Abiotic limitation and the C3 hypothesis: isotopic evidence from Gunnison's prairie dog during persistent drought

Abstract

AbstractGunnison's prairie dog (Cynomys gunnisoni) is an herbivore that ranges from desert grasslands to high‐montane meadows and is limited by disease across much of its range. The importance of abiotic drivers to the population dynamics of the species is poorly known. We employed stable isotope analysis to investigate energy assimilation patterns as indicators of abiotic limitation in arid grassland and montane populations of C. gunnisoni during a multi‐year drought. Standard ellipse areas of plasma and red blood cell carbon (δ13C) and nitrogen (δ15N) isotope values, representing population‐level foraging niche widths, declined during years and seasons of drought stress at both study sites. Prairie dogs at the montane site, but not at the desert grassland site, maintained seasonal shifts in dietary niche width corresponding to periods of favorable growth conditions for the more nutritious C3 plants. Production of offspring was strongly and positively correlated with C3 resource use as indicated by δ13C values in metabolically active tissues (plasma and red blood cells), but not with δ13C values in adipose tissues used for long‐term energy storage, or with foraging niche widths. These findings demonstrate that assimilation of energy from C3 plants is associated with increased reproductive output and that drought conditions importantly constrain the resource base available to C. gunnisoni. The link between plant nutritional quality and demographic parameters highlights the role of abiotic regulation within this reportedly disease‐limited species.