Rainforest Ants Research Articles

Arboreality drives heat tolerance while elevation drives cold tolerance in tropical rainforest ants.

Determining how species thermal limits correlate with climate is important for understanding biogeographic patterns and assessing vulnerability to climate change. Such analyses need to consider thermal gradients at multiple spatial scales. Here we relate thermal traits of rainforest ants to microclimate conditions from ground to canopy (microgeographic scale) along an elevation gradient (mesogeographic scale) and calculate warming tolerance to assess climate change vulnerability in the Australian Wet Tropics Bioregion. We test the thermal adaptation and thermal niche asymmetry hypotheses to explain interspecific patterns of thermal tolerance at these two spatial scales. We tested cold tolerance (CTmin ), heat tolerance (CTmax ), and calculated thermal tolerance range (CTrange ), using ramping assays for 74 colonies of 40 ant species collected from terrestrial and arboreal habitats at lowland and upland elevation sites and recorded microclimatic conditions for one year. Within sites, arboreal ants were exposed to hotter microclimates and on average had a 4.2°C (95% CI: 2.7-5.6°C) higher CTmax and 5.3°C (95% CI: 3.5-7°C) broader CTrange than ground-dwelling ants. This pattern was consistent across the elevation gradient, whether it be the hotter lowlands or the cooler uplands. Across elevation, upland ants could tolerate significantly colder temperatures than lowland ants, whereas the change in CTmax was less pronounced, and CTrange did not change over elevation. Differential exposure to microclimates, due to localized niche preferences, drives divergence in CTmax , while environmental temperatures along the elevation gradient drive divergence in CTmin . Our results suggest that both processes of thermal adaptation and thermal niche asymmetry are at play, depending on the spatial scale of observation, and we discuss potential mechanisms underlying these patterns. Despite the broad thermal tolerance range of arboreal rainforest ants, lowland arboreal ants had the lowest warming tolerance and may be most vulnerable to climate change.

Digging Deeper into the Ecology of Subterranean Ants: Diversity and Niche Partitioning across Two Continents

Soil fauna is generally understudied compared to above-ground arthropods, and ants are no exception. Here, we compared a primary and a secondary forest each on two continents using four different sampling methods. Winkler sampling, pitfalls, and four types of above- and below-ground baits (dead, crushed insects; melezitose; living termites; living mealworms/grasshoppers) were applied on four plots (4 × 4 grid points) on each site. Although less diverse than Winkler samples and pitfalls, subterranean baits provided a remarkable ant community. Our baiting system provided a large dataset to systematically quantify strata and dietary specialisation in tropical rainforest ants. Compared to above-ground baits, 10–28% of the species at subterranean baits were overall more common (or unique to) below ground, indicating a fauna that was truly specialised to this stratum. Species turnover was particularly high in the primary forests, both concerning above-ground and subterranean baits and between grid points within a site. This suggests that secondary forests are more impoverished, especially concerning their subterranean fauna. Although subterranean ants rarely displayed specific preferences for a bait type, they were in general more specialised than above-ground ants; this was true for entire communities, but also for the same species if they foraged in both strata.

Human disturbance promotes herbivory by leaf‐cutting ants in the Caatinga dry forest

AbstractAnthropogenic disturbances are known to modify plant–animal interactions such as those involving the leaf‐cutting ants, the most voracious and proliferating herbivore across human‐modified landscapes in the Neotropics. Here, we evaluate the effect of chronic anthropogenic disturbance (e.g., firewood collection, livestock grazing) and vegetation seasonality on foraging area, foliage availability in the foraging area, leaf consumption and herbivory rate of the leaf‐cutting ant Atta opaciceps in the semiarid Caatinga, a mosaic of dry forest and scrub vegetation in northeast Brazil. Contrary to our initial expectation, the foraging area was not affected by either disturbance intensity or the interaction between season and disturbance intensity. However, leaf consumption and herbivory rate were higher in more disturbed areas. We also found a strong effect of seasonality, with higher leaf consumption and herbivory rate in the dry season. Our results suggest that the foraging ecology of leaf‐cutting ants is modulated by human disturbance and seasonality as these two drivers affect the spectrum and the amount of resources available for these ants in the Caatinga. Despite the low productivity of Caatinga vegetation, the annual rates of biomass consumption by A. opaciceps are similar to those reported from other leaf‐cutting ants in rain forests and savannas. This is made possible by maintaining high foraging activity even in the peak of the dry season and taking benefit from any resource available, including low‐quality items. Such compensation highlights the adaptive capacity of LCA to persist or even proliferate in human‐modified landscapes from dry to rain forests.

