Predicting declines in avian species richness under nonrandom patterns of habitat loss in a Neotropical landscape

Abstract

Abstract. One of the key concerns in conservation is to document and predict the effects of habitat loss on species richness. To do this, the species-area relationship (SAR) is frequently used. That relationship assumes random patterns of habitat loss and species distributions. In nature, however, species distribution patterns are usually nonrandom, influenced by biotic and abiotic factors. Likewise, socioeconomic and environmental factors influence habitat loss and are not randomly distributed across landscapes. We used a recently developed SAR model that accounts for nonrandomness to predict rates of bird species loss in fragmented forests of the Panama Canal region, an area that was historically covered in forest but now has 53% forest cover. Predicted species loss was higher than that predicted by the standard SAR. Furthermore, a species loss threshold was evident when remaining forest cover declined by 25%. This level of forest cover corresponds to 40% of the historical forest cover, and our model predicts rapid species loss past that threshold. This study illustrates the importance of considering patterns of species distributions and realistic habitat loss scenarios to develop better estimates of losses in species richness. Forecasts of tropical biodiversity loss generated from simple species-area relationships may underestimate actual losses because nonrandom patterns of species distributions and habitat loss are probably not unique to the Panama Canal region.

Conserving biodiversity in managed forest landscapes: The use of critical thresholds for habitat

“…These are the mechanisms that are altered once a threshold is passed and that explain the short-or long-term decline of the population. Several recent studies (Betts et al 2006, Rompré et al 2009) have shown that thresholds do indeed exist for species with large home ranges, which confirms predictions made using models (Lande 1987;Andrén 1994;Andrén et al 1997;With and King 1999;Fahrig 2001Fahrig , 2003. In forest environments, regardless of the type of forest, habitat loss is defined as a decrease in the area occupied by the forest type.…”

“…The scientific literature describes two types of thresholds, the first refers to one or more species populations affected by habitat loss (Andrén 1994, With and King 1999, Fahrig 2003, while the second, more recently described, concerns the number of species (species richness) affected by a loss in habitat (Radford et al 2005, Rompré et al 2009). …”

“…This indicates that a species would have a greater chance of surviving in large areas of continuous habitat, but will become more at risk for extinction if there is a loss of habitat or if the habitat becomes fragmented. Thus, the proportion of habitat below which a population cannot maintain itself varies with (1) the species in question (Mönkkönen and Reunanen 1999, Guénette and Villard 2004, Saint-Laurent et al 2009), (2) the degree of fragmentation of the original habitat (Rompré et al , 2009, and (3) the spatial configuration of the residual habitat (Drapeau et al 2000;Fahrig 2003, Betts andVillard 2009).…”

“…According to this approach, the critical habitat threshold can be found not only at the level of a population, but also for the species richness found within an ecological community Rompré et al 2007Rompré et al , 2009). Few studies have been conducted in this area of ecology with most of the results coming from tropical environments where the loss of habitat and fragmentation are typically synonymous with species extinction (Pimm et al 1995, Brooks et al 1999.…”

“…This phenomenon has not only been observed in the tropical forests of Panama , and Australia (Radford et al 2005), but also in the mixed boreal forest (Drapeau et al 2000), and within urban forests (Marzluff 2005). By using the species-area relationship (Rosenzweig 1995, Seabloom et al 2002 to compare bird species communities within forest fragments in Panama, Rompré and collaborators recently published predictions calculated from empirical data representing the reduction in the number of species following a decrease in habitat area (Rompré et al 2009). They predicted a massive loss of species following the loss of habitat to a level of residual habitats between 30% and 40% of their original area ( Fig.…”