument known as a CO2 coulumeter. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Aquatic abiotic factors: Density Significance: Density is the weight of the water per unit volume and it is important in determining the ability of planktonic organisms to float in water. The density of fresh water is 1.000, while that of sea water is slightly higher at 1.028. For an organism to float, the specific gravity or relative gravity (which is a measure of the density of a substance in comparison to the density of water) of its soft tissues must be less than or equal to the density of the water. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Larger organisms have evolved various mechanisms to avoid drowning such as active swimming, adjustable gas filled swim bladders etc. However, planktonic organisms are sensitive to small changes in the density of the water and as a result some possess structures e.g. evolution of spines to increase the surface area to enable floating. Measurement of density: Density is measured using specialized equipment known as a hydrometer. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Fig. 23: A hydrometer for measurement of density Photo credit (Image to the right): www.quora.com ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Aquatic abiotic factors: Currents Rainfall causes fast currents in lotic freshwater bodies (streams, rivers) during the rainy season. Increased currents causes mixing and agitation of the underlying sediment leading to reduced transparency of the water body. This in turn affects the distribution of photosynthetic organisms and the fauna (animals) that depend on them. Measurement of water current speed: The speed of the current can be measured by floating a buoyant object between two fixed points (A & B) of known (measured) distance apart. The time taken for the object to float from point A to point B and the distance between the two points is used to determine the speed of the current. The results are expressed in m/s. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Light: Significance: This factor is of importance in both aquatic and terrestrial habitats as light is important for photosynthesis to occur in both habitats. In the aquatic environment, the depth to which light penetrates ultimately determines the distribution of photosynthetic organisms. Photosynthetic algae are limited to the photic zone which extends from the upper water surface to the maximum depth to which light can penetrate into the water body. Light is also important in determining the activity of certain animals. Some animals are more active during the day when light intensity is increased (diurnal) while some others are more active at night when light is absent (nocturnal). ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Furthermore, a number of aquatic organisms such as zooplankton exhibit a phenomenon known as diurnal vertical migration in response to increased light intensity. These animals descend to greater depths during the day when light intensity is increased to reduce the risk of predation and ascending to the surface waters to feed at night when light intensity is reduced and predators absent. Measurement: Light is measured using a special instrument known as an illuminometer. In aquatic habitats, a special kind of illuminometer known as a submersible illuminometer is used to measure light intensity. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Fig. 24: An illuminometer / Lux meter Photo credit: www.sigmainstruments.com ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Pressure: This refers to the force exerted on the earth’s surface by the air around it. This factor is of importance in both aquatic and terrestrial habitats as it influences the earth’s weather and climate. A change in the weather conditions in an area is as a result of changes in the atmospheric pressure. In the terrestrial environment, atmospheric pressure drops with increasing altitude. At sea level, the range of the earth’s atmospheric pressure is 101 kPa to near 0 kPa at an altitude of about 30,000m. In the aquatic habitat, pressure increases by 1 atmosphere (atm) for every 10m increase in depth. Animals found at greater depths in the ocean are thus adapted for survival at these depths. Pressure is measured using Barometers, while special pressure gauges are used for measurements of pressure below the water surface. Pressure is measured in Pascal, kiloPascal, bar (1 bar = 100kPa) or atm ( 1 atm = 101325 Pa or 1.01325 bar). ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Rainfall Significance: This is the most important climatic factor in tropical regions just like temperature is the most important climatic factor in temperate regions. Rainfall is important for terrestrial plant growth and also for replenishing the fresh water habitat which gradually dries up in the absence of rain. There is a direct relationship between the amount of rainfall and water levels in rivers with the highest water level in rivers lagging behind the peak levels of rainfall. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Lack of rainfall impacts resident aquatic organisms some of which are adapted to survive low or no rainfall periods For example, the lung fish builds a mud cocoon around itself in the dry season, while small invertebrates lay resistant eggs). Those not adapted to survive dry periods have to migrate to other water bodies to survive. Measurement of rainfall: Rainfall is measured using a rain gauge. It is measured in mm. Fig. 25: Types of rain gauges Photo credit: www.indiamart.com; www.maximum-inc.com. Abiotic Factors: Rainfall measurement The Rain Gauge is used to measure rainfall. A Rain Gauge should be placed 30 cm above the ground in an open area where there are no trees or buildings to block the rain, and where only rainfall can enter the rain gauge. The rain collected in the rain gauge is usually measured every morning with a measuring cylinder at a fixed time. The measurement constitutes the daily rainfall and is recorded in millimetres (mm). By adding up the amount of rain collected in a month, we get the monthly rainfall. The total amount of rainfall collected over 12 months is the annual rainfall (Bulat, 2012). ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Winds Winds influence aeration in open waters thus promoting faster diffusion of oxygen into the water. Specific kinds of winds known as Trade winds play a role in the formation of ocean currents. Winds also play a role in the formation of waves in the oceans. Wind speed is measured using an anenometer and the results can be expressed in miles per hour (mph), meters per second, feet per second or knots. Wind direction is measured using a wind vane. ABIOTIC FACTORS: SIGNIFICANCE AND MEASUREMENTS Fig. 26: An anemometer for the measurement of wind speed Photo Credit: www.mrclab.com Fig. 27: Wind vane used to measure wind direction Photo Credit: www.slideshare.net DEPARTMENT OF ZOOLOGY, UNIVERSITY OF IBADAN, IBADAN. ZOO 115: INTRODUCTORY ECOLOGY LECTURER: DR. ADEOLA A. ONI SCHEDULED OUTLINE Weeks 2 & 3: Biotic and Abiotic factors; Week 4: Population Ecology; Week 5: Production: 1o, 2o and 3o Production WEEK 4: POPULATION ECOLOGY POPULATION ECOLOGY Population Ecology: Population ecology deals with the study of populations, their characteristics, e.g. size/abundance, the dynamics (i.e. how the population changes over time) as well as the factors affecting the population. What is a population? A population is a group or a collection of individuals of the same species living together in a specific geographical region or a particular space. POPULATION ECOLOGY Importance of population studies: Identification of high quality habitats: Population studies can help in identifying high quality habitats. This can be achieved by comparing the growth rates of a population of organisms in different habitats to identify the habitat in which that population would thrive best, as well as to identify the factors which enable the population to thrive successfully within a particular habitat. Such information is necessary for the management of our biodiversity considering the important role each species plays within its particular habitat. Identification of threatened/endangered species: The International Union for the Conservation of Nature (IUCN) relies on population estimates to classify a species into various categories from least concern to near threatened to vulnerable, endangered, critically endangered, extinct in the wild or extinct. These estimates help in identifying species on the verge of extinction so conservation strategies can be introduced to preserve the species. Assess the success or otherwise of conservation efforts: Conservation biologists also rely on population estimates to assess the success or otherwise of conservation strategies in saving endangered species. POPULATION ECOLOGY Importance of population studies: Population studies are also important in: sustainable fisheries and aquaculture (increase the population of species we want to harvest) Pest control (reduce the population of pests on crop fields) Human population growth (study of the dynamics of the world ‘s population) POPULATION ECOLOGY Attributes / characteristics of a population include: Density is the size of the population in relation to a specific unit of space. It is the first attribute of attention in population studies because the effect an organism has on its environment or the ecosystem depends not only on what kind of organism it is, but on how many of the organism, there are. The effect of ten white flies (Aleurodicus dispersus) on a mango tree plantation will not be as devastating as if they were a 100,000. Examples of density: – 100 fingerlings of Tilapia zilli fishes per hectare of water surface. – 10 Mangifera indica (Mango) trees per hectare. – 306 cells of Oscillatoria sp. (phytoplankton) per ml of water. Distribution: This refers to the arrangement of organisms within an area. Age structure: This is the proportion of individuals in the different age groups in a population. Growth: All populations will grow abundantly in the presence of abundant resources e.g. food, space, water etc. Methods for the estimation of population abundance: Direct count for large conspicuous organisms: This can also be aided with photography if the organisms is highly mobile. POPULATION ECOLOGY Sampling: For microscopic and small sized organisms, where direct count of every member of the population is not practicable, a sample (a portion of the population taken to represent the whole population) is taken. The number of samples to be taken would depend on the size of the area under investigation but whatever the number of samples taken, the sample size must be sufficient to represent the whole population (i.e. it must be representative). The samples must also be unbiased. Sampling of terrestrial habitats: In sampling terrestrial habitats, the use of transects, plots and quadrats may be used. A transect is a straight line taken across the area to be sampled and individuals touching the line at specific intervals apart (e.g. every 10m across a 100m transect is sampled). Alternatively, a belt transect (two straight lines equal distant apart delineated within the area to be sampled) can also be used. The quadrat can be placed within the belt transect at systematic intervals along the transect, just as obtains with a line transect. Fig. 1: Line and belt transects Source:www.pinterest.ca POPULATION ECOLOGY The area to be sampled may be divided into smaller, uniformly-sized plots which may be sampled either randomly, or systematically (e.g. every 3rd plot may be selected and sampled). In sampling terrestrial habitats, a quadrat is also necessary. A quadrat is a square, rectangular or circular frame of known dimension. The most common type of quadrat is a square framed quadrat. Various dimensions of the square framed quadrat are available (0.25m2, 0.5m2, 1m2 etc). The size of the quadrat to be used will depend on the size of the species to be sampled and the size of the area to be sampled. POPULATION ECOLOGY The quadrat can be thrown randomly within an area or used in conjunction with transects and plots. Any organism found within the quadrat is sampled. Soil samples may be obtained using a soil corer or soil auger and invertebrates separated from the soil by a Tullgren funnel or intensive hand sorting. Flying insects in the terrestrial habitat may be sampled using a sweep net while birds and bats may be sampled using a mist net. Soil invertebrates, amphibians and small mammals can be caught using pitfall traps. In the aquatic habitat, random or systematic