Lesson Notes By Weeks and Term v5 - Grade 11

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Performance objectives

• Define population ecology and its key factors.
• Calculate and interpret population growth.
• Explain exponential and logistic growth models.
• Analyze human impact on South African ecosystems.
• Discuss sustainable development solutions.

Lesson summary

Population ecology is the study of populations in relation to their environment, including environmental influences on population density and distribution, age structure, and variations in population size. Understanding these dynamics is crucial, especially in South Africa, where we face unique challenges related to population growth, resource management, and conservation of our rich biodiversity. The impacts of human activities are particularly relevant as they directly influence the sustainability of ecosystems and the well-being of communities.

Lesson notes

2.1 Population Ecology: Core Principles Population ecology focuses on understanding the size, density, distribution, and age structure of populations and how they change over time. A population is a group of individuals of the same species living in the same area and interacting with each other. 2.1.1 Factors Affecting Population Size: Birth Rate (Natality): The number of new individuals born per unit time. A high birth rate increases population size.

Death Rate (Mortality): The number of deaths per unit time. A high death rate decreases population size.

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

Emigration: The movement of individuals out of a population to another area. Emigration decreases population size. Population Change = (Births + Immigration) - (Deaths + Emigration) 2.1.2 Population Density: Population density is the number of individuals per unit area or volume. High population density can lead to increased competition for resources, while low population density can make it difficult to find mates. Population Density = Number of Individuals / Area (or Volume) 2.1.3 Population Distribution: Population distribution describes how individuals are spaced out within their area.

Three common patterns: Clumped: Individuals are aggregated in patches (e.g., herds of wildebeest, flocks of birds). This is often due to resource availability or social behavior.

Uniform: Individuals are evenly distributed (e.g., penguins nesting on a beach). This is often due to competition for resources or territoriality.

Random: Individuals are distributed randomly (e.g., trees in a rainforest). This is relatively rare and indicates a lack of strong interactions or resource limitations. 2.2 Population Growth Models: 2.2.1 Exponential Growth: Exponential growth occurs when a population increases at a constant rate. It assumes unlimited resources and ideal conditions. This model is unrealistic in the long term but can occur temporarily when a population colonizes a new habitat or recovers from a population crash. The graph of exponential growth is J-shaped.

Formula: dN/dt = r max N Where: dN/dt = rate of population change r max = intrinsic rate of increase (maximum per capita rate of population growth) N = population size

Example: A population of bacteria in a petri dish doubles every hour. If it starts with 100 bacteria, it will grow exponentially. 2.2.2 Logistic Growth: Logistic growth is a more realistic model that considers the carrying capacity (K) of the environment. Carrying capacity is the maximum population size that a particular environment can sustain, given available resources. As the population approaches carrying capacity, growth slows down due to increased competition for resources, increased predation, and/or increased disease. The graph of logistic growth is S-shaped.

Formula: dN/dt = r max N(K - N)/K Where: dN/dt = rate of population change r max = intrinsic rate of increase N = population size K = carrying capacity Explanation: The term (K - N)/K represents the proportion of available resources. When N is small compared to K, (K - N)/K is close to 1, and the population grows exponentially. As N approaches K, (K - N)/K approaches 0, and the population growth rate slows down.

Example: Imagine a population of springbok in a national park. Initially, they reproduce rapidly.

However, as the springbok population increases, the available grazing decreases, leading to competition and a slower growth rate. Eventually, the population stabilizes around the carrying capacity of the park. 2.3 Human Impact on the Environment Human activities have a profound impact on the environment, often leading to habitat destruction, pollution, and overexploitation of resources. 2.3.1 Deforestation: The clearing of forests for agriculture, urbanization, and logging reduces biodiversity, increases soil erosion, and contributes to climate change. In South Africa, deforestation is a significant issue in areas like KwaZulu-Natal, where forests are cleared for sugarcane plantations and timber. 2.3.2 Pollution: Air pollution: Caused by industrial emissions, vehicle exhaust, and burning of fossil fuels. It leads to respiratory problems and acid rain. In areas like Gauteng, high levels of air pollution are a major concern due to industrial activity and vehicle traffic.

Water pollution: Caused by industrial waste, sewage, and agricultural runoff. It contaminates water sources, harming aquatic life and human health. In South Africa, water pollution is a significant problem in many rivers and dams, affecting access to clean drinking water.

Soil pollution: Caused by pesticides, herbicides, and industrial waste. It contaminates soil, affecting plant growth and potentially entering the food chain. Mining activities in South Africa have contributed significantly to soil pollution.