Showing papers in "Journal of Tropical Ecology in 1998"
TL;DR: In this article, the authors quantified the aboveground and belowground biomass of plant communities in the Brazilian Cerrado ecosystem, and the quantity of biomass consumed by fires were measured in four plant communities.
Abstract: Conversion to permanent agriculture is rapidly occurring over vast areas of the 1.8 million km2 Brazilian Cerrado; a region that is naturally a mosaic of grasslands, savannas and evergreen tropical woodlands. Yet, few studies have quantified total biomass of plant communities in this ecosystem, particularly the belowground component; a C pool of potential global significance. Total biomass (aboveground and belowground), and the quantity of biomass consumed by fires were measured in four plant communities comprising a vegetation gradient from pure grassland (campo limpo) to a woodland with a closed canopy of tall shrubs and scattered trees (cerrado denso) near Brasilia, DF, Brazil. Total aboveground biomass (TAGB) increased along this gradient from 5.5 Mg ha-' in campo limpo to 29.4 Mg ha-' in cerrado denso. Vegetation structure varied among communities; trees were nonexistent in campo limpo, but were at a density of 1000 ha-' and a biomass of 12.9 Mg ha-' in cerrado denso. Fires consumed 92 and 84% of the TAGB in campo limpo (pure grassland) and campo sujo (savanna), respectively. In cer- rado aberto and cerrado denso, trees and tall shrubs were little affected by fire. Combustion factors of the TAGB in these communities was 54 and 33%, respect- ively. The total biomass consumed by fire ranged from 5.0 Mg ha-' in campo limpo to 13.5 Mg ha-' in cerrado aberto. Compared to other widespread Brazilian ecosys- tems (tropical dry forest and evergreen forest), the Cerrado has a lower aboveground biomass. The TAGB of cerrado denso is <9% of that of Amazonian tropical evergreen forest. The total quantity of biomass consumed by fire, and hence emissions to the atmosphere is lower in intact Cerrado communities com- pared to fires in slashed tropical forest. Total belowground biomass (TBGB) increased from 16.3 Mg ha-' in campo limpo, to 30.1 Mg ha-' in campo sujo, to 46.5 Mg ha-' in cerrado aberto, and to 52.9 Mg ha-' in cerrado denso. This quantity of belowground biomass is similar to, or exceeds that reported for many tropical dry and moist forests. More than 80% of the TBGB occurred in the upper 30 cm of the soil, except for cerrado denso (71%) where a greater proportion of tree roots were present at deeper levels. Root:shoot ratios were very high in all sites ranging from 2.9 in cerrado denso to 7.7 in campo sujo. Total ecosystem plant biomass (the total aboveground biomass and TBGB combined) ranged from 21.9 Mg ha-' in campo limpo to 77.9 Mg ha-' in
318 citations
TL;DR: The phenomenon called ecosystem engineering is considered with a case study of the mound building termite Macrotermes michaelseni, and it is argued that this species acts as an ecosystem engineer across a range of spatial scales.
Abstract: Many organisms create or alter resource flows that affect the com- position and spatial arrangement of current and future organismal diversity. The phenomenon called ecosystem engineering is considered with a case study of the mound building termite Macrotermes michaelseni. It is argued that this species acts as an ecosystem engineer across a range of spatial scales, from alteration of local infiltration rates to the creation of landscape mosaics, and that its impacts accrue because of the initiation of biophysical processes that often include feedback mech- anisms. These changes to resource flows are likely to persist for long periods and constrain the biological structure of the habitat. The value of ecosystem engineer- ing is discussed as a holistic way of understanding the complexity of tropical ecology.
306 citations
TL;DR: In this paper, an analysis was conducted of floristic patterns contained in 48 1-ha tree plots distributed at 29 sites in seven neotropical countries, with a primary emphasis on the Amazonian region.
Abstract: An analysis was conducted of floristic patterns contained in 48 1-ha tree plots distributed at 29 sites in seven neotropical countries, with a primary emphasis on the Amazonian region. Analyses were made with family level data, using detrended correspondence analysis and multidimensional scaling to generate two-dimensional ordinations. Dissimilarity values for all pairs of plots were then used to compare forest composition at both local (flooded vs unflooded forests) and regional scales (e.g., western vs central vs eastern Amazonia). The predomin- ate family of trees in a large majority of Amazonian and Guianan forests (by number of stems) is either Palmae or Leguminosae (sensu latu), followed by Mora- ceae and Euphorbiaceae. The forests of western Amazonia are particularly rich in palms, Moraceae, and Myristicaceae, whereas those of eastern Amazonia and the Guianas are rich in Lecythidaceae and Chrysobalanaceae. Dissimilarity between sites increases with distance for both flooded and unflooded forests. The tree com- munities of flooded and unflooded forests within a region tended to resemble one another more closely than forests of either type resembled the homologous forests of the adjoining regions. Within Amazonia the edaphic properties of each region and its geological history are tightly interrelated. it is therefore difficult to distin- guish between evolutionary and ecological interpretations of the results.
245 citations
TL;DR: The ant fauna of a rain forest in Sabah, Malaysia was sampled by using different collecting methods in three strata and the ant community described is the most species rich published for a primary tropical rain forest.
