Ecology by B.O. Odiyi PDF

ECOLOGY BY B.O. ODIYI  DEFINITION OF ECOLOGY The term ecology is coined from two Greek words: – Oikos meaning “home” or “house” – Logy meaning “the study of” Literally, it is therefore “the study of an organism in its natural home.” This word was coined by a German zoologist...

ECOLOGY BY B.O. ODIYI  DEFINITION OF ECOLOGY The term ecology is coined from two Greek words: – Oikos meaning “home” or “house” – Logy meaning “the study of” Literally, it is therefore “the study of an organism in its natural home.” This word was coined by a German zoologist Ernst Haeckel in 1869 as Oekologie to refer to the total relations of the animal to its organic and inorganic environment.  Since this definition of ecology by Haeckel, numerous other definitions have been given. Some will be considered here: Frederick Clements (1916) considered ecology to be the science of community. Charles Elton (1927) defined it as the scientific natural history concerned with the sociology and economics of animals. Taylor (1936) saw ecology as the science of relations of all organisms to all their environments.  Andrewaetha (1961) saw ecology as the study of the distribution and abundance of organisms. Kendeigh (1974) defined ecology as the study of animals and plants in their relation to each other and to their environment. According to Kinako (1988), ecology is seen as the branch of science that deals with the qualitative and quantitative analyses of the inter- relationships between organisms and their abiotic and biotic environment.  As seen from the above definitions, there are probably as many definitions for ecology as they are ecologist. The uniting factor in these definitions is that ecology is interested in studying the relationship between organisms in one hand and also the relationship with their environment in the other. Ecology can therefore be defined as the scientific study of the relationship between organisms and their environment.  It can also be defined as the scientific study of interactions that determine the distribution and abundance of organisms. Distribution refers to where organisms are found. We can study distribution on different scales: – Where they are found geographically – Where they are found in terms of habitat – How they are distributed spatially within habitat  Abundance refers to how many organisms occur. We ask different questions about abundance: – Does a species occur in many habitats? If so, it will appear abundant on a large scale (we will encounter it in many places). – Are there large numbers of individuals of a species in a habitat where it occurs? If so, a species may be rare or abundant on a large scale, but in certain localities it will be abundant.  We can also look at abundance in terms of species, rather than in terms of individuals of a single species. We can ask whether an area has many different species or only a few species. Interactions refer to the relationships between an organism or species and aspects of its environment. The environment refers to the surroundings of an organism or species, and is generally considered to consist of two categories of factors:  Biotic factors refer to other organisms that interact with an organism or species, or the organic products of those organisms. Examples of biotic factors include: – The species that produce the food eaten by the organism – Species that feed on and harm the organism, including: – Predators: species that kill and eat their prey and have no long term interaction with them. – Parasites: species that live on or in their host over a long period of time and harm, but are unlikely to directly kill the host. – Parasitoids: species whose eggs are laid on the host (typically on the larval stages of insect hosts) and which then develop in or on the host, harming it as parasites do, but that eventually grow large and kill the host. – Brood parasites: species (typically birds) that lay eggs in the nest of their host species. The hosts care for these young and their own young are usually harmed or killed. – Mutualists: species whose presence is helpful or essential to the organism, and who are helped by the organism.  Abiotic factors refer to non-living aspects of the environment that affect an organism, such as oxygen, water, pH, salinity, temperature etc. Biotic and abiotic factors interact. For example, plants (biotic factors) in an environment tend to increase the amount of oxygen (an abiotic factor). Ecology is part of Biology because it deals with life – probing into the secrets of various levels living systems – organism, population. It is a multidisciplinary science that uses the tools of other discipline to explain natural observed phenomena.  Ecology is a practical science involving; – the measurement of factors affecting the environment – studying the distribution of living organisms, and – finding out how living organisms depend on one another and their non-living environment for their survival. ECOLOGY SEEKS TO EXPLAIN Life processes and adaptations Distribution and abundance of organisms The movement of materials and energy through living communities The successional development of ecosystems The abundance and distribution of biodiversity in context of the environment  SUB-DIVISION OF ECOLOGY Ecology is broadly divided into Autecology and Synecology. Autecology focuses on the ecological study of one species of organism. Thus an autecologist may study the life history, population dynamics, behaviour, home range and so on of a single specie. Synecology deals with ecological studies of communities or entire ecosystems.  