Spatial Variation in Army Ant Swarm Raiding and its Potential Effect on Biodiversity

Invertebrate communities of the tropical rain forest floor are highly diverse, characterized by patchy species distribution patterns and high variation in species density. Spatial variation in the foraging activity of swarm raiding army ants, prime invertebrate predators in tropical rain forests, is discussed as a mechanism contributing to these patterns, but highly resolved long‐term data on army ant raiding on the local and landscape scale are hitherto lacking. In this study, 196 positions in 11 study sites in a tropical rain forest in western Kenya were continuously monitored over ~4 mo for the occurrence of swarm raids of army ants. Using population simulation analyses, the consequences of army ant raiding for prey communities were assessed. We found an unexpectedly high variation in raid rates at the study site and landscape scale. The weekly chance of communities to become raided by army ants was on average 0.11, but ranged from 0 to 0.50 among the 196 positions. Simulating population developments of two Lotka–Volterra species—showing slight trade‐offs between competitive strength and resistance to army ant raids—in the real raiding landscapes showed that the observed spatial variation in raid rates may produce high prey diversity at larger spatial scales (due to high β‐diversity) and strong variation in species density. Our results indicate that high spatial variation in army ant swarm raiding is a mechanism capable of generating patchy species distribution patterns and maintaining the high biodiversity of invertebrate communities of the tropical rain forest floor.     

Dietary partitioning promotes the coexistence of planktivorous species on coral reefs

Theories involving niche diversification to explain high levels of tropical diversity propose that species are more likely to co‐occur if they partition at least one dimension of their ecological niche space. Yet, numerous species appear to have widely overlapping niches based upon broad categorizations of resource use or functional traits. In particular, the extent to which food partitioning contributes to species coexistence in hyperdiverse tropical ecosystems remains unresolved. Here, we use a molecular approach to investigate inter‐ and intraspecific dietary partitioning between two species of damselfish (Dascyllus flavicaudus, Chromis viridis) that commonly co‐occur in branching corals. Species‐level identification of their diverse zooplankton prey revealed significant differences in diet composition between species despite their seemingly similar feeding strategies. Dascyllus exhibited a more diverse diet than Chromis, whereas Chromis tended to select larger prey items. A large calanoid copepod, Labidocera sp., found in low density and higher in the water column during the day, explained more than 19% of the variation in dietary composition between Dascyllus and Chromis. Dascyllus did not significantly shift its diet in the presence of Chromis, which suggests intrinsic differences in feeding behaviour. Finally, prey composition significantly shifted during the ontogeny of both fish species. Our findings show that levels of dietary specialization among coral reef associated species have likely been underestimated, and they underscore the importance of characterizing trophic webs in tropical ecosystems at higher levels of taxonomic resolution. They also suggest that niche redundancy may not be as common as previously thought.     

Cryptic termites avoid predatory ants by eavesdropping on vibrational cues from their footsteps

Eavesdropping has evolved in many predator–prey relationships. Communication signals of social species may be particularly vulnerable to eavesdropping, such as pheromones produced by ants, which are predators of termites. Termites communicate mostly by way of substrate‐borne vibrations, which suggest they may be able to eavesdrop, using two possible mechanisms: ant chemicals or ant vibrations. We observed termites foraging within millimetres of ants in the field, suggesting the evolution of specialised detection behaviours. We found the termite Coptotermes acinaciformis detected their major predator, the ant Iridomyrmex purpureus, through thin wood using only vibrational cues from walking, and not chemical signals. Comparison of 16 termite and ant species found the ants‐walking signals were up to 100 times higher than those of termites. Eavesdropping on passive walking signals explains the predator detection and foraging behaviours in this ancient relationship, which may be applicable to many other predator–prey relationships.     

Dietary and Temporal Niche Differentiation in Tropical Ants—Can They Explain Local Ant Coexistence?

How species with similar ecological requirements avoid competitive exclusion remains contentious, especially in the species‐rich tropics. Niche differentiation has been proposed as a major mechanism for species coexistence. However, different niche dimensions must be studied simultaneously to assess their combined effects on diversity and composition of a community. In most terrestrial ecosystems, ants are among the most abundant and ubiquitous animals. Since they display direct, aggressive competition and often competitively displace subordinate species from resources, niche differentiation may be especially relevant among ants. We studied temporal and trophic niche differentiation in a ground ant community in a forest fragment in French Guiana. Different baits were presented during day and night to assess the temporal and dietary niches of the local species. They represented natural food resources such as sugars, carrion, excrements, seeds, and live prey. In addition, pitfalls provided a background measure of ant diversity. The communities attracted to the different baits significantly differed from each other, and even less attractive baits yielded additional species. We detected species specialized on living grasshoppers, sucrose, seeds, or dead insects. Community‐level differences between day and night were larger than those between baits, and many species were temporally specialized. In contrast to commonness, foraging efficiency of species was correlated to food specialization. We conclude that many ant species occupy different temporal or dietary niches. However, for many generalized species, the dietary, and temporal niche differentiation brought forward through our sampling effort, cannot alone explain their coexistence.     