Abstract: The ant fauna of a rain forest in Sabah, Malaysia was sampled by using different collecting methods in three strata. In total, 524 morphospecies of ants could be distinguished. They belong to seven subfamilies and 73 genera. So far, the ant community described is the most species rich published for a primary tropical rain forest. Regarding the stratification in the forest, the leaf litter com- munity comprised as many ant species as the lower vegetation or canopy. Further- more the litter stratum had the highest generic diversity. The stratification of ants in rain forests seems to be a very strict one with the majority of species (75%) being related to only one stratum. This is in contrast to findings on the stratifica- tion of beetles in rain forests. The stratification and a radiation of some groups into vegetation and canopy, where a broad spectrum of permanent habitats exist, is responsible for the high diversity of ants in tropical rain forests.
174 citations
TL;DR: In this article, the authors measured meteorological variables, bulk cloud water and precipitation (BCWP), and bulk precipitation (BP) were measured above the canopy, and throughfall (TF; n = 20) was collected beneath an epiphyte-laden canopy of a tropical tropical montane forest (TMF) for 1 y at Monteverde, Costa Rica.
Abstract: Meteorological variables, bulk cloud water and precipitation (BCWP), and bulk precipitation (BP) were measured above the canopy, and throughfall (TF; n = 20) was collected beneath an epiphyte-laden canopy of a trop- ical montane forest (TMF) for 1 y at Monteverde, Costa Rica. Total deposition (cloud + wet + dry) of inorganic ions to the canopy was estimated using a sodium (Na+) mass balance technique. Annual BCWP and BP depths were 2678 mm and 1792 mm for events where mean windspeeds (u) > 2 m s-1, and 4077 mm and 3191 mm for all events, respectively. Volume-weighted mean pH and concentra- tions of nitrate-N (NO3--N) and ammonium-N (NH4+-N) were 4.88, 0.09 and 0.09 mg 1-1 in BCWP, and 5.00, 0.05 and 0.05 mg 1-1 in BP, respectively. Cloud water and mist deposition to the canopy was estimated to be 356 mm. Estimated deposition of free acidity (H+), NO3--N, and NH4-N to the canopy was 0.49, 3.4 and 3.4 kg ha-' y-1, respectively. Mean TF depth was 1054 ? 83 mm (mean ? S.E.) for events where u > 2 m s-', and 2068 ? 132 mm for all events. Volume-weighted mean pH and concentrations of NO3- -N and NH4+-N in TF were 5.72, 0.04 mg I-', and 0.07 mg I1-, respectively. Mean fluxes of H+, NO3- -N, and NH4+-N in TF were 0.04 + 0.01, 0.6 ? 0.2 and 1.3 ? 0.2 kg ha-' y-', and percent net retention of these ions by the canopy was 92 ? 2, 80 ? 6, and 61 + 6%, respectively. Phosphate, potas- sium, calcium and magnesium were leached from the canopy. Seasonal data sug- gest that biomass burning increased concentrations of NO3- and NH,' in cloud water and precipitation at the end of the dry season. Regardless, a large majority of the inorganic N in atmospheric deposition was retained by the canopy at this site.
166 citations
TL;DR: 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, while pastures were the least species- rich habitat.
Abstract: 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.
164 citations
TL;DR: Comparat heterogeneity was studied using ordination procedures based on floristic data and to identify the characteristic species of three plant communities: granite outcrops, valley forest and upland forest.
Abstract: An exhaustive floristic inventory was conducted in a 400-ha block of tropical semideciduous forest in the Chiquitania region of Santa Cruz, Bolivia A total of 501 species were collected using both quantitative and traditional plant collecting methods Trees represented the most diverse life form (124 spp), fol- lowed by herbs (101 spp), lianas (85), shrubs (66), herbaceous climbers epiphytes (15) and parasites (two) Floristic diversity was greatest for the forest floor com- munity, when compared to either the understorey or canopy tree communities Quantitative data were obtained for 336 species in 100 plots which contained a series of nested subplots to sample smaller-stature plants Stem density for trees (dbh ? 5 cm) was 914 trees ha-', with a total density for all life forms estimated to be 135,000 plants ha-'; the total basal area for the forest was estimated to be 276 m2 ha-' Species richness when measured by standard methods was found to be one of the highest for a dry forest region reported for the Neotropics with a mean of 708 spp 01 ha-' (dbh > 25 cm) and 50 spp ha-' (dbh > 10 cm) Compar- ison of life forms and vertical strata showed that the flora on the forest floor was more diverse than all other vertical strata combined Habitat heterogeneity was studied using ordination procedures based on floristic data and to identify the characteristic species of three plant communities: granite outcrops, valley forest and upland forest The most abundant tree species in the study area were Acosmium cardenasii, Neea hermaphrodita, Aspidosperma tomentosa and Galipea trifoliata, while the species with the greatest basal area were Anadenanthera colubrina, Acosmium cardena- sii, Caesalpiniafloribunda, Aspidosperma tomentosa, Piptadenia viridiflora, Chorisia speciosa, Tabebuia impetiginosa, Centrolobium microchaete, and Machaerium scleroxylon Most canopy and understorey tree species had a population structure characterized by
143 citations
TL;DR: Results suggest that by burying seeds dung beetles increase the probability that seeds will escape predation and germinate, and demonstrates the potential ecological importance ofdung beetles in facilitating seed survival and provides data to con- sider the role of dung beetle in the evolution of seed attributes.
