Interacting impacts of land use and climate changes on ecosystem processes: from cyclic herbivores to predators of conservation concern.

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In recent years, evidence has emerged that dramatic changes in ecosystem processes and functioning are taking place across Europe under the joint impact of climate change and human-induced shift in land use. One of the most spectacular change concerns the populations of keystone herbivore species such as voles and moths with cyclical dynamics that took place nearly simultaneously in much of Europe in the 1990s (Ims et al 2008). Changes in small herbivore dynamics have the potential to lead to ecosystem re-organisation and therefore represent a challenge for the conservation of biodiversity, for which clear management and policy have to be addressed quickly. Indeed several European species of high conservation concern, as well as many birds of prey, are intimately linked to cyclically fluctuating prey. This project encompasses ecosystems as diverse as Lapland tundra, Norwegian taiga forest, UK upland grassland, agricultural plains of France, and agro-steppe in Spain, where small rodents are widely seen as key-stone species for a diverse guild of predators, including species of high conservation concern such as Artic fox, hen and Montagu's harrier or red kite. Interestingly, the dynamics of voles or lemmings have lost their large amplitude and regular cycles in northern areas during the last decades (Norway, UK, France), while the first outbreaks were recently recorded in the south (Spain). The impact of the rodent cycle is likely to be transmitted in the food web of these ecosystems by indirect interactions through, for instance, prey-switching by generalist predators to alternative prey and might lead to a profound re-assembly of predator, parasite and plant communities. Trophic cascades might indeed propagate and amplify between trophic levels subtle changes in primary producer phenology in response to climate change. Understanding how ecosystem processes are affected by the cascading effects of changing small herbivore dynamics is a knowledge gap with tremendous conservation implications. Along with outstanding issues of theoretical interest in population and community dynamics, the main objective of this proposal is to tackle the corollary conservation issues. Acquiring a better knowledge of these complex interactions appears to be essential for designing effective conservation initiatives for top predators and the communities to which they belong. This European collaborative project has been designed around five nested work packages progress from fundamental to decidedly applied issues. First, we will test the following nested set of four hypotheses: 1. that there is currently a geographically extensive syndrome of environmentally-driven (climate and land use), season-specific, changes in small herbivore dynamics across widely different eco-regions in Europe; 2. that these changes have disproportionate (non-linear) impacts on demographic parameters of predators that exploit cyclically fluctuating herbivore prey; 3. that these demographic changes, in turn, impact directly on population viability of predators; 4. and indirectly influence other species in the food web through a cascading effect. The issue of changing rodent dynamics is thus critically important at the European scale, with implications of profound importance to conservation and ecosystem management. Within the last work package (5), we will systematically explore the conservation corollaries of the hypotheses tested that pertain to the impacts of climate and land use changes on biodiversity and to the conservation management of exploited and pristine ecosystems in the face of global change. These include the scope for mitigating and adapting to the changes through alterations of seasonal patterns of land use, and active management of influential species. Together with policy makers and stakeholders, we will explore the ecosystem-level consequences of our findings, alternative management practices and highly-relevant policy implications.