Regulation of populations

Factors affecting population size

A population is a group of individuals of the same species which makes up part of an ecosystem.

Factors affecting population size

Factors affecting population size

The number of individuals of the same type present per unit area of a habitat is called the population density

Factors affecting population size

When a population colonises a new environment, it grows in number until it reaches a certain size which the available environmental resources can just maintain. This limit is called the carrying capacity

The population remains in a state of dynamic equilibrium and remains stable despite short-term fluctuations in number

Factors affecting population size

Factors influencing population change

Each species has an enormous reproductive potential but under natural conditions a population is prevented from increasing in size indefinitely by environmental resistance

- The DIDDy factors….

Density-Independent FactorsDensity-independent factors affect the growth of a

population regardless of the population’s density e.g.

a forest fire excessive rainfall spells of unusually high or low temperatureUsually a population will return to normal after such

an event.

Density Dependent Factors

A density-dependent factor is one which only affects the population once it has grown to a certain size.

Competition for food

Density Dependent Factors

Toxic wastes

Parasites and disease

Predation

Predator-Prey Interactions In predator-prey relationships,

increases in prey numbers (due to plentiful food supply or favourable environmental conditions for example) can, in turn, lead to an increase in predator numbers.

Similarly, any decrease in prey numbers is followed by a drop in predator numbers

Predator-Prey Interactions

Changes in predator numbers follow the same trend as those of prey numbers but there is a lag in changes to prey numbers due to time taken for changes in prey numbers to take effect

Predator-Prey Interactions

Monitoring PopulationsMany species of animals and plants are kept

under close surveillance by scientists in order to obtain information about their population numbers. This information is required for:

Monitoring Populations1.The management of species which provide

food or raw materials

Food species: if the death rate exceeds the birth rate of a species it’s population size decreases. The maximum sustainable yield (MSY) is a measure of the maximum rate individuals can be removed from the population without affecting the population’s future productivity.

Monitoring Populationse.g. Fish

There are several cases of fish stocks that have crashed due to over-fishing such as cod & herring. EU regulations now ensure catches are within fixed quotas.

Monitoring Populationse.g. Red Deer

Monitoring Populations2. Pest species

Monitoring of populations of pest species is required to effectively control their numbers / distribution

Monitoring Populationse.g. Greenfly (aphids) Locusts Pathogenic fungi Mosquitoes (malaria)

Monitoring Populations3. Pollution – indicator species

Certain species serve as indicators of the environment’s health by their abundance or scarcity.

Monitoring Populationse.g. Freshwater invertebrates

The presence of large populations of mayfly and stonefly indicate water is clean and rich in oxygen

Abundance of rat-tailed maggots and sludgeworms indicate a low oxygen content and organic matter pollution

Monitoring Populationse.g. Lichens

e.g. peppered moths

Monitoring Populations4. Endangered species

The monitoring of populations of plants and animals enables us to recognise and protect rare species for their aesthetic value and genetic diversity

Succession in plant communities

Succession in plant communities

Succession in plant communities

Soil fertility increasing

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Succession in plant communities

Primary succession: is the series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes.

Secondary succession:is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, after felling trees in a woodland, land clearance or a fire.

Succession in plant communities

Characteristics of a climax community:

The final product of long-term unidirectional change in a community

Self-perpetuating and not replaced by another community

A mature community in dynamic equilibrium with its environment

Biomass and species diversityCharacteristic Pioneer Climax

Community Community

Growth rateHeight of vegetationLife spanNo. seedsSize of seedsDistance seeds dispersedFood productivityBiomassSpecies diversityNutrient supply in soilFood chains/webs