Using binary and probabilistic habitat availability indices derived from graph theory to model bird occurrence in fragmented forests
Marcelo Awade • Danilo Boscolo Jean Paul Metzger
Received: 30 May 2011 / Accepted: 11 October 2011 / Published online: 2 November 2011 Ó Springer Science+Business Media B.V.2011
Abstract Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are several difﬁculties in quantifying connectivity, including the need for species movement behavioral data and the existence offew consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indicesand to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability indices were considered as explanatory variables.
Two of these were landscape-level indices, which varied in terms of how inter-patch connections are deﬁned, using either a binary or probabilistic approach. This study produced four striking results. First, even shortopen gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability indices should consider probabilistic and notbinary inter-patch connections when intending to explain the occurrence of bird species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an ecologically scaled graph theoretical framework. Keywords Habitat connectivity Á Equivalent connected area (ECA) Á Playback technique Á Pyriglena leucoptera Á Atlantic forest Á Brazil
Electronicsupplementary material The online version of this article (doi:10.1007/s10980-011-9667-2) contains supplementary material, which is available to authorized users.
M. Awade (&) Á J. P. Metzger Department of Ecology, Institute of Biosciences, ˜ ˜ University of Sao Paulo (USP), Rua do Matao, trav. 14, ˜ No 321, Cid. Universitaria, Sao Paulo 05508-900, Brazil e-mail: email@example.com D. Boscolo ˜ FederalUniversity of Sao Paulo—UNIFESP, Campus Diadema, Rua Prof. Artur Riedel, 275, Jd. Eldorado, Diadema 09972-270, Brazil
Introduction The landscape patterns of nearly all regions of the world have been substantially altered by human activities. In particular, by converting large tracts of continuous habitat into many types of non-habitat matrices (e.g., pastures, croplands), mankind has not onlydestroyed but has also fragmented the habitats of
Landscape Ecol (2012) 27:185–198
many species. Therefore, understanding how humandriven processes that lead to reduction of habitat availability and that affect species occurrence or abundance is crucial for proposing efﬁcient management practices meant to restrain biodiversity losses. Studies using individual-based models haveshown that habitat availability is an important factor that regulates patterns of species spatial distribution and population survival in a particular area (e.g., Fahrig 1997, 1998; Flather and Bevers 2002). Nevertheless, the results of empirical studies conducted in fragmented landscapes are sometimes contradictory (e.g., Trzcinski et al. 1999; Villard et al. 1999). Plausible reasons for these...