Webinar - 30 Years of Change: Linking Habitat, Predators and Alternative Prey to Explain Recruitment Variations of an Endangered Caribou Population

Martin-Hugues St-Laurent
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Woodland 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 habitat structure and in interspecific interactions triggered by apparent competition between moose and caribou via the responses of two incidental predators, coyote and black bear. We also documented calf recruitment rates and analysed temporal trends in this vital rate. Our results show that the loss of high-quality habitat for caribou in the area surrounding the Gaspésie National Park varied from -30 to -56%, while the gain of preferential habitat for predators varied from +3 to +66%, mainly driven by logging. 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 in the Gaspésie Peninsula following anthropogenic habitat modifications seems to be the main mechanism responsible for the current decline in this caribou population. Our analyses revealed some impacts of habitat alteration and the complexity of the resulting trophic cascades. Moreover, we pointed out that an 802-km2 protected area is not enough to prevent the decline of a caribou herd if we drastically increase the disturbance level in the surrounding matrix.