Brain volumetry from CT-scan endocasts of three neotropical carnivores

Studies on brain anatomy can clarify specific evolutionary and behavioural aspects of wild animals. The rich diversity in a broad range of habitats makes carnivorans especially eligible for studying the relations between the brain form and behaviour, cognitive, sensorial and motor traits. This study compared the brain's contour and total and segmented brain volumetry in three species of neotropical carnivorans. CT images of 17 skulls of three species were acquired: Conepatus chinga (n = 6), Galictis cuja (n = 6) and Lontra longicaudis (n = 5). Three-dimensional endocasts allowed for estimating the brain's total and segmented volumes (olfactory bulb, rostral cerebrum, caudal cerebrum and cerebellum/brain stem). The average volume percentage of the segments was compared interspecifically and intraspecifically between the sexes. The otter has a notably more complex gyrification, typical for semiaquatic carnivorans. Proportionally, the olfactory bulb was significantly larger in hog-nosed skunks, possibly due to a better sense of smell for capturing insects. The proportional volumes of the rostral cerebrum, caudal cerebrum and cerebellum/brain stem segments did not differ between these species. Social behaviour traits and tactile, motor and balance skills were probably not sufficiently distinct to reflect differences in the brain segments analysed in these three species.

Inferring predator-prey interactions from camera traps: A Bayesian co-abundance modeling approach

Predator-prey dynamics are a fundamental part of ecology, but directly studying interactions has proven difficult. The proliferation of camera trapping has enabled the collection of large datasets on wildlife, but researchers face hurdles inferring interactions from observational data. Recent advances in hierarchical co-abundance models infer species interactions while accounting for two species' detection probabilities, shared responses to environmental covariates, and propagate uncertainty throughout the entire modeling process. However, current approaches remain unsuitable for interacting species whose natural densities differ by an order of magnitude and have contrasting detection probabilities, such as predator-prey interactions, which introduce zero inflation and overdispersion in count histories. Here, we developed a Bayesian hierarchical N-mixture co-abundance model that is suitable for inferring predator-prey interactions. We accounted for excessive zeros in count histories using an informed zero-inflated Poisson distribution in the abundance formula and accounted for overdispersion in count histories by including a random effect per sampling unit and sampling occasion in the detection probability formula. We demonstrate that models with these modifications outperform alternative approaches, improve model goodness-of-fit, and overcome parameter convergence failures. We highlight its utility using 20 camera trapping datasets from 10 tropical forest landscapes in Southeast Asia and estimate four predator-prey relationships between tigers, clouded leopards, and muntjac and sambar deer. Tigers had a negative effect on muntjac abundance, providing support for top-down regulation, while clouded leopards had a positive effect on muntjac and sambar deer, likely driven by shared responses to unmodelled covariates like hunting. This Bayesian co-abundance modeling approach to quantify predator-prey relationships is widely applicable across species, ecosystems, and sampling approaches and may be useful in forecasting cascading impacts following widespread predator declines. Taken together, this approach facilitates a nuanced and mechanistic understanding of food-web ecology.

Prey tracking and predator avoidance in a Neotropical moist forest: a camera-trapping approach

Whether prey species avoid predators and predator species track prey is a poorly understood aspect of predator–prey interactions, given measuring prey tracking by predators and predator avoidance by prey is challenging. A common approach to study these interactions among mammals in field situations is to monitor the spatial proximity of animals at fixed times, using GPS tags fitted to individuals. However, this method is invasive and only allows tracking of a subset of individuals. Here, we use an alternative, noninvasive camera-trapping approach to monitor temporal proximity of predator and prey animals. We deployed camera traps at fixed locations on Barro Colorado Island, Panama, where the ocelot (Leopardus pardalis) is the principal mammalian predator, and tested two hypotheses: (1) prey animals avoid ocelots; and (2) ocelots track prey. We quantified temporal proximity of predators and prey by fitting parametric survival models to the time intervals between subsequent prey and predator captures by camera traps, and then compared the observed intervals to random permutations that retained the spatiotemporal distribution of animal activity. We found that time until a prey animal appeared at a location was significantly longer than expected by chance if an ocelot had passed, and that the time until an ocelot appeared at a location was significantly shorter than expected by chance after prey passage. These findings are indirect evidence for both predator avoidance and prey tracking in this system. Our results show that predator avoidance and prey tracking influence predator and prey distribution over time in a field setting. Moreover, this study demonstrates that camera trapping is a viable and noninvasive alternative to GPS tracking for studying certain predator–prey interactions.

