Barro Colorado Island Research Articles

Review of <i>Scolia</i> (Hymenoptera: Scoliidae) from Central America, including seasonal flight activity in <i>Scolia guttata</i>

A taxonomic revision of the genus Scolia Fabricius, 1775 (Hymenoptera: Scoliidae) from Central America is presented. Two species of Scolia are present in Central America: S. (Discolia) guttata Burmeister, 1853 and S. (Hesperoscolia) rufiventris Fabricius, 1804, the latter representing the first record for Costa Rica, Panama and Colombia. The male of S. rufiventris is described and illustrated for the first time. Seasonal flight activity for S. guttata from two years of continuous Malaise trapping in Barro Colorado Island, Panama, is described.

Competition for light and persistence of rare light-demanding species within tree-fall gaps in a moist tropical forest.

Current evidence suggests that tree-fall gaps can influence forest structure and dynamics by enabling certain species guilds to persist over the long term. Here we assessed the development of local size hierarchies and asymmetric competition for light in tree-fall gaps, and the role played by these two processes for the persistence of rare light-demanding species in the Barro Colorado Island Forest Dynamics Plot (Panama). We performed spatial point pattern analysis, considering both the spatial locations (x,y) and the diameter at breast height (DBH) of all the woody plant recruits from the 1985 and 2000 censuses located in tree-fall gaps, and followed their fate up to the 1990-2010 and 2005-2010 censuses, respectively. For these two recruit cohorts, we found that, from the initial census until 5-10yr later, close neighbors presented a larger DBH than the mean DBH of all individuals within gaps, which points to a positive growth response of recruits to the increased light levels in the gap centers. However, close neighbors of the 1985 cohort also showed larger than expected DBH differences that disappeared in subsequent censuses, indicating an enhancement of size differences between neighbors and the mortality of the smaller individuals. Finally, for both recruit cohorts, we found that 10-15yr after gap formation, surviving individuals of rare light-demanding species had a negative impact on survival of neighboring individuals of other species. Our results indicate that gaps favor the persistence of rare light-demanding species through the development of local size hierarchies and asymmetric competition for light. The strength of this process, however, apparently depends upon gap size and the role played by the woody plants already existing at the time of gap formation in early colonization. Moreover, our findings suggest that in this forest, gaps may enhance colonization of plant species typical of nearby dry tropical areas, and that, over the coming decades, similar processes could strongly modify the structure and dynamics of moist tropical forests in the region.

An analysis of forest biomass sampling strategies across scales

Abstract. Tropical forests play an important role in the global carbon cycle as they store a large amount of carbon in their biomass. To estimate the mean biomass of a forested landscape, sample plots are often used, assuming that the biomass of these plots represents the biomass of the surrounding forest. In this study, we investigated the conditions under which a limited number of sample plots conform to this assumption. Therefore, the minimum number of sample sizes for predicting the mean biomass of tropical forest landscapes was determined by combining statistical methods with simulations of sampling strategies. We examined forest biomass maps of Barro Colorado Island (50 ha), Panama (50 000 km2), and South America, Africa, and Southeast Asia (3 × 106–11 × 106 km2). The results showed that around 100 plots (1–25 ha each) are necessary for continent-wide biomass estimations if the sampled plots are randomly distributed. However, locations of current inventory plots often do not meet this requirement, for example, as their sampling design is based on spatial transects among climatic gradients. We show that these nonrandom locations lead to a much higher sampling intensity being required (up to 54 000 plots for accurate biomass estimates for South America). The number of sample plots needed can be reduced using large distances (5 km) between the plots within transects. We also applied novel point pattern reconstruction methods to account for aggregation of inventory plots in known forest plot networks. The results implied that current plot networks can have clustered structures that reduce the accuracy of large-scale estimates of forest biomass if no further statistical approach is applied. To establish more reliable biomass predictions across South American tropical forests, we recommend more spatially randomly distributed inventory plots (minimum: 100 plots) and ensuring that the analyses of inventory plot data consider their spatial characteristics. The precision of forest attribute estimates depends on the sampling intensity and strategy.

Counting niches: Abundance-by-trait patterns reveal niche partitioning in a Neotropical forest.

