Application of random forest algorithm for studying habitat selection of colonial herons and egrets in human-influenced landscapes
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Understanding the mechanisms of habitat selection is fundamental to the construction of proper conservation and management plans for many avian species. Habitat changes caused by human beings increase the landscape complexity and thus the complexity of data available for explaining species distribution. New techniques that assume no linearity and capable to extrapolate the response variables across landscapes are needed for dealing with difficult relationships between habitat variables and distribution data. We used a random forest algorithm to study breeding-site selection of herons and egrets in a human-influenced landscape by analyzing land use around their colonies. We analyzed the importance of each land-use variable for different scales and its relationship to the probability of colony presence. We found that there exist two main spatial scales on which herons and egrets select their colony sites: medium scale (4 km) and large scale (10–15 km). Colonies were attracted to areas with large amounts of evergreen forests at the medium scale, whereas avoidance of high-density urban areas was important at the large scale. Previous studies used attractive factors, mainly foraging areas, to explain bird-colony distributions, but our study is the first to show the major importance of repellent factors at large scales. We believe that the newest non-linear methods, such as random forests, are needed when modelling complex variable interactions when organisms are distributed in complex landscapes. These methods could help to improve the conservation plans of those species threatened by the advance of highly human-influenced landscapes.
KeywordsBreeding-site selection Colonial birds Habitat selection Landscape ecology Predictive models
We thank S. Ikeno, M. Seido, and K. Takeda for supplying information about the location of some colonies. We also thank K. Ohashi and members of the Population Ecology laboratory for helpful discussions. This study was supported in part by Grant-in-Aids for Scientific Research (13740433 and 19570014) to YT from the MEXT and JSPS. Additional financial support was provided through a Monbukagakusho scholarship to L. Carrasco from MEXT.
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