Forest Fragmentation Modifies Habitat Quality for Alouatta palliata

Fragmentation reduces habitat area, increases the number of habitat patches, decreases their size, and increases patch isolation. For arboreal mammals such as howlers (Alouatta palliata), canopy modifications from fragmentation processes could also negatively affect habitat quality. We analyzed changes in the composition and plant structure of 15 fragments (1–76 ha) and compared them with vegetation from a continuous tropical rain forest reserve (700 ha) in Los Tuxtlas, Mexico. At each site, we sampled 1000 m² of all trees, shrubs, and lianas with a diameter at breast height (DBH) ≥10 cm. We obtained estimates of species richness, density, and basal area for different ecological groups, DBH ranges, and top food resources for howlers. We used a stepwise multiple regression analysis to determine relationships between fragment characteristics (size, shape index, and isolation) and plant variables. Compared to continuous forest, fragments have altered composition and plant structure, with large trees absent from the canopy. The basal area of top food resources is higher in continuous forest. Fragment size is the best explanation for the differences in composition and plant structure. The largest fragments had greater basal area of top food resources and more large primary trees in the canopy. Overall, our results suggest that fragmentation altered the habitat quality for howlers.     

Effects of forest fragmentation on the physiological stress response of black howler monkeys

Habitat loss and fragmentation can create severe environmental problems for forest species, and may ultimately lead to local population extinction. One mechanism that might play a role in this process is the physiological stress response of individuals, because animals that experience chronic stress might show reduced rates of reproduction and survival. In this study, we investigated whether black howler monkeys Alouatta pigra inhabiting forest fragments experienced greater physiological stress than those in continuous forest. Faecal cortisol metabolite levels were compared between monkeys inhabiting fragmented and continuous forests in Southern Mexico. The sex of the animals was taken into consideration, while activity patterns and aggressive events were also recorded to examine differences in behaviour and sociality. A chemiluminescent enzyme immunoassay was utilized to determine faecal cortisol metabolite levels. Our results showed that cortisol metabolite levels were higher in howler monkeys from forest fragments, and that they vary through time. Patterns of locomotion also differed between forest types, as monkeys from fragments travelled at higher frequencies, while monkeys from continuous forests performed more of their movements within tree crowns. There was no difference in the frequency of feeding, resting and social interactions between fragmented and continuous forest monkeys. Higher faecal cortisol metabolite levels in fragmented areas are likely the result of suboptimal environments and could have long-term adverse effects on monkey health, fertility and survival. We propose that faecal cortisol metabolite measurements can be a useful conservation tool for monitoring populations of long-lived species subsisting under suboptimal conditions.     

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.     

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.     

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.     

The Importance of Tropical Rain Forest Fragments to the Conservation of Plant Species Diversity in Los Tuxtlas, Mexico

Of what value are forest fragments to the conservation of the tropical rain forest diversity for a landscape? We compared the changes in composition, diversity, and plant structure of 15 small (1–76 ha) relatively unprotected forest fragments with those of a large (700 ha) well protected fragment (LWPF) in Los Tuxtlas, Mexico. The trees, shrubs, lianas, palms, and herbs with dbh?≥?2.5 cm were sampled in 1000 m² at each site. For each ecological group (based on light requirements for germination: primary, secondary, and non-secondary light demanding, NSLD, species) and life form, estimates of species diversity, density, and basal area were analyzed using a stepwise multiple regression to determine whether there were any relationships between these variables and fragment characteristics (size, shape index, and isolation). The composition and plant structure of LWPF were different from those of the small fragments and large trees are absent from the canopy of the latter. Fragment size best explained the differences in composition and plant structure. Species composition in the largest fragments was similar to that of LWPF, but there was no significant difference in total richness between LWPF and the fragments, even though both the richness and abundance of secondary and NSLD species did differ. LWPF had more large primary trees in the canopy, and a greater abundance and basal area of palms and herbs. For tropical rain forest conservation, it is important to maintain the greatest possible number of large fragments and establish policies that prevent forest remnants from being further reduced in size and increasingly isolated from each other.     

Feeding and general activity patterns of a howler monkey (Alouatta palliata) troop living in a forest fragment at Los Tuxtlas,Mexico

The feeding behavior and general activity patterns of a howler monkey troop living in a 3.6 ha forest fragment were studied at Los Tuxtlas, Mexico, for an annual cycle. Monthly samples of their feeding behavior indicated that they used 52 species of 24 plant families as sources of food. Of these, 67% were trees, which accounted for 96% of total feeding time recorded. Ten species of Moraceae, Cecropiaceae, Anacrdiaceae. and Sapotaceae contributed to 70% of the trees used and to almost 90% of feeding time. The number of plant species used per monthly record varied from 7 to 31 with an average of 19.9 species. Young leaves and ripe fruit were the principal items in the monthly diet of howlers and average percent of time spent consuming these plant parts was 46.7% and 34.8%, respectively. The use of tree species was found to be associated to their importance value and to their pattern of spatial dispersal in the study site. Availability of young leaves was fairly constant from month to month, but it presented a seasonal pattern, and there was a significantly lower number of tree species bearing ripe fruit through the year with brief pulses of production. The monthly activity pattern was found to be related to variations in the availability of young leaves and ripe fruit as well as to the values of the intermonthly overlap in plant species used. Resting and feeding presented a bimodal pattern of occurrence throughout the day that seemed to be related to variations in maximum ambient temperatures. Results are discussed in light of the small size and shape of the forest fragment inhabited by the howler troop. Am. J. Primatol. 48:167–183, 1999. © 1999 Wiley‐Liss, Inc.     

Chromosome studies in Alouatta belzebul

The chromosome constitution of Alouatta belzebul was studied with G-, C-, and silver staining. In ten specimens identified as Alouatta belzebul, the chromosome constitution of males (2n = 49) differed from that of females (2n = 50) owing to a Y-autosome translocation. In another single female specimen, probably Alouatta belzebul nigerrima, the diploid chromosome number was also 50, though its karyotype was drastically different from that of Alouatta belzebul belzebul. Chromosome studies, taken together with phenotypic and field observations, suggest that Alouatta belzebul belzebul is phenotypically variable in respect to pelage coloration. This attribute is therefore unreliable for the precise identification of Alouatta belzebul subspecies. Conversely, relatively minor phenotypic differences, allowing for the characterization of subspecies within a same species, coexist with unparalleled, drastic karyotypic divergence. These findings clearly question gross morphological attributes as discriminative characteristics of Alouatta belzebul subspecies.