Tropical forests challenge us to understand biodiversity, as numerous seemingly similar species persist on only a handful of shared resources. Recent ecological theory posits that biodiversity is sustained by a combination of species differences reducing interspecific competition and species similarities increasing time to competitive exclusion. Together, these mechanisms counterintuitively predict that competing species should cluster by traits, in contrast with traditional expectations of trait overdispersion. Here, we show for the first time that trees in a tropical forest exhibit a clustering pattern. In a 50-ha plot on Barro Colorado Island in Panama, species abundances exhibit clusters in two traits connected to light capture strategy, suggesting that competition for light structures community composition. Notably, we find four clusters by maximum height, quantitatively supporting the classical grouping of Neotropical woody plants into shrubs, understory, midstory, and canopy layers.

Seasonal and annual variation in the abundance of Ephuta (Hymenoptera: Mutillidae) in Panama

Introduction: Ephuta Say is a widespread New World genus of mutillid wasp whose ecology is poorly understood. Objective: The objective of this study was to determine how Ephuta species abundance varies annually and seasonally driven by weather conditions and hosts. Methods: Ephuta specimens, located in the “old forest” at Barro Colorado Island, were examined from weekly samples (2001-2006) of ten Malaise traps. The monthly abundance of each Ephuta species was compared with monthly average humidity, solar radiation, temperature and rainfall. Results: Nine species and ten morphospecies were identified. Most specimens were collected from March to June. April was the month reported with the greatest abundance. Of the four abiotic variables measured, only average monthly temperature was correlated with Ephuta abundance. Months with the highest number of Ephuta specimens were correlated with suspected host abundance, as indicated by the monthly abundance of Pompilidae (Hymenoptera) captured during the year 2007. Conclusions: We concluded that Ephuta display strong seasonal variation in abundance, with the peaks occurring during the end of the dry season and beginning of the rainy season, which correlate broadly with temperature and the abundance of their pompilid hosts.

Assessing the potential for indirect interactions between tropical tree species via shared insect seed predators

AbstractNatural enemies of plants have the potential to influence the dynamics of plant populations and the structure of plant communities. In diverse tropical forests, research on the effects of plant enemies has largely focused on the diversity‐enhancing effects of highly specialized enemies, while the community‐level effects of enemies with broader diets have rarely been considered. We investigated the community of insect seed predators interacting with seven tree species in the family Lauraceae on Barro Colorado Island (Panama). We present one of the first quantitative food webs for pre‐dispersal insect seed predators and their host plants, and use the information in the web to assess the potential for indirect interactions between the tree species. Our data suggest that there is high potential for indirect interactions between Lauraceae species via their shared seed predators. The strength and direction of these interactions are largely unrelated to the phylogenetic distance and trait similarity between species but are likely governed by the volume of fruit produced by each tree species.Abstract in Spanish is available with online material.

Host Records for Tortricidae (Lepidoptera) Reared from Seeds and Fruits in Panama

A survey of Lepidoptera reared from seeds and fruits primarily on Barro Colorado Island, Panama, yielded 444 specimens of Tortricidae representing 20 species. Nearly 90% of reared tortricids and 65% of the species are members of the tribe Grapholitini, a group that includes numerous economically important pests of fruit worldwide. We present host records for the following species: Histura panamana Brown, Platynota obliqua Walsingham complex, Platynota subargentea Walsingham, Spinipogon triangularis Brown, Cryptaspasma perseana Gilligan and Brown, Steblopotamia streblopa (Meyrick), Cydia pyraspis (Meyrick) complex, Eriosocia guttifera (Meyrick), Riculorampha ancyloides Rota and Brown, Grapholita mabea Razowski, Ricula croceus Brown, Ricula lacistema Brown, Ricula sp. 1, Ricula sp. 2, Talponia sp. 1, Talponia sp. 2, and four unidentified Grapholitini. In a comparison of studies focused on fruit- and seed-feeding insects in Thailand, Panama, and Kenya, Grapholitini represented 73% (in Thailand) to 90% (in Panama) of the total number of reared specimens of Tortricidae, and 45% (in Kenya) to 65% (in Panama) of the total number of tortricid species. However, a similar survey in Papua New Guinea produced considerably different results, with Grapholitini representing 46% of the tortricid specimens and only 20% of the species.

