In a 1-y study of vegetation harvested by the leaf-cutting ants, Atta colombica Guérin, daily harvesting activity of two nests was observed for 24 h at c. 1-wk intervals (colony I: June 1993-June 1994; colony II: February-June 1994) on Barro Colorado Island. The average daily quantity of green leaves harvested by colony I was higher during the wet season (11.4 m2 d−1) than during the dry season (9.0 m2 d−1), but was highly variable between survey days. Total annual herbivory of green leaves was estimated to be 3,855 m2 foliage area for colony I and 1,707 m2 for colony II. Total dry weight of biomass harvested was higher in the dry season because most material collected during the wet season consisted of green leaves, while during the dry season, more than 50% of the total collected biomass was non-green plant material (stipules of Ficus sp., fruits, seeds, and flower parts of a variety of other species) which represented c. one third (111 kg y−1) of the total annual intake (370 kg y−1) of plant material. Total daily biomass intake was negatively correlated with daytime rainfall. The peak of daily foraging was affected by timing and duration of rainfall events. Highest input rates normally occurred between 15:00 and 16:00 h (colony I).Dry weight and surface area of harvested leaf fragments differed between plant species, with thicker leaves generally being cut into smaller pieces. Significant linear correlations were found between total daily harvest of fragments and the respective harvesting rate at the maximum of daily activity. High correspondence was found between estimates using this relationship and the measured daily leaf harvest of four other Atta colonies and of two colonies reported in published literature. The use of this relationship as a research tool is discussed.

Green, P. T. (1997)

Red crabs in rain forest on Christmas Island, Indian Ocean: activity patterns, density and biomass. Vol. 13 Part 1: 17–38. On page 29 the phrase: “but a significant correlation existed across sites (r=0.81, n=44, P<0.001).” should read: “but a significant correlation existed across sites (r=-0.69, n=44, P<0.001).”

On page 33 the phrase “but the same correlation accounted for 81% of total variation when all sites were analysed together.” should read: “but the same correlation accounted for 48% of total variation when all sites were analysed together.”

The structure and functioning of Acacia koa-Metrosideros polymorpha forests between 1200 and 1800 m elevation on the island of Hawaii are being threatened by Passiflora mollissima, an aggressive introduced liana from South America. This study was done to evaluate the short-term decomposition dynamics of Passiflora and selected native leaf and twig litter. The nutrient-rich, non-sclerophyllous Passiflora leaves completely disappeared in less than 5 mo. The estimated time for native leaf litter to lose 95% of initial dry weight ranged from 1.65 y for N-rich Acacia phyllodes to 6.67 y for Cibotium glaucum; for woody litter, the time ranged from 4.5 y for Acacia twigs to 23 y for Acacia bark. Except for Cibotium frond litter, decay rates were significantly correlated with initial lignin-ash ratios. Passiflora litter did not accelerate decomposition of Acacia and Metrosideros leaf litter. Passiflora, Acacia, and Metrosideros leaf litter showed net mineralization of N, P, Ca, K, and Mg during the study. Cibotium frond litter showed significant accumulation of N, Ca, and Mg; P levels stayed constant and K was rapidly lost. In general, twigs experienced a net loss of most nutrients, while bark experienced either no change or a significant net gain of nutrients. Nutrient cycling has increased in P. mollissima infested forests.

Studies of predation on propagules of the mangroves Avicennia marina, Bruguiera exaristata, Ceriops tagal and Rhizophora stylosa were made in a forest in northern Australia to test the generality of the dominance-predation model. This model states that an inverse relationship exists between the dominance of a species in the canopy of mangrove forests and the rate of predation on the propagules of that species. Significant differences in predation were found among the four species, and among patches of forest dominated by the different species. Predators attacked more than 50% of the propagules of all species except R. stylosa, so are likely to significantly affect forest structure. The intensity of predation did not, however, vary as the dominance-predation model predicted. Instead, predation on the propagules of a species appeared to depend on the availability of propagules of other, more highly preferred, species.

Isolated in forest patches, mangrove stands often experience different physical conditions (rainfall, tide, salinity) despite similar floristic composition and structure. These abiotic factors are known to influence mangrove phenology but their potential effect on the local invertebrate and bird fauna have not been investigated. This study contrasts two sites of black mangrove (Avicennia germinans) located on the Caribbean and Pacific coasts of Panama. The two mangrove sites are characterized by different rainfall and tide patterns, and consequently ground inundation and salinity. These mangrove sites also differed in their plant phenology as well as invertebrate and bird composition. Although 95% of the bird species sampled occur on both coasts, the two mangrove sites shared only 34%. Moreover, each bird community was composed of a particular feeding guild assemblage consistent with the abundance distribution of their invertebrate-prey. Because floristically similar mangrove stands can support different invertebrate and bird faunas, conservation efforts should target mangrove patches submitted to different physical factors in order to preserve biodiversity.

As a consequence of its relatively high productivity in primary successional sites on Mauna Loa, Hawai'i, the mat-forming fern Dicranopteris linearis can influence attributes of soil detrital pools. Decomposition, nutrient release and rates of asymbiotic N fixation in Dicranopteris litter were determined over an elevational range of oligotrophic sites. ‘Hot spots’ of nitrogen fixation occurred in Dicranopteris litter, as evidenced by acetylene reduction rates as high as 22 nmol g−1 h−1. However, potential N fixation rates for the entire litter mass were 0–0.1 g m−2 y−1, less than other N inputs such as rainfall. Dicranopteris' decomposition rates were low compared to other tropical species, even under high temperature and rainfall conditions, with ≥50% of the original leaf and >77%of the stem mass remaining after 2 y of decomposition. Slow decomposition was related to high ligninrnitrogen ratios (56–129) in litter and above-ground positioning of unabscised, decomposing litter. As a result of its slow decomposition rates, Dicranopteris is an major contributor to soil detrital pools. Aggradation of the detrital pool is an important process whereby nutrients are accrued within these ecosystems. Consequently, Dicranopteris exerts an important influence on soil genesis and ecosystem development during primary succession on pahoehoe lava.

