Community Ecology & Biogeography

Question 1

19. What is diversity? What are the drivers of diversity? And what is the importance of diversity – at the population, species, and genotype level – for ecosystem function?

Question 2

20. Considering any particular lineage or group of organisms, discuss factors involved in the origin, maintenance and distribution of species-level diversity.

Question 3

21. What mechanisms are postulated to explain coexistence of species, and hence underlie the maintenance of species diversity? Which mechanisms have the strongest theoretical support? Which have the strongest empirical support?

Question 4

22. The theory of island biogeography predicts species richness based upon the distance of the island from the mainland and the size of the island. Describe how these two factors interact with colonization and extinction rates to predict species richness. Under what conditions (i.e. island size and distance from mainland) would species richness peak?

Question 5

23. Briefly describe the unified neutral theory of biodiversity and biogeography in terms of its major postulates, and evidence for these. In particular, discuss the issue of ecological equivalence, both the role it plays in the theory and some of the ways that it has been interpreted and misinterpreted by the wider ecological community.

Question 6

24. What is the current state of understanding with respect to the global latitudinal gradient in diversity?

Question 7

25. In early 1970, Dan Janzen and Joe Connell independently postulated a mechanism that sustains tropical rainforest biodiversity. The Janzen-Connell hypothesis suggests that diversity is maintained by host-specific “enemies” that cause offspring to perform poorly underneath the parent plant. This results in negative density dependence of individual species. Summarize evidence for or against the hypothesis, with reference to specific systems where possible, that need not be restricted to the tropical biome.

Question 8

26. In general, how is predator (or consumer) diversity related to prey (or resource) diversity? What alternative hypotheses might lead to the expectations of positive, negative, complex, or no relationship between diversity at these trophic levels?

Question 9

27. In the literature, there has been continuing discussion of the relative importance of top-down versus bottom-up processes in structuring systems and in determining their resulting complexity and function. Start by discussing the concepts of top-down and bottom-up processes giving examples of these processes, then discuss the role that bottom-up versus top-down processes play in structuring communities. Include in your answer your position on the relative importance of these two types of processes in structuring systems. Also, the vast majority of studies investigating relationships between organismal diversity and community processes involve tens of species. What do you think you might learn if you could do the same community experiments using thousands of species?

Question 10

28. In a given area, the number of species interactions is hypothesized to asymptote more quickly than the diversity of unique species. Explain why this pattern may happen. Would you expect this pattern to hold for both tropical and temperate communities? Why or why not?

Question 11

29. Under what circumstances would you expect change in a plant or animal community aboveground to be reflected in change in the biotic community belowground?

Question 12

30. What is the stress gradient hypothesis? What research approaches have been used to test it against empirical data, and what are strengths and weaknesses of these approaches? What are implications of the stress gradient hypothesis for how species respond to environmental change (e.g., global warming)?

Question 13

31. What is a niche? Describe how the niche concept serves to bridge the fields of ecology and evolutionary biology. How do niches evolve?