Arboreal and terresterial soil and lilter were sampled for macro-and microinvertebrates at two locations in a Venezuelan cloud forest. Fauna were most abundant in forest floor soil and associated litter. However, media suspended in the canopy and particularly those trapped in bromeliad shoots were most densely populated, while the diversities of the arboreal and terrestrial soil fauna were indistinguishable. Rates of leaf litter decomposition in the arboreal and terrestrial soils were similar, but the arboreal soils contained higher concentrations of mineral nutrients and carbon. Implications of these findings for the definition of soil in humid tropical forests, and related differences between temperate and tropical forests are discussed. The similarities in diversity and differences in species composition between arboreal and terrestrial soil fauna raise questions concerning the evolution of tropical soil fauna, as well as the estimate of global biotic diversity.

The competitive interactions between two species of characins (Astyanax fasciatus and Astyanax bimaculatus) were investigated by studying their horizontal distribution, relative abundance and feeding habits in littoral and limnetic zones of Americana Reservoir, southern Brazil.

Differences in horizontal distribution of the species mainly as adults led to their partial habitat segregation. Most adult A. bimaculatus were littoral dwellers, whereas A. fasciatus adults were distributed from inshore to offshore waters, but with most in the latter region.

Both are facultative zooplanktivores in the reservoir, feeding mostly on planktonic crustaceans, insects (chiefly chironomids), some higher plant material, detritus and even fish scales (A. bimaculatus). Food overlap coefficients, considering adult and juvenile stages of both species are large in dry as well as wet seasons, although in the dry season the overlaps are significantly reduced for juveniles of both species and for juveniles of A. bimaculatus versus adults of A. fasciatus. Both species prey more on cladocerans than on cyclopoid copepods, and the adults selectively take larger forms (Daphnia gessneri and Moina micrura) in the reservoir (as in previously reported enclosure experiments). Juveniles prey heavily on Bosmina longirostris.

These two formerly riverine species may reduce competition, in the reservoir, by partial habitat segregation in older stages, a mechanism to avoid competition, which may have existed in their previous interactive history in rivers.

Soil microbial biomass (Cmic.) and is relation with soil carbon and nutrient contents in a tropical rain forest (Bawangling Nature Reserve, Hainan Island, P.R. China) were studied. Cmic. was determined by the substrate induced respiration (Sir) method; bacterial and fungal fractions were measured using a selective inhibition technique. For the A horizon, Cmic ranged between 350 and 700μgg-1 soil in April (beginning of the rainy season) and 250–600μg g-1 in October (end of the rainy season). Cmic. contents of the AB and B horizons were lower, ranging from 80 to 350 μg Cmic g-1 soil. On average, 75% of the biomass was bacterial, in the AB and B horizon this was slightly higher than in the A horizon. Cmic was closely correlated with Corg and N content. N and P contents as well as the respiratory response upon glucose addition indicated that towards the end of the rainy season compared with the start the soils were depleted in nutrients. These observations stress the importance of microbial biomass as a factor for nutrient retention in tropical forest ecosystems.

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.

Ant species in the genera Chelaner, Meranoplus and Pheidole were found to be seed-harvesters in a tropical savanna woodland in northern Australia. Despite the availability of other seed types (legume seeds in particular were abundant), all five seed-harvesting species studied are specialists in that they store only grass seeds. Depot experiments, in which seeds were placed along foraging trails, also indicate a preference for grass seeds over legume seeds. At least for some ant species the handling efficiency of legume seeds may be less than that of grass seeds. Marked differences in seed composition of granaries were observed among different seed-harvesting ant species and among colonies of the same species at different sites. All ant species studied, except Pheidole sp. 1, stored only one type of grass seed in granaries at any site despite the availability of other seed types. This contrasts with studies conducted elsewhere in Australia in which generalist foraging by seed-harvesters was found to be common. With the possible exception of Pheidole, dietary specialization docs not appear to arise from a low diversity or abundance of seed supplies. In addition to differences in seed preferences, species of seed-harvesting ants also exhibited some differences in temporal foraging behaviour and some partitioning of resources may be occurring among these co-occurring species. Temporal overlap in foraging, however, was much greater than dietary overlap. The viability of granary seeds was very low for three ant species suggesting that seeds stored by these ants were largely predated rather than dispersed.