Cp. Beaudoin et al., Individual specialization and trophic adaptability of northern pike (Esox lucius): an isotope and dietary analysis, OECOLOGIA, 120(3), 1999, pp. 386-396
Northern pike (Esox lucius) are often considered to be specialist piscivore
s, but under some circumstances will continue to eat invertebrates as adult
s. To examine effects of fish assemblage composition on the trophic ecology
of pike, we combined stable isotope analysis (SIA) of carbon and nitrogen
and stomach content analysis (SCA) on pike from five lakes in northern Albe
rta, three of which contain only pike ("pike-only") and two that also conta
in yellow perch (Perca flavescens) or white sucker (Catostomus commersoni)
("pike-other"). Fish were more important as prey and empty stomachs, which
often characterize piscivores, were significantly more frequent in pike-oth
er than in pike-only lakes. However, even though invertebrates were more im
portant for pike in pike-only lakes, SIA and SCA indicated that invertebrat
es were also an important component of pike diets in pike-other lakes. SIA
and SCA also revealed considerable intrapopulation variation in trophic eco
logy, with individuals in some populations differing by as much as two trop
hic levels. Comparisons of stomach contents and isotope signatures of the s
ame fish suggested that within these variable populations, specialization o
n invertebrates or fish was a long-term trait of some individuals. SIA indi
cated that trophic position increased and diets shifted to a greater import
ance of littoral prey as pike grew in pike-only lakes, but not in lakes wit
h other fish present. Trophic adaptability in northern pike is expressed at
both the population level, where the trophic ecology is sensitive to diffe
rences in prey regimes, and at the organismal level, in the form of intrapo
pulation variation and individual specialization.