Haag, Wendell R.; Warren, Melvin L., Jr. 2000. Effects of light and presence
of fish on lure display and larval release behaviours in two species of
freshwater mussels. Animal Behaviour. 60: 879-886.
We investigated how two sympatric species of freshwater mussels
transmit their parasitic larvae to fish hosts. We found that Villosa
nebulosa and V. vibex both display large mantle lures to attract potential
host fish, but V. nebulosa displayed only at night and V. vibex displayed
mostly by day. Display periods were similar in the laboratory and in the
field. In two laboratory experiments, we found that the frequency of lure
display in both mussel species was unrelated to the presence of fish or to
the species of fish present. However, both species released more larvae in
the presence of a suitable host fish (Micropterus spp.) and a nonhost
species (Cyprinella camura) than in the absence of fish. In all treatments,
females released low numbers of larvae on a daily basis throughout the
experiment. We also observed several, irregularly occurring major release
events in which numbers of larvae released were from one to three orders of
magnitude larger than minor, daily releases. In V. nebulosa, major releases
occurred with suitable and nonsuitable host species; in V. vibex major
releases occurred mostly with suitable host species. In an additional
laboratory experiment, we found that V. vibex released large numbers of
larvae only when the host fish was able to make physical contact with the
mussel. Few larvae were released when no fish were present or when host fish
were present but physical access to the mussel was restricted. These results
show that, in mussel species that display lures, physical interaction with a
fish is necessary to stimulate large releases of larvae and suggest that
interactions with a suitable host species stimulate larger and more frequent
releases than with nonhosts.
http://www.srs.fs.fed.us/pubs/rpc/2001-11/rpc_01november_08.pdf
Taylor, Christopher M.; Warren, Melvin L., Jr. 2001. Dynamics in species
composition of stream fish assemblages: environmental variability and nested
subsets. Ecology. 82(8): 2320-2330.
Stream landscapes are highly variable in space and time and, like
terrestrial landscapes, the resources they contain are patchily distributed.
Organisms may disperse among patches to fulfill life-history requirements,
but biotic and abiotic factors may limit patch or locality occupancy. Thus,
the dynamics of immigration and extinction determine, in part, the local
structure of assemblages. We sampled fishes and stream habitat at 12
localities for two years (96 samples) to examine the deterministic nature of
immigration and extinction processes in stream fish assemblages. Mean
immigration rates for assemblages were highest at large stream localities,
where the pool of potential immigrants was largest. Mean extinction rates
were highest where variability in the flow regime was high, though local
refugia appeared to modify the extinction process at one locality.
Significant nested subset patterns in species composition occurred over time
for 7 of the 12 localities. The strength of the nesting was associated with
mean immigration and extinction rates. Higher extinction rates corresponded
to stronger nestedness, whereas higher immigration rates were associated
with weaker nestedness. Across all species, both immigration and extinction
rates were strongly associated with mean abundance. Species with high local
abundances had higher immigration rates and lower extinction rates than did
species with low local abundances. There were no significant associations
between trophic guild or body size and immigration and extinction rate. This
work supports the hypothesis that immigration and extinction rates for
assemblages are predictable along environmental gradients, and that species
are less prone to local extinction and more prone to colonize areas when
they maintain high local abundances. The extinction process in local
assemblages can be a highly ordered event leading to strong nested subset
patterns, but immigration appears to be more stochastic.
http://www.srs.fs.fed.us/pubs/rpc/2001-11/rpc_01november_12.pdf
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