Contrasts between habitat generalists and specialists: an empirical extension to the basic metacommunity framework

Abstract

Emergence of the metacommunity concept has made a substantial contribution to better understanding of the community composition and dynamics in a regional context. However, long-term field data for testing of available metacommunity models are still scarce, and the extent to which these models apply to the real world remains unknown. Tests conducted so far have largely sought to fit data on the entire regional set of species to one of several metacommunity models, implicitly assuming that all species operate similarly over the same set of sites. However, species differ in their habitat use. These differences can, in the most general terms, be expressed as a gradient of habitat specialization (ranging from habitat specialists to habitat generalists). We postulate that such differences in habitat specialization will have implications for metacommunity dynamics. Specifically, we predict that specialists respond more to local processes and generalists respond to regional spatial processes. We tested these predictions using natural microcosm communities for which long-term (nine-year) environmental and population dynamics data were available. We used redundancy analysis to determine the proportion of variation explained by environmental and spatial factors. We repeated this analysis to explain variation in the entire regional set of species, in generalist species only, and in specialists only. We further used ANOVA to test for differences in the proportions of explained variation. We found that habitat specialists responded primarily to environmental factors and habitat generalists responded mainly to spatial factors. Thus, from the metacommunity perspective, the dynamics of habitat specialists are best explained by a combination of species sorting and mass effects, while that of habitat generalists are best explained by patch dynamics and neutral models. Consequently, we infer that a natural metacommunity can exhibit complicated dynamics, with some groups of species (e.g., habitat specialists) governed according to environmental processes and other groups (e.g., habitat generalists) governed mainly by dispersal processes.

Using network analysis to explore co-occurrence patterns in soil microbial communities

“…The generalists network was less connected and more compartmentalized (19 significant co-occurrences and five compartments) than the specialists network (29 significant co-occurrences and two compartments) probably because of the highest habitat variability covered by the former and the presence in restricted environments by the latter. Thus, the two somehow arbitrary ecological categories that we established allowed us to capture additional information on the community assembling structure as previously shown for macroorganisms (Pandit et al, 2009).…”

Species sorting and neutral processes are both important during the initial assembly of bacterial communities

“…Thus, even though we found species sorting processes, they were relatively weak and established themselves via differences in relative abundances of generalist taxa among the different media, as well as media-specific occurrences of a few specific taxa. It has been shown earlier that species sorting has strong effects on specialists, whereas regional forces (patch or neutral dynamics) are stronger for generalists (Pandit et al, 2009). Hence, the lack of strong species sorting effects could be because of the fact that specialists are disfavoured during the growth in initially empty patches, which selected fast growing, opportunistic species.…”

Understanding specialism when the jack of all trades can be the master of all

“…The existence of specialists-organisms that are more fit in some environments than in others (box 1)-influences taxonomic diversity [3], geographical variability [4] and complex community dynamics [5]. Developing a better understanding of why specialists evolve and persist will therefore result in a better understanding of what gives rise to the tremendous variability that exists in nature.…”