Canopy Ants Research Articles

Scattered trees as crucial elements in maintaining urban diversity: A case study with canopy ants in a biodiversity hotspot

Urban environments are characterized by profound differences in abiotic conditions compared to natural environments, which filter one part of the biotic communities that endure living in these environments. A conspicuous element in many cities are scattered trees, often included in urban planning around the world. These trees are key elements for urban ecological processes and services and act as habitat islands, providing resources (i.e., food and shelter) for a considerable arthropod diversity, such as ants. Studies involving ants in urban environments often focus on ground-dwelling ants, and few studies seek to glimpse the ants that occupy scattered trees and, even less, how these ants and trees interact within cities. This study aimed to investigate the ant communities foraging day and night on trees in an urban area inside a biodiversity hotspot, the Brazilian Atlantic Forest. Specifically, we investigated how tree characteristics (tree size, tree isolation, and the tree origin, i.e., native and exotic) modulate ant diversity and ant-plant interactions. We found that the ant species composition is different between day and night, as well as the central core of generalist ant species of day and night interaction networks. The tree size increases beta-diversity among trees only of the nocturnal ant community, while none of the tree characteristics shaped the ant community. This study is the first to address the role of scattered trees in maintaining the diversity of arboreal ants in urban landscapes, focusing on species diversity and their interaction networks. Overall, we provide insights supporting the conservation value of scattered trees in maintaining urban biodiversity.

Diversity and species composition of ants at coffee agroforestry systems in East Java, Indonesia: Effect of habitat condition and landscape composition

Abstract. Muhammad FN, Rizali A, Rahardjo BT. 2022. Diversity and species composition of ants at coffee agroforestry systems in East Java, Indonesia: Effect of habitat condition and landscape composition. Biodiversitas 23: 3313-3321. Habitat condition and landscape composition are the main factors that shape biodiversity in agroecosystems. However, information on the effect of habitat conditions and landscape composition on biodiversity in agroforestry systems is lacking. Agroforestry systems possess habitats that are characterized by a high diversity of vegetation, that can support biodiversity both on the field or landscape scale. This research aimed to study the diversity and species composition of ants in coffee (Coffea spp.) agroforestry systems, and to investigate the effects of habitat conditions and landscape composition on ant communities. Field research was conducted in twelve coffee agroforestry systems in East Java, Indonesia. Ants were sampled with the fogging method for canopy ants and pitfall traps for ground-dwelling ants in 40 m x 30 m plots. In each location, habitat conditions aspects (such as cultural technique and tree age) were identified by interviews with farmers and vegetation observation. Meanwhile, landscape composition was characterized by ground checking and mapping the land-use type within a 500 m radius from plot centers. This research recorded 35 species and 4,622 individuals of ants from all coffee plantations. Dolichoderus thoracicus was the most dominant canopy ant, while Pheidole sp.2 was the most dominant ground-dwelling ant in all plantations. Based on the GLM analysis, different responses were found between canopy and ground-dwelling ants in relation to habitat conditions and landscape composition. Canopy and ground-dwelling ants were affected by habitat conditions (such as tree age and canopy cover). The species composition of ground-dwelling ants was also affected by habitat conditions. In conclusion, habitats in coffee plantations can affect ant communities with ground-dwelling ants being more sensitive than canopy ants. Meanwhile, landscape composition can affect the species richness of all ants and not affect each stratum (canopy and ground-dwelling ants).

Behavioral response to heat stress of twig-nesting canopy ants

Tropical forests experience a relatively stable climate, but are not thermally uniform. The tropical forest canopy is hotter and thermally more variable than the understory. Heat stress in the canopy is expected to increase with global warming, potentially threatening its inhabitants. Here, we assess the impact of heating on the most abundant tropical canopy arthropods—ants. While foragers can escape hot branches, brood and workers inside twig nests might be unable to avoid heat stress. We examined nest choice and absconding behavior—nest evacuation in response to heat stress—of four common twig-nesting ant genera. We found that genera nesting almost exclusively in the canopy occupy smaller cavities compared to Camponotus and Crematogaster that nest across all forest strata. Crematogaster ants absconded at the lowest temperatures in heating experiments with both natural and artificial nests. Cephalotes workers were overall less likely to abscond from their nests. This is the first test of behavioral thermoregulation in tropical forest canopy ants, and it highlights different strategies and sensitivities to heat stress. Behavioral avoidance is the first line of defense against heat stress and will be crucial for small ectotherms facing increasing regional and local temperatures.