Ecological complexity and the biosphere: the next 30 years

Global warming, habitat loss and overexploitation of limited resources are leading to alarming biodiversity declines. Ecosystems are complex adaptive systems that display multiple alternative states and can shift from one to another in abrupt ways. Some of these tipping points have been identified and predicted by mathematical and computational models. Moreover, multiple scales are involved and potential mitigation or intervention scenarios are tied to particular levels of complexity, from cells to human–environment coupled systems. In dealing with a biosphere where humans are part of a complex, endangered ecological network, novel theoretical and engineering approaches need to be considered. At the centre of most research efforts is biodiversity, which is essential to maintain community resilience and ecosystem services. What can be done to mitigate, counterbalance or prevent tipping points? Using a 30-year window, we explore recent approaches to sense, preserve and restore ecosystem resilience as well as a number of proposed interventions (from afforestation to bioengineering) directed to mitigate or reverse ecosystem collapse. The year 2050 is taken as a representative future horizon that combines a time scale where deep ecological changes will occur and proposed solutions might be effective.

This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’.

Occupancy winners in tropical protected forests: a pantropical analysis

The structure of forest mammal communities appears surprisingly consistent across the continental tropics, presumably due to convergent evolution in similar environments. Whether such consistency extends to mammal occupancy, despite variation in species characteristics and context, remains unclear. Here we ask whether we can predict occupancy patterns and, if so, whether these relationships are consistent across biogeographic regions. Specifically, we assessed how mammal feeding guild, body mass and ecological specialization relate to occupancy in protected forests across the tropics. We used standardized camera-trap data (1002 camera-trap locations and 2-10 years of data) and a hierarchical Bayesian occupancy model. We found that occupancy varied by regions, and certain species characteristics explained much of this variation. Herbivores consistently had the highest occupancy. However, only in the Neotropics did we detect a significant effect of body mass on occupancy: large mammals had lowest occupancy. Importantly, habitat specialists generally had higher occupancy than generalists, though this was reversed in the Indo-Malayan sites. We conclude that habitat specialization is key for understanding variation in mammal occupancy across regions, and that habitat specialists often benefit more from protected areas, than do generalists. The contrasting examples seen in the Indo-Malayan region probably reflect distinct anthropogenic pressures.

Abundance of the exploited red-rumped agouti (Dasyprocta leporina Rodentia: Dasyproctidae) on the island of Trinidad

Despite their economic, ecological and cultural importance, few studies have examined the population size, distribution and trends of the red-rumped agouti (Dasyprocta leporina) on the island of Trinidad. This study reports densities of agouti on Trinidad during a three-year period, including two years of a moratorium on hunting. Diurnal transect surveys were conducted and density estimates were calculated using the DISTANCE programme and King’s Estimator. Density varied between 7 and 44 individuals/km2 between different sites, 19–28 individuals/km2 island-wide, and with two of four sites showing a potential decline in estimated density in the final year of sampling after hunting resumed.

Elevation patterns and critical environmental drivers of the taxonomic, functional, and phylogenetic diversity of small mammals in a karst mountain area

Understanding how biodiversity components are related under different environmental factors is a fundamental challenge for ecology studies, yet there is little knowledge of this interplay among the biotas, especially small mammals, in karst mountain areas. Here, we examine the elevation patterns of the taxonomic diversity (TD), phylogenetic diversity (PD), and functional diversity (FD) of small mammals in a karst mountain area, the Wuling Mountains, Southwest China, and compare these patterns between taxa (Rodentia and Eulipotyphla) and scales (broad‐ and narrow‐range species). We also disentangle the impacts of the human influence index, net primary productivity (NPP), normalized difference vegetation index (NDVI), annual precipitation (AP), and annual mean temperature (AMT) on these three facets of biodiversity by using structural equation modeling. We recorded a total of 39 small mammal species, including 26 rodents and 13 species of the order Eulipotyphla. Our study shows that the facets of biodiversity are spatially incongruent. Net primary productivity has a positive effect on the three facets for most groups, while the effect of the NDVI is negative for TD and PD in most groups. AMT temperature and AP have negative effects on FD and PD, whereas TD is dependent on the species range scale. The human influence index effect on TD and PD also depends on the species range scale. These findings provide robust evidence that the ecological drivers of biodiversity differ among different biotas and different range scales, and future research should use multifacet approach to determine biodiversity conservation strategies.

