Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key population ecology terms.
• Explain and interpret population growth curves (J-shaped and S-shaped).
• Describe the impact of human activities on biodiversity in South Africa.
• Discuss strategies for sustainable resource management.
• Explain the impact of alien invasive species in South Africa.

Lesson summary

Population ecology is the study of populations of organisms in relation to their environment, including environmental influences on population density and distribution, age structure, and variations in population size. Understanding population ecology is crucial because it provides insights into how populations grow, decline, and interact with their environment. This knowledge is essential for managing natural resources, conserving biodiversity, and understanding the impact of human activities on ecosystems.

Lesson notes

2. 1.

Population Ecology Basics: Population: A group of individuals of the same species living in the same area and interbreeding. For example, a population of African elephants in Kruger National Park or a population of Blue Cranes in the Overberg region.

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

Population Density: The number of individuals per unit area or volume.

Calculated as: Population Density = Number of Individuals / Area (or Volume)

Example:* If there are 500 springbok in a 10 km 2 area, the population density is 50 springbok/km 2 .

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

This can be: Clumped:* Individuals are grouped together (e.g., herds of wildebeest).

Uniform:* Individuals are evenly spaced (e.g., territorial birds).

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

Birth Rate: The number of births per individual in a given time period.

Death Rate: The number of deaths per individual in a given time period.

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

Emigration: The movement of individuals out of a population to another area.

Population Growth Rate: The rate at which a population is increasing or decreasing, determined by the balance between births, deaths, immigration, and emigration. Population Growth Rate = (Birth Rate + Immigration Rate) - (Death Rate + Emigration Rate) 2.

2. Population Growth Patterns: Exponential Growth: Occurs when resources are unlimited, and the population increases at a constant rate. This results in a J-shaped growth curve. It's not sustainable in the long term.

The equation for exponential growth is: dN/dt = r max N Where: dN/dt is the rate of population growth. r max is the intrinsic rate of increase (the maximum potential growth rate). N is the population size.

Example:* Imagine a population of bacteria in a petri dish with ample nutrients. Initially, they reproduce rapidly, leading to exponential growth.

Logistic Growth: Occurs when resources are limited, and the population growth rate slows as it approaches the carrying capacity. This results in an S-shaped growth curve.

Carrying Capacity (K): The maximum population size that a particular environment can sustain, given the available resources.

The equation for logistic growth is: dN/dt = r max N (K - N)/K Where: dN/dt is the rate of population growth. r max is the intrinsic rate of increase. N is the population size. K is the carrying capacity.

Example:* A population of zebras in a game reserve. Initially, the population grows rapidly, but as the population increases, competition for resources (food, water) intensifies, slowing the growth rate until it reaches the carrying capacity of the reserve. 2.

3. Limiting Factors: Factors that restrict population growth.

These can be: Density-Dependent Factors: Factors that affect population growth more strongly as the population density increases.

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

Predation:* Predators may focus on prey populations when they are abundant.

Parasitism & Disease:* These spread more easily in dense populations.

Density-Independent Factors: Factors that affect population growth regardless of population density.

Examples: Natural Disasters:* Floods, droughts, fires, and extreme weather events.

Climate Change:* Changes in temperature and rainfall patterns.

Human Activities:* Pollution, deforestation, and habitat destruction. A drought in the Karoo would impact springbok populations whether the initial population density was high or low. 2.

4. Human Impact on Populations and Biodiversity: Human activities have a profound impact on populations and biodiversity, both locally and globally.

Deforestation: Clearing forests for agriculture, urbanization, and logging leads to habitat loss, fragmentation, and soil erosion. This reduces the carrying capacity for many species. For example, deforestation for cattle farming in the Amazon affects global biodiversity, including insect populations.

Pollution: Air and water pollution from industrial activities, agriculture, and sewage contaminate ecosystems, harming or killing organisms. Acid rain affects fish populations, as seen in some polluted rivers.

Urbanization: The expansion of cities and towns destroys natural habitats and replaces them with concrete and asphalt, leading to habitat loss and reduced biodiversity. Urban sprawl affects many ecosystems, especially near major cities.

Agriculture: Intensive agriculture practices, such as monoculture farming and pesticide use, reduce biodiversity and can lead to soil degradation and water pollution.

Overexploitation: Overfishing, hunting, and harvesting of resources can deplete populations and even lead to extinction. Examples include the overfishing of snoek, a South African staple, and illegal rhino poaching.