First Approach of Abiotic Drivers of Soil CO2 Efflux in Barro Colorado Island, Panama

Soil CO2 fluxes from tropical forests into the atmosphere are expected to increase due to global warming. Studies of environmental conditions that contribute to carbon flux are now an important focus for climate change research. However, carbon flux in tropical areas such as Panama has received less attention. In Panama, water sources, rainforests, and soil conditions are vital natural resources, particularly within the Panama Canal watershed. Mature and secondary forests represent around 60% of Panama land cover. Secondary forests are considered potential carbon sinks and they are of economic interest as a means of mitigating increasing anthropogenic CO2 emissions; however, the dynamics of carbon fluxes in the soil of secondary forests remain poorly understood. This research investigated which environmental factors influence soil CO2 efflux. We used a closed chamber method to measure soil CO2 in the tropical forest of Barro Colorado Island, Panama. During 2016 to 2017, humidity had a significant effect on CO2 flux (average: 4.36 μmol/m2s), which was substantially lower than expected for this type of tropical forest. These findings will contribute to a better understanding of the complex and dynamic interrelationships between the water and carbon cycle, as well as abiotic drivers of soil CO2 fluxes. Our use of soil respiration chambers and infrared gas analyzer systems represents an innovative contribution to the water-carbon nexus of Panama and potentially of other countries.

Seed-to-seedling transitions exhibit distance-dependent mortality but no strong spacing effects in a Neotropical forest.

Patterns of seed dispersal and seed mortality influence the spatial structure of plant communities and the local coexistence of competing species. Most seeds are dispersed in proximity to the parent tree, where mortality is also expected to be the highest, because of competition with siblings or the attraction of natural enemies. Whereas distance-dependent mortality in the seed-to-seedling transition was often observed in tropical forests, few studies have attempted to estimate the shape of the survival-distance curves, which determines whether the peak of seedling establishment occurs away from the parent tree (Janzen-Connell pattern) or if the peak attenuates but remains at the parent location (Hubbell pattern). In this study, we inferred the probability density of seed dispersal and two stages of seedling establishment (new recruits, and seedlings 20cm or taller) with distance for 24 tree species present in the 50-ha Forest Dynamics Plot of Barro Colorado Island, Panama. Using data from seed traps, seedling survey quadrats, and tree-census records spanning the 1988-2014 period, we fit hierarchical Bayesian models including parameters for tree fecundity, the shape of the dispersal kernel, and overdispersion of seed or seedling counts. We combined predictions from multiple dispersal kernels to obtain more robust inferences. We find that Hubbell patterns are the most common and Janzen-Connell patterns are very rare among those species; that distance-dependent mortality may be stronger in the seed stage, in the early recruit stage, or comparable in both; and that species with larger seeds experience less overall mortality and less distance-dependent mortality. Finally, we describe how this modeling approach could be extended at a community scale to include less abundant species.

Performance of tropical forest seedlings under shade and drought: an interspecific trade-off in demographic responses

Seedlings in moist tropical forests must cope with deep shade and seasonal drought. However, the interspecific relationship between seedling performance in shade and drought remains unsettled. We quantified spatiotemporal variation in shade and drought in the seasonal moist tropical forest on Barro Colorado Island (BCI), Panama, and estimated responses of naturally regenerating seedlings as the slope of the relationship between performance and shade or drought intensity. Our performance metrics were relative height growth and first-year survival. We investigated the relationship between shade and drought responses for up to 63 species. There was an interspecific trade-off in species responses to shade versus species responses to dry season intensity; species that performed worse in the shade did not suffer during severe dry seasons and vice versa. This trade-off emerged in part from the absence of species that performed particularly well or poorly in both drought and shade. If drought stress in tropical forests increases with climate change and as solar radiation is higher during droughts, the trade-off may reinforce a shift towards species that resist drought but perform poorly in the shade by releasing them from deep shade.