Assessing the population density of the spotted paca, Cuniculus paca, (Rodentia: Cuniculidae) on an Atlantic Forest island, southeastern Brazil

The spotted paca,Cuniculuspaca (Linnaeus, 1766), is a Neotropical, opportunistic, frugivorous caviomorph rodent, that inhabits primarily broadleaf forests. We aimed to provide the first estimates of density of C.paca for the Ilha Grande, an island located in the Atlantic Rain Forest biome of Brazil. Density and population size were estimated using the total number of individuals observed along each trail through the program DISTANCE 7. Our estimates of density and population size reinforces the importance of the Ilha Grande as an important reservoir of the species. Therefore, the results presented herein can be a starting point to support future action plans for the species, making predictions regarding the ecosystem and management and conservation of the spotted paca. Furthermore, the results can be used as a surrogate for other regions in which the species occurs.

Small mammal responses to Amazonian forest islands are modulated by their forest dependence

Hydroelectric dams have induced widespread loss, fragmentation and degradation of terrestrial habitats in lowland tropical forests. Yet their ecological impacts have been widely neglected, particularly in developing countries, which are currently earmarked for exponential hydropower development. Here we assess small mammal assemblage responses to Amazonian forest habitat insularization induced by the 28-year-old Balbina Hydroelectric Dam. We sampled small mammals on 25 forest islands (0.83-1466 ha) and four continuous forest sites in the mainland to assess the overall community structure and species-specific responses to forest insularization. We classified all species according to their degree of forest-dependency using a multi-scale approach, considering landscape, patch and local habitat characteristics. Based on 65,520 trap-nights, we recorded 884 individuals of at least 22 small mammal species. Species richness was best predicted by island area and isolation, with small islands (< 15 ha) harbouring an impoverished nested subset of species (mean ± SD: 2.6 ± 1.3 species), whereas large islands (> 200 ha; 10.8 ± 1.3 species) and continuous forest sites (∞ ha; 12.5 ± 2.5 species) exhibited similarly high species richness. Forest-dependent species showed higher local extinction rates and were often either absent or persisted at low abundances on small islands, where non-forest-dependent species became hyper-abundant. Species capacity to use non-forest habitat matrices appears to dictate small mammal success in small isolated islands. We suggest that ecosystem functioning may be highly disrupted on small islands, which account for 62.7% of all 3546 islands in the Balbina Reservoir.

Annual and spatial variation in composition and activity of terrestrial mammals on two replicate plots in lowland forest of eastern Ecuador

Terrestrial mammals are important components of lowland forests in Amazonia (as seed dispersal agents, herbivores, predators) but there are relatively few detailed studies from areas that have not been affected by human activities (e.g., hunting, logging). Yet, such information is needed to evaluate effects of humans elsewhere. We used camera traps to sample medium to large-sized terrestrial mammals at a site in lowland forests of eastern Ecuador, one of the most biologically rich areas in the world. We deployed cameras on two study plots in terra firme forest at Tiputini Biodiversity Station. Sixteen cameras were arranged 200 m apart in a 4 × 4 grid on each plot. Cameras were operated for  60 days in January–March, 2014–2017, for a total of 3,707 and 3,482 trap-days on the two plots (Harpia, Puma). A total of 28 species were recorded; 26 on Harpia and 25 on Puma. Number of species recorded each year was slightly greater on Harpia whereas overall capture rates (images/100 trap-days) were higher on Puma. Although most species were recorded on each plot, differences in capture rates meant that yearly samples on a given plot were more similar to each other than to samples on the other plot. Images of most species showed a clumped distribution pattern on each plot; Panthera onca was the only species that did not show a clumped distribution on either plot. Images at a given camera location showed no evidence of autocorrelation with numbers of images at nearby camera locations, suggesting that species were responding to small-scale differences in habitat conditions. A redundancy analysis showed that environmental features within 50 or 100 m of camera locations (e.g., elevation, variation in elevation, slope, distance to streams) accounted for significant amounts of variation in distribution patterns of species. Composition and relative importance based on capture rates were very similar to results from cameras located along trails at the same site; similarities decreased at increasing spatial scales based on comparisons with results from other sites in Ecuador and Peru.