Community structure affects trophic ontogeny in a predatory fish

While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. Northern Scandinavian freshwater fish communities were used as a study system, including nine subarctic lakes with contrasting fish community configurations: (i) trout‐only systems, (ii) two‐species systems (brown trout and Arctic charr [Salvelinus alpinus] coexisting), and (iii) three‐species systems (brown trout, Arctic charr, and three‐spined sticklebacks [Gasterosteus aculeatus] coexisting). We expected that the presence of profitable small prey (stickleback) and mixed competitor–prey fish species (charr) supports early piscivory and high individual dietary specialization among trout in multispecies communities, whereas minor ontogenetic shifts were expected in trout‐only systems. From logistic regression models, the presence of a suitable prey fish species (stickleback) emerged as the principal variable determining the size at ontogenetic niche shifts. Generalized additive mixed models indicated that fish community structure shaped ontogenetic niche shifts in trout, with the strongest positive relationships between body length, trophic position, and individual dietary specialization being observed in three‐species communities. Our findings revealed that the presence of a small‐sized prey fish species (stickleback) rather than a mixed competitor–prey fish species (charr) was an important factor affecting the ontogenetic niche‐shift processes of trout. The study demonstrates that community structure may modulate the ontogenetic diet trajectories of and individual niche specialization within a top predator.     

Birds and army ants in a fragment of the Atlantic Forest of Brazil

ABSTRACT Little is known about the birds associated with army‐ant swarms in the Brazilian Atlantic forest. Our objectives were to locate and monitor army‐ant swarms in the Atlantic rainforest of Brazil and to identify the species of birds that attended the swarms and exhibited bivouac‐checking behavior. From July 2004 to August 2005, we located 49 swarms of army ants, including 28 Eciton burchelli, 19 Labidus praedator, and 2 Eciton vagans swarms. No birds were present at 17 (35%) swarms. At 32 swarms where birds were present, 22 (69%) were E. burchelli swarms and 10 (31%) were L. praedator swarms. No birds were observed at the two E. vagans swarms. We identified 66 species of birds attending the swarms, but only 43 species were observed foraging on prey flushed by the ants. Eighteen of these species had not been previously reported to forage in association with army‐ant swarms. Most birds observed during our study attended army‐ant swarms opportunistically, with White‐shouldered Fire‐eyes (Pyriglena leucoptera) the only obligate ant follower. Our observations suggest that the arthropods and other organisms flushed by army ants represent an important food resource for several species of birds in the Atlantic forest ecosystem.     

Chimpanzees prey on army ants with specialized tool set

Several populations of chimpanzees have been reported to prey upon Dorylus army ants. The most common tool‐using technique to gather these ants is with “dipping” probes, which vary in length with regard to aggressiveness and lifestyle of the prey species. We report the use of a tool set in army ant predation by chimpanzees in the Goualougo Triangle, Republic of Congo. We recovered 1,060 tools used in this context and collected 25 video recordings of chimpanzee tool‐using behavior at ant nests. Two different types of tools were distinguished based on their form and function. The chimpanzees use a woody sapling to perforate the ant nest, and then a herb stem as a dipping tool to harvest the ants. All of the species of ants preyed upon in Goualougo are present and consumed by chimpanzees at other sites, but there are no other reports of such a regular or widespread use of more than one type of tool to prey upon Dorylus ants. Furthermore, this tool set differs from other types of tool combinations used by chimpanzees at this site for preying upon termites or gathering honey. Therefore, we conclude that these chimpanzees have developed a specialized method for preying upon army ants, which involves the use of an additional tool for opening nests. Further research is needed to determine which specific ecological and social factors may have shaped the emergence and maintenance of this technology. Am. J. Primatol. 72:17–24, 2010. © 2009 Wiley‐Liss, Inc.     

