populations in an ecosystem

Define community

All the differnt species that live in one area and interact with each other

Ecosystem

All Irving and non living organisms and aspects in an environment

Habitat

A place where an organism lives within an ecosystem

Niche

The role of species in a habitat, consisting of both it biotic and abiotic interactions

• e.g what it eats or what time of day its active

Assumptions made with capture, mark, release, recapture

• the marking doesn’t increase the impact of a selection pressure e.g predation

• The marking wont fade or rub off over the course of the sampling

• There are no brirt’s or deaths over the course of the sampling

• The animas have sufficient time to redistribute themselves before they are recaptured

• The equation only works if the proportion of marked individuals in the first sample is equal to the proportion of marked individuals in the second sample

How to calculate percentage frequency

Frequency is the number of quadrats in which a species occurs, as a percentage of the quadrats thrown:

number of quadrats present in/ total number of quadrants thrown

x 100 = percentage frequency

How to calculate density of population

The number of times a particular species occurs in all the quadrats expressed as the number per unit area

total number of individuals/ area sampled (m2) = density m-2

What is systematic sampling

• Samples are taken at intervals (e.g using transects)

• Place a transect down in a habitat in a straight

  line

• Used to investigate change over distance in an ecosystem

• Use a belt quadrant - uses quadrants

• Line transect - without quadrants

Pros and cons of systematic sampling

• Good for showing change across a distance e.g what happens t the percentage cover of grass as you move away for the river

• It’s easy to miss species if they aren’t in your transect line

What is succession in ecosystems and why does it happen

• describes how communities of organisms that have colonised an area change - over time - and get replaced by other, more varied organisms

• Because ecosystems are dynamic meaning they are constantly changing

Key points about pioneer species

• are always photynthetic

• Are usually hardy ‘opportunistic’ species which are able to grow rapidly to exploit a sudden new opening in a ground plant cover

• Able to grow quickly and are short - lived

• They usually have the ability to produce a lot of wind - carried seeds or produce spores

• E.g mosses, lichens, algae, some grasses

Why may a graph not be able to be extrapolated

Not a linear relationship

What will increase over time as a pioneer species turns into a climax community

• soils depth

• Habitats

• Biomass and productivity

• Soil fertility

• Soil and water content

• Food availability

• Niches

• Species richness

Features of climax community

• stable community - species diversity status consistent

• Stable population sizes - no massive fluctuation in population sizes; populations stay around carrying capacity

• Stable abiotic factors

How is heathland an example of deflected succession

• they are the result of human activities - clearance and grazing

• Of left to their own devices, trees and tall shrubs would colonise

• Becassue the normal succession has been artificially changed it is often referred to as a deflected succession

Why do we do conservation

• personal reasons - increase biodiversity helps support own lives

• Ethical reasons - respect for other species

• Economic reasons - e.g discovery of medicines, ecotourism, preventing flooding

• Cultural and aesthetic - enrichment, socialisation, enjoyment