7.4 Populations in ecosystems Flashcards
What is a community?
all the populations of different species living in the same place
What is an ecosystem?
dynamic systems made up of a community and all the non-living factors of its environment
What is a population?
group of individuals of one species that occupy the same habitat and are potentially able to interbreed
What is a niche?
- the specific role of a species within its habitat
- governed by its adaptation to both abiotic and biotic conditions
Explain the advantage of species occupying different niches
- less competition for food/resources
- if two species tried to occupy the same niche, one would out-compete the other
What is carrying capacity?
The maximum stable population size of a species that an ecosystem can support
What are factors that influence carrying capacity?
- light intensity
- temperature
- soil pH
- mineral content
- humidity
What are the interactions between organisms that influence carrying capacity?
- interspecific competition -> between organisms of different species
- intraspecific competiton -> between organisms of the same species
- predation
Explain how abiotic factors may affect population size/carrying capacity
- If conditions favourable, organisms more likely to survive and reproduce -> increasing carrying capacity
- Increases the number and variety of habitats, niches and food sources for animals
Explain how interspecific competetion may affect population size
- Reduces … available to both species, limiting their chances of survival and reproduction
- So reduces population size of both species
- If one species is better adapted, it will out-compete the other
- So population size of less well adapted species declines, potentially leading to extinction
Explain how intraspecific competition may affect population size
- As population size increases, resource availability per organism decreases, so competition increases
- So chances of survival and reproduction increases hence population size decreases - As population size decreases. resource availability per organism increases, so competition decreases
- So chances of survival and reproduction increase hence population size increases
Describe how the size of a population of slow moving or non motile organisms can be estimated
- Divide area into a grid
- Generate a pair of coordinates using a random number generator
- Place a quadrat here and count number of named species
- Repeat a large number of times and calculate mean per quadrat
- Then to calculate population size divide the total area of habitat by quadrat area and multiply by mean per quadrat
Describe how the mark release recapture method can be used to estimate the size of a population of motile organisms
- Capture sample of species, mark and release
- Ensure marking is not harmful
- Allow time for organisms to randomly distribute before collecting second sample
- Population = (number in sample 1 x number sample 2)/ number marked in sample 2
What assumption does the mark-release-recapture method make?
- That there is sufficient time for marked individuals to mix within the population
- Marking not removed so marked are recaptured
- Marking is not toxic so doesn’t affect chances of survival
- Limited/ no immigration or emigration
- No change in population size
Suggest why the mark- release-recapture method can produce unreliable results in very large areas
- unlikely that organisms will distribute evenly
- less chance of recapturing organisms that were marked initially
Describe and explain how primary succession occurs
- Colonisation by pioneer species
- Pioneer species change abiotic conditions
- So environment becomes less hostile/more suitable for other species with different adaptations and less suitable for previous species, so better adapted species outcompete previous species
- As succession goes on, biodiversity increases
- Finally climax community reached- final stable community so there’s no further succession
What are some characteristics of the pioneer species that help them thrive in the harsh conditions?
- production of huge number of spores
- rapid germination
- able to fix nitrogen from the atmosphere
Describe features of a climax community
- same species present/ stable community over a long time
- abiotic factors fairly constant overtime
- populations fairly stable around carrying capacity
Explain how conservation of habitats involves management of succession
- Further succession can be prevented to stop a climax community forming
- By removing or preventing growth of species associated with later stages
- This preserves an ecosystem in its current stage of succession (plagioclimax)
- So earlier species are not outcompeted by later species and habitats/niches are not lost
What is succession?
directional, predictable change in community overtime
