Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define a population and its characteristics.
• Explain exponential and logistic growth.
• Analyse age-structure diagrams.
• Understand factors limiting population growth.

Lesson summary

Population ecology investigates how populations interact with their environment. It's not just about counting animals; it's about understanding the dynamics of birth, death, immigration, and emigration and how these factors are affected by environmental resources and human activities. This knowledge is vital for South Africa because our growing population places increasing pressure on our natural resources, leading to challenges like water scarcity, deforestation, and habitat loss. Understanding population ecology helps us manage these resources sustainably and mitigate the negative impacts of human activities.

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. Key characteristics used to describe and study populations include: Population Size: The total number of individuals in the population. Direct counting is rarely possible, so estimation methods like mark and recapture are used.

Population Density: The number of individuals per unit area or volume. High densities can lead to increased competition for resources and increased disease transmission. Low densities can make it difficult for individuals to find mates.

Population Distribution: The pattern of spacing among individuals within the population. It can be clumped (aggregated in patches, e.g., herds of wildebeest), uniform (evenly spaced, e.g., territories of birds), or random (unpredictable spacing, e.g., distribution of plants in a forest).

Age Structure: The proportion of individuals in different age groups. Age structure provides insights into the potential for future population growth or decline. It is often represented graphically as an age-structure diagram (population pyramid). 2.2 Population Growth Patterns: Exponential Growth: Occurs when a population increases at a constant rate per capita (per individual), resulting in a J-shaped growth curve. This typically happens when resources are abundant and there are few limitations on growth. The equation for exponential growth is dN/dt = r max N, where dN/dt is the rate of population change, r max is the intrinsic rate of increase (birth rate minus death rate), and N is the population size. Exponential growth is unsustainable in the long term.

Logistic Growth: Occurs when a population's growth rate slows as it reaches its carrying capacity (K). The carrying capacity is the maximum population size that a particular environment can sustain given the available resources. The logistic growth equation is dN/dt = r max N(K-N)/K. As N approaches K, the growth rate (dN/dt) approaches zero. This results in an S-shaped growth curve.