Using certified timber extraction to benefit jaguar and ecosystem conservation

The jaguar Panthera onca requires large areas of relatively intact habitats containing adequate amounts of prey to survive. Since a substantial portion of jaguar range occurs outside of strict protected areas, there is a need for economic incentives for habitat conservation, which carefully managed selective logging can provide. Forest Stewardship Council and Pan European Forest Council certifications intended to regulate wood extraction to maintain the ecological functions of forests require evidence of biodiversity and ecosystem conservation. We draw on twelve surveys across four countries and a range of biomes to present evidence that adequate logging management can maintain jaguar populations, but that they are at risk without efficient control of secondary impacts of access and hunting. Where resident, the presence of jaguars can serve as an indication that the ecological requirements of certified timber extraction are being met. We present a gradient of rigor for monitoring, recommending cost-effective options.

Nonvolant mammalian populations in primary and secondary Central American rainforests as revealed by transect surveys

Secondary forests are now prominent features in Neotropical landscapes, yet little is known about their conservation value for nonvolant mammalian communities. We performed a 20-month study using transect walks to survey the nonvolant mammal fauna in primary and secondary forests at La Selva Biological Station in the Caribbean lowlands of northeastern Costa Rica. We found that secondary forests can hold complex mammalian communities and no species exhibited habitat preferences between primary and secondary forests. With few exceptions, behavioral and group dynamic characteristics of mammal species were similar between forest types. Our research allows us to address methodological questions and assess the effectiveness of transect sampling. Monthly detection rates vary widely by species and likely reflect short-term changes in behavior rather than population fluctuations. Air temperature and rainfall are the factors most associated with monthly detection rates for various species. Small-scale areas of higher and lower use are evident for several species. Neither time of morning for surveys nor number of observers per trail affects detection rate. We report current abundances for the most commonly observed species and note generally lower densities in the Caribbean lowlands than elsewhere in the Neotropics. This research highlights that in less seasonal, evergreen forests climatic factors can still affect mammalian behavior. Overall, we find that secondary forests are of high conservation value and that transect walks are an effective methodology to sample many nonvolant mammal species, and we present recommendations on how to sample properly to conduct rigorous and long-term studies.

Los bosques secundarios son mucho más comunes en el neotrópico, pero poco se sabe sobre su importancia en la conservación de comunidades de mamíferos no voladores. Durante 20 meses llevamos a cabo un estudio usando líneas de transectos para investigar la fauna de mamíferos no voladores en bosques primarios y secundarios en la Estación Biológica La Selva en las tierras bajas caribeñas al noreste de Costa Rica. Pudimos constatar que los bosques secundarios pueden albergarcomplejas comunidades de mamíferos y ninguna especie exhibe preferencias de hábitat entre bosque primario y secundario. Con pocas excepciones, las características dinámicas de grupo y comportamiento de especies de mamíferos fueron similares entre los dos tipos de bosque. Nuestra investigación nos permite abordar cuestiones metodológicas y evaluar la eficacia del muestreo con transectos. Las tasas mensuales de detección varían de acuerdo a la especie y probablemente reflejan cambios a corto plazo en las fluctuaciones del comportamiento en vez de la población. La temperatura del aire y la precipitación son los factores más asociados con las tasas mensuales de detección de distintas especies. Encontramos que varias especies muestran diferentes incidencias de uso en zonas pequeñas. Ni la hora de la mañana, ni el número de observadores en las encuestas por transecto afectan la tasa de detección. Presentamos la abundancia actual de las especies más comúnmente observadas y notamos en general bajas densidades en las tierras bajas del Caribe más que en otras partes del neotrópico. Esta investigación resalta que en los bosques menos estacionales, factores climáticos aún pueden afectar el comportamiento de mamíferos. En general, encontramos que los bosques secundarios son de alto valor para la conservación y que los muestreos en transectos son una metodología eficaz para estudiar muchas especies de mamíferos no voladores y presentamos recomendaciones sobre cómo llevar a cabo muestreos adecuados para realizar estudios rigurosos a largo plazo.