Is thermal limitation the primary driver of elevational distributions? Not for montane rainforest ants in the Australian Wet Tropics.

Terrestrial ectotherms are likely to be especially sensitive to rising temperatures over coming decades. Thermal limits are used to measure climatic tolerances that potentially affect ectotherm distribution. While there is a strong relationship between the critical thermal maximum (CTmax) of insects and their latitudinal ranges, the nature of this relationship across elevation is less clear. Here we investigated the combined relationships between CTmax, elevation and ant body mass, given that CTmax can also be influenced by body mass, in the World Heritage-listed rainforests of the Australian Wet Tropics. We measured the CTmax and body mass of 20 ant species across an elevational gradient from 350 to 1000m a.s.l. Community CTmax did not vary systematically with increasing elevation and there was no correlation between elevation and elevational ranges of species. However, body mass significantly decreased at higher elevations. Despite the negative correlation between CTmax and body mass at the community level, there was no significant difference in CTmax of different-sized ants within a species. These findings are not consistent with either the climatic variability hypothesis, Rapoport's rule or Bergmann's rule. Models indicated that elevation and body mass had limited influences on CTmax. Our results suggest that the distribution of most montane ants in the region is not strongly driven by thermal limitation, and climate change will likely impact ant species differently. This is likely to occur primarily through changes in rainfall via its effects on vegetation structure and therefore thermal microhabitats, rather than through direct temperature changes.

Dramatic Differences in Gut Bacterial Densities Correlate with Diet and Habitat in Rainforest Ants.

Abundance is a key parameter in microbial ecology, and important to estimates of potential metabolite flux, impacts of dispersal, and sensitivity of samples to technical biases such as laboratory contamination. However, modern amplicon-based sequencing techniques by themselves typically provide no information about the absolute abundance of microbes. Here, we use fluorescence microscopy and quantitative polymerase chain reaction as independent estimates of microbial abundance to test the hypothesis that microbial symbionts have enabled ants to dominate tropical rainforest canopies by facilitating herbivorous diets, and compare these methods to microbial diversity profiles from 16S rRNA amplicon sequencing. Through a systematic survey of ants from a lowland tropical forest, we show that the density of gut microbiota varies across several orders of magnitude among ant lineages, with median individuals from many genera only marginally above detection limits. Supporting the hypothesis that microbial symbiosis is important to dominance in the canopy, we find that the abundance of gut bacteria is positively correlated with stable isotope proxies of herbivory among canopy-dwelling ants, but not among ground-dwelling ants. Notably, these broad findings are much more evident in the quantitative data than in the 16S rRNA sequencing data. Our results provide quantitative context to the potential role of bacteria in facilitating the ants' dominance of the tropical rainforest canopy, and have broad implications for the interpretation of sequence-based surveys of microbial diversity.

Thermal adaptation and phosphorus shape thermal performance in an assemblage of rainforest ants.

We studied the Thermal Performance Curves (TPCs) of 87 species of rainforest ants and found support for both the Thermal Adaptation and Phosphorus-Tolerance hypotheses. TPCs relate a fitness proxy (here, worker speed) to environmental temperature. Thermal Adaptation posits that thermal generalists (ants with flatter, broader TPCs) are favored in the hotter, more variable tropical canopy compared to the cooler, less variable litter below. As predicted, species nesting in the forest canopy 1) had running speeds less sensitive to temperature; 2) ran over a greater range of temperatures; and 3) ran at lower maximum speeds. Tradeoffs between tolerance and maximum performance are often invoked for constraining the evolution of thermal generalists. There was no evidence that ant species traded off thermal tolerance for maximum speed, however. Phosphorus-Tolerance is a second mechanism for generating ectotherms able to tolerate thermal extremes. It posits that ants active at high temperatures invest in P-rich machinery to buffer their metabolism against thermal extremes. Phosphorus content in ant tissue varied three-fold, and as predicted, temperature sensitivity was lower and thermal range was higher in P-rich species. Combined, we show how the vertical distribution of hot and variable vs. cooler and stable microclimates in a single forest contribute to a diversity of TPCs and suggest that a widely varying P stoichiometry among these ants may drive some of these differences.

