Unit 7

Question 1

Community

Answer 1

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

Question 2

Ecosystem

Answer 2

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

Question 3

Niche

Answer 3

-The specific role of a species within its habitat.
-Governed by its adaptation to both abiotic and biotic conditions.

Question 4

Advantage of species occupying different niches

Answer 4

-Less competition for food/ resources.
-If two species tried to occupy the same niche, one would outcompete the other.

Question 5

Carrying capacity

Answer 5

Maximum (stable) population size of a species that an ecosystem can support.

Question 6

Factors that influence carrying capacity

Answer 6

-Abiotic factors
-Interspecific competition (between different species)
-Intraspecific competition (between same species)
-Predation

Question 7

How abiotic factors affect pop size/ carrying capacity?

Answer 7

-If conditions are favourable, organisms are more likely to survive and reproduce.
-Increases carrying capacity.

Question 8

How interspecific competition may affect pop size/ carrying capacity?

Answer 8

-Reduced resources available to both species, limiting their chances of survival and reproduction.
-Reduces population size of both species.
-If one species is better adapted, it will outcompete the other.
-So pop size of less adapted reduces, leading to extinction.

Question 9

How intraspecific competition may affect pop size/ carrying capacity?

Answer 9

-As pop size increases, resources availability per organism decreases, so competition increases.
-Chances of survival and reproduction decreases, pop size decreases.
-As pop size decreases, resource availability per organism increases, so competition decreases.
-Chances of survival and reproduction increases, pop size increases.

Question 10

Explain pop change of predator and prey

Answer 10

-Prey increase so predators have more food, more predators survive and reproduce.
-Predator increase so more prey likely to be killed and eaten, less prey survive and reproduce.
-Prey decreases so predators have less food, less predators survive and reporduce.
-Predator decreases so less prey killed and eaten, so more prey survive and reproduce.
-Cycle repeats.

Question 11

Pop of slow-moving/ non-motile organisms

Answer 11

-Divide area into grid/squares.
-Generate a pair of co ordinates using a random number generator.
-Place quadrat here and count frequency of species.
-Repeat for a large number of times and calculate a mean per quadrat.
-Pop size= (total area of habitat/ quadrat area) x mean per quadrat.

Question 12

Mark-release-recapture for motile organisms

Answer 12

-Capture sample of species, mark and release.
-Ensure marking isn’t harmful/ doesn’t affect survival.
-Allow time for organisms to randomly distribute before collecting second sample.
Pop= (Number in S1 x Number in S2) / Number marked in S2

Question 13

Assumptions of mark-release-recapture

Answer 13

-Sufficient time for marked individuals to distribute evenly in pop.
-Marking not removed and doesn’t affect chances of survival/ predation.
-Limited immigration/emigration.
-No/few births/deaths/breeding/changes in pop size.

Question 14

Reliability of mark-release-recapture

Answer 14

-Unlikely that organisms distribute evenly.
-Less chance of recapturing organisms.

Question 15

Succession

Answer 15

Change in community over time due to change in abiotic factors.

Question 16

Primary succession

Answer 16

-Colonisation by pioneer species (first to colonise).
-Pioneer species change abiotic conditions (die and decompose to form soil).
-So environment becomes less hostile for other species with different adaptations and less suitable for previous species.
-Better adapted species outcompete previous species.
-As succession goes on, biodiversity increases.
-Climax community reached- final stable community.

Question 17

Climax community- features

Answer 17

-Same species present over a long time.
-Abiotic factors remain constant.
-Pop stable

Question 18

Management of succession- conservation of habitats

Answer 18

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

Question 19

Managing conservation- human needs

Answer 19

-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.