Thus a synecologist might study deserts or caves or tropical forests. He is interested in describing the overall energy and material flow through the system rather than in concentrating on the finer details of a particular organism.  Besides these major ecological sub-divisions, there are following specialised branches of ecology: – Habitat ecology – Applied ecology – Community – Production ecology ecology – Paleoecology – Population ecology – Space ecology – Evolutionary – Radiation ecology ecology – Systems ecology – Taxonomic ecology etc. – Human ecology  SCOPE OF ECOLOGY Ecology has a wide scope of coverage and is significant in many fields such as – range, forest and game managements; – agriculture – livestock raising; fish culture; conservation of land and its products (minerals, soil, vegetation, water); – space ecology; – problems of increasing population; – pollution; – urbanization; – town planning; – disaster mitigation.  LEVELS OF ORGANISATION IN ECOLOGY Organism= fundamental unit of ecology. No smaller unit in biology has an independent life in the environment. Study of individual organisms' behavior, physiology, morphology, etc. in response to environmental challenges. Population= a group of individuals of a single species inhabiting a specific area (all the individuals of a given species). Study of factors that affect and change the size and genetic composition of populations of organisms.  Community= an association of interacting species living in a particular area. Study of how community structure and organization are changed by interactions among living organisms. Ecosystem= a biological community plus all of the abiotic factors influencing that community. The study of entire ecosystems, including the responses and changes in the community in response to the abiotic components of the ecosystem. This field is concerned with such large-scale topics as energy and nutrient cycling.  Biosphere= the aggregation of all ecosystems (the sum of all of the organisms of the earth and their environment). The living zone of the planet. ECOLOGICAL HIERARCHY  ORGANISM An organism is a distinct unit of life in nature. It is said to be the smallest level and basic unit of ecological hierarchy. Characteristics of an organism An organism performs all the life processes independently. It is a quantitative unit (that can be counted) has the ability to grow and regenerate.  It resembles its parents and has a definite life span. It ensures continuity of its race through transmission of characters to its offspring through the process of reproduction. It cannot live in isolation i.e. shows interdependence with other biotic and abiotic factors of the environment. It is a functional unit that interacts with the environment.  POPULATION Population is the next level in ecological hierarchy the word population has its origin in the Latin word populus meaning 'people'. Population is defined as the total number of organisms of the same species, which breed among themselves in a specific geographical area at a given time.  THE CHARACTERISTICS OF POPULATION Individuals living in the same area are called local populations. They all experience similar ecological processes at a particular stage of the life cycle. Similar populations of a species occupying different geographical areas are called sister populations.  Population is a dynamic unit. Number of individuals may increase or decrease due to many factors such as birth rate, death rate, migration etc. Variation is expressed as population size and population density in a given area at a particular time. In a geographical area, the population is further divisible into sub-groups called demes. Deme is a local population of closely related interbreeding species.  The chances of sexual communication are more between the members of same deme than between the members of different demes. Due to this mating ability, there is free flow of genes in a species. Population of an area is described on the basis of three parameters: a) Number and kind of individuals of a species. b) A given space or an area. c) Time.  FACTORS AFFECTING POPULATION 1. Birth rate or Natality rate: Natality rate is the rate at which new individuals are added to a particular population by reproduction (birth of young ones or hatching of eggs or germination of seeds/spores). It is generally expressed as number of births per 1,000 individuals of a population per year. Absolute', 'physiological or maximum natality', refers to the theoretical maximum production of new individuals under ideal conditions. But it is never realised because of environmental resistance (factors like inter and intra specific competitions, availability of food, space etc.) Actual birth rate being achieved under existing conditions, which is much lesser than 'absolute natality is called realized natality. Higher realized natality rate increases the population size and population density. 