section 7: populations & sustainability - topic 1: variation in population size Flashcards
what is a population?
all the organisms of one species in a habitat.
what is population size?
the total number of organisms of one species in a habitat.
what are abiotic factors?
the non-living features of the ecosystem.
what are biotic factors?
the living features of the ecosystem.
examples of abiotic factors.
the amount of light.
water/space available.
the temperature of the surroundings.
chemical composition of their surroundings.
what happens when abiotic factors are ideal for a species?
organisms can grow fast and reproduce successfully.
what happens when abiotic factors are not ideal for a species?
organisms can’t grow as fast or reproduce as successfully.
what 2 things can affect population size?
abiotic factors.
biotic factors.
examples of biotic factors.
interspecific competition.
intrapsecific competition.
predation.
what is interspecific competition?
when organisms of different species compete with each other for the same resources.
what can interspecific competition do to resources?
the resources available to both populations will be reduced i.e. if they both share the same source of food, there will be less available to both of them.
- so both populations will be limited by a lower amount of food.
they’ll have less energy for growth and reproduction, so the population sizes will be lower for both species.
how can interspecific competition affect the distribution of species?
if 2 species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.
^ it won’t be able to exist alongside the better adapted species.
what is intraspecific competition?
when organisms of the same species compete with each other for the same resources.
what can infraspecific competition do to population size?
it can cause a cyclic change, where the population grows, shrinks, grows again and so on.
why is there a cyclic change in population size?
- the population of a species increases when resources are plentiful.
- as the population increases, there’ll be more organisms competing for the same amount of space and food.
- eventually, resources such as food and space become limiting (there isn’t enough for all the organisms).
- the population then begins to decline.
- a smaller population then means that there’s less competition for space and food, which is better for growth and reproduction.
- so the population starts to grow again.
what is carrying capacity?
the maximum stable population size of a species that an ecosystem can support.
what is predation?
where an organism (the predator) kills and eats another organism 9the prey).
how are the population sizes of predator and prey interlinked?
as the population of one changes, it causes the other population to change through negative feedback.
what is negative feedback?
when a system reacts to a change in a way that pushes it back towards a stable state.
how does the predator-prey system work?
- as the prey population increases, there’s more food for predators, so the predator population grows.
- as the predator population increases, more prey is eaten, so the prey population then begins to fall.
^ this is a negative feedback effect that restores the prey population to a more stable size. - this means there’s less food for the predators, so their population decreases (another negative feedback effect) and so on.
what else influences the predator-prey system?
other factors i.e. availability of food.
prey population - too big for amount of food - begins to decline - accelerated by predation.
what do limiting factors do?
stop the population size of a species increasing.
they determine the carrying capacity of an ecosystem.
what can limiting factors be?
biotic or abiotic.
example of a biotic limiting factor.
interspecific competition limits the population size of a species because the amount of resources available to a species is reduced.