sampling may also be applied in the aquatic habitat. Benthic (bottom-dwelling organisms) and sediment samples may be sampled using a Van Veen or Ekman grab; while phytoplankton and zooplankton may be sampled using a plankton net. Fig. 2: Mist net for sampling birds and bats Fig. 3: Optimized pitfall trap design Source: www.link.springer.com POPULATION ECOLOGY Mark-recapture methods: A sample of the population is captured, marked in a way that does not affect the animal and the animals released back into the population. The ratio / proportion of marked individuals in a second capture is used to estimate the number of individuals in the population as indicated below: No. of animals marked & released at 1st capture (n1) No. of marked animals in 2nd capture (m2) = Unknown Population estimate ??? (N) Total no. of animals in 2nd capture (n2) Therefore N = No. of animals marked & released at 1st capture (n1) X Total number of animals in 2nd capture (n2) Number of marked animals in 2nd Capture (m2) POPULATION ECOLOGY A large grassy field had a large number of moles. A first sample of 130 moles were marked and released. A second sample pulled out a total of 145 moles, fifty of which were marked. Calculate the estimated population of moles in the field. n1 = 130 (number of animals marked and released at first capture) m2 = 50 (number of marked animals in second capture) n2 = 145 (total number of animals in second capture) N??? = Unknown population estimate Equation: n1/N = m2/n2; therefore N = (n1 x n2)/m2 = (130 x 145)/50 = 377 moles POPULATION ECOLOGY Assumptions of the mark-recapture method of determining population estimates: The population is closed (no births, no deaths, no immigration and no emigration). The marks do not affect the animal’s survival in any way. The marks / tags are not lost or wear off which may lead to unreliable population estimates. There is enough time between capture and recapture to allow for the marked animals to mix with the rest of the population. The marks should not make the animals easier to capture or make them avoid being captured (i.e. it should not make them trap-happy or trap shy). POPULATION ECOLOGY Methods of estimating population abundance (cont.): Indirect methods: This involves the use of signs of an animal to give estimates of the population abundance e.g. using the: Number of an animal’s faecal pellets within a defined unit area (m2) or Number of birds calling within a specific unit of time (1 hour), Number of bird nests within a defined unit area (per square kilometer) Number of rodent burrows per square meter (m2). Attributes / characteristics of populations: Distribution (arrangement of organisms within an area). There are three major patterns of population distribution: – Clumped distribution – Uniform distribution – Random distribution POPULATION ECOLOGY Attributes/characteristics of population: Distribution: Three major types: Clumped distribution: This kind of distribution is found in areas where the resources and abiotic conditions are not uniformly distributed. As a result of this, organisms aggregate together in areas with suitable resources and abiotic conditions, forming a patchy, non-uniform type of distribution. Uniform distribution: When resources are very limited or scarce, there is fierce competition among individuals for the limited resources available. This results in each individual in the population being more or less evenly spaced apart. This kind of distribution is however rare in nature. Random distribution: This type of distribution occurs where resources and suitable abiotic conditions are uniformly distributed such that the individuals in a population have an equal chance of occurring anywhere within the environment. POPULATION ECOLOGY Fig. 4: Types of population distribution in nature Fig. 5: Types of population distribution in nature Source: www.slideplayer.com POPULATION ECOLOGY Attributes/characteristics of population: Age structure: This refers to the proportion of individuals in different age groups in the population. The different age groups in a population can be considered on the basis of the age in days, weeks, months or years depending on the lifespan of the species being studied. However, for convenience purposes, the age groups can also be broadly categorized into three ecological ages as indicated below: – Pre-reproductive/juvenile phase – Reproductive/adult phase – Post-reproductive/old age Illustration of the above ecological ages using the human population: – Pre-reproductive/juvenile phase maybe between ages 0 (i.e. few months old)- 21 years; – Reproductive/adult phase maybe between 22-55years; – Post-reproductive/old age ≥ 56 POPULATION ECOLOGY Importance of age structure/age distribution: The proportion of individuals (i.e. juveniles, adults or aged) members of a population can be used to indicate if a population is growing (rapidly or slowly); stable (i.e. neither increasing or decreasing) or if the population is declining. 1. Rapidly expanding population/positive growth: This population is characterized by a large proportion of young/juvenile individuals. Using human population (e.g. Nigerian population) as an example, close to 60% of the Nigerian population is made up of youths. Therefore, the Nigerian population is said to be a rapidly expanding population or a population that is showing positive and rapid growth. 2. Slow growth: This population also shows a greater proportion of juveniles compared to adults and aged, but the differences between the three broad groups is not as wide. Such a population is said to show positive but slow growth. POPULATION ECOLOGY 3. Stable population/zero-growth: The proportion of juveniles, adults and aged members of the population are almost equally distributed indicating that the population is neither growing nor reducing. 