Abstract: Dispersal of seeds away from the parent plant may facilitate escape from density-dependent seed mortality. However, many post-dispersal events can have a profound influence on the survival of dispersed seeds. By incorporating seeds in the dung that dung beetles process for consumption and oviposition, dung beetles could enhance seed survival if they remove seeds from areas of high pre- dation risk and place them in locations that avoid subsequent predation and that are suitable for germination. The role of dung beetles in seed survival was investig- ated over 15 mo in Kibale National Park, Uganda. Depths of seeds buried by beetles, levels of predation on buried and unburied seeds, and germination success of seeds buried to different depths were examined. Results suggest that by burying seeds dung beetles increase the probability that seeds will escape predation and germinate. Of seeds placed in dungpiles, 69% remained at the surface, while 25% were buried from 1-3 cm in depth. Larger seeds were buried more shallowly than smaller seeds. Buried seeds were less likely to be removed by predators than seeds at the surface. Germination of seeds buried at 1- and 3-cm depths was significantly higher than seeds buried at 10 cm. For the species tested, many seeds were buried by dung beetles between 1 and 3 cm and at this depth there was a high probability of escaping predators and germinating. This demonstrates the potential ecological importance of dung beetles in facilitating seed survival and provides data to con- sider the role of dung beetles in the evolution of seed attributes.
135 citations
TL;DR: In this paper, throughfall and soil solution chemistry were studied for 1 y in a tropical montane forest in the Luquillo Mountains of Puerto Rico, showing no strong seasonal patterns in concentration and variability was highest for elements with high biological activity.
Abstract: Throughfall and soil solution chemistry were studied for 1 y in a tropical montane forest in the Luquillo Mountains of Puerto Rico. Passage of pre- cipitation through the forest canopy resulted in an increase in the concentration and flux of all solutes except H' and NO3-. Throughfall chemistry showed no strong seasonal patterns, but concentrations of many solutes declined during weeks of high rainfall. Enrichment in throughfall relative to precipitation was similar to values reported recently for several other tropical sites, with the exception of NH4+, which was particularly high at this site. Based on net throughfall deposition of Cl-, dry deposition of marine aerosols appears to be a relatively minor component (c. 15%) of total deposition. In soil solution, no seasonal patterns in concentration were evident and variability was highest for elements with high biological activity (especially N). Concentrations and fluxes of K+ and dissolved organic carbon (DOC) showed the largest declines as throughfall passed through the soil profile; concentrations of most other elements increased or were relatively constant. Declining DOC flux through the soil profile appears to be due to sorption processes similar to those observed in many temperate forests. Concentrations and fluxes of HCO3- and SiO2 increased substantially in soil solution, but never approached those observed in the stream. This suggests that additional weathering must occur as groundwater moves from this ridgetop site to the stream.
134 citations
TL;DR: It is argued that interactions between small herbivore such as impala or buffalo and large herbivores such as elephant or giraffe may provide a plausible alternative hypothesis that the interplay of competition and facilitation between these types of Herbivores could explain transitions between grassland and woodland and vice versa.
Abstract: Current hypotheses to explain dynamic transitions between savanna grasslands and woodlands in Africa focus on grazing by elephant or the influence of fire. Using a simple mathematical model, this paper argues that interactions between small herbivores such as impala or buffalo and large herbivores such as elephant or giraffe may provide a plausible alternative hypothesis. The interplay of competition and facilitation between these types of herbivores could explain transitions between grassland and woodland and vice versa. A review of the literat- ure is presented in support of this hypothesis.
128 citations
TL;DR: In this article, the authors investigated factors contributing to the resistance of gallery forests in savannas to the entry of fire were investigated using field observations and manipulation experiments, and concluded that fire entry into forests was faciliated by deep root mats and the presence of a superficial litter layer, both of which become attenuated at the forest/savanna contact.
Abstract: Factors contributing to the resistance of gallery forests in savannas to the entry of fire were investigated using field observations and manipulation experiments. Mass of savanna fuels did not decrease close to forest boundaries, and in some instances increased, while savanna fuels adjacent to forests were moister than in the savanna beyond for only 1 d after rainfall. A fuel drying experiment conducted in both forest and savanna microclimates indicated that both fuel type and microclimate contributed to the resistance of forests to fire entry, although the former played a larger role. While savanna fuels in a savanna microclimate became ignitable in c. 1 d after rain, forest fuels in a forest microclimate required 4 wk to achieve ignitability. A further experiment juxtaposing forest fuels to burning savanna indicated that fire entry into forests was faciliated by deep root mats and the presence of a superficial litter layer, both of which become attenuated at the forest/savanna contact. It is concluded that fuels in these forests can reach an ignitable state late in the dry season, but that frequent fire entry is probably precluded by the tendency of savanna fires to occur earlier in the dry season and by discontinuities in fuels at the savanna/forest contact. RESUMEN. Se investigaron los factores que contribuyen a la resistencia de la entrada del fuego a los bosques en galeria de las savanas mediante observaciones de campo y experimentos de manipulacion. La masa de los combustibles de la savana no decrecieron cerca de los bordes del bosque; por el contrario, en algunos casos se incrementaron, mientras que los combustibles de la savana cercanos al bosque eran mas huimedos que en la savana restante, solamente por un dia despues de un evento de lluvia. Un experimento de secado de combustible, que fue conducido en los microclimas de bosque y de savana, indica que tanto el tipo de combustible como el microclima contribuyen a la resistencia de los bosques a la entrada del fuego, aunque el primer factor tuvo un papel de mayor importancia. Mientras que los combustibles de la savana en el microclima de la savana se volvieron 'encendibles' cerca de un dia despues de lluvia, los combustibles del bosque dentro del microlima del bosque tomaron cuatro semanas para llegar a dicho estado. Un experimento que sobrepuso combustibles del bosque a la savana ardiente indico que la entrada del fuego a los bosques se facilito por la presencia de mantillos Corresponding author.
