Classical metapopulation model Area effects How does island area - PDF document

Classical metapopulation model Area effects How does island area affect the number species on the island? How does size affect colonization rate? Colonization Rate Extinction S small < S large Equilibrium S s E s metapopulation C l size E l Rate C s P S l 0.5 1 Fraction of patches occupied S l Island species number S s What explains total diversity in a Distance effects community? How does distance from the mainland affect the number species on the island? How does size affect colonization rate? S far < S near E Keystone species can influence diversity C n Equilibrium theory of island biogeography Rate C f S n S n Disturbance P isn S S f S f Disturbance Disturbance An event that moves the community away from its equilibrium state An event that moves the community Equilibrium state? away from its equilibrium state In Southeast = long-leaf pine forest In Midwest = tall grass prairie Disturbance events can be caused by biotic (e.g. disease) and abiotic factors (e.g. fire)

Succession Disturbance vs. Equilibrium the process by which a community moves towards its equilibrium state following a disturbance When disturbances are very frequent, then equilibrium may never happen. Some species specialize on disturbance Furbish � s lousewort What explains total diversity in a What is the relationship between community? disturbance and species diversity? How does diversity vary with the frequency of �� � disturbance? Keystone species can influence diversity How does species diversity vary with the time since disturbance? Equilibrium theory of island biogeography How does species diversity vary with the magnitude Disturbance of disturbance? Productivity Productivity Productivity vs Species richness amount of sunlight turned into primary producers (plants, algae, etc), often estimated using biomass of primary producers Species richness Many empirical studies have found a hump-shaped relationship between the productivity of a system and the number of species in that system Biomass

Productivity and Productivity and Biodiversity Biodiversity Habitat heterogeneity: the Habitat heterogeneity: the Increase in Competition relationship between species relationship between species productivity begins to allows for richness and biomass varies richness and biomass varies Number of species remove less coexistence among microhabitats among microhabitats competitive of more species species Competition Biomass What explains total diversity in a Habitat heterogeneity and community? Biodiversity Ecosystems with more heterogeneous habitats have more potential niches, allowing the coexistence of more Keystone species can influence diversity species. Equilibrium theory of island biogeography Number of species Disturbance Productivity Habitat heterogeneity Habitat heterogeneity What explains total diversity in a Habitat heterogeneity and Biodiversity community? Keystone species can influence diversity -MacArtur and MacArthur (1961) found that the bird diversity of a Equilibrium theory of island biogeography habitat increased with the Bird species complexity of the habitat’s diversity Disturbance vegetation Productivity -Similar relationships have been Habitat heterogeneity demonstrated in other taxa Foliage height diversity

Is biodiversity important for No relationship More diversity is more stable Ecosystem function Ecosystem function ecosystem structure and function? Do ecosystems with high species diversity “function” Species richness Species richness better? Redundancy Idiosyncratic Are ecosystems with high species diversity more Ecosystem function Ecosystem function stable? Species richness Species richness Do ecosystems with more species function better? Do ecosystems with high species diversity “function” better ? What do the empirical data tell us? Empirical evidence shows that in many 1. Experiments in The Ecotron: ecosystems there is a positive relationship between productivity and species richness. But some studies show that there is either no correlation or a negative correlation. The Ecotron is facility designed to establish simplified experimental communities Do ecosystems with high species diversity “function” better ? Do ecosystems with high species diversity What do the empirical data tell us? “function” better ? 1. Experiments in The Ecotron What do the empirical data tell us? high -High biodiversity communities 1. Experiments in The Ecotron had denser canopies and higher vegetation cover medium photosynthetic rates Naeem et al. (1994) created communities with 3 % Change in -low diversity communities also levels of biodiversity (low, medium, and high) low consumed less CO 2 and examined the relationship between biodiversity and ecosystem function in these artificial communities. Time

Are ecosystems with more Are ecosystems with more species more stable? species more stable? Minnesota grassland plot experiment Tilman and Downing (1994) Biodiversity and stability in grassland. Nature 367: 363-365. Biomass varies less from year to year in plots with high species richness METHODS Experimental design. In a 7-ha field at Cedar Creek Natural History Area, Minnesota, USA, we controlled the number of plant species in 168 plots, each 9 m £ 9 m. Plots were randomly assigned to be seeded with 1, 2, 4, 8 or 16 perennial grassland species, with 39, 35, 29, 30 and 35 replicates, respectively, of the diversity levels. The composition of each plot was randomly chosen from a set of 18 perennials (four C 4 grasses, four C 3 grasses, four legumes, four non- legume forbs and two woody species). All plots received 10 g m 2 2 of seed in May Coe ffi cient of variation = standard deviation mean 1994 and 5 g m 2 2 in May 1995, with seed mass divided equally between species. Are ecosystems with more Are ecosystems with more species more stable? species more stable? Minnesota grassland plot experiment Minnesota grassland plot experiment: resource usage Relationship between drought resistance of vegetation in a Minnesota grassland and plant Tilman et al (1996, 1997) Resource availability species richness prior to the examined the effect of drought. Drought resistance was species diversity on measured as the log of the ratio productivity and soil of plant biomass at the height of nutrients. the drought to plant biomass before the drought. Data are shown as means + SE (redrawn Species richness from Tilman and Downing 1994). Are ecosystems with more Are ecosystems with more species more stable? species more stable? Hypothetical relationship between species richness and invasion resistance Minnesota grassland plot experiment: Species rich communities are less susceptible to invasion because they resource usage use more of the available resources. Resistance to invasions Resource availability Plots with more species less nitrogen in their soil lower resource availability Species richness Species richness

Are ecosystems with more species Is biodiversity important for more resistant to invaders? ecosystem function? Some studies show that species rich communities are more Species Diversity and Invasion productive, but some other studies show alternative Resistance in a Marine Ecosystem interpretation. John J. Stachowicz, Robert B. Whitlatch, Richard W. Some studies show that species rich communities are more Osman. 1999. Science 286:1577-1579 stable and recover from disturbances faster and are less vulnerable to invasive species. Theory predicts that systems that are more diverse should be more resistant to exotic species, but experimental tests are needed to verify this. In experimental communities of sessile More studies are needed to allow generalizations beyond marine invertebrates, increased species richness significantly some model systems. decreased invasion success, apparently because species-rich communities more completely and efficiently used available space, the limiting resource in this system. Declining biodiversity thus facilitates invasion in this system, potentially accelerating the loss of biodiversity and the homogenization of the world's biota.