7C - Variation in population size

Question 1

What is population size?

Answer 1

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

Question 2

What is the maximum stable population size of a species that an ecosystem can support called?

Answer 2

Carrying capacity.

Question 3

What is carrying capacity?

Answer 3

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

Question 4

What does carrying capacity vary as a result of?

Answer 4

Both abiotic and biotic factors.

Question 5

What do abiotic factors include?

Answer 5

The amount of light, water or space available, the temperature of the surroundings or the chemical composition of the surroundings.

Question 6

What happens when abiotic conditions are ideal for a species?

Answer 6

Organisms can grow fast and reproduce successfully.

Question 7

Why will the temperature of the organism’s surroundings being ideal increase the population size of the species?

Answer 7

When the temperature of the surroundings is the ideal temperature for metabolic reactions to take place, they don’t have to use up as much energy maintaining their body temperature. This means more energy can be used for growth and reproduction, so their population size will increase.

Question 8

What happens when abiotic conditions aren’t ideal for a species?

Answer 8

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

Question 9

Why will the temperature of the organism’s surroundings being significantly lower or higher than ideal decrease the population size of the species?

Answer 9

When the temperature of the surroundings is significantly lower or higher than their optimum body temperature, they have to use a lot of energy to maintain the right body temperature. This means less energy will be available for growth and reproduction, so their population size will decrease.

Question 10

Why does temperature have an effect on population size?

Answer 10

Because of the denaturing of enzymes in the organism.

Question 11

Why does light have an effect on population size?

Answer 11

It is a source of energy for most ecosystems.

Question 12

Why does pH have an effect on population size?

Answer 12

It affects enzyme action.

Question 13

Why do water and humidity have an effect on population size?

Answer 13

They affect transpiration rates.

Question 14

What are biotic factors that affect population size?

Answer 14

Competition (interspecific and intraspecific), predators and, parasites and disease.

Question 15

What is competition?

Answer 15

Striving to gain or win something by establishing superiority over others.

Question 16

When does competition occur?

Answer 16

When the niche of any two species overlaps.

Question 17

What are the 2 types of competition?

Answer 17

Interspecific and intraspecific.

Question 18

What is interspecific competition?

Answer 18

Competition between different species.

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

Question 19

Give an example of interspecific competition

Answer 19

Red and grey squirrels compete for the same food resources and habitats in the UK.

Question 20

What can interspecific competition mean to resources?

Answer 20

The resources to both populations are reduced meaning that both populations will be limited by a lower amount of food.

Question 21

Why is interspecific competition of resources an issue?

Answer 21

Because the resources to both populations are reduced meaning that both populations will be limited by a lower amount of food. This means they’ll have less energy for growth and reproduction, so the population sizes will be lower for both species.

Question 22

How does interspecific competition affect population size?

Answer 22

Because the resources to both populations are reduced meaning that both populations will be limited by a lower amount of food. This means they’ll have less energy for growth and reproduction, so the population sizes will be lower for both species.

Also, if two 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 23

What happens if two species are competing but one is better adapted to its surroundings than the other?

Answer 23

The less well adapted species is likely to be out-competed - it won’t be able to exist alongside the better adapted species.

Question 24

What happens to the populations of the two species competing in interspecific competition?

Answer 24

One population will grow and the other will shrink.

Question 25

What is intraspecific competition?

Answer 25

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

Question 26

Explain how intraspecific competition affects population size

Answer 26

1) 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.
2) Eventually, resources such as food and space become limiting - there isn’t enough for all the organisms. The population then begins to decline.
3) 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 27

Organisms in intraspecific competition occupy the same _____ so they compete for _____.

Answer 27

Niche.

Almost everything.

Question 28

What is the competitive exclusion principle?

Answer 28

Where populations of 2 species initially occupy the same niche, one will normally have the competitive advantage.

Question 29

What is it called where populations of 2 species initially occupy the same niche and one will normally have the competitive advantage?

Answer 29

The competitive exclusion principle.

Question 30

What is predation?

Answer 30

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

Question 31

How does predation cause variation in population sizes?

Answer 31

1) Predators eat prey, thereby reducing the population of prey.
2) With fewer prey available the predators are in greater competition with each other.
3) The predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce.
4) With fewer predators left, fewer prey are eaten and so more survive and are able to reproduce.
5) The prey population therefore increases.
6) With more prey now available as food, the predator population in turn increases.

Question 32

The population sizes of predators and prey are _____.

Answer 32

Interlinked - as the population of one changes, it causes the other population to change.

Question 33

What does it mean that the population sizes of predators and prey are interlinked?

Answer 33

As the population of one changes, it causes the other population to change.

Question 34

Why are the predator-prey relationships usually more complicated than just as the population of one changes, it causes the other population to change?

Answer 34

Because there are other factors involved, like availability of food for the prey.

Question 35

Why are predator-prey relationships complicated?

Answer 35

Because there are lots of other extra factors involved, like availability of food for the prey.