TL;DR: In this article, the chemical and physical properties of these licks were studied and the chemical characteristics and particle sizes of geophagical lick soils were compared with soils from the forest and from licks where evidence of the geophagy was absent.
Abstract: Geophagy (soil eating) by the forest elephant (Loxodonta africana cyclotis) and other mammal species in the Dzanga National Park, Central African Republic, has led to large treeless licks. The geological and physical properties of these licks were studied and the chemical characteristics and particle sizes of geophagical lick soils were compared with soils from the forest and from licks where evidence of geophagy was absent. Average lick size of 20 licks in the Hokou lick area was 12,900 m2 (SE = 3,400 m2). Licks were situated exclusively in areas of outcropping dolerite intrusions. Physico-chemical analysis of the geophagical lick soil showed significantly higher quantities of sodium, potassium, calcium, magnesium, phosphorus, manganese and clay compared with the other soils. Several samples of the geophagical lick soil had lower nutrient levels than the mean level of forest topsoil, indicating that nutrient supplementation is probably not the only reason for geophagy. The high clay content of the geophagical soil may help absorbing and combating secondary plant compounds. Pronounced geophagy in rainforests may be a sign for poor habitat quality for large mammals living in these ecosystems.
TL;DR: It is suggested that Ceratogymna hornbills rank among the most important seed dispersers found in Afrotropical forests, and they deserve increased conservation attention.
Abstract: Seed dispersal is a process critical to the maintenance of tropical forests, yet little is known about the interactions of most dispersers with their communities. In the Dja Reserve, Cameroon, seed dispersal by the hornbills Cerato- gymna atrata, C. cylindricus and C. fistulator (Aves: Bucerotidae) was evaluated with respect to the taxonomic breadth of plants dispersed, location of seed deposition and effects on seed germination. Collectively, the three hornbill species consumed fruits from 59 tree and liana species, and likely provided dispersal for 56 of them. Hornbill-dispersed tree species composed 22% of the known tree flora of the site. Hornbill visit lengths, visit frequencies, and seed passage times indicated that few seeds were deposited beneath parent trees; in five hornbill/tree species pairings studied, 69-100% of the seeds ingested were deposited away from the parent trees. Germination trials showed that hornbill gut passage is gentle on seeds. Of 24 tree species tested, 23 germinated after passage by hornbills; of 17 planted with con- trols taken directly from trees, only four species showed evidence of inhibition of germination rate, while seven experienced unchanged germination rates and six experienced enhanced germination rates. Results suggested that Ceratogymna horn- bills rank among the most important seed dispersers found in Afrotropical forests, and they deserve increased conservation attention. Ceratogymna hornbills are likely to become increasingly important in forest regeneration as populations of larger mammalian seed dispersers (such as forest elephants and primates) diminish.
TL;DR: In this paper, spatial patterns of trees ≥ 30 cm gbh were investigated from three contrasting 0.4-ha plots that differed in topography and amount of disturbance due to treefall.
Abstract: In a primary dense moist evergreen forest of southern India, spatial patterns of trees ≥30 cm gbh were investigated from three contrasting 0.4-ha plots that differed in topography and amount of disturbance due to treefall. Exploratory data analysis is based on second-order neighbourhood and pair-correlation statistics used to describe the degree of clustering/regularity in patterns of all trees, and the degree of attraction/repulsion between young trees and adults. Stochastic simulations from the Markov point process models are then used to fit spatial interaction models. The results show that spatial patterns can be related to particular dynamic processes which depend on both exogenous and endogenous factors: on steep slopes disturbed by many treefalls, spatial pattern displays large clusters which can be interpreted as within-gap regeneration stages of various ages, while in areas undisturbed over a long period, interactions between young trees and adults give rise to spatial patterns consistent with substitution dynamic processes implying standing mortality rather than treefalls. Characterizing forest dynamics through spatial patterns of trees opens up the possibility of mapping structural units that might be considered as elementary functional patches of the forest mosaic.
TL;DR: The results suggest that slow-growing epiphytes such as D. emarginata can attain considerable age and that their longevity – after an initial vulnerable juvenile stage – is almost exclusively limited by substrate durability.
Abstract: Vegetative growth, reproductive effort, seedling establishment, and mortality of the bark epiphyte, Dimerandra emarginata (Orchidaceae), were studied over a 3-y period in the moist lowland tropical forest on Barro Colorado Island, Panama. The study included more than 350 individuals growing on 12 branches of five different host tree species. Mortality was highest among small individuals. Most deaths occurred during the dry season and were probably related to drought. Mortality among older individuals, on the other hand, was always related to the instability of the substrate, i.e. flaking bark, breaking branches or falling trees. Vegetative growth was slow. The average increase in size (= height of the most recent, fully developed shoot) was 2.7 cm over 3 y (not considering ‘stemless’ seedlings). This increase was negatively correlated with initial plant size. Growth was highly seasonal, with little variation between years. The reproductive effort increased strongly with plant size. Larger individuals produced fruits more frequently, in larger numbers and of larger size. After reproduction, plants showed reduced vegetative growth in the following year (in 1994). There was no negative effect on future reproduction. Compared to seed production, annual recruitment was very low and showed large year-to-year variation. Fewer than 50% of the seedlings survived the first dry season after germination. After 3 y, their average size was 0.5 cm. The results suggest that slow-growing epiphytes such as D. emarginata can attain considerable age and that their longevity – after an initial vulnerable juvenile stage – is almost exclusively limited by substrate durability.
