7.4 Populations in ecosystems Flashcards
(21 cards)
What is a community?
All the populations of different species living in the same place (habitat) at the same time
What is an ecosystem?
A community and the non-living (abiotic) components of its environment
Ecosystems can range in size from very small to very large and they are dynamic systems (populations rise / fall over time)
What is a niche?
● The specific role of a species within its habitat, eg. what it eats, where and when it feeds
● Governed by its adaptation to both abiotic (non-living) and biotic (living) 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 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
List the factors that influence carrying capacity - 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-mobile 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
Equation for mark recapture
(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 and explain how primary succession occurs
- Colonisation by pioneer species (first to colonise)
- Pioneer species (and other species at each stage in succession) change abiotic conditions
○ Eg. they die and decompose, forming soil which retains water (humus / organic matter) - 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)
What is succession?
Succession = change in a community over time due to change in abiotic factors / species
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
