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SCALETOOL IntroductionDriversBiodiversityPolicies and managementConnectivity and protected areas

Evaluating the connectivity of a protected areas network under the prism of global change: the case of four birds of prey

To preserve biodiversity, networks of protected areas have been established worldwide, like the Natura 2000 network across the European Union (EU), currently consisting of more than 26,000 sites covering 17.5% of EU terrestrial territory. Previous studies have shown that climate change and land use changes could significantly alter the effectiveness of conservation networks. These studies have attempted to quantify these sources of threat by providing evidence on the number of sites becoming unfavorable for species persistence. Still, the efficiency of the Natura 2000 network to mitigate the detrimental effects of land use and climate change remains an open research question. Here, we show that current distribution of the Natura 2000 network could facilitate connectivity between sites for some birds of prey, providing rather robust sub-networks that could favor species conservation. Here, an attempt was made to examine the current and future geographical ranges of four birds of prey under scenarios of both land use and climate changes.

The proposed framework includes three basic steps: a) development of species distribution models using climate and habitat variables, b) design of graph models based on current and future distributions of species and c) estimation and comparison of graph properties and statistics. We focused our analysis on four birds of prey with different dispersal abilities: Gyps fulvus, Aquila chrysaetos, Neophron percnopterus and Aquila pomarina. The first step of the analysis consisted of the development of a series of models to predict present and future species distribution under scenarios of climate and land-use change. Details on model development can be found in Barbet-Massin et al., 2012. In short, presence/absence species data were related to climate and land use variables across the species' distribution at a 0.5° spatial resolution (~50km). The future consensus distributions were then obtained by projecting the models under different climate and land use scenarios (SRES: A1B, A2 and B1). Current and future modeled distributions of the selected species were overlaid to the Natura 2000 network map. Next, sites that have been recognized to support each species of interest were selected and used for the development of graph-based models by considering each site as a node. The linkage between any two sites was plausible only if their Euclidean distance was smaller or equal to the median dispersal distance of the species. Graphs were also produced considering the future distribution of species under climate and land-use changes. A series of network statistics were employed to evaluate the properties of species-networks and identify potential differences in these properties between those networks describing current and future distribution.

Despite the fact that some protected areas currently occupied by the species are predicted to become unsuitable due to global change, the connectivity of the remaining occupied network should only slightly change from present day conditions. Existing protected areas that would become unsuitable for the studied species are not a random sample of areas, but are characterized by lower connection to other sites and low values of network centrality and therefore their removal causes less disruption of the network flow than random node removal. Our findings highlight that there is a need to adapt more species specific conservation policies with a flexible conservation strategy that would ensure inclusion of sites that would ensure future range expansions. Aquila pomarina is predicted to disappear from the southern part of its range and to become restricted to northeastern Europe (see Figure). Corridors or assisted migration may help to preserve this species' genetic diversity. Gyps fulvus, Aquila chrysaetos, and Neophron percnopterus are predicted to locally lose some suitable sites; hence, some isolated small populations may go extinct. However, their geographical range and metapopulation structure will remain relatively unaffected throughout Europe. These species would benefit more from improved habitat quality and management of the existing network of protected areas than from increased connectivity or assisted migration. As a concluding remark, it is suggested that it is critical for efficient conservation under the prism of global change, that a flexible design of the networks should ensure the addition of new sites but also the expansion of the size of already existing protected areas. This is mainly due to the fact that, although future species ranges might include new sites that are not protected under a conservation network, extinctions that could occur at the southern areas might not be balanced by potential colonization of such sites.



Network structure of Gyps fulvus, Aquila chrysaetos, Neophron percnopterus, Aquila pomarina (from top to bottom) based on current (left column) and future (right column) distributions (Mazaris et al. 2012.



References

Barbet-Massin M, Thuiller W, Jiguet F (2012) The fate of European breeding birds under climate, land-use and dispersal scenarios. Global Change Biology 18: 881-890.

Mazaris AD, Papanikolaou AD, Barbet-Massin M, Kallimanis AS, Jiguet F, Schmeller D, Pantis JD (2013) Evaluating the connectivity of a protected areas' network under the prism of global change: The efficiency of the European Natura 2000 network for four birds of prey. Plos One 10.1371/journal.pone.0059640

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