Quantifying the uncertainty of variance partitioning estimates of ecological datasets

An important objective of experimental biology is the quantification of the relationship between predictor and response variables, a statistical analysis often termed variance partitioning (VP). In this paper, a series of simulations is presented, aiming to generate quantitative estimates of the expected statistical uncertainty of VP analyses. We demonstrate scenarios with considerable uncertainty in VP estimates, such that it significantly reduces the statistical reliability of the obtained results. Especially when a predictor variable of a dataset shows a low between-group variance, VP estimates may show a high margin of error. This becomes particularly important when the respective predictor variable only explains a small fraction of the overall variance, or the number of replicates is particularly small. Moreover, it is demonstrated that the expected error of VP estimates of a dataset can be approximated by bootstrap resampling, giving researchers a tool for the quantification of the uncertainty associated with an arbitrary VP analysis. The applicability of this method is demonstrated by a re-analysis of the Oribatid mite dataset introduced by Borcard and Legendre in 1994 and the Barro Colorado Island tree count dataset by Condit and colleagues. We believe that this study may encourage biologists to approach routine statistical analyses such as VP more critically, and report the error associated with them more frequently.

Testing for changes in biomass dynamics in large-scale forest datasets.

Tropical forest responses to climate and atmospheric change are critical to the future of the global carbon budget. Recent studies have reported increases in estimated above-ground biomass (EAGB) stocks, productivity, and mortality in old-growth tropical forests. These increases could reflect a shift in forest functioning due to global change and/or long-lasting recovery from past disturbance. We introduce a novel approach to disentangle the relative contributions of these mechanisms by decomposing changes in whole-plot biomass fluxes into contributions from changes in the distribution of gap-successional stages and changes in fluxes for a given stage. Using 30years of forest dynamic data at Barro Colorado Island, Panama, we investigated temporal variation in EAGB fluxes as a function of initial EAGB (EAGBi ) in 10×10m quadrats. Productivity and mortality fluxes both increased strongly with initial quadrat EAGB. The distribution of EAGB (and thus EAGBi ) across quadrats hardly varied over 30years (and seven censuses). EAGB fluxes as a function of EAGBi varied largely and significantly among census intervals, with notably higher productivity in 1985-1990 associated with recovery from the 1982-1983 El Niño event. Variation in whole-plot fluxes among census intervals was explained overwhelmingly by variation in fluxes as a function of EAGBi , with essentially no contribution from changes in EAGBi distributions. The high observed temporal variation in productivity and mortality suggests that this forest is very sensitive to climate variability. There was no consistent long-term trend in productivity, mortality, or biomass in this forest over 30years, although the temporal variability in productivity and mortality was so strong that it could well mask a substantial trend. Accurate prediction of future tropical forest carbon budgets will require accounting for disturbance-recovery dynamics and understanding temporal variability in productivity and mortality.

Probability distributions of extinction times, species richness, and immigration and extinction rates in neutral ecological models

In community ecology, neutral models make the assumption that species are equivalent, such that species abundances differ only because of demographic stochasticity. Despite their ecological simplicity, neutral models have been found to give reasonable descriptions of expected patterns of biodiversity in communities with many species. Such patterns include the expected total number of species and species-abundance distributions describing the expected number of species in different abundance classes. However, the expected patterns represent only the central tendencies of the full distributions of possible outcomes. Thus, ecological inferences and conclusions based only on expected patterns are incomplete, and may be misleading. Here, we address this issue for the spatially implicit neutral model, by using classic results from birth–death processes to derive (1) the probability distribution of extinction time of a species with given abundance for the metacommunity; (2) the probability distributions of total species richness and number of species with given abundance for both the metacommunity and local community; and (3) the probability distributions of the average immigration and extinction rates in the local community, across different values of total species richness. We illustrate the utility of these probability distributions in providing greater ecological insight via statistical inference. Firstly, we show that under the neutral metacommunity model, there is only 2.65×10−9 probability that the age of a common tree species in the Amazon is ≤ 3 × 108 yr, which is approximately the oldest estimated age of the first angiosperm. Thus, species ages from the model are unrealistically high. Secondly, for a tree community in a 50 ha plot at Barro Colorado Island in Panama, we show that the spatially implicit model can be fitted to observed species richness and an independent estimate of the immigration parameter, with the fitted model predicting a species-abundance distribution close to the observed distribution. Our results complement those using sampling formulae that specify the multivariate probability distribution of species abundances from neutral models.

