Ta. Crowl et al., SCALES AND CAUSES OF PATCHINESS IN STREAM INVERTEBRATE ASSEMBLAGES - TOP-DOWN PREDATOR EFFECTS, Journal of the North American Benthological Society, 16(1), 1997, pp. 277-285
Streams are organized with a spatial hierarchical pattern. Investigati
ons of patterns or processes, or both, could be designed to ask questi
ons about Variance among basins, stream channels, geomorphic reaches,
habitats or solely with respect to physical/biotic processes independe
nt of spatial scale. In this paper, we present data from large-/and me
so-scale experiments performed in the Taieri River, New Zealand, and i
n a stream in the Uinta Mountains, Utah. For each of these experiments
, large-scale variance (such as land use in New Zealand) was investiga
ted with finer-scale sources of Variance such as fish predators nested
within the overall design. These designs have allowed us to make infe
rences regarding the relative importance of native Versus nonnative pr
edators in the context of existing background variation such as ripari
an vegetation, geomorphic form, and land uses within the watershed. We
use these hierarchically organized data to ask whether the spatial sc
ale of variation in abundance of mayflies and caddisflies (the most nu
merically abundant aquatic invertebrates) is dependent on the type of
predator in the stream. Specifically, we hypothesize that large, relat
ively mobile predators such as trout should homogenize local environme
nts (within riffle variation), show moderate effects within streams, a
nd result in highly variable distributions among streams. Benthic fish
, because of their moderate mobility should cause the highest Variance
at intermediate scales. Finally, in the absence of fish, stoneflies,
which show localized predator effects, should cause a high level of: v
ariation in the distribution of prey within riffles with decreasing Va
riance as scale increases.