Populations in ecosystems

Question 1

Population

Answer 1

A group of organisms of the same species, living in the same habitat at the same time

Question 2

Community

Answer 2

All the populations of different species living in the same habitat at the same time

Question 3

Ecosystem

Answer 3

A community, plus all the non-living (abiotic) conditions of their environment.

Ecosystems are dynamic systems and can range in size from the very small to the very large.

Question 4

Niche

Answer 4

The role of a species within its habitat, e.g. what it eats, where and when it feeds.

Each species has its own unique niche; if two species try to occupy the same niche, one will outcompete the other.

Question 5

Abiotic conditions

Answer 5

The non-living features of the ecosystem

e.g. temperature, pH

Question 6

Biotic conditions

Answer 6

The living features of the ecosystem

e.g. predation, food supply, disease

Question 7

Carrying capacity

Answer 7

The maximum stable population an ecosystem can support

Question 8

Why does population size vary? (abiotic conditions)

Answer 8

Population size can vary as a result of the effect of abiotic factors.

e.g. light, water and temperature

If you have the ideal conditions for a species, organisms can grow fast and reproduce successfully

Question 9

Interspecific competition

Answer 9

Competition between species

Reduces resources available to both which limits both populations.

If one species is better adapted, it will outcompete the others.

Question 10

Intraspecific competetition

Answer 10

Competition within a species

A smaller population means less competition which is better for growth and reproduction, and eventually a larger population.

A larger population means more competition, leading to less growth and reproduction, and eventually a smaller population

Question 11

Predation

Answer 11

Population sizes of predators and prey are interlinked.

Increased predator population size leads to more prey eaten so that the prey population falls.

Less food for predators so the predator population size falls and the prey population rises again.

Question 12

Randomly placed quadrats

Answer 12

Use a grid/area split into squares

Obtain random coordinates using a random number generator/calculator and place quadrats here

To decide what number of quadrats to use to collect representative data, calculate the running mean and when there are enough quadrats, shows little change.

Count frequency of non-motile species in quadrat

Calculate the mean per quadrat

Calculate population size by multiplying the mean by the number of quadrats that would cover the habitat.

Question 13

Quadrats along a belt transect

Answer 13

Used to look at changes in distribution in non-motile organisms.

Lay a tape measure from one place to another

Place quadrats at regular intervals along the line.

Count frequency/percentage coverage in quadrats

Question 14

Mark-release-recapture

Answer 14

The mark-release-recapture technique can be used for motile organisms.

Capture sample of species and mark (harmlessly) and release

Leave enough time for organisms to randomly distribute before collecting second sample

Population size = number in sample 1 x number in sample 2/number marked in sample 2

Question 15

Assumptions made with the mark-release-recapture technique

Answer 15

Sufficient time for marked individuals to mix within the population

Marking is not removed and does not affect the chances of survival

No immigration/emigration

No births/deaths/breeding

Question 16

Succession

Answer 16

Process by which an ecosystem changes over time.

Question 17

How does succession occur

Answer 17

Colonisation by pioneer species (first species to colonise)

Pioneer species (or generally just certain species at each stage in succession) change the abiotic conditions and make the environment less hostile e.g. die and decompose, forming soil that retains water.

Environment becomes more suitable for other species with different adaptations, and may be less suitable for the previous species - the better adapted species outcompetes previous species.

As succession goes on, biodiversity increases.

Climax community: final complex, stable community.

Question 18

Conservation of habitats

Answer 18

Conservation of habitats frequently involves management of succession.

Human activities can prevent succession and stop a climax community from forming: plagioclimax

Conservation sometimes involves preventing succession in order to preserve an ecosystem in its current stage of succession.