A deep convolutional neural network based classifier for passive acoustic monitoring of neotropical katydids

Insects occupy a central position in terrestrial trophic webs, consuming large amounts of vegetation and being consumed by other fauna. Changes in insect communities can have widespread effects across an ecosystem. In addition, having relatively small dispersal distances and stereotyped calls, insects make for an excellent choice as a monitoring target. Here, passive acoustic monitoring is employed for studying katydids, a relative of crickets and grasshoppers that are often charismatic mimics of leaves and sticks. In a prior study, call repertoires of over 60 species of katydids were established using individuals captured on Barro Colorado Island, Panama. These recordings are used in training a deep convolutional neural network based classifier, for subsequent analyses of long-term field recordings that are currently being collected. Coarse imbalances in the number of captured individuals per species and in their calling rates resulted in an unbalanced dataset. Furthermore, differences in recording equipment and in the recording practices posed challenges to achieving a well-rounded dataset. The measures taken to address these impediments will be discussed along with the classifier design choices. The classifier yielded >98% mean-average-precision over 60 classes on an exclusive validation split. Results of its application on field recordings will be presented.

Ant Morphology Mediates Diet Preference in a Neotropical Toad (Rhinella alata)

Despite the widespread occurrence of myrmecophagy in anurans, it is unclear whether ant-specialists feed on ants opportunistically or whether they prefer species with specific morphological, ecological, or nutritional traits. We flushed 105 stomachs of a lowland neotropical toad, Rhinella alata, and identified each consumed ant to species level. We calculated linear selectivity to determine predator preference for ants by comparing the abundances of consumed species to their relative abundances in the leaf litter community on Barro Colorado Island, Panama. We conducted linear regression models to test whether linear selectivity or general predator preference related to seven morphological characteristics and two measurements of nutritional content. Rhinella alata preferentially ate 24 ant species. Other species were either avoided (n = 34) or were eaten opportunistically (n = 26). Preferred ant species were large and textured with hair and/or rugosity. We found that prey preference did not relate to prey nutritional content, that small ants were avoided even if they were superabundant in the environment, and that chemically defended and aggressive ants were preferred if they were large enough. We propose that R. alata prefers large ants because they represent a more efficient prey item in terms of prey handling time and because they are easier to see than are smaller ants. Furthermore, we hypothesize that predation attempts are more successful when prey are textured because microstructures on the tongue and prey surface may increase prey adhesion. The ant specialist R. alata is not specializing on any particular ant species but rather maximizing prey quantity over quality by only eating the largest ants, despite their scarcity in the environment.

Redescription and new records of the monotypic genus Trynocoris Herring, 1976 (Heteroptera: Miridae: Cylapinae: Fulviini).

Trynocoris lawrencei Herring, the only representative of the genus Trynocoris and only known from Barro Colorado Island, Canal Zone, Panama, is recorded for the first time from Mexico, Nicaragua, Panama: Chinqui and Ecuador. Redescription of the genus and species are given along with color photographs of the adults, scanning electron micrographs of selected structures of T. lawrencei. Illustrations of the tarsi and male genitalia are presented for the first time.

Analyzing community structure subject to incomplete sampling: hierarchical community model vs. canonical ordinations

