Costa Rican Rain Forest Research Articles

Anthropogenic edges impact howler monkey (Alouatta palliata) feeding behaviour in a Costa Rican rainforest.

Anthropogenic forest fragmentation impacts many aspects of animal behaviour, including feeding ecology. With forests increasingly fragmented in tropical regions due to human development, the proportion of forest edge (≤ 100m from clear-cut regions) is higher relative to forest interior. Forest edges differ in vegetation from interior, making it important to better understand how anthropogenic edges impact the feeding behaviour of primates such as mantled howler monkeys (Alouatta palliata). We predicted that howler monkeys would feed on higher-quality plant resources, from a larger number of tree families, and from larger trees in forest interior compared to anthropogenic forest edge. We surveyed howler monkey feeding behaviour across forest zones in a fragmented rainforest in Costa Rica, La Suerte Biological Research Station. We observed individual monkeys for 30-minute periods, collecting data on their feeding behaviour and tree use at 2-minute intervals. We measured feeding trees and recorded the plant parts and taxonomy of resources consumed. Monkeys consumed more leaves and fewer stems and fed from a smaller number of tree families in the forest interior, while they consumed fewer leaves and more stems and fed from a larger number of tree families in the forest edge. Monkeys also fed from larger, taller trees in the forest interior than the edge. The differences in howler monkey feeding behaviour between forest zones attest to the impact of human disturbance on howler monkey feeding ecology.

The role of learning, acoustic similarity and phylogenetic relatedness in the recognition of distress calls in birds

Many groups of vertebrates produce distress calls when attacked by predators as a last attempt to survive. However, few studies investigate whether recognition of distress calls involves learning or acoustic similarity to familiar calls. This study assesses the importance of these two factors as well as phylogenetic relatedness in distress call recognition by tropical rainforest birds. We measured the avian community responses to familiar and unfamiliar distress calls in a lowland tropical rainforest in Costa Rica using playbacks of a sympatric species, the orange-billed sparrow, Arremon aurantiirostris , and a closely related allopatric species, the white-eared ground-sparrow, Melozone leucotis . In addition, to test whether recognition is driven by phylogenetic relatedness to the call sender, we compared the phylogenetic distance of approaching individuals to A. aurantiirostris when using different playback stimuli. We found that individuals called back to sympatric and allopatric calls within similar amounts of time, supporting the role of acoustic similarity in distress call recognition. We also found that individuals approached faster and spent more time inside the observation zone for sympatric distress calls than for allopatric distress calls, and both responses were stronger than the response to white noise (control), which supports the roles of acoustic similarity and learning in distress call recognition. Sympatric distress calls elicited approaching reactions from species that were more closely related to the sympatric species than did white noise, which suggests that phylogenetically related species are more likely to identify and respond to the sympatric distress signaller, while white noise elicited responses from a random subset of species that were on average more distantly related to the sympatric signaller. We conclude that learning, acoustic similarity and phylogenetic relatedness play important roles in the response to distress calls. • We performed a playback experiment of distress calls in a Neotropical forest. • We compared responses to sympatric and allopatric species' distress calls. • Both learning and acoustic similarity played a role in distress call recognition. • Species related to the distress signaller were more likely to respond to the calls.

Antlion allometry suggests a greater importance of prey capture among first larval instars

First larval stages require adequate feeding to reach subsequent instars. However, the accumulation of reserves is also important in the last larval instar because it is vital to pupate and successfully perform metamorphosis into adulthood. We indirectly determined the presence of changes in the relative importance of prey capture through larval ontogeny in the antlion larvae (Neuroptera Myrmeleontidae), a sit-and-wait predator with three instar stages that capture preys that fall into their pit-traps. We used scaling relationships between the size of body parts directly related to prey capture (prothorax) versus those that are not (thorax + abdomen). The prothorax (neck, head, and mandibles) is used in the pit building, prey capture, and re-capture, and pit cleaning. We measured the body parts of 70 larvae of Myrmeleon crudelis in a tropical rain forest of Costa Rica. The prothorax showed negative allometry: it was proportionally larger in the first than in the last instars. These results support the growth hypothesis, which states that food acquisition is key in the earlier stages of larval development. First instars can be more food-limited than later instars because they build small pit-traps where only very small arthropods can fall; have smaller mandibles and relatively lower grab force, increasing the probability of the prey escaping; and have smaller fat reserves and thus, are unable to resist long periods of starvation. This illustrates the relevance of using scaling relationships to better understand how ecological pressures change along ontogeny, emphasizing the role of food acquisition at earlier ontogenetic stages

