Biotropica最新文献

Belowground resources are key determinants of seedling growth and survival in tropical forests. Nutrients and light may limit plant growth the most in tropical wet forests, whereas water may limit plant growth more in tropical dry forests. Nitrogen (N)-fixing species play an important role in the nitrogen and carbon cycles across tropical dry forests. However, studies investigating the joint effects of water and nutrients on the physiology and performance of N-fixing species are scarce. We implemented a full factorial shade house experiment that manipulated water and nutrients (NPK 20:20:20 and complete micronutrients) using eight tree species representing N-fixing and non-fixing tree species in the tropical dry forest of Costa Rica to determine: (1) How plant responses to water and nutrient availability vary between N-fixing and non-fixing tree species?; and (2) How nutrient and/or water availability influences seedling water- and nutrient-use traits? We found that growth and physiological responses to water and nutrient addition depended directly on the capacity of species to fix atmospheric N₂. N-fixing species responded more strongly to nutrient addition, accumulating 67% more total biomass on average (approximately double that of non-fixing taxa) and increasing average height growth rate by 41%. N-fixing species accumulated more biomass without compromising water-use efficiency, taking full advantage of the increased nutrient availability. Interestingly, results from our experiment show that increased water availability rarely influenced tropical dry forest seedling performance, whereas nutrient availability had a strong effect on biomass and growth. Overall, our results highlight the ability of N-fixing seedlings to take advantage of local soil resource heterogeneity, which may help to explain the dominance of N-fixing trees in tropical dry forests.

Spotted hyenas (Crocuta crocuta) are a large carnivore species known to range across broad savanna regions of sub-Saharan Africa. Although hyenas have occasionally been observed in rainforest habitat, they have been considered largely transient through these ecosystems. Odzala-Kokoua National Park (OKNP) in the Republic of Congo is known to harbor a resident hyena population in the forest-savanna mosaic region of the park, and while there have been observations of hyenas at large natural clearings called bais in the park's rainforest regions, these individuals have been assumed to be transient rather than representing a persistent rainforest population. We used more than 5 years of camera trap images of hyenas and their prey, 4 months of hyena GPS telemetry data, and remote sensing imagery of habitat to quantify the presence, distribution, and drivers of hyena occurrence at 10 bai complexes across OKNP. We found evidence of a perennial, stable hyena population in the rainforest, with hyena presence being positively associated with increased availability of large prey and open-canopy area in the surrounding landscape. Our results suggest that hyenas can persist in rainforest ecosystems by taking advantage of small patches of open-canopy habitat (i.e., bais) that support sufficiently large populations of preferred prey species. Our findings reveal that spotted hyenas exhibit remarkable behavioral flexibility in their habitat use and suggest that current distribution maps for the species be extended to include the forested regions of OKNP and possibly beyond.

പകൽ സമയങ്ങളിൽ നിഷ്ക്രിയമായി ഇരിക്കുന്ന Raorchestes jayarami എന്ന ജയറാമി ഇലത്തവളയുടെ നിറം അനൈച്ഛികമായി മാറുന്നതായി കാണപ്പെട്ടു. വിശ്രമവേളയിൽ പരിസരത്തിനനുസരിച്ചു നിറം മാറാൻ ഈ പ്രക്രിയ അവയ്ക്ക് ഉപകരപ്പെടുന്നതായും ഈ പഠനത്തിലൂടെ തെളിയിക്കപ്പെട്ടു. സാധാരണമായി ജീവികൾ ഇതിനായി ഉപയോഗിക്കുന്ന നാഡീവ്യൂഹ മാർഗ്ഗങ്ങളോ അന്തർഗ്രന്ഥീ ശ്രവങ്ങളോ ഉപയോഗിക്കാതെയാണ് ജയറാമി ഇലത്തവള ഇത്തരത്തിൽ നിറം മാറുന്നത് എന്നത് കൗതുകകരമാണ്. പകരം ദേഹത്തിൽ വന്നു വീഴുന്ന വെളിച്ചത്തിലെ തീവ്രതാവ്യതിയാനങ്ങൾ ചർമ കോശങ്ങളിലൂടെ തന്നെ തിരിച്ചറിഞ്ഞ്, വെളിച്ചം വീഴുന്ന ചർമഭാഗങ്ങളിൽ മാത്രമായി സൂക്ഷ്മമായ നിറമാറ്റങ്ങൾ നടത്താൻ ഇവയ്ക്ക് കഴിവുണ്ട്. പാരിസ്ഥിതിക ഘടകങ്ങളുമായുള്ള പരസ്പരബന്ധവും, പരീക്ഷണങ്ങളിലൂടെ കൃത്രിമമായി നിറം മാറ്റാൻ സാധിച്ചതും ഈ ആശയത്തെ പിന്തുണയ്ക്കുന്നു.

