Populations in ecosystems (A-level only)

Question 1

Habitat

Answer 1

The habitat is where an organism lives.

Different individuals within a species tend to occupy the same type of habitat.

Individuals in different species are more likely to occupy a different habitat.

Many species could occupy the same habitat (e.g. thousands of species live in a coral reef habitat).

Question 2

Ecosystem components

Answer 2

When many individuals of the same species occupy the same habitat, they are a population.

Multiple populations of different species in the same habitat form a community.

A community and the abiotic conditions (e.g. climate) in the environment together form an ecosystem.

Ecosystems can be huge (e.g. the Amazon Rainforest).

Ecosystems can be relatively small (e.g. rock pools).

Question 3

Conditions

Answer 3

Abiotic conditions are non-living environmental factors.
E.g. Climate, shade cover.

Biotic conditions are living environmental factors.
E.g. Predation, competition.

Question 4

Niche

Answer 4

Every species has a specific role in an ecosystem.

E.g. Decomposing bacteria have the role of breaking down waste material and dead organisms.

The role is called a niche.

Question 5

Adaptation

Answer 5

If an individual is well-suited to surviving in its ecosystem it is said to be adaptive.

The characteristics of an individual that help it survive and reproduce are adaptations.

Question 6

Occupying a niche

Answer 6

Species occupy a specific niche in their habitat.

Every species has evolved to occupy one niche.

A species cannot occupy more than one niche and two different species cannot overlap in this niche.

Question 7

Adaptation to a niche

Answer 7

Every species has evolved for a specific role (their niche).

This means that natural selection has selected for traits that help the species survive and reproduce in their niche.

The traits that increase the ability to survive and reproduce are called adaptations.

Question 8

Types of adaptations

Answer 8

Adaptations can be:

Behavioural (e.g. the superb bird of paradise displays its wings and ‘dances’ to attract a mate).

Anatomical (e.g. pelicans have a pouch-like beak which allows them to scoop fish from the water).

Physiological (e.g. bears have special fat cells that release heat during hibernation).

Question 9

Examples of Abiotic conditions

Answer 9

Climate
Sunlight
Water availability

Question 10

Climate

Answer 10

Species must be well-adapted to their climate.

E.g. Walruses live in habitats with a very cold climate.

Walruses have evolved thick layers of fat as an adaptation to the climate.

Question 11

Sunlight

Answer 11

Species must be well-adapted to the light levels.

E.g. Plants that live on the rainforest floor are shaded by many other plants.

Plants have evolved special pigments in their leaves that are better at absorbing light in the shade.

This is an adaptation.

Question 12

Water availability

Answer 12

Species must be well-adapted to water availability.

E.g. Plants that live in very dry habitats only open their stomata at night to reduce water loss.

This is an adaptation.

Question 13

Examples of Biotic conditions

Answer 13

Predation
Interspecific competition
Intraspecific competition

Question 14

Predation

Answer 14

Species must be well-adapted to the risk of predation.

E.g. Peppered moths have evolved bodies that are the same colour as the trees they inhabit.

This allows the moths to avoid detection by predators.

This is an adaptation.

Question 15

Interspecific competition

Answer 15

Species must be well-adapted to competition with other species.

E.g. Different species of finches have evolved different sized beaks so that they feed on different sized seeds and are not competing with each other.

This is an adaptation.

Question 16

Intraspecific competition

Answer 16

Species must be well-adapted to competition with individuals of the same species.

E.g. Nightingales use birdsong to attract female mates.

The quality of the song allows females to identify the best mates.

This is an adaptation.

Question 17

Carrying capacity

Answer 17

The number of individuals in a population cannot increase continuously because resources will eventually run out.

The maximum size a population can maintain is called the carrying capacity.

Question 18

Exponential growth

Answer 18

Exponential growth of a population is the continuous growth in population size.

Exponential growth is only possible where there is an infinite supply of resources.

In real ecosystems, this is not the case.

Question 19

Limited resources

Answer 19

There is a limited supply of resources in ecosystems.

Individuals in an ecosystem are competing to use the resources.

Species that have adaptations that allow them to gain resources better than other species are more likely to reproduce.

Reproduction causes the size of a population to increase.

Question 20

Influences of abiotic factors on carrying capacity:

Answer 20

Promoting growth
Slowing growth

Question 21

Promoting growth

Answer 21

Abiotic conditions can promote the growth of a population.

This is when the abiotic conditions are favourable for the species so more of the population reproduce.

E.g. during the summer there is more light exposure in a day.