A whole‐ecosystem method for experimentally suppressing ants on a small scale

Abstract Ant suppression experiments have emerged as a powerful method for assessing the role of ants in ecosystems. However, traditional methods have been limited to canopy ants, and not assessed the role of ants on and below ground. Recent advances have enabled whole‐ecosystem ant suppression in large plots, but large‐scale experiments are not always feasible. Here, we develop a small‐scale, whole‐ecosystem suppression method. We compare techniques for monitoring suppression experiments, and assess whether habitat complexity in oil palm influences our method's effectiveness. We conducted ant suppression experiments in oil palm agroforestry in Sumatra, Indonesia. We used targeted poison baits, a physical barrier and canopy isolation to suppress ants in 4 m radius arenas around single palms. We sequentially tested three suppression methods that increased in intensity over 18 months. We sampled ant abundance before and after suppression by fogging, using pitfall traps and extracting soil monoliths. We also monitored ants throughout the experiment by baiting. We tested the soil for residual poison and monitored other invertebrates (Araneae, Coleoptera, Orthoptera and Chilopoda) to test for cross‐contamination. Plots were established under four oil palm management treatments that varied in their habitat complexity: reduced, intermediate and high understorey complexity treatments in mature plantation, and a recently replanted plantation. Post‐treatment ant abundance was 92% lower in suppression than control plots. Only the most intensive suppression method, which ran for the final 9 months, worked. Baiting rarely reflected the other monitoring methods. The treatment negatively affected Orthoptera, but not other taxa. There was no residual poison in the soil. Coleoptera abundance increased in suppression plots post‐treatment, potentially due to reduced competition with ants. Our findings were consistent across management treatments. We developed a whole‐ecosystem method for suppressing ants on a small scale in oil palm plantations. Our method represents a significant advance; previous reductions in ant abundance have not exceeded 38%. We provide the first example of ants being experimentally suppressed belowground. Baiting alone is not adequate for assessing suppression effectiveness, and testing a range of taxa for confounding impacts is important. Our study can act as a blueprint for developing suppression methods for other taxa, which offer unique insights into community ecology.

Ant Community Structure in Secondary Logged Forest of Malua Forest Reserve, Sabah, Borneo

Ants are ecologically dominant and important in the functioning of an ecosystem. Thus, understanding their community structure has become fundamental in ecological studies. This study aims to examine the ant richness, abundance, and composition in the secondary logged forests of Sabah, Malaysia. Ground-based fogging was employed to collect canopy ants (n=38) and Winkler extraction method for leaf litter ants (n=63). A total of 12,810 ant individuals were collected, representing 389 morphospecies, 65 genera, and 11 subfamilies. The most species-rich subfamily for canopy and leaf litter ants were Formicinae (112 morphospecies, 49.34%) and Myrmicinae (116 morphospecies, 58.00%) respectively. Polyrhachis (56 morphospecies, 24.67%) was the most diverse genera in the canopy, while Pheidole (23 morphospecies, 11.50%) was the most speciose genera on the leaf litter. The most abundant species for canopy and leaf litter ants were Dolichoderus 1 (876 individuals) and Carebara 2 (1,215 individuals) respectively. The randomized species accumulation curves and species richness estimators reveal that additional sampling is required. We suggest that incorporating a variety of ant sampling methods and high sampling efforts are important to thoroughly sample the ant assemblage in an area.

