Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define population ecology and identify factors influencing population size.
• Calculate and interpret population growth rates.
• Describe human impacts on South African ecosystems.
• Explain the concept of carrying capacity.
• Evaluate potential solutions for environmental problems.

Lesson summary

This week, we delve into the fascinating world of population ecology and examine the profound impact humans are having on our environment. Understanding population dynamics and our environmental footprint is crucial, especially in South Africa, where we face unique challenges related to resource management, biodiversity conservation, and the impacts of climate change. From the spread of invasive species that threaten our indigenous plants to the increasing pressure on our water resources, population ecology and human impact are directly relevant to our daily lives and the future of our country.

Lesson notes

Population Ecology: This is the study of how populations of organisms interact with each other and their environment. A population is a group of individuals of the same species living in the same area at the same time. Key factors influencing population size are: Birth Rate (Natality): The number of births per individual in a population per unit of time (e.g., per year). Higher birth rates generally lead to population growth.

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

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 Growth Rate: This is calculated as: `(Birth Rate + Immigration) - (Death Rate + Emigration)` A positive growth rate indicates population growth, while a negative growth rate indicates population decline. A growth rate of zero indicates a stable population.

Example 1: Population Growth Calculation Suppose a population of 1000 springbok in the Kruger National Park has 200 births and 50 deaths in a year. 30 springbok immigrate into the area, and 20 emigrate out. Birth Rate = 200/1000 = 0.2 Death Rate = 50/1000 = 0.05 Immigration Rate = 30/1000 = 0.03 Emigration Rate = 20/1000 = 0.02 Population Growth Rate = (0.2 + 0.03) - (0.05 + 0.02) = 0.23 - 0.07 = 0.16 This means the springbok population is growing at a rate of 16% per year. This is a relatively high growth rate!

Carrying Capacity (K): This is the maximum population size that an environment can sustain indefinitely, given the available resources (food, water, shelter, etc.) and the impact of limiting factors (disease, predation, competition). When a population exceeds its carrying capacity, resources become scarce, leading to increased death rates, decreased birth rates, or increased emigration until the population returns to a sustainable level. Overgrazing in the Karoo provides a stark example of exceeding carrying capacity; too many livestock deplete the vegetation, leading to soil erosion and desertification.

Human Impact on the Environment: Human activities have a significant and often detrimental impact on ecosystems and biodiversity. Some key examples in the South African context include: Pollution: Air Pollution: From industrial emissions, burning of fossil fuels (coal power plants), and vehicle exhaust. This leads to respiratory problems, acid rain, and contributes to climate change.

Water Pollution: From industrial waste, agricultural runoff (fertilizers and pesticides), and sewage. This contaminates drinking water sources, harms aquatic life, and can lead to eutrophication (excessive nutrient enrichment) causing algal blooms that deplete oxygen. An example is the pollution of the Vaal River which threatens water security.

Soil Pollution: From industrial waste, mining activities (acid mine drainage), and improper disposal of waste. This contaminates soil, making it unsuitable for agriculture and harming soil organisms.

Deforestation: Clearing forests for agriculture, urbanization, and timber. This leads to habitat loss, soil erosion, loss of biodiversity, and contributes to climate change (trees absorb carbon dioxide).

Overgrazing: Allowing livestock to graze excessively in a particular area. This leads to soil erosion, loss of vegetation cover, and desertification. This is a significant problem in arid and semi-arid regions like the Karoo.

Alien Plant Invasions: The introduction and spread of non-native plant species. These invasive species can outcompete native plants, alter ecosystems, and reduce biodiversity. Examples include Acacia mearnsii (Black Wattle) and Eucalyptus species, which consume excessive amounts of water.

Overexploitation of Resources: Harvesting resources (e.g., fish, timber, minerals) at a rate faster than they can be replenished. This can lead to resource depletion, habitat destruction, and extinction of species. An example is the overfishing of certain fish species along the South African coast.

Climate Change: Burning fossil fuels releases greenhouse gases, leading to global warming and climate change. South Africa is particularly vulnerable to climate change impacts, including increased droughts, floods, and rising sea levels.

Example 2: Impact of Alien Plant Invasions Black Wattle (Acacia mearnsii), introduced for tannin production, has become a major invasive species in South Africa. It spreads rapidly, displacing native vegetation and consuming large amounts of water, reducing water availability for agriculture and human consumption. The dense thickets it forms also increase fire risk.

Example 3: Impact of Mining Mining activities, particularly gold and coal mining, can cause significant environmental damage.