Leaf traits of tropical tree species are known to operate as intrinsic determinants of insect herbivory. However, we know little about how habitat fragmentation affects these traits and what, if any, are the consequences of this process on herbivory. We tested the effects of forest fragmentation on the leaf traits of sapling of four light-demanding species: Acalypha diversifolia, Hampea nutricia, Myriocarpa longipes, Siparuna thecaphora, and two shade-tolerant species: Pseudolmedia glabrata and Garcinia intermedia, in Los Tuxtlas, Mexico. We also conducted an acceptability assay with a generalist herbivore Spodoptera frugiperda. Plant traits did not change with forest fragmentation, but did with plant regeneration mode and species identity. Light-demanding species had significantly higher water content, nitrogen concentration and specific leaf area than shade-tolerant species. The latter had significantly higher leaf strength, carbon concentration and carbon:nitrogen ratio. Acceptability was affected by fragmentation but only in P. glabrata; plant tissue from forest fragments was consumed 2.6 times more than that from continuous forest. We conclude that forest fragmentation did not affect leaf traits in this site.

Contemporary defaunation of fragmented forests potentially alters patterns of seed predation and dispersal. Alternatively, the remaining fauna may compensate for missing animals, resulting in equivalent rates of seed dispersal and predation. In the Los Tuxtlas region of southern Mexico, populations of large terrestrial fruit-eating mammals are diminished or absent from many forest remnants. This study reports fruit removal and seed predation patterns of Poulsenia armata (Moraceae), in forest fragments and a continuous forest (LTBS). Contrary to expectation, we found no differences in seed predation (mean ± SD) between LTBS (7.2 ± 1.8 seeds per station) and forest fragments (5.6 ± 1.1). However more fruits were removed in the LTBS (11.4 ± 0.9 fruits per station) than in forest fragments (8.1 ± 0.8). Animal activity, recorded by camera traps, differed between animal guild with fewer seed dispersers in forest fragments (mean = 0.43 ± 0.02 photos wk−1) than in the LTBS (mean = 0.68 ± 0.05). Fruits and seeds attracted many species of mammal (n = 12) in both habitats, indicating substantial redundancy. Remnant forest patches in the Los Tuxtlas landscape retain great ecological value, both as refuges for mammals and habitats for trees, such as P. armata.

A comparison is made of the light acclimation potential of seedlings of three canopy species of the tropical rain forest of Los Tuxtlas, Mexico: Cordia megalantha, Lonchocarpus guatemalensis, and Omphalea oleifera. These species showed similar growth rates in a range of microhabitats. Gap dynamics were simulated by transferring plants between three environments: beneath a closed canopy, a small gap, and a large gap. Plants of all three species were able to adjust their morphology and growth rates in response to changes in light availability. Growth rates increased when plants were moved to a (larger) gap, and decreased when plants were moved to a more shaded environment. Shade-grown plants were able to acclimate faster to increasing light availability than sun-grown plants to decreasing light availability. Also, plants moved from shady to sunny conditions showed higher relative growth rates than sun control plants, whereas sun-grown plants when moved to the shade showed lower relative growth rates than shade control plants. Species differed in their response to gap dynamics. Omphalea could not acclimate morphologically to shading, but reacted faster than the other species in response to the occurrence of a large gap. Acclimation potential seemed to be related to plasticity in physiological rather than in morphological traits. Suppressed seedlings of all three species performed well in the shade, and were able to acclimate rapidly to gap-conditions.

