Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms in population ecology.
• Explain factors affecting population growth.
• Calculate population growth rate.
• Describe major human impacts like pollution and deforestation.
• Explain the consequences for biodiversity.

Lesson summary

Population ecology is the study of populations of organisms, especially the numerical regulation of population size and its interactions with the environment. Understanding population ecology is crucial, particularly in South Africa, as it helps us address critical issues like sustainable resource management, conservation efforts for endangered species (like the rhino), and managing invasive alien species that threaten our biodiversity and agricultural productivity. Human activities have profound impacts on population dynamics, making this a vital topic for creating informed and responsible citizens.

Lesson notes

2. 1. Population Characteristics Population Size: The total number of individuals in a population. This is influenced by births, deaths, immigration (individuals entering the population), and emigration (individuals leaving the population).

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

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

Example:* If there are 500 springbok in a 10 km² area in the Karoo, the population density is 50 springbok/km².

Birth Rate (Natality): The number of births per individual in a population per unit time (usually per year).

Death Rate (Mortality): The number of deaths per individual in a population per unit time (usually per year).

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

Emigration: The movement of individuals out of a population to another area. 2.

2. Population Growth Population growth is determined by the balance between births, deaths, immigration, and emigration.

Population Growth Rate (r): The rate at which the number of individuals in a population increases (or decreases) in a given time period, expressed as a percentage.

Formula: `r = (Birth Rate + Immigration Rate) - (Death Rate + Emigration Rate)`

Example:* If a population of wildebeest has a birth rate of 0.15, a death rate of 0.05, an immigration rate of 0.02, and an emigration rate of 0.01, the growth rate (r) would be: `r = (0.15 + 0.02) - (0.05 + 0.01) = 0.11` or 11%. This means the wildebeest population is increasing by 11% per year.

Exponential Growth: Occurs when resources are unlimited, and the population grows at its maximum potential rate. This results in a J-shaped growth curve. Not sustainable in the long term.

Logistic Growth: Occurs when resources become limited. Population growth slows down as it approaches the carrying capacity of the environment. This results in an S-shaped growth curve.

Carrying Capacity (K): The maximum population size that an environment can sustain indefinitely, given the available resources (food, water, shelter, space). This is limited by limiting factors.

Limiting Factors: Factors that restrict population growth.

These can be: Density-dependent factors:* Their effect depends on the population density (e.g., competition, predation, disease). For example, if a dense population of dassies exists, competition for food resources becomes much stronger, leading to some dassies not getting enough food. This increases the mortality rate and reduces the birth rate.

Density-independent factors:* Their effect is independent of the population density (e.g., natural disasters, weather conditions, human activities). For example, a drought will impact a population regardless of the population density. 2.

3. Human Impact on the Environment Human activities significantly impact the environment and population dynamics.

Pollution: Water Pollution:* Contamination of water bodies (rivers, lakes, oceans) with pollutants such as sewage, industrial waste, agricultural runoff (pesticides, fertilizers).

Example: Acid mine drainage from abandoned mines in Gauteng pollutes water sources.

Air Pollution:* Release of harmful substances into the atmosphere, such as smoke, dust, gases (e.g., carbon dioxide, sulfur dioxide, nitrogen oxides) from industries, vehicles, and burning fossil fuels.

Example: High levels of air pollution in industrial areas like Sasolburg.

Land Pollution:* Contamination of soil with pollutants such as solid waste (e.g., plastics, electronic waste), chemicals, and radioactive materials.

Example: Improper disposal of waste leading to landfill sites leaking chemicals into the surrounding environment.

Deforestation: Clearing forests for agriculture, urban development, mining, and logging. This leads to habitat loss, soil erosion, climate change, and reduced biodiversity.

Example: Deforestation to make space for cattle farming.

Invasive Alien Species: Species introduced into an environment where they do not naturally occur. These species can outcompete native species, disrupt ecosystems, and cause economic damage.

Example: The water hyacinth in South African rivers and dams, or the Black Wattle trees in grassland.

Overexploitation: Harvesting resources at a rate faster than they can be replenished. This leads to the depletion of natural resources and can result in extinction.

Example: Overfishing of snoek, leading to declining fish populations.

Climate Change: Alteration of global weather patterns, primarily caused by the increase in greenhouse gases (e.g., carbon dioxide) in the atmosphere due to burning fossil fuels and deforestation. Climate change leads to rising sea levels, changes in rainfall patterns, extreme weather events (droughts, floods), and shifts in species distributions. South Africa is particularly vulnerable to droughts and water scarcity due to climate change. 2.4.