2. Death or Mortality rate: Mortality rate is the rate at which the individuals die or get killed. It is the opposite of natality rate. Mortality rate is generally expressed as number of deaths per 1,000 individuals of a population per year. Lowest death rate for a given species in most favourable conditions is called potential mortality while the actual death rate being observed in existing conditions is called realized mortality. Realized mortality decreases the population size and population density. 3. Age distribution (Age composition): The relative abundance of the organisms of various age groups in the population is called age distribution of population. With regard to age distribution, there are three kinds of populations. i. Rapidly growing population is a population, which has high birth rate and low death rate, so there are more number of young individuals in the population. ii. Stationary population is a population, which has equal birth and death rates, so population shows zero population growth.  iii. Declining population is a population, which has higher death rate than birth rate, so the population has more numbers of older individuals. 4. Immigration: Immigration is the permanent entry of new individuals of same species into a population from outside. It increases the size of local population. 5. Emigration: Emigration is the permanent movement/departure of individuals of same species out of the local population due to several reasons such as lack of food, scarcity of space (over crowding), etc. Emigration decreases the size of local population, but the species spread to new areas. If more individuals are added than lost, then the population will show positive growth. If more individuals are lost than added, then the population will show negative growth.  But if the two rates are equal, then the population will become stationary and is called zero growth. 6. Natural calamities A drastic change in the environment destabilizes or even exterminates a population. Natural calamities such as earthquake, volcanic eruptions etc. cause drastic changes in the environment leading to the destruction of the resources. 7. Abiotic and biotic factors: Abiotic factors like temperature, wind, humidity, rainfall, intensity of light has its effect on the density of population.  Biotic factors like organisms of other species living in the same area affect the population, as they involve in different types of food relationships. For e.g., if the population happens to increase in size, it is brought down by an increase in its predators number or decrease in the amount of available food. Different populations have different ability to tolerate changes in weather, physico-chemical and biotic factors. This is called resilience.  In nature, factors like predators, diseases, food scarcity etc. prevent a population to move towards infinity. The sum of all these factors, which prevent a population from growing at its maximum rate, is called environmental resistance or population regulation  COMMUNITY This is group of organisms of different species living together in the same environment at a given time There are 2 characteristics of communities namely: Composition - this is the list of various species in the community i.e the floral (plants) and fauna (animals). Diversity - it includes both number of species (species richness) and evenness (the relative abundance of individuals of different species).  A number of interactions occurs at the community level and they are: 1. Predation: This occurs when one living organism called the predator, feeds on another called the prey (food). The prey has some defense mechanisms that prevents them from being eaten by a predator and they include: i. Some prey possess structures that can harm the predator e.g sharp pines of the cactus, pointed leaves of the holly, production of poisonous chemicals by plants. For animals, they use: ii. Camouflage: this is a mechanism by which predators fool their prey and the prey avoid capture by their predators e.g. stick caterpillars that looks like twigs, katydids that looks like sprouting green leaves. iii. Causing harm or fright: the large false head of the south American lantern fly that looks like that of a alligator, the arrow like quills of the porcupine with barbs that digs into the predator’s flesh and penetrate even deeper as the enemy struggles after being struck. iv. Flocking together of prey: when prey stays together in order to protect themselves against the predator e.g. antelopes who detect predators by smell can forage together giving double protection against stealthy predators. v. Mimicry: this occurs when one species resembles another that possesses an overt anti- predator defense.  2. Commensalism: This is a symbiotic relationship between two species in which one species benefits and the other neither benefits nor harmed e.g. Remoras are fishes that attach themselves to the bellies of sharks by means of a modified dorsal fin. 3. Parasitism: This is an obligatory relationship between two different organisms in which one organism called parasite derives nourishment from another organism called the host and in turns hurt the host. E.g Viruses, tapeworm, hookworm and HIV that reproduce inside human lymphocytes are parasitic and are called endoparasites because they live within their host  While ectoparasites are those parasites that remain attached to the exterior of the body by means of specialized organs and appendages e.g lice, mosquito, bedbug, flea Host serves the parasite with the following functions: – Provides nourishment – Provides a place to live and reproduce – Provides a mechanism for dispersing offspring to new hosts. 