Territorial aggressiveness and predation: two possible origins of snapping in the ant Plectroctena minor

Plectroctena minor workers have long mandibles that can snap and deliver a sharp blow to intruders or prey, stunning or killing them. Encounters between homocolonial P. minor workers separated for 24 h or 15 days never resulted in snapping, while this behaviour was always noted during encounters between heterocolonial workers on neutral arenas or on the territory of a colony. In the latter case, only the aliens, that generally tried to escape, were snapped at. Snapping also occurred during encounters with workers belonging to sympatric ponerine species. During predation, the percentages of snapping varied according to prey nature, suggesting prey discrimination. Termite soldiers were always snapped at, while other prey were more often snapped close to rather than far from the nest entrances, indicating an intermingling of territorial aggressiveness and predatory behaviour. We discuss the adaptive value of snapping for hunting in galleries.     

Specialized predation on Wasmannia auropunctata by the army ant species Neivamyrmex compressinodis

Abstract:  We report here the first case of an efficient and specialized predator of the invasive ant species Wasmannia auropunctata : the army ant Neivamyrmex compressinodis . Our results are based on a study that we conducted in French Guiana, a part of the Wasmannia's native range. When N . compressinodis workers attacked W . auropunctata nests, the assaulted workers panicked and left the nests, some of them carrying brood. Nevertheless, during its raids on W . auropunctata , N . compressinodis was able to capture nearly all of the W . auropunctata brood and winged sexuals, whereas none of the attacks by N . compressinodis on other sympatric ant species were successful. Laboratory experiments revealed that the workers of eight compared sympatric species attacked the N . compressinodis individuals and that N . compressinodis workers accepted W . auropunctata brood as well as that of most of the tested species, showing that its specificity probably depends on the reaction of the W . auropunctata workers.     

Risk of predation for two reptile tick species

Experiments were conducted in the Mount Mary region of South Australia where the distributions of the two reptile-tick speciesAponomma hydrosauri andAmblyomma limbatum narrowly overlap. Engorged larvae and nymphs were placed in boxes with and without access to predators and left for 1 week. At two out of five sites there was greater loss from open access boxes in replicates during warmer periods of the year. Predation by ants appears to be the most likely explanation for the loss of ticks.     

Egg-hatch phenology and intraguild predation between two mantid species

Relative timing of egg hatch between two cooccurring, congeneric mantids, Tenodera angustipennis and T. sinensis, was experimentally manipulated in replicated field enclosures to test the importance of intraguild predation to survivorship and development of T. angustipennis. T. angustipennis is normally smaller than its congener because of later egg-hatch. Delaying introduction of T. sinensis relative to normal egg hatch phenology reduced mortality for T. angustipennis, but did not affect its rate of development. The results indicate that intraguild predation by normally earlierhatching T. sinensis can be an important factor in the early life history of T. angustipennis, but that interspecific competition is not a strong selective factor in developmental asynchrony between these two species.     

Isozymes of two fire ant species and their hybrid

Electrophoretic banding patterns of eight enzyme systems in Solenopsis xyloni, S. germinata and their hybrid were studied. Repression of paternal alleles was found in aldehyde oxidase, isocitrate dehydrogenase, leucine amino peptidase and malic enzyme.     

Ecosystem engineering impact of Limnoperna fortunei in South America

Limnoperna fortunei, or golden mussel, has invaded aquatic ecosystems in the Americas following it introduction from Southeast Asia. It is not only an aggressive invasive species, it is also a very effective ecosystem engineer, altering both ecosystem structure and function, and causes great ecological and economic impacts. This paper describes its impact as an ecosystem engineer (on benthic communities and the water column). A review of the existing scientific literature is presented, and the impact and the mechanisms by which the golden mussel modifies, maintains, and creates new environmental conditions in the invaded South American inland freshwater environments are analyzed. Understanding the ecosystem engineering roles of L. fortunei is important for its management and/or control in the invaded areas, and in cases of future invasions.     

Competition, predation and the relative abundances of two species of Daphnia

We investigated the factors controlling the relative abundancesof two Daphnia species, D.pulex and D.laevis, in a small Wisconsinpond. D.pulex was the dominant Daphnia species in fall 1977and summer-fall 1978; D.laevis was the only Daphnia speciespresent in summer 1979. The abundance of D.laevis was positivelycorrelated with the abundance of the notonectid, Buenoa confusa.In predation trials, notonectides exhibited a distinct preferencefor D.pulex over similarly-sized D.laevis, but Chaoborus larvaefed at similar rates on both Daphnia species. Behavioral observationsrevealed that Buenoa adults were much less efficient at capturingD.laevis than D.pulex. Quantitative results of these predationtrials were combined with estimates of predator and prey densityand distribution to evaluate the effect of predation on thedaphnid populations. The effect of predation varied throughtime and microhabitat, and only infrequently could predationaccount for total prey mortality. D.laevis was most abundantat times and in places where Buenoa predation was most intense.Competition experiments illustrated the competitive superiorityof D.pulex over D.laevis. D.pulex was able to competitivelyexclude D.laevis in long term experiments, and D.pulex's fecunditywas higher than that of D.laevis in shorter experiments. Inlong-term experiments, Chaoborus larvae at natural densitieswere able to keep both Daphnia species at low, constant levelsand neither species clearly dominated when Chaoborus was present.The relative abundances of D.pulex and D.laevis were controlledby a complex of biotic and abiotic factors. Pond depth and predatordensity determined the intensity of predation on daphnid populations.When notonectid predation was intense, D.laevis dominated; whenthe intensity of predation by notonectids was low, D.pulex dominateddue to its superior competitive abilities. At different timesselective predation or high resource levels promoted the co-existenceof these two species. ¹Current address of both authors: Department of Biological Sciences,University of California, Santa Barbara, CA 93106, USA     

