Populations in ecosystems

Succession

The gradual change in an ecological community over time

Community

Populations of different species in a habitat

Ecosystem

A community and the non-living components in its environment

Niche

• A species’ role within an ecosystem

• This is governed by its adaptation to both biotic and abiotic conditions

• Only one species can occupy a niche at a given time

What happens if 2 species try to occupy the same niche at the same time?

They will compete with each other

Biotic

Living features of an ecosystem

Abiotic

Non-living features of an ecosystem

Carrying capacity

The maximum stable population size of a species that an ecosystem can support

What are the 4 factors that affect carrying capacity?

• Abiotic factors

• Predation

• Interspecific competition

• Intraspecific competition

Abiotic factors that affect carrying capacity

• Light intensity

• Water availability

• Food availability

• Soil pH

• Temperature

What do favourable abiotic conditions increase the chances of?

Survival and reproduction

Predation

When one organism eats another

Interspecific competition

When organisms of different species compete for resources → Less resources available to both species → Decrease in population size

Intraspecific competition

When organisms of the same species compete with each other for resources

What are the 2 methods used for estimating population sizes of non-motile/slow moving organisms?

• Randomly placed quadrats

• Quadrats along belt transect

What are the method is used for estimating population sizes of motile organisms?

Mark-release-recapture

Method for mark-release-recapture

1. Capture a sample of individuals from the population

2. Count no. of individuals (S1) and mark them

3. Release organisms and allow time to distribute evenly amongst the rest of the population

4. Capture a 2nd sample from the population

5. Count the number caught (S2) as well as the number caught who are marked (R)

6. Population size = (S1 x S2) / R

Mark-release-recapture equation

Population size = (No. of individuals marked x No. of individuals caught 2nd time) / No. of individuals who are marked when caught 2nd time

What are the criteria for the marking in mark-release-recapture?

• Marking is harmless

• Marking doesn’t come off

• Mrking doesn’t increase chances of predation

What are the 4 assumed criteria for mark-release-recapture?

• Marking doesn’t affect survival

• Marked individuals mix randomly and evenly with population

• No change in population size

• Marking not lost

Outline randomly placed quadrats method (6 steps)

1. Plot coordinates and use a random number generator to generate coordinates

2. Place quadrat (1m x 1m)

3. Count number of individuals

4. Repeat many times

5. Calculate mean

6. Multiply mean by total area

Primary succession

Succession on land that has newly formed/exposed

What are 4 extreme abiotic/hostile conditions where the pioneer species could habitat?

• Little nutrients available

• Unstable substrate

• Little water available

• Exposed

What are 4 possible adaptations of pioneer species?

• Ability to reproduce asexually

• Ability to fix N₂

• Tolerant to salt

• Rapid germination

What are 3 possible ways that pioneer species change the environment to make conditions less hostile?

• Erode rock to release minerals

• Add more humus

• Increase nitrate content

(Occurs when they die and decompose)

What happens when succession continues after the pioneer species?

1. Conditions become less hoss hostile

2. Different organisms are better adapted for the improved conditions, so outcompete those already there and dominate the ecosystem

3. More species move in → Biodiversity increases

Climax community

Largest and most complex community

What are 4 features of climax community?

• Same species present over long period of time

• Stable community and stable population

• Constant abiotic factors

• Highest biodiversity reached before climax community

When does secondary succession occur? Give an example

• When climax community has been cleared in same way

• Forest fire

How is secondary succession different from primary succession?

• Succession occurs much quicker as there’s already soil which contains seeds and nutrients to start a new community (so pioneer species are larger plants)

• Climax community is reached much faster as not starting with extreme hostile conditions

Conservation

Involves managing succession

Purpose of conservation

• Preventing succession from continuing to preserve an ecosystem in its current stage of succession

• Because if another species arrived and dominated, existing species would be outcompeted and die out

What are 2 methods of conservation?

• Grazing/mowing

• Managed fires

Outline grazing/mowing

• Removes growing tips from plants such as tree saplings or small shrubs → Preventing them from developing

• No climax community is reached

Outline managed fires

• All species wiped out in fire and secondary succession will occur

• Small species are pioneer species and will grow more quickly than larger trees/shrubs