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| Aim To evaluate the influence of environment and biogeographical region, as a
proxy for historical influence, on the ecological structure of Holarctic
communities from similar environments. It is assumed that similarities among
communities from similar environments in different realms are the result of
convergence, whereas their differences are interpreted as being due to different
historical processes.
Location Holarctic realm, North America and Eurasia above 25 N.
Methods Checklists of mammalian species occurring in 96 Holarctic localities
were collected from published sources. Species were assigned to one of 20
functional groups defined by diet, body size and three-dimensional use of space.
The matrix composed of the frequencies of functional groups in the 96 localities is
used as input data in a correspondence analysis (CA). The localities are classified
into nine groups according to Bailey’s ecoregions (used as a surrogate of regional
climate), and the positions of the communities in the dimensions of the CA are
compared in relation to ecoregion and realm. Partial regression was used to test
for the relative influence of ecoregion and realm over each dimension and to
evaluate the effect of biogeographical realm on the variation in the factor scores of
the communities of the same ecoregion.
Results In some cases, mammalian communities from areas with similar regional
climates exhibit convergence in community structure, irrespective of the
biogeographical realm where they are located. However, all of them are clearly
subdivided into Nearctic and Palearctic subsets. Differences in the composition of
the regional pools only partially explain differences in local communities between
realms.
Main conclusions Holarctic mammalian communities from regions with
widely different climates differ in ecological structure irrespective of their
biogeographical location. On the other hand, the structures of Nearctic and
Palearctic communities from regions of similar climate radically differ in some
features. Thus, although present climatic conditions influence community
structure, contingent historic processes associated with each region also play a
major role in determining community structure. | |
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