4.Symbiosis/ mutualism: this is a relationship in which both members of the association benefits e.g. bacteria that reside in the human intestinal tract are provided with food but they also provide us with vitamins, molecules we are unable to synthesize for ourselves.  ECOSYSTEM This can be defined as a place or a natural unit where organisms interact among themselves and with physical and chemical environment. It can also be defined as a place where interaction occurs between biotic and abiotic factors An ecosystem is characterized by energy flow and chemical cycling. The populations within the biotic community of an ecosystem are classified into trophic or feeding levels namely  Autotrophs They require only inorganic nutrients and an outside source to produce sugars and other organic compounds for their own use and as a source of organic nutrients for other members of the community. Therefore, they are called producers i.e. they produce food. there are 2 forms of autotrophs: Chemoautotroph: they are bacteria that obtain energy by oxidizing inorganic compounds like ammonia, nitrites and sulphides and they use this energy to synthesize organic compounds.  Photoautotroph: they are photosynthesizers that produce most of the organic nutrients for the biosphere. Algae of all types possess chlorophyll and carry on photosynthesis in freshwater habitats and marine habitats. Algae make up the phytoplankton which are the photosynthesizing organisms suspended in water. Green plants are the dominant photosynthesizers on land.  Heterotrophs They need preformed source of organic nutrients. they are consumers. There are three types of consumers: Primary 1 consumers: they are the least among the consumers e.g. grasshoppers Secondary 2 consumers: e.g. lizards Tertiary 3 consumers sometimes they are referred to as top predators e.g. hawks  There are different types of heterotrophs namely: 1. Herbivores: these are animals that graze directly on plants or algae. In terrestrial habitats, insects are small herbivores, while in aquatic habitats, zooplanktons such as protozoans play that role. 2. Carnivores: they feed on other animals for example, birds that feed on insects are carnivores, and so are hawks that feed on birds. 3. Omnivores: they are animals that feed on both plants and animals e.g. humans 4. Detrivores/decomposers: they are organisms that feed on detritus which is decomposing particles of organic matter e.g. maggots, termites, earthworms are all terrestrial detrivores.  Non- photosynthetic bacteria and fungi including mushrooms carry out decomposition which is the breakdown of dead organic matter including animal wastes. They perform a very valuable service because they release inorganic nutrients that are taken up by plants once more, otherwise plants will have to wait for minerals to be released from rocks.  BIOSPHERE The term biosphere is derived from two words: bios, meaning life, and sphere meaning globe. Therefore the biosphere is the earth's relatively thin zone of air, soil, and water that is capable of supporting life. This ranges from about 10 km into the atmosphere, to the deepest ocean floor.  The biosphere can be viewed as a system or a set of functions that operates together and is dependent on each other, i.e a global ecosystem composed of both biotic and abiotic components. The biotic part of the biosphere is all the plants and animals while the abiotic part of the biosphere consists of all the non-living parts of the ecosystem The biosphere is made up of the hydrosphere, lithosphere, atmosphere and geosphere.  HABITATS The habitat of an organism is the place where it lives, a physical area, and some specific part of the earth's surface, air, soil or water. It may be as large as the ocean or a forest or as small and restricted as the underside of a rotten log or the intestine of a termite. However, it is always tangible, physically demarcated region.  It is a place where an organism makes its home. It meets all the environmental conditions an organism needs to survive. More than one animal or plant may live in a particular habitat. There are basically 2 types of habitats. These are terrestrial and aquatic.  TERRESTRIAL HABITAT Ecologists have divided the terrestrial communities of the world into general groupings called Biomes, which are areas that can be recognized by the distinctive life forms of their dominant species. In most cases, the key characteristic of a biome is its dominant type of vegetation. It could also be said that a biome is a complex of communities' characteristic of a regional climatic zone.  