Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key population ecology terms with South African examples.
• Explain and graph population growth patterns.
• Describe the impact of human activities on biodiversity.
• Analyze case studies of human impact in South Africa.
• Discuss strategies for mitigating human impact.

Lesson summary

Population ecology is the study of how populations of organisms interact with their environment. It is crucial for understanding how populations grow, decline, and interact with other species. Understanding population ecology is especially important in South Africa due to the delicate balance between human population growth, resource utilization, and the conservation of our unique biodiversity. Human activities have profound effects on the environment, impacting populations of various species. This topic helps us understand those impacts and develop sustainable strategies for managing our natural resources.

Lesson notes

Population: A group of individuals of the same species living in a specific area at a given time. Examples include a population of African elephants in Kruger National Park or a population of sugar cane plants in a KwaZulu-Natal farm.

Population Size: The total number of individuals in a population. Determining population size can be done through various methods, like direct counting (for small populations) or using sampling techniques (for larger populations).

Population Density: The number of individuals per unit area or volume. This tells us how crowded a population is.

Example: 5 lions per 100 km 2 in a specific section of the Kalahari.

Formula: Population Density = Number of Individuals / Area.

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

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

Immigration: The movement of individuals into a population.

Emigration: The movement of individuals out of a population.

Population Growth Rate: The rate at which a population is increasing or decreasing.

Formula: Population Growth Rate = (Birth Rate + Immigration Rate) – (Death Rate + Emigration Rate)

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

Limiting Factors: Environmental factors that restrict population growth. These can be density-dependent (e.g., competition, predation, disease – become more intense as population density increases) or density-independent (e.g., natural disasters, weather events – affect populations regardless of density).

Examples in South Africa include: Density-dependent:* Overgrazing in communal grazing lands leading to soil erosion and reduced carrying capacity for livestock.

Density-independent:* Droughts in the Karoo affecting the survival of plant and animal populations.

Exponential Growth: Population growth under ideal conditions with unlimited resources. It results in a J-shaped curve when plotted on a graph. This is unsustainable in the long run.

Example: A newly introduced population of rabbits in an area with abundant food and no predators might initially exhibit exponential growth.

Logistic Growth: Population growth that slows down as it approaches the carrying capacity. It results in an S-shaped curve when plotted on a graph. This is more realistic as resources are always limited. The growth rate slows down as the population nears the carrying capacity due to increased competition and other limiting factors.

Worked example

Calculating Population Density: A survey of a 10 km 2 area in the Drakensberg Mountains reveals 250 Drakensberg rock lizards. What is the population density of the rock lizards in this area?

Solution:* Population Density = Number of Individuals / Area = 250 lizards / 10 km 2 = 25 lizards/km 2

Calculating Population Growth Rate: A population of springbok in the Free State has a birth rate of 0.15, a death rate of 0.05, an immigration rate of 0.02, and an emigration rate of 0.

0

1. What is the population growth rate? Express this as a percentage.

Solution:* Population Growth Rate = (Birth Rate + Immigration Rate) – (Death Rate + Emigration Rate) = (0.15 + 0.02) – (0.05 + 0.01) = 0.17 – 0.06 = 0.11

Percentage Growth Rate = 0.11 100 = 11%

Human Impact:

Pollution: The introduction of harmful substances into the environment.

Examples in South Africa:

Water pollution from mining activities (acid mine drainage) contaminates rivers and harms aquatic life.

Air pollution from coal-fired power plants contributes to respiratory problems and climate change.

Plastic pollution in oceans threatens marine animals and ecosystems.

Deforestation: The clearing of forests for agriculture, urbanization, or logging. This leads to habitat loss, soil erosion, and decreased biodiversity.

Example: Deforestation in KwaZulu-Natal for sugarcane farming impacts indigenous forests.

Urbanization: The growth of cities and towns, leading to habitat destruction, increased pollution, and altered drainage patterns.

Example: Rapid urbanization in Gauteng puts pressure on water resources and creates waste management challenges.

Agriculture: Intensive farming practices can lead to soil degradation, water pollution from fertilizers and pesticides, and loss of biodiversity.

Example: Overuse of fertilizers in maize farming in the North West province pollutes water sources.

Introduced Species (Alien Invasive Species): Species introduced to an area outside their native range. They can outcompete native species, alter ecosystems, and cause significant economic damage.

Examples in South Africa:

Australian wattles (Acacia species) invade fynbos ecosystems, competing with native plants for water and nutrients.

Water hyacinth clogs waterways, hindering navigation and reducing oxygen levels in water.

European starling competes with native bird species for nesting sites.

Guided Practice (With Solutions)

Question 1: Define carrying capacity and explain how it is related to limiting factors, using an example from the Kruger National Park.