Population in ecosystems

Question 1

Define the terms population, community and ecosystem

Answer 1

• Population: a group of organisms of the same species, living in the same place (habitat) at the same time
• Community: all the populations of different species living in
  the same place (habitat) at the same time
• Ecosystem: a community, plus all the non-living (abiotic) conditions of their environment. Ecosystems are dynamic systems and can range in size from the very small to the very large.

Question 2

niche,

Answer 2

• Niche: the role of a species within its habitat, e.g. what it eats, where and when it feeds. Each species has its own unique niche; if two species try to occupy the same niche, one will outcompete the other

Question 3

• Abiotic conditions:

Answer 3

the non-living features of the ecosystem

• e.g. temperature, pH

Question 4

Biotic conditions:

Answer 4

the living features of the ecosystem

• e.g. predation, food supply, disease

Question 5

What determines the niche occupied by a species within a habitat?

Answer 5

• Within a habitat, each species occupies a different niche, governed by its adaptations
• to the specific abiotic and biotic conditions within that
  habitat.

Question 6

Define the term carrying capacity

Answer 6

maximum stable population size an ecosystem can support

Question 7

Explain how population size can vary due to interactions
between living organisms

Answer 7

Population size can vary as a result of interactions between organisms …
- Interspecific competition = competition between species
- Reduces resources available to both 🡪 limits both populations
- If one species is better adapted, it will out-compete the others
- Intraspecific competition = competition within a species
- Smaller population = less competition 🡪 better for growth and reproduction
🡪 larger population = more competition 🡪 less growth and reproduction 🡪
smaller population…
- Predation
- Population sizes of predators and prey are interlinked
Increased predator population size 🡪 more prey eaten 🡪 prey population
falls 🡪 less food for predators 🡪 predator population size falls 🡪 prey
population rises 🡪 predator population rises again…

Question 8

Describe how you would estimate the size of a plant
population in a given area

Answer 8

Randomly placed quadrats
- Use a grid / split area into squares
Obtain random coordinates using a random number generator / calculator
- place quadrat at coordinates
Deciding the number of quadrats to use to collect representative data:
- Calculate running mean
- When enough quadrats, this shows little change in mean
- Count frequency of the species in quadrat
- Calculate mean per quadrat
- Calculate population size by multiplying the mean by the number of quadrats
that would cover the entire area of the habitat

Question 9

Describe how you would measure the change in
distribution of a plant species across a habitat

Answer 9

• Quadrats along a belt transect
• Used to look at changes in distribution
• Lay tape measure from one place to another
• Place quadrats at regular intervals along the line
• Count frequency / percentage cover in quadrats

Question 10

Describe how you could estimate the population size of motile organisms.

Answer 10

Capture sample of species, mark (harmlessly) and release
2. Leave enough time for organisms to randomly distribute
before collecting second sample, then calculate:
(sample1xsample)/marked in sample 2

Question 11

What assumptions are made when using the mark-release-recapture method?

Answer 11

1. Sufficient time for marked individuals to mix within the
   population
2. Marking not removed and doesn’t affect chances of
   survival e.g. more visible to predators
3. Noimmigration/emigration
4. No births/deaths/breeding

Question 12

succession.

Answer 12

process by which an ecosystem changes
over time

Question 13

Describe the process of succession.

Answer 13

1. Colonisation by pioneer species (pioneer species = first species to colonise)
2. Pioneer species (or generally just certain species at each stage in
   succession) change the abiotic conditions and make the environment less hostile e.g. die and decompose, forming soil which retains water
3. Environment becomes more suitable for other species with
   different adaptations, and may be less suitable for the previous species – better adapted species outcompetes previous species
4. As succession goes on, biodiversity increases
5. Climax community: final, complex, stable community

Question 14

Explain how succession can be managed for conservation purposes

Answer 14

• Human activities can prevent succession and stop a climax community forming: plagioclimax
• Conservation sometimes involves preventing succession in order to preserve an ecosystem in its current stage of succession