Similar yet different: differential response of a praying mantis to ant‐mimicking spiders

Batesian mimics typically dupe visual predators by resembling noxious or deadly model species. Ants are unpalatable and dangerous to many arthropod taxa, and are popular invertebrate models in mimicry studies. Ant mimicry by spiders, especially jumping spiders, has been studied and researchers have examined whether visual predators can distinguish between the ant model, spider mimic and spider non‐mimics. Tropical habitats harbour a diverse community of ants, their mimics and predators. In one such tripartite mimicry system, we investigated the response of an invertebrate visual predator, the ant‐mimicking praying mantis (Euantissa pulchra), to two related ant‐mimicking spider prey of the genus Myrmarachne, each closely mimicking its model ant species. We found that weaver ants (Oecophylla smaragdina) were much more aggressive than carpenter ants (Camponotus sericeus) towards the mantis. Additionally, mantids exhibited the same aversive response towards ants and their mimics. More importantly, mantids approached carpenter ant‐mimicking spiders significantly more than often that they approached weaver ant‐mimicking spiders. Thus, in this study, we show that an invertebrate predator, the praying mantis, can indeed discriminate between two closely related mimetic prey. The exact mechanism of the discrimination remains to be tested, but it is likely to depend on the level of mimetic accuracy by the spiders and on the aggressiveness of the ant model organism.     

Dietary overlap and seasonality in three species of mormoopid bats from a tropical dry forest

Competing hypotheses explaining species’ use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or behavioural specialization, permitting the coexistence of closely related species through resource partitioning and niche differentiation. Alternatively, when resources are unlimited, fluctuations in resources availability will cause concomitant shifts in resource use regardless of species identity. Here, we used next‐generation sequencing to test these hypotheses and characterize the diversity, overlap and seasonal variation in the diet of three species of insectivorous bats of the genus Pteronotus. We identified 465 prey (MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with the highest value between Pteronotus parnellii and Pteronotus personatus in the wet season. We found higher dietary overlap between species during the same seasons than within any single species across seasons. This suggests that diets of the three species are driven more by prey availability than by any particular predator‐specific characteristic. P. davyi and P. personatus increased their dietary breadth during the dry season, whereas P. parnellii diet was broader and had the highest effective number of prey species in all seasons. This supports the existence of dietary flexibility in generalist bats and dietary niche overlapping among groups of closely related species in highly seasonal ecosystems. Moreover, the abundance and availability of insect prey may drive the diet of insectivores.     

Effect of agricultural land‐use change on the structure of a temperate forest ant–plant interaction network

Studies on the responses of ant–plant interactions to land‐use change have mainly focused on tropical habitats, usually without considering the impacts on the structure of interaction networks. Here we show that land‐use modifies the structure of the ant–plant interaction networks in a temperate habitat. Ant–plant interactions and plant diversity were recorded in an oak forest and agricultural land in central Mexico. We registered five ant species in the oak forest, and four ant species in the agricultural land. Plant diversity was higher in the agricultural land than in the oak forest. In the ant–plant networks of both sites, our results showed a higher dependence of ants on the plants on which they feed than vice versa, and the ants Formica spp. and the plants Barkleyanthus salicifolius were the species with the most strength and greatest influence in the network structure. The ant–plant network in the oak forest showed a nested structure. However, the network at the agricultural land site showed non‐nestedness; the identity of both ants and plants with the highest values of specialization was different and the number of ant species in the network was decreased, but the number of plant species with which they interacted significantly increased. Both ant–plant networks were equally tolerant to simulated extinction of individual species. We conclude that temperate forest ant–plant networks can be inherently fragile and susceptible to the effects of agricultural land‐use change, not on the number of interacting species but on their identity.     

The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades

Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free‐ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.     

Determinants of predation on phytophagous insects: the importance of diet breadth

To evaluate the role of predation in the evolution of diet specialization and to determine the effectiveness of various larval defenses, we offered lepidopteran larvae to colonies of the tropical ant Paraponera clavata. We recorded behavioral and physical characteristics of prey items and used log-linear models to analyze their importance as deterrents to predation by P. clavata. The most important determinant of probability of prey rejection by P. clavata was a prey's diet breadth; specialists were rejected by the ants significantly more than generalists. Other less important, but significant, predictors of prey rejection included ontogeny, morphology and chemistry. Late instar caterpillars were rejected more frequently than early instars, hairy caterpillars were rejected more frequently than caterpillars with other morphologies, and one caterpillar species with an unpalatable extract was rejected more frequently than two species with palatable extracts.     