Thermal adaptation and phosphorus shape thermal performance in an assemblage of rainforest ants

Thermal adaptation and phosphorus shape thermal performance in an assemblage of rainforest ants

Can changes in ant diversity along elevational gradients in tropical and subtropical Australian rainforests be used to detect a signal of past lowland biotic attrition?

Increasing temperatures are predicted to have profound effects on montane ecosystems. In tropical forests, biotic attrition may reduce lowland diversity if losses of species due to upslope range shifts are not matched by influxes of warmer-adapted species, either because there are none or their dispersal is impeded. Australian rainforests consist of a north-south chain of patches, broken by dry corridors that are barriers to the dispersal of rainforest species. These rainforests have repeatedly contracted and expanded during Quaternary glacial cycles. Many lowland rainforests are expansions since the Last Glacial Maximum and may, therefore, show a signal of historical biotic attrition. We surveyed ants from replicated sites along three rainforest elevational transects in eastern Australia spanning 200 to 1200m a.s.l. and nearly 14 degrees of latitude. We examined elevational patterns of ant diversity and if there was possible evidence of lowland biotic attrition. Each transect was in a different biogeographic region; the Australian Wet Tropics (16.3 degrees S), the central Queensland coast (21.1 degrees S) and subtropical south-eastern Queensland (28.1 degrees S). We calculated ant species density (mean species per site) and species richness (estimated number of species by incorporating site-to-site species turnover) within elevational bands. Ant species density showed no signal of lowland attrition and was high at low and mid-elevations and declined only at high elevations at all transects. Similarly, estimated species richness showed no evidence of lowland attrition in the Wet Tropics and subtropical south-east Queensland; species richness peaked at low elevations and declined monotonically with increasing elevation. Persistence of lowland rainforest refugia in the Wet Tropics during the Last Glacial Maximum and latitudinal range shifts of ants in subtropical rainforests during the Holocene climatic optimum may have counteracted lowland biotic attrition. In central Queensland, however, estimated richness was similar in the lowlands and mid-elevations, and few ant species were indicative of lower elevations. This may reflect historical biotic attrition due perhaps to a lack of lowland glacial refugia and the isolation of this region by a dry forest barrier to the north.

Biodiversity of leaf-litter ants in fragmented tropical rainforests of Borneo: the value of publically and privately managed forest fragments

In view of the rapid rate of expansion of agriculture in tropical regions, attention has focused on the potential for privately-managed rainforest patches within agricultural land to contribute to biodiversity conservation. However, these sites generally differ in their history of forest disturbance and management compared with other forest fragments, and more information is required on the biodiversity value of these privately-managed sites, particularly in oil-palm dominated landscapes of SE Asia. Here we address this issue, using tropical leaf-litter ants in rainforest fragments surrounded by mature oil palm plantations in Sabah, Borneo as a model system. We compare the species richness and composition of ant assemblages in privately-managed forest fragments (‘high conservation value’ fragments; HCVs) with those in publically-managed fragments of forest (virgin jungle reserves; VJRs) and control sites in extensive tracts of primary forest. In this way, we test the hypothesis that privately-managed and publically-managed forest fragments differ in their species richness and composition as a result of differences in history and management and hence in habitat quality. In support of this hypothesis, we found that HCVs had much poorer habitat quality than VJRs, including lower sizes and densities of trees, less canopy cover, fewer dipterocarp trees and shallower leaf litter. Consequently, HCVs supported only half the species richness of ants in VJRs, which in turn supported 70 % of the species richness of control sites, with vegetation structure and composition explaining 77 % of the variation among forest fragments in ant species richness. HCVs were also much smaller than VJRs but there was only a weak relationship between fragment size and habitat quality, and species richness was not related to fragment size. VJRs supported 78 % of the 156 species found in extensive tracts of forest whereas HCVs supported only 22 %, which was only slightly higher than the proportion previously recorded in oil palm (19 %). These data support previous findings that publically-managed VJR fragments can make an important contribution to biodiversity conservation within agricultural landscapes. However, we suggest that for these HCVs to be effective as reservoirs of biodiversity, management is required to restore vegetation structure and habitat quality, for instance through enrichment planting with native tree species.

