Aerial lakes photo

The Regional View All habitat is patchy Species colonize patches by dispersal All species go extinct

The Local View Communities are made up of populations Population persistence depends on the physical and biological environment

What are the roles of local and regional processes in structuring communities?

Zooplankton photograph

The importance of scale What are the roles of local and regional processes in zooplankton communities? Observational test global patterns of local and regional richness Experimental tests measuring community invasibility measuring dispersal rates The importance of scale modeling spread of invaders

Regional vs. local control of local diversity Regional processes colonization local extinction Local processes abiotic constraints species interactions if colonization  extinction if colonization >> extinction Regional richness Regional richness Local richness

“In a clear majority of studies, possibly the great majority, the main driver of local species richness appears to be the size of the regional species pool… Strong dependence of local richness on regional richness may arise because species interactions- the stuff of traditional community ecology- are weak” or… J.H. Lawton (1999). Are there general laws in ecology? Oikos 84: 177-192.

2,832 lakes Shurin et al. 2000. Ecology 81: 3062 17 11,12 17 20 4,14 23 19 1,3,5-10, 15,16,18, 22,24,25 21 13 2,832 lakes Shurin et al. 2000. Ecology 81: 3062

Local vs. residual regional richness -20 -10 10 20 30 1 2 3 4 5 6 7 8 A- Cladocerans -5 15 B- Cyclopoids Residual regional richness C- Calanoids 40 D- Crustaceans Local richness

Zooplankton show linear patterns of local and regional richness Predictions Local communities are open to invasion from the regional pool Species interactions have little impact on invasion success

The importance of scale What are the roles of local and regional processes in zooplankton communities? Observational test global patterns of local and regional richness Experimental tests measuring community invasibility measuring dispersal rates The importance of scale modeling spread of invaders

Invasion experiment questions Shurin 2000. Ecology 81: 3074 Are zooplankton dispersal limited? species will colonize the invasion treatment What are the effects of relaxing dispersal limitation? zooplankton diversity and biomass will increase Does invasibility relate to native diversity? invasibility will decline at high native diversity

Invasion experiment results 0.2 0.4 0.6 0.8 1 1.2 Exotic biomass [log (ug/L) + 1] 1 2 3 4 5 6 7 8 Bird 1 Lab L.A. 11 Hut Norris Ent. Rock Bird 2 Shaw Upton L.A. 12 % introduction success

Why would more diverse communities be harder to invade Why would more diverse communities be harder to invade? (Elton’s 1958 hypothesis) Fewer potential invaders in regional pool more likely a species is already present Less available niche space prediction: lower per invader success rate prediction: lower invader biomass once established

Invasibility vs. native diversity 2 4 6 8 Exotic biomass (ug/L) 1 EXPERIMENT % introduction success Native diversity (Fisher’s alpha) 3 rs = -0.70 P < 0.025 rs = -0.57 P < 0.05

No effects of invasion on total zooplankton diversity or biomass biomass or extinction of native species phytoplankton biomass

How important are interspecific interactions to invasion success? treatment Resistance treatment 11 ponds 4 Ponds

Biological resistance to invasion 0.5 1 1.5 2 2.5 Exotic biomass [log (ug/L) + 1] 3 4 5 6 7 Bird Shaw Upton L.A. % introduction success Resistance= 16X Invasion 4X Invasion

Conclusions from invasion experiment Weak dispersal limitation Dispersal does not limit biomass or diversity Invasibility declines at high diversity Interspecific interactions play a major role big effect of resistance treatment Suggests colonization >> extinction for most species

Cohen and Shurin 2003, Oikos 103: 603 Experimental design: pools at 5, 10, 30 and 60m from 2 real ponds plus a non-dispersal limited control Cohen and Shurin 2003, Oikos 103: 603

Fast colonization: one new species every four days

A paradox? Observational evidence: strong regional control linear patterns of local and regional diversity Experimental evidence: strong local control resistance to invasion strong species interactions rapid dispersal

Theoretical and empirical resolution? Facilitation versus inhibition The effects of predators on local and regional coexistence Shurin and Allen 2001. American Naturalist 158: 624 Shurin 2001. Ecology 82: 3404 The influence of scale Modeling the spread of exotic species Havel, Shurin and Jones 2002. Ecology  83: 3306 Shurin and Havel 2002. Biological Invasions 4: 431

Modeling spread of exotics with John Havel and Jack Jones (Ecology 83:3306) How can we use spread to estimate dispersal at broad scales? Is invasion limited by dispersal or local constraints?

Modeling invasion probability surface area temperature conductivity total nitrogen total phosphorus chlorophyll volatile solids non-volatile solids secchi depth turbidity How do we include dispersal potential? invasion probability + local variables  dispersal potential

Modeling dispersal potential from spatial position P 1T P 2T * * source 1 source 2 target d1,T d2,T # propagules = P 1T + P 2T What is the shape of the dispersal function?

# propagules = e(-d/a) The shapes of different dispersal functions 0.2 0.4 0.6 0.8 1 20 40 60 80 100 Distance (km) # propagules a=10 30 # propagules = e(-d/a) What is the most likely value for a?

The likelihood profile approach to estimate a 47 48 49 50 51 52 20 40 60 80 100 a -2 log likelihood 1995 The most likely a = 17

The dispersal function for 1995 Pi = exp(-d/17) 20 40 60 80 100 0.03 0.06 0.09 0.12 # dispersal events Distance (km)

Do spatial or local models best predict invasion? probability + local variables  dispersal potential 1995 10 20 30 40 50 60 70 80 90 local dispersal local + AIC

Do spatial or local models best predict invasion? probability + local variables  dispersal potential 90 80 70 local 60 dispersal 50 AIC local + dispersal 40 30 20 10 1993 1994 1995 1996 year

Conclusions from invasion model Dispersal of Daphnia lumholtzi localized up to 20-30 km Invasion limited by local environment and dispersal Local control more important than dispersal

How does dispersal ability vary among aquatic taxa How does dispersal ability vary among aquatic taxa? How does dispersal ability affect patterns of diversity at different scales? with Karl Cottenie and Helmut Hillebrand (Ecology Letters, in review)

How should β-diversity change with distance? bad dispersers good dispersers Tilman, Lehman and Kareiva. 1997. Spatial Ecology

β-diversity versus distance for different taxa

Vertebrates show higher β-diversity, clumpier distributions Slope (β vs. distance)

Conclusions Zooplankton show linear local-regional richness patterns Experiments found strong invasion resistance, rapid dispersal Importance of dispersal increases with distance and body size