On the roles of time, space and habitat in a boreal small mammal assemblage: predictably stochastic assembly

Ecologists continue to debate the roles of deterministic versus stochastic (or neutral) processes in the assembly of ecological communities. The debate often hinges on issues of temporal and spatial scale. Resolution of the competing views depends on a detailed understanding of variation in the structure of local communities through time and space. Analyses of twelve years of data on a diverse assemblage of 13 boreal small mammal species revealed both deterministic and stochastic patterns. Stochastic membership in the overall community created unique assemblages of species in both time and space. But the relative abundances of the two codominant species were much less variable, and suggest a significant role for strong interactions that create temporal and spatial autocorrelation in abundance. As species wax and wane in abundance, they are nevertheless subject to probabilistic rules on local assembly. At the scales I report on here, poorly understood large scale processes influence the presence and absence of the majority of (sparse) species in the assembly. But the overall pool of species nevertheless obeys local rules on their ultimate stochastic assembly into groups of interacting species.