7.4 Population in ecosystems Flashcards
What is a population?
A group of organisms of the same species, living in a habitat.
What is a habitat?
The place where an organism lives.
What is a community?
All the populations of different species in a habitat.
What is an ecosystem?
A community, and its biotic and abiotic factors.
What is a niche?
An organism’s role within an ecosystem.
What is the carrying capacity?
The maximum population size an ecosystem can support.
What are abiotic factors?
Non-living components in an ecosystem.
What are biotic factors?
Living components of an ecosystem.
What are the factors affecting population size?
Biotic + abiotic.
Examples of abiotic factors?
Temperature, oxygen + CO2 concentration, light intensity, pH and soil conditions.
Plants and animals are _______ to the abiotic factors within their ecosystem.
Adapted.
This develops through natural selection over many generations.
The less harsh the abiotic factors…
The larger the range of species, + the larger the population sizes.
What are the 2 types of competition?
Interspecific and intraspecific.
What is interspecific competition?
When members of different species are in competition for the same resource that is in limited supply.
What makes an individual more likely to succeed at competition?
If they are better adapted.
What is intraspecific competition?
When members of the same species are in competition for resources and a mate.
Regardless of the species, what trends does the predator-prey graph always follow?
- The size of the predator + prey populations both fluctuate.
- There will always be more prey than predators.
- The size of the populations will always change in the prey + the predators.
Why is sampling a good method?
It is more time efficient and can be more accurate.
How is it ensured that sampling accurately represents the population?
- Random sampling in uniform areas to eliminate bias.
- Line transect to examine a change over distance.
- Large number of samples (30+).
What method do you use if you’re measuring a slow-moving or non-motile organism?
Sampling using a quadrat.
What method do you use if you’re measuring a motile organism?
Mark, recapture, release.
When sampling using a quadrat, what do you do if there’s a uniform distribution?
Random sampling.
When sampling using a quadrat, what do you do if there’s an uneven distribution?
Line transect.
Random sampling method steps?
- Lie 2 tape measures at a right angle to create a gridded area.
- Use a random number generator to generate two coordinates.
- Place the quadrat and collect the data.
- Repeat at least 30 times + calculate a mean.
Line transect method steps?
- Place the tape measure at a right angle to the shoreline.
- Place the quadrat every 5m/every position.
- Collect the data.
- Repeat by placing another 30 transects along the beach at right angles to the shoreline.
Methods to measure the abundance of a species?
- Local frequency.
- Density.
- Percentage cover.
What is mark, recapture, release used for?
Estimating the population size of motile animals.
Mark, recapture, release step 1?
An initial sample of the population is captured.
Mark, recapture, release step 2?
These individuals are then marked + then released back into the wild + the number caught is recorded.
Mark, recapture, release step 3?
These marked individuals are released, + are left for a period of time to allow them to randomly disperse throughout the habitat.
Mark, recapture, release step 4?
Then a second sample is captured.
Mark, recapture, release step 5?
The total number captured in the second sample, + the number recaptured with the marking is recorded.
Mark, recapture, release step 6?
The size of the population is then estimated on the principle that the proportion marked in the second sample equals the proportion of marked individuals in the population as a whole.
The more times mark, recapture, release is repeated…
The more reliable the results.
Mark, recapture, release calculation?
Estimated total population = (number of organisms initially caught x number of organisms in the second sample)/number of marked organisms recaptured.
Ethics of mark, recapture, release?
How you mark and how you capture the animals must cause no permanent harm.
Considerations of the mark?
- Non-toxic.
- Must not increase chances of predation.
- Must not reduce chances of reproduction.
Assumptions of mark, recapture, release?
- The population size is constant (no births/deaths and no migration).
- The animals always distribute evenly (they may all huddle near food in reality).
What is succession?
The change in an ecological community over time.
How does primary succession start?
With a pioneer species colonising bare rock or sand.
What are pioneer species adapted to do?
Survive in harsh biotic conditions.
