Populations and sustainability

Chapter 24

Population size factors

Population size depends on birth rate, death rate, immigration and emigration. It is also affected by limiting factors such as food, water, space, disease, predation and competition.

These factors determine the carrying capacity, which is the maximum population size an environment can support sustainably. As population size approaches carrying capacity, resources become limited, increasing competition and death rate and reducing birth rate, so population size levels off.

Interactions between populations

Predator–prey relationships: when prey numbers increase, predator numbers increase because more food is available. Increased predation then reduces prey numbers, causing predator numbers to fall. This produces cyclical fluctuations in both populations.

Intraspecific competition is competition between members of the same species for resources such as food, territory and mates.

Interspecific competition is competition between different species for the same limited resources.

Conservation vs preservation

Conservation is the active management of ecosystems and resources so they can be used sustainably, while maintaining biodiversity.

Preservation aims to protect habitats and species from human interference, often by preventing their use.

Reasons for conservation

Reasons for conservation include economic reasons, such as food, timber, medicines and tourism; social reasons, such as recreation and cultural importance; and ethical reasons, as species have value and should be protected for future generations.

Sustainable ecosystem management

Timber: selective cutting, replanting trees, coppicing and controlling the size and age of trees harvested allow forests to regenerate.

Fishing: quotas, minimum net mesh sizes, minimum landing sizes, closed seasons and protected areas allow fish to reproduce and populations to recover.

Sustainable management means resources are used at a rate that allows them to replenish, so they remain available in the future.

Managing environmental recourses whilst balancing conservation and human needs

Ecosystems are managed to balance the need to protect biodiversity with human needs for food, land, energy and resources.

Human activities such as deforestation, pollution, hunting, fishing and habitat destruction can reduce animal and plant populations. Their effects can be controlled using measures such as protected areas, hunting and fishing restrictions, quotas, habitat restoration, pollution controls and sustainable resource use.