Classical metapopulation model. Area effects. What explains total diversity in a community? Distance effects. Disturbance

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1 Classical metapopulation model Colonization Rate Area effects How does island area affect the number species on the island? How does size affect colonization rate? Extinction Ssmall < Slarge Equilibrium metapopulation size 0.5 Ss Rate Fraction of patches occupied How does distance from the mainland affect the number species on the island? How does size affect colonization rate? Sn Island species number E Cn Cf Sl Distance effects Rate El Sl Ss Sfar < Snear Es Cs P 1 Cl Sn P Sf isn S Sf 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

2 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? 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? vs amount of sunlight turned into primary producers (plants, algae, etc), often estimated using biomass of primary producers Many empirical studies have found a hump-shaped relationship between the productivity of a system and the number of species in that system Biomass

3 and and Habitat heterogeneity: the relationship between species richness and biomass varies among microhabitats Habitat heterogeneity: the relationship between species richness and biomass varies among microhabitats Competition Number of species Increase in productivity allows for coexistence of more species Biomass Competition begins to remove less competitive species Habitat heterogeneity and Ecosystems with more heterogeneous habitats have more potential niches, allowing the coexistence of more species. Habitat heterogeneity Number of species Habitat heterogeneity Habitat heterogeneity and Bird species diversity Foliage height diversity -MacArtur and MacArthur (1961) found that the bird diversity of a habitat increased with the complexity of the habitat s vegetation -Similar relationships have been demonstrated in other taxa Habitat heterogeneity

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

5 emporal d across However, 1 05 on do not n earlier requires with its d, with abilizing ariances ¼ 15.7, biomass o effect. increase , ass than greater olio and on, and society natural e shown duction ty of an Minnesota grassland plot experiment Tilman and Downing (1994) and service the stability in grassland. annual ecosystem Nature 367: production of biomass and thus of potential biofuels and livestock fodder1 6 also depends on biodiversity. can therefore be an important element for the reliable and sustainable provisioning of ecosystem services. 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 C4 grasses, four C3 grasses, four legumes, four nonlegume forbs and two woody species). All plots received 10 g m22 of seed in May 1994 and 5 g m22 in May 1995, with seed mass divided equally between species. Treatments were maintained by weeding three or four times each year. Weeds were removed while still small, with care being taken to minimize any disturbance. Plots were burned annually in spring before growth began. Five woody monocultures are not included in analyses because burning effectively eliminated woody species from multispecies plots. Plots were annually sampled in mid-august for aboveground living plant biomass by clipping, drying and weighing four parallel and evenly spaced 0.1 m 3.0 m vegetation strips per plot from 1996 to 1999 and four 0.1 m 6.0 m strips per plot from 2000 to Different locations were clipped each year. Biomass from one strip per plot was sorted to species from 2001 to The Shannon diversity index, H 0, used abundancesminnesota of each species, grassland planted or weedy, in each plot by means of estimates plot experiment of percentage cover for (four 0.5 m2 subplots per plot) and sorted biomass for See ref. 4 for further details. Sampling effort. To eliminate potential bias from different sampling efforts for the first four in comparison with the last six Relationship years, for each of the last six years between drought two clipped strips per plot were randomly chosen for an analysis of ecosystem resistance of vegetation in a stability. The full data gave similarly significant and positive effects of diversity on all three measures of ecosystem stability. Minnesota grassland and plant priorbytomeans the Detrending and other analyses. Detrending species was done,richness for each plot, Drought resistance of linear regression of annually measured plotdrought. biomass on the logarithm of yearwas measured the loga of the ratio and used all ten years of plot data. The logarithm of yearas provided generally of The plant biomass at the height better fit than year; both gave similar results. standard deviation, j d, of of residuals for each regression measures detrended variation. The biomass detrended the drought to plant. Each plot a singledata detrended temporal stability, S d, of a plot was S d ¼ m/j dbefore thehad drought. are stability value for the ten-year period. In contrast, when were+divided into shown as data means SE (redrawn shorter intervals that did not require detrending, there were multiple values of1994). S, from Tilman and Downing calculated as S ¼ m/j, per plot. We divided the data either into two subsets, each five years in duration ( and ) or into five subsets, each two years in duration ( , , , and ). These temporal sequences of S values for each plot were analysed with the use of repeated-measures MANOVA. Coefficient of variation = Minnesota grassland plot experiment: resource usage Naeem, S., Ha kenson, K., Lawton, J. H., Crawley, M. J. & Thompson, L. J. and plant productivity in a model assemblage of plant species. Oikos 76, (1996). 2. Tilman, D., Wedin, D. & Knops, J. and sustainability influenced by biodiversity in grassland ecosystems. Nature 379, (1996). 3. Hector, A. et al. Plant diversity and productivity experiments in European grasslands. Science 286, (1999). 4. Tilman, D. et al. Diversity and productivity in a long-term grassland experiment. Science 294, (2001). 5. Hector, A., Bazeley-White, E., Loreau, M., Otway, S. & Schmid, B. Overyielding in grassland communities: Testing the sampling effect hypothesis with replicated biodiversity experiments. Ecol. Lett. 5, (2002). 6. Hooper, D. U. et al. Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecol. Monogr. 75, 3-35 (2005). 7. Elton, C. S. The Ecology of Invasions by Animals and Plants (Methuen, London, 1958). 8. May, R. M. Stability and Complexity in Model Ecosystems (Princeton Univ. Press, Princeton, 1973). 9. McNaughton, S. J. Stability and diversity of ecological communities. Nature 274, (1978). 10. Tilman, D. & Downing, J. A. and stability in grasslands. Nature 367, (1994). 11. Tilman, D. : Population versus ecosystem stability. Ecology 77, (1996). 12. Huston, M. A. Hidden treatments in ecological experiments: Re-evaluating the ecosystem function of biodiversity. Oecologia 110, (1997). 13. Pfisterer, A. B. & Schmid, B. Diversity-dependent production can decrease the stability of ecosystem functioning. Nature 416, (2002). Minnesota grassland plot experiment: resource usage Plots with more species less nitrogen in their soil lower resource availability 631 Tilman et al (1996, 1997) examined the effect of species diversity on productivity and soil nutrients. Received 20 December 2005; accepted 23 March standard deviation mean Hypothetical relationship between species richness and invasion resistance Species rich communities are less susceptible to invasion because they use more of the available resources. Resistance to invasions ory that r species bility at iance in (covarin species aging or s abunosystem LETTERS Resource availability ots had studies fects of, higher Resource availability mean he mean e five -number etrended. ral n).

6 species more resistant to invaders? Is biodiversity important for ecosystem function? Species Diversity and Invasion Resistance in a Marine Ecosystem John J. Stachowicz, Robert B. Whitlatch, Richard W. Osman Science 286: 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 marine invertebrates, increased species richness significantly 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. Some studies show that species rich communities are more productive, but some other studies show alternative interpretation. Some studies show that species rich communities are more stable and recover from disturbances faster and are less vulnerable to invasive species. More studies are needed to allow generalizations beyond some model systems.