Conversion of tropical evergreen forests to crops or pastures results in significant depletions of terrestrial carbon (C) pools. Root biomass and root C pools were quantified in tropical evergreen primary forest, and in secondary forests and pastures of different ages, in the Los Tuxtlas Region, Veracruz, Mexico. Total root biomass to 1-m depth ranged from 19 to 27 Mg ha-1 in primary forest, from 5.5 to 22.5 Mg ha-1 in secondary forests (8-, 20- and 30-y-old), and from 3.1 to 5.4 Mg ha-1 in pastures (12-, 20- and 28-y-old). Large roots (> 20 mm in diameter) were largely absent below 40 cm depth in secondary forests and pastures. Roots in the 0–40 cm soil depth represented 60–76% of the total root biomass in primary forest, 77–93% in secondary forests, and 89–96% in pastures. Root biomass comprised 4.7–6.2% of the total biomass in primary forests and between 6.8–8.5% in secondary forests. These low values, the relatively high concentration of roots in the top 40 cm of soil, and the shallow depth at which large roots occurred in secondary forests suggest forest susceptibility to natural disturbances. Root C pools ranged from 7.9 to 11.6 Mg ha-1 in primary forests, from 2.1 to 9.6 Mg ha-1 in secondary forests and from 1.0 to 1.9 Mg ha-1 in pastures. The estimated total ecosystem C pool in primary forest was 415 Mg ha-1, it ranged from 187-246 Mg ha-1 in secondary forests, and was 179 Mg ha-1 in pastures. Tropical forest conversion to pasture decreased the root C pool by nearly 80% and represented a 94% loss of C in ecosystem biomass. Absolute losses of root C were nevertheless small when compared with the above-ground C loss. Carbon distribution among ecosystem biomass components is key to adequately understanding the consequences of land-use/cover change on C dynamics in tropical regions.

In lowland tropical and temperate forests, nitrogen (N) and phosphorus (P) resorption from senesced leaves may reflect a mechanism of conservation of a limiting nutrient (Edwards & Grubb 1982, Killingbeck 1996, Proctor et al. 1989, Scott et al. 1992, Songwe et al. 1997, Vitousek & Sanford 1986). At the ecosystem level it has important implications for element cycling. The nutrients which are resorbed during leaf senescence are directly available for further plant growth, which makes a species less dependent on current nutrient uptake. Nutrients which are not resorbed, however, will be circulated through litterfall in the longer term (Aerts 1996).

Rain forests at Los Tuxtlas are islands surrounded by anthropogenic vegetation containing invasive species. Epizoochory is an important dispersal syndrome among invasive species but ecological studies are scant. In order to evaluate the movement of epizoochore diaspores into the mature forest, we selected two abundant secondary herbs with contrasting diaspore morphology, and five dispersers with different pelage type. We used stuffed mammals as a dummy and passed them through patches of these two plant species, counting the number of adhered diaspores. For dispersal into the forest, diaspores were manually adhered to dispersers, these were pulled along 100-m forest transects, counting the number of diaspores remaining at distance intervals. We observed the highest amount of detachment in the first 20 m of the forest edge. For Desmodium incanum diaspores with sticky hairs, adhesion to dispersers showed no differences among pelage types, therefore dispersal is determined mainly by diaspore detachment. Dispersers with long pelage (Didelphis marsupialis, Nasua narica and Procyon lotor) move diaspores for shorter distances, while dispersers with short pelage (Silvilagus floridanus and Philander opossum) are more likely to move diaspores for longer distances. In Pavonia schiedeana more diaspores (seeds with spines and hooks) were attached and remained attached on dispersers with long and thick pelage. Mean distance travelled for P. schiedeana diaspores varied between 11 and 2700 m. In D. incanum the distance travelled did not exceed 500 m. Based on comparisons between dispersal patterns and on ecological data of these two plant species and their potential dispersers, P. schiedeana has a higher probability of invading the forest and finding suitable habitats for establishment than D. incanum.

Effects of litter cover on insect herbivory, leaf-fungal damage, and seedling performance (survival, growth in height and leaf number), were assessed on established Nectandra ambigens seedlings in three sites of a Mexican tropical rain forest. Naturally occurring seedlings were measured for height, leaf number and standing levels of leaf damage by herbivores and pathogens. Thereafter, seedlings were exposed for 1 y to three litter treatments: (1) litter addition, (2) control and (3) continuous litter removal. There was a significant effect of site on the proportion of surviving seedlings and on the relative growth rates in terms of leaf number. Overall, seedlings with higher initial leaf number showed higher survival and produced more leaves after 12 mo than seedlings with lower initial leaf number. Litter addition resulted in seedlings with lower relative growth rates in height and higher levels of damage by herbivores and pathogens. On average, leaf area damaged by pathogens was < 6% and herbivory was < 27%. Seedlings with higher levels of herbivory showed higher levels of pathogen attack. Herbivory and pathogen attack had no effect on seedling performance. This study reveals the importance of litter-cover on the interactions between seedlings, herbivores and pathogens, as well as on the performance of tropical seedlings.

