Ph. Warren, THE EFFECTS OF BETWEEN-HABITAT DISPERSAL RATE ON PROTIST COMMUNITIES AND METACOMMUNITIES IN MICROCOSMS AT 2 SPATIAL SCALES, Oecologia, 105(1), 1996, pp. 132-140
The effect of manipulation of between-habitat dispersal rates in multi
ple patch systems was examined experimentally using protist communitie
s in laboratory microcosms. Replicate ''landscapes'' of eight microcos
ms (patches) at two spatial scales (patch sizes) were inoculated with
13 species of protists. Dispersal was carried out by transferring a sm
all random sample of medium and protists from one randomly selected mi
crocosm to another within a landscape. Four dispersal rates (24, 6, 2
and 0 transfers every 3 days) were used, and the microcosms were sampl
ed after 6 and 12 weeks. Patch size had a consistent effect on within-
patch (community) and within-landscape (metacommunity) diversity, both
being lower in small patch systems. Higher dispersal rates had a slig
ht effect on community and metacommunity diversity after 12 weeks, wit
h a tendency for higher dispersal to slightly offset the rate of loss
of species. Both dispersal and patch size had effects on the abundance
of many individual species, though in a variety of ways. The individu
al species results suggest that extinction is selective with respect t
o both patch size and dispersal rate treatments, and may be influenced
by species interactions. It seems likely that in metacommunity system
s of this sort, rather than mainland-island systems, the potential eff
ect of between-patch dispersal rate in rescuing and recolonizing where
local extinctions occur may be much reduced by the effect of selectiv
e extinction, relative to that expected under the assumption of random
extinction.