TL;DR: Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest.
Abstract: This study examined whether postdispersal fruit and seed removal by terrestrial mammals of common plant species was affected by the type of item, item density (low, medium, high), and habitat (gap, mid-succession, mature). Fruits of Brosimum alicastrum and Ficusyoponensis (Moraceae), Astrocaryum mexicanum (Palmae), and Nectandra ambigens (Lauraceae), and seeds of Omphalea oleifera (Euphorbiaceae) and Cymbopetalum baillonii (Annonaceae) were tested at the Los Tuxtlas rainforest in Mexico. Item removal from 108 experimental patches (N= 2340 fruits or seeds for each plant species tested) after 5 d was lower for F. yoponensis (6.6%) than for N. ambigens (68.8%), B. alicastrum (67.8%) C. baillonii (64.0%) and A. mexicanum (60.0%). No seeds of 0. oleifera were removed. A higher fruit or seed removal was observed from high density than low density food patches in A. mexicanum, C. baillonii and N. ambigens, but not in B. alicastrum and Fyoponensis. A higher fruit or seed removal was observed from food patches in mature forest than in gaps in all plant species tested. Similar removal values between open (open to all terrestrial mammals) and caged (open to small rodents) fruit and seed patches, abundant rodent live-trapping, and a scarcity of large terrestrial mammals, indicated that forest-dwelling small rodents were the main postdis- persal removal agents. Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest. RESUMEN. Se determino si la remocion postdispersion de frutos y semillas de plantas comunes, por parte de los mamiferos terrestres, es afectada por la especie de planta, la densidad de los lotes de frutos o semillas y por el habitat (claro, sucesion secundaria y selva madura). Frutos de Brosimum alicastrum y Ficus yoponensis (Moraceae), Astrocaryum mexicanum (Palmae) y Nectandra ambigens (Lauraceae) y semillas de Omphalea oleifera (Euphorbiaceae) y Cymbopetalum baillonii
TL;DR: The results strongly suggest that the most important factor determining spatial heterogeneity of organic matter and element dynamics on the forest floor is the site-specific amount of leaf fall, rather than spatially variable decomposition rates.
Abstract: The spatial heterogeneity of element fluxes was quantified by meas- uring litterfall, throughfall and litter decomposition for 1 y in 30 randomly located sampling areas in a lowland dipterocarp rain forest. The idea tested was that turnover of elements is more variable than turnover of dry matter in a forest with extremely high tree species diversity. In spite of the low fertility of the soil (an ultisol), total litter production (leaves, trash, and wood <2 cm in diameter) was high (1105 g m -2 y -1 ) with inputs to the forest floor of carbon, nitrogen, phos- phorus, calcium, magnesium, potassium, manganese and iron of 550, 15.3, 0.47, 6.26, 2.49, 4.75, 0.95 and 0.14 g m -2 y -1 respectively. Throughfall was 81% of the annual rainfall and transferred 22.2, 1.37, 0.14, 1.07, 0.67, 0.39, 7.92, <0.06, and <0.06 g m -2 y -1 of organic carbon, nitrogen (all forms), phosphorus, sulphur, cal- cium, magnesium, potassium, manganese and iron, respectively. Average turnover rates of nutrients in litter were highest for potassium and decreased in the sequence calcium, magnesium, carbon, nitrogen and phosphorus. Concentrations of phosphorus, nitrogen and potassium in litterfall, litter mass and topsoil were closely correlated with each other. Concentrations of calcium and manganese were positively correlated with each other and with elevation. Variations in leaf chem- istry and total litterfall caused the spatial heterogeneity of element input to the forest floor to have a coefficient of variation of 30 - 70%, depending on the ele- ment. Due to the strong positive correlation between element fluxes and pools, the spatial variability of turnover rates (CV c. 20%) was lower than that of element input. Turnover rates for K varied by a factor of 4, and for Ca by a factor of 2.8 when the different sites were compared. The results strongly suggest that the most important factor determining spatial heterogeneity of organic matter and element dynamics on the forest floor is the site-specific amount of leaf fall, rather than spatially variable decomposition rates. 1 Corresponding author.
TL;DR: Sympatric lizards in a transitional forest of Roraima, Brazil, dividing Amazon rain forest from savanna, contained a lizard assemblage of 16 species representing six families suggesting that composition of the local assemblages limits the species that can enter the assem- blage.