There is more light for photosynthesis so plants have more energy for reproducing.

Question 22

Slowing growth

Answer 22

Abiotic conditions can slow or stop the growth of a population.

This is when the abiotic conditions are unfavourable for the species so less of the population reproduce.

E.g. cold climate means that mammals use more energy in maintaining their body temperature and less energy is available for reproducing.

Question 23

Influences of biotic factors on carrying capacity:

Answer 23

Interspecific competition
Out-competing
Intraspecific competition
Predation

Question 24

Interspecific competiton

Answer 24

Interspecific competition is competition between individuals in different species.

Interspecific competition can reduce the amount of resources available.

This slows the rate of population growth.

E.g. Lions and cheetahs compete for the same prey.

When lions and cheetahs inhabit the same area, both species have a smaller population size than when they inhabit different areas.

Question 25

Out-competing

Answer 25

When two species compete for the same resource, one species can out-compete the other.

A species is out-competed when one species is more well-adapted to the environment than the other.

This species is better at gaining resources and reproducing.

Out-competing allows one species to increase in population size and causes the other species to decrease in population size.

Question 26

Intraspecific competition

Answer 26

Intraspecific competition is competition between individuals of the same species.

Intraspecific competition causes fluctuations in population size.

E.g. When a population of lions increases, competition for food, space and mates increases.

Fewer individuals survive and reproduce so the population size decreases.

If the population size decreases, there is more food available so population size increases.

Question 27

Predation

Answer 27

Predation is when one species (prey) is killed and eaten by another species (predator).

Predators and prey interact to influence each other’s population size.

If the prey population size is small, resources are limited for predators and predator population size decreases.

When the predator population size falls, the risk of death is lower for prey so the prey population size increases.

More prey are available, so predator population size increases.

Question 28

Quadrat

Answer 28

Quadrats are normally 1m2 square frame divided into 100 squares.

Each square represents 1% of the total area of the quadrat.

If an individual covers more than half of a square, it is counted as representing 1% of the quadrat.

Quadrats are used to count the population size within a large area.

Question 29

Sampling

Answer 29

If you wanted to investigate the size of a population, it would take hours to count every individual.

Taking samples (a small section of the total area) allows the population size to be estimated.

It is important that the samples accurately represent the total population size.

Question 30

Random sampling

Answer 30

Random sampling can be applied by dividing the area of interest into a grid and labelling the grid with coordinates.

A random number generator provides a set of random coordinates.

The quadrats can be placed using the coordinates.

Question 31

Transects

Answer 31

Quadrats could also be placed at regular intervals along a transect.

A transect is a line across a habitat, usually placed using a tape measure.

Transects are used when there is a change, or gradient, in abiotic conditions across the habitat.

Transects are used when looking for changes in the abundance or distribution of a species across the environment (e.g. how abundance changes from open field to forest).

Question 32

Line transect

Answer 32

A line transect records the species that makes contact with the tape measure at regular intervals along the transect.

Question 33

Belt transect

Answer 33

A belt transect uses quadrats.

Quadrats are placed at regular intervals along the transect.

An abundance of different species in the quadrat can be measured by:
Percentage cover – estimate how much of the quadrat is covered by a particular species
Frequency – count how many individuals of a particular species are present in the quadrat.

Question 34

Mark-release-recapture

Answer 34

Mark-release-recapture is a technique used to investigate population size of mobile organisms (e.g. a tree shrew).

The steps involved are:

1) Capture
The first step in mark-release-recapture involves the capturing of animals.
Small mammals can be captured using a Sherman trap (a box with a trap door) and ground insects can be captured using a pitfall trap.

2) Mark
Captured animals are marked in some way (e.g. using tags, bands, paint, or other body markings).
Marking the animals allows you to identify which animals have already been counted and which animals have not.

3) Release
The marked animals are released back into the environment and the traps are set up again.
Releasing the animals back into the environment allows them to mix with the rest of the population.

4) Recapture
A new sample is collected from the traps. The unmarked individuals that are captured are counted, marked and released.

5) Calculate population size
Total population size can be calculated using the following equation:
population size = number caught in first sample x number caught in second sample / number marked in secnd sample

Question 35

Succession

Answer 35

The changes in an ecosystem over time is called succession.

Question 36

Dynamic ecosystems

Answer 36

Ecosystems are affected by changes in the structure and composition of the communities within them.

Ecosystems can also be affected by environmental disturbances (e.g. volcanoes, earthquakes, storms).