Widespread Forest Vertebrate Extinctions Induced by a Mega Hydroelectric Dam in Lowland Amazonia

Mega hydropower projects in tropical forests pose a major emergent threat to terrestrial and freshwater biodiversity worldwide. Despite the unprecedented number of existing, under-construction and planned hydroelectric dams in lowland tropical forests, long-term effects on biodiversity have yet to be evaluated. We examine how medium and large-bodied assemblages of terrestrial and arboreal vertebrates (including 35 mammal, bird and tortoise species) responded to the drastic 26-year post-isolation history of archipelagic alteration in landscape structure and habitat quality in a major hydroelectric reservoir of Central Amazonia. The Balbina Hydroelectric Dam inundated 3,129 km2 of primary forests, simultaneously isolating 3,546 land-bridge islands. We conducted intensive biodiversity surveys at 37 of those islands and three adjacent continuous forests using a combination of four survey techniques, and detected strong forest habitat area effects in explaining patterns of vertebrate extinction. Beyond clear area effects, edge-mediated surface fire disturbance was the most important additional driver of species loss, particularly in islands smaller than 10 ha. Based on species-area models, we predict that only 0.7% of all islands now harbor a species-rich vertebrate assemblage consisting of ≥80% of all species. We highlight the colossal erosion in vertebrate diversity driven by a man-made dam and show that the biodiversity impacts of mega dams in lowland tropical forest regions have been severely overlooked. The geopolitical strategy to deploy many more large hydropower infrastructure projects in regions like lowland Amazonia should be urgently reassessed, and we strongly advise that long-term biodiversity impacts should be explicitly included in pre-approval environmental impact assessments.

Seed dispersal by rodents in a lowland forest in central Panama

We studied the removal of seeds of three species of large-seeded tree (Astrocaryum standleyanum, Attalea butyracea and Dipteryx oleifera) from three different heights within six study plots in a lowland forest in central Panama. Fresh fruits with intact seeds fitted with industrial sewing bobbins were placed within semi-permeable exclosures. Removed seeds were tracked to deposition sites, and seed fate was determined. Removals were likely perpetrated by two small rodents, the strictly terrestrial Proechimys semispinosus and the scansorial Sciurus granatensis, because they were the most abundant small rodents in the study site during the study period and were of sufficient size to remove large seeds. Rodent abundance and fruit availability were estimated by conducting censuses. Nine microhabitat variables were measured at each deposition site to determine if these two rodents were preferentially depositing seeds in sites with certain characteristics or were randomly depositing seeds. During the study, rodents handled 98 seeds, 85 of which were not predated upon and could potentially germinate. Removal rates were not influenced by rodent abundance or fruit availability. Seeds were most frequently moved <3 m and deposited with the fruit eaten and the seed intact. However, some seeds did experience relatively long-distance dispersal (>10 m). Rodents preferentially deposited seeds in locations with large logs (>10 cm diameter), dense herbaceous cover, and an intact canopy. The number of large logs was different from random locations. Despite not being able to determine long-term fate (greater than c. 1 y), we show that these small rodents are not primarily seed predators and may in fact be important mutualists by dispersing seeds relatively long distances to favourable germination sites.

Diversity and habitat preference of medium and large-sized mammals in an urban forest fragment of southwestern Amazon

We assessed the species composition and abundance of medium and large-sized mammals in an urban forest fragment in the Brazilian Amazon, and recorded the preference of some species for particular phytophysiognomies. We placed nine transects with 20 sand plots each in three phytophysiognomies: open rainforest with a dominance of bamboos (OFB), open rainforest with palm trees (OFP), and dense rainforest (DF). We calculated species abundance as the number of records/plot.day, in a total of 2,700 plots.day. We recorded twelve mammal species; Sylvilagus brasiliensis (Linnaeus, 1758) and Dasyprocta fuliginosa (Wagler, 1831) were the most abundant. The results differed among phytophysiognomies: DF presented the highest mammal diversity, whereas the species composition of OFP was less similar than that of other phytophysiognomies. Rodents showed higher preference for OFP and Sylvilagus brasiliensis was more abundant in OFB. The study area showed high species richness, with the occurrence of mesopredators, but there was a predominance of common species adaptable to disturbed environments, which reflects the severe isolation degree of the forest fragment and the hunting pressure that is still present.