Rainforest ants of the Tiwi Islands: a remarkable centre of endemism in Australia’s monsoonal tropics

The small and isolated rainforest patches that are embedded in the predominantly savanna landscape of Australia’s monsoonal tropics support a highly distinctive and biogeographically significant ant fauna. This fauna features shade-tolerant taxa of Indo-Malayan origin, in contrast to the arid-adapted, endemic Australian taxa that dominate the surrounding savanna. The Tiwi Islands north of Darwin in the Northern Territory (NT) receive the highest mean annual rainfall (up to 2,000 mm) in monsoonal Australia, and have a particularly extensive rainforest estate that has been poorly surveyed for invertebrates. Here we describe results from intensive ant surveys at 17 sites representing the full range of Tiwi rainforest types, using subterranean traps, Winkler sacs, pitfall traps and arboreal traps, supplemented by opportunistic hand collections. Our surveys yielded a total of 87 species from 37 genera, with the richest genera being Pheidole (9 species collected), Polyrhachis (8), Camponotus (5), Rhytidoponera (5) and Strumigenys (5). The overall structure and diversity of the Tiwi rainforest fauna is comparable to that of rainforest ant faunas on the Australian mainland. However, the species have exceptional biogeographic significance. At least 21 species across 12 genera have apparently never previously been collected, three species from subcoastal northeastern Australia are recorded for the first time in the NT, and the genera Mesoponera and Onychomyrmex are documented for the first time in the NT. There was a very low incidence of exotic species, which further highlights the conservation values of this remarkable fauna.

Salt intake in Amazonian ants: too much of a good thing?

Although herbivory is widespread among insects, plant tissues rarely provide the optimal balance of nutrients for insect growth and reproduction. As a result, many herbivorous insects forage elsewhere for particular amino acids and minerals. Recent studies have shown that both herbivory and recruitment to sodium are commonplace among tropical rainforest ants, but little is known about how ants regulate their sodium intake at the individual and colony levels. In social insects, foragers may respond not only to their own nutritional deficiencies but also to those of their nestmates, who may have different nutritional requirements depending on their developmental stage, sex, or caste. Here, we investigate how salt stress among rainforest ants affects their preferences for salt and subsequent survival. We found that ants recruited more to salt than to any other bait type tested, confirming the strong preference for salt of ants in this region. Initially, we observed similarly high recruitment to salt among workers of the arboreal, herbivorous/omnivorous ant species Camponotus mirabilis. However, when provided with unrestricted access to high concentrations of salt, C. mirabilis workers suffered significantly higher mortality relative to controls, suggesting that C. mirabilis workers forage for sodium to the point of toxicity. Nonetheless, surviving workers showed reduced preference for salt at the end of the experiment, so some but not all individuals were able to regulate their salt intake beneath lethal dosages. We discuss how salt intake regulation may depend on colony members other than workers.

Is nest temperature an important factor for niche partitioning by leaf-litter ants (Hymenoptera: Formicidae) in Bornean rain forests?

Abstract:We tested the hypothesis that species of a diverse leaf-litter ant community are separated by the temperature preferences of their broods along a thermal gradient. Therefore, temperature preferences of brood-tending workers from 41 ant species co-occurring in four types (alluvial, limestone, kerangas and dipterocarp forest) of primary rain forest in Sarawak, Malaysia were measured in an experimental set-up. Preferred temperatures of species ranged from 16.0 °C to 31.7 °C, with the median at 25.8 °C. The ten commonest species (n ≥ 4) showed significantly different temperature preferences. In particular, species of the genus Pheidole differed clearly in their preferences over a broad range of temperatures. Temperature preferences varied significantly among ant assemblages from different forest types and nest sites. Experimentally obtained temperature preferences of species correlated significantly with vegetation density in the plots inhabited by the respective species, but not with plot canopy cover. When we tested the temperature preferences of all ant species with null models for niche overlap, we found a significant niche separation only among the tested species from the kerangas. Our results suggest that nest temperature is an important ecological factor for leaf-litter ants in rain forests on Borneo, but other factors may override its influence during community assembly.