Rainforest conversion to monocultures favors generalist ants with large colonies

AbstractThe conversion of natural ecosystems to agricultural land is one of the most important drivers of biodiversity decline worldwide, particularly in the tropics. Species loss is typically trait‐associated, leading to filtering of disturbance‐resistant species during community assembly, which affects ecosystem functioning and evolutionary potential of communities. To understand the ecological and phylogenetic impact of rainforest conversion to agricultural systems, we combine analysis of nesting habit, feeding habit, colony size, and body size of canopy ants (Formicidae) with a phylogenetic analysis of species collected in four land‐use systems in Sumatra, Indonesia: (1) lowland tropical rainforest, (2) jungle rubber (extensive rubber agroforest), and smallholder plantations of (3) rubber and (4) oil palm. Canopy ant communities in these land‐use systems differed in trait composition, with a larger proportion of generalist nesting and generalist‐omnivore feeding species in oil palm compared to rainforest and a larger proportion of generalist nesters and species with large colonies (>1000 individuals) in rubber than in rainforest. Traits of canopy ant communities in jungle rubber were more similar to those in rainforest than to those in rubber and oil palm plantations. In rainforest, mean pairwise phylogenetic distance was lower than expected for random community assembly, but did not differ from random in the other land‐use systems. Of the traits nesting habit, feeding habit, and colony size, only feeding habit exhibited phylogenetic signal. Our results show that rainforest conversion to agricultural systems is accompanied by shifts in trait composition of canopy ant communities. Further, our results argue against environmental filtering of closely related canopy ant species as the major community assembly mechanism in plantation systems, but suggest that the Sumatran lowland rainforests harbor recently diverged endemic ant species that are particularly vulnerable to rainforest conversion to agricultural systems. Given the importance of ants for tropical ecosystems, the ecological differences among ant communities along the land‐use gradient might have important consequences for ecosystem functioning and services in plantation systems.

Discovery-defense strategy as a mechanism of social foraging of ants in tropical rainforest canopies

AbstractMany hypotheses have been proposed to explain the coexistence of ants sharing similar food resources, including ecological trade-offs, however, these hypotheses have mostly been tested in ground-dwelling ant communities. For instance, the discovery-dominance trade-off hypothesis states that species with overlapping food resources differ in their ability to find and dominate resources. However, ant species may use different strategies to share food resources, including discovery-defense, in which the first species to arrive at a food resource maintains control of it. Here, we evaluated whether the discovery-dominance trade-off hypothesis, or the discovery-defense strategy could be a mechanism that promotes coexistence of ant species in the canopy of highly diverse tropical forest canopies. We evaluated the succession of ant species on 72 baits exposed on 24 trees during 13 observation periods (15–195 min) in the canopy of a tropical rain forest in Mexico. In general, we observed little variation in ant species composition (i.e., low β-diversity values) during the 195 min of bait exposure. Moreover, we found that ant species with the greatest ability to discover new food resources were those that dominated them. These findings empirically show that the discovery-defense strategy can be a social foraging strategy in rain forest canopy ants and reject the discovery-dominance trade-off. In short, our results highlight the importance of the discovery of a food resource in the canopy of a tropical rain forest, allowing it to be dominated.

Ant-gardens: a specialized ant-epiphyte mutualism capable of facing the effects of climate change

It is suggested that specialized mutualisms are more vulnerable to climate change. Ant-gardens (AGs) are a complex and specialized mutualistic system represented by epiphytic plants that specifically inhabit the arboreal nest built by canopy ants in tropical forests. Different ant-epiphyte ensembles constitute the AGs throughout the Neotropics. However, neither the environmental factors that determine their geographical distribution nor the effects of climate change on this canopy biological system are known. Here, we estimated the ecological niche and elevational distribution of the Neotropical AGs as an entity (regardless of species composition), and individually for six AG ant and 16 AG epiphyte species in order to determine and compare their current and future distributions (vulnerability), using two unrelated Global Circulation Models for the year 2070 under two Representative Concentration Pathways (RCP4.5: optimistic and RCP8.5: pessimistic). The current potential distribution of the AGs is discontinuous from Tamaulipas, Mexico, to Rio Grande do Sul, Brazil, in low elevation areas with high mean annual temperatures (> 25 °C) and precipitation (> 2400 mm). In contrast, the individual distributions of the AG ants and epiphytes tended not to follow to this climatic profile and were segregated by both latitude and elevation. The geographic distribution of most AG ant and epiphyte species diminished under climate change, while that of the AGs increased, even under the pessimistic scenario. This suggests that AGs allow the species that comprise them to broaden their ecological niche and be more resistant to climate change than they would be outside of this system.

