Linking habitat, predators and alternative prey to explain recruitment variations of an endangered caribou population

Abstract

Habitat loss, fragmentation and alteration are frequently identified as important threats to biodiversity, inducing major changes in the structure and composition of species communities and the resulting interspecific interactions. North American woodland caribou (Rangifer tarandus caribou) populations suffer from habitat modifications and most are currently in decline. It has been suggested that the conversion of old-growth coniferous forests into early-seral stages has increased cervid abundances, which have, in turn, stimulated a numerical response of predator populations, ultimately threatening caribou populations via a habitat-mediated apparent competition mechanism. Using a long-term dataset (1984–2012) of the Atlantic-Gaspésie caribou population, we quantified changes in interspecific interactions triggered by apparent competition between moose (Alces americanus) and caribou via the responses of two incidental predators, coyote (Canis latrans) and black bear (Ursus americanus). We also documented calf recruitment rates and analysed temporal trends (last three decades) in this vital rate. Inter-annual variations in autumn calf recruitment were mostly affected by the proxy of regional abundance of coyotes, which was highly correlated with moose and black bear proxies of abundance. The increase in coyote abundance proxy in the Gaspésie Peninsula following anthropogenic habitat modifications seems to be the main mechanism responsible for the current decline in the Atlantic-Gaspésie caribou population. Our analyses revealed some impacts of habitat alteration and the complexity of the resulting trophic cascades.

Keywords

• Apparent competition
• Incidental predators
• Landscape ecology
• Rangifer tarandus caribou
• Variance partitioning
• Vital rates