7.4 Populations in ecosystems

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 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 abiotic and biotic conditions

Question 4

What is the advantage of species occupying different niches?

Answer 4

• Less competition for food / resources
• If two species occupied the same niche, one would outcompete the other

Question 5

What is carrying capacity?

Answer 5

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

Question 6

What factors influence carrying capacity?

Answer 6

• Abiotic factors (eg. Light intensity)
• Interspecific competition
• Intraspecific competition
• Predation

Question 7

How can the population size of non-motile organisms be estimated?

Answer 7

• Divide area into grid
• Generate random coordinates using a random number generator
• Place a quadrat here and count number/frequency of named spaces
• Repeat a large number of times and calculate mean per quadrat
• Population size = (total area of habitat / area of quadrat) x mean

Question 8

How can the population size of motile organisms be estimated?

Answer 8

• Capture sample, mark and release
• Ensure marking is not harmful
• Allow time for organisms to randomly redistribute before collecting second sample
• Population size = (number in sample 1 x number in sample 2) / number marked in sample 2

Question 9

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

Answer 9

• Sufficient time for marked individuals to distribute evenly
• Marking not visible to predators so doesn’t affect predation
• Marking is non toxic so doesn’t affect chances of survival
• No immigration
• No births / deaths

Question 10

How does primary succession occur?

Answer 10

• Colonisation of pioneer species
• Pioneer species change abiotic conditions
• So environment becomes less hostile for other species with different adaptations
• Better adapted species outcompete previous species
• Biodiversity increases
• Climax community is reached

Question 11

What are some features of climax community?

Answer 11

• Same species present over long period of time
• Abiotic factors constant over time
• Stable population size

Question 12

Why is conservation important?

Answer 12

• Protect habitats / niches / species / biodiversity
• Maintain sustainability of natural resources, meeting current needs without compromising the ability of future generations to meet theirs