Individual trophic niche specialization in American beaver (Castor canadensis)

Abstract

The American beaver (Castor canadensis) has been described as a choosy generalist at the species/population scale, yet observational studies have shown little variation in diet among individuals. We compared isotopic values of δ13C or δ15N taken from hair of 32 beaver, representing seven colonies in northern Alabama, USA to determine 1) if colonies of beaver show overlap in isotopic niche width as a result of the similar use of food resources and 2) if individual trophic niche specialization occurs within colonies. Total Trophic Niche Width varied across the wetland with the widest being twice the narrowest. Each of the five niche ellipses overlapped with ≥ two other wetlands studied. The percentages of observed variance attributed to Within Individual Component, Between Individual Component, and Between Location Component for δ13C were 37%, 33%, 30%; and those for δ15N were 16%, 56%, and 28%. Dietary nitrogen differentiated the trophic niches of individual beavers. Our results revealed that colonies across the landscape showed separation in trophic niche, lending support that the choosy generalist classification is correct at the colony scale. Our results also support individual trophic niche specialization within colonies, as seen by the substantial amount variation in both δ13C (33%) and δ15N (56%) between individuals.