A comparison of fruit removal in Ficus colubrinae between birds and Ectophylla alba (Chiroptera: Phyllostomidae) in a Costa Rican rain forest

ABSTRACT Ectophylla alba almost exclusively feeds on the fruits of Ficus colubrinae therefore significantly contributing to dispersal of its seeds. The objective of this research was to quantify the fruit removal of F. colubrinae by E. alba and compare it with that of birds in a F. colubrinae tree at the La Selva Biological Station, Costa Rica. We established seven quadrats randomly at different heights of the tree. We took photographs of each quadrat, quantified the fruits in each photograph, and compared the number of fruits removed during periods of high and low activity. The on-site persistence time of birds (9:05 min) was higher than that of E. alba (0.32 s). Birds removed more fruits (46) than E. alba (41). Birds defecated on site more times (13.08 feces per day) than E. alba (7.5 feces per day). Thus, E. alba is a more important seed disperser of F. colubrinae than are birds, because it persisted a short time at the feeding site, and consumed food beyond the individual trees’ canopies. Most importantly, by defecating during flight or away from the fruiting tree, E. alba disperse seeds some distance from the F. colubrinae tree, thereby contributes more effectively toward seed dispersal.

A new genus and two new species of planthopper in the tribe Cenchreini (Hemiptera: Auchenorrhyncha: Derbidae) from lowland tropical rainforest in Costa Rica.

Recent survey work for planthoppers at La Selva Biological Station in Costa Rica found two new species allied with Cenchrea Westwood. The cytochrome c oxidase subunit I (COI) and 18S were sequenced for the new taxa and used these data to assess the genus-level standing of the new taxa. The new taxa do not cluster with Cenchrea dorsalis Westwood, the type species of Cenchrea. A new genus Tico gen. n. described for the reception of new species described as Tico emmettcarri sp. n. (the type species) and Tico pseudosororius sp. n. Cenchrea sororia Fennah is moved to Tico gen. n., to form the new combination Tico sororius (Fennah). Tico gen. n. is compared with allied genera, and review genus-level diagnostic features and the species composition of Cenchrea, which appears to be compositionally heterogenous, but additional data is needed to evaluate genus-level placement of most species.

Macrocybin, a Natural Mushroom Triglyceride, Reduces Tumor Growth In Vitro and In Vivo through Caveolin-Mediated Interference with the Actin Cytoskeleton.

Mushrooms have been used for millennia as cancer remedies. Our goal was to screen several mushroom species from the rainforests of Costa Rica, looking for new antitumor molecules. Mushroom extracts were screened using two human cell lines: A549 (lung adenocarcinoma) and NL20 (immortalized normal lung epithelium). Extracts able to kill tumor cells while preserving non-tumor cells were considered “anticancer”. The mushroom with better properties was Macrocybe titans. Positive extracts were fractionated further and tested for biological activity on the cell lines. The chemical structure of the active compound was partially elucidated through nuclear magnetic resonance, mass spectrometry, and other ancillary techniques. Chemical analysis showed that the active molecule was a triglyceride containing oleic acid, palmitic acid, and a more complex fatty acid with two double bonds. The synthesis of all possible triglycerides and biological testing identified the natural compound, which was named Macrocybin. A xenograft study showed that Macrocybin significantly reduces A549 tumor growth. In addition, Macrocybin treatment resulted in the upregulation of Caveolin-1 expression and the disassembly of the actin cytoskeleton in tumor cells (but not in normal cells). In conclusion, we have shown that Macrocybin constitutes a new biologically active compound that may be taken into consideration for cancer treatment.