Teste da regra de equivalência energética para formigas de serapilheira: efeitos de diferentes métodos de estimativa de abundância em floresta ombrófila

The Energetic Equivalence Rule (EER) states that species tend to consume energy independent of their body size. Here, the EER was tested for litter ants using body size and abundance data. Rainforest ants were obtained using pitfall traps and Winkler extractor. The abundance data from the Winkler extractions confirmed the EER, while the pitfall traps rejected it. Combination of abundance from pitfall catches and Winkler extractions either confirmed or rejected the EER. Further studies should focus on the interaction between sampling techniques and habitat types in the test of EER for ant communities.

Species compensation maintains abundance and raid rates of African swarm-raiding army ants in rainforest fragments

Habitat clearance and fragmentation is increasingly threatening the biodiversity of tropical rainforests, however, the response of many insect species, even of key organisms, is still little understood. Using an extensive data set spanning over four years, we analyzed the effects of clearance and fragmentation of a Congo-Guinean rainforest in western Kenya on the abundance and the raid rates of two species of swarm-raiding army ants, which are considered keystone organisms of tropical rainforests. The abundance of army ants was measured by transect monitoring and by short-term pitfall trapping while raid rates were measured by long-term pitfall trapping over a period of five months. Dorylus wilverthi was the most abundant army ant in undisturbed rainforest and its abundance and raid rate strongly declined in small forest fragments. In contrast, the abundance of Dorylus molestus increased with decreasing fragment size and compensated for the decline of D. wilverthi in terms of abundance and ecological functionality (i.e. raiding rates). D. molestus appears to have a higher ability of using the agricultural land surrounding the Kakamega Forest than D. wilverthi, which may explain the species-specific differences in the susceptibility to habitat fragmentation. Our study demonstrates that habitat fragmentation may have a differential effect on two ecologically highly similar keystone species. Moreover, it shows that species compensation might help in maintaining an important ecosystem function (i.e. raiding by swarm-raiding army ants) in fragmented tropical rainforests.

Are there differences in structure between marine and terrestrial assemblages?

Recently, interest in species abundance (SAD) distributions has been revived by introduction of a new model, the zero-sum multinomial (ZSM). Yet detailed statistical analyses show that the model does not differ from the lognormal distribution proposed in the 1940s. These analyses were based on data from tropical trees where all individuals in a defined area were identified to species. For many ecological data sets it is not possible to identify and count all individuals in a given area. Here we compare data on marine benthos and fish assemblages with data on terrestrial microfauna and ants. We show that these assemblages show similar SAD patterns and that the SADs are best described by a two-group lognormal model. Whereas the 2-group model fitted all data sets the single group model fitted all except the tropical rainforest ants. However, tests comparing the fits to the 2-group versus the single lognormal model showed that the 2-group model was a significantly better fit to the fish and insect data. The two groups are of rare and common species and the rare group dominates in all four data sets. We suggest that the reason for this is that rare species are continuously immigrating from outside the sampled area. Data on tropical tree assemblages where complete accounts were made do not show such high dominance of rare species where the sampled area is large. We conclude that SAD patterns are similar in marine and terrestrial systems that are open to immigration and that the lognormal distribution is still a valid model for SADs.

A revision of the Aphaenogaster phalangium complex (Hymenoptera: Formicidae: Myrmicinae)

The Aphaenogaster phalangium complex is a lineage of rainforest ants endemic to Central America. The complex is revised and interpreted as two parapatric species, A. phalangium and A. araneoides, with extensive geographic variation. Character variation is discordant within species, but in some cases appears to vary in parallel between the two species, such that both species vary the same way in montane versus lowland sites. Aphaenogaster inermis Forel 1899, A. nitidiventris Forel 1912, and A. canalis Enzmann 1947 are synonymized under A. phalangium Emery 1890; and A. brevicollis Forel 1899 is synonymized under A. araneoides Emery 1890. The complex lacks winged queens and instead has ergatoid queens with enlarged postpetiole and gaster.

