section 7: populations & sustainability - topic 1: variation in population size

Question 1

what is a population?

Answer 1

all the organisms of one species in a habitat.

Question 2

what is population size?

Answer 2

the total number of organisms of one species in a habitat.

Question 3

what are abiotic factors?

Answer 3

the non-living features of the ecosystem.

Question 4

what are biotic factors?

Answer 4

the living features of the ecosystem.

Question 5

examples of abiotic factors.

Answer 5

the amount of light.
water/space available.
the temperature of the surroundings.
chemical composition of their surroundings.

Question 6

what happens when abiotic factors are ideal for a species?

Answer 6

organisms can grow fast and reproduce successfully.

Question 7

what happens when abiotic factors are not ideal for a species?

Answer 7

organisms can’t grow as fast or reproduce as successfully.

Question 8

what 2 things can affect population size?

Answer 8

abiotic factors.
biotic factors.

Question 9

examples of biotic factors.

Answer 9

interspecific competition.
intrapsecific competition.
predation.

Question 10

what is interspecific competition?

Answer 10

when organisms of different species compete with each other for the same resources.

Question 11

what can interspecific competition do to resources?

Answer 11

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.

Question 12

how can interspecific competition affect the distribution of species?

Answer 12

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.

Question 13

what is intraspecific competition?

Answer 13

when organisms of the same species compete with each other for the same resources.

Question 14

what can infraspecific competition do to population size?

Answer 14

it can cause a cyclic change, where the population grows, shrinks, grows again and so on.

Question 15

why is there a cyclic change in population size?

Answer 15

• 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.

Question 16

what is carrying capacity?

Answer 16

the maximum stable population size of a species that an ecosystem can support.

Question 17

what is predation?

Answer 17

where an organism (the predator) kills and eats another organism 9the prey).

Question 18

how are the population sizes of predator and prey interlinked?

Answer 18

as the population of one changes, it causes the other population to change through negative feedback.

Question 19

what is negative feedback?

Answer 19

when a system reacts to a change in a way that pushes it back towards a stable state.

Question 20

how does the predator-prey system work?

Answer 20

• 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.

Question 21

what else influences the predator-prey system?

Answer 21

other factors i.e. availability of food.

prey population - too big for amount of food - begins to decline - accelerated by predation.

Question 22

what do limiting factors do?

Answer 22

stop the population size of a species increasing.

they determine the carrying capacity of an ecosystem.

Question 23

what can limiting factors be?

Answer 23

biotic or abiotic.

Question 24

example of a biotic limiting factor.

Answer 24

interspecific competition limits the population size of a species because the amount of resources available to a species is reduced.

Question 25

example of an abiotic limiting factor.

Answer 25

the amount of shelter in an ecosystem limits the population size of a species as there’s only enough shelter for a certain number of individuals.