Chapter 3

What are the two main types of population growth?

• Exponential growth (J-curve) – the per-capita growth rate remains constant; population size increases rapidly.

• Logistic growth (S-curve) – growth rate decreases as population size approaches the carrying capacity (K).

What is carrying capacity (K)?

The maximum population size an environment can sustain indefinitely given its resources, space, and other limiting factors.

Write the formula for population growth (ΔN).
A:

ΔN=B+I−D−E

Where:
B = births, I = immigration, D = deaths, E = emigration.

What are r-selected species?

Species that produce many offspring with little parental care; population size fluctuates greatly and grows quickly when conditions are favourable.

What are K-selected species?

Species that produce few offspring with high parental investment; populations are stable and remain close to carrying capacity.

Define a population.

A population is a group of individuals of the same species that live in the same geographic area at the same time and are capable of interbreeding.

Identify two biotic limiting factors that can affect carrying capacity and explain how they affect it.

Biotic factor	Effect on carrying capacity

Competition

When population density increases, individuals compete for limited resources such as food or mates. This reduces survival and reproduction rates, lowering carrying capacity.

Predation

An increase in predators can reduce prey numbers, decreasing the population’s ability to reach or maintain its carrying capacity.

Identify two abiotic limiting factors that can affect carrying capacity and explain how they affect it.

Abiotic factor	Effect on carrying capacity

Temperature

Extreme or unsuitable temperatures can reduce survival rates or reproduction, lowering carrying capacity.

Availability of water

Limited freshwater supply restricts growth and reproduction, reducing carrying capacity.

Describe what effect biotic factors have on the growth of a population.

Biotic factors such as competition, predation, disease, and availability of food directly influence birth and death rates.
When resources are abundant and competition is low, populations grow rapidly. However, increased predation, disease spread, or resource competition slows growth and can stabilise or decrease population size.

Describe what effect abiotic factors have on the distribution of a population.

Abiotic factors such as temperature, rainfall, soil composition, and light intensity determine where species can survive and reproduce.
Favourable abiotic conditions result in higher population densities, while extreme or unsuitable conditions restrict species to smaller or more specific habitats.