short answer please Ecosystem ecologists may identify \"top down effects\" or \"
ID: 94866 • Letter: S
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short answer please
Ecosystem ecologists may identify "top down effects" or "bottom up effects" as being responsible for changes in community structure and/or function. Considering the coral reef ecosystem, give an example of a bottom up effect and an example of a top down effect and explain in each case how the ecosystem is affected. Under some conditions, sea urchins can be "potentials" for corals populations, and under other conditions (different species +/or different population sizes), sea urchins can be "resistances" to coral populations. Explain.Explanation / Answer
1) In ecosystems with bottom-up control, increased production results in greater productivity at all trophic levels. In top-down control ecosystems, consumers depress the trophic level on which they feed, and this indirectly increases the next lower trophic level.
The food web in coral reef consists of corals ---> herbivorous fish ---> predatory fish ----> sharks/seals
When inorganic nutrients are preseent in abundant quantities and under favorable environmental conditions bottom-up control is seen. There will be an increase in the size of corals which increases the population of herbivorous fish which subsequently increase the population size of carnivorous fishes and sharks. When there is migration of tertiary consumers like sharks into the area, they will feed on predatory fishes which in turn will increase the population size of herbivorous fish. This is called as top-down control.
2) Sea urchins can have both positive and negative effects on coral reef ecosystems. Sea urchins are herbivores feding on corals. In some ecosystems, they are key herbivores and play a critical role in maintaining the balance between coral and algae. In some other situations, when sea urchin populations reach outbreak densities, they lead to bio-erosion of coral reefs.
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