3.7.4 Populations in ecosystems (Genetics , population , evolution and ecosystems 3.7)

Question 1

what is a community

Answer 1

all the populations of different species living in the same place at the same time

Question 2

what is an ecosystem

Answer 2

a community and the non loving ( abiotic ) components of its environment

Question 3

what is a niche

Answer 3

the specific role of a species within its habitat
governed by its adaptation to both abiotic and biotic conditions

Question 4

explain the 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

what is carrying capacity

Answer 5

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

Question 6

list the factors that can influence carrying capacity

Answer 6

abiotic :
- light intensity
- temperature
- soil pH
- humidity
interactions between organisms :
- inter specific competition = between organisms of different species
- intraspecifc competition= between organisms of the same species
- predation

Question 7

explain how abiotic factors may affect population size / carrying capacity

Answer 7

• if conditions favourable , organisms more likely to survive and reproduce increasing carrying capacity
• increasing light intensity e.g increases rate of photosynthesis increasing nitrates increases protein production and increasing phosphates increasing phospholipid production in plants
• this increases carrying capacity of variety of plant species
• so increased the number and variety of habitats , niches and food sources for animals
• so increasing carrying capacity of a variety of animal species

Question 8

explain how interspecific competition may affect population size

Answer 8

• reduces ( named resource ) available to both species , limiting their changxes of survival and reproduction
  so reduces population size of both species
• if one species is better adapted , it will outcompete the other
  so population size of less adapted species declines potentially leading to extinction

Question 9

explain how intraspecific competition may affect population size

Answer 9

1) as population size increases , resource availability per organism decreases so competition increases
- chance of survival and reproduction decrease so poplilation decreases
2) as population size decreases , resource availability per organism increases so competition decreases
- so chances of survival and reproduction increase - population size increases

Question 10

explain the changes which occur in populations of predator and prey

Answer 10

1) prey population increases so predators have more food
- so predators survive and reproduce
2) predator population increases so more prey killed and eaten
- so less prey survive and reproduce
3) prey population decreases so predators have less food
- so less predators survive and reproduce
4) predator poplilation decreases so less prey killed and eaten
- so more prey survive and reproduce

Question 11

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

Answer 11

1) divide area into grid or squares ( place 2 tape measurements at right angles )
2) generate a pair of coordinates using a random number generator
3) place a quadrant here and count number / frequencies of species
4) repeat a large number of times and calculate a mean per quadrat
4) population size = total area of habitat / quadrat area x mean per quadrat

Question 12

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

Answer 12

• capture sample of species , mark and release
• ensure marking is not harmful
• allow time for organism to randomly distribute before collecting second sample
• population = ( number in sample 1 x number in sample 2) / number marked in sample 2

Question 13

explain how the mark release recapture equation can be derived

Answer 13

number marked in sample 1 / total population size
= number marked in sample 2 / total number in sample 2

Question 14

what assumptions does the mark release recapture method make

Answer 14

1) sufficient time for marked individuals to mix or distribute evenly within the population
2) marked not removed so they’re recaptured or not toxic so it doesn’t affect chances of survival or marking not visible so doesn’t affect predation
3) no immigration
4) no births deaths or breeding which can change the population size

Question 15

suggest why the mark release recapture method can produce unreliable results in a very large area

Answer 15

• unlikely that organisms will distribute randomly
• less chance of recapturing organisms

Question 16

describe and explain how primary succession occurs

Answer 16

succession = change in a community over time dude to change in abiotic factors or species
1) colonisation by pioneer species
2) pioneer species change abiotic conditions
3) so environment becomes more suitable for other species with different adaptations and less suitable for previous species do better adapted species outcompete previous species
4) as succession goes on , biodiversity increases
5) climax community reaches - final stable community

Question 17

describe features of a climax community

Answer 17

• same species present / stable community over time
• abiotic factors constant over time
• populations stable

Question 18

explain how conservation of habitats involves management of succession

Answer 18

• further succession can be prevented to stop a climax community forming
  • by removing or preventing growth of species associated with later stages e.g by allowing grazing
• this perserves an ecosystem at a certain point
• so early species are not outcompeted by later species and habitats are not lost

Question 19

describe the conflict between humans needing and conservation as well as the importance of managing this

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