Differential importance of niche availability and random processes for common and rare species as an explanation of species coexistence.
Münzbergová, Zuzana 1, 2, 3, Vandvig, Vigdis1, 4, Goldberg, Deborah1, 1 Department of Ecology and Evolutionary biology, Ann Arbor, USA2 Institute of Botany, Academy of Sciences of the Czech Republic, Pruhonice, Czech Republic3 Department of Botany, Faculty of Science, Charles University, Prague, Czech Republic4 Department of Botany, University of Bergen, Bergen, Norway
ABSTRACT- Niche availability and effect of random processes (such as dispersal and small scale disturbances) are two competing explanations for species coexistence in a community. While both have been shown to be feasible, it is not clear which process is important when. We suggest that Caswells (1978) observation that a community may consist of a core of dominant species, which interact strongly enough among themselves to arrive at equilibrium, surrounded by a larger set of non-equilibrium species playing their roles against the background of the equilibrium species, might provide an explanation. We develop this into a testable hypothesis by arguing that in homogenous environment species affected mainly by random processes should be randomly distributed or clustered relative to species affected mainly by deterministic processes such as niche availability. If Caswells observation holds, there should be a general trend for common, competitive, species to be more evenly distributed over space. We test this prediction using over 80 datasets from herbaceous communities. We compare spatial patterns of rare and common species within datasets using a model that accounts for random sampling effects. Our results show that common species are significantly more evenly distributed than rare species and that the magnitude of this difference increases as the difference in the abundance between common and rare species increases. Both of these patterns are in concordance with our predictions. We conclude that the hypothesis that niche availability is more important for the maintenance of the dominant species and random processes for the rare species within communities is a feasible explanation for diversity patterns observed in natural communities.
Key words: dispersal, species abundance, species coexistence, niche theory
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