Each biome has its pattern of rainfall, season, temperature and changes of day length all of which combine to support a certain kind of vegetation. Starting at the polar region the major biomes of planet earth are:  Tundra Tundra is the northern most of the world's landmasses. Found in the Arctic region. It is characterized by permanently frozen subsoil called Permafrost, which has low rainfall. Dominant vegetation is moss, grass and some small perennials. Arctic tundra are found on high-latitude landmasses, above the Arctic Circle—in Alaska, Canada, Russia, Greenland, Iceland, and Scandinavia.  Taiga Taiga is a Russian world meaning " Swampy forest". Taiga is mostly identified with its abundant coniferous forest. The trees available, mostly conifers are less diverse in number of species than those in the deciduous trees forests found further south from Taiga and the soil has different kind of humus which is more acid.  It is in the subarctic zone just south of the tundra. Precipitation is low, but like Tundra there are a number of bogs and lakes available. Taiga can be found in Canada, Sweden, Finland, Siberia.  Temperate deciduous forest This occurs in a belt south of the Taiga where climate is milder and where rainfall is abundant relative to the amount of evaporation. The deciduous forest has a great variety of mammals, birds, and insects as well as modest number of reptiles and amphibians. Because of the annual leaf drop deciduous forest generate soils rich in nutrients, which in turn supports a multitude of soil microbes.  Temperate deciduous forests are mainly found in North America, Europe, Eastern Asia, part of Australia and Japan.  Grassland In regions where annual rainfall is not sufficient to sustain the growth of trees and evaporation rates are high we find the grassland of the world. Example of such a biome is the Savannah of tropical Africa. The dominance of grass and herds of grazing animals characterize all grasslands. Carnivores are also abundant.  Such biome has a higher concentration of organic matter in its soil than does any other biome, the amount of humus being 12 times greater than that in forested soils. Grasslands typically occur in the interiors of continents and include tall grass prairies, short grass prairies and arid grasslands of North America as well as the steppes of Eurasia, the veldt of Africa and the pampas of South America (Argentina).  Desert This is an area, which is receiving less than 10 inch of rainfall per year. Lack of moisture is the essential factor that shapes the desert biome Examples include the Antarctic (Antarctica), Sahara (Africa), Arabian (Middle East), Gobi (Mongolia, China), Patagonia (Argentina), Great Victoria (Australia), Atacama (Chile) and Kalahari deserts (Southern Africa).  Tropical rain forest It is characterized by high temperature and high annual rainfall (100 inch or more). Year round temperature variations is slight. Tropical rain forest is characterized by a great diversity of plants and animal species and by four distinct layers of plant growth: Top canopy of trees reaching 60 meters, Lower canopy reaching 30 meters, Sparse under story and Very few plants growing at ground level.  Both plants and animal species exist in greater diversity in the tropical rain forest than anywhere else does in the world. Tropical rain forest soils in general are exceedingly thin and nutrient poor relative to temperate regions. As a result nutrients are locked in the biomass in the tropics and removal of vegetation may severely disrupt nutrient cycling leading to ecological disaster. Main Biomes of the World  AQUATIC HABITAT They are classified into 3 types which are the: Freshwater (inland) Marine (salt) water. Brackish water This listing is based on ascending order of salinity. Fresh waters have a salt content of less than 0.5 parts per thousand as against as much as 30 to 37 parts per thousand for sea or marine water.  Salinity differentials constitute ecological barriers to the movement of fresh water organisms from fresh water ecosystems into marine ones and vice versa. There is a species diversity gradient from fresh water through brackish water to the marine habitat. The least level of diversity occurs in fresh water while the highest is the marine one.  The aquatic habitats includes the oceans, seas, lakes, ponds, streams, rivers and groundwater. Approximately 70% of the earth is covered with water. Of this 97% is salt water while 3% is freshwater. Out of this 3%, 2% is locked up in ice caps and glaciers. Only about 1% is available for human use. When rain falls, some of the water percolates or sinks into the ground and results in the saturation of the earth with water to a certain level.  The top of the saturation level is called the ground water table or the water table. Wherever the earth contains basins or channels, water will appear to the level of the water table. The water within basins (lentic) is called lakes and ponds and the water within channels (lotic) are called streams or rivers. Also, sometimes groundwater is also located in underground rivers called aquifers.  Freshwater habitat The study of freshwater ecosystem is called limnology. Freshwater habitat is conventionally divided into 2. These are: Lotic or running water habitats e.g springs, streams and rivers. lentic or standing or still water habitats e.g ponds and lakes. Ecological factors that are likely to be of crucial importance in fresh water ecosystems are:  Temperature Temperature is less variable in water than in air but it is nevertheless an important limiting factor because aquatic organisms often have narrow temperature tolerance rate (they are Stenothermal). Temperature fluctuations produce characteristic patterns of water movement (circulation) and stratification in freshwater lakes. Thermometers and electronic sensors such as thermistors are used in the measurement of temperature in aquatic ecosystems.  Transparency This refers to the ability of the water body to allow light to go through it easily. Turbidity is directly related to transparency. It is caused by materials in suspension. Its main effect is to reduce light intensity and as a result lower primary productivity. Effects of turbidity are shown when the water contains more than 4% (by volume) of solid materials in suspension. Transparency is normally measured with a simple instrument called a Secchi disc.  Currents This is the steady flow of water in a particular direction. A current meter is a useful instrument for the measurement of current speed. The behavioural responses of resident animals include rheotaxis and thigmotaxis. Rheotaxis is the ability to face and move against the current upstream. Thigmotaxis on the other hand is the tendency to cling to any surface with which the body comes in contact thus avoiding being washed downstream by the current.  Biogenic salts: Nitrates and phosphates are limiting to some extent in all fresh water systems. The concentration of other salts, especially calcium, affects pH of the water with significant impact on the distribution of aquatic organisms. Fish generally tolerates a wide range of pH from 5 to 9. Below pH 5, high mortality occurs. Over concentration of biogenic salts can result in eutrophication. Respiratory gases: These play important roles in the ecology of freshwater ecosystems. Oxygen and carbon dioxide concentrations are often limiting.  The longest rivers in the world are River Nile (Africa), Amazon (South America) and Yangtze (Asia). The largest lakes in the world are the Caspian sea (Eastern Europe), Lake Superior (North America) and Lake Victoria (East Africa).  Marine habitat The marine habitat refers specifically to seas and oceans. Some features of the marine ecosystem that are of ecological significance include: The marine ecosystem is very big, indeed, the largest ecosystem on earth, covering about 71% of the earth’s surface. It is very deep with an average depth of 3.75 km with their greatest depth reaching more than 11.5 km below sea level. Life extends to all its depths.  It contains more than 200,000 species of unicellular forms, plants and animals. About 98% of these forms live on the seabed (benthic); only 2% live freely in the open ocean (pelagic).  Of the benthic forms, the largest biomass occurs in intertidal zone or shallow depths of oceans, but species diversity increases from the shallow waters to a maximum at 2000 to 3000 m depth and then declines at greater depths.  The sea is continuous and not separated as terrestrial and fresh water ecosystems which are disjointed.  The sea is always in continuous and tumultuous circulation due to varying wind patterns.  The sea is dominated by waves of many kinds and by tides produced by attraction forces between the sun and the moon. The tidal range varies from less than 30 cm in the open sea to about 1500 cm or 15m in certain enclosed bays.  The sea is very salty relative to fresh water and brackish water ecosystems.  The concentration of dissolved nutrients is low and constitutes a major limiting factor in determining the size of marine populations.  The oceans of the world from the largest to the smallest are: Pacific, Atlantic, Indian, Southern (Antarctic) and the Arctic Oceans. Examples of popular seas include Mediterranean, Caspian, Caribbean, Red, Bering, Baltic, South China Seas etc.  Brackish water habitat Waters of all streams and rivers ultimately drain into the sea; the place where this freshwater joins the salt water is called an estuary. They are more or less transitory zones (ecotones) between the freshwater and marine habitats and are the sites of unique ecological properties. The brackish water includes deltas, estuaries, tidal marshes and bodies of water behind beaches.  The 2 main physical features of the brackish water habitat are: Considerable expanses of soft mud which are exposed at low tide. Fluctuating salinity where the flow of the tide inlands meets that of the water seawards. The Niger Delta is a good example of a brackish water in Nigeria.  This vast region of Nigeria experiences considerable siltation as a result of the deposition of the loads of silt from the numerous rivers, creeks and streams that flow into it. The typical vegetation of brackish water habitats are dominated by halophytes. The biotic community is salt-tolerant. The area supports a vibrant fishing industry based on snails, bivalves, crayfish and prawns, sardine, mullet, croakers, tilapia and catfish among others.  The biggest deltas in the world are the Ganges – Brahmaputra Delta (India, Bangladesh), Okavango Delta (Southern Africa; Botswana) and the Mekong River Delta (South East Asia; Cambodia and Vietnam).