Together these factors make ecosystems very dynamic.

Over time, an ecosystem can change dramatically.

Question 37

Primary succession

Answer 37

Primary succession takes place on newly exposed or newly formed land.

The land is colonised by living things.

Question 38

Secondary succession

Answer 38

Secondary succession takes place where part of an ecosystem is disturbed and remnants of the previous community remain.

Question 39

Primary succession takes place on newly exposed or newly formed land. The land is initially colonised by pioneer species. The stages involved are:

Answer 39

Pioneer species
Soil formation
Colonisation by new species
Altering abiotic conditions

Question 40

Pioneer species

Answer 40

Pioneer species are the first species to colonise the newly exposed land.

Pioneer species are specialised to live in the harsh conditions of the exposed land.

E.g. There is no soil so water and nutrient levels are poor.

E.g. Marram grass is a pioneer species that can survive in the sand because it has very long roots.

Question 41

Soil formation

Answer 41

Pioneer species help to break down substances on the exposed land to form soil.

When pioneer species die, they are also decomposed which contributes to soil formation.

Question 42

Colonisation by new species

Answer 42

The formation of the soil makes the environment less hostile.

New species colonise the less hostile land.

When the new species die, the organic matter within the species is released into the soil by decomposition.

Question 43

Altering abiotic conditions

Answer 43

When species die, the composition of the soil is changed. Soil is an abiotic (non-living) factor.

When new species colonise the area, they are also altering the abiotic conditions.

E.g. If taller species or species with larger leaves grow, the light exposure in the environment is changed.

New species may also alter the environment so that the pioneer species can no longer survive.

E.g. Sand sedge colonises coastal ecosystems and makes the environment less suitable for marram grass.

Question 44

Secondary succession takes place when parts of the ecosystem are disturbed. The stages involved are:

Answer 44

Pioneer species
Colonisation by new species
Increased complexity
Climax community

Question 45

Pioneer species

Answer 45

Pioneer species colonise the damaged land.

The pioneer species tend to be larger in secondary succession than primary succession.

The environment in secondary succession is more nutrient-rich than in primary succession because there is already a soil layer.

Question 46

Colonisation of new species

Answer 46

As pioneer species die, the soil becomes more nutrient-rich and more stable.

New species can colonise the land.

The new species out-compete the older species and become dominant.

This competition causes a shift in the species present in the ecosystem.

Question 47

Increased complexity

Answer 47

As more species colonise the land, the complexity of the ecosystem increases.

If there are more species in the ecosystem, the ecosystem is more biodiverse.

Question 48

Climax community

Answer 48

The ecosystem eventually reaches an equilibrium point.

The equilibrium point is where species composition is no longer changing and resembles the community that existed before it was disturbed.

The equilibrium state is called the climax community.

Question 49

Managing grasslands

Answer 49

Many rare and protected species can be found in grasslands.

Without management, grassland would quickly turn into shrubs and then woodland by succession.

Managing grassland prevents succession from taking place.

Question 50

Management techniques

Answer 50

Succession can be managed in two ways:
Grazing - animals graze to prevent growth of vegetation.
Burning - burning kills vegetation and allows secondary succession to take place.

Question 51

Managing heather moors

Answer 51

Heather moors provide an ideal habitat for game birds like red grouse.

Red grouse feed on young, succulent heather shoots and makes nesting sites in the longer heather.

If left to succession, the heather would be unsuitable as either food or nesting sites for the red grouse.

Heather moorland is burnt approximately every 12 years to manage succession.

Question 52

Need for conservation

Answer 52

Humans pose a huge threat to biodiversity on the planet.

The two main threats from humans are:
Population growth.
Resource exploitation.

Conservation helps oppose the effects from humans.

Conservation protects ecosystems and the species within them to help prevent decreasing biodiversity.

Question 53

Methods of conservation

Answer 53

There are a number of ways that species and ecosystems can be conserved:
Protected areas (e.g. national parks) - protect habitats.
Seedbanks - store seeds to avoid extinction.
Protected species - avoid extinction.
Fishing quotas - prevent overfishing.

Question 54

Conflict- needs vs conservation

Answer 54

Conflict exists between human needs and conservation.

Conservation can be expensive.

Human population growth means there is high demand for food, space and other resources.

Conservation can sometimes make meeting these demands difficult.

Question 55

Evaluation evidence of censervation

Answer 55

When evaluating evidence about conservation, you should look at the methods used in a study.

Has the study used a control?
Is the sample size big enough?
Was only one factor changed?