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Grain is defined as the finest level of spatial resolution possible within a given data set, and extent is the size of the study area (Turner et al. 2). Geographers use cartographic scale, in which “large scale” refers to a relatively small study area; whereas ecologists commonly view large scale as equivalent to large geographic areas. In this book, we use coarse and fine to distinguish differences in grain and large and small to distinguish extent. While coarse-scale habitat models may predict the presence of species broadly across a region, more fine-scale analyses indicate that species’ distributions are often not homogenous but instead are patchy within a region.

1992). In some places, especially in the northern latitude locations that were logged more extensively in the past than they are now, forest cover is increasing due to forest regeneration (FAO 2003). In most countries, forestry is regulated, in part for environmental protection. These regulations often include the retention of corridors, especially along water courses, but few generalizations can be made about the design and ultimate utility of these efforts (Bierregaard et al. 1997, Simberloff 2001).

Brown 1971, Knowles 2001, DeChaine and Martin 2004). During interglacial periods, refugia often become reconnected. On the other hand, the rapid human-induced habitat loss and fragmentation affecting much of the globe has largely occurred in recent history (Sanderson et al. 1). Many natural processes that cause fragmentation, ranging from fire and avalanches to volcanoes and windthrow, occur with different frequency and result in an altered landscape mosaic than human-induced fragmentation. The impacts of these natural events are often significantly different than ip-hilty corrected 2-21 3/29/06 2:30 PM Page 34 34 co r r i d o r e co lo g y those of human-induced changes on the same ecosystem.