Effect of forest disturbance on ant (Hymenoptera: Formicidae) diversity in a Mexican tropical dry forest canopy

Abstract1. Ants are the dominant insects in tropical forest canopies. The α and β diversities of ants change in response to forest disturbance. Understanding the response of ants to forest disturbance will help to guide ant conservation and forest management plans, especially in endangered ecosystems such as the tropical dry forest. 2. We analysed ant α and β diversities in 15 fragments (5 mature, 5 disturbed, and 5 secondary) of a tropical dry forest in central Mexico. We identified and measured all of the trees in two transects (10 × 50 m) established within each fragment. Pit‐fall traps were used to sample ants in all of the trees. 3. We identified 52 ant species (from a total of 11,524 individuals). The mature forest presented the greatest quantity of exclusive species and the highest α diversity. Ant composition differed among the mature forest but not between disturbed and secondary forest, and was related to tree size and richness. The β diversity was lower in the disturbed forest, reflecting the cost of biotic homogenization (15%). Among the β diversity components in all three forest types, this diversity was mainly influenced by turnover, while nestedness diminished in the disturbed forest. 4. In the tropical dry forest studied, anthropogenic disturbance homogenises the ant community, probably because the availability of resources is also homogenised, decreasing the α diversities of the canopy ants. Our results show the importance of the conservation of mature forests in terms of maintaining the diversity of canopy ants.

Arboreal ant abundance tracks primary productivity in an Amazonian whitewater river system

AbstractLittle is known about consumer productivity in the tropics despite the key feedbacks that animals impose on primary productivity. In the Amazon basin, seasonally flooded and unflooded forests exist side by side, and ants (Formicidae) dominate animal biomass. Although flooding has a direct negative effect on soil‐dwelling ants, it is less clear whether flooding has indirect effects on arboreal ants via associated changes in tree communities. To test whether seasonal inundation by whitewater affects arboreal ants, we investigated ant communities in adjacent flooded and unflooded forests along a major whitewater river in central‐western Amazonia. Whitewater‐flooded forest exhibits higher primary productivity than unflooded forest. We thus hypothesized that forest type would affect the productivity and the foraging traits of arboreal ants and that these changes would be mediated by increases in plant‐derived food for ants in flooded forest. We compared ant and plant communities between flooded‐ and unflooded‐forest transects along the Juruá River in Amazonas, Brazil. We collected, identified, and counted terrestrial and arboreal ants, and we measured ant traits with putative relationships to foraging strategy. We also identified plant stems to characterize the abundance of ant food rewards. Flooding negatively affected the diversity and abundance of terrestrial ants but did not change the diversity of arboreal ants. Arboreal ants were more abundant and exhibited higher biomass in flooded forest than in unflooded forest. Arboreal ant traits also suggested that ants may rely more heavily on plant‐derived food in flooded forest than in unflooded forest. These differences were associated with a higher abundance of plant stems predicted to contain ant food rewards in flooded forest than in unflooded forest. Our results indicate that the productivity of arboreal ants is affected by that of the underlying forest. Such effects may be mediated by the predominantly herbivorous foraging strategy of canopy ants, which would link ant populations closely to primary production and stoichiometry. Given ants’ important functional roles, these differences in ant productivity between forest types may have consequences for other arthropods and feedbacks to plants throughout the Amazon basin.