Seeds of the Brazilnut tree (Bertholletia excelsa Humb. & Bonpl., Lecythidaceae) sustain one of the most important extractive industries in neotropical forests. Yet little is known about the demography and seed dispersal ecology of Bertholletia, particularly in natural stands which have not been previously harvested. This study presents data on the population density, spatial distribution, and seed dispersal ecology of Brazilnut trees at a pristine stand located within the Kayapó Indian Area of southeastern Amazonia, Pará, Brazil. Brazilnut trees were primarily found within groves (castanhais) of 75 to 149 trees, with a few isolated trees in between. Although the density of trees ≥ 10 cm in diameter at breast height (hereafter, dbh) at two groves was 4.8 to 5.1 trees ha–1, the overall density for the entire study area of c. 950 ha was estimated at 1.3 tree ha–1. Within-grove nearest neighbour distances averaged 21 m and were markedly skewed towards even shorter distances. Seed dispersal experiments using 709 marked seeds indicated that this pattern can be largely explained by the highly restricted seed shadows imparted by the main seed dispersal agents of Bertholletia at this site, the red-rumped agouti (Dasyprocta leporina). Agoutis on average scatterhoard Bertholletia seeds to an average distance of 5 m, and rarely beyond 20 m, from seed stations. We suggest that, once edaphic and climatic conditions are suitable, the highly contagious spatial distribution of Bertholletia trees at the landscape level can be largely accounted for by the quantitatively dominant effect of short-distance dispersal by caviomorph rodents, and rare events of long-distance dispersal provided by other vectors. This mechanism of grove formation need not resort to untested conjectures of human dispersal and intentional planting in prehistoric and historic times as it has often been suggested in the literature.

The amounts and chemical composition of bulk precipitation were investigated over a continuous 21-mo period (January 1990 to September 1991) at four sites along an East-West transect perpendicular to the coast of Southwest Viti Levu, Fiji. Measured rainfall totals in 1990 ranged from 1796 mm at the coastal Korokula station to 2113 mm at the inland Tulasewa station, which is somewhat higher than the long-term average of 1707 mm at a reference weather station located in the centre of the study area. The first 9 mo of 1991 were relatively dry (range 1027–1533 mm) with a total of 1157 mm at the reference site as compared to a long-term average of 1330 mm. Concentrations of all investigated constituents in bulk rainfall were low, except during the passage of cyclone Sina due to the deposition of large amounts of, especially, chloride, sodium and sulphate in sea spray. Concentrations of sodium and magnesium could be explained fully by maritime contributions to the rainfall composition at all sites. Maritime contributions to the concentrations of calcium, sulphate and potassium accounted for 10–40% of the total, whereas bicarbonate, ammonium, nitrate, silicon, aluminium, iron and manganese were derived exclusively from terrestrial sources. The annual atmospheric nutrient deposition rates were low by pan-tropical standards, particularly when the contribution of cyclone Sina was excluded. Annual totals (in kg ha−1) ranged from 2.4–8.8 for nitrogen, 0.4–1.1 for phosphorus, 2.3–4.9 for potassium, 1.4–1.9 for calcium and from 1.1–1.3 for magnesium. The inclusion of the contribution by the cyclone more than doubled the deposition of potassium, calcium and magnesium, although values still remained well within the range reported for humid tropical areas. The estimated atmospheric deposition of nutrients over a typical rotation period (16 y) was sufficient to balance losses in harvested Pinus caribaea logs (stemwood plus bark) of potassium, calcium and magnesium, but not of nitrogen and, probably, phosphorus. Nutrient losses associated with the harvesting of stemwood alone were compensated entirely by the atmospheric inputs.

The change of mound structure of the fungus growing termite, Macrotermes gilvus, which has no clear air passage system in the mound, was examined in relation to the mound growth in a rubber plantation of southern Thailand. The nest proper consisted of the hive with a royal chamber and nursery, and diffused chambers with fungus combs. The location of the hive became higher with the growth of the mound. Therefore, colonies with a very large mound utilize only the upper mound part and this may be due to the lack of air passage systems in this species. A colony with a very large mound is not in reality commensurately large in colony size and this may be the reason why the density of huge mounds of M. gilvus in Thailand is much higher than that of Macrotermes in Africa.

A new technique for estimation of tree species richness in tropical forests was developed and tested in this study. The missing species extrapolation technique is based on the assumption that the rate of accumulation of new species with increasing area is the same within sampled and unsampled areas of similar habitat within a region. This new technique was tested on four 1-ha sites of subtropical moist forest in Rio Bravo, Belize for which complete species counts of trees ≥10cm dbh are available. Estimates given by the technique are 115, 98, 93 and 106% of the actual species counts within the four sites. The accuracy of these estimates was found to be equal to or better than most others obtained by using existing methods of extrapolation. The missing species extrapolation technique was also applied to a 21-ha riparian forest patch in the Mountain Pine Ridge, Belize, where it was used to obtain an estimate of the number of tree species ≥10cm dbh in the entire patch.