Modeling land surface processes over a mountainous rainforest in Costa Rica using CLM4.5 and CLM5

Abstract. This study compares the performance of the Community Land Models (CLM4.5 and CLM5) against tower and ground measurements from a tropical montane rainforest in Costa Rica. The study site receives over 4000 mm of mean annual precipitation and has high daily levels of relative humidity. The measurement tower is equipped with eddy-covariance and vertical profile systems able to measure various micrometeorological variables, particularly in wet and complex terrain. In this work, results from point-scale simulations for both CLM4.5 and its updated version (CLM5) are compared to observed canopy flux and micrometeorological data. Both models failed to capture the effects of frequent rainfall events and mountainous topography on the variables of interest (temperatures, leaf wetness, and fluxes). Overall, CLM5 alleviates some errors in CLM4.5, but CLM5 still cannot precisely simulate a number of canopy processes for this forest. Soil, air, and canopy temperatures, as well as leaf wetness, remain too sensitive to incoming solar radiation rates despite updates to the model. As a result, daytime vapor flux and carbon flux are overestimated, and modeled temperature differences between day and night are higher than those observed. Slope effects appear in the measured average diurnal variations of surface albedo and carbon flux, but CLM5 cannot simulate these features. This study suggests that both CLMs still require further improvements concerning energy partitioning processes, such as leaf wetness process, photosynthesis model, and aerodynamic resistance model for wet and mountainous regions.

Functional traits of broad-leaved monocot herbs in the understory and forest edges of a Costa Rican rainforest.

Broad-leaved monocot herbs are widespread and dominant components of the shaded understories of wet neotropical forests. These understory habitats are characterized by light limitation and a constant threat of falling branches. Many shaded understory herb species have close relatives that occupy forest edges and gaps, where light availability is higher and defoliation threat is lower, creating an opportunity for comparative analysis of functional traits in order to better understand the evolutionary adaptations associated with this habitat transition. We documented ecological, morphological and ecophysiological traits of multiple herb species in six monocot families from each of these two habitats in the wet tropical rainforest at the La Selva Biological Station, Costa Rica. We found that a mixture of phylogenetic canalization and ecological selection for specific habitats helped explain patterns of functional traits. Understory herbs were significantly shorter and had smaller leaves than forest edge species. Although the mean number of leaves per plant and specific leaf area did not differ between the two groups, the larger leaf size of forest edge species gave them more than three times the mean plant leaf area. Measures of leaf water content and nitrogen content varied within both groups and mean values were not significantly different. Despite the high leaf nitrogen contents, the maximum photosynthetic rates of understory herbs were quite low. Measures of δ13C as an analog of water use efficiency found significantly lower (more negative) values in understory herbs compared to forest edge species. Clonality was strongly developed in several species but did not show strong phylogenetic patterns. This study highlights many functional traits that differ between broad-leaved monocot species characteristic of understory and forest edge habitats, as well as traits that vary primarily by phylogenetic relatedness. Overall, plant functional traits do not provide a simple explanation for the relative differences in abundance for individual understory and forest edge species with some occurring in great abundance while others are relatively rare.

Lone males: Solitary and group-living male howler monkey (Alouatta palliata) behavioral ecology in a Costa Rican rainforest.

Many group-living primate species have evolved the capacity for some individuals to live alone for part of their lives, but this solitary life stage has rarely been the subject of focused research. The mantled howler monkey (Alouatta palliata) is a social primate species with bisexual dispersal that lives in mixed-sex groups with low male-to-female sex ratios. Consequently, males often spend a long period of their lives as solitary individuals. This study compares the tree use, feeding, and long-distance vocalization behavior of solitary and group-living mantled howler monkey males living within a fragmented rainforest in Costa Rica, La Suerte Biological Research Station. Based on differences in competitive ability between solitary and group-living males, we predicted that lone males would be found in significantly smaller feeding and resting trees, consume more low-quality foods, and produce shorter howling bouts made at lower rates than group-living males. We collected data on tree use and feeding during 30-min focal samples on male focal animals, recording data at 2-min intervals. We measured the trees in which the monkeys fed and rested for two or more intervals, and recorded the plant parts consumed. We recorded howling behavior using all-occurrences sampling. Lone males used significantly smaller feeding and resting trees, consumed more low-quality foods, and howled at lower rates but had longer howling bouts triggered by anthropogenic noise more than group-living males. Our results demonstrate that lone males differ in their behavioral ecology compared to group-living males, thus improving understanding of the solitary male life stage in primates.