4. Declining population/negative growth: This population is characterized by a large proportion of aged individuals. Thus the population is said to be declining/reducing indicative of negative growth. POPULATION ECOLOGY Fig. 6: Patterns of Population growth in nature Source: bio.utexas.edu POPULATION GROWTH Population growth: Concept of exponential growth All populations will grow at a constant rate in the presence of abundant resources such as food, space, water etc. If this growth is not checked, the population growth will approach infinity. This type of growth is termed exponential growth. The best example of exponential growth is seen in bacteria. Bacteria are prokaryotes that reproduce by binary fission. This division takes about an hour for many bacterial species. POPULATION GROWTH If 1000 bacteria are placed in a large flask with an unlimited supply of nutrients (so the nutrients will not become depleted), after an hour there will be one round of division (with each organism dividing once), resulting in 2000 organisms. In another hour, each of the 2000 organisms will double, producing 4000; after the third hour, there should be 8000 bacteria in the flask; and so on. The important concept of exponential growth is that the population growth rate, the number of organisms added in each reproductive generation, is accelerating; that is, it is increasing at a greater and greater rate. After 1 day and 24 of these cycles, the population would have increased from 1000 to more than 16 billion. When the population size, N, is plotted over time, a J-shaped growth curve is produced. Fig. 7: Exponential growth of bacteria Source: math.commons.bcit.ca POPULATION GROWTH However exponential growth will not continue forever, because the resources in the environment (food, space, water etc) are limited in supply. Exponential growth occurs in a population only for a short / brief period of time when resources are in abundant supply. After a while the resources diminish (i.e. become limiting) and the population approaches what is known as its carrying capacity. Carrying capacity is the maximum number of a species an environment can support. POPULATION GROWTH Population growth: Concept of carrying capacity Carrying capacity: This is the maximum population size of a species that a given environment or ecosystem can support and it is denoted by the symbol (k). As stated earlier, populations tend to grow exponentially but not for long, eventually their growth is limited by the available resources and interferences come in to check population growth. As a population approaches its carrying capacity, there is overcrowding which results in reduced resources (food, space, water etc) for each individual in the population. The resources available to each individual in the population reduces due to overcrowding. Parasitic infections and disease outbreaks also increase with overcrowding Consequently, the birth rate decreases and the death rate increases. POPULATION GROWTH Fig. 8: Logistic growth Source: legacy.hopkinsville.kctcs.edu POPULATION GROWTH Factors that check population growth: density dependent factors Certain factors help to contribute to the increased death rate to eliminate excess individuals and ensure that the population stabilizes at the carrying capacity of the environment. These factors are known as density dependent factors because the effects of these factors increase as the population size increases to the point of overcrowding and examples of these density dependent factors include: – Food, water, space (with increased population size, there is reduced access to these resources). – Increased attraction to predators with increased population size – Increased disease outbreak and spread of infectious diseases with increased number of individuals due to overcrowding. POPULATION GROWTH Density dependent factors (cont.): The above mentioned factors serve to reduce the population growth rate until it stops and stabilizes at the carrying capacity of the environment. They are known as density dependent factors because they are factors that increase with an increase in the population size especially to the point of overcrowding. They serve to check unlimited population growth. POPULATION GROWTH Density independent factors: These are factors that act to reduce population size regardless of its density, i.e. they act to reduce population growth whether the population is large or small, increasing or decreasing (i.e. they act independent of the population size). They can keep population sizes small if they occur commonly and severely. Examples include natural disasters such as fires, hurricanes, flooding and impacts of climate change such as global warming, fires, storms, floods and impacts of human activity such as pollution, etc. WEEK 5: PRIMARY (1O), SECONDARY (2O) AND TERTIARY (3O) PRODUCTION OR PRODUCTIVITY PRODUCTION ECOLOGY Introduction to the concept of productivity: Biomass refers to the quantity or mass of living organisms. Although it is often used to refer to the mass of living organisms, it can also refer to the remains of dead organisms which constitutes dead organic matter. Thus, the biomass in an ecosystem includes the mass of all living organisms as well as dead organic matter. In simple terms, the bodies of organisms, plants, animals or micro-organisms whether living or dead constitute the biomass. The amount of biomass produced within a unit area per unit of time is known as the Productivity. Productivity can be expressed in terms of the weight of dry organic matter (in g, kg or tonnes) produced per unit area (m2, km2 or ha, i.e. hectare) within a specific time frame (e.g. per year) [i.e. g/m2/yr or kg/km2/yr or t/ha/yr]. PRODUCTION ECOLOGY Productivity can also be expressed in terms of the amount of energy produced (measured in calories) per unit area (m2 or cm2 km2) within a specific time frame (e.g. per year)[i.e. calories/m2/yr]. All living organisms require energy for all their life activities. Recollect that energy is the capacity/ability to do work and the 1st law of thermodynamics states that energy can neither be created or destroyed but is merely transformed from one form to another. Green plants and/or photosynthetic algae fix solar energy from the sun and transform this form of energy into chemical energy which is stored in these producers in the form of carbohydrates, proteins, etc. PRODUCTION ECOLOGY The rate at which producers fix this solar energy and accumulate it in their bodies as chemical energy is known as primary productivity. Types of productivity: Primary productivity: the amount of energy or organic matter produced per unit area per unit time by the autotrophs or producers (i.e. green plants or photosynthetic algae) during the process of photosynthesis. Primary productivity may also refer to the amount of energy produced