Populations In Ecosystems

Question 1

What is an ecosystem?

Answer 1

All the organisms living in a community plus all the non-living (abiotic) conditions in the area in which they live

Question 2

Define community

Answer 2

A group of interacting populations of a different species living in the same place at the same time

Question 3

Define population

Answer 3

A group of organisms belonging to the same species found in the same area at the same time and potentially able to interbreed

Question 4

Define habitat

Answer 4

The environment in which an organism or population of organisms usually lives

Question 5

Define biotic

Answer 5

the living features of an ecosystem eg the presence of predators or food

Question 6

Define abiotic

Answer 6

The non-living features of an ecosystem eg the temperature and the soil

Question 7

Define niche

Answer 7

The role of a species within its habitat eg what it eats, when and where it feeds

Question 8

How many species can occupy a niche?

Answer 8

A niche can only be occupied by one species however it could look like two species are filling the same niche. Eg two species could be eaten by the same predator but eat a different variety of organisms

Question 9

What does a niche a species occupies include?

Answer 9

1) biotic interactions - living interactions, what the organism eats and what it is eaten by

2) abiotic interactions - non living interactions, the temperature range and organism can live in or the time of day when an organism is active

Question 10

What is competitive exclusion?

Answer 10

If 2 species try to occupy the same niche, they will be in competition with one another. One species will eventually be more successful than the other, until only one species is left

Question 11

What is an adaption and what are they caused by?

Answer 11

An adaptation is a characteristic that members of a species have, that increases their chance of survival and reproduction. These are caused by random and spontaneous mutations. Can be physicological, anatomical or behavioural.

Question 12

Define population size

Answer 12

Total number of organisms of one species in a habitat. This number changes over time because of the effect of various factors.

Question 13

Define carrying capacity

Answer 13

The maximum population size that can remain sustainable in an ecosystem. It varies due to both biotic and abiotic factors

Question 14

How can abiotic factors affect population size?

Answer 14

Abiotic Factors such as:
Temperature
Water availability
Space availability
Light intensity
Chemical composition of surroundings
Can:
1) cause population size to increase when at optimum as it enable organisms to grow and reproduce much quicker eg plants will grow much quicker if there is a higher temp, higher light intensity etc
2) cause population size to decrease as organisms may grow much more slowly when conditions are less favourable eg if mammals are living in colder than optimal temperatures they are having to use a lot of energy to maintain body temp and therefore less energy available for growth and reproduction

Question 15

What are the 3 main ways biotic factors can influence population size?

Answer 15

1) interspecific competition

2) intraspecific competition

3) predation

Question 16

How does interspecific competition influence population size?

Answer 16

Interspecific competition occurs between different species. The species can be competing for the same resources such as food or habitats. Interspecific competition for food can reduce the population size. If both species are competing for the same food resource, there will be less available from both species meaning they will have. Less energy for growth and reproduction and population size will decrease

Question 17

What is the competitive exclusion principle?

Answer 17

When two species are competing from the same resources, one species will have a competitive advantage, the population size of this species will increase whilst the other population will reduce.

This principles states that no two species can occupy the same ecological niche

Question 18

How does intraspecific competition influence population size?

Answer 18

Intraspecific competition is competition occurring between members of the same species. This causes fluctuation in the population size around the carrying capacity. When there are large food resources available the population size increases, more food leads to more energy for growth and reproduction. When there are fewer resources available the individuals in the species are competing with one another for food, less food leads to less energy for growth and reproduction, a cyclical pattern forms.

The carrying capacity is always between the lowest population size and the largest population size.

Question 19

How does predation influence population size?

Answer 19

Predation is where an organism kills d eats another organism. The population sizes of predators and prey are interlinked, as the population of one changes it causes a change in the other.

Eg the population size of buffalo (prey) increases, there is more food available for the lion (predator) therefore the population size of lion will increase. However if the population size of lions increases the population size of the buffalo will start to decrease, causing the population size of the lion to then decrease. The relationship between the predator and prey causes a selection pressure meaning that those members of the species who are better adapted to escape or hide from predators are more likely to be able to survive and reproduce this ensures that each new population is better adapted for survival