Selectively Logging Old Growth Rain Forest Twice Changes Canopy Ant Species Composition, While Conversion to Oil Palm Changes Composition and Reduces Species Richness and Diversity

Tropical forests around the world, and particularly in Southeast Asia, are being affected by anthropogenic habitat conversion and degradation. Ants, an ecologically important group in the rainforest canopy, have previously been demonstrated to be robust to a single round of selective logging, but are strongly affected by conversion to oil palm. However, the impacts of multiple rounds of selective logging on canopy ants remain unexplored. We studied the ant assemblages across a habitat gradient comprising old growth forest, twice-logged forest and oil palm plantation in Sabah, Malaysian Borneo. Canopy ants were collected using insecticide fogging across 36 sampling sites. Old growth forest and twice-logged forest had similar species richness and Shannon species diversity. These two forest habitats were significantly higher in species richness and Shannon diversity than oil palm plantation. Abundance of canopy ants was similar across all three habitats. There was a significant difference in species composition between all pairs of habitats. Leaf litter depth on the ground was positively related to ant species richness, while canopy cover was positively related to ant abundance. Hence, multiple rounds of logging cause shifts in ant species composition, while forest conversion to oil palm additionally causes reductions in ant diversity. This is of concern, since forests in Sabah and elsewhere are becoming increasingly degraded. Our results indicate that both old growth and twice-logged rain forests can be useful for conservation of canopy ants.

Thermal constraints on foraging of tropical canopy ants.

Small cursorial ectotherms risk overheating when foraging in the tropical forest canopy, where the surfaces of unshaded tree branches commonly exceed 50°C. We quantified the heating and subsequent cooling rates of 11 common canopy ant species from Panama and tested the hypothesis that ant workers stop foraging at temperatures consistent with the prevention of overheating. We created hot experimental "sunflecks" on existing foraging trails of four ant species from different clades and spanning a broad range of body size, heating rate, and critical thermal maxima (CTmax). Different ant species exhibited very different heating rates in the lab, and these differences did not follow trends predicted by body size alone. Experiments with ant models showed that heating rates are strongly affected by color in addition to body size. Foraging workers of all species showed strong responses to heating and consistently abandoned focal sites between 36 and 44°C. Atta colombica and Azteca trigona workers resumed foraging shortly after heat was removed, but Cephalotes atratus and Dolichoderus bispinosus workers continued to avoid the heated patch even after >5min of cooling. Large foraging ants (C. atratus) responded slowly to developing thermal extremes, whereas small ants (A. trigona) evacuated sunflecks relatively quickly, and at lower estimated body temperatures than when revisiting previously heated patches. The results of this study provide the first field-based insight into how foraging ants respond behaviorally to the heterogeneous thermal landscape of the tropical forest canopy.

Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community.

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7 h to 97.9 h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) – the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CT max), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CT max were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation‐resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.

Surface roughness affects the running speed of tropical canopy ants

AbstractCursorial central‐place foragers like ants are expected to minimize travel costs by choosing the least resistive pathways to food resources. Tropical arboreal and semi‐arboreal ants locomote over a variety of plant surfaces, and their choice of pathways is selective. We measured the roughness of tree trunk and liana stem surfaces using laser scanning technology, and explored its consequences for running speed in various ant taxa. The average amplitude of tree trunk surface roughness differed interspecifically, and ranged from 1.4–2.2 mm among three common tree species (Anacardium excelsum, Alseis blackiana, and Dipteryx panamensis). The roughness of liana stems also varied interspecifically (among Tontelea ovalifolia, Bauhinia sp. and Paullinia sp.) and was an order of magnitude lower than tree surface roughness (mean amplitude ranged 0.09–0.19 mm). Field observations of various ant species foraging on tree trunks and liana stems, and on dowels covered with sandpaper, showed that their running speed declined with increasing amplitude of roughness. The effect of roughness on running speed was strongest for mid‐sized ants (Azteca trigona and Dolichoderus bispinosus). The accumulation rate of ants at baits did not vary with tree surface roughness, but was significantly lower on moss‐covered versus moss‐free bark. Collectively, these results indicate that the quality of plant substrates can influence the foraging patterns of arboreal ants, but likely is more important for resource discovery than for dominance on bare tree surfaces.

