Populations in Ecosystems (Chapter 19) Flashcards
Define Community
All the populations of different organisms living and interacting in a particular place at the same time.
Define Population
Group of individuals of the same species occupying the same habitat at the same time.
Define Ecosystem
All the interacting biotic and abiotic features in a specific environment.
Define Habitat
Place where organisms normally live.
Define Niche
All conditions and resources needed for an organism to survive and reproduce. How an organism fits into the environment. Governed by the abiotic and biotic conditions.
Define Abiotic Factors and give examples
Non-living features of an environment
Temperature, pH, Light
Define Biotic Factors
Living features of an environment.
What is a carrying capacity and what is it affected by?
Ecosystems can only support populations of a certain size.
Affected by abiotic factors, inter, and intraspecific competition.
Define Intraspecific Competition
Between members of the same species.
Define Interspecific Competition
Between members of different species. Happens until 1 outcompetes another. Compete for things like food, space, light, breeding territory.
Describe the stages in succession
1) Colonisation by pioneer species
2) Change in the environment by pioneers.
3) Environment becomes less hostile.
4) Enables new species to colonise.
5) Change in biodiversity e.g. species becomes better competitors and others die out as they are outcompeted.
6) Climax community forms.
What are some features of a climax community?
- Same species present over a long time
- Abiotic factors more or less constant.
- Population is stable around carrying capacity.
Describe how quadrats are used
1) Set up a grid
2) Choose random co-ordinates using a random number generator
3) Measure %cover or species frequency in a quadrat (say how you do this)
4) Place a large number of quadrats on co-ordinates and calculate a mean per quadrat
5) Use a valid method for counting total number of organisms e.g. number of organisms per quadrat multiplied by total number of quadrats.
If there is a large number then do a running mean until the mean stays stable and there is enough for a statistical test
Why is random sampling used?
It avoids bias
What is %cover used for and pros and cons?
Measures abundance (estimate of the area within a quadrat a specific plant species occupies.
Useful when counting individual organisms is impractical (e.g. too many, too hard to distinguish, grows in clumps)
Underestimates small organisms/overestimates large ones
Define Species Frequency
Number of individuals of each species in a quadrat
Why are transects sometimes used and what is the disadvantage?
When there is a transition in sampling (systematic sampling)
May not be representative of area
Describe how to use a transect
1) Place quadrats at regular intervals along the line
2) Count plants/percentage cover (in quadrats)
3) Use several quadrats
Describe how to use mark-release recapture
1) Capture sample, mark and release
2) Appropriate method of marking suggested - doesn’t harm/rub off
3) Take second sample and count marked organsims
4) Population = (no. in sample 1 x number in sample 2)/Number marked in sample 2
What are the assumptions made when using mark-release recapture?
- Population remains stable
- No emigration/immigration
- Marking does not affect survival
- Birth rate and death rate equal
- (In some cases) all belong to one population
What is the equation for net productivity?
Net productivity = gross productivity minus respiratory loss
