Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key population characteristics with South African examples.
• Explain the factors that change population size.
• Describe and interpret exponential and logistic growth forms.
• Discuss the impact of human activities on the environment.
• Understand the concept of an ecological footprint.

Lesson summary

Population ecology is crucial for understanding how populations of organisms, including humans, interact with their environment. Understanding population dynamics and the impact humans have on them is essential for informed decision-making regarding resource management, conservation efforts, and sustainable living, particularly within the South African context where we face unique environmental challenges like water scarcity, biodiversity loss, and rapid urbanization. Understanding these dynamics is vital for mitigating the negative impacts of human activities on ecosystems and ensuring the long-term well-being of both the environment and human communities.

Lesson notes

2. 1.

Defining a Population: A population is a group of organisms of the same species living in the same area at the same time and capable of interbreeding. Understanding a population requires understanding its characteristics.

Population Size: The total number of individuals in a population. This is crucial for conservation efforts; small populations are more vulnerable to extinction.

Example: The number of African wild dogs in Kruger National Park. Tracking population size helps monitor their conservation status.

Population Density: The number of individuals per unit area or volume. This affects resource availability and competition.

Example: The number of mealie plants per hectare in a maize farm in the Free State. High density can lead to nutrient depletion.

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

There are three main types: Clumped (Aggregated):* Individuals are clustered together. This is often due to uneven distribution of resources or social behavior.

Example: Elephants gathering near waterholes during the dry season in Botswana.

Uniform (Even):* Individuals are evenly spaced. This is often due to competition for resources or territoriality.

Example: Certain species of aloes in the Karoo exhibiting uniform distribution due to competition for water.

Random:* Individuals are distributed randomly. This is less common and usually occurs when resources are abundant and there is little competition.

Example: Wind-dispersed seeds of certain pioneer plant species colonizing a recently disturbed area.

Population Growth: The change in the size of a population over time. This is influenced by several factors discussed below. 2.

2. Factors Affecting Population Size: Population size is dynamic and constantly changing due to four key factors: Natality (Birth Rate): The number of new individuals added to the population through reproduction. High birth rates increase population size.

Example: A high birth rate in a rapidly expanding informal settlement can strain resources like water and sanitation.

Mortality (Death Rate): The number of individuals dying in the population. High death rates decrease population size. Factors like disease (e.g., HIV/AIDS in South Africa), lack of access to healthcare, and poverty contribute to high mortality rates in some communities.

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

Example: People migrating from rural areas to urban centers like Johannesburg in search of employment opportunities.

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

Example: The "brain drain" of skilled professionals leaving South Africa for better opportunities elsewhere. 2.

3. Population Growth Forms: Exponential Growth: Occurs when a population has unlimited resources and ideal conditions. The population grows at an accelerating rate. This is represented by a J-shaped curve. Mathematically, dN/dt = rN, where dN/dt is the rate of change of population size, N is the population size, and r is the intrinsic rate of increase (birth rate minus death rate). This type of growth is unsustainable in the long term.

Example: The initial growth of an Eichhornia crassipes (water hyacinth) population in a nutrient-rich dam, before it covers the entire surface.

Logistic Growth: Occurs when population growth slows down as it approaches the carrying capacity of the environment. This is represented by an S-shaped curve. The carrying capacity (K) is the maximum number of individuals that an environment can sustain indefinitely, given the available resources. Mathematically, dN/dt = rN(K-N)/

K. As N approaches K, the growth rate slows down.

Example: The growth of a springbok population in a game reserve, initially rapid, but then slowing as resources become limited.