Population Ecology

Learning Objectives

Distinguish between exponential and logistic growth models.

Define carrying capacity (K) and identify factors that limit population growth.

Differentiate between density-dependent and density-independent limiting factors.

The Dynamics of Populations

Population ecology is the study of how populations of organisms interact with their environment, including how their size, density, and distribution change over time.

Models of Population Growth

1.Exponential Growth:

Describes population growth in an idealized, unlimited environment. The rate of population increase is constant, leading to a J-shaped growth curve.

This occurs when resources are abundant and there are no limiting factors. It cannot be sustained indefinitely in nature.

2.Logistic Growth:

A more realistic model that incorporates limiting factors. The rate of population growth slows as the population size approaches the environment's carrying capacity. This results in an S-shaped (sigmoid) growth curve.

Carrying Capacity (K)

Carrying capacity (K) is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available.

As a population (N) approaches K, the growth rate slows to zero. If N exceeds K, the population will decline due to resource scarcity.

Limiting Factors

These are environmental factors that restrict population growth.

Density-Dependent Factors: Their effect on a population increases as the population density increases. They are often biotic factors.

Examples: Competition for resources, predation, disease, accumulation of waste.

Density-Independent Factors: They affect a population regardless of its density. They are often abiotic factors.

Examples: Natural disasters (fires, floods, earthquakes), unusual weather, climate change.

Key Terms

Population Ecology: The study of populations in relation to their environment, including environmental influences on density and distribution, age structure, and population size.
Exponential Growth: Growth of a population in an ideal, unlimited environment, represented by a J-shaped curve when population size is plotted over time.
Logistic Growth: Population growth that is controlled by limiting factors, resulting in an S-shaped curve as the population size approaches the carrying capacity (K).
Carrying Capacity (K): The maximum population size that can be supported by the available resources of a given environment.
Density-Dependent Factor: A limiting factor whose effects on a population intensify as the population density increases.