Escape to the high canopy-thermal deficiency causes niche expansion in a forest-floor ant.

The small formicoxenine ant Temnothorax saxonicus was known from about 40 localities in Central Europe nesting in anorganic substrates on floor of xerothermous forests whereas investigations of 198 tree canopies in 19 forest sites of the same region provided no indication for arboreal nesting or foraging. We present the first evidence for canopy-nesting populations of T. saxonicus on old Quercus trees in 3 sites having maximum calibrated topsoil temperatures of 17.9 ± 0.3 °C which were significantly (P < 0.007) lower than 22.8 ± 2.0 °C measured in 5 sites with ground-nesting populations. The thermal deficit on forest floor inhibits brood development in ground nests and caused a moving to canopy were maximum calibrated temperatures of the, now wooden, substrates are at least 26.1 °C for the whole canopy and 30.8 °C in more sun-exposed spots. T. saxonicus competed here successfully with the obligatory canopy ants T. affinis and T. corticalis. The distributional data of this rope-climbing study support former results that highest nest densities of small arboreal ants occur in temperate climate over the entire canopy mantle of single trees situated in open land or in park-like environments but occur in the top of the canopy in tree stands with high degree of canopy closure.

Mechanisms of carbohydrate‐fuelled ecological dominance in a tropical rainforest canopy‐foraging ant

1. Canopy‐foraging ants have carbohydrate‐rich diets and the stoichiometric excess of carbon may result in energetic allocation decisions that facilitate ecological dominance.2. If dietary carbohydrates facilitate ecological dominance in canopy ants, then the mechanism for this relationship is unknown.3. Four hypotheses were posit that may explain how a carbohydrate‐rich diet might facilitate ecological dominance in canopy ants: Aggressive Defense, Metabolic Fuel, Foraging Success, and Prey Acquisition.4. To assess these hypotheses, experiments were conducted on the canopy‐foraging bullet ant, Paraponera clavata (Fabricius), an omnivorous species that demonstrates high variability in the relative contribution of carbohydrates to the diets of colonies.5. No support was found for the Aggressive Defense, Metabolic Fuel and Prey Acquisition hypotheses.6. The Foraging Success hypothesis was supported, as the proportion of nectar in the diet predicted the overall foraging success.7. It was argued that there is no explicit advantage in the exploitation of nectar over other food resources, other than the fact that it is the most accessible food resource in the rainforest canopy.

Experimentally testing and assessing the predictive power of species assembly rules for tropical canopy ants.

Understanding how species assemble into communities is a key goal in ecology. However, assembly rules are rarely tested experimentally, and their ability to shape real communities is poorly known. We surveyed a diverse community of epiphyte-dwelling ants and found that similar-sized species co-occurred less often than expected. Laboratory experiments demonstrated that invasion was discouraged by the presence of similarly sized resident species. The size difference for which invasion was less likely was the same as that for which wild species exhibited reduced co-occurrence. Finally we explored whether our experimentally derived assembly rules could simulate realistic communities. Communities simulated using size-based species assembly exhibited diversities closer to wild communities than those simulated using size-independent assembly, with results being sensitive to the combination of rules employed. Hence, species segregation in the wild can be driven by competitive species assembly, and this process is sufficient to generate observed species abundance distributions for tropical epiphyte-dwelling ants.

Thermal adaptation generates a diversity of thermal limits in a rainforest ant community.

