Budy, P., G.P. Thiede, J. Lobon-Cervia, G. Gonzales, P. A McHugh, A. McIntosh, L.A. Vollestad, E. Becares and P. Jellyman. 2013. Limitation and facilitation of one of the world's most invasive fish: an intercontinental comparison. Ecology 94:356-367.
Abstract
Purposeful species introductions offer opportunities to inform our understanding
of both invasion success and conservation hurdles. We evaluated factors determining the
energetic limitations of brown trout (Salmo trutta) in both their native and introduced ranges.
Our focus was on brown trout because they are nearly globally distributed, considered one of
the world’s worst invaders, yet imperiled in much of their native habitat. We synthesized and
compared data describing temperature regime, diet, growth, and maximum body size across
multiple spatial and temporal scales, from country (both exotic and native habitats) and major
geographic area (MGA) to rivers and years within MGA. Using these data as inputs, we next
used bioenergetic efficiency (BioEff ), a relative scalar representing a realized percentage of
maximum possible consumption (0–100%) as our primary response variable and a multi-scale,
nested, mixed statistical model (GLIMMIX) to evaluate variation among and within spatial
scales and as a function of density and elevation. MGA and year (the residual) explained the
greatest proportion of variance in BioEff. Temperature varied widely among MGA and was a
strong driver of variation in BioEff. We observed surprisingly little variation in the diet of
brown trout, except the overwhelming influence of the switch to piscivory observed only in
exotic MGA. We observed only a weak signal of density-dependent effects on BioEff;
however, BioEff remained ,50% at densities .2.5 fish/m2. The trajectory of BioEff across the
life span of the fish elucidated the substantial variation in performance among MGAs; the
maximum body size attained by brown trout was consistently below 400 mm in native habitat
but reached ;600 mm outside their native range, where brown trout grew rapidly, feeding in
part on naive prey fishes. The integrative, physiological approach, in combination with the
intercontinental and comparative nature of our study, allowed us to overcome challenges
associated with context-dependent variation in determining invasion success. Overall our
results indicate ‘‘growth plasticity across the life span’’ was important for facilitating invasion, and should be added to lists of factors characterizing successful invaders.