1. Prediction of richness (local vs regional curves to assess community saturation?) David Luther Biology 255 Oct. 7, 2003

2. Why do we care? “Resolving relative contributions of local vs regional processes may be the key to understanding global patterns of species diversity” Huston 1999 “Can one comprehend the ruin of natural systems without understanding how they are built?.” Ricklefs 1987

3. Background 1st half of century regional factors were favored as explanations of local diversity. 2nd half of century local factors were favored as explanations of local diversity. Key reason local and regional diversity were divorced is the idea of limiting similarity. Ricklefs 1987

4. Local-Regional Richness Plots If linear then the local richness is independent of biotic interactions and increases proportionally with the regional richness (type I community) If curvilinear then the local community is saturated and the local richness is independent of regional richness (type II community). Cornell & Lawton 1992

5. Local Richness An area small enough that all species could encounter each other within ecological time and possibly interact. Ex. All fish species in a lake or all grass species in a meadow. Srivastava 1999 Limitations are ecological that result in species being actively excluded from communities by local effects such as an upper limit of niche packing. There is little or no regional effect.

6. How do we detect effects of local processes? Huston 1999 Organisms must be potential competitors, ducks and warblers don’t interact, need similar functional types. Size of local area needs to be small enough for local species to interact competitively. Conditions suitable for competitive equilibrium to be achieved.

7. Regional Richness An area that comprises all species that could eventually colonize a location if no competitive exclusion occurred. Ex. All fish species in Britain, all grass species in the Serengeti. Srivastava 1999 Limitations are evolutionary and involve regional controls on local community richness such as rate of speciation and fixation rate of mutations.

8. 4 methods of testing for saturation Srivastava 1999 1REGIONAL POOL SUMS OVER HABITATS 2ANALAGOUS HABITATS IN THE SAME GEOGRAPHIC AREA 3IDENTICAL HABITATS IN GEOGRPAPHICALLY DIFFERENT REGIONS 4COMPARISONS IN A GIVEN REGION OF A PARTICULAR COMMUNITY THROUGH EVOLUTIONARY TIME

9. Effect of Scale Karlson and Cornell 2002 Relationship is more likely to be curvilinear as regional influences get lost. Because the community is saturated or because species coexistence is precluded by spatial constraints? Local Regional Local EXPECT L R

10. Effect of Scale cont. Relationship is more likely to be linear. Because it is regionally enriched or because there are multiple saturated habitats? Local Regional L R EXPECT

11. Psuedosaturation Definition- detection of curvilinearity when the true relation is linear Reasons Underestimate local richness Overestimate regional richness but not local richness Griffiths 1997

12. Psuedoreplication Definition- when replicates used in analysis are not truly independent because they are spatially or temporally correlated. Srivastava 1999 Confuses the differences between regions with differences between regional species pools

13. Ricklefs 2000 This paper addresses the problems of estimating regional species pools and establishing the independence of these pools. He also comments on L-R relationships as they relate to saturation. He used data on avifauna of the West Indies L is the average # of species observed in each of 9 habitats on one island R(obs) is the # of species observed in all habitats together R(total) # of species known to occur In the region (island or continental area) observed or not.

14. Ricklefs 2000 cont. “ L-R plots are not enough info on there own to determine ecological processes.” “Interactions between species constrain membership in local assemblages but do not place an upper limit on their size.” “Ecologists should be less concerned about whether populations interact within local assemblages than with the mechanisms responsible for Generating the regional pool of species Distribution of those species over habitats within the region Evolutionary adjustments that accompany invasion of a local assemblage

15. Levine 2000 This paper addresses the classic hypothesis that species diversity enhances community resistance to invasion. -Support from theoretical models & lab experiments -Yet natural studies show that the most diverse communities are most likely to be invaded To address this contradiction he couples patterns of diversity and invasion with in situ manipulations of diversity in a natural context, tussocks forming sedges in the South Fork Eel River, CA. Each tussock forms a discrete micro island.

16. Levine 2000 cont. METHODS 1st surveyed similar sized tussocks along 7km of river, all 3 exotic species were significant & positively related to species richness –possibly not just due to richness but endemic & exotic both respond to environmental conditions 2nd He tested the effect of diversity on invasions, he ‘invaded’ tussocks and manipulated the # of residential species. To do this he removed species from 65 equal size tussocks & assigned 5 species richness treatments and covered about 90% of each tussocks with the natives 3rd he added 200 seeds of each exotic species per tussock

17. Levine 2000 cont. RESULTS As species richness increased the proportion of propagule survival went down in 2 out of 3 exotics per island & the size of the largest invader declined thus showing an effect of diversity to enhance resistance to biological invasion. Results were similar after 3 weeks and 5 months suggesting the effect of diversity at germination/seedling stage.

18. Closing questions issues and thoughts Ecological plasticity can fill all niches with out saturation Griffiths 1997 Saturation is a physical limitation regardless of species interactions Loureau 2000 Species interaction only limit the community from a given species pool, a novel invader could still invade and do just fine even if saturation occurred. Loureau 2000 Pick systems that are undisturbed or else local species interactions could not be in equilibrium. Huston 1999 Taxa evolve at different rates so some taxa may be saturated while others are not, the study taxa could give different results. We’ve had a lot of extinctions in the last 10,000 years how does this effect community equilibrium and saturation? Why isn’t local richness simply a product of resource availability?