Tropical rainforests are biodiversity hotspots that provide a variety of ecosystem functions and services. Seed dispersal by fruit-eating birds is an important ecosystem process in the regeneration of tropical rainforests, which is increasingly threatened by widespread deforestation. In particular, the expansion of agricultural land often leads to forest fragmentation, which can have a negative impact on the interactions between plants and frugivores and thus on seed dispersal. However, little is known about how forest fragmentation affects the structure and robustness of plant–frugivore interaction networks. Here, we examined the effects of forest fragmentation on species richness of frugivorous birds interacting with focal tree species, and the structure and robustness of plant–frugivore interaction networks in the tropical lowland forests of northern Costa Rica. Species richness of frugivorous birds at the forest edges increased with fragment size and forest cover in the surrounding landscape as well as with local fruit availability. Modularity and robustness of plant–frugivore networks increased with enhanced fragment size and forest cover, while network specialization (H2′) increased only with greater forest cover. Additionally, the three common tanager species (Ramphocelus passerinii, Thraupis palmarum, and Thraupis episcopus) were identified as key bird species for network functioning by promoting among-module and within-module connectivity. Conservation measures should therefore not only focus on threatened specialist species, but more on the key species that enhance network structure and consequently increase the robustness of these trophic interaction networks. Ultimately, our study demonstrates that tropical forest fragmentation simplifies network structure, making these interactions more vulnerable to anthropogenic disturbances.

Records of wildlife animals have improved with the use of smartphones that permit people to take photographs and videos anywhere. Short videos of hummingbirds visiting artificial feeders in the Quinde Ecotourist-route covering an elevational range from 400 to 3110 m a.s.l. were taken to describe hummingbird aggression networks, to identify hummingbird hierarchies, and the effect of hummingbird traits on interspecific dominance hierarchies using data obtained through a low-cost, non-invasive method such as videos recorded with smartphones, which could be collected by the average tourist, and to relate them to morphological specialization and distributions. Smartphones can record the behavior of diverse tropical hummingbird assemblages at supplemental feeding sites, although they permit recording only during short periods. Heavier, more dominant hummingbird species monopolized access to feeders in the northwestern slopes of the Ecuadorian Andes, were more widespread, and had greater feeding rates. Our results therefore suggest that differences in body mass may lead to the formation of interspecific dominance hierarchies, leaving the heaviest and most aggressive species in the greatest control of artificial feeders' stations.

Ferns, as a large and biodiverse group, significantly contribute to the vascular plant diversity of the lowland tropical forests of Brunei Darussalam, Borneo. These forests encompass three main types: Mixed Dipterocarp Forest (MDF), Peat Swamp Forest (PSF), and Heath Forest (HF). This study aims to describe and compare fern communities in these three forest types, focusing on species richness, diversity, and the identification of indicator species. Additionally, it investigates the environmental factors that shape these communities. We conducted fieldwork in 48 plots across Brunei's lowland forests. We identified fern species and abundance through a visual census and analyzed environmental parameters, including soil pH, organic matter (OM) content, nutrient availability, and soil texture. The results showed 83 fern species, with MDF having the most (57 species). Peat Swamp and HFs had similar fern species richness (33 and 34 species, respectively). Our environmental analysis indicated that specific combinations of fern species and environmental parameters significantly correlate and effectively discriminate between the three forest types. Finally, we identified a selection of indicator species for each forest type. Our findings highlight the heterogeneity of Bornean lowland forests and the importance of preserving a diversity of habitats to maintain fern biodiversity. The study underscores the intricate interplay between environmental factors and fern diversity.

According to the neophobia threshold hypothesis, species with greater dietary specialization should be less exploratory. Few studies have measured the repeatability of exploration behavior of individually marked animals in the wild, so we lack a robust test of the neophobia threshold hypothesis. We tested this hypothesis across six landbird species, including four Darwin's finches, in a species assemblage renowned for its foraging diversity. First, we tested whether color-banded individuals showed consistent exploration behavior across two different contexts: (1) in response to a novel environment, during short-term captivity, and (2) in response to a novel object in the field. Second, to test the predictions of the neophobia threshold hypothesis, we correlated foraging diversity for each species (diversity of foraging substrates and techniques, calculated using the Shannon diversity index) against its mean exploration score. We found that individual differences in exploration behavior in the novel environment were significantly repeatable across a 2-year period (consistent over time) and also correlated with individual differences in exploration towards the novel object (consistent across contexts). Specifically, individuals that visited many sectors in the novel environment also approached the novel object in the field more quickly. At the species level, foraging substrate diversity was positively associated with the proportion of birds to approach the novel object, and species with higher foraging technique diversity were quicker to approach the novel object. These findings are consistent with the neophobia threshold hypothesis. Furthermore, our results suggest that consistent differences in exploration behavior can shape population-level patterns of foraging diversity.