121 Abstract The Brazilian Northeast is dominated by the Caatinga, a xeric scrub forest characterized by “semiarid” climatic conditions, with annual precipitation often below 600 mm, and an unpredictable rainy season. North of 13ºS, the Atlantic Forest forms a narrow coastal strip, of only a few dozen kilometers in width, with a relatively humid climate. Both biomes have been subjected to intense anthropo- genic habitat fragmentation over the past few decades, although this process has different implications for each ecoregion. In Sergipe, the geographic ranges of two titi species, Callicebus barbarabrownae and Callicebus coimbrai, appear to corre- late with the Caatinga and Atlantic Forest, respectively. Titis are relatively rare in the Caatinga, in terms of both the number of populations and their density. In the lower Rio São Francisco basin, 41.2 % of Atlantic Forest fragments ( n = 17) had titi populations, whereas only 28.1 % of Caatinga sites ( n = 32) had titis. In the ecotone between the two (the Agreste), however, no populations were found ( n = 21), sug- gesting a lacuna in their distribution. Population surveys at sites representative of the distribution of the two titi species indicate that the density of C. coimbrai may be two to four times higher than that of C. barbarabrownae. Overall, the data appear to indicate that while the survival of titi populations in the Caatinga may be depen- dent on factors such as fragment size and the presence of groundwater, the survival of the populations of the Atlantic Forest may be more closely related to more ran- dom factors such as the history of colonization. Chapter 9 Living on the Edge: Habitat Fragmentation at the Interface of the Semiarid Zone in the Brazilian Northeast Stephen F. Ferrari, Eduardo M. Santos Junior, Evellyn B. Freitas, Isadora P. Fontes, João Pedro Souza-Alves, Leandro Jerusalinsky, Raone Beltrão-Mendes, Renata R.D. Chagas, Renato R. Hilário, and Sirley A.A. Baião S.F. Ferrari (*) • E.B. Freitas • I.P. Fontes • S.A.A. Baião Federal University of Sergipe, São Cristóvão, Sergipe, Brazil e-mail: ferrari@pq.cnpq.br E.M. Santos Junior Chico Mendes Institute for Biological Diversity, Macapá, Amapá, Brazil J.P. Souza-Alves • R. Beltrão-Mendes • R.R.D. Chagas • R.R. Hilário Federal University of Paraíba, João Pessoa, Paraíba, Brazil L. Jerusalinsky Brazilian Primate Protection Center, João Pessoa, Paraíba, Brazil L.K. Marsh and C.A. Chapman (eds.), Primates in Fragments: Complexity and Resilience, Developments in Primatology: Progress and Prospects, DOI 10.1007/978-1-4614-8839-2_9, © Springer Science+Business Media New York 2013