Mandible strike: the lethal weapon of Odontomachus opaciventris against small prey

In order to study both the hunting efficiency and the flexibility of their predatory behavior, solitary hunters of the trap-jaw ant Odontomachus opaciventris were offered small prey (termites, fruit flies and tenebrionid larvae), presenting different morphological or defensive characteristics. The monomorphic hunters showed a moderately flexible predatory behavior characterized by short capture sequences and a noteworthy efficiency of their mandible strike (76.7-100% of prey retrievals), even when presented with Nasutitermes soldiers. Contrary to most poneromorph ants, antennal palpation of the prey before the attack was always missing, no particular targeted region of the prey's body was preferred, and no 'prudent' posture was ever exhibited. Moreover, stinging was regularly performed on bulky, fast moving fruit flies, very scarcely with sclerotized tenebrionid larvae, but never occurred with Nasutitermes workers or soldiers despite their noxious chemical defense. These results suggest that, whatever the risk linked to potentially dangerous prey, O. opaciventris predatory strategy optimizes venom use giving top priority to the swiftness and strength of the lethal trap-jaw system used by hunters as first strike weapon to subdue rapidly a variety of small prey, ranging from 0.3 to 2 times their own body size and from 0.1 to 2 times their weight. Such risk-prone predatory behavior is likely to be related to the large size of O. opaciventris colonies where the death of a forager might be of lesser vital outcome than in small colony-size species.     

Resource Assessment, Recruitment Behavior, and Organization of Cooperative Prey Retrieval in the Ant Formica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussi recruit nestmates to large anthropod prey and cooperatively transport the prey to the nest. The size of the group of ants retrieving prey is significantly correlated with the prey mass at the point at which the retrieval group reaches the nest entrance. To understand the mechanism involved in this size matching process, the regulation of retrieval group size was investigated by examining the modulatory role of trail pheromones in recruitment communication and the behavioral processes that might adjust retrieval group size to prey mass. Laboratory studies of hindgut, poison, and Dufour's gland extracts showed that the contents of the hindgut, which was determined to be the source of trail pheromone, induced recruitment and orientation behavior in ants and regulated the recruitment response of ants in the absence of any other communication signal. However, chemical mass communication alone did not appear to explain the regulation of retrieval group size. Scout ants assess whether to collect prey individually or recruit nestmates to group-retrieve 100-, 200-, or 400-mg prey but did not vary group size in relation to either the prey mass or the presence of interspecific competitors once the decision to initiate group retrieval was made. The number of recruits leaving the nest was independent of these factors and first matched prey mass during prey transport, possibly through a process of differential individual response to immobile versus mobile prey items. Unpredictable factors such as prey resistance to movement and rapidly changing degrees of interspecific competition may preclude scouts from fine-tuning the retrieval group size before it reaches the prey.     

The Effect of Food Size and Dispersion Pattern on Retrieval Rate by the Argentine Ant, Linepithema humile (Hymenoptera: Formicidae)

Food acquisition in central-place foraging animals demands efficient detection and retrieval of resources. Most ant species rely on a mass recruitment foraging strategy, which requires that some potential foragers remain at the nest where they can be recruited to food once resources are found. Because this strategy reduces the number of workers initially looking for food, it may reduce the food detection rate while increasing the postdiscovery food retrieval rate. In previous studies this tradeoff has been analyzed by computer simulation and mathematical models. Both kinds of models show that food acquisition rate is greatly influenced by food distribution and resource patch size: as food is condensed into fewer patches, the maximal acquisition rate is achieved by a shift to fewer initial searchers and more potential recruits. In general, these models show that a mass recruitment strategy is most effective when resources are clumped. We tested this prediction in two experiments by letting laboratory colonies of the Argentine ant (Linepithema humile) forage for resources placed in different distributions. When all prey were small, retrieval rate increased with increasing resource patch size, in support of foraging models. When prey were large, however, the mass of prey returned to the colony over time was much lower than when prey were small and widely distributed. As more ants reached a large prey item, the distance the prey item was transported decreased due to a greater emphasis on feeding rather than transport. Because Argentine ants can transport more biomass externally than they can ingest, food retrieval that depends only on ingestion can depress the biomass retrieval rate. Thus, our results generally support theoretical foraging models, but we show how prey size, through differential prey-handling behavior, can produce an outcome greatly different from that predicted only on the distribution of resources.     

