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Habitat Suitability And Distribution Models: Wi...


Habitat Suitability And Distribution Models: Wi...

Montane and alpine species are expected to be considerably influenced by global warming (e.g., the American pika [13], the White-tailed Ptarmigan [14], the Black Grouse [15]). In particular, alpine plants and animals in Japan are considered to be vulnerable to climate change, because they already inhabit mountain tops, and consequently cannot shift to higher elevation refuges in response to global warming. The Rock Ptarmigan Lagopus muta, which has low fecundity, high survival, a long generation time, and slow population recovery [16], is adapted to arctic and alpine environments, with some southern populations being isolated in alpine habitats as relicts of the glacial epoch [17]. In the Swiss Alps, Revermann et al. [18] predicted that up to two-thirds of potential L. muta helvetica habitat will be lost by 2070 and showed that potential habitat would shift toward mountaintops by using several statistical modeling approaches, including species distribution models. Consistent with this prediction, in some regions of the Swiss Alps, volunteer observers have increasingly recorded Ptarmigans at higher elevations over the last three decades [19]. In Europe, L. muta populations are likely to decline under warming scenarios, with a projected 54% decline in suitable climate space from the present to the 2080s [20].

To assess the impact of climate change on the distribution of L. muta japonica in the alpine zones of central Japan, we developed a species distribution model that included three sub-models (Fig. 2). The model was constructed based on the hypotheses that the functional relationships of L. muta japonica depend highly on the alpine plant communities in terms of quantity and quality, which depend on climate at macro-scales and topography at small scales. The model was constructed in two main parts. The first part of the model aimed to predict potential habitat for L. muta japonica based on the area fractions of three alpine vegetation communities and distance from the ridge (sub-model A). The second part of the model aimed to predict the area fractions of alpine vegetation communities based on climatic and topographic variables (sub-model B1 and B2). Potential habitats for L. muta japonica under future climate change scenarios were projected by applying the future area fractions of alpine vegetation communities, which were predicted from sub-model B2, on sub-model A. All of the models (sub-model A, B1 and B2) were developed by using R2.15.2 [42]. Detailed explanations of each model are provided in the following sections.

We developed two sub-models to predict the area fractions of alpine vegetation communities (B1 and B2). In general, plant species distributions are assumed to be controlled by climate at large scales and by non-climatic factors at small scales, including topography, soil conditions, and biotic interactions [47]. In the present study, we assumed that climatic conditions control the occurrence of alpine vegetation zones at macro-scales, whereas topographic conditions with climatic suitability control the area fractions of alpine vegetation communities at micro-scales. On the basis of this assumption, we constructed two sub-models by using different explanatory variables at different spatial scales for each sub-model as follows.

The predicted potential habitat for L. muta japonica was comparatively similar to the actual distribution of the territories in the study area (Figs. 1 and 3). However, empty habitat (i.e. areas with suitable environmental conditions but no current occurrence of the species) was found in some areas (Fig. 3).

Incorporating both large scale (i.e. climatic) and smaller scale factors, including biological interactions, microtopography, and microclimate, is important for realistic predictions of species distributions, which is essential for practical spatial conservation planning [46, 52]. Previous studies that have predicted the poten


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