Viability of small seeds found in feces of the Central American tapir on Barro Colorado Island, Panama

Tapirs are known as effective dispersers of large-seeded tree species, but their role in dispersing small-seeded plant species has yet to be established. Tapir feces have been reported to contain large numbers of small seeds, but whether these are viable has rarely been evaluated. We determined the abundance and viability of small seeds in feces of Central American tapir (Tapirus bairdii) on Barro Colorado Island, Panama. A total of 72 fecal samples were collected opportunistically from 4 tapir latrine sites. Seeds were manually extracted from feces and classified by size. Seed viability was estimated by opening each seed and examining for the presence of at least 1 intact firm white endosperm. In total, we obtained 8166 seeds of at least 16 plant species. Small-seeded species dominated, with 96% of all seeds found measuring <5 mm. The canopy tree Laetia procera was the most abundant species in the samples. Of all small seeds found, 69% contained an intact endosperm and appeared viable. This suggests that small seeds, like large seeds, often pass through the digestive tract of T. bairdii intact. Thus, tapirs potentially serve as effective dispersers of a wide range of small-seeded plant species.

Seed predation and defleshing in the agouti-dispersed palm Astrocaryum standleyanum

The agouti (Dasyprocta punctata) meticulously defleshes Astrocaryum standleyanum palm seeds before scatter hoarding. On Barro Colorado Island, Panama, we experimentally tested three hypotheses on how this behaviour could reduce seed predation to the mutual benefit of the tree and the rodent. The first and established hypothesis – that defleshing reduces seed predation by bruchid beetles by intercepting larvae – was rejected. Experiments in which manually defleshed seeds or entire fruits were incubated at different times showed that defleshing reduced bruchid infestation before fruit fall but not after fruit fall. The second hypothesis – that defleshing reduces cache pilferage by making seeds less conspicuous – was supported. An experiment in which intact fruits and manually defleshed seeds were placed in mimicked agouti caches and followed showed that seeds with flesh were pilfered at higher rates than defleshed seeds. The third hypothesis – that defleshing reduces post-dispersal infestation of cached seeds – was rejected. An experiment in which intact fruits and manually defleshed seeds were placed in mammal exclosures and later collected to assess infestation showed that burial reduced seed infestation but defleshing did not. Thus, seed defleshing reduced palm seed predation, but in a different way than previously believed. We also found that (1) bruchid beetles can be pre-dispersal rather than post-dispersal seed predators, (2) seed infestation by scolytid beetles may control bruchid larvae, and (3) scolytids rather than bruchids are the main invertebrate seed predators of this palm.

Understanding long-term primate community dynamics: implications of forest change

Understanding the causes of population declines often involves comprehending a complex set of interactions linking environmental and biotic changes, which in combination overwhelm a population's ability to persist. To understand these relationships, especially for long-lived large mammals, long-term data are required, but rarely available. Here we use 26-36 years of population and habitat data to determine the potential causes of group density changes for five species of primates in Kibale National Park, Uganda, in areas that were disturbed to varying intensities in the late 1960s. We calculated group density from line transect data and quantified changes in habitat structure (cumulative diameter at breast height [dbh] and food availability [cumulative dbh of food trees]) for each primate species, and for one species, we evaluated change in food nutritional quality. We found that mangabeys and black-and-white colobus group density increased, blue monkeys declined, and redtails and red colobus were stable in all areas. For blue monkeys and mangabeys, there were no significant changes in food availability over time, yet their group density changed. For redtails, neither group density measures nor food availability changed over time. For black-and-white colobus, a decrease in food availability over time in the unlogged forest surprisingly coincided with an increase in group density. Finally, while red colobus food availability and quality increased over time in the heavily logged area, their group density was stable in all areas. We suggest that these populations are in nonequilibrium states. If such states occur frequently, it suggests that large protected areas will be required to protect species so that declines in some areas can be compensated for by increases in adjacent areas with different histories.

