Productivity What explains total diversity in a community? amount - PDF document

Productivity What explains total diversity in a community? amount of sunlight turned into primary producers (plants, algae, etc), often estimated using biomass of primary producers Keystone species can influence diversity Many empirical studies have found a hump-shaped Equilibrium theory of island biogeography relationship between the productivity of a system Disturbance and the number of species in that system Productivity Productivity Productivity vs Species richness Number of species Species richness Biomass 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 Number of species allows for richness and biomass varies richness and biomass varies 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 Bird species habitat increased with the 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 structure and function? Ecosystem function Ecosystem 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 Are ecosystems with more species function better? species more stable Productivity 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. Time Are ecosystems with more Are ecosystems with more species more stable species more stable Productivity Productivity Time Time Are ecosystems with more Are ecosystems with more species more stable? species more stable? Hypothetical relationship between species richness and invasion resistance Hypothetical relationship between productivity and species richness Species rich communities are less susceptible to invasion because they use more of the available resources. Ecosystems with more Variance of species should be more Productivity resistant to disturbances Resistance to invasions Resource availability and will recover faster than species poor communities Species richness Species richness Species richness

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? 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 The Ecotron is facility designed to artificial communities. establish simplified experimental communities Are ecosystems with more species more stable? Do ecosystems with high species diversity “function” better ? What do the empirical data tell us? Tilman and Downing (1994) Biodiversity and stability in grassland. 1. Experiments in The Ecotron Nature 367: 363-365. high -High biodiversity communities had denser canopies and higher vegetation cover medium photosynthetic rates % Change in low -low diversity communities also consumed less CO 2 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 Time 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 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 Relationship between drought Biomass varies less from resistance of vegetation in a year to year in plots with Minnesota grassland and plant high species richness species richness prior to the drought. Drought resistance was measured as the log of the ratio of plant biomass at the height of the drought to plant biomass before the drought. Data are shown as means + SE (redrawn from Tilman and Downing 1994). Coe ffi cient of variation = standard deviation mean

Are ecosystems with more Are ecosystems with more species more stable? species more stable? Minnesota grassland plot experiment: resource usage Minnesota grassland plot experiment: resource usage Tilman et al (1996, 1997) Resource availability examined the effect of Plots with more species species diversity on less nitrogen in their soil productivity and soil nutrients. lower resource availability Species richness Are ecosystems with more species Figure 1 | Dependence of temporal stability of each plot on experimentally imposed species-number treatment. a , Ecosystem temporal stability for the decade from 1996 to 2005 was an increasing function of the number of more resistant to invaders? planted species. Ecosystem stability is the ratio of mean plot total biomass to its temporal standard deviation, determined after detrending. The regression line and its 95% confidence interval are shown (untransformed data: F 1, 159 ¼ 43.7, P , 0.0001). To reduce the difference in y axis scale between the two parts of this figure, a single data point (species number of 16, ecosystem stability of 15.76) is not shown but was included in all analyses. b , Plot-average species temporal stability, determined with species biomass data for 2001–2005, was a declining function of the number of planted species. The regression curve and 95% confidence intervals are based on a fit of log(species stability) on log(species number), with Species Diversity and Invasion F 1, 159 ¼ 72.3, P , 0.0001. Resistance in a Marine Ecosystem John J. Stachowicz, Robert B. Whitlatch, Richard W. Osman. 1999. Science 286:1577-1579 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. Tilman et al 2006, nature Is biodiversity important for ecosystem function? 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.