Abstract: Sympatric lizards in a transitional forest of Roraima, Brazil, dividing Amazon rain forest from savanna, contained a lizard assemblage of 16 species representing six families. Lizards varied in size, activity (diurnal versus nocturnal), microhabitats used, exposure to various conditions of light availability, prey types, and prey sizes. Overlaps in microhabitat occurrence varied from 0 (no overlap) to 1.0 (total overlap) whereas overlaps in prey types varied from 0.005 to 0.607. Microhabitat overlaps were higher overall than dietary overlaps. Pseudocommunity analyses on microhabitat data indicate that the community is not randomly assembled and that two distinct guilds exist, a leaf-litter guild and an arboreal guild, each with four species. Similar analyses on diet data revealed no apparent guild structure ast the first rank (nearest neighbour). Lizard diets did not differ from a random assortment based on prey type. At lower levels, the assemblage was structured with respect to food. Variation in prey use among lizard species was tied more closely to the effect of lizard body size on prey size (lizards ate different-sized prey items). Although exploitative competition among species may maintain structure within this assemblage it does not necessarily cause the observed differences. Several species are nearly identical ecologically to sister taxa in other environments and within different lizard assemblages suggesting that composition of the local assemblage limits the species that can enter the assemblage. Finally, lack of structure at the lowest (most similar) neighbour ranks may reflect the impact of a transitional habitat on stability of species interactions at the local level.
TL;DR: Le Leaf-cutting ant nests create gaps in the plant understorey when active, but serve as centres of recruitment for small plants after they are abandoned, and could play an important role in recruitment of new individuals and maintenance of plant species diversity in tropical forests.
Abstract: Nests of leaf-cutting ants (Hymenoptera: Formicidae: Attini) are abundant disturbances in Neotropical rain forests, and could affect the plant community both while the nests are active and after they are abandoned. We measured the diversity and abundance of understorey plants (>1 m in height) in the area around active and abandoned nests of leaf-cutting ants (Atta cephalotes) at the La Selva Biological Station in Costa Rica. Sampel quadrats on active nests had reduced diversity (number of morphospecies) and abundance of both small (height >10 cm) and large (10 cm–1 m) understorey plants, when compared to the nearby forest floor (3 and 13 m from the nest edge). Abandoned nests had greater diversity and marginally greater abundance of small understorey plants relative to nearby forest; there was no difference in diversity or abundance of large understorey plants. Leaf-cutting ant nests create gaps in the plant understorey when active, but serve as centres of recruitment for small plants after they are abandoned. Thus, like canopy gaps, ant nests could play an important role in recruitment of new individuals and maintenance of plant species diversity in tropical forests.
TL;DR: Metcalfe et al. as discussed by the authors showed that small-seeded species with small seed size, dormancy mechanisms, potentially rapid growth, and requirement of direct sunlight for germination and establishment can be found in the soil seed bank in Sabah.
Abstract: The vast array of species found in the humid lowland tropical forests of the world are frequently divided into two general groups, light-demanders and shade-tolerators (Denslow 1980, Swaine & Whitmore 1988). In this dichotomy the characteristics of the gap-demanders are often given to include small seed size, dormancy mechanisms, potentially rapid growth, and requirement of direct sunlight for germination and establishment. Conversely, shade-tolerators are considered to have large, short-lived seeds, the potential to germinate in canopy shade and an ability to grow slowly in deep shade (Swaine & Whitmore 1988). Failing to conform to either general pattern, small-seeded shade-tolerant species have been documented from both the Central American and South-east Asian tropics (Ellison at al., Metcalfe & Grubb 1995). Some of these small-seeded species have been shown to be able to germinate in filtered light approximating to canopy shade (Metcalfe 1996), and seedlings of other small-seeded species have been recorded growing under a closed canopy (Grubb 1996, Kiew 1988, Raich & Gong 1990). Several taxa shown by Metcalfe (1996) and Metcalfe & Grubb (1997) to be small-seeded and shade-tolerant were found in considerable numbers in the soil seed bank in Sabah by Kennedy (1991), and one (Urophyllum glabrum) by Putz & Appanah (1987) in Peninsular Malaysia. Species with small seeds (less than about 1-10 mg) do not have the resources to emerge from underneath a covering of leaf litter, and require litter-free sites for successful establishment (Guzman-Grajales & Walker 1991, Molofsky & Augspurger 1992, Putz 1983).
TL;DR: It is suggested that folivory (by leaf fractionation) should be energetically more advantageous than the ingestion of large amounts of low protein fruit or the active pursuit of mobile insects.
Abstract: Information on the feeding habits of the lesser dog-faced fruit bat, Cynopterus brachyotis, was obtained by the collection of food remains directly beneath daytime and feeding roosts. The bats were found to feed on the fruits of 54 plant species, the leaves of 14 species and the flower parts of four species. The seasonal phenological differences among congeneric plant species led to a steady production of fruit throughout the year and the data suggest that Ficus spp. are a key compon- ent in the diet. Judging from its wide selection of fruits, C. brachyotis, is considered to be an important seed disperser. Folivory in C. brachyotis appears to be more common than previously thought. Of the leaves consumed by the bats, seven spe- cies belonged to the family Leguminosae, followed by Myrtaceae, Moraceae, Rhizo- phoraceae and Euphorbiaceae. Fruits, in general, provide an energy-rich diet for phytophagous bats but most are low in protein. In contrast, leaves consumed by bats have a relatively high protein content. We suggest that folivory (by leaf fractionation) should be energetically more advantageous than the ingestion of large amounts of low protein fruit or the active pursuit of mobile insects.
TL;DR: The results show that seedling establishment, early growth and survival of the three tree species were affected by canopy gaps and by the environmental heterogeneity within a large gap.
