Patterns of frugivore species richness and abundance in forest islands and in agricultural habitats at Los Tuxtlas,Mexico

Destruction and fragmentation of tropical rain forest result in a loss of species and of generating capacity of the ecosystem via animal vectors such as seed dispersal agents. To gather quantitative data regarding this ecological problem, birds and mammals were censused in 30 forest fragments, 15 agricultural islands representing five types of vegetation (coffee, cacao, citrus, pepper and mixed-crops) and in three pastures in Los Tuxtlas, southern Veracruz, Mexico. More than 6000 animals of 257 species were detected thus suggesting the existence of a rich species pool in the fragmented landscape. Frugivores accounted for 60% of species, for 72% of individuals censured and for 85% of the total animal biomass recorded. Clusters of small forest fragments (<100 ha) were richer in species and individuals than clusters of large area (>100 ha) forest islands. Pastures were especially poor in forest birds and mammals. While the agricultural islands studied contributed to only 1% of the total area of vegetation sampled, they contained 58% of all species detected and 34% of all individual birds and mammals censured. Recaptures indicated inter-island movements of forest birds and mammals. Forty percent of the species were detected in forest habitats only, the rest were detected in forest and in agricultural habitats. Seeds of forest interior plants dispersed by birds and bats were detected in the agricultural habitats. The value of agricultural islands as landscape features providing some degree of biotic connectivity among fragmented animal populations is discussed.     

Bat species richness and abundance in tropical rain forest fragments and in agricultural habitats at Los Tuxtlas, Mexico

Faced with the rapid and extensive conversion of tropical rain forests to pasture lands and agricultural fields and with the need to preserve the remaining mammalian fauna, it is imperative to determine how the different species that form the mammalian community have responded to the anthropogenic alterations of their natural habitats To provide data in this direction, we sampled bats m 45 forest islands, m 20 agricultural habitats representing five types of vegetation (cocoa, coffee, mixed, citrus and allspice), in four live-fence sites and in four pasture sites at Los Tuxtlas, Veracruz, Mexico Sampling effort resulted in the capture of 2587 bats representing 35 species In forest habitats we detected 32 species We did not capture any bats at the four pasture sites, but the at the other agricultural habitats studied, we captured 38% of the bats and 77% of the species recorded Thirty-four percent of the species recorded were present at the live-fence habitats Isolating distance was an important variable influencing species richness in forests and in agricultural habitats Only 10% of the species recorded occurred m all the habitats studied, but 77% of the species occurred m a habitat other than ram forest Recaptures of bats indicated inter habitat movements in the fragmented landscape We discuss the conservation value for the bat fauna of agricultural islands of vegetation as elements reducing isolating distances among forest fragments     

Bat species richness in live fences and in corridors of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of lowland tropical rain forests has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas. Mexico, lowland rain forests are particularly diverse in the bat fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bat species. To assess the effectiveness of corridors, among other options, to ameliorate the negative effects of fragmentation, we investigated bat species richness and relative abundance in one 6 km long section of live fences (LF) bordering a dirt road and in three 6 km long sections of residual forest vegetation along the sides of three permanent streams (BS. MS. HS). Netting of bats resulted in the capture of 967 bats. At the LF site we captured 12 bat species. 15 at the BS site. 18 at the MS site and 23 at the HS site. Species richness was associated with average area of forest fragments within a 1000 m band on each side of each corridor (r = 0.97. p = 0.01). Only 28% of the species were common among sites. Frugivorous and insectivorous species accounted for 48% each of bat captures while nectarivores accounted for 3%, sanguinivores for 0.5% and carnivore-frugivores for 0.5% Edge habitat species such as Pteronotus parnelli and Sturnira lilium accounted for 50% of the captiures. Frugivorous species such as Carollia brevicauda. Vampyrodes caraccioli. Dermanura phaeotis, D. toltecus and A. jamaicensis accounted for another 25% of bat captures. Recaptures of bats indicated bat movements from forest fragments to corridors and between corridors, with recapture distances ranging from 200 to 2000 m. Within corridor recaptures separated by several months from the original recapture date indicated individual bat revisitation to these sites. We discuss the value of these corridors to bats as stepping stones in the fragmented landscape.     

