Parasites and their hosts maintain an evolutionary relationship that keeps a dynamic equilibrium between their populations.1,3,13 However, during the process of fragmentation, as available habitat decreases, organisms get clumped into the remaining fragments, with the consequence that transmission of infectious diseases and parasites is facilitated.8,10,16,17 In fact, the incidence of parasitism is much higher near edges than in forest interiors and in more fragmented than in less fragmented forests.18 It is already known, for example, that fragmentation promotes higher infestation indexes due, probably, to the limited space available which forces visitation to the same trees and increases population densities.13,6 This condition may contribute to population declines and even to the total extinction of a population.
Loss of habitat is considered as the main reason for biodiversity decline and it is clearly causing a loss of species from tropical forests.2,4 In particular, the destruction of habitat is the principal factor affecting the conservation of primate species in Mexico.5,14 Like most rainforest ranges around the world, the one of Sierra de Santa Marta, Veracruz, Mexico, has been subject of important transformation; therefore, howler monkeys (Alouatta palliata mexicana) inhabiting this landscape have been isolated for many years due to deforestation. Several studies at Santa Marta have already suggested connecting fragments of forest to increase chances of long-term survival of these primates. However, there is concern that corridors may allow the movement of undesirable species, i.e., exotic species and parasites, along with the target species.9,11 Thus, increased movement of the host individuals among fragments may result in higher prevalence, higher parasitic loads and increased rate of spread of contagious diseases and parasites.7
At Santa Marta, the risk of transmission of endoparasites between howler monkey populations inhabiting forest fragments was assessed at two different scales: First, veterinary techniques allowed the determination of the diversity and endoparasite burden in the howler groups. Finally, we evaluated potential scenarios at a landscape scale, in the event connections between patches were implemented in the future. Since parasite diversity and parasite burden are related to the area and the extent of fragmentation, parasitology studies may formulate important recommendations to conservation and management programs of species such as howler monkeys.
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