Abstract: The effect of natural canopy gaps on the performance of naturally occurring tree seedling populations was studied in a tropical rain forest in French Guiana. This was done at two levels of scale. Firstly, on a 20 m x 250 m forest transect intersecting four canopy gaps, it was investigated how patterns of recruit- ment, growth and survival of seedlings of Cecropia obtusa, Dicorjnia guianensis and Pourouma bicolor differed between canopy gaps and closed forest. Secondly, for one large natural canopy gap, performance of seedling cohorts established before ('pre-gap' cohorts) and after ('post-gap' cohorts) gap formation was studied in relation to environmental heterogeneity. The direct site factor (DSF) was used as an indicator of light availability in the gap zone. Cecropia specialised in large gaps, and also in specific sites within the large gap: seedling performance was increased by light, and by dead wood. Pourouma mainly germinated under closed forest condi- tions, where it can survive for a long period until a canopy gap is formed nearby. Pourouma seedlings adjusted well to the new gap environment but they did not specialise in specific places within the gap. Seedling location of Pourouma seedlings was mainly determined by accidental positioning before gap formation. Dicorynia was able to germinate both in gaps and under closed forest conditions. Although the number of gaps studied in this study was low, the results show that seedling establishment, early growth and survival of the three tree species were affected by canopy gaps and by the environmental heterogeneity within a large gap.
TL;DR: The coccids varied in their host-plant specificity from species that occurred in most of the sampled Macaranga to one species that was found almost exclusively only on a single host species.
Abstract: Myrmecophytic species of the Paleotropical plant genus Macaranga (Euphorbiaceae) have hollow stems that are almost always occupied by ants of the genus Crematogaster and scale insects of the family Coccidae (Hemiptera: Coccoidea). The coccids have a cryptic endophytic lifestyle and are confined to this microhabitat. They are much more diverse than previously recognised. First data are presented on the diversity, prevalence, specificity and distribution of the coccids associated with myrmecophytic Macaranga species. Twenty-two species of Coccidae in total, including 15 previously unknown from Macaranga, were disco- vered from 19 species of Macaranga in Peninsular Malaysia and Borneo. The ori- ginal describers tentatively assigned the known coccid species to Coccus (Coccinae) but the Macaranga coccids still require taxonomic research to establish their correct placing. The coccids varied in their host-plant specificity from species that occurred in most of the sampled Macaranga to one species that was found almost exclusively only on a single host species. In addition to their occurrence on Macar- anga, only three species, C. macarangae and C. secretus and morphospecies C. 214 were found on rare occasions in the stem interior of a few other myrmecophytes and in a non-myrmecophytic liana, but did not regularly colonise these plants. Most of the coccids can be regarded as highly specific at the plant genus level.
TL;DR: Promotion of phosphorus uptake by arbuscular mycorrhizas and ectomycorrhiza in tropical rain forests where available soil phosphorus is low is consistent with the co- occurrence of the two types of mycorRhiza in Tropical rain forests, however, ectomyCorrhizal colonisation may also be of advantage where inputs of phosphorus rich litter raise the phosphorus status of the soil.
Abstract: The relationship between mycorrhizal colonisation and phosphorus acquired by seedlings of the arbuscular mycorrhizal tree Oubanguia alata Bak f. (Scytopetalaceae) and the ectomycorrhizal tree Tetraberlinia moreliana Aubr. (Caesalpiniodeae) was evaluated at low and high inorganic phosphorus availability. AM colonisation was positively correlated with phosphorus uptake by O. alata at low, but not at high phosphorus availability. Seedlings growth was positively related to arbuscular mycorrhizal colonisation at both low and high phosphorus availability, suggesting that growth promotion by arbuscular mycorrhizas is not simply related to an increase of phosphorus uptake. In contrast, phosphorus uptake by T. moreliana was correlated with EM colonisation at both low and high phosphorus availability, but there was no relationship between growth and ectomycorrhizal colonisation. Promotion of phosphorus uptake by arbuscular mycorrhizas and ectomycorrhizas at low phosphorus availability is consistent with the co-occurrence of the two types of mycorrhiza in tropical rain forests where available soil phosphorus is low. However, ectomycorrhizal colonisation may also be of advantage where inputs of phosphorus rich litter raise the phosphorus status of the soil, as seen in the groves of ectomycorrhizal trees in Korup National Park, and may be one of the factors reinforcing local dominance by these trees.
TL;DR: While leaf-cutter ants are thought to collect mainly vegetative plant material, they have also been observed collecting seeds or fruit parts on the forest floor (Alvarez-Buylla & Martinez-Ramos 1990, Kaspari 1996).
Abstract: While leaf-cutter ants are thought to collect mainly vegetative plant material, they have also been observed collecting seeds or fruit parts on the forest floor (Alvarez-Buylla & Martinez-Ramos 1990, Kaspari 1996). For example, leaf-cutter ants have been observed carrying considerable numbers of Brosimum alicastrum Sw. and Cecropia spp. seeds into their nests (Wirth 1996) and Leal & Oliveira (1998; pers. comm. ) found them foraging on the fruits and seeds of 19 different species of Brazilian cerrado vegetation, including six Miconia species. Under some circumstances, seed removal and relocation by leaf cutter ants might even be sufficient to affect local recruitment patterns of trees. For example, in Costa Rica, Atta cephalotes can remove all fallen fig fruit from beneath a Ficus hondurensis crown in a single night (Roberts & Heithaus 1986), while in Venezuela, seedling recruitment of the savanna tree Tapirira velutinifolia was positively associated with the seed harvesting and seed cleaning activities of the ant Atta laevigata (Farji Brenner & Silva 1996).