Dung beetles in continuous forest, forest fragments and in an agricultural mosaic habitat island at Los Tuxtlas, Mexico

With the aim of determining what kind of landscape mosaics might sustainmaximum diversity and minimum species loss, dung beetles were sampled withbaited pitfall traps to compare species richness and species composition in atract of continuous forest, forest fragments and a habitat island consisting ofa mosaic of forest and arboreal crops in Los Tuxtlas, southern Mexico. Wecaptured 7332 dung beetles representing 33 species. Similar numbers of specieswere captured in the three habitats. However, 56% of individuals were capturedin the continuous forest, 29% in the mosaic habitat and 15% in the forestfragments. Eight species (Canthon femoralis,Copris laeviceps, Canthidium centrale,Onthophagus batesi, Deltochilumpseudoparile, O. rhinolophus, Canthonviridis vazquezae and Dichotomius satanus) accounted for 90% of thecaptures, but their relative dominance varied among habitats. A clear trend wasevident in the number of dung beetles captured in the dung processing guilds(rollers/tunnelers) as well as in the diurnal and nocturnal guilds, withcaptures decreasing from the continuous forest to the mosaic habitat to theforest fragments. A similar trend was detected in detection rates for medium andsmall size dung producing mammals. Species richness of forest fragments andmosaic habitat did not differ from that found in the continuous forest, butthese habitats differ significantly in species richness from isolated shaded andunshaded plantations, linear strips of vegetation, the forest–pasture edge andpastures according to rarefaction analysis. The co-occurrence of the continuousforest, the mosaic habitat and the cluster of forest fragments in closeproximity seems to be preserving a diverse assemblage of dung beetle species inthe local landscape.     

Tropical rain forest conversion and perspectives in the conservation of wild primates (Alouatta and Ateles) in Mexico

The original distribution of the tropical rain forest and of the populations of Alouatta palliata, Al. pigra, and the two subspecies of Ateles geoffroyi in southern Mexico have been reduced by at least 90% in the last 40 years as a result of conversion of natural habitat to pasture and agricultural fields. This dramatic conversion has been caused mainly by the rapid growth of the human population in the southern states of the country. In the region of Los Tuxtlas in southern Veracruz, where the only longitudinal popululational and ecological studies of A. palliata and At. g. vellerosus have taken place, only 15% of the original extension of the tropical rain forest remains today. The intensive destruction of suitable primate habitat in this region has resulted in an accelerated process of extinction of the primate species. It is estimated that only about 200 At. g. vellerosus and about 1200 Al. palliata exist in the remaining small portion of their original habitat. Today, the distribution of the three primate species in Mexico is intensively and extensively fragmented, and only five potential foci for conservation exist in the country. Urgent action is required to protect the primate populations in the region of Los Tuxtlas and at the other four foci, as some of these populations may disappear by 1995.     

A preliminary study of resource overlap between howling monkeys (Alouatta palliata) and other arboreal mammals in the tropical rain forest of Los Tuxtlas,Mexico

Potential resource overlap between howling monkeys and other arboreal mammals was studied in the rain forest of Los Tuxtlas, Veracruz, Mexico. Eight species of mammals belonging to the orders Primates, Carnivora, Rodentia, and Marsupialia were found to share the canopy and to overlap trophically with howling monkeys. These mammals made up 77% and Alouatta 23% of the arboreal mammalian biomass under consideration. The arboreal porcupine and spider monkey were the only mammals that also fed on leaves. However, in this feeding niche, Alouatta is the only important mammalian folivore in Los Tuxtlas, and resource depression derived from leaf-eating insects is more important. The eight arboreal mammals may exert more pressure upon fruit resources, for they consumed 75% of the estimated total dry weight of fruit/ha/yr consumed by arboreal mammals.     

Bird species richness in vegetation fences and in strips of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of the lowland tropical rain forest has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas, Mexico, lowland rain forests are particularly diverse in the avian fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bird species. In these landscapes, linear strips of residual rain forest vegetation along streams as well as linear strips of vegetation fences (live fences) crossing the pastures might provide some connectivity to bird populations existed in forest fragments. We investigated bird species richness and relative abundance in one 6-km long section of live fences (LF) bordering a dirt road and in two 6-km long sections of residual forest vegetation along a river (MR) and one permanent stream (BS). We used point count procedures which resulted in the count of 2984 birds representing 133 species. At the LF site we detected 74% of the species, 72% at the BS site and 57% at the MR site. Only 38% of the species were common among sites. Neotropical migratory birds accounted for 34–41% of the species counted at all sites. While edge and open habitat birds accounted for 6–10% of the species and for 50% of the records at the three vegetation strips, about 90% of the species were forest birds. Distance to forest fragments and degree of disturbance of the vegetation seemed to negatively influence bird species presence at the BS and MR strips. Rarefaction analysis indicated that the LF strip was richer in species than the other two sites, but the occurrence of the three vegetation strips in the landscape seem to favor the presence of many more species. We discuss the value of these vegetation strips to birds as stepping stones in the fragmented landscape.     