per unit area per unit time by chemosynthetic micro-organisms. PRODUCTION ECOLOGY Primary productivity is of two types: – Gross primary productivity (GNP); and – Net primary productivity (NPP) Gross primary productivity: This is the total amount of energy or organic matter produced per unit area per unit time by the producers. However some of this energy will utilized during the respiration of these autotrophs or producers. The amount of energy or organic matter produced that remains after respiration is known as Net primary productivity (NPP). Thus the NPP = GPP – Energy utilized or lost due to respiration of producers PRODUCTION ECOLOGY It is this Net Primary Productivity (NPP) that results in the accumulation of plant biomass. Net Primary Productivity is also known as Apparent Photosynthesis or Net Assimilation. This plant biomass serves as food for consumers in the form of herbivores that feed directly on the plants; and detritivores and decomposers that will break down the dead remains of these plants. It is this food in the form of energy that will be transferred to the consumers beginning from the primary consumers or herbivores to the tertiary consumers (secondary carnivores or omnivores) that will be used to generate or produce animal biomass for these consumers. PRODUCTION ECOLOGY This introduces the concept of secondary productivity which is the biomass (i.e. the amount of living material) produced by all the heterotrophs [i.e. consumers (1o, 2o or 3o) including the detritivores and decomposers] in an ecosystem. Secondary productivity may also refer to the quantity of biomass generated by the herbivores or primary consumers only; while the quantity of biomass generated by the carnivores feeding on these herbivores in turn constitutes what is known as tertiary production or tertiary productivity. PRODUCTION ECOLOGY The concept of secondary productivity as the biomass produced by all the heterotrophs is the more common concept or definition of secondary productivity. In summary, secondary productivity is the rate of energy storage by all the consumers (herbivores, carnivores, decomposers etc) or the rate at which consumers convert chemical energy of their food into their own biomass. These consumers will utilize some of the energy from these food materials in their respiration, while the rest is converted and stored in these consumers as secondary productivity. The organic matter or energy that is stored in the heterotrophs (secondary productivity) is however mobile, in the sense that this energy can be passed from one organism to another unlike primary productivity which is retained within the producers. PRODUCTION ECOLOGY Importance of productivity: The determination of the productivity of an ecosystem implies that the productivities of different ecosystems can be compared. For example, the productivity of a tropical rainforest ecosystem (expressed as the mean plant biomass in tons/hectare/year) can be compared with that of a savanna or a temperate grassland ecosystem. PRODUCTION ECOLOGY Measurement of productivity: This method measures Primary productivity in an aquatic environment. This method involves the measurement of the oxygen produced and consumed in a known volume of water with a known concentration of phytoplankton within a specific unit of time. Principle: We know that photosynthetic phytoplankton in the water will produce oxygen as a by-product in the process of photosynthesis. However, some of the oxygen produced will also be used up for their respiration. Method: Two glass bottles, a light bottle and a dark bottle (or a light bottle covered in order to exclude light) is immersed into water at a specific level and the water collected into both bottles and sealed. The initial oxygen content of the water in both bottles is measured using a dissolved oxygen meter or via the Winkler’s titrimetric method. PRODUCTION ECOLOGY The bottles are then immersed again into the water at the same level from which water was initially obtained and left for 24 hours. The assumption is that the oxygen produced in the light bottle during photosynthesis is directly proportional to the total amount of organic matter produced during photosynthesis (i.e. the gross primary productivity). However, we also know that some of the oxygen will be used up in the respiration of these photosynthetic phytoplankton. Thus the difference between the initial and final measurement of oxygen in the light bottle gives an indication of the Net Primary Productivity (NPP). PRODUCTION ECOLOGY The dark bottle excludes light so no oxygen is produced as photosynthesis will not occur due to light being excluded. However the oxygen within the water will be used up in respiration by the photosynthetic algae which will give the amount of oxygen used up in respiration (R). The addition of the Net Primary Productivity (NPP) as indicated by the difference between the initial and final oxygen levels in the light bottle and; the amount of oxygen used up in respiration (R), indicated by the difference between the initial and final measurement of oxygen in the dark bottle gives the gross primary productivity (GPP) of producers in the water. PRODUCTION ECOLOGY Fig. 9: Light and dark bottle measurement of primary productivity Source: www.slideplayer.com PRODUCTION ECOLOGY Other methods of measuring primary productivity: Diel method: The diel method which modifies the above method with the light bottle measurement indicating day time and the dark bottle indicating night time. Changes in the level of oxygen during a 24 hour period is used to obtain an estimate of productivity. C14 method: This method uses radioactive carbon to trace and measure productivity. The radioactive carbon is added to a bottle of water containing phytoplankton. PRODUCTION ECOLOGY C14 method (cont.): After a short period of time, the phytoplankton is separated from the water, dried and processed and the quantity of radioactive carbon fixed by the phytoplankton is measured to give an indication of the net primary productivity. Harvest: Secondary productivity can be measured using e.g. the harvest of fish from a fish pond. This measure is indicative of the net productivity (i.e. excluding the amount lost to respiration). It is usually expressed as the wet weight per unit area of water surface within a specific time