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chapter 5 Tropical Dry-Forest Mammals of Palo Verde ECOLOGY AND CONSERVATION IN A CHANGING LANDSCAPE Kathryn E. Stoner and Robert M. Timm Mesoamerica contains some of the world’s most diverse forests. It has at least 20 major life zones, based on variations of temperature and precipitation that can be broadly summarized in five tropical forest types—dry forest, wet forest, montane forest, coniferous forest, and mangrove swamp (Holdridge et al. 1971). When the Spaniards arrived in the New World, there were perhaps 550,000 km2 of dry forest on the Pacific side of lowland tropical Mesoamerica. This dry forest occupied as much or more of the Mesoamerican lowlands as did wet forests. Unfortunately, no habitat type in Mesoamerica has been more influenced by humans than the tropical dry forest; today less than 1 percent remains intact, with less than 0.01 percent under protection. In Costa Rica tropical dry forests occur throughout the Pacific lowlands of Guanacaste Province and adjacent Puntarenas Province from sea level to about 500 m. Costa Rica’s dry forest is characterized by a five- to six-month dry season from December through May, an annual precipitation of approximately 1,500 mm, and an average annual temperature higher than 24°C (Maldonado et al. 1995). These dry forests are largely deciduous today and encompass heterogeneous habitats varying in species composition , abundance, rainfall, and soils. These characteristics contribute to creating a harsh and heterogeneous, yet seasonally resource-rich, environment for the native mammals. Mesoamerica has a diverse mammal fauna that includes elements from both North and South America as well as endemic species. More than 275 species in 28 families are recognized from the region, at least 17.8 percent of which are endemic to Mesoamerica. The mammals of the tropical dry forest are among the most poorly known of any of the bioclimatic life zones. Mammals that inhabit tropical dry-forest areas must be capable of dealing with high temperatures (to 40–41°C), very low precipitation in the dry season, and large fluctuations in the availability 48 of food resources over time. Most mammals of the dry forest can be characterized as resident generalists that shift their diets to utilize seasonally available food resources, as resident specialists that forage on insects, seeds, or fruit and nectar, or as migrants that occupy dry forests only seasonally and migrate to different habitats during periods of low food availability in search of available food sources. As in all tropical ecosystems, a wide variety of mammals contribute to the maintenance of dry tropical forests through their role in seed dispersal and pollination (Heithaus et al. 1975; Chapman 1989; Helversen 1993; see chapter 13). Bats visit, and presumably pollinate, at least 14 species of flowers in the tropical dry forest of Palo Verde, and 29 species of fruits are consumed by bats, which in turn disperse their seeds (K. Stoner and R. Timm unpubl. data). In Guanacaste there are two peak periods of flowering activity: one during the long dry season and the other during the middle of the rainy season (Frankie et al. 1974). Primates, many rodents, and several generalist carnivores also are important seed dispersers in Costa Rica’s tropical dry forests. Thus the preservation of wildlife and its habitats are interrelated challenges, and conservation efforts in Guanacaste’s tropical dry forests need to consider both of these issues together. DIVERSITY, DISTRIBUTION, AND ENDEMISM At least 207 species of mammals, including 110 species of bats, have been documented within Costa Rica’s borders, and more will undoubtedly be discovered (Timm 1994; Rodríguez and Chinchilla 1996; Timm and LaVal 1998; Timm et al. 1999). The majority of mammals found in Costa Rica’s tropical dry forest are distributed northward through Mesoamerica (sometimes as far as western Mexico), and many occur southward into South America. Of the approximately 114 species of mammals originally present in Guanacaste ’s tropical dry forest, perhaps 110 are still found in this habitat. Bats are by far the most diverse group, with more than 66 species, followed by 11 species of rodents, 7 species of marsupials , 6 species in the weasel family, 5 species of cats, 3 species in the raccoon family, 3 species of primates, 3 species of artiodactyls, 2 species of canids, 2 species of xenarthrans (edentates), 1 rabbit (Sylvilagus floridanus), and 1 tapir (Tapirus bairdii). Species reaching the southern boundary of their distribution in Costa Rica’s dry forest include opossum (Didelphis virginiana), gray sacwinged bat...

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