Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key population ecology terms.
• Describe and interpret population growth curves.
• Explain the impact of human activities on ecosystems.
• Discuss the causes and consequences of pollution.
• Explain conservation and sustainability strategies.

Lesson summary

Population ecology examines how populations of organisms interact with their environment. It's incredibly relevant to us in South Africa because understanding population dynamics helps us manage our natural resources (like fish stocks, wildlife populations, and water), address challenges related to human population growth, and mitigate the impacts of environmental degradation. Think about issues like the impact of invasive alien plants on water availability, the overexploitation of marine resources, or the challenges of urbanization and waste management – all directly related to population ecology and human impact.

Lesson notes

2.1 Population Ecology Basics Population: A group of individuals of the same species living in a specific area at a specific time.

Population Size: The total number of individuals in a population. Population size changes due to births, deaths, immigration (individuals moving into the area), and emigration (individuals moving out of the area).

Mathematically: Population Change = (Births + Immigration) - (Deaths + Emigration)

Population Density: The number of individuals per unit area or volume. For example, the number of Blue Cranes (South Africa's national bird) per square kilometer in a specific grassland.

It is calculated as: Population Density = (Number of Individuals) / (Area or Volume)

Population Distribution Patterns: Describe how individuals are spatially arranged within a population.

There are three main types: Clumped: Individuals are grouped together, often due to resource availability (e.g., a herd of elephants around a waterhole) or social behavior (e.g., a flock of birds).

Uniform (or Even): Individuals are evenly spaced, often due to competition for resources (e.g., plants secreting chemicals to inhibit the growth of nearby plants).

Random: Individuals are scattered randomly, with no predictable pattern. This is less common in nature.

Carrying Capacity (K): The maximum population size that a particular environment can support, given the available resources (food, water, shelter, space). Carrying capacity is NOT a fixed value; it fluctuates depending on environmental conditions.

Limiting Factors: Environmental factors that restrict population growth.

These can be: Density-Dependent Factors: Their effects increase as population density increases.

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

Predation: Predators may focus on areas with high prey densities.

Disease: Diseases spread more easily in dense populations.

Parasitism: Parasites can easily find new hosts in dense populations.

Density-Independent Factors: Their effects are not related to population density.

Examples include: Natural Disasters: Floods, droughts, fires, and volcanic eruptions can kill large numbers of individuals regardless of population density.

Climate Change: Changes in temperature and rainfall patterns can affect populations.

Human Activities: Deforestation, pollution, and habitat destruction can impact populations regardless of their density. 2.2 Population Growth Patterns Exponential Growth: Population growth that occurs when resources are unlimited. The population increases at a constant rate, resulting in a J-shaped growth curve. This is often seen in populations that are newly introduced to an environment or after a drastic reduction in population size (e.g., after a fire). Exponential growth cannot continue indefinitely because resources are always limited.

The equation for exponential growth is: dN/dt = rN Where: dN/dt is the rate of population change r is the intrinsic rate of increase (birth rate minus death rate) N is the population size

Example: Imagine a bacterial colony in a lab with unlimited nutrients. The bacteria will reproduce at a constant rate, doubling their population size in short periods. This creates a J-shaped exponential growth curve.

However, in reality, the bacteria will eventually deplete the nutrients and the growth will slow.

Logistic Growth: Population growth that slows down as the population approaches carrying capacity. It results in an S-shaped growth curve.

The equation for logistic growth is: dN/dt = rN(K-N)/K Where: dN/dt is the rate of population change r is the intrinsic rate of increase (birth rate minus death rate) N is the population size K is the carrying capacity

Example: Consider a population of springbok in a fenced game reserve. Initially, the population may grow rapidly.

However, as the springbok population increases, they will start to compete for grazing. Eventually, the population growth will slow down as it approaches the carrying capacity of the reserve. 2.3 Human Impact on Ecosystems Human activities have a profound impact on ecosystems, often leading to biodiversity loss, habitat destruction, and environmental degradation.

Some major impacts include: Deforestation: Clearing forests for agriculture, logging, and urbanization. This leads to habitat loss, soil erosion, and climate change. In South Africa, deforestation is a significant issue in areas where subsistence farming practices involve clearing land for crops and firewood collection.

Pollution: The introduction of harmful substances into the environment.

Pollution can take many forms: Air pollution: From burning fossil fuels (coal-fired power plants, vehicle emissions), industrial processes, and agricultural practices. Contributes to respiratory problems, acid rain, and climate change. South Africa relies heavily on coal for electricity generation, leading to significant air pollution, especially in industrial areas like Secunda and eMalahleni.