frame. It is the simplest method of determining productivity. Introductory Ecology (ZOO 115) Topics: Trophic Levels Food chain Food web Population Growth Instructor: Akindayo A. Sowunmi, Ph.D Office: Rm C1B Department of Zoology e-mail: [email protected] 1 Ecology is…………………. the study of the distribution and abundance of organisms AND the flow of energy and materials between abiotic and biotic components of ecosystems 2 Ecosystem (Biocoenose) concept The ecosystem is the basic functional unit in ecology a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment, both interacting and exchanging materials between them. 3 What is an ecosystem? Ecosystem = an ecological system = a community and its physical environment treated together as a functional system System = regularly interacting and interdependent components forming a unified whole 4 Ecosystem services – production services as we know them from agriculture, fishery, forestry, etc – regulation services due to cycling, filtration, translocation, and stabilization processes – cultural services such as recreation, spiritual inspiration and aesthetics 5 Ecosystem is……………. Space-time unit in which there is flow of energy and exchange of materials leading to biomass accumulation and trophic structure 6 Ecosystems: Fundamental Characteristics: Structure Function Interaction Complexity Change with time Succession 7 ▪ Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest ▪ Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling ▪ Energy flows through ecosystems while matter cycles within them 8 Fig.1 Main Structural Components of an Ecosystem 9 Fig. 2 Ecosystem classification using stable structure 10 Ecosystem classification using energy sources Unsubsidized natural solar-powered ecosystems e.g. open oceans, upland forests. These systems constitute the basic life-support for Earth. Naturally subsidized solar-powered ecosystems e.g. tidal estuary, some rain forests. These are naturally productive system of nature that not only have high life-support capacity but also produce excess organic matter that may be exported to other systems or stored. 11 Human-subsidized solar powered ecosystems e.g agriculture, aquaculture. These are food and fiber producing systems supported by auxiliary fuel or other energy supplied by humans Fuel-powered urban industrial systems e.g. cities, suburbs, industrial parks. These are wealth generating also pollution generating systems in which fuel replaces the sun as the chief energy source. 12 Ecosystem was coined by Tansley in 1935, refers to an integrated system composed of a biotic community, its abiotic environment, and their dynamic interactions. Ecosystems can be thought of as energy transformers and nutrient processors composed of organisms that require continual input of energy to balance that lost during metabolism, growth, and reproduction. 13 Lindeman’s Foundations of Ecosystem Ecology The ecosystem is the fundamental unit of ecology. Within the ecosystem, energy passes through many steps or links. Each link is a trophic level (or feeding level). Inefficiencies in energy transformation in the ecosystem. 14 Ecosystem and Thermodynamics ▪ Study of energy and its transformations ▪ System-the object being studied Closed system: does not exchange energy. Rare In nature Open system: exchanges energy with the surroundings. 15 Physical laws governing energy flow and chemical cycling in ecosystems ✓ Ecologists study the transformations of energy and matter within their system ✓ Laws of physics and chemistry apply to ecosystems, particularly energy flow Conservation of Energy ✓ The first law of thermodynamics states that energy cannot be created or destroyed, only transformed Translation: Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat 16 The second law of thermodynamics states that every exchange of energy increases the entropy of the universe Translation: In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat 17 Conservation of Mass The law of conservation of mass states that matter cannot be created or destroyed Translation: Chemical elements are continually recycled within ecosystems o Ecosystems are open systems, absorbing energy and mass and releasing heat and waste product 18 Ecosystem components: Certain organisms in an ecosystem convert abiotic components into living matter. These are the producers; they support the ecosystem by producing new biological matter (biomass). Organisms that cannot make their own food eat other organisms to obtain energy and matter. They are consumers. The position that an organism or a group of organisms in a community occupies in the exchange process is called the trophic level. 19 Fig. 3 Trophic ecology investigates the structure of feeding (trophic) relationships among organisms in an ecosystem. In general, feeding or trophic relationships are represented as a food web or as a food chain (often depicted as a pyramid). (Copyright © McGraw Hill) 20 Remember……. ……Ecosystem …….. flow of energy exchange of materials biomass accumulation trophic structure 21 Organisms that perform similar types of ecosystem functions can be broadly categorized by their functional group Classifying organisms according to their feeding relationships is the basis of defining an organism’s trophic level Ecosystem components that make up a trophic level are quantified in terms of biomass (the weight or standing crop of organisms), while ecosystem dynamics, the flow of energy and materials among system components, are quantified in terms of rates. 