Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms in population ecology.
• Describe factors influencing population size.
• Explain exponential and logistic growth forms.
• Calculate population density and growth rate.
• Discuss the impact of human activities on biodiversity.

Lesson summary

This week, we delve into population ecology and how human activities impact our environment. Population ecology is the study of populations of organisms, including factors that affect their size, distribution, and interactions with their environment. Understanding population dynamics is crucial because it helps us to predict how populations might change over time, and how our actions influence these changes. This is particularly important in South Africa, where we face unique challenges such as rapid population growth, biodiversity loss, and environmental degradation.

Lesson notes

2. 1.

Basic Definitions and Concepts: Population: A group of individuals of the same species living in a particular geographic area at the same time. For example, all the African elephants in Kruger National Park.

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

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

Formula: Population Density = Total number of individuals / Area (or Volume). For example, the population density of wildebeest in a specific area of the Serengeti could be 5 wildebeest per square kilometer.

Natality (Birth Rate): The rate at which new individuals are born into a population.

Mortality (Death Rate): The rate at which individuals die in a population.

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

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

Limiting Factors: Environmental factors that restrict population growth. These can be density-dependent (e.g., competition for resources, disease) or density-independent (e.g., natural disasters, climate).

Carrying Capacity (K): The maximum population size that an environment can sustainably support, given the available resources (food, water, shelter, etc.). 2.

2. Factors Affecting Population Size and Density: Population size changes over time due to the interplay of natality, mortality, immigration, and emigration.

A simple equation demonstrates this: Population Change = (Natality + Immigration) - (Mortality + Emigration) A positive value indicates population growth, while a negative value indicates population decline.

Natality: Higher natality rates lead to population increases. Factors influencing natality include food availability, water access, and breeding success.

Mortality: Higher mortality rates lead to population decreases. Factors influencing mortality include predation, disease, starvation, and natural disasters.

Immigration: Immigration can boost population size, especially when resources are abundant in the new area. This is relevant in South Africa, where some species migrate across borders.

Emigration: Emigration can reduce population size if individuals leave due to resource scarcity, overcrowding, or unfavorable environmental conditions.

Limiting Factors: Limiting factors prevent populations from growing indefinitely.

Density-Dependent Limiting Factors: Their effect increases as population density increases.

Examples include: Competition: Organisms compete for resources (food, water, space, mates).

Example: Lions competing for the same prey in Kruger National Park.

Predation: Predators control prey populations.

Example: A larger predator population can limit the antelope population.

Disease: Disease spreads more easily in dense populations.

Example: Foot and mouth disease outbreaks in livestock.

Density-Independent Limiting Factors: Their effect is not related to population density.

Examples include: Natural Disasters: Floods, droughts, fires, and volcanic eruptions can decimate populations regardless of their density. South Africa is prone to droughts, which significantly impact livestock and wildlife populations.

Climate: Extreme temperatures or changes in rainfall patterns can affect survival and reproduction. 2.

3. Population Growth Forms: Populations exhibit different growth patterns depending on environmental conditions and resource availability.

Exponential Growth (J-shaped Curve): Occurs when resources are unlimited, and a population grows at its maximum potential rate. This is often observed in new or sparsely populated environments or after a population crash. For example, if a small number of alien invasive plants are introduced into an area with suitable climate and lacking natural predators, they might exhibit exponential growth initially.

However, exponential growth is unsustainable in the long term.

Logistic Growth (S-shaped Curve): Occurs when resources become limited, and population growth slows down as it approaches the carrying capacity (K). Initially, the population grows exponentially, but as resources become scarcer, the growth rate slows down, and the population eventually stabilizes around

K. This model is more realistic as it accounts for environmental constraints.

Lag Phase: Initial slow growth as the population establishes itself.

Exponential Growth Phase: Rapid growth due to abundant resources.

Deceleration Phase: Growth slows down as resources become limited and competition increases.

Stable Phase (Equilibrium): Population stabilizes around the carrying capacity, with birth and death rates roughly equal. 2.

4. Human Impact on Population Sizes and Biodiversity: Human activities have profoundly altered population sizes and biodiversity across the globe, including South Africa.

Deforestation: Clearing forests for agriculture, urbanization, and logging destroys habitats, reduces biodiversity, and disrupts ecosystem services.