Abstract 6544: Macrocybin, a mushroom natural triglyceride, reduces tumor growth in vitro and in vivo through interference with the actin cytoskeleton

Abstract Mushrooms have been used for millennia in Eastern traditional medicine as cancer remedies and recent scientific studies have corroborated the presence of anticancer molecules in mushroom extracts. Our goal in this study was to screen a number of scarcely known mushroom species collected in the rain forest of Costa Rica looking for new antitumor molecules. Mushroom pieces were subjected to diverse extraction procedures involving water or ethanol at different temperatures. Extracts were screened using two human cell lines: A549 (lung adenocarcinoma) and NL20 (immortalized normal lung epithelium). Extracts able to kill tumor cells while preserving the integrity of non-tumor cells were considered “anticancer”. Positive extracts were fractionated with different techniques and the purification of the active compound was guided by its biological activity on the cell lines. When the compound was pure enough, its chemical structure was elucidated through nuclear magnetic resonance, mass spectrometry, and other ancillary techniques. The new molecule was synthesized and tested for biological activity both in vitro and in vivo with a xenograft assay. The mechanism of action was investigated through confocal microscopy, qRT-PCR, and Western blotting. The mushroom species with a better therapeutic window was Macrocybe titans, a local edible mushroom of very large proportions. The active ingredient was found in the precipitated phase of a 95% ethanol extraction with ultrasounds for 30 min, kept at -20°C for 24 h. To purify the active compound this extract was subjected to alkaloidal separation followed by column chromatography with polymeric resin (HP20-SS). The fraction obtained at pH 12 contained the active substance. Chemical analysis of the active molecule showed that it was a triglyceride containing oleic acid, palmitic acid, and a more complex fatty acid with 2 double bonds. Synthesis of all possible triglycerides with those characteristics and biological testing identified the natural compound as the R enantiomer of the triglyceride, which was named Macrocybin. A xenograft study showed that Macrocybin significantly reduces A549 tumor growth. In addition, Macrocybin treatment resulted in the dismantlement of the actin cytoskeleton in tumor cells (but not in normal cells). In conclusion, we have shown that the mushroom Macrocybe titans has anticancer properties and that the active principle is the new triglyceride, Macrocybin. This molecule constitutes a first-in-class new drug that works through the dismantlement of the actin cytoskeleton. Future experiments will establish the usefulness of Macrocybin for different types of cancer, either alone or in combination with other therapies. Citation Format: Marcos Vilariño, Josune García-Sanmartín, Laura Ochoa-Callejero, Rafael Peláez, Alfredo Martinez. Macrocybin, a mushroom natural triglyceride, reduces tumor growth in vitro and in vivo through interference with the actin cytoskeleton [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6544.

Ge and Si Isotope Behavior During Intense Tropical Weathering and Ecosystem Cycling

AbstractChemical weathering of volcanic rocks in warm and humid climates contributes disproportionately to global solute fluxes. Geochemical signatures of solutes and solids formed during this process can help quantify and reconstruct weathering intensity in the past. Here, we measured silicon (Si) and germanium (Ge) isotope ratios of the soils, clays, and fluids from a tropical lowland rainforest in Costa Rica. The bulk topsoil is intensely weathered and isotopically light (mean ± 1σ: δ30Si = −2.1 ± 0.3‰, δ74Ge = −0.13 ± 0.12‰) compared to the parent rock (δ30Si = −0.11 ± 0.05‰, δ74Ge = 0.59 ± 0.07‰). Neoforming clays have even lower values (δ30Si = −2.5 ± 0.2‰, δ74Ge = −0.16 ± 0.09‰), demonstrating a whole‐system isotopic shift in extremely weathered systems. The lowland streams represent mixing of dilute local fluids (δ30Si = 0.2 − 0.6‰, δ74Ge = 2.2 − 2.6‰) with solute‐rich interbasin groundwater (δ30Si = 1.0 ± 0.2‰, δ74Ge = 4.0‰). Using a Ge‐Si isotope mass balance model, we calculate that 91 ± 9% of Ge released via weathering of lowland soils is sequestered by neoforming clays, 9 ± 9% by vegetation, and only 0.2 ± 0.2% remains dissolved. Vegetation plays an important role in the Si cycle, directly sequestering 39 ± 14% of released Si and enhancing clay neoformation in surface soils via the addition of amorphous phytolith silica. Globally, volcanic soil δ74Ge closely tracks the depletion of Ge by chemical weathering (τGe), whereas δ30Si and Ge/Si both reflect the loss of Si (τSi). Because of the different chemical mobilities of Ge and Si, a δ74Ge‐δ30Si multiproxy system is sensitive to a wider range of weathering intensities than each isotopic system in isolation.