22 Species in ecological communities interact directly with another species through consumer–resource, competitive, or mutualistic interactions. Feeding or trophic relationships are represented as a food web or food chain. Food webs depict trophic links between all species sampled in a habitat, whereas food chains simplify this complexity into linear arrays of interactions among trophic levels 23 Trophic Levels Ecosystems have a limited number of trophic levels What limits them??? As energy is transferred from one trophic level to another, energy is degraded. Limited assimilation Consumer respiration Heat production 24 Question time 25 Introductory Ecology (ZOO 115) Topics: Trophic Levels Food chain Food web Population ecology Population Growth Instructor: Akindayo A. Sowunmi, Ph.D Office: Rm C1B Department of Zoology [email protected] Trophic Levels Ecosystems have a limited number of trophic levels What limits them??? As energy is transferred from one trophic level to another, energy is degraded. Limited assimilation Consumer respiration Heat production Ecosystem communities interaction Species in ecological communities interact directly with another species through consumer–resource, competitive, or mutualistic interactions. Feeding or trophic relationships are represented as a food web or food chain. Food webs depict trophic links between all species sampled in a habitat, whereas food chains simplify this complexity into linear arrays of interactions among trophic levels 3 The flow of energy and matter from organism to organism can be shown in a food chain. The path of energy and matter from one trophic level to another is often outlined by constructing food chains. A food chain is simply a listing of which organism eats a different organism in the ecosystem. Energy Flow Feeding relationship Linear pattern of eating and being eaten and can be traced to producers Linear transfer of energy in succession 2 types of Food Chain Grazing food chain-dependent on living green plants Detritus food chain-dependent on detritus/decaying/dead materials Grazing food chain Grazing food chain is a type of food chain in which energy at the lowest trophic level is acquired via photosynthesis. -grazing food chains begin with producers like green plants, who create their own food through the process of photosynthesis and later move from herbivores to carnivores. In the grazing food chain, energy is acquired from the sun. Implications of Grazing Food Chain This food chain is directly dependent on the flow of solar energy. Therefore, the gross production of plants might meet the following consequences: 1. they may be oxidized during respiration, they can be eaten by herbivores or they may die and decay. 2. Sunlight energy serves as the primary source of energy in the grazing food chain. 3. The grazing food chain always adds energy to the ecosystem. 4. Fixation of inorganic nutrients. 5. It involves every macroscopic organism. Why are food chains short Rarely are things as simple as grass, rabbit, hawk, or indeed any simple linear sequence of organisms. Food chains are greatly simpliﬁed, however, and usually the eating relationships are more accurately depicted as a food web Organisms feed at more than one trophic levels/more than one organisms More typically, there are multiple interactions, so that we end up with a FOOD WEB. Problems Too simplistic No detritivores Chains too long FOOD CHAIN LENGTH (FCL): measure the number of energy transfers or trophic links between primary producers and the top predator in an ecosystem………….. or: ….number of energy or nutrients transfers from the base to the top of a food web a fundamental ecosystem attribute influencing community structure by altering the organization of trophic interactions importance for ecosystems and their functioning widely documented for: food chain dynamics and the structuring of ecosystems via trophic cascades mediating the relationship between species diversity and ecosystem function regulating biogeochemical fluxes fisheries productivity contaminant bioaccumulation in top predators Despite the central importance of FCL understanding of variability in FCL remains limited FOOD CHAIN EFFICIENCY (FCE), defined as the proportion of energy fixed by primary producers that is transferred to the top trophic level, depends on the ecological efficiencies at each trophic coupling FCE can regulate: attributes such as: food-chain length and biomass eco- system services: such as fisheries production export of carbon from ecosystems concentrations of contaminants in organisms FOOD WEBS…….. describe the trophic links between producers and consumers, and consumers and their predators are the most widely recognized representation of the species interactions in an ecosystem. Food web research has increasingly focused on what food webs can reveal about the vulnerability of ecosystems to species loss. Numerous studies have investigated the cascading impacts of removing a species from a food web and thus the ‘robustness’ of different food-web structures to species extinction. The most obvious interpretation of these results is that those species on which the robustness of a food web is most dependent should be the highest priority for management. Energy transfers among trophic levels How much energy is passed from one trophic level to the next? How efficient are such transfers? Question time Introductory Ecology (ZOO 115) Topics: Trophic Levels Food chain Food web Ecological pyramids Population Growth Instructor: Akindayo A. Sowunmi, Ph.D Office: Rm C1B Department of Zoology [email protected] 1 Reminders…………. Transfer of energy and resources is done through links called a food chain Organisms at same step in relations to food source are said to be on same trophic level Trophic classification is based on function NOT on species, which are often placed on multiple trophic level depending on food choices 2 Fig.1 Ecosystem Biota-Resource Interactions 3 Fig. 2 Forest food web 4 Energy transfers among trophic levels How much energy is passed from one trophic level to the next? How efficient are such transfers? 5 Food chains and food webs do not give any information about the numbers of organisms involved/quantitative information. Elton (1927) …food pyramid This information can be shown through ecological pyramids. Pyramid of numbers Pyramid of biomass Pyramid of energy 6 Ecological pyramids Graphic representation of trophic structure and function of an ecosystem, starting with producers at the base and successive trophic levels forming the apex is known as an ecological pyramid An ecological pyramid is a diagram that shows the relationship amounts of energy or matter contained within each trophic level in a food web or food chain. 7 Ecological pyramids (Contd.) Pyramids are graphical models of the quantitative differences that exist between the trophic levels of a single ecosystem These models provide a better understanding of the workings of an ecosystem by showing the feeding relationship in a community. 