Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define population and explain factors influencing its size.
• Describe and interpret exponential and logistic growth curves.
• Discuss human impacts like pollution, deforestation, and invasive species.
• Explain carrying capacity in the context of human populations.
• Suggest strategies for sustainable resource use in South Africa.

Lesson summary

Population ecology is the study of how populations of organisms interact with each other and their environment. Understanding population ecology is crucial because it allows us to understand how populations grow, shrink, and are distributed. This knowledge is particularly important in South Africa where we face challenges such as managing endangered species, controlling invasive species, and mitigating the impact of human activities on biodiversity and resource availability. Overpopulation in some areas can lead to increased pressure on resources like water and arable land, exacerbating socio-economic inequalities.

Lesson notes

2. 1. Defining a Population A population is defined as a group of individuals of the same species living in the same area at the same time and capable of interbreeding. The area can be anything from a small pond to the entire planet. 2.

2. Factors Affecting Population Size Population size is influenced by four key factors: Birth Rate (Natality): The number of new individuals born into the population per unit of time.

Death Rate (Mortality): The number of individuals that die in the population per unit of time.

Immigration: The movement of individuals into a population from another area.

Emigration: The movement of individuals out of a population to another area. Population size changes according to this basic equation: `Change in population size = (Births + Immigration) - (Deaths + Emigration)` 2.

3. Population Growth Curves Populations don't grow indefinitely. Two main types of growth curves describe population growth: Exponential Growth (J-curve): This occurs when resources are unlimited and there are no constraints on reproduction. The population grows at a constant rate, resulting in a rapid increase in population size. This is unsustainable in the long term.

Formula: dN/dt = rN Where: dN/dt = rate of population change r = intrinsic rate of increase (birth rate - death rate) N = population size

Example: Imagine a bacterial colony in a petri dish with ample nutrients. Initially, the bacteria reproduce rapidly, doubling their population size every few hours. This rapid growth continues until the nutrients are depleted or waste products accumulate to toxic levels.

Logistic Growth (S-curve): This is a more realistic model that takes into account the limiting factors that affect population growth. As a population grows, it eventually reaches its carrying capacity.

Carrying Capacity (K):* The maximum population size that an environment can sustain indefinitely, given the available resources (food, water, shelter, etc.).

Formula: dN/dt = rN(K-N)/K Where: dN/dt = rate of population change r = intrinsic rate of increase (birth rate - death rate) N = population size K = carrying capacity

Example: Consider a population of springbok in a national park. Initially, the population grows rapidly. As the population increases, competition for grazing land intensifies. This leads to a decrease in the birth rate and an increase in the death rate. Eventually, the population stabilizes at a level that the available grazing land can support – the carrying capacity. 2.

4. Human Impact on the Environment Human activities have a significant and often detrimental impact on the environment, affecting population sizes of various species, including our own.

Key impacts include: Pollution: The introduction of harmful substances into the environment.

Air Pollution:* Caused by emissions from vehicles, industries, and burning fossil fuels. Contributes to respiratory problems, acid rain, and climate change.

Example: High levels of air pollution in industrial areas of Gauteng affect the health of local populations.

Water Pollution:* Caused by sewage, industrial waste, agricultural runoff, and plastic waste. Contaminates drinking water sources, harms aquatic life, and can lead to the spread of diseases.

Example: Sewage spills into rivers in KwaZulu-Natal, impacting water quality and public health.

Soil Pollution:* Caused by pesticides, herbicides, heavy metals, and improper waste disposal. Reduces soil fertility, contaminates crops, and can harm human health.

Example: Improper mining practices leaving behind toxic soil in mining areas of the North West Province.

Deforestation: The clearing of forests for agriculture, urbanization, and logging. Reduces biodiversity, contributes to soil erosion, disrupts water cycles, and releases carbon dioxide into the atmosphere.

Example: Large-scale deforestation for agriculture in Limpopo.

Alien Invasive Species: Species introduced into an ecosystem outside their natural range. They often lack natural predators and can outcompete native species, disrupt food webs, and cause economic damage.

Example: Water hyacinth clogging waterways in Gauteng, hindering navigation and affecting aquatic ecosystems. The invasive Prosopis trees in the Northern Cape outcompete native vegetation, decreasing grazing land for livestock. 2.

5. Carrying Capacity and Human Populations While the concept of carrying capacity is often applied to animal populations, it's also relevant to human populations. The Earth has a finite amount of resources. As the human population grows, we exert increasing pressure on these resources, including food, water, energy, and land. Exceeding the Earth's carrying capacity can lead to resource depletion, environmental degradation, and social unrest. In South Africa, water scarcity, particularly in drought-prone regions like the Western Cape, highlights the challenges of managing resources to meet the needs of a growing population. 2.6.