A population of Garra ceylonensis in a rocky, hill stream was studied by monthly sampling over a period of two years. The monthly population density, which varied from 1.28 to 4.16 m-2 with a mean of 2.37 m-2, was negatively correlated with the water speed. Asymptotic length (L∞) and the growth constant (K) were found to be 180.5 mm total length and 0.62. Maximum size observed was 174 mm, which is attained in about five years, but 99% of the population had a life expectancy of less than 3.4 years. The overall male to female ratio of the population was 0.58. The sex ratio was 1.0 in smaller size classes but decreased steadily with increasing size. There was a major spawning season following the main rainy period in contrast to the trend of most tropical freshwater fish species, which show enhanced breeding during the rainy season. The mean length and age at sexual maturity in females appear to be 109 mm and eighteen months. Fecundity varied between 740 and 4390. Average longevity and natural mortality were 4.8 years and 1.86. The mean biomass, average annual production and turnover ratio of the population were about 23.7 gm-2 wet weight, 41.2gm-2 and 1.7, respectively.

A comparative analysis of earthworm populations in seral Khasi pine forest represented by Pinus kesiya 5- and 35-year old stands, and a climax broad-leaved mixed forest represented by a sacred grove was done at altitudes of 1500 m in Meghalaya in north-east India. Tonoscolax horaii occurred under all forest types whereas Amynthas diffringens and Eulyphoeus feslivus were confined to pine forest stands only. Perionyx sp. and Drawida assamensis were restricted to the sacred grove. T. horaii had larger numbers in all three different forest types. This species offers possibilities of vermicullurc for biologically improving soil fertility in manmade ecosystems because of its wide range of tolerance.

Generally earthworm populations were more active during the monsoon season; A. diffringens was however, more active during the winter, thereby conferring an advantage on this species as it was enabled to avoid competition during the monsoon season when other species dominate. Earthworm activity was generally higher in the sacred grove than in the pine forest stands. Population size was significantly correlated with soil moisture, temperature and pH. Wormcasts had a higher pH and nutrient status than the soil.

In the highly leached soils of the humid tropics where there is a large concentration of fine root biomass in the surface soil layers, earthworm activity is beneficial because it helps incorporate detritus into the mineral soil rapidly and locally concentrates nutrients in the surface layers.

Litterfall was sampled during one year in two undisturbed Andean forests at altitudes of 2550 and 3370 m in the Colombian Cordillera Central. Total small litterfall at 2550 and 3370 m was 7.03 and 4.31 tha-1 y-1 respectively, of which 4.61 and 2.82 were leaves, 1.06 and 0.76 woody parts, 0.66 and 0.27 reproductive parts, 0.22 and 0.23 epiphytes, 0.47 and 0.23 unclassified.

Clear differences were also found in nutrient concentrations, both between different litter fractions from one site and between equivalent litter fractions from different sites. Weighted mean concentrations for total small litterfall were (mgg-1, at 2550 and 3370m respectively): 11.7 and 7.3 for nitrogen; 0.86 and 0.44 for phosphorus; 8.4 and 3.1 for potassium. Comparison of nutrient concentrations in crown leaves and shed leaves indicated important reallocation of nitrogen (39% at both sites) and phosphorus (45% at 2550m, 65% at 3370m) before leaf shedding.

The results for litterfall amounts, litter nutrient concentrations and reallocation of nutrients in the two forests are consistent with such data obtained in other montane forests in the wet tropics.

Natural levels and consequences of insect herbivory were studied for a Kandelia candel (Rhizophoraceae) dominated mangal at the Mai Po Marshes, Hong Kong. Grazing insects (mainly lepidopteran larvae) consumed, on average, 10.3% of the leaf area on K. candel, with >90% of the leaves suffering <30% loss. Natural median leaf longevity was significantly different between winter and summer-exposed leaves, being, respectively, 423.2 and 269.6 days. Observations showed that herbivore damage caused a reduction of leaf longevity, as severely damaged leaves were abscissed before intact, older leaves on the same branch. Experimental leaf area removal suggested that leaf life span reduction was significantly influenced by leaf age and degree of damage. However, the reduction was only significant (>40 days) when area loss was >40%. Leaves produced in summer were also more sensitive to damage than those produced in winter. As <5% of the leaves suffered >40% of area removal by insect grazing in nature, insect herbivory is considered an unimportant regulator of leaf litter dynamics for K. candel. At this intensity level, herbivory consumes 2.8–3.5% of the net above-ground primary production of the mangrove. There was also no significant difference in the final number of leaves and twigs produced by the branches with various degrees of leaf area removal. Other observed impacts of insects on the structure and function of the K. candel mangal are discussed.

The insular distribution and abundance of the spiny rat (Proechimys semispinosus) were studied by live-trapping rats on 50 small forested islands in Gatun Lake, Republic of Panama. Rats were found on 29 of these islands. Rat abundance was not correlated with island size or isolation, in contrast to temperate rodents, and may be due to the highly patchy nature of tropical forests and the differing floristic compositions of the study islands. Rat occurrence on islands was related positively to island size and negatively to island isolation. All islands greater than 2.1 ha contained spiny rats, whereas most islands less than 0.9 ha did not contain rats. The relationship between occurrence, size, and isolation are illustrated by a three-dimensional response surface. Results suggest that colonization and extinction regularly occur on these islands and that (1) larger islands with year-round fruit production, regardless of isolation, will have persistent populations of rats, (2) small isolated islands will never or only very rarely have rats owing to a lack of a year-round food source and the difficulty of immigration, and (3) small near islands frequently will have rats when fruits arc present. No other species of mouse-or rat-like rodents were captured on the islands. We suggest that P. semispinosus is a better colonist than other sympatric forest species, is more of a habitat generalist, and has a more flexible demographic structure allowing persistence in heterogeneous and changing environments.

In comparing the population structure of epiphytic and saxicolous Tillandsia species I found no significant differences between polycarpic species. Epiphytic T. ionochroma populations had a higher seedling:adult ratio than saxicolous T. ionochroma populations, but the difference was not statistically significant. Tillandsia ultriculala, a monocarpic epiphyte, had a significantly higher seedling:adult ratio than the polycarpic species. T. utriculata's higher ratio may result from its greater seed production and lack of vegetative propagation. Unlike the polycarpic species, all adult-size rosettes grow from seeds in T. utriculata. Tillandsia sphaerocephala, an obligate saxicole, occurred in larger clusters (i.e. more rosettes per genet) than T. ionochroma. The increased tendency for vegetative reproduction in T. sphaerocephala suggests that spatial patchiness is less of a constraint than with epiphytes.

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.

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.