Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key concepts of population ecology.
• Calculate population growth rates.
• Describe factors limiting population growth.
• Analyze human impact on populations in South Africa.
• Evaluate strategies for sustainable resource management.

Lesson summary

Welcome to Week 3 of our exploration into the fascinating world of Life Sciences! This week, we delve into the crucial topic of population ecology and its profound connection to human impact on the environment. Understanding how populations grow, interact, and are affected by our actions is not just an academic exercise; it's about understanding the future of South Africa's biodiversity, our resources, and our overall well-being. From the growing strain on water resources in the Western Cape to the challenges of managing wildlife populations in Kruger National Park, population ecology principles are at play everywhere.

Lesson notes

2.1 What is Population Ecology? Population ecology is the study of how populations of organisms interact with their environment and how factors like birth rate, death rate, immigration, and emigration influence their size, density, and distribution over time. A population is defined as a group of individuals of the same species living in the same area at the same time. 2.2 Key Population Characteristics: Population Size (N): The total number of individuals in a population. Estimating population size can be tricky.

Methods include: Direct Counting:* Suitable for small, easily observable populations.

Quadrat Sampling: Used for stationary organisms like plants. A defined area (quadrat) is sampled, and the individuals are counted. This data is extrapolated to the entire area.

Example: Estimating the number of Aloe ferox plants in a region by counting them in several randomly placed 1m x 1m quadrats.

Mark-Recapture Method: Used for mobile animals. A sample of animals is captured, marked (e.g., with tags), and released. Later, another sample is captured. The proportion of marked animals in the second sample allows estimation of the total population size.

Formula: N = (M C) / R, where: N = Estimated population size M = Number of individuals initially captured and marked C = Total number of individuals captured in the second sample R = Number of marked individuals recaptured in the second sample

Example: You capture and mark 50 dassies (rock hyrax) in a colony. A week later, you capture 40 dassies, and 10 of them are marked.

Using the mark-recapture formula: N = (50 * 40) / 10 =

2

0

0. Therefore, the estimated population size of dassies in that colony is

2

0

0. Population Density: The number of individuals per unit area or volume. High population density can lead to increased competition for resources and higher rates of disease transmission. Low population density can make it harder to find mates. Density = Number of Individuals / Area or Volume

Example: If there are 500 wildebeest living in a 10 km² area in the Kruger National Park, the population density is 500 / 10 = 50 wildebeest/km².

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

Common patterns include: Clumped:* Individuals are clustered together (e.g., herds of elephants, schools of fish). This often results from resource availability or social behavior.

Uniform:* Individuals are evenly spaced (e.g., territorial birds nesting). This often results from competition.

Random:* Individuals are distributed randomly (e.g., wind-dispersed plant seeds).

Population Growth Rate (r): The change in population size over time. It depends on birth rate (b), death rate (d), immigration (i), and emigration (e). Change in Population Size = (Births + Immigration) - (Deaths + Emigration) Population Growth Rate (r) = (Birth Rate - Death Rate) = (b-d). Often expressed as a percentage.

Example: In a population of 1000 springbok, there are 200 births and 50 deaths in a year. Immigration is 10, and emigration is

5. Calculate the change in population size and the population growth rate. Change in Population Size = (200 + 10) - (50 + 5) = 155 Population Growth Rate (r) = (200/1000) - (50/1000) = 0.2 - 0.05 = 0.15 or 15%. This represents a positive growth rate. 2.3 Population Growth Models: Exponential Growth: Occurs when resources are unlimited, and the population grows at its maximum potential rate. This results in a J-shaped curve. While possible in the short term, it is unsustainable in the long run.

Logistic Growth: A more realistic model that considers limiting factors such as resource scarcity. The growth rate slows down as the population approaches the carrying capacity (K), the maximum population size that the environment can sustain. This results in an S-shaped curve. The formula representing the population growth rate is: dN/dt = rN(K-N)/K, where dN/dt is the change in population over time, r is the per capita rate of increase, N is the population size and K is carrying capacity. 2.4 Factors Limiting Population Growth: Density-Dependent Factors: Factors whose effect on population growth depends on the population density.

Examples include: Competition:* For resources like food, water, space, and mates.

Predation:* As prey density increases, predators may become more efficient at finding and capturing them.

Disease:* Disease spreads more easily in dense populations.

Parasitism:* Parasites thrive in dense populations.

Density-Independent Factors: Factors whose effect on population growth is independent of population density.

Examples include: Natural Disasters:* Floods, droughts, fires, and extreme weather events. The severe drought in the Western Cape had a density-independent impact on many populations.

Pollution:* Affects all individuals regardless of population density.

Climate Change:* Can alter habitats and affect populations regardless of their density.