Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define population ecology and its importance.
• Explain population size, density, distribution, and age structure.
• Describe factors influencing population growth.
• Discuss human impacts on populations in South Africa.
• Calculate population density.

Lesson summary

Population ecology is the study of populations in relation to their environment, including environmental influences on population density and distribution, age structure, and variations in population size. Understanding these dynamics is crucial for managing our natural resources sustainably and addressing the environmental challenges we face, particularly in South Africa, with its rich biodiversity and pressing socio-economic needs. Our unique ecosystems are increasingly threatened by human activities, impacting everything from access to clean water to food security.

Lesson notes

2. 1. What is a Population? A population is a group of individuals of the same species living in the same area at the same time. Understanding population dynamics is vital. 2.

2. Key Population Characteristics: Population Size (N): The total number of individuals in a population. Estimating population size accurately is essential for conservation efforts.

Example: Estimating the number of African wild dogs in Kruger National Park.

Population Density: The number of individuals per unit area or volume. Density provides insight into resource competition and disease transmission.

Formula: Population Density = Number of individuals / Area (or Volume)

Example: Calculating the density of Acacia trees in a section of the savanna. High density may indicate overgrazing in surrounding areas, preventing seedling establishment.

Population Distribution (Dispersion): The pattern of spacing among individuals within the boundaries of the population.

There are three main patterns: Clumped: Individuals aggregate in patches (e.g., herds of elephants, flocks of birds). This is often due to resource availability or social behavior.

Uniform: Individuals are evenly distributed (e.g., nesting seabirds). This is often driven by territoriality or competition for resources.

Random: The position of each individual is independent of other individuals (e.g., wind-dispersed seeds).

Example: Aloe plants may exhibit a clumped distribution near reliable water sources in a dry region, while certain territorial birds in the Fynbos biome may display a uniform distribution to maximize access to hunting grounds.

Age Structure: The relative number of individuals of each age in a population. Age structure affects future population growth. It's often represented by age pyramids.

Example: A population with a high proportion of young individuals will likely grow rapidly, while a population with a high proportion of older individuals may decline. Age structures are essential in understanding human populations. South Africa's age structure influences government policies on healthcare, education, and employment. 2.

3. Factors Affecting Population Growth: Birth Rate (b): The number of births per individual in a given time period.

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

Immigration (i): The influx of new individuals from other areas.

Emigration (e): The movement of individuals out of a population. The rate of population change (r) can be calculated as: r = (b - d) + (i - e).

Biotic Potential: The maximum rate at which a population could increase under ideal conditions (unlimited resources, no limiting factors). Different species have different biotic potentials. For example, bacteria have a much higher biotic potential than elephants.

Environmental Resistance: The sum of all factors (limiting factors) that restrict population growth.

Limiting Factors: Factors that restrict population growth.

These can be: Density-dependent factors: Factors that become more intense as population density increases (e.g., competition for resources, predation, disease).

Example: The spread of tuberculosis in a densely populated informal settlement.

Density-independent factors: Factors that affect population size regardless of density (e.g., natural disasters, weather).

Example: A drought that decimates crops and livestock, regardless of the population density of farmers.

Carrying Capacity (K): The maximum population size that a particular environment can sustain. Carrying capacity is determined by the availability of resources (food, water, shelter, etc.) and the impact of limiting factors. Populations often exhibit logistic growth, where growth slows as the population approaches carrying capacity. 2.

4. Population Growth Models: Exponential Growth: Population increases at a constant rate. Occurs under ideal conditions. Represented by a J-shaped curve.

Equation: dN/dt = r max N dN/dt is the rate of change in population size r max is the intrinsic rate of increase N is the population size Logistic Growth: Population growth slows as it approaches carrying capacity. Represented by an S-shaped curve.

Equation: dN/dt = r max N(K-N)/K K is the carrying capacity 2.

5. Human Impact on Populations Human activities significantly alter population dynamics and carrying capacities.

These include: Habitat Destruction: Conversion of natural habitats (e.g., deforestation for agriculture, urbanization) reduces available resources and carrying capacity for many species.

Pollution: Pollution of air, water, and soil can directly kill organisms or reduce their reproductive success.

Overexploitation: Overfishing, overhunting, and unsustainable harvesting of resources can lead to population declines and even extinction.

Invasive Species: Introduction of non-native species can outcompete native species and disrupt ecosystem balance.

Climate Change: Alters environmental conditions, affecting species distribution, phenology, and survival rates.