Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms like population size, density, and carrying capacity.
• Explain exponential and logistic population growth models.
• Describe the impact of human activities on South African ecosystems.
• Evaluate the impact of alien invasive species in South Africa.
• Propose sustainable strategies for managing natural resources.

Lesson summary

Population ecology is the study of populations and how they interact with their environment. This is critically important in South Africa. Our rapidly growing population, combined with our unique biodiversity and socio-economic challenges, means understanding population dynamics and the impact of human activities is crucial for sustainable development and conservation. From managing water resources to addressing food security and mitigating the effects of climate change, population ecology provides vital insights. Ignoring these concepts can lead to resource depletion, environmental degradation, and social unrest.

Lesson notes

2. 1. Population Characteristics Population Size: The total number of individuals of a species in a given area at a specific time. Population size can fluctuate due to births, deaths, immigration (individuals entering the population), and emigration (individuals leaving the population).

Population Density: The number of individuals per unit area or volume. For example, the number of wildebeest per square kilometer in the Kruger National Park. High population density can lead to increased competition for resources like food and water. Low density may make it difficult for individuals to find mates.

Population Distribution: The spatial arrangement of individuals within a population. This can be clumped (aggregated in patches, e.g., herds of zebra), uniform (evenly spaced, e.g., territorial birds), or random (unpredictable spacing, e.g., scattered plants). Distribution patterns are influenced by resource availability, social behavior, and competition. 2.

2. Population Growth Populations do not grow indefinitely. Their growth is limited by various factors.

Exponential Growth: Occurs when a population has unlimited resources and experiences no constraints. It is characterized by a J-shaped curve on a graph. The population increases at an accelerating rate. This is not sustainable in the long term.

Formula: N t = N 0 e rt N t = Population size at time t N 0 = Initial population size e = Euler's number (approximately 2.718) r = Intrinsic rate of increase (birth rate - death rate) t = time

Example: Imagine a population of 100 bacteria cells in a petri dish with unlimited nutrients. If the bacteria double every hour (r = 1), after 5 hours, the population size would be: N 5 = 100 2.718 (15) ≈ 100 * 148.4 = 14840 bacteria cells. This illustrates the rapid increase associated with exponential growth.

Logistic Growth: A more realistic model that considers the limitations imposed by the environment. As a population grows, resources become scarcer, competition increases, and the growth rate slows down. Eventually, the population reaches its carrying capacity. This is characterized by an S-shaped curve.

Formula: dN/dt = r max N(K-N)/K dN/dt = rate of population change r max = maximum per capita rate of increase N = population size K = carrying capacity Explanation: The formula calculates the rate of population change. When N is small relative to K, the term (K-N)/K is close to 1, and the population grows exponentially. As N approaches K, (K-N)/K approaches 0, and the growth rate slows down. When N = K, the growth rate is

0. Example: Consider a population of springbok in a fenced game reserve. The carrying capacity (K) of the reserve is 500 springbok. If the current population (N) is 200, and r max is 0.5, the population growth rate (dN/dt) would be: dN/dt = 0.5 200 (500-200)/500 = 0.5 200 (300/500) = 0.5 200 0.6 = 60 springbok per year. This means the population is growing, but not as rapidly as it would under exponential conditions. 2.

3. Limiting Factors Factors that restrict population growth.

These can be: Density-dependent factors: Their effect on the population depends on the population density.

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

Predation: As prey population increases, predators may increase and consume more prey.

Disease: Spreads more easily in dense populations.

Parasitism: Parasites can weaken individuals in dense populations.

Density-independent factors: Their effect on the population is not related to the population density.

Examples: Natural disasters: Floods, droughts, fires, and volcanic eruptions can drastically reduce population size regardless of density.

Climate change: Changes in temperature and rainfall patterns can affect the survival and reproduction of organisms.

Pollution: Can negatively affect organisms regardless of population density. 2.

4. Human Impact on the Environment in South Africa South Africa faces significant environmental challenges due to human activities.

Pollution: Air pollution: From burning fossil fuels (coal-fired power plants are a major contributor), vehicles, and industrial processes. Contributes to respiratory problems and climate change. In areas like the Highveld, air pollution is a serious health concern.

Water pollution: From industrial waste, agricultural runoff (fertilizers and pesticides), sewage, and mining activities (acid mine drainage). Pollutes rivers, lakes, and groundwater, harming aquatic life and threatening water security. Many rural communities rely on these polluted water sources.

Soil pollution: From industrial waste, mining, and improper waste disposal. Contaminates soil and reduces its fertility, affecting agriculture and plant growth.

Deforestation: Clearing forests for agriculture, urbanization, and timber. Leads to habitat loss, soil erosion, and climate change. Indigenous forests in areas like Knysna are particularly vulnerable.

Urbanization: The growth of cities and towns.