Avoiding predation by army ants: Defensive behaviours of three ant species of the genus Camponotus

Antipredation behaviours of three ant species of the genus Camponotus were investigated in field and laboratory studies. Contact with the army ant Neivamyrmex nigrescens was shown to produce nest evacuation and removal of brood by colonies of Camponotus festinatus. Colonies of Camponotus ocreatus and Camponotus vicinus defended their nests through recruitment of the major caste. The initiation of evacuation or aggressive recruitment was dependent upon tactile contacts between Camponotus nestmates. Other sorts of disturbance which did not involve army ant contact did not produce evacuation or recruitment, indicating a high degree of enemy specification by Camponotus. The comparison of worker morphology revealed a close relationship between each species' strategy for nest defence and the degree of worker polymorphism exhibited. These findings suggest that interspecific ant predation has been a significant factor in the evolution of colony defence systems and caste polymorphism.     

Memory and chemical communication in the orientation of two mass-recruiting ant species

Summary The relative contribution of visual and chemical components in the orientation ofLasius niger andIridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number ofL. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues.I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. InL. niger, the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all theI. humilis workers initially lay a trail, whereas only half theL. niger foragers do so. This proportion decreases considerably with the number of trips performed byL. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology.     

Separating effects of species identity and species richness on predation,pathogen dissemination and resistance to invasive species in tropical ant communities

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Interference interactions and nest usurpation between two subordinate ant species

Camponotus foreli (Emery) and Cataglyphis iberica (Emery) are two sympatric, subordinate ant species that have been found to fight in attacks that usually conclude with the death of many workers of both species and with nest abandonment by C. iberica. These harassment episodes have been observed in two different areas and over many years of study. No such attacks of C. foreli were observed in the study areas against any other ant species, nor did any other ants attack C. iberica nests, and laboratory confrontations confirmed this specificity. These attacks neither eliminated C. iberica colonies, nor distanced them from C. foreli nests. Moreover, there was no real competition for food between the species: in an experiment where all C. iberica colonies were eliminated from an area, rates of prey and liquid food collection by C. foreli nests in the exclusion zone were similar to those found in the control zone with C. iberica, and the activity rhythms of C. foreli did not change in the absence of C. iberica. The hypothesis of competition for a nest site is more consistent. Both in the laboratory and the field, the most frequent outcome of these aggressive interactions was the occupation of the C. iberica nest by C. foreli. This behavior may be advantageous for C. foreli, because it is much less skilful at excavating than C. iberica. One of the chief concerns of this study is to show that such interference interactions, typical especially of dominant, very aggressive species, are also found between subordinate, apparently nonaggressive species. Received: 20 March 1997 / Accepted: 29 September 1997     

Seed predation of two alien Opuntia species invading Mediterranean communities

Invasibility depends on the interaction of the introduced species with the abiotic and biotic factors of the recipient community. In particular, the biotic resistance posed by native herbivores has been claimed to be of great importance in controlling plant invasion. We investigated fruit and seed predation of two exotic Opuntia species within and between Mediterranean communities in order to determine how patterns of predation matched patterns of invasion. Predators were small mammals, presumably mice, which could consume more than 50% of the seeds produced. Predators could be equally effective in consuming fruit and single seeds. O. maxima fruits were slightly preferred to O. stricta fruits, but predators did not distinguish between seeds. Seed predation was more intense in invaded than in non-invaded communities. However, there was a high spatial variation in seed predation that did not always match patterns of invasion, suggesting that seed predation alone is not a good predictor of community invasibility to Opuntia. According to these results invasibility to Opuntia is limited in some (but not all) communities by native mice. Seed losses by predation were high for both species. However, we estimated that more than 75% of seeds dispersed by birds to non-invaded areas are not predated.     