Vertebrate predation of Brazil-nuts (Bertholletia excelsa, Lecythidaceae), an agouti-dispersed Amazonian seed crop: a test of the escape hypothesis

The effects of escape distance to parental trees and tree clusters on the removal of Brazil-nut seeds (Bertholletia excelsa, Lecythidaceae) by vertebrate seed predators were examined in an entirely undisturbed stand of Brazil-nut trees of eastern Amazonia. Population density estimates, based on line-transect censuses, are also presented for Bertholletia trees and agoutis (Dasyprocta leporina), the most important scatterhoarder and seed predator of Brazil-nuts at this site. Seed removal experiments were conducted within and outside a natural Bertholletia tree cluster (castanhal) during both the wet and dry seasons. While there were no within-cluster effects of escape distance from parent trees on seed removal rates, overall seed removal within the cluster was significantly greater than that well outside the cluster. Moreover, removal rates in the wet season were consistently higher than those in the dry season both within and outside the tree cluster. Results suggest that the probability of early seed survival for Bertholletia, in relation to distance to seed sources, operates on different spatial scales, and that seed predators allocate greater foraging effort to scattered seeds during the fruitfall (wet) season, when buried seed stocks are being cached by agoutis.

Home-range use by the Central American agouti (Dasyprocta punctata) on Barro Colorado Island, Panama

This study investigates the movements and home range of the agouti (Dasyprocta punctata) on Barro Colorado Island, Panama. We captured and tracked 12 agoutis from January to December 2003. Home-range size (95% kernel) ranged from 1.56–2.45 ha (n = 6) for males and 1.34–1.97 ha (n = 5) for females. Agouti ranges overlapped and we estimated a density of approximately 100 agoutis km−2. We compared agouti movement with the locations of refuges and food trees, and the results suggest that the agoutis are central-place foragers. Agoutis moved an average of 850 m d−1 covering approximately 35% of their range daily. These movement data help us understand the potential impacts of agoutis as seed dispersers, predicting that D. punctata will encounter and hoard fallen fruit within 10–200 m (i.e. radius of home range) of its source, and move seeds towards refuges such as ground holes and dense vegetation around recent tree falls.

The herb community of a tropical forest in central Panamá: dynamics and impact of mammalian herbivores

Mammals are hypothesized to either promote plant diversity by preventing competitive exclusion or limit diversity by reducing the abundance of sensitive plant species through their activities as browsers or disturbance agents. Previous studies of herbivore impacts in plant communities have focused on tree species and ignored the herbaceous community. In an experiment in mature-phase, tropical moist forest sites in central Panamá, we studied the impact of excluding ground-dwelling mammals on the richness and abundance of herbs in 16, 30x45-m plots. Within each plot, we censused the herbaceous community in 28, 2x2-m subplots (1,792 m2 total area sampled). We identified over 54 species of herbs averaging 1.21 ramets m-2 and covering approximately 4.25% of the forest floor. Excluding mammals for 5 years had no impact on overall species richness. Within exclosures, however, there was a significant two-fold increase in the density of rare species. Overall herbaceous density and percent cover did not differ between exclosures and adjacent control plots, although cover did increase over time. Mammalian exclusion significantly increased the total cover of three-dominant herb species, Pharus latifolius, Calathea inocephala, and Adiantum lucidum, but did not affect their density. This study represents one of the most extensive herbaceous community censuses conducted in tropical forests and is among a few that quantify herbaceous distribution and abundance in terms of both density and cover. Additionally, this work represents the first community level test of mammalian impacts on the herbaceous community in a tropical forest to date. Our results suggest that ground dwelling mammals do not play a key role in altering the relative abundance patterns of tropical herbs in the short term. Furthermore, our results contrast sharply with prior studies on similar temporal and spatial scales that demonstrate mammals strongly alter tree seedling composition and reduce seedling density. Thus, we question the pervasiveness of top-down control on tropical plant communities and the paradigm that defaunation will inexorably lead to widespread, catastrophic shifts in plant communities.