Tropical rain forest fragmentation and wild populations of primates at Los Tuxtlas,Mexico

In view of the extensive destruction, fragmentation, and conversion of primate habitats to anthropogenic vegetation, information on Neotropical primate ability to use a landscape consisting of forest fragments and agricultural habitats is necessary to understand the ecological flexibility of the species involved and it is of relevance to the design of conservation scenarios at the landscape level. We censused howlers and spider monkeys in 126 forest fragments and in 44 agricultural sites at Los Tuxtlas, southern Veracruz, Mexico, and used the IDRISI Geographic Information System to assess the extent of primate habitat remaining. We conducted economic surveys to assess the productivity of several systems of land management, including cattle ranching. Seventy- five percent of native habitat has been lost at Los Tuxtlas, 20% remains in the form of isolated fragments of vegetation, and only 5% consists of contiguous rain forest at high elevations (> 800 m). Howlers and spider monkeys were present in only 60 and 8% of the forest sites investigated, respectively, attesting to extensive local extinction. Populations of both species are small and found in a fragmented and isolated condition throughout the landscape. A large number of howlers were detected in artifactual habitats such as cacao, coffee and mixed (cacao and coffee) plantations shaded by rain forest trees. Residual rain forest vegetation along streams, rivers, and lakes facilitated the interfragment and interhabitat movement of howlers. Economic surveys showed that some of the agricultural habitats were more productive than cattle ranching. Conservation of spider monkeys requires large areas of contiguous forest, but only small areas are present at high elevations. Howlers are restricted to elevations < 800 m, where most of the forest has disappeared, but can apparently exist in a matrix of forest fragments, arboreal agricultural habitats, and pasture lands. Structural aspects of the vegetation and connectivity among habitat islands may be indispensable components of both landscape scenarios.     

Diversity of Neotropical migratory landbird species assemblages in forest fragments and man-made vegetation in Los Tuxtlas,Mexico

We investigated the presence of Neotropical migratory landbirds in a 90-km² landscape in the region of Los Tuxtlas, Veracruz, Mexico. Using the fixed-radius count point procedure, migratory landbirds were surveyed in 21 forest fragments and in four replicates of shaded (coffee, cacao and mixed) and unshaded (citrus and allspice) plantations, live fences, non-arboreal crops (corn and jalapeño chili pepper) and pastures. The surveys resulted in the count of 4732 birds representing 72 species. While forest fragments accounted for 65% of the total species count, 73% of the birds were counted in the arboreal man-made habitats. Pastures contributed to 10% of the species and to 1% of the individuals counted. Live fences were particularly rich in individuals, accounting for 28% of the birds counted. Rarefaction analysis showed that forest fragments were the sites richest in species, followed by shaded and unshaded plantations and by live fences. Pastures were the habitats poorest in species, followed by non-arboreal crops. Species richness of Neotropical migratory landbirds was associated to vertical and horizontal diversity of vegetation in the habitats investigated. Shaded and unshaded plantations as well as live fences were more similar to forest fragments in species assemblages than non-arboreal crops and pastures. We discuss the conservation value of arboreal agricultural habitat and of live fences in conjunction with forest fragments as temporary habitats for Neotropical migratory landbirds that stop over or winter in Los Tuxtlas.     

Non flying mammals and landscape changes in the tropical rain forest region of Los Tuxtlas, Mexico

The rapid and extensive conversion of Neotropical rain forests to a landscape consisting of pasture lands and other agricultural habitats has meant the local disappearance fragmentation and isolation of vertebrate populations To avoid further losses in biodiversity in Neotropical rain forests, it is imperative to determine how the different species that constitute the different vertebrate communities have responded to the anthropogenic alterations of their natural habitats To provide data in this direction we sampled non flying mammals in 35 forest fragments, in six disturbed forest sites in 12 regenerating forests, in 20 arboreal agricultural habitats (cacao coffee, mixed, citrus and allspice), in four live fence sites and in four pasture sites at Los Tuxtlas, Veracruz Mexico Sampling indicated that area of forest fragments and isolating distance were important variables influencing species richness Disturbed forest had fewer species and individuals present and supported a lower non flying mammal biomass than undisturbed and regenerating forests Shaded plantations (cacao coffee and mixed) were richer in species and in individuals than unshaded ones (citrus, allspice) Species richness in forests and agricultural habitats were associated to horizontal plant diversity and vertical foliage diversity Pasture habitats were the poorest man-made habitats in non flying mammal species Live fences supported a higher biomass and species of non flying mammals than pastures and were similar to forest and shaded man-made habitats in species assemblages