Grade 11 Population Ecology Term 4 PDF

Summary

This document is about population ecology, focusing on estimating population size through direct methods. It discusses concepts like census, aerial photographs, and the importance of considering the area size. It also briefly covers the overview of the topic, and goes into detail about population parameters and limiting factors. It then further introduces competition, resources, and types of interaction between living organisms.

Full Transcript

L1 | POPULATION ECOLOGY | Estimating Population Size: Direct Methods POPULATION ECOLOGY Estimating Population Size: Direct Methods DIRECT METHODS An example of a direct method is a census, during which every single individual in a populatio...

L1 | POPULATION ECOLOGY | Estimating Population Size: Direct Methods POPULATION ECOLOGY Estimating Population Size: Direct Methods DIRECT METHODS An example of a direct method is a census, during which every single individual in a population is counted. This method can only be used when: organisms are large enough to be seen the area in which the animals are being counted is not too large Direct methods can be used for individuals that are: slow-moving, e.g. snails, tortoises, or stationary, e.g. plants, or usually stay in a fixed position, e.g. barnacles, mussels. If the area is too large to count every individual at one time: aerial photographs can be taken of the whole area, e.g. penguins, seals or a species of a large tree. helicopters can be used to count larger animals, e.g. elephant. census forms can be filled in by humans, accounting for everyone in a household on a particular day. Image Source: National Geographic Society Note: In South Africa, there is a population census every five years to determine how many people live in this country. L1 | POPULATION ECOLOGY | Overview | Introduction | Population Parameters POPULATION ECOLOGY Lesson Objectives In this Topic you will learn the following: the definition of individual, population, community and ecosystem. that the size of a population is affected by immigration, emigration, mortality and births. Population size fluctuates seasonally and annually, depending on resource availability. the effects of limiting factors on population growth i.e. density dependant/independent factors and environmental resistance; the concept of carrying capacity and its implication for a species. sampling methods: Mark-recapture – method, precautions, calculation of population size Quadrats – method, precautions, calculation of population size Census – method, limitations the importance of random sampling. the definition of predator-prey relationships Study TWO examples of predator-prey relationships from the South African context to show how these operate as a mechanism for regulating populations, e.g. lion – zebra; aphid – ladybird; shark – fish. the impact of food webs and social organisation on populations that species compete with each other for resources, e.g. light, space, water, shelter, food, and that this results in specialisation for particular modes of life. Interspecific and intraspecific competition for food, space, shelter, water, and access to mates. Survival is determined by successful access to resources. Ecological niche defines resources and conditions necessary for the survival of each species. ways of reducing competition: ONE strategy among plants, e.g. resource partitioning as in a forest ecosystem ONE strategy among animals, e.g. coexisting shorebirds; coexisting large herbivores in African savanna; coexisting predators, e.g. lions and leopards the concept of ecological succession: the sequence of organisms that occupy a new habitat (primary succession) or a disturbed habitat (secondary succession). Pioneers are replaced by a succession of species; with numerous possible endpoints, depending on environmental fluctuations; variety and number of species determined by constraints of succession. that social organization enhances survival: benefits of herds or flocks as a predator avoidance strategy as in zebra packs as a successful hunting strategy as in wild dogs animals with a dominant breeding pair as in wild dogs division of tasks among castes as in termites the application of population dynamics to human populations. Reasons for exponential human population growth. Forecasts of human population growth in South Africa over the next twenty years. Overview 1. Population Size 2. Population growth forms 3. Interaction in the environment 4. Predation 5. Competition 6. Mutualism, Commensalism, Parasitism 7. Social organisation 8. Community Change 9. Human Population 10.Population Pyramids Terminology ECOLOGY is the study of the interactions between organisms and their physical and biological environments, plus how these determine the distribution and size of populations within an ecosystem. POPULATION ECOLOGY studies changes in population size and the factors that influence it. SPECIES is a group of similar organisms that are able to interbreed and create fertile offspring. Can you name one example? POPULATION is a group of organisms of the same species that occupy the same area and can breed freely with each other. Can you think of some examples? Content Source: Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 0:00 / 4:31 0:00 / 10:25 Population Parameters Population size is the total number of individuals in a population. Factors that influence population size: Natality – the birth rate in animals or the production of seeds in plants Immigration – individuals move into a population and stay Mortality – the death rate Emigration – individuals leave a population and do not return For humans: the birth rate is the number of births per 1000 people per year the death rate is the number of deaths per 1000 people per year Image Source: BioNinja (2020) 5.3 Populations. Standard Level. Topic 5 Ecology and Evolution. Available at: http://www.old-ib.bioninja.com.aU Note: In a closed population with no immigration or emigration, e.g. fish in a small pond, the only parameters affecting any change in population numbers will be births or deaths. 0:00 / 15:37 L2 | POPULATION ECOLOGY | Estimating Population Size: Indirect Methods POPULATION ECOLOGY Estimating Population Size: Indirect Methods Indirect methods involve counting a sample number of the population and then using simple calculations to estimate the total size of the population. Two such methods are the quadrat method and mark-recapture method. Content Source: Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 Quadrat Method The number of individuals in small measured areas (quadrats) are counted, then the following formula is used to estimate the population size: N = total population The distribution of individuals may not be the same everywhere, therefore it is important to sample different parts of the total area. This is known as random sampling. Image Source: Amazing World of Science with Mr Green Method: 1. Measure the size of the total area. 2. Use a wooden frame with known diameters (usually about 1 sq meter) as a quadrat. The same quadrat size must be used for each sample. 3. Distribute quadrats at random in the area. 4. Count the individuals in each quadrat. Several samples should be taken and the number of individuals per quadrat calculated. This is the ‘number in sample’ in the formula. 5. Using the above formula, calculate the size of the population. Mark-Recapture Method Mark-recapture method This method is used for organisms that are: mobile, e.g. butterflies, birds, antelope not easily visible, e.g. fish in a dam. Method: 1. Mark out a well-defined area. 2. Capture as many individuals as possible and mark them (see examples in the image). 3. Release the marked individuals back into the environment. 4. Allow enough time to mix with the unmarked individuals, but not too much time for too many deaths and births to occur (this depends on the species). 5. Recapture as many individuals as possible. 6. Count the total number and count the number of those which have been marked. 7. Calculate the total population size by using the Petersen index as below: P = estimated Population size M = total number of Marked animals C = total number of animals Caught in the second sample R = total number of marked animals in the second sample, i.e. Recaptured. Note: Sometimes different letters are used but the calculation stays the same. Image Source: EcoReach WordPress How do we ensure a reliable result? No immigration or emigration is allowed, i.e. the population must be closed. The marking must not damage the individual or affect its movement or behaviour. The marked animal must have enough time to mix freely with the rest of the population before a new sample is taken. Yet, only a short enough time should pass between the first and second sampling so that no significant number of births and deaths can occur. Sampling should be repeated several times and an average population calculated. 0:00 / 0:00 L2 | POPULATION ECOLOGY | Population Growth Forms POPULATION ECOLOGY Population Growth Forms There are 2 types of population growth forms (or how a population will grow), and these depend on specific conditions in an environment. Content Source: Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 Exponential / Geometric Growth Pattern Known as the J curve, Occurs in an ideal, and unlimited environment (i.e. unrestricted growth) Exponential Growth: In an environment where resources are unlimited, There will be no competition that will impact the exponential growth of the population, The growth rate of the population will be exponential, resulting in a J-curve. Logistic Growth Pattern Known as the S curve, Occurs when the environmental conditions slow down the growth rate of the population (i.e. restricted growth). Logistic Growth: The population will approach a carrying capacity, the maximum number of individuals an environment can sustainably support the population, As the population will approach the carrying capacity, environmental resistance will slow down the rate of growth of the population. Limiting Factors Can you think of the factors in an environment that will limit the growth rate of a population? We can categorize these ‘limiting factors’ into two: 2. Density dependent factors – these are dependent on the relative population size. 3. Density independent factors – these are NOT dependent on the relative population size. (Source: bioninja.com.au) 0:00 / 7:32 L3 | POPULATION ECOLOGY | Competition POPULATION ECOLOGY Competition 0:00 / 0:00 Ecological Niches An ecological niche is the role an individual plays within a community, or its natural habitat. These roles will include what the individual eats, how it interacts with its physical environment, as well as other individuals within the community. One way of understanding the difference between a ‘niche’ and ‘habitat’: An ecological niche = the ‘occupation’ of an individual, A habitat = the ‘address’ of an individual. (Source: pathwayz.org) Types of Competition When there is a limited supply of resources, or space, an individual will have to compete to acquire these resources to survive. How do you think competition will affect the growth rate and size of a population? There are two types of competition: 1. Intraspecific competition, 2 Interspecific competition. Intraspecific Competition This type of competition occurs between individual of the SAME species. What do you think individuals of the same species will compete for? (source: biologygrasslands.weebly.com/population-interactions) Interspecific Competition (Source: differencebetween.com) This type of competition occurs between individuals of two or more species within similar habitats. What do you think these individuals will be in competition for? Specialisation What do you think would happen if the niches of competitors overlap? Let us use the Galapagos finches as an example. The many species of finches have adapted a variety of beak shapes and sizes to specialize in eating different food sources, therefore creating their own ecological niches to avoid competition. Competitive Exclusion This principle states that if two species are competing for the same, scarce resource one of the species will out-compete and displace the other species. This will lead to the displaced species facing extinction, either by migrating to a new habitat (changing their physical address), or death. Resource Partitioning Resource partitioning – competing species will partition the similar resources that both species use. The species will evolve specialized traits to use the resources in a different way to minimize interspecific competition. How can resources be partitioned? By using resources: 1. At different times, 2. In different parts of a habitat. 3. At different parts of the same plant. L3 | POPULATION ECOLOGY | Interactions in the Environment POPULATION ECOLOGY Interactions in the Environment We now understand that there are abiotic factors within an environment that will impact the growth rate of a population. Now we will look at how the interactions between living organisms will also influence and affect the growth rate and success of a population. Populations and communities within an ecosystem will depend on these interactions for their survival in terms of reproduction and growth rate. These interactions will determine the composition and structure of communities within natural environments. Loading embedded media... Types of Interactions Between Living Organisms There are 5 types of interactions between living organisms in an environment: 1. Predation, 2. Competition, 3. Commensalism, 4. Mutualism, 5. Parasitism. Commensalism, mutualism, and parasitism are also known as symbiotic relationships, in that one individual will at least always benefit from the relationship between two individuals of different species. Content Source: Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 L3 | POPULATION ECOLOGY | Predation POPULATION ECOLOGY Predation The word ‘predation’ is derived from the Latin word ‘praedari’, which means to plunder. Predation – where one organism (predator) will hunt and kill another organism (prey) for food; or the flow of energy from prey to predator. (Sources: biologydictionary.net) What are the roles of predators in an environment? They regulate the population size of prey, Prevent a single species from becoming the dominant species, and thus increasing the biodiversity of communities, By preying on the weaker individuals of the prey population predators help keep the prey species genetically fit. Content Source: Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 Loading embedded media... The Predator-Prey Relationship The population sizes of both predators and prey depend on each other. If one population increases in size, this will influence and determine the population size of the other. L4 | POPULATION ECOLOGY | Social Organisation POPULATION ECOLOGY Social Organisation Many animals live in social groups. Social organization is the pattern of the relationships the individuals within a population will have. If a group of animals are socially organized, this means that there are certain tasks that will be divided and allocated among certain individuals within the population. For example, some will be responsible for resources (food and territories) and other will be responsible for activities (reproduction and protection). Two highly specialized social groups of animals are mammals and insects. Can you think of an example of each? Social organization may improve both the chances of survival (survivability rate) of the individual as well as, by implication, the population as a whole. The group is stronger together, than the individual on their own. Predator Avoidance Collective Hunting 0:00 / 2:12 Labour Tasks L4| POPULATION ECOLOGY | Symbiotic Relationships POPULATION ECOLOGY Symbiosis Symbiotic relationships are close interactions between individuals where at least one individual will benefit from the interaction, or relationship. 0:00 / 0:00 Mutualism Mutualism is a relationship between two individuals where both individuals will benefit. A common example is the mutualistic relationship between plants and their pollinators (with the exception of a few devious plants, for example orchids that allure their pollinators and provide no sweet nectar as a reward). There are two types of mutualistic interactions: 1. Facultative mutualism – both species can benefit from each other, but they can also both survive with out the other. 2. Obligate mutualism – neither of the two species can survive with out the other. Can you think of an example of obligate mutualism? How do you think the population size of each species will be affected in a mutualistic relationship? (Source: Amoeba Sisters) (Source: Mikael Kvist/ Moment/Getty Images) Commensalism During this type of interaction, only one individual will benefit from the interaction. The other individual will gain nothing, nor will they be harmed or be impacted negatively from the relationship. An example of commensalism includes barnacles that will take safe shelter on a whale, while the whale will receive nothing in return. How do you think the population size of each species will be affected in a commensalism relationship? Parasitism Parasitism is a symbiotic relationship between individuals of two different species where one individual (the parasite) will live on or in the other individual (the host), causing harm to the host. Although parasites can eventually kill their host, it is in the parasite’s best interest to not kill the host as they are dependent on the host for their survival. Ectoparasites are parasites that attach themselves to the outside of the host. For example, lice, ticks, and fleas. Endoparasites are parasites that are highly specialized to take advantage and live inside their hosts, for example tapeworms and liver flukes. The parasite will help themselves to the host’s shelter, food, and other resources for their own survival. Can you think of some parasites that use humans as a host? 0:00 / 6:49 L5 | POPULATION ECOLOGY | Age & Gender Distribution POPULATION ECOLOGY Population Pyramids Population pyramids = a bar graph showing the population composition, by age and sex, of a country. Population pyramids can also be referred to as an age-sex pyramid. Reading population pyramids: The percent of the population is plotted on the x-axis, and age is plotted on the y-axis. The top of the pyramid shows the older population, while the bottom of the graph shows the younger population. The male population is shown of the left, and the female population is shown on the right. Loading embedded media... Types of Population Growth There are 3 different pyramid shapes that show 3 types of population growth: 1. Rapid growth / increasing population, 2. Stable / slow growth population, 3. Zero growth / declining population. 1. Rapid growth: 2. Stable: 3. Declining: High birth rate Declining birth rate Low birth rate High death rate as with the higher age Low death rate Low death rate groups Longer life expectancy Higher dependency ratio Short life expectancy Longer life expectancy Examples: Canada and Australia. Examples: Africa, Asia and South America. Examples: Japan, Norway, and S Look at Niger in 2022 Look at Australia in 2022 Look at South Korea in 2022 (https://www.populationpyramid.net/niger/2022/) (https://www.populationpyramid.net/australia/2022/) (https://www.populationpyramid.n of-korea/2022/) 0:00 / 5:01 Homework Complete the Quiz: (https://teneo.instructure.com/courses/117555/quizzes/875923?module_item_id=8308773) L5 | POPULATION ECOLOGY | Ecological Succession POPULATION ECOLOGY Ecological Succession Ecological succession: the gradual growth and change of an ecosystem over time. An ecosystem is not static, it is constantly changing, especially if a disturbance occurs that forces the ecosystem to regrow and reestablish itself. Disturbances can include fires, floods, storms, animal, or human disturbance. There are 2 types of succession: 1. Primary Succession, 2. Secondary Succession. Stages in each type of succession: 1. Pioneer species stage, 2. Intermediate species stage, 3. Climax Community. Content source: The Ecology Book. 2019. Dorling Kindersley Limited. A Penguin Random House Company. Mind Action Series. Life Sciences Textbook & Workbook. Grade 11 NCAPS. ISBN - 13: 978-1-86921-433-3 Product Code: LFS 30. Authors: Jen Grogan & Ruth Suter. First Edition: May 2012 Primary Succession Primary Succession Primary succession occurs on a brand-new habitat, one that has not previously been colonized by any plant species - the building of an ecosystem from scratch. The pioneer species of a primary succession include lichen that will begin to grow on the bare rocks. Lichens do not need soil to grow. Lichens and physical weathering will break down rocks, and this will lead to the formation of soil. As lichen decompose, they add small amounts of organic matter to the newly forming soil. Simple plants will follow, such as moss, followed by ferns and grasses as the soil layers deepen. Small insects, such as mites and ants, will be the first fauna to occupy the developing habitat. As the habitat develops and advances, complex fauna and flora species will follow. Secondary Succession Secondary Succession Secondary succession will occur after a disturbance has hit, such as a flood or a fire, destroying the plant community. However, the flora will re-establish itself and soon will develop into an ecosystem that was similar to the one before the disturbance. The pioneer plants of a secondary succession include grasses, herbs, and weeds. During the intermediate species stage the soil can retain more water and is more fertile. As a result, small non-woody herbaceous species will begin to grow, followed by small hardy, woody plant species. Shade intolerant plants will begin to grow, such as pine trees. As these trees grow higher, they will block out sunlight and the grasses will be replaced with shade tolerant plants, leading to the climax community. The climax community will be the end- point of succession. Different biomes will have different climax communities. For example, if a forest had been disturbed by a fire, it will develop once more into a forest, or Acacia trees will regrow in a savannah biome. 0:00 / 6:23 L5 | POPULATION ECOLOGY | Human Population POPULATION ECOLOGY Human Population Let us just sit and reflect on the development and growth of the human population. 10 000 years ago, there was an estimated 10 million people living on our planet. There were many factors, such as disease and high infant mortality rates, that kept this almost stable population number. Only until recently, 1000 years ago, has our species population grown exponentially. There were many trials and tribulations we, as a species, had to endure to get to a population that is close to 8 billion in 2022. What do you think had led to the success of this exponential growth? Check out the current human population at this exact moment! www.worldometers.info (http://www.worldometers.info)   More-Developed and Less-Developed Countries The world can be divided into two broad groups: 1. More-developed Countries (MDCs) Slow population growth, High standard of living. Examples: North America, Europe, and Japan. 2. Less-Developed Countries (LDCs) Rapid population growth, Lower standard of living. Examples: Africa, Asia, and South America.

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