A multi-scaled analysis of forest structure using individual-based modeling in a costa rican rainforest

Consideration of scale is essential when examining structural relationships in forests. In this study, we present a parameterization of the FORMIND individual-based forest model for old growth Atlantic lowland rainforest in La Selva, Costa Rica. Results show that the simulated forest reproduces the structural complexity of Costa Rican rainforest within 2.3% of aboveground biomass values, based on comparisons with CARBONO inventory plot data. The Costa Rica FORMIND simulation was then used to investigate the relationship between canopy height and aboveground biomass (AGB), leaf area index (LAI) and gross primary productivity (GPP) at different spatial scales (20 × 20 m, 60 × 60 m, 100mx100m). The relationship between aboveground biomass and height is of particular importance toward the calibration of various remote sensing products including lidar and radar, whereas the LAI and GPP relationships are understudied in this context. We found that the relationship between all three variables and height varies considerably: the relationship is stronger at finer scales and weaker at coarser resolution. However, in all three comparisons, RMSE also decreased as scales coarsened, with the largest difference shown between 100 m and 10 m resolutions in relating AGB to Lorey's height (R2 decreased by 0.3; RMSE decreased by 114.5 Mg/ha). This suggests that a trade-off between accuracy and precision exists, and further highlights the importance of spatial scale in determining the relatability of forest structure variables.

A new species of planthopper in the genus Haplaxius (Hemiptera: Auchenorrhyncha: Fulgoroidea: Cixiidae) on palms in Costa Rica and a new country record for Haplaxius skarphion.

The genus Haplaxius is a large taxon of cixiid planthoppers that is of economic importance due to the ability of Haplaxius crudus to transmit lethal yellowing in coconut palms. Haplaxius dougwalshi sp. n. is established as a new taxon of Cixiidae in the tribe Oecleini collected from native palms in lowland tropical rainforest in Costa Rica. Placement in the genus Haplaxius is supported both by molecular evidence based on the COI and 18S genes as well as by morphological characters. This novel taxon was discovered during survey work in Costa Rica to look for phytoplasmas and document planthopper diversity on palms. Furthermore, Haplaxius skarphion was also collected from coconut palms during survey work and is reported for the first time in Costa Rica.

Leaf litter inputs reinforce islands of nitrogen fertility in a lowland tropical forest

The role of lowland tropical forest tree communities in shaping soil nutrient cycling has been challenging to elucidate in the face of high species diversity. Previously, we showed that differences in tree species composition and canopy foliar nitrogen (N) concentrations correlated with differences in soil N availability in a mature Costa Rican rainforest. Here, we investigate potential mechanisms explaining this correlation. We used imaging spectroscopy to identify study plots containing 10–20 canopy trees with either high or low mean canopy N relative to the landscape mean. Plots were restricted to an uplifted terrace with relatively uniform parent material and climate. In order to assess whether canopy and soil N could be linked by litterfall inputs, we tracked litter production in the plots and measured rates of litter decay and the carbon and N content of leaf litter and leaf litter leachate. We also compared the abundance of putative N fixing trees and rates of free-living N fixation as well as soil pH, texture, cation exchange capacity, and topographic curvature to assess whether biological N fixation and/or soil properties could account for differences in soil N that were, in turn, imprinted on the canopy. We found no evidence of differences in legume communities, free-living N fixation, or abiotic properties. However, soils beneath high canopy N assemblages received ~ 60% more N via leaf litterfall due to variability in litter N content between plot types. The correlation of N in canopy leaves, leaf litter, and soil suggests that, under similar abiotic conditions, litterfall-mediated feedbacks can help maintain soil N differences among tropical tree assemblages in this diverse tropical forest.