8 Pyramid of numbers Shows the number of organisms at each trophic level per unit area of an ecosystem with producers forming the base and top carnivores the tip. The shape of the pyramid of numbers vary from ecosystem to ecosystem. We may have upright or inverted pyramid of numbers, depending upon type of ecosystem and food chain. 9 Fig. 3 Pyramid of Numbers 10 Fig 5. Pyramid of numbers 11 Pyramid of biomass  The total amount of matter present in organisms of an ecosystem at each trophic level is biomass.  Biomass is preferred to the use of numbers of organisms because individual organisms can vary in size. It is the total mass not the size that is important.  Pyramid of biomass records the total dry organic matter of organisms at each trophic level in a given area of an ecosystem. 12 Fig. 6 Pyramid of Biomass 13 Fig.7 Pyramid invertion 14 Pyramid of Energy Shows the amount of energy input to each trophic level in a given area of an ecosystem over an extended period with producers forming the base and the top carnivores at the tip. Pyramid of energy is always upright It is so because at each transfer about 80 - 90% of the energy available at lower trophic level is used up to overcome its entropy and to perform metabolic activities. Only 10% of the energy is available to next trophic level 15 Fig. 8 Pyramid of Energy 16 In nature, ecological efficiency varies from 5% to 20% energy available between successive trophic levels (95% to 80% loss). About 10% efficiency is a general rule. Fig. 9 Pyramid of Energy 17 Ecological efficiencies: measures of efficiency of energy transfer Photosynthetic efficiency: % of available sunlight used in photosynthesis whether or not the carbon is respired. Exploitation efficiency: % of production of one trophic level that is ingested by the trophic level above. The unassimilated (excess) either accumulates or pass directly to decomposers. Assimilation efficiency: % of energy ingested that is actually absorbed across the wall of gut rather than egested 18 Reproductive efficiency: % of energy assimilated that is devoted reproduction rather than being respired or devoted to growth Production efficiency: % of energy assimilated (i.e. devoted to growth or reproduction) rather than respired. Trophic efficiency: efficiency of energy transfer from one trophic level to one above e.g. for herbivores = % of net production converted to herbivore production 19 Question time 20 ZOO 115: INTRODUCTORY ECOLOGY TOPIC: IMPACT OF MAN ON THE ENVIRONMENT BY PROF. ADIAHA UGWUMBA INTRODUCTION ▪ Man has made a lot adverse impacts on the environment. ▪ The development of agriculture and technology in the last two centuries have increased human impacts on the environment ▪ With widespread of industrialization, the potentials for damaging the environment has also increased. Some of the impacts of man on the environments are: Pollution Habitat Destruction Extinction of species POLLUTION This is defined as the release into the environment of substances or energy in such quantities and duration that cause harm not only to the environment, but also to the people and other organism. It is one of the greatest harm by man to the environment Pollution can affect all aspects of the environment:– biotic and abiotic components Pollution and its control is now a global issue since it has become apparent that pollutants can be transported to long distances their sources. Hence, pollution is now addressed globally and so it demands international cooperation. TYPES OF POLLUTION AIR POLLUTION Important atmospheric pollutants include gases such as: Chlorofluorocarbons ----- CFCs Sulphur dioxide ------------ SO2 Hydrocarbons ----------- HC e.g methane, Oxides of Nitrogen -------- Nox Carbon monoxide -------- CO Increasing levels of natural gases like Carbon dioxide as well as Dust, Noise, Wastes, Heat, Radioactivity and Electromagnetic pulses may also pollute the atmosphere WATER POLLUTION This results from the following Run offs from farmlands where the fertilizer is used in intensive agriculture Discharge of sewage effluents Domestic and industrial wastes dumped into water bodies. Thermal pollution Oil pollution These affect both freshwater as well as marine ecosystems. Acid rain is dangerous because It damages surfaces of buildings corroding and weathering them. It damages ecosystems e.g. - making water bodies poisonous and killing the resident organisms. - destroys forest by killing trees and destroying the homes of arboreal animals. It is harmful to human health when the gases in it are inhaled, causing respiratory diseases like asthma, chronic bronchitis, heart attacks and even death. AIR POLLUTION AND ACID RAIN In a complex process, large amounts of acid gases i.e. sulphur dioxide, carbon dioxode and oxides of nitrogen are produced by burning fossil fuels. Incomplete combustion of these fuels also releases hydrocarbons These gases during rainfall or snowing mix and react with water in the air to produce carbonic, nitric and sulphuric acid which fall as acid rain. Acid rain is an acidic pollutant with low pH of less than 4 It is often experienced in industrialized areas of the world e.g. Europe, USA, China, Japan. Greenhouse effect results into the following: - Ozone layer depletion - Global warming - rise in sea level due to thawing of glaciers/ice-caps causing flooding particularly in coastal areas. - increase and more devastating natural disasters like hurricanes. - desertification of fertile areas due to high temperature, thus adversely affecting agriculture and food supplies. - Environmental degradation - Migration of species - Species extinction - Climate change Furthermore, Greenhouse gases (GHGs) such as methane, carbon dioxide, carbon monoxide, nitrous oxide, hydrochlorofluorocarbon (HCFCs), hydrofluorocarbons (HFCs), and water vapour are mostly in the lower atmosphere. When solar radiation hits the earth, a lot is radiated back into space. Some of the reflected radiation is absorbed in the atmosphere by these green house gases, trapping heat, thereby keeping the earth warm. However, due to pollution, the concentrations of these gases have increased tremendously as that they now absorb and trap so much of the solar radiation that would have been reflected back into space, thereby over-heating the earth and causing global warming. AIR POLLUTION AND GREEN HOUSE EFFECT The earth is naturally protected from solar radiation by an o

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