Populations in ecosystems Flashcards
What is a community
All the populations of different species living in the same place at the same time
What is an ecosystem
A community and the non-living (abiotic) components of its environment.
What is a niche?
Specific role of a species within the habitat governed by its adaptation to north abiotic and biotic factors
Explain the advantage of species occupying different niches
Less competition for food / resources
If two species tried to occupy the same niche, one would outcompete the other
What is carrying capacity?
The maximum (stable) population size of a species that an ecosystem can support.
List the factors that influence carrying capacity
Abiotic factors
Eg. light intensity, temperature, soil pH & mineral content, humidity
Interactions between organisms
a. Interspecific competition - between organisms of different species
b. Intraspecific competition - between organisms of the same species
c. Predation (predators kill and eat other animals, called prey)
Explain how abiotic factors may affect population size / carrying capacity
If conditions favourable, organisms more likely to survive & reproduce
This increases carrying. capacity so more variety of habitats and niches
Explain how interspecific competition may affect population size
Reduces [named resource] available to both species, limiting their chances of survival & reproduction ○ So reduces population size of both species
● If one species is better adapted, it will outcompete 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 & reproduction decrease → population size decreases
- As population size decreases, resource availability per organism increases, so competition decreases ● So chances of survival & reproduction increase → population size increases
Explain the changes which occur in populations of predators & prey
1.Prey population increases so predators have more food ● So more predators survive & reproduce
- Predator population increases so more prey killed & eaten ● So less prey survive & reproduce
- Prey population decreases so predators have less food ● So less predators survive & reproduce
- Predator population decreases so less prey killed & eaten ● So more prey survive & reproduce (cycle repeats)
Describe how the size of a population of slow-moving or non-motile organisms can be estimated
Divide area into a grid / squares eg. place 2 tape measures at right angles
2. Generate a pair of coordinates using a random number generator (eg. on a calculator)
3. Place a quadrat here and count number / frequency of [named species]
4. Repeat a large number of times (10 or more) and calculate a mean per quadrat
5. Population size = (total area of habitat / quadrat area) x 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 / does not affect survival
● Allow time for organisms to randomly distribute before collecting second sample
● Population = (number in sample 1 x number in sample 2) / number marked in sample 2
What assumptions does the mark-release-recapture method make?
Sufficient time for marked individuals to mix / distribute evenly within the population
2. Marking not removed and doesn’t affect chances of survival / predation
3. Limited / no immigration / emigration
4. No / few births / deaths / breeding / change in population size (or birth & death rate are equal)
Suggest why the mark-release-recapture method can produce unreliable results in very large areas
Unlikely that organisms will distribute randomly / 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
- Climax community reached - final stable community (no further succession)
Describe features of a climax community
Same species present / stable community over a long time
● Abiotic factors (fairly) constant over time
● Populations (fairly) stable
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
preserves ecosystem
Describe the conflict between human needs and conservation as well as the importance of managing this
Human demand for natural resources (eg. timber) is leading to habitat destruction
Conservation is needed to protect habitats
Management of this conflict maintains the sustainability of natural resources
Describe how you could investigate the effect of a factor on the distribution of a species in a habitat (systematic sampling)
Place a transect line (tape measure) across an area with an environmental gradient eg. tree to full sun
- Place quadrats at regular intervals eg. 1m (until end of transect) and record the number of organisms of
[named species] and [named environmental factor] eg. light intensity using a light meter - Repeat in other parallel areas and calculate mean number of plants at each point along the transect