How do pioneer species change harsh abiotic factors?
Their death and decomposition change the abiotic factors to become less harsh, and form a thin layer of soil ‘humus.’
What can survive on the humus?
Mosses and smaller plants.
How do mosses and smaller plants affect the soil?
- They further increase the depth + nutrient content of the soil.
- The pattern continues + the abiotic factors continue to be less harsh, larger plants can survive + change the environment further.
How can each new species change the environment?
- Each new species may change the environment in such a way that it becomes less suitable for the previous species.
- Therefore, each species is outcompeted by a new species colonising.
What can changes that organisms produce in their abiotic environment lead to?
A less hostile environment + increased biodiversity.
What is the final stage in succession?
Climax community - dominated by trees.
What happens in secondary succession?
- The succession is disrupted + the plants are destroyed.
- Succession starts again, but the soil is already created, so it does not start from the bare rock seral stage.
Succession summary?
- The species richness + number of organisms increases (biodiversity increases).
- As succession occurs, larger plant species + animals start to colonise the area.
- Therefore, food webs become more complex.
Describe how you would determine the mean percentage cover for beach grass on a sand dune.
- Generate coordinates using a random number generator.
- Large number of quadrats.
- Divide total percentage by number of quadrats.
Give two features of a climax community.
- Same species present over a long time.
- Abiotic factors constant over time.
Why did the scientist use percentage cover rather than frequency to record the abundance of algae present?
Individual organisms are too small to identify.
Why were scientists concerned about using concrete blocks for the growth of algae?
Concrete is flat.
Use the results of this investigation to describe and explain the process of succession.
- Pioneer species increases then decreases.
- A species changing the conditions, and making them less hostile.
- New species is a better competitor, + pioneer species is outcompeted.
- G. coulteri / Gelidium increases and other / named species decreases.
Give two conditions for results from mark-release-recapture investigations to be valid.
- Marking is not removed/does not affect survival.
- Limited migration.
- Sufficient time for marked individuals to mix within the population.
Why do species change during succession?
- Species changes the environment.
- Other species are better competitors.
How do pine trees result in low species diversity of plants in the forest?
Only plants which can photosynthesise with less light remain.
Describe how you would investigate the distribution of marram grass from one side of the dune to the other.
- Place a transect from one side of the dune to the other.
- Place quadrats at regular intervals along the line.
- Count plants/percentage cover in quadrats.
Explain the advantage to a plant that colonises after 50 years of having a high rate of photosynthesis at low light intensities.
Plant will grow/survive in the shade, when overshadowed by taller plants/when receiving less light.
Name the type of competition between livestock and ibex.
Interspecific competition.
Describe how you could estimate the size of a population of sundews in a small marsh.
- Use a grid.
- Use a random number generator to generate random coordinates.
- Count number/frequency in a quadrat.
- Large sample and calculate mean/average number.
- Mean number of plants per quadrat x number of quadrats in marsh.
Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients.
- Digestion of proteins provides amino acids.
- Digestion of DNA provides phosphate containing product (nucleotides).
Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation.
- Capture / collect / sample, mark and release.
- Leave time for mosquitoes to disperse before second sampling.
- Population = number in first sample × number in second sample divided by number of marked in second sample.
Apart from availability of water, describe and explain how two abiotic factors may have caused differences in the species of algae growing at sites A and B.
- Less humid = more evaporation at site A.
- Temperature (link to respiration/photosynthesis).
What is a species?
Organisms that can breed and produce fertile offspring.
What is meant by uniformly distributed?
Same number of organisms in each region.
How do the assumptions made in proportional sampling differ from those made in mark-release-recapture?
In mark-release-recapture: - No assumption that organisms are uniformly distributed.
- Size of total area / size of sampled region not required.
Give one assumption about the animals caught that is made in both methods.
Animals are all part of the same population.
suggest why the mark reason recapture method can produce unreaable results In a very large lake
less chance of recapturing fish
unlikely fish distribute evenly
