Populations in Ecosystems

Ecosystem

All the organisms living in an area and the non-living components of their environment

Community

All the living organisms in a particular area

Abiotic factors

Non-living factors that affect organisms

Biotic factors

Living factors that affect organisms

Examples of abiotic factors

Light temperature pH water humidity

Examples of biotic factors

Predators disease competition

Niche

The role of a species in its habitat including biotic and abiotic interactions

Distribution of organisms

Where organisms are found in a habitat

Abundance of organisms

How many individuals of a species are present in a habitat

Population size

The number of individuals of a species in a population

Limiting factors

Abiotic and biotic factors that restrict population growth

Temperature effect

Survival decreases as temperature moves away from optimum

Light effect

Increased light increases rate of photosynthesis

pH effect

Extreme pH affects enzyme activity reducing survival

Water availability

Limited water supports only small adapted populations

Humidity effect

Affects transpiration and survival of plants

Carrying capacity

The maximum population size an ecosystem can support

Intraspecific competition

Competition between members of the same species

Resources competed for

Food shelter water mates minerals

Example of intraspecific competition

Male robins competing for territory in winter

Interspecific competition

Competition between members of different species

Cause of interspecific competition

Species occupying the same niche

Example of interspecific competition

Red and grey squirrels in the UK

Predation

One species is caught and eaten by another

Predator-prey relationship

Populations of predator and prey affect each other

Predator-prey cycle

Populations fluctuate in an oscillating pattern

Effect of increased predation

Prey population decreases

Effect of reduced prey

Predator population decreases

Recovery of prey

Less predation allows prey numbers to increase

Quadrat sampling

Used to estimate population size of slow moving or non-motile organisms

Belt transect

Quadrats placed along a line to show changes across a habitat

Percentage cover

Measure of abundance for plants or algae

Frequency

Proportion of quadrats an organism is found in

Mark-release-recapture

Method used to estimate population size of mobile or hidden animals

MRR first stage

Capture mark and release a known number of individuals

MRR second stage

Recapture a second sample and count marked individuals

MRR population estimate

N1 × N2 ÷ number of marked recaptured

MRR assumption

Marked individuals mix evenly back into the population

MRR assumption

Marked and unmarked individuals have equal chance of recapture

MRR assumption

Population is closed with no immigration or emigration

MRR assumption

Few births or deaths occur during investigation

MRR assumption

Marking does not affect survival

MRR assumption

Marks do not rub off

Succession

The change in species composition of a community over time

Primary succession

Succession on land previously devoid of life

Primary succession example

Bare rock after volcanic eruption

Pioneer species

First species to colonise harsh environments

Example of pioneer species

Lichens

Soil formation

Dead organisms add humus forming soil

Later succession

Increase in soil minerals allows shrubs and larger plants to grow

Climax community

Final stable and self-sustaining community

Secondary succession

Succession in an area previously inhabited

Secondary succession example

Regrowth after forest fire

Difference in secondary succession

Soil already present so succession starts later

Conservation

Human management of ecosystems and resources

Conservation example

Controlled burning to prevent climax community formation