Intraguild predation and cannibalism among Dicyphini: Dicyphus cerastii vs. two commercialized species

Dicyphine mirids are one of the most important groups of predators on tomato. In the Mediterranean region, several species in the genera Dicyphus, Macrolophus, and Nesidiocoris (Hemiptera: Miridae, Bryocorinae, Dicyphini) colonize protected horticultural crops. In Portugal, Nesidiocoris tenuis (Reuter) is increasingly abundant in the mirid species complex of tomato crops and appears to be displacing the native Dicyphus cerastii Wagner. In order to know whether intraguild predation (IGP) can explain the decreasing abundance of D. cerastii, we evaluated predatory interactions between adult females and first instars of D. cerastii vs. N. tenuis but also D. cerastii vs. Macrolophus pygmaeus (Rambur), as this species is also naturally present in horticultural crops in Portugal. Cannibalistic interactions were also tested for the same three species. All experiments were performed under laboratory conditions, in Petri dish arenas, in the presence or absence of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as alternative prey. Predation on both heterospecific and conspecific nymphs occurred only in the absence of alternative food. Intraguild predation was mutual and symmetrical between D. cerastii and M. pygmaeus. However, IGP was asymmetrical between D. cerastii and N. tenuis, favouring the first. Cannibalism was not significantly different among these mirid species. Our results show that D. cerastii has a greater capacity to feed on intraguild prey than N. tenuis. Therefore, IGP on small nymphs does not explain the abundance shift between D. cerastii and N. tenuis.     

Guards and thieves: antagonistic interactions between two ant species coexisting on the same ant-plant

Abstract.  1. The simultaneous occupation of a rare understorey ant-acacia Acacia mayana by its guarding ant Pseudomyrmex ferrugineus , and an apparent opportunist parasite of the mutualism, the generalist ant Camponotus planatus is described. The two ant species occur together in 30.7% of the 26 mature A. mayana plants [23.5% of all trees ( n  = 34)] surveyed, but C. planatus is absent from saplings below 1 m in height ( n  = 8).
2. While P. ferrugineus shows behaviour compatible with effective host-tree defence, C. planatus does not attack phytophagous insects and appears ineffective as an ant-guard. Camponotus planatus does, however, occupy swollen thorns (pseudogalls) on the host tree, and harvests nectar from extrafloral leaf nectaries. It is proposed that C. planatus is a parasite of the Acacia–Pseudomyrmex mutualism.
3. Camponotus planatus does not harvest the second trophic reward produced by the tree for its Pseudomyrmex ant-guards, protein-rich food (Beltian) bodies. Camponotus planatus lack the specialised larval adaptations needed to use Beltian bodies as brood food, suggesting that this resource is potentially more resistant to exploitation by generalists than extrafloral nectar.
4. In competition for access to nectaries, C. planatus effectively displaced P. ferrugineus in 99.8% of encounters. These results suggest not only that C. planatus is a parasite of this mutualism, but also that it is able to effectively counteract the aggression shown to other insects by the resident ant-guards.     

Genetic marker investigation of the source and impact of predation on a highly endangered species

In September and October 2000, the remains of a number of apparently predated northern hairy-nosed wombats (Lasiorhinus krefftii) were discovered in Epping Forest National Park, the site of the only known population of this highly endangered species. Analysis of DNA recovered from six carcasses and a section of intestine found nearby was carried out using microsatellite and Y-specific primers. This identified seven individual wombats, the identity of three of which was inferred from a genotype database prepared from animals sampled during trapping programmes. Six victims were male and one female, suggesting that female-biased predation rates are unlikely to be the cause of the current male-biased population sex ratio. DNA isolated from four canid faeces found in the vicinity revealed three distinct canid microsatellite genotypes with very high probabilities of belonging to dingoes (Canis familiaris dingo). A wombat genotype matching that of one of the dead individuals was identified from scats of two of the dingoes. In addition, two macropod microsatellites were amplified from two dingo scats. These observations provided vital information regarding predation on northern hairy-nosed wombats, and prompted the permanent exclusion of dingoes from the park by the erection of a dingo-proof fence.     

Relative susceptibility to predation of two species of caterpillar on plantain

Summary The relative susceptibility to predators of a cryptic generalist caterpillar (Spilosoma congrua: Arctiidae) and a non-cryptic specialist (Junonia coenia: Nymphalidae) using the same hostplant species (Plantago lanceolata) was examined. In a laboratory experiment using predatory stinkbugs (Podisus maculiventris), more Junonia caterpillars than Spilosoma caterpillars were killed (70% vs. 16%). This result was a consequence of the Spilosoma spending some time under cover, moving frequently, feeding on leaves while under or adjacent to them, and spending little time on the leaves. In a field experiment using predatory wasps (Polistes fuscatus), the wasps found 7 times as many of the Junonia as the Spilosoma, and overall 6 times as many Junonia were killed as Spilosoma. Initially, 71% of the Junonia caterpillars encountered by wasps were killed, but by the fourth day of the test, only 22% of the Junonia encountered by wasps were killed. Over three full days of observations, a constant 50% of the Spilosoma caterpillars encountered by the wasps per day were killed. For the Junonia, evasion of predators rested on passive chemical defense. For the Spilosoma, evasion depended on being unapparent, speedy movement between feeding and resting sites and, if found, on fleeing immediately and quickly. These results indicate that Spilosoma caterpillars, by way of cryptic and escape behaviors, can be less susceptible to insect predators than Junonia caterpillars.