TL;DR: The intra-crop variation in the concentrations of major nutrients in the embryo-cum-endosperm (EE) fraction of seeds of 12 tree species of SE Asian lowland rain forest was investigated, potentially relevant to competition among young seedlings, optimal foraging by predators, allocation to defence by plants, and understanding the effect of filling of seeds.
Abstract: The intra-crop variation in the concentrations of major nutrients in the embryo-cum-endosperm (EE) fraction of seeds of 12 tree species of SE Asian lowland rain forest was investigated. Increased seed size was associated with a significant decrease in the EE concentration of N in 10 species, P and K in seven, Mg in six, and Ca in four. In contrast, the EE nutrient content increased with seed size, typically by about 1.6-fold where seed mass was 2-fold greater. In three species the allocation to protective tissues decreased with increased seed size. The results are potentially relevant to competition among young seedlings, optimal foraging by predators, allocation to defence by plants, and understanding the controls on filling of seeds.
TL;DR: Phyllostomide bats are the most important consumers of Piper fruits in the Neotropics and Carollia perspicillata and Glossophaga soricina are the species which demonstrate distinct preferences for these fruits.
Abstract: Phyllostomide bats are the most important consumers of Piper fruits in the Neotropics (Heithaus et al. 1975) and, in particular, Carollia perspicillata and Glossophaga soricina are the species which demonstrate distinct preferences for these fruits (Charles-Dominique 1991, Fleming 1981, Fleming et al. 1977, Marinho-Filho 1991, Palmeirim el al. 1989). This is also true of Piper arboreum Aubl. (Piperaceae) in the gallery forests of Central Brazil (Bizerril & Raw 1997).
TL;DR: Monitoring of the growth and survival of many seedlings of Tetragastris panamensis, Protium panamense and DesmopsisPanamensis in artificially created treefall gaps and under intact-canopy control plots suggests an estimate of 4y for the duration of the gap phase in this tropical forest.
Abstract: Despite the importance of treefall gaps in tropical forest dynamics, few studies have followed gap-phase processes for more than 2 y. We monitored, for five years, the growth and survival of many seedlings of Tetragastris panamensis (Engler) 0. Kuntze, Protium panamense (Rose) I. M. Johnston, and Desmopsis pana- mensis (Rob.) Saff. (three common tree species of the Panamanian tropical moist forest) in artificially created treefall gaps and under intact-canopy control plots. On these same plots, we also monitored light levels using hemispherical photo- graphs taken over an 8-y period. Seedling height growth was faster in gaps than under intact canopies during the first 42 mo of regrowth, then declined to rates similar to those under intact canopies. Light levels in gaps similarly rose and fell, returning to pre-gap levels by month 48. Only Tetragastris panamensis showed higher survival in gaps, contrary to the general assumption that seedling survival is enhanced by gap creation. Our results document important transition points that mark the conclusion of the gap phase, suggesting an estimate of 4y for the dura- tion of the gap phase in this tropical forest.
TL;DR: It is suggested that factors contributing to the organization of tropical lizard assemblages are complex including historical differences in morphology, prey types and sizes, habitat structure and species interactions.
Abstract: The diets of 17 lizard species (seven families) studied simultaneously in a Caribbean lowland forest of Nicaragua were compared. Lizards varied in body size over nearly one order of magnitude. Twelve species for which there were adequate samples separated by prey types and most diet overlaps were low. A pseudocommunity analysis on volumetric diet data revealed significant guild struc- ture in the assemblage. At each nearest neighbour rank in niche space, observed overlaps were higher than expected based on chance alone when all values in the consumer-resource matrix were randomized. There was no difference between observed and pseudocommunity overlaps with zero positions in the consumer- resource matrix retained (conserved-zero overlaps) indicating that the zero struc- ture of the community matrix was important in maintaining structure and that lizards were converging on key resources. Individual prey size varied among species and mean prey size was significantly correlated with body size of lizard species. A phylogenetic analysis revealed no relationship between similarity in prey use (dietary overlap) and evolutionary relationships - more closely related species did not eat more similar prey types. Based on this analysis of Nicaraguan lizard diets and comparisons with other New World tropical lizard assemblages, it is suggested that factors contributing to the organization of tropical lizard assemblages are complex including historical differences in morphology (size), prey types and sizes, habitat structure and species interactions.
TL;DR: In this article, the effects of wet and dry seasons on soil termites within a humid tropical West African forest were examined and the strongest correlations were generally found with the 2-d period, suggesting that short-term movement of termites up and down the soil profile may be the most important factor in the observed differences.
Abstract: The effects of wet and dry seasons on soil termites within a humid tropical West African forest are examined. Samples were taken monthly, over a 14-mo period, and termite abundances and species richness were estimated. These estimates were compared with the total cumulative rainfall for 30-d, 7-d and 2-d periods before each sampling. For all these time periods abundances and species richness of termites were significantly negatively correlated with rainfall. However, the strongest correlations were generally found with the 2-d period, suggesting that short-term movement of termites up and down the soil profile may be the most important factor in the observed differences, rather than longer term changes in overall abundance or species composition. This conclusion was sup- ported by a detrended correspondence analysis which showed no significant changes in species composition between dry and wet months.