Cooperation in the neotropical pseudoscorpion, <Emphasis Type="Italic">Paratemnoides nidificator</Emphasis> (Balzan, 1888): feeding and dispersal behavior

Social behavior is rare among arachnids, and “permanent-sociality” is a strategy documented only in a few spider species. Here we describe the feeding and dispersal behavior of Paratemnoides nidificator, a Neotropical pseudoscorpion presenting “non-territorial permanent-sociality”. Field and laboratory observations (100 hours and 200 sessions over four years) and manipulative experiments revealed that P. nidificator is a generalist predator that lives in rough bark of trees, in groups of 2 to 175 individuals (42.62 ± 28.27; N=35 colonies; solitary individuals were never found), including reproductive adults and nymphs. Individuals in groups cooperatively capture prey four times larger than solitary individuals. Adult hunters share food with siblings. Reproduction in natural conditions occurs during the hot/wet season, when food availability is high. Prey diversity and abundance seem to be the main factor limiting reproduction in this species. Phoresy (attachment to a transporter animal) is the basic mode of dispersion in P. nidificator. Grouped individuals use large animals as vectors for dispersal, and once established they use the vector as the first food item of the new colony. However, they can also disperse by colony fission, newly documented herein for this taxon. The elaborate, cooperative behavior in P. nidificator is unique among pseudoscorpions and represents an excellent model for studies on the evolution of sociality in invertebrates. Received 10 August 2006; revised 17 November 2006; accepted 23 January 2007.     

Modal analysis of the deep-water solitary scleractinian, <Emphasis Type="Italic">Desmophyllum dianthus</Emphasis>, on SW Pacific seamounts: inferred recruitment periodicity,growth, and mortality rates

Little is known about the demography of corals inhabiting deep-sea features due to the logistical difficulties of working at the extreme depths they inhabit. To obtain basic information about growth, mortality, and recruitment dynamics for such a coral, we applied modal analysis to the size frequency distributions of live-caught and sub-fossil specimens of the widely distributed solitary cup coral, Desmophyllum dianthus, collected on SW Pacific seamounts. Comparison of live-caught material collected in 1997 and 2007–2009 indicated modal progression over time and an implied maximum age of approximately 190 years, which is similar to ages determined previously for D. dianthus using radiometric techniques. A log-linear decline in the number of individuals with increasing size further implies a constant adult mortality rate, of 15.1% per annum in 1997 and 9.2% per annum in 2007–2009. The spacing of size modes in the 2007–2009 samples suggests regularly episodic recruitment events, at 22- to 32-year intervals, which may relate to periodic variability in large-scale Southern Ocean circulation. Preliminary analyses of size frequency distributions of the sub-fossil material suggest that the trophodynamics, growth, and adult mortality schedules of D. dianthus in the SW Pacific have remained basically similar throughout the Holocene.     

Comparison of the Hunting Behavior of Four Piscine Predators Attacking Schooling Prey

Four piscine predator species were observed repeatedly attacking large (> 100,000) schools of flat-iron herring, Harengula thrissina. The predators could be categorized into two groups. Stalking predators (two species) were slow-moving, predominantly solitary hunters attacking from positions beneath the school. Attacks were directed at individual prey and the sequence of events was orient-approach-strike. Although the stalking species were seen most often and were responsible for the majority of the attacks, capture success was low. The remaining two species were fast-moving, pelagic hunters regularly occurring in groups of up to 8 individuals. These predators were extremely proficient at capturing prey, either by orienting on individuals (stragglers) or accelerating into the school and ramming their prey (impact attacks). Group size was positively associated with capture success, but not significantly so. Because stalking predators orient towards individual prey, they may suffer from the effect of confusion when attacking schooling prey. Use of the impact strategy, by comparison, may allow predators to overcome the confusion effect either by attacking prey already separated from the school, or by orienting towards aggregated prey rather than particular individuals.     

Behavioral mechanisms of collective nest-site choice by the ant Temnothorax curvispinosus

This paper examines the individual behavior underlying collective choice among nest sites by the ant Temnothorax (formerly Leptothorax) curvispinosus. Colonies can actively compare options, rejecting a mediocre site when it is paired with a good one, but accepting the same mediocre design if it is instead paired with a worse site. This ability emerges from the behavior of an active minority of workers who organize emigrations. When one of these finds a promising site, she recruits nest mates to it, but only after a delay that varies inversely with site quality. Ants first recruit fellow active ants via slow tandