Lesson Notes By Weeks and Term v5 - Grade 11

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Performance objectives

• Define population ecology and its relevance to South Africa.
• Describe factors influencing population size.
• Calculate population growth using two models.
• Explain human impacts on South African ecosystems.
• Discuss sustainable practices to mitigate these impacts.

Lesson summary

Population ecology is the study of populations and how they interact with their environment. It’s crucial for understanding how species survive, grow, and change over time. This understanding is vitally important in South Africa because our country faces unique environmental challenges, including rapid urbanization, water scarcity, biodiversity loss, and the impact of climate change on agricultural practices and human health. Understanding population dynamics helps us manage resources sustainably, protect endangered species like the rhino, and develop strategies to mitigate the effects of environmental degradation on our communities.

Lesson notes

2. 1.

Definition of Population Ecology: Population ecology is the branch of ecology that studies the structure and dynamics of populations. A population is a group of individuals of the same species living in the same area at the same time. Population ecologists study characteristics such as population size, density, distribution, age structure, and how these characteristics change over time. 2.

2. Factors Influencing Population Size and Growth: Population size changes due to four main factors: Birth Rate (Natality): The number of births per unit time (usually per year) in a population. High birth rates lead to population growth.

Death Rate (Mortality): The number of deaths per unit time in a population. High death rates lead to population decline.

Immigration: The movement of individuals into a population from another area. Immigration increases population size. Think of people migrating from other African countries to South Africa seeking job opportunities – this increases South Africa’s population.

Emigration: The movement of individuals out of a population to another area. Emigration decreases population size. For example, skilled South Africans leaving the country ("brain drain") reduces the population size. 2.

3. Population Growth Models: Exponential Growth: This model describes population growth under ideal conditions, with unlimited resources. The population increases at a constant rate.

The equation for exponential growth is: ``` dN/dt = rN ``` Where: `dN/dt` = rate of population change `r` = per capita rate of increase (birth rate - death rate) `N` = population size

Example: Suppose a population of bacteria starts with 100 individuals and has a per capita rate of increase (r) of 0.5 per hour. What will the population size be after 2 hours assuming exponential growth? At t = 0, N = 100 r = 0.5 t = 2 We can calculate the population size at any time 't' using the integrated form of the exponential growth equation: ``` Nt = N0 * e^(rt) ``` Where Nt is the population size at time t, N0 is the initial population size, e is the base of the natural logarithm (approximately 2.718), r is the per capita rate of increase, and t is time. Nt = 100 e^(0.5 2) Nt = 100 * e^(1) Nt = 100 * 2.718 Nt = 271.8 Therefore, after 2 hours, the population size will be approximately 272 bacteria. Important

Note: Exponential growth cannot continue indefinitely in the real world because resources are limited.

Logistic Growth: This model describes population growth that is limited by carrying capacity. The carrying capacity (K)* is the maximum population size that a particular environment can sustain given the available resources. As the population approaches carrying capacity, the growth rate slows down.

The equation for logistic growth is: ``` dN/dt = rN(K-N)/K ``` Where: `dN/dt` = rate of population change `r` = per capita rate of increase `N` = population size `K` = carrying capacity

Example: Suppose a population of impala in Kruger National Park has a carrying capacity of

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0. The current population size is 200, and the per capita rate of increase (r) is 0.

2. What is the population growth rate (dN/dt)? K = 500 N = 200 r = 0.2 ``` dN/dt = 0.2 200 (500 - 200) / 500 dN/dt = 40 * (300 / 500) dN/dt = 40 * 0.6 dN/dt = 24 ``` Therefore, the population growth rate is 24 impala per unit time. This means that the impala population is increasing by 24 individuals. 2.

4. Human Impact on the Environment: Human activities have profound impacts on biodiversity and ecosystems.

These impacts include: Pollution: The introduction of harmful substances into the environment. This can include air pollution from factories and vehicles (e.g., in Gauteng), water pollution from agricultural runoff and industrial waste (e.g., in KwaZulu-Natal rivers), and soil pollution from mining activities (e.g., around Johannesburg). Pollution can harm or kill organisms and disrupt ecosystems.

Deforestation: The clearing of forests for agriculture, urbanization, and logging. Deforestation reduces biodiversity, increases soil erosion, and contributes to climate change. In South Africa, deforestation is a concern in areas like the Eastern Cape and KwaZulu-Natal, where indigenous forests are being cleared for agriculture and timber.

Overexploitation of Resources: The unsustainable harvesting of natural resources such as fish, timber, and minerals. Overfishing can deplete fish stocks, while unsustainable logging can lead to deforestation and habitat loss. The illegal rhino poaching in South Africa for their horns is a prime example of overexploitation.

Invasive Species: The introduction of non-native species into an ecosystem. Invasive species can outcompete native species for resources, disrupt food webs, and cause economic damage. Examples in South Africa include the water hyacinth (Eichhornia crassipes) which clogs waterways, and the black wattle (Acacia mearnsii) which depletes water resources.