The Thermal Adaptation Hypothesis posits that the warmer, aseasonal tropics generates populations with higher and narrower thermal limits. It has largely been tested among populations across latitudes. However, considerable thermal heterogeneity exists within ecosystems: across 31 trees in a Panama rainforest, surfaces exposed to sun were 8°C warmer and varied more in temperature than surfaces in the litter below. Tiny ectotherms are confined to surfaces and are variously submerged in these superheated boundary layer environments. We quantified the surface CTmin and CTmax s (surface temperatures at which individuals grew torpid and lost motor control, respectively) of 88 ant species from this forest; they ranged in average mass from 0.01 to 57mg. Larger ants had broader thermal tolerances. Then, for 26 of these species we again tested body CTmax s using a thermal dry bath to eliminate boundary layer effects: body size correlations observed previously disappeared. In both experiments, consistent with Thermal Adaptation, CTmax s of canopy ants averaged 3.5-5°C higher than populations that nested in the shade of the understory. We impaled thermocouples in taxidermy mounts to further quantify the factors shaping operative temperatures for four ant species representing the top third (1-30mg) of the size distribution. Extrapolations suggest the smallest 2/3rds of species reach thermal equilibrium in <10s. Moreover, the large ants that walk above the convective superheated surface air also showed more net heating by solar radiation, with operative temperatures up to 4°C higher than surrounding air. The thermal environments of this Panama rainforest generate a range of CTmax subsuming 74% of those previously recorded for ant populations worldwide. The Thermal Adaptation Hypothesis can be a powerful tool in predicting diversity of thermal limits within communities. Boundary layer temperatures are likely key to predicting the future of Earth's tiny terrestrial ectotherm populations.

Water surface locomotion in tropical canopy ants.

Upon falling onto the water surface, most terrestrial arthropods helplessly struggle and are quickly eaten by aquatic predators. Exceptions to this outcome mostly occur among riparian taxa that escape by walking or swimming at the water surface. Here we document sustained, directional, neustonic locomotion (i.e. surface swimming) in tropical arboreal ants. We dropped 35 species of ants into natural and artificial aquatic settings in Peru and Panama to assess their swimming ability. Ten species showed directed surface swimming at speeds >3 body lengths s(-1), with some swimming at absolute speeds >10 cm s(-1). Ten other species exhibited partial swimming ability characterized by relatively slow but directed movement. The remaining species showed no locomotory control at the surface. The phylogenetic distribution of swimming among ant genera indicates parallel evolution and a trend toward negative association with directed aerial descent behavior. Experiments with workers of Odontomachus bauri showed that they escape from the water by directing their swimming toward dark emergent objects (i.e. skototaxis). Analyses of high-speed video images indicate that Pachycondyla spp. and O. bauri use a modified alternating tripod gait when swimming; they generate thrust at the water surface via synchronized treading and rowing motions of the contralateral fore and mid legs, respectively, while the hind legs provide roll stability. These results expand the list of facultatively neustonic terrestrial taxa to include various species of tropical arboreal ants.

Trophic Guild Structure of a Canopy Ants Community in a Mexican Tropical Deciduous Forest

Ants constitute a very important element in the canopies of tropical forest. The species richness, composition and diversity of ant canopy community in a tropical deciduous forest in the Pacific Cost of Mexico was studied. The sampling was performed by fogging method in a watershed of the Chamela Biological Station, Jalisco State, Mexico. Ants represented 0.5% of all invertebrates in the tree canopy of Chamela, and a total of 46 ant morphospecies from 17 genera were collected. Camponotus and Cephalotes contributed with 13 and 6 species respectively, and the most abundant ants were species of Crematogaster, Tapinoma, Cephalotes and Camponotus. Ant composition was broadly similar at the two sites, and on different canopy species, although significant differences in abundance were apparent for some individual ant species. The dominant guild in the canopy was the omnivourous in all study, but differences in guild trophic composition were recorded in each fogging. The ant community in the canopy of Chamela has shown low spatial variation, but the composition of ant species and trophic guilds have important seasonal variations, demonstrated variations in the exploitation of resources along the year, and vertical migrations of ant species from soil and shrub layer to canopy in the tropical deciduous forest.