Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms in population ecology with South African examples.
• Explain and interpret population growth curves.
• Analyze human impacts on biodiversity in South Africa.
• Evaluate local conservation strategies.
• Discuss ecological footprints and consumption patterns in South Africa.

Lesson summary

This week, we delve into the fascinating and critically important world of population ecology and the significant impact humans have on the environment. Understanding these concepts is crucial for every South African. Our nation faces unique environmental challenges, including water scarcity, biodiversity loss, and pollution, all of which are directly linked to population dynamics and human activities. As future leaders and responsible citizens, you will need to understand these issues to make informed decisions and contribute to a sustainable future for our country.

Lesson notes

2.1 Population Ecology Fundamentals Population: A group of individuals of the same species living in the same area at the same time. For example, a population of Blue Cranes (South Africa's national bird) in the Drakensberg mountains.

Population Size: The total number of individuals in a population. Estimating population size can be challenging, especially for mobile or elusive species. Techniques like mark-recapture are often used.

Population Density: The number of individuals per unit area or volume. For example, the number of Aloe ferox plants per square kilometer in a specific region of the Eastern Cape.

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

This can be: Clumped: Individuals are clustered together (e.g., a herd of springbok). Often due to resource availability or social behaviour.

Uniform: Individuals are evenly spaced (e.g., some territorial birds). Often due to competition.

Random: Individuals are distributed randomly (e.g., some plants dispersing seeds by wind).

Carrying Capacity (K): The maximum population size that an environment can sustain indefinitely, given the available resources (food, water, shelter, etc.). This is NOT a fixed value; it fluctuates with environmental conditions. For example, the carrying capacity of a game reserve for elephants will decrease during a severe drought.

Limiting Factors: Environmental factors that restrict population growth.

These can be: Density-Dependent: Factors that have a greater impact as population density increases (e.g., disease, competition for resources, predation). For example, the spread of foot-and-mouth disease in cattle herds becomes more rapid with higher cattle density.

Density-Independent: Factors that affect population growth regardless of population density (e.g., natural disasters, weather events, pollution). A veld fire, for instance, will impact a population regardless of how dense it is. 2.2 Population Growth Curves Exponential Growth: Population growth under ideal conditions with unlimited resources. The population increases at a constant rate. This is represented by a J-shaped curve. While possible for brief periods (e.g., after a species is introduced to a new, resource-rich environment), it is unsustainable in the long term.

Example:* A newly introduced population of invasive alien plants, such as water hyacinth, in a South African dam may exhibit exponential growth initially.

Equation: dN/dt = rN dN/dt = rate of population change r = per capita rate of increase (birth rate - death rate) N = population size Logistic Growth: Population growth that slows down as it approaches carrying capacity. This is represented by an S-shaped curve. As the population nears K, resources become more limited, increasing competition and slowing down growth.

Equation: dN/dt = rN(K-N)/K dN/dt = rate of population change r = per capita rate of increase N = population size K = carrying capacity (K-N)/K = accounts for the slowing of growth as N approaches K