A. Environmental variability: A fluctuating environment over time can promote diversity. Temporal fluctuation prevents competitive exclusion by altering competitive hierarchy. Example: plankton and algae species coexist because conditions rarely favor one species long enough to exclude others.
B. Foundation species: have a large effect on community composition because of their size/abundance, example: kelp forest/trees -increases diversity - creates habitat that allows other species to live there.
C. Resource Availability: Adding nutrients typically decreases diversity. Paradox of Enrichment: Increased nutrients leads to higher productivity and biomass, but decreased diversity and increased dominance. example: Rothamsted, England. Adding different types of resources might favor diversity though.
D. Habitat Complexity: example:Niche partitioning. A more complex habitat could potentially house more animals.increases diversity by allowing resource partitioning by habitat type. habitat alteration (loss and fragmentation) decreases diversity. More diverse systems are more productive. More diverse systems are better able to withstand environmental variability. And prevent invasion.
E. Competition: generally reduces diversity by removing inferior competitors
F. Keystone predators: increases diversity by allowing inferior competitors to coexist with prey items that are competitively dominant (remove competitive dominant). Prevents competitive exclusion. Example: Otter's eat sea urchins, controlling their population. If the otters didn't eat the urchins, the urchins would eat up the habitat's kelp. Kelp, is a major source of food and shelter for the ecosystem.
G. Disturbance: Community composition can be reset with disturbance. Low diversity with low disturbance AND high disturbance. Highest diversity with mediated disturbance and coexistence. The Intermediate Disturbance Hypothesis (IDH) justifies that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At high levels of disturbance, all species are at risk of going extinct. At intermediate levels of disturbance, diversity is maximized because species that thrive at both early and late successional stages can coexist. Disturbances act to disrupt stable ecosystems and clear species' habitat. As a result, disturbances lead to species movement into the newly cleared area. Once an area is cleared there is a progressive increase in species richness and competition takes place again. Once disturbance is removed, species richness decreases as competitive exclusion increases.
As a result of road building, a formerly contiguous patch of tropical rain forest is now subdivided into smaller patches. The charismatic 8-‐‐striped purple newt lives in the forest, where it has long been among the most abundant species. The newt moves slowly and so cannot cross extensive areas of open ground that lack forest cover (e.g., a road) because it will dry out and die. Conservation groups are interested in understanding the effect of all this road building on the newt, and have enlisted your services as a biological consultant. In your report, you should be able to provide short, well-‐‐justified answers to what you think the effects of road building will be on the ecology and evolution of the newt. For example, how will building roads affect: the risk of newt extinction, recolonization of patches after disturbance, gene flow among newt populations, potential for local adaptation, species richness within a patch, spread of disease, etc. Can you propose an engineering solution that might help avoid these impacts, yet still allow the roads to be built?