In abandoned pastures where the seed bank of forest species has been depleted and a seedling bank does not exist, dispersal events are the only source of forest seeds for natural regeneration (Gómez-Pompa & Vázquez-Yanes 1981). Lack of dispersal has been reported as an important limitation for rain-forest regeneration in pastures (Hardwick et al. 1997 in Thailand; Holl 1999 in Costa Rica; Nepstad et al. 1990 in Brazil) or colonization of fallow land (Kollmann 1995). A high percentage of tropical plant species have fleshy fruits that are dispersed by birds and flying and terrestrial mammals (Howe & Smallwood 1982, Snow 1981). In this study we report the spatial distribution of fleshy-fruited species dispersed to tropical pastures at different distances from the vegetation border in 12 tropical pastures as a measure of the instant regenerative potential of these sites.

The structure, composition and reproductive phenology of a bat assemblage were investigated in the tropical region of Los Tuxtlas, Mexico. A 90-km2 landscape, originally occupied by rain forest, consisted of forest fragments and natural corridors of vegetation surrounded by pasturelands. Artificial strips of vegetation also were present as live fences. Bats were sampled with mist nets set at ground level in 52 forest fragments, three corridors, nine shaded plantations, six unshaded plantations and three live fences. We sampled each site twice, each time for a 5-h period for two consecutive nights. Bats were captured and released and the species identity and reproductive condition of adult females were recorded. Annual fruiting phenology and fruit production was measured with fruit traps in a forest site in three 500 × 20-m transects. We captured 4799 bats of 39 species. At forest sites we recorded 97% of the species and captured 44% of the bats. In corridors we captured 76% of the species and 16% of the total individuals. In the plantations we captured 71% of the species and 32% of the individuals. In the live fences we captured 32% of the species and 8% of the individuals. Three species, Pteronotus parnelli, Carollia brevicauda and Glossophaga soricina, accounted for 52% of all bat captures. Fruit-eating species and fruit-eating insectivores accounted for 65% of captures. Fleshy fruits were available year-round, but a seasonal pattern was evident. Presence of lactating females seemed to be associated, in general, with rainfall and fruiting seasonality, but individual species displayed different patterns ranging from aseasonal polyoestry to seasonal bimodal polyoestry, seasonal polyoestry and seasonal monoestry. Despite extensive fragmentation of the original rain forest, a species-rich bat assemblage still exists in the landscape studied. Short distances among remaining forest fragments and man-made habitats seem to facilitate persistence and reproductive connectivity among members of this bat assemblage.

At Los Tuxtlas, Mexico, presence of dung and carrion beetles, were sampled using baited pitfall traps, at the following habitats: isolated forest fragments, forest edges, plantations (coffee, cacao, mixed, citrus and allspice), live fences and pastures. A total of 14,269 beetles representing 36 species were captured. Onthophagus batesi, Canthon femoralis, Canthidium centrale, Copris laeviceps, O. rhinolophus and Deltochilium pseudoparile accounted for 75% of the captures in the overall sample from 79 sites. Across forest fragments capture rates of species and individuals were associated positively to area and negatively to isolating distance. Rarefaction analysis showed that forest fragments were the most species-rich habitats followed by the mixed and cacao plantations, the forest edge, live fences and coffee, citrus and allspice plantations. Pastures were the least species-rich habitat. Horizontal and vertical diversity of the vegetation at the habitats studied influenced the species richness of dung and carrion beetles and the number of species in common between forest fragments and human-made habitats. A significant relationship existed between the number of non-flying mammals recorded at the study sites and the richness of species and individuals of dung beetles at the habitats investigated. The relevance of this information is discussed in the light of the ecological flexibility of dung and carrion beetle species and of possible conservation scenarios involving landscapes in which isolation of forest fragments is reduced by the presence in open areas of human-made vegetation such as plantations of cacao, coffee, cacao and coffee and live fences.