Diet and feeding strategy of blackmouth catshark Galeus melastomus

Diet and feeding strategy of the blackmouth catshark Galeus melastomus in the deep waters of the eastern Ionian Sea were investigated. Sampling was carried out using experimental bottom longline fishing at depths ranging from 300 to 855 m in summer and autumn 2010. Diet variability with fish size, season, area, sex and depth zone was tested and only season was found to significantly affect the diet of the species. Of the 870 stomachs examined, only 1·4% were empty. Cumulative prey curves showed that the sample sizes were adequate to describe the main prey items of the diet for both seasons. Prey identified belonged primarily to three major groups: fishes, cephalopods and dendrobranchiatan and caridean shrimps. In autumn, the above three major groups were found as principal prey, whereas in summer cephalopods followed by fishes were the principal prey and shrimps were found as secondary prey. SIMPER analysis indicated high dissimilarity between seasons and highlighted that Sepiolidae, Myctophidae, fishes, cephalopods, shrimps and other crustaceans contributed to seasonal differences in the diet of G. melastomus. The prey diversity index was higher in autumn than in summer. A high dietary overlap was observed between the two seasons. Galeus melastomus behaved as an opportunistic predator with a variety of unimportant prey in its diet. Feeding strategy indicated that G. melastomus holds a generalist niche with a considerable specialization at the individual level. This strategy seems to be an adaptation to a food‐scarce environment, as typified in deep‐water habitats.     

Spine and dine: A key defensive trait promotes ecological success in spiny ants

A key focus of ecologists is explaining the origin and maintenance of morphological diversity and its association with ecological success. We investigate potential benefits and costs of a common and varied morphological trait, cuticular spines, for foraging behavior, interspecific competition, and predator–prey interactions in naturally co‐occurring spiny ants (Hymenoptera: Formicidae: Polyrhachis) in an experimental setting. We expect that a defensive trait like spines might be associated with more conspicuous foraging, a greater number of workers sent out to forage, and potentially increased competitive ability. Alternatively, consistent with the ecological trade‐off hypothesis, we expect that investment in spines for antipredator defense might be negatively correlated with these other ecological traits. We find little evidence for any costs to ecological traits, instead finding that species with longer spines either outperform or do not differ from species with shorter spines for all tested metrics, including resource discovery rate and foraging effort as well as competitive ability and antipredator defense. Spines appear to confer broad antipredator benefits and serve as a form of defense with undetectable costs to key ecological abilities like resource foraging and competitive ability, providing an explanation for both the ecological success of the study genus and the large number of evolutionary origins of this trait across all ants. This study also provides a rare quantitative empirical test of ecological effects related to a morphological trait in ants.     

Effects of Management Intensity and Season on Arboreal Ant Diversity and Abundance in Coffee Agroecosystems

Agricultural intensification decreases arthropod predator diversity, abundance and population stability, and may affect interactions between top predators and their arthropod prey – ultimately affecting ecosystem services. Coffee management intensification (reduction or removal of shade trees) reduces diversity of arthropod predators (ground-foraging ants). Because ants provide ecosystem services by controlling pests, influences of intensification on arboreal, coffee-foraging ant diversity and abundance are important. We here address how coffee intensification affects: (1) coffee-foraging ant diversity and abundance and (2) seasonal fluctuations in ant abundance. In each of four coffee sites of varying management intensity in Chiapas, Mexico, we sampled vegetation and using two methods, sampled ant diversity and abundance over two years. Sites significantly differed in vegetation and management intensity. Coffee-foraging ant diversity generally decreased with increasing management intensity (16–26% fewer species observed in the most intensively-managed site). Ant abundance was higher in the wet season. Management intensity, however, did not influence ant abundance or seasonal fluctuations in abundance. Our results highlight the importance of diverse agricultural systems in maintaining arthropod predator diversity, and point to one model system in which we may effectively test how diversity per se affects ecosystem services.     

Foraging Trade‐offs between Prey Size,Delivery Rate and Prey Type: How Does Niche Breadth and Early Learning of the Foraging Niche Affect Food Delivery?

Optimal foraging theory suggests that avian parents should prefer the most energetically efficient (largest) prey items when delivering food to offspring at a central place. However, during periods of high demand, selectivity of prey may decline, leading to the delivery of smaller and/or less nutritious items. We compared foraging trade‐offs between great tits (Parus major) which had a wider feeding niche than blue tits (Cyanistes caeruleus). We also compared the foraging efficiency of cross‐fostered young, which had learned the spatial foraging niche and prey size of the foreign species, to that of control conspecifics. Mean delivery rates did not differ between control and cross‐fostered parents of either species but as delivery rates increased, prey size declined for both species and both treatment groups. However, across the range of increasing delivery rates, parents were able to increase the total biomass of prey delivered. Cross‐fostering did not alter the proportion of different prey taxa in the diet, but cross‐fostered birds shifted the size of the prey taken to that of their foster species. Consistent with their broader feeding niche, great tits, but not blue tits, incorporated more unpalatable items (flies) as delivery rates increased. Although great tits foraged less efficiently in the blue tit niche, paradoxically, blue tits seem to deliver more prey biomass when foraging in the great tit niche.     

