7.4 Populations in ecosystems

Question 1

What is ecology?

Answer 1

the study of the inter-relationships between organisms and their environment. The environment includes both non-living factors, such as temperature, and living factors such as competition and predation

Question 2

What are ecosystems?

Answer 2

made up of a community and all the non-living factors of its environment. The 2 major processes are:
- the flow of energy through the system
- the cycling of elements within the system
Within an ecosystem, there are a number of species made up of a group of individuals making up a population

Question 3

What is a population?

Answer 3

group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed

Question 4

What can the size of a population vary as a result of?

Answer 4

• the effect of abiotic factors
• interactions between organisms, for example intraspecific and interspecific competition and predation

Question 5

What is a community?

Answer 5

all the populations of different species living and interacting in a particular place at the same time

Question 6

What is a habitat?

Answer 6

where an organism normally lives and is characterised by physical conditions and other organisms present

Question 7

What is a niche?

Answer 7

how an organism fits into the environment. Refers to where an organism lives and what it does there

Question 8

What is an abiotic factor? give examples

Answer 8

• non-living things that influence populations
• temperature, pH, water, light

Question 9

What is a biotic factor? give examples

Answer 9

• living things that influence populations
• predators, disease, prey, food

Question 10

What is carrying capacity?

Answer 10

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

Question 11

Name 4 abiotic factors that affect population growth

Answer 11

• temperature
• light
• pH
• water/humidity

Question 12

What is intraspecific competition?

Answer 12

competition between organisms of the same species

Question 13

What is interspecific competition?

Answer 13

competition between organisms of different species

Question 14

What resources might organisms compete for?

Answer 14

food, water, shelter, minerals, light, mates

Question 15

Describe the pattern of a typical predator-prey relationship in terms of population change

Answer 15

• prey is eaten by predator, resulting in predator population increasing and prey population decreasing
• fewer prey means increased competition for food, so predator population decreases
• fewer predators means more prey survives and the cycle begins again

Question 16

How are quadrats used for estimating population size?

Answer 16

can be placed on grid coordinates, or at intervals along a belt transect. Results reported as either percentage cover or frequency. For slow-moving or non-motile organisms

Question 17

What is random sampling?

Answer 17

employed when trying to eliminate bias. Two numbered axis can be laid out over the sample area. Generation of random numbers provides coordinates for areas to study

Question 18

What is systematic sampling?

Answer 18

a similar grid is laid over the entire area, but samples are taken at regular intervals

Question 19

What are things to consider when sampling?

Answer 19

• the sizes of the quadrat - size of species, kind of groups or colonies the species live in
• number of samples being taken in the area - the more you take, the more reliable the results
• position of each quadrat - to produce unbiased results

Question 20

How do you calculate the estimated mean density?

Answer 20

total number of individuals counted/number of quadrats x area of quadrat

Question 21

What is the equation for mark-release-recapture?

Answer 21

estimated population size = total number of individuals in 1st sample x number in the second/number of marked individuals recaptured

Question 22

What is species richness?

Answer 22

number of different species in a habitat

Question 23

What is species abundance?

Answer 23

number of individuals per species

Question 24

How is mark-release-recapture used for estimating population size?

Answer 24

• a sample of a species is captured, marked then released back into the same area they were caught
• after a certain period of time another sample of the species is captured, and the number of marked organisms are counted

Question 25

What assumptions does the mark-release-recapture method make?

Answer 25

- no marked individuals distribute evenly - no migration in or out of the population - few births or deaths - method of marking does not affect survival - mark does not come off

Question 26

Why are ecosystems described as being dynamic?

Answer 26

- populations constantly rise and fall - any small change can have a large effect - biotic and abiotic factors may alter the conditions of the ecosystem

Question 27

What is primary succession?

Answer 27

where an area previously devoid of life is colonised by a community of organisms

Question 28

What is the brief process of primary succession?

Answer 28

- Pioneer species can survive harsh conditions and colonise the area - they change abiotic factors of their environment e.g. decomposition adds nutrients to ground - overtime, this allows more complex organisms to survive

Question 29

What is the climax community and how is it reached?

Answer 29

the final stage of succession, where the ecosystem is balanced and stable. It is reached when the soil is rich enough to support large tress or shrubs, and the environment is no longer changing

Question 30

How might species alter the environment that develops during succession?

Answer 30

- a species may improve the environment to make it more suitable for other species. - Alternatively, a species may worsen the environment by making it less suitable for other species

Question 31

What is conservation?

Answer 31

the protection and management of species and habitats, in order to maintain biodiversity. Methods need to be adapted to the ecosystem in question

Question 32

How might succession be managed in order to aid conservation?

Answer 32

sometimes succession needs to be prevented in order to preserve an ecosystem at a certain point, e.g. stopping moorland from progressing into spruce forest. This is called a plagioclimax

Question 33

What is secondary succession?

Answer 33

occurs in an area where life once existed but has been destroyed

Question 34

What is the first stage of primary succession?

Answer 34

* the pioneer community - lichen or moss - lichen hold water, which freezes and cracks the rock, beginning to form a 'soil' of powdered rock and organic matter - asexual reproduction so they can build up a population rapidly - able to withstand desiccation, extremes of temperature and low levels of nutrients - ability to fix nitrogen from the atmosphere as if there is any soil it has little nutrients

Question 35

What is stage 2 of primary succession?

Answer 35

* moss builds up and thickens - the lichen and moss live, reproduce and decay. The rock also erodes, forms a soil layer. is receptive to seeds - mosses and ferns cast shade to stop further growth of lichens - their roots are longer and so further break up the rock - large plants grow once soil is established - they succeed the moss and lichen

Question 36

What is the 3rd stage of primary succession?

Answer 36

- the continual decay of dead organic matter allows nutrients to build up, soil to become trapped and roots to establish - larger plants grow fast and outcompete the pioneer species

Question 37

What is stage 4 of primary succession?

Answer 37

- once nutrients have built up and soil is stable, tree seedlings and hedges can root. Eventually shade and out compete the shrubs - each organism modifies the environment, so creating ideal conditions for growth for the next organism - different habitats have different climax communities - a climax community is in its equilibrium. The dominant species is determined by environmental factors

Question 38

What is the process of secondary succession?

Answer 38

- much the same as primary except it occurs when the final stage is removed abruptly - may be due to a natural disaster or by human influence such as deforestation and strip mining - happens rapidly as soil structure, spores and seeds are already present

Question 39

Why do people not always agree with conservation methods?

Answer 39

there is often a conflict between human needs e.g. income of food/resources and conservation

Question 40

How can reintroduction of hedgerows help conserve species?

Answer 40

increases biodiversity by increasing sources of food and habitat for animals. Allows animals to migrate

Question 41

Why may you not want succession to take place?

Answer 41

sometimes succession needs to be prevented in order to preserve an ecosystem at a certain point e.g. stopping moorland from progressing into a forest

Question 42

How can fire prevent succession?

Answer 42

it allows secondary succession to occur so that pioneer plant species are being conserved as they will grow back first, tree species won't have time to grow back before the next burning

Question 43

How can mowing of grazing of animals be used to prevent succession?

Answer 43

grazing or regular mowing prevents large shrubs or trees growing and keeps vegetation low