population in ecosystems Flashcards
(16 cards)
List the factors that influence carrying capacity
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 → increasing carrying capacity
● Eg. increasing light intensity increases rate of photosynthesis, increasing nitrates increases protein
production and increasing phosphates increases phospholipid production in plants
○ This increases carrying capacity of a variety of plant species
○ So increases the number and variety of habitats, niches and food sources for animals
○ So increasing carrying capacity of a variety of animal species
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
- 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
- Generate a pair of coordinates using a random number generator (eg. on a calculator)
- Place a quadrat here and count number / frequency of [named species]
- Repeat a large number of times (10 or more) and calculate a mean per quadrat
- 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
- Marking not removed so marked organisms are recaptured OR marking is not toxic so doesn’t
affect chances of survival OR marking not visible (to predators) so doesn’t affect predation - Limited / no immigration / emigration
- 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 features of a climax community
● Same species present / stable community over a long time
● Abiotic factors (fairly) constant over time
● 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 eg. by allowing grazing
● This preserves an ecosystem at a certain point / in its current stage of succession (plagioclimax)
● So early species are not outcompeted by later species and habitats / niches are not lost
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 / biodiversity loss
● Conservation is needed to protect habitats / niches / species / biodiversity
● Management of this conflict maintains the sustainability of natural resources
○ Meeting current needs without compromising the ability of future generations to meet theirs
Describe how you could investigate the effect of an environmental factor on
the distribution of a species in a habitat (random sampling in two areas)
- Divide two areas into grids / squares eg. place 2 tape measures at right angles
- Generate a pair of coordinates using a random number generator (eg. on a calculator)
- Place a quadrat here and count number / frequency of [named species]
○ Standardise this eg. only count it if it is more than half in the quadrat - Repeat a large number of times (10 or more) and calculate a mean per quadrat for both areas
- Measure environmental factor in each area eg. take soil moisture readings with a soil moisture meter
Explain the limitations of using systematic
sampling to estimate the population of a
species in a field. (1)
● Not appropriate unless an environmental gradient
● Transects run in one direction, but to cover the entire
field, they would need placing in multiple directions
Explain the importance of a large sample size.
(2)
● Minimises the effect of anomalies
● Ensures sample is representative of the population
Describe how you could decide the number of quadrats that should be used in order to
collect representative data. (2)
● Calculate a running mean
● When enough quadrats, this shows little change
● Enough to carry out a statistical test