Networks of prey specialization in an Arctic monomorphic seabird

Generalist predator populations are sometimes made up of individuals that specialize on particular prey items. To examine specialization in thick‐billed murres Uria lomvia during self‐feeding we obtained stomach contents and muscle stable isotope values for 213 birds feeding close to five colonies in the Canadian Arctic. Adults were less specialized during self‐feeding than during chick‐provisioning. Nonetheless, particular specialists clustered together within the foraging network. While sexes showed similar levels of specialization, individuals of the same sex clustered together within the foraging network. The significant degree of clustering regardless of sex showed that individuals specializing on one prey item tend to also specialize on another, although network topology varied from colony to colony. Adult muscle stable isotope values correlated with the stable isotope values of the prey found in stomachs, at least at the one colony with relevant prey data, suggesting that specializations are maintained over time. Degree of specialization increased with niche width across the five colonies, but similarity in gastro‐intestinal and bill morphology was independent of dietary similarity. Thus, although individual specialization is thought to play a key role in sympatric speciation through trophic specialization, we found no support for an association between morphology and foraging patterns in our species. We conclude that self‐feeding murres show clustered dietary specialization, and that specialization is highest where diet is most diverse.     

Extraordinary Predation by the Neotropical Army Ant Cheliomyrmex andicola: Implications for the Evolution of the Army Ant Syndrome1

Workers of the genus Cheliomyrmex are unique among the New world army ants (subfamily Ecitoninae) in that their mandibles are armed with elongate, spine‐like teeth. We present the first prey records for this genus. Cheliomyrmex andicola prey on large‐bodied ground dwelling invertebrates and, possibly, on vertebrates. Unlike other army ants, C. andicola workers use their sting during prey capture. The workers' unusual mandibles and potent stings may be adapted for piercing and gripping the integument of nonarthropod prey animals, and for rapidly subduing large‐bodied prey, respectively. The genus Cheliomyrmex may be the sister taxon to other Neotropical army ants (Ecitoninae), and Cheliomyrmex shares features of mandibular morphology and prey selection with Old World driver ants in the genus Dorylus. Mass cooperative foraging, an important element of army ant behavior, may have arisen in part as an adaptation for exploiting large‐bodied prey.     

Trophic niche,capture efficiency and venom profiles of six sympatric ant‐eating spider species (Araneae: Zodariidae)

The arms race between specialist predators and their prey has resulted in the evolution of a variety of specific adaptations. In venomous predators, this can include venom composition, particularly if predators are specialized on dangerous prey. Here, we performed an integrative study using six species of highly specialized ant‐eating spiders of the genus Zodarion to investigate their phylogeny, realized trophic niche, efficacy in the capture of various ant species and venom composition. Data on natural diet obtained by next‐generation sequencing and field observations showed that the six Zodarion species exploit different ant species. Their phylogeny, based on mitochondrial and nuclear genes, correlated with the composition of their natural prey, indicating that closely related Zodarion species specialize on similar ant species. Prey‐capture parameters differed among Zodarion species suggesting prey‐specific efficacy. Similarly, the venom profiles of both low and high molecular compounds differed among species. Only the profiles of low molecular compounds were correlated with capture efficacy parameters, suggesting that the venom of Zodarion spiders contains prey‐specific components. Our study suggests that Iberian Zodarion spiders are specialized on particular ant species.     

Native predator eats invasive toxic prey: evidence for increased incidence of consumption rather than aversion-learning

Contemporary adaptation of native prey species to invasive predators has been relatively well documented, but that of native predators to invasive prey has received less attention. Because the level of impact an invasive species will have on its predators versus its prey will determine changes in community trophic structure, it is important to understand how native predators respond to novel prey. Here we examine the response of native fence lizards to the invasion of red imported fire ants, a novel toxic prey. Examining invaded and uninvaded lizard populations, we tested whether or not aversion-learning occurs in juvenile fence lizards over successive feedings (within lifetime), how previous fire ant exposure may affect avoidance behavior (over generations), and whether population differences are consistent when prey choice exists. We also examine rates of phenotypic divergence in traits associated with the native species as both predator and prey. Aversion-learning did not occur in either population. Instead, the incidence of fire ant consumption increased over both successive feedings and generations. Lizards from the fire ant invaded population had a higher propensity to eat fire ants than fire ant-naïve lizards, even when given a choice between prey items. We found greater phenotypic divergence in traits associated with the native species as predator on, versus as prey to, fire ants. Although the strategy of eating these novel toxic prey can impose survival costs in the short term, over the longer-term, eating fire ants may cost little or even benefit survivors.