Ocr A2 Biology - Factors Affecting Population Size

Front 1

Population size varies because of both .......... and ......... factors.

Back 1

1. abiotic

2. biotic

Front 2

Define population size.

Back 2

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

Front 3

State five abiotic factors that could affect the growth of an organism.

Back 3

• Light
• Water
• Space
• Temperature
• Chemical composition of their surroundings

Front 4

Explain how temperature could affect population size of a species.

Back 4

• At the optimum temperature, the organism does not have to use a lot of energy trying to maintain its body temperature. This leaves more energy to be used for growth or reproduction, increasing population size.
• At temperatures significantly higher or lower than their optimum temperature, the organism has to use energy to maintain an optimal internal environment. This leaves less energy to be used for growth or reproduction, decreasing the population size.

Front 5

Name three biotic factors affecting population size.

Back 5

• Interspecific competition
• Intraspecific competition
• Predation

Front 6

What is interspecific competition?

Back 6

Interspecific competition is when different species compete with each other for the same resources.

Front 7

Interspecific competition affects .......... size and .......... of .......... .

Back 7

1. populations

2. distribution of species

Front 8

Explain how interspecific competition affects population size and give an example.

Back 8

• Interspecific competition between two species can mean that the resources available to both populations are reduced.
• This means both populations will be limited by the lower amount of food, resulting in less energy for growth and reproduction, causing both of the population sizes to drop.
• In areas where both red and grey squirrels live, their populations are smaller than they would be if only one species lived there.

Front 9

Explain how interspecific competition affects distribution of species and give an example.

Back 9

• If two species are competing but one is better adapted to its surroundings than the other, the less well-adapted species will be out-competed - it wont be able to exist alongside the better adapted species.
• Since the introduction of the grey squirrel in the UK, the native red squirrel has disappeared from large areas. This is due to the grey squirrel having a better chance of survival due to being larger and storing more fat during the winter.

Front 10

What is intraspecific competition?

Back 10

Intraspecific competition is when organisms of the same species compete for the same resources.

Front 11

Explain what is happening at each labelled part of this graph.

Back 11

• 1. The population of a species increases when the resources are plentiful. As the population increases, there'll be more organisms competing for the same amount of space and food.
• 2. Eventually, resources such as food and space become limited - there isn't enough for all the organisms. The population starts to decline.
• 3. A smaller population means that there is less competition for space and food, which is better for growth and reproduction. This causes the population to grow again.
• 4. That line is the carrying capacity - which is the maximum stable population of a species an ecosystem can support.

Front 12

What is predation?

Back 12

Predation is when an organism kills and eats another organism.

Front 13

What is the name of the system that controls the population sizes of the predators and prey in predation?

Back 13

Negative feedback.

Front 14

Explain what is happening at each of the labelled points on this graph. Also state another reason for a drop in population other than predation.

Back 14

• 1. As prey population increases, there is more food for predators, so the predator population also grows due to more energy for growth and reproduction.
• 2. The prey population drops due to higher predator population. This is an example of negative feedback, as the prey population is restored to a more stable size.
• 3. Due to the drop in prey population, there is less food available for the predators which result in the population of predators also dropping (also negative feedback). This process continues to repeat.
• A factor for a drop in the hare population may be that there are too many hares in comparison to the food available for them. The decline in population is then accelerated by predation.

Front 15

Limiting factors .......... the ............ size of a species ............ .

Back 15

1. stop

2. population

3. increasing

Front 16

Limiting factors can be abiotic or biotic. Give an example of an abiotic factor limiting population size.

Back 16

The amount of shelter in an ecosystem limits the population size because there is only enough shelter for a certain number of individuals.

Front 17

Limiting factors can be abiotic or biotic. Give an example of a biotic factor limiting population size.

Back 17

Interspecific competition limits the population size of a species as the amount of resources available to a species is reduced.

Front 18

Limiting factors determine the .......... capacity of an ecosystem.

Back 18

carrying