Metacommunities

1. Metacommunities

2. (meta)community Local community: all individuals of all species that have the potential to interact within a given habitat patch Metacommunity: a set of local communities that are interconnected by dispersal of species that have the potential to interact Parallel to “metapopulation”: strong local dynamics, but also regional dynamics that should not be ignored Landmark paper: Leibold et al. 2004, Ecol. Letters [TOLEDO]

3. Karl Cottenie

4. Metacommunities are everywhere • heather vegetation • forest • hosts for parasite metacommunities • islands • ponds • water in leaves of Sarracenia • … Critical question: spatial scales – where does a metacommunity end?

5. Metacommunity ecology provides a framework to integrate regional and local factors In contrast to metapopulation ecology, it includes species interactions Critical question: would it not be a good idea to explore metacommunities as a sum of metapopulations? Why metacommunity ecology

6. Total regional species pool (biogeography, speciation) regional Processes (dispersal, colonization) local processes (filter by abiotic conditions, biotic interactions) local community structure

7. The four metacommunity perspectivesaccording to Leibold et al. 2004, Ecol. Lett. Species-sorting Mass effects Neutrality Patch dynamics Mathew Leibold

8. Species sorting Local environmental conditions differ among patches and have a dominant impact on species composition of the local community. Enough dispersal so that the right species colonizes the right habitat. Local population dynamics act at a shorter time scale than colonization-extinction dynamics There are trade-offs in performance of species in different habitats (niche differences) Species sorting results in a good match between local environmental conditions and species composition of local communities

9. Species sorting “Close match” between community and environment Dispersal rates are high enough so that species can colonize the habitats that match their niche preferences, while not being so high that communities are homogenized

10. Mass effects Patch quality differs, but high dispersal rates result in source-sink dynamics. High dispersal rates result in homogenization of the communities. Mass effects result in a weaker match between environment and species composition and an increased impact of “space” (regional factors) ME reduces regional diversity

11. Neutral models All species are ecologically equivalent (“null model” to niche-based models) Stochastic extinctions are compensated by dispersal within the metacommunity. As these processes are fully neutral, this results in ecological drift. Diversity at the metacommunity level is maintained by local speciation NM predicts no match between the environment and species composition of local communities

12. Neutrality Al species can be present in all patches Differences in community composition are the result of random extinctions and colonizations, speciation, and dispersal limitation Ecological drift

13. Patch dynamics Identical patches (islands) Stochastic and deterministic extinctions Extinctions are countered by dispersal Species are characterized by trade-offs between dispersal ability and competitive strength Intermediate levels of dispersal lead to regional coexistence Strong temporal dynamics Species B has high dispersal rate while species A is the stronger competitor in the patches

14. Differences among the perspectives Species and patch characteristics Neutral models: no niche differences among species Patch dynamics: trade-off dispersal and overall competitive strength Mass effects & species sorting: niche differences among species; trade-offs in performance across patches Patch connectivity Difference insynchronicitybecause of difference in linkage through dispersal Differences in local and regional diversity because of different impact of dispersal

15. Problems – the four perspectives have their limitations • No full coverage of the spectrum of possibilities by the four perspectives (e.g. patch dynamics refers to a specific model, whereas we need more general concepts) • Overinterpretation of “fit”: neutral model is a good null model to test niche-based models but: fit to the null model does not imply absence of niche differences among species

16. Karl Cottenie’s view on the metacom perspectives Gradient in environmental heterogeneity and dispersal Environmental heterogeneity Species sorting Environment Neutrality and patch dynamics Mass effects Habitat connectivity Dispersal

17. Karl Cottenie’s view on the metacom perspectives Gradient in environmental heterogeneity and dispersal Environmental heterogeneity Species sorting Neutrality and “apparent neutrality” (incl. priority effects, patch dynamics,…) Mass effects Habitat connectivity

18. Similarity among communities along a spatial gradient Patch dynamics Mass effects similarity Neutrality Species sorting Environmental gradients can have a spatial component Distance

19. Multiple interpretations of spatial effect “Real” dispersal limitation (little dispersal; few sources for colonization) or Diminishing dispersal rate (high dispersal; mass effects) or Association between environment and space

20. Similarity among communities along an environmental gradient Patch dynamics Mass effects similarity Neutrality Species sorting Environmental gradient

21. Data analysis L1 L2 L3 … Species 1 Species 2 … Species matrix [C]: species in sites (presence/absence or relative abundances) Spatial matrix [S]: spatial coordinates of sites (polynomial, GIS,…) Environmental matrix [E]: quantify relevant environmental variables Variance partitioning through partial redundancy analysis (Borcard et al., 1992, Ecology; Peres-Neto et al., 2006, Ecology) Problems: - need to measure the environmental factors that matter - but number of variables should not differ too much among explanatory matrices - select most relevant ones using statistical procedures

22. Variance partitioning E S E/S E∩S S/E explained by regional variables unexplained variation explained by local variables

23. Problems - limitations • Most analyses so far only overall assessment of structure – need for more detailed analysis - patch characteristics: e.g. to assess effect of isolation more directly (method: remove successively the more isolated patches) - species characteristics: e.g. rare vs abundant species, generalist vs specialist species, species with different dispersal modes

24. Body size impacts metacommunity structure dispersal and environmental sorting Tom De Bie Steven Declerck Spatial component Environmental component body size Body size De Bie et al., Ecol Letters 2012

25. Problems - limitations Local Regional 2 Spatial scale: what are the limits of a given metacommunity? – metacommunity structure will depend on scale of study

26. Problems - limitations • As patterns are taxon dependent – what happens across food webs ?

27. Topics for discussion / assignments (see readings on TOLEDO) How to recognize / analyse the relative importance of the four different perspectives for a particular metacommunity – how to interpret data ? Experimental designs to test the impact of regional and local dynamics – how would you do such experiments. Can you think of good model ssytems ? How to interpret a spatial signal in the data ? Can one view metacommunity ecology as a sum of metapopulation ecologies ? Think of an interesting model and question in the framework of metacommunity ecology and provide a brief outline of how you could tackle it (through field work and/or experiments)

28. Topics for discussion / assignments How to relate metacommunity ecology to the framework provided by Vellend (2010 & Princeton book), i.e. with the four basic processes that determine community assembly ? How to link metacommunity ecology to biogeography ? What are the issues involved ? The metacommunity ecology presented here is based on species abundances. Would we gain by focusing on traits or by including phylogenetic information in our analyses ? Think about advantages and potential problems. Most metacommunity ecology deals with “patches”. How to deal with e.g. continuous habitats or “dendritic systems” such as rivers ? Any critical comments / problems you identify ?