Diel pattern driven by free convection controls leaf-cutter ant nest ventilation and greenhouse gas emissions in a Neotropical rain forest.

Leaf-cutter ant nests are biogeochemical hot spots where ants live and import vegetation to grow fungus. Metabolic activity and (in wet tropical forests) soil gas flux to the nest may result in high nest CO2 concentrations if not adequately ventilated. Wind-driven ventilation mitigates high CO2 concentrations in grasslands, but little is known about exchange for forest species faced with prolonged windless conditions. We studied Atta cephalotes nests located under dense canopy (leaf area index > 5) in a wet tropical rainforest in Costa Rica, where wind events are infrequent. We instrumented nests with thermocouples and flow-through CO2 sensing chambers. The results showed that CO2 concentrations exiting leaf-cutter ant nests follow a diel pattern with higher values at night. We developed an efflux model based on pressure differences that evaluated the observed CO2 diel pattern in terms of ventilation by (1) free convection (warm, less dense air rises out the nest more prominently at night) and (2) episodic wind-forced convection events providing occasional supplemental ventilation during daytime. Average greenhouse gas emissions were estimated through nest vents at about 78kg CO2eq nest-1year-1. At the ecosystem level, leaf-cutter ant nest vents accounted for 0.2% to1% of total rainforest soil emissions. In wet, clayey tropical soils, leaf-cutter ant nests act as free convection-driven conduits for exporting CO2 and other greenhouse gases produced within the nest (fungus and ant respiration, refuse decay), and by roots and soil microbes surrounding the nest. This allows A. cephalotes nests to be ventilated without reliable wind conditions.

Combining Unmanned Aerial Systems and Satellite Data to Monitor Phenological Changes in Tropical Forests: A Case Study from Costa Rica

The migration of vegetation under the influence of climate change is of great interest to ecologists, but can be difficult to quantify—especially in less accessible landscapes. Monitoring land cover change through remote sensing has become the best solution, especially with the use of unmanned aerial systems (UASs; drones) as low-cost remote sensing platforms are able to collect data at high spatial and spectral resolutions. Unfortunately, in the context of climate change studies, the lack of comparative UAS data sets over decadal timescales has been limiting. Here, we describe a technique for the integration of historical, low spatial resolution satellite-based Normalized Difference Vegetation Index (NDVI) data with short-term high-resolution multispectral UAS data to track the vegetation changes in a Costa Rican rainforest over a 33-year time frame. The study reveals the transition of a mixed forest from strongly deciduous to weakly deciduous phenology in the Hacienda Barú National Wildlife Refuge (HBNWR), southwestern Costa Rica. This case study presents an approach for researchers and forest managers to study and track vegetation changes over time in locations that lack detailed historical vegetation data. Vegetation migration due to climate change is not well documented and difficult to monitor, especially in remote or inaccessible locations. This case study presents researchers, students, and forest managers an approach for leveraging freely available satellite imagery and UASs to track these changes over time.

Hydrology at Aberdeen – thinking about water locally and globally

ABSTRACTAlthough geographical hydrology research at Aberdeen contributed significant insights into the connections between river channel processes and landscape evolution in the early twentieth century it was not until the 1980s that hydrology became a discernible research theme in the Department of Geography. Whilst the research initially focused on understanding the linkages between fluvial geomorphology, hydrology and in-stream hydraulics, since the mid-1990s a burgeoning research community has made significant contributions to advancing physical hydrology, understanding water quality issues and elucidating inter-connections between hydrology and both terrestrial and aquatic ecosystems. A particular research strength has been the use of isotopic tracers (especially high-resolution, field-based data) to advance hydrological models. Work at Aberdeen has also been internationally leading in terms of understanding the role of hydrology in shaping the life cycle of Scottish Atlantic salmon and other aquatic organisms. Ideas and research approaches developed at local Scottish field sites are being increasingly applied and adapted to advance hydrological understanding in geographical regions as diverse as the rain forests of Costa Rica, the karst of south west China, aquifers in east Africa, the Chilean high Andes, Arctic Canada, peatlands in western Siberia and forests in northern Germany.

