The understory bat community in a fragmented landscape in the lowlands of the Los Tuxtlas, Veracruz, Mexico

Resumen

Bat species in Neotropical regions are known to reach a high diversity. The Chiropteran fauna contributes significantly to the ecological dynamics of tropical forests and are excellent indicators of the state of conservation. The Los Tuxtlas, Veracruz has suffered severe habitat degradation and forest fragmentation in the last four decades, mostly due to anthropogenic activities. The main objective of the present study was to describe in terms of species richness, feeding guild, biomass, and dominance, the little known bat community of the Parque de Flora and Fauna Silvestre Tropical (PAFFASIT) in the municipality of Catemaco, Veracruz. We expected that after nearly 30 years of ambient protection that this study site would maintain its functional diversity, as well as complexity in the bat understory assemblage. Since the relationship between richness and abundance is regulated by area size and the structural complexity of the vegetation, we hypothesize that in the PAFFASIT, a small number of species in the understory are dominant in terms of abundance and biomass. Fieldwork was conducted from November 2007 to November 2008. Sixteen mist nets were operated on four consecutive nights monthly from dusk until 0300 hours. All bats captured were processed and released in the field. We estimate the overall species diversity. A species accumulation curve over time was constructed. All species were assigned a feeding guild. Sampling effort totaled 1344 net/hours. We captured a total of 509 individuals, which represented 22 species. The Phyllostomidae family accounted for 98% of the total captures. Four species of this family, Sturnira parvidens, Carollia sowelli, Artibeus jamaicensis and Glossophaga soricina, alone accounted for 79 % of the total captures. The frugivore guild had the highest number of species (68 % of total captures). Two species, S. parvidens and C. sowelli, represented 57 % of the total gross biomass of the sample. The Shannon-Wiener Index value was 1.97 for the overall sample. New species were added slowly each month, but after nine months the accumulation curve tended to reach an asymptote. Nine species were added to the bat inventory for this site. In PAFFASIT due to the slow accumulation of species the number of bat species may increase as more surveys are carried out. In our study, we initially hypothesized a dominance by a few species. Our results concur with our prediction; as we found four species, S. parvidens, C. sowelli, A. jamaicensis and G. soricina that dominated the bat assemblage. In agreement with our hypothesis, results revealed the presence of a rich understory assemblage of bat species, which is similar to other findings in neotropical forests, but with a different species composition. The four species, belonging to the Phyllostomidae family accounted for 79 % of all captures, as well as 68 % of the total captures of the frugivore guild. The PAFFASIT forest reserve probably serves as an important link between two large areas of relatively well-preserved rainforest immersed in an anthropogenic landscape. The bat community, we observed at the PAFFASIT seems to be a simplification of that of mature rainforests in Los Tuxtlas, and it is noteworthy the absence of rare or sensitive animalivorous bat species such a as Chrotopterus auritus, Lophostoma evotis, Trachops cirrhosus and Vampyrum spectrum.