Populations In Ecosystemns

Question 1

What is a community?

Answer 1

All the populations of different species living in the same habitat at the same time.

Question 2

What is an ecosystem?

Answer 2

A community and the non-living (abiotic) components of its environment.

Question 3

What is a niche?

Answer 3

● The specific role of a species within its habitat, eg. what it eats,
● Governed by its adaptation to both abiotic (non-living) and biotic (living) conditions

Question 4

Explain the advantage of species occupying different niches

Answer 4

● Less competition for food and resources
● If two species tried to occupy the same niche, one would outcompete the other

Question 5

What is carrying capacity?

Answer 5

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

Question 6

List the factors that influence carrying capacity

Answer 6

• abiotic factors
  -interactions between organisms

Question 7

Give examples of abiotic factors that influence carrying capacity

Answer 7

Eg. light intensity, temperature, soil pH & mineral content, humidity

Question 8

How has interactions between organisms influenced carrying capacity?

Answer 8

a. Interspecific competition - between organisms of different species
b. Intraspecific competition - between organisms of the same species
c. Predation (predators kill and eat other animals, called prey)

Question 9

Explain how abiotic factors may affect population size / carrying capacity

Answer 9

● If conditions favourable, organisms more likely to survive & reproduce → increasing carrying capacity

Question 10

How has light intensity [abiotic factor] affect population size/ carrying capacity of plants

Answer 10

Increasing light intensity increases rate of photosynthesis in plants
○ This increases carrying capacity of a variety of plant species
○ So increases the number and variety of habitats, niches and food sources for animals
○ So increasing carrying capacity of a variety of animal species

Question 11

Explain how interspecific competition may affect population size

Answer 11

● Reduces resource available to both species, limiting their chances of survival & reproduction
○ So reduces population size of both species
● If one species is better adapted, it will outcompete the other
○ So population size of less well adapted species declines, potentially leading to extinction

Question 12

Explain how intraspecific competition may affect population size

Answer 12

1. As population size increases, resource availability per organism decreases, so competition increases
   ● So chances of survival & reproduction decrease → population size decreases
2. As population size decreases, resource availability per organism increases, so competition decreases
   ● So chances of survival & reproduction increase → population size increases

Question 13

Describe how the size of a population of slow-moving or non-motile organisms can be estimated

Answer 13

1. Divide area into a grid eg. place 2 tape measures at right angles
2. Generate a pair of coordinates using a random number generator
3. Place a quadrat in area and count frequency of species
4. Repeat a large number of times (10 or more) and calculate a mean per quadrat
5. Population size = (total area of habitat / quadrat area) x mean per quadrat

Question 14

Describe how the mark-release-recapture method can be used to estimate the size of a population of motile organisms

Answer 14

● Capture sample of species, mark and release
● Ensure marking is not harmful / does not affect survival
● Allow time for organisms to randomly distribute before collecting second sample
● Population = (number in sample 1 x number in sample 2) / number marked in sample 2

Question 15

Explain how the mark release recapture equation can be derived

Answer 15

Number [marked] in sample 1/ total population size= number marked in sample 2/ total number in sample 2

Question 16

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

Answer 16

1. Sufficient time for marked individuals to mix / distribute evenly within the population
2. Marking not removed and doesn’t affect chances of survival / predation
3. no immigration
4. No deaths or breeding or change in population size

Question 17

Suggest why the mark-release-recapture method can produce unreliable results in very large areas

Answer 17

● Unlikely that organisms will distribute randomly evenly
● Less chance of recapturing organisms

Question 18

Describe features of a climax community

Answer 18

● Same species present / stable community over a long time
● Abiotic factors (fairly) constant over time
● Populations (fairly) stable

Question 19

Describe and explain how primary succession occurs

Answer 19

1. Colonisation by pioneer species
2. Pioneer species and other species at each stage in succession change abiotic conditions
   ● Eg. they die and decompose, forming soil which retains water
3. So environment becomes less hostile / more suitable for other species with different adaptations
   AND less suitable for previous species, so better adapted species outcompete previous species
4. As succession goes on, biodiversity increases
5. Climax community reached - final stable community (no further successio

Question 20

Explain how conservation of habitats involves management of succession

Answer 20

● Further succession can be prevented to stop a climax community forming
○ By removing or preventing growth of species associated with later stages eg. by allowing grazing
● This preserves an ecosystem at a certain point / in its current stage of succession
● So early species are not outcompeted by later species and habitats / niches are not lost

Question 21

Describe the conflict between human needs and conservation as well as the importance of managing this

Answer 21

● Human demand for natural resources is leading to habitat destruction / biodiversity loss
● Conservation is needed to protect habitats ,niches , species ,biodiversity
● Management of this conflict maintains the sustainability of natural resources
○ Meeting current needs without compromising the ability of future generations to meet theirs