Nitrogen-fixing and non-fixing trees differ in leaf chemistry and defence but not herbivory in a lowland Costa Rican rain forest

AbstractNitrogen-fixing plants provide critical nitrogen inputs that support the high productivity of tropical forests, but our understanding of the ecology of nitrogen fixers – and especially their interactions with herbivores – remains incomplete. Herbivores may interact differently with nitrogen fixers vs. non-fixers due to differences in leaf nitrogen content and herbivore defence strategies. To examine these potential differences, our study compared leaf carbon, nitrogen, toughness, chemical defence and herbivory for four nitrogen-fixing tree species (Inga oerstediana, Inga sapindoides, Inga thibaudiana and Pentaclethra macroloba) and three non-fixing species (Anaxagorea crassipetala, Casearia arborea and Dipteryx panamensis) in a lowland tropical rain forest. Leaf chemical defence, not nutritional content, was the primary driver of herbivore damage among our species. Even though nitrogen fixers exhibited 21.1% higher leaf nitrogen content, 20.1% lower C:N ratios and 15.4% lower leaf toughness than non-fixers, we found no differences in herbivory or chemical defence between these two plant groups. Our results do not support the common hypotheses that nitrogen fixers experience preferential herbivory or that they produce more nitrogen-rich defensive compounds than non-fixers. Rather, these findings suggest strong species-specific differences in plant–herbivore relationships among both nitrogen-fixing and non-fixing tropical trees.

Gone with the rain: negative effects of rainfall on male reproductive success in a nest-building arachnid

AbstractIn nest-building species, offspring survival and reproductive success of parental individuals are strongly influenced by nest quality. Thus, quantifying the influence of abiotic conditions on nest integrity is important to predict the effects of weather variability on the fitness of parental individuals. Here, we investigated how rainfall affects nest integrity and how nest integrity influences males’ attractiveness and nest tenure. Our study species was the harvestman Quindina limbata, in which males build mud nests on fallen logs and protect the eggs against predators and fungi. Our data set comprises 12 months of regular inspections of 149 nests in a Costa Rican rainforest. We found that almost 50% of the nests were destroyed by rainfall. The drag force caused by rainfall running on the fallen log surface negatively affected nest integrity. Fungi cover on nests was influenced by an interaction between rainfall and nest position on the fallen log. Irrespective of their body size, males in nests with high integrity received more eggs than males in nests with low integrity. Fungi cover did not influence the number of eggs received by the males. Finally, nest integrity and fungi cover did not affect nest tenure, but males that did not receive eggs for a long time tended to abandon their nests. Considering that intense rainfall occurs all year long in tropical forests, males should build their nests in protected sites that preserve nest structure. Protected sites may keep nest structure better preserved, improve offspring survival, attract more females, and increase males’ reproductive success.

Howling on the edge: Mantled howler monkey (Alouatta palliata) howling behaviour and anthropogenic edge effects in a fragmented tropical rainforest in Costa Rica

AbstractThe function of long calling is a subject of interest across animal behaviour study, particularly within primatology. Many primate species have male‐specific long‐distance calls, including platyrrhines like the folivorous howler monkey (Alouatta spp.). Howler monkeys may howl to defend resources such as feeding trees or areas of rich vegetation from other monkey groups. This study tests the ecological resource defence hypothesis for howling behaviour in the mantled howler monkey (Alouatta palliata) and investigates how anthropogenic forest fragmentation may influence howling behaviour. More specifically, this study examines how howling bout rate, duration, precursors and tree species richness, DBH, and canopy cover vary in 100 m anthropogenic edge and interior forest zones at La Suerte Biological Research Station (LSBRS), a fragmented tropical rainforest in Costa Rica. Results show that tree species richness and canopy cover are higher in forest interior at this site, suggesting that monkeys should howl at greater rates in the interior to defend access to these higher‐quality vegetation resources. Overall, our results supported the ecological resource defence hypothesis. The main howl precursor was howling from neighbouring groups. Although howling rate did not differ between forest zones, howling bouts from forest interior were longer, had a greater number of howls per bout and were preceded by different precursors than howls from anthropogenic edge zones, including more howls from neighbouring groups. Our findings provide some of the first evidence for behavioural edge effects in primate vocal communication behaviour.