Les symbioses entre plantes et fourmis arboricoles

In communities of tree-nesting ants in tropical rain forests, energy-rich resources from plants enable ants to achieve high densities and permit the evolution of energy-intensive strategies of prédation. Ants are more abundant, and can maintain populations of phytophagous insects at lower densities than if ant populations were limited simply by insect prey. A large proportion of woody plants in tropical forests are involved in such loose protection mutualisms. Many epiphytes are also involved in loose associations with ants, in which benefits to plants may include nutrition and seed dispersal as well as protection. From such opportunistic interactions numerous symbiotic mutualisms have evolved, in which ants and plants are more intimately and often more specifically associated. The diversity of these symbiotic interactions between ants and plants make these associations good models for examining many general questions in ecology. Plants that have evolved specialised structures (‘ant-domatia’) to house ants are termed ‘myrmécophytes’ or ‘ant-plants’, and their specialised associates are termed ‘plant-ants’. In these symbioses, plants and ants have coevolved. Ant colonies that provide increased benefits to the host plant enhance its growth and survival, thus receiving more benefits from it, and vice versa. Selection favours mutualistic traits, and interests of the two partners tend to converge. However, because these associations are horizontally transmitted, neither partner obtains benefits from reproduction of the other. Because reproduction draws away resources from growth (from which the partner benefits), it introduces conflicts of interest between ants and plants, and several examples show the importance of such conflicts in the dynamics of coevolution. Antplant coevolution has produced parasites as well as mutualists. Much is still unknown on the evolutionary ecology of these symbioses. Mechanisms of interaction at the chemical level (chemical ecology) are little explored. The functioning of ant-plant associations at the level of populations and communities is poorly understood, and information in this domain is crucial for the conservation of these intricate symbioses in forests increasingly subjected to disturbance and fragmentation.

IMPROVING INVENTORY EFFICIENCY: A CASE STUDY OF LEAF-LITTER ANT DIVERSITY IN MADAGASCAR

For most invertebrates, ecologists lack efficient inventory methods for assessing geographic patterns of species richness, complementarity (distinctness), and areas of endemism. I evaluated the efficiency of quantitative inventory methods developed for leaf-litter ants in tropical rain forests in eastern Madagascar. The aim was to maximize the number of species captured per sampling effort in a systematic design subject to standard statistical analysis. I used species and complementarity accumulation curves to evaluate the efficiency of the inventory design based on all ant species sampled and based on four species-rich genera that could potentially act as surrogates for estimating total ant diversity. I evaluated: (1) efficiencies of pitfall and Winkler sifting methods to capture leaf-litter ant assemblages, (2) effects of sample size and spacing on completeness and ranking of species richness, (3) completeness of complementarity values, and (4) four species-rich ant genera that could potentially act as ...

Stratification of ants (Hymenoptera, Formicidae) in a primary rain forest in Sabah, Borneo

The ant fauna of a rain forest in Sabah, Malaysia was sampled by using different collecting methods in three strata. In total, 524 morphospecies of ants could be distinguished. They belong to seven subfamilies and 73 genera. So far, the ant community described is the most species rich published for a primary tropical rain forest. Regarding the stratification in the forest, the leaf litter community comprised as many ant species as the lower vegetation or canopy. Furthermore the litter stratum had the highest generic diversity. The stratification of ants in rain forests seems to be a very strict one with the majority of species (75%) being related to only one stratum. This is in contrast to findings on the stratification of beetles in rain forests. The stratification and a radiation of some groups into vegetation and canopy, where a broad spectrum of permanent habitats exist, is responsible for the high diversity of ants in tropical rain forests.

Seasonal and Spatial Patterns in Ground Foraging Ants in a Rain Forest in the Western Ghats, India1

ABSTRACTSeasonal variation and spatial distribution in ground foraging rain forest ants were studied in South Kannada–Kodagu District in Karnataka (India) between 1990 and 1991 by pit‐fall trap sampling. All ant species showed marked seasonality. A total of 31 species were recorded from the primary forest over a period of two years. More species were recorded from the closed canopy forest than from tree fall gaps in primary forest. All ant species showed marked seasonality with fewer species and individuals sampled/plot during the wetter seasons. The numerically dominant species, Pheidole sp., was markedly lower in abundance during the wet seasons. Spatial patterns were also studied during a dry season both in the primary forest and an adjacent logged forest. More species were recorded from the logged forest than the primary forest. Community composition in primary forest was different from that in logged forest. Common species were more ubiquitous than rarer species. Species were distributed bimodally across sampling plots. Probable underlying processes behind these seasonal and spatial patterns have been discussed.