Dispersal limitation is stronger in communities of microorganisms than macroorganisms across Central European cities
2012
Aim It is generally believed that communities of small
organisms, or those with small propagules, are structured
mainly by local niche-based processes, and less by dispersal
limitation. Conversely, weaker environmental and stronger
spatial structure, indicating dispersal limitation, are
expected to occur more frequently in communities of large
organisms. However, this hypothesis has rarely been tested by
comparing spatial and environmental effects across groups of
organisms of different size (or with different size of
propagules) sampled at the same set of sites. Here, we test it
in urban environments. Location Thirty-two cities in 10
countries of Central Europe and Benelux. Methods Wecompared
effects of spatial location and climate on species composition
of different groups of organisms sampled in corresponding types
of urban habitats. The studied groups were: (1) subaerial
cyanobacteria and algae, (2) vascular plants, (3) land snails;
and subgroups of vascular plants with different life form and
dispersal mode, namely: (4) herbs, (5) animal-dispersed trees
and shrubs, and (6) wind-dispersed trees and shrubs. Data were
analysed by variation partitioning based on redundancy analysis
(RDA) with principal coordinates of neighbour matrices (PCNM).
Eighteen PCNM eigenvectors (expressing spatial effects) and
mean annual temperature, July–January temperature difference
and annual precipitation sum (expressing environmental effects)
were used as explanatory variables. Results Pure effects of
climate on species composition, indicating niche-based
processes, were not significant for any group or subgroup of
the studied organisms. In contrast, pure effects of space,
indicating dispersal limitation, were significant for all
groups and subgroups except herbs. Surprisingly, the community
of cyanobacteria/algae possessed much stronger spatial
structure independent of climate than communities of larger
organisms, although cyanobacteria/algae had the lowest beta
diversity among the studied cities. Main conclusions We
hypothesize that the community of subaerial cyanobacteria/
algae is structured by natural processes which involve
dispersal limitation, whereas communities of urban plants and
snails are influenced by human-assisted dispersal of their
propagules between cities, which results in weaker dispersal
limitation. Our study indicates that dispersal vectors can be
more important for community structure than size of organisms
or of their propagules.
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