The Shurin (2001) study considered the roles of predation and dispersal on the s

Question

The Shurin (2001) study considered the roles of predation and dispersal on the species richness of zooplankton communities. Shurin also measured the abundance of phytoplankton, which is eaten by the zooplankton. The figure below shows the amount of chlorophyll a (a measure of phytoplankton abundance) in the four predation treatments, with and without dispersal, imposed in the experimental ponds: (1) no predators, (2) fish predators only (juvenile bluegill sunfish, Lepomis macrochirus), (3) insect predators only (the backswimmer bug Notonecta undulata), and (4) both fish and insect predators.

Question 3. Was there a difference in the effect of predation and zooplankton dispersal treatments on phytoplankton abundance? If so, what does this suggest about the role of different predators on phytoplankton abundance?

Question 4. Suppose an additional treatment, that of doubling the dispersal of zooplankton, was added to this experiment. What would you predict this treatment would do to phytoplankton abundance in the fish-only versus insect-only predation treatments? Consider the entire range of zooplankton dispersal, from none to intermediate to heavy. What type of relationship between dispersal and phytoplankton abundance would be produced?

No dispersal Dispersal Control FishInsects Fish and insects (no predators) Predation treatment Note: for the control treatment, there was no statistical difference in phytoplankton abundance in the ponds with and without zooplankton dispersal

Explanation / Answer

Q.3. Answer:Communities of organisms who exist together are produced by both dispersal amongst habitat patches in a region plus local interactions within patches. The supply of colonists from the local pool has the capability to modify the result of local relations by providing species that fill up dissimilar ecological roles. While examining the consequence of invasion by the fish and insect predators on investigational plankton communities which were either linked to or cut off from the local pool of zooplankton species. The effects of predators on zooplankton composition and variety depended on dispersal by members of the local zooplankton species pool. Fish and notonectids abridged the abundance of large zooplankton and thus helped incursion by new species from the adjacent region. As the predators decreased zooplankton species richness in the nonexistence of dispersal, whereas fish had constructive effects and notonectids had no effects with speedy dispersal. Fish helped assault by more species than they expelled, whereas similar numbers of species assaulted with notonectids as were wiped out. The effects of predators on planktonic trophic arrangement were without any doubt independent of the level of dispersal. As both predators decreased zooplankton mean body size, while only fish increased phytoplankton concentration or density. Incursion by members of the local species pool to some extent enhanced zooplankton mean body size while reducing phytoplankton biomass; nevertheless, the effects were little and autonomous of the predator treatment. Predator which facilitated incursion of new species changed the effects of predators on zooplankton species composition and variety, although not on plankton trophic structure. The outcome put forward that spatial heterogeneity in predator abundance promoted local coexistence amongst zooplankton. Correlation to a diverse local species pool via dispersal may well therefore be significant for determination of the impact of local interactions as ofpredation on communities.

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