Do small-scale exclosure/enclosure experiments predict effects of large-scale extirpation of freshwater migratory fauna?
Abstract: A variety of theoretical and empirical studies indicate that the
abilities of small-scale experiments to predict responses to
large-scale perturbations vary. Small-scale experiments often do not
predict the directions of large-scale responses, and relatively few
empirical studies have examined whether small-scale experiments predict
the magnitudes of large-scale responses. Here we present an empirical
example of small-scale manipulations predicting not only the directions
but also the magnitudes of the effects of whole-catchment, decades-long
decimation of migratory freshwater shrimp populations. In streams of
Puerto Rico (USA), we used arena sizes of < 2 m2 in 1-
to 4-week exclosure/enclosure experiments. Effects of small-scale
experiments largely matched those of large-scale shrimp loss above dams
for a variety of response variables (abiotic and biotic factors
including epilithic fine sediments, algae and organic matter, and
invertebrate grazers, detritivores, and predators). The results of our
extrapolation contrast with studies of small- versus large-scale
perturbations in the temperate zone. Our findings are likely explained
by: a set of response variables that are more dominated by within-patch
processes than exchange processes, an experimental manipulation that
encompassed the characteristic scales of response variables, our use of
open arenas lacking cage artifacts, and/or our combination of two
distinct experimental approaches (exclosures and enclosures). Based on
our study design, we suggest that extrapolation across experimental
scales can be greatly enhanced by embedding open arenas within
large-scale conditions that represent all treatment levels.
Greathouse, E. , C. M. Pringle, and W. McDowell. 2006. Do small-scale exclosure/enclosure experiments predict effects of large-scale extirpation of freshwater migratory fauna? Oecologia. 149: 709-717.
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