Lesson Notes By Weeks and Term v5 - Grade 11

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Performance objectives

• Define key population ecology terms.
• Describe exponential and logistic population growth models.
• Analyse the impact of human activities on ecosystems.
• Explain the concept of carrying capacity.
• Discuss the importance of conservation and sustainable practices.

Lesson summary

This week, we delve into the fascinating world of population ecology and examine the significant impact humans have on our environment. Understanding how populations grow, interact, and are affected by human activities is crucial, especially in South Africa, where we face unique environmental challenges like water scarcity, biodiversity loss, and the impacts of climate change on vulnerable communities. These challenges directly affect our food security, health, and overall well-being. By learning about population dynamics and human impact, we can make informed decisions and contribute to sustainable practices that protect our environment for future generations.

Lesson notes

2.1 Population Ecology: The Basics Population: A group of individuals of the same species living in the same area at the same time. Think of a population of wild dogs in the Kruger National Park, or a population of fynbos plants on Table Mountain.

Population Size: The total number of individuals in a population.

Population Density: The number of individuals per unit area or volume. For example, the number of Acacia trees per hectare in a savanna ecosystem.

Population Distribution: The spatial arrangement of individuals within a population.

This can be: Clumped: Individuals are grouped together (e.g., a herd of elephants).

Uniform: Individuals are evenly spaced (e.g., plants competing for resources in a desert).

Random: Individuals are distributed randomly (e.g., seeds dispersed by wind).

Birth Rate (Natality): The number of births per unit time.

Death Rate (Mortality): The number of deaths per unit time.

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

Emigration: The movement of individuals out of a population to another area. 2.2 Population Growth Models Exponential Growth: Population growth under ideal conditions, with unlimited resources. This results in a J-shaped curve. The growth rate is constant.

This is described by the formula: `dN/dt = rN` Where: `dN/dt` is the rate of population change `r` is the intrinsic rate of increase (birth rate - death rate) `N` is the population size

Example: Imagine a population of bacteria in a petri dish with unlimited nutrients. They will reproduce rapidly, doubling their numbers in short periods, exhibiting exponential growth until resources are depleted.

Logistic Growth: Population growth that is limited by carrying capacity (K). As the population approaches K, the growth rate slows down, resulting in an S-shaped curve. `dN/dt = rN (K-N)/K` Where: `K` is the carrying capacity (the maximum population size the environment can sustain). The term `(K-N)/K` represents the environmental resistance, slowing down growth as N approaches

K. Example: Consider a population of springbok in a fenced-off reserve. Initially, with abundant grazing, the population will grow rapidly.

However, as the population increases, competition for food intensifies, and the growth rate slows down until the population reaches a stable size that the available resources can support (carrying capacity). 2.3 Factors Affecting Population Growth Density-Dependent Factors: Factors whose effect on population growth depends on population density.

These include: Competition: For resources like food, water, shelter, and mates.

Predation: Predators may focus on areas with higher prey density.

Disease: Diseases spread more easily in dense populations.

Parasitism: Parasites thrive in dense populations.

Density-Independent Factors: Factors whose effect on population growth is independent of population density.

These include: Natural Disasters: Floods, droughts, fires, volcanic eruptions, and storms can affect populations regardless of their density.

Climate Change: Changes in temperature and rainfall patterns can impact population sizes.

Human Activities: Deforestation, pollution, and habitat destruction. 2.4 Human Impact on the Environment Deforestation: Clearing forests for agriculture, urbanization, and logging. This leads to habitat loss, soil erosion, climate change (loss of carbon sinks), and reduced biodiversity. South Africa has experienced significant deforestation, particularly in coastal forests and grasslands.

Pollution: Air Pollution: From industrial emissions, vehicle exhaust, and burning fossil fuels. This can lead to respiratory problems and climate change. Examples include air pollution from coal-fired power plants in Mpumalanga.

Water Pollution: From sewage, industrial waste, agricultural runoff, and mining activities. This can contaminate drinking water, harm aquatic life, and disrupt ecosystems. The Witwatersrand gold mining area is a significant source of water pollution due to acid mine drainage.

Soil Pollution: From pesticides, herbicides, fertilizers, and industrial waste. This can reduce soil fertility and contaminate food crops.

Agriculture: Intensive farming practices can lead to soil degradation, water pollution (from fertilizers and pesticides), and habitat loss. Monoculture farming reduces biodiversity.

Urbanization: Expansion of cities and towns leads to habitat destruction, increased pollution, and altered water cycles.

Overexploitation of Resources: Unsustainable harvesting of natural resources, such as overfishing, illegal hunting (poaching of rhinos), and deforestation, can lead to population declines and ecosystem collapse.

Introduction of Alien Invasive Species: The introduction of non-native species can outcompete native species, disrupt ecosystems, and cause economic damage. Examples include hakea and wattle trees invading fynbos ecosystems and water hyacinth clogging waterways.