Recently developing hierarchical community models (HCMs) accounting for incomplete sampling are promising approaches to understand community organization. However, pros and cons of incorporating incomplete sampling in the analysis and related design issues remain unknown. In this study, we compared HCM and canonical redundancy analysis (RDA) carried out with 10 different dissimilarity coefficients to evaluate how each approach restores true community abundance data sampled with imperfect detection. We conducted simulation experiments with varying numbers of sampling sites, visits, mean detectability and mean abundance. Performance of HCM was measured by estimates of "expected" (mean) abundance ( ) and realized abundance ( : direct estimate of site- and species-specific abundance). We also compared HCM and different types of RDA (normal, partial, and weighted), all performed with the same ten different dissimilarity coefficients, with unequal number of visits to sampling sites. In addition, we applied the models to a virtual survey carried out on the Barro Colorado Island tree plot data for which we know true community abundance. Simulation experiments showed that yielded by HCM best restored the underlying abundance of constituent species among 12 abundance estimates by HCM and RDA regardless if the sampling was equal or unequal. Mean abundance predominantly affected the performance of HCM and RDA while yielded by HCM had comparable performance to percentage difference and Gower dissimilarity coefficients of RDA. Relative performance of RDA types depended on the combination of dissimilarity coefficients and the distribution of sampling effort. Best performance of followed by , percentage difference and Gower dissimilarity were also observed for the analysis of tree plot data, and graphical plots (triplots) based on rather than clearly separated the effects of two environmental covariates on the abundance of constituent species. Under our conditions of model evaluation and the method, we concluded that, in terms of assessing the environmental dependence of abundance, HCMs and RDA can have comparable performance if we can choose appropriate dissimilarity coefficients for RDA. However, since HCMs provide straightforward biological interpretations of parameter estimates and flexibility of the analysis, HCMs would be useful in many situations as well as conventional canonical ordinations.

Successional loss of two key food tree species best explains decline in group size of Panamanian howler monkeys (Alouatta palliata)

AbstractNegative impacts of discrete, short‐term disturbances to wildlife populations are well‐documented. The consequences of more gradual environmental change are less apparent and harder to study because they play out over longer periods and are often indirect in their action. Yet, they can drive the decline of wildlife populations even in seemingly pristine and currently well‐protected habitats. One such environmental change is a successional shift in a community's species composition as it regenerates from disturbance caused by past human land use. Early and middle successional tree species often provide key foods to folivores and frugivores, but the abundance of these resources drops as the forest matures, with adverse repercussions for these consumers. Our 44‐year record (1974–2018) of howler monkey (Alouatta palliata) group sizes and demographic composition from Barro Colorado Island, Panama, a protected reserve, documents an example of this phenomenon. After 70 years of relative stability, the mean size of howler monkey groups exhibited a marked decline, beginning in 2003. This downward trajectory in group size has continued through the most recent census in 2018. The composition of howler groups also changed significantly during the study period, with the patterns of decline differing among age/sex classes. There is no evidence that these changes were caused by increased rates of emigration, group fission, predation, parasitism, or disease. Rather, they are best explained by an island‐wide, succession‐driven decline in the densities of two species of free‐standing fig trees, Ficus yoponensis and F. insipida, which together were providing ~36% of BCI howlers’ annual diet.Abstract in Spanish is available with online material.

Dry season soil water potential maps of a 50 hectare tropical forest plot on Barro Colorado Island, Panama

Fine scale spatial variation in soil moisture influences plant performance, species distributions and diversity. However, detailed information on local soil moisture variation is scarce, particularly in species-rich tropical forests. We measured soil water potential and soil water content in the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, one of the best-studied tropical forests in the world. We present maps of soil water potential for several dry season stages during a regular year and during an El Niño drought. Additionally, we provide code that allows users to create maps for specific dates. The maps can be combined with other freely available datasets such as long-term vegetation censuses (ranging from seeds to adult trees), data on other resources (e.g. light and nutrients) and remote sensing data (e.g. LiDAR and imaging spectroscopy). Users can study questions in various disciplines such as population and community ecology, plant physiology and hydrology under current and future climate conditions.

Comparing Allee effect-based and dispersal-based neutral models for species abundance distribution patterns

Dispersal is important for biodiversity maintenance in both neutral and niche theories. However, little is known about the potential role of Allee effect at the community level. In the present study, we developed neutral models for quantifying the separate and joint influences of the Allee effect and dispersal process, respectively, on species abundance distribution (SAD) patterns. Tree census data from Barro Colorado Island (BCI), Panama were used as the case to compare different neutral SAD models. Results showed that Allee effects were not detected in the BCI tree SAD curve. By contrast, the neutral models with the incorporation of dispersal process (including both immigration and emigration) can remarkably improve the fitting power of neutral models on the BCI tree SAD curve. Finally, even though the influence is not detectable, the Allee effect-based SAD models still might be alternative SAD models for model comparison and null hypothesis testing.