Species interactions Community. Species interaction grid. Species interaction grid. Species 2. Species 1. Predation. Species 2.

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1 Species interactions Community The number of bumblebees in any district depends in a great measure upon the number of field-mice, which destroy their combs and nests. [Because] the number of mice is largely dependent, as everyone knows, on the number of cats... It is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district! Charles Darwin: The Origin of Species by means of Natural Selection, 6th Edition, 1859 Species interaction grid Species Species Species interaction grid Species redation + Mutualism redation Herbivory Disease Species 2 - redation Herbivory Disease Competition

2 Competition Hawks Mutualism Indirect effect Examples of species interactions: Competition House gecko introduced to acific islands where there is a native gecko (mourning gecko) Examples of species interactions: Mutualism fig trees fig wasps 750 species of figs most with a single species of pollinator

3 Examples of species interactions: redation Wolves increased since reintroduction Keystone species Wolves Species with a disproportionate effect on community structure Coyotes Elk ronghorn Total effect Keystone Dominant Effect of introduction of wolves on plants and elks? Abundance What explains the total diversity in a community? Island biogeography Keystone species can influence diversity Equilibrium theory of island biogeography Theory describing the diversity in a community as a function of extinction and colonization

4 Colonization versus Extinction Mainland Island Colonization, the rate at which new species are gained Extinction, the rate at which island species are lost Equilibrium island species number Number of species = Number of species = S 0 S Number of island species Island biogeography and metapopulations Island biogeography Metapopulations Area effects How does island area affect the number species on the island? How does size affect extinction rate? C E s E l Balance of E and C Balance of E and C Number of species in a patch Number of patches occupied Island species number Area effects How does island area affect the number species on the island? How does size affect extinction rate? Area effects How does island area affect the number species on the island? How does size affect colonization rate? mall < arge mall < arge C E s E l C l E s E l C s Island species number Island species number

5 Bird species in the Lesser Antilles (D. Lack's data) Distance effects How does distance from the mainland affect the number species on the island? How does size affect colonization rate? S far < S near E S n C f C n S n S f isn S S f Bird species in the Lesser Antilles (D. Lack's data) Dan Simberloff (a former FSU Biology Sciences member) Test of the Equilibrium theory of island biogeography (ETIB) Experimental Zoogeography of Islands: The Colonization of Empty Islands, by Daniel S. Simberloff, Edward O. Wilson Ecology 1969

6 Contribution of ETIB for conservation biology E2: closest to mainland Reserve = island Rules for reserve design E1: farthest from mainland Hanski, I. A., and G. M.E., editors Metapopulation biology: ecology, genetics, and evolution. San Diego, CA: Academic ress. 512 p. Island Biogeography and Reserve rules: IUCN, UN,WWF better What explains total diversity in a community? worse Bigger is better Connectivity is good One large is better than several small Keystone species can influence diversity Equilibrium theory of island biogeography Less edge is better An event that moves the community away from its equilibrium state An event that moves the community away from its equilibrium state Equilibrium state? In Southeast = long-leaf pine forest events can be caused by biotic (e.g. disease) and abiotic factors (e.g. fire) In Midwest = tall grass prairie

7 vs. Equilibrium When disturbances are very frequent, then equilibrium may never happen. Some species specialize on disturbance Succession the process by which a community moves towards its equilibrium state following a disturbance Furbish"s lousewort What is the relationship between disturbance and species diversity? Intermediate disturbance hypotheses How does diversity vary with the frequency of!!! disturbance? How does species diversity vary with the time since disturbance? How does species diversity vary with the magnitude of disturbance? Number of species frequent shortly after large - rate infrequent long after small Intermediate disturbance hypotheses Number of species frequent Community is dominated by a few colonizing species Community is a mosaic of patches at different stages of succession - rate Community is dominated by a few superior competitors infrequent