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The maintenance of habitat quality and connectivity are listed among basic conservation priorities. Towards improving our understanding on the spatial patterns of animal distribution, habitat suitability models have been widely used for quantifying the landscape mosaic, detecting favourable habitats and recognising potential locations that could be of importance to species persistence. Under the same context various methods have been developed to assess connectivity (ecological, habitat or landscape). Still, such methods (i.e. habitat suitability models and connectivity assessments) are often performed separately by each other, ignoring that the spatial arrangement and connectivity of habitat patches, along with the information on their quality, could provide a more detailed picture of species' ecological responses and preferences. Habitat patches in which animals fulfill their main needs (e.g. food, mating, resting) are often recognized as highly suitable for a given species and thus are considered as of a first priority for conservation actions. As a result, a limited attention is given to the importance of the lower quality patches, which might drive movement patterns and thus could provide insights on the arrangement and succession of spatial locations.

In the present study, the proposed methodological framework is seeing connectivity as a result of the interaction between habitat selection and movement, developed using information on the movement patterns and habitat selection of male Brown bears (Ursus arctos). The brown bear is a wide-ranging predator that moves across large areas, crossing various habitats of different types. By using data on 8 male brown bears and landscape variables (north-eastern part of Pindos mountain range, in Greece), provided by NGO Calisto" - Wildlife and Nature Conservation Society, Greece - http://www.callisto.gr/en/callisto.php - collected over year of observations", a two step framework was developed that allowed the combination of habitat selection and movement as interacting processes towards revealing connectivity properties (Figure 1). The first step involved the development of habitat suitability models using satellite tracking data of brown bears. As the next step, a series of graph based models was developed by selecting and using one individual at a time to withhold from the habitat suitability models (Figure 2).

Network analyses revealed that the movement network itself demonstrates some well-studied properties regarding its structure and robustness (i.e. scale free and small world), providing insights on the contribution of patches of different quality to connectivity. Although highly suitable patches occupy central positions in the network, less suitable patches are also critical for facilitating brown bear's movement and landscape connectivity. The findings of this study raise some first insights on the importance of considering the entire habitat of brown bears in conservation planning rather than isolated patches of high quality that may have been revealed by simple habitat suitability models. The applied approach highlights the need of assessing the importance of the intervening matrix for facilitating connectivity and movement, specifically in the case of large and highly mobile species that don't perceive the landscape as strictly dichotomous.

As general methodological note, it is acknowledged that habitat suitability models are extremely useful in conservation biology since they rank the quality of the patches and provide information on the underlying landscape properties. Still, considering that these models largely ignore the selected routes as underlying processes that link spatial elements and species decisions, it becomes apparent that the combination of habitat suitability and graph models could offer an additional source of information by paying considerable attention to individuals' behavioral responses, and thus allow scientists or conservationists to judge information and quality of the landscape from an animal's perception level.

Figure 1: Methodological flow chart. Steps 1-3 involve the development of a habitat suitability model. Steps 4-5 involve the construction of a movement network by using inter-connected patches as the nodes.

Figure 2: Habitat suitability map of a male brown bear produced using telemetry data of 8 individuals, collected in the north-eastern part of Pindos mountain range, Western Greece, over a twenty-month period (April 2007 - December 2008) provide by Calisto-Greece. Habitat suitability index is classified in ten classes. Habitat maps (panel a-d) were produced by using data on 7 bears while withholding one bear to be used for the development of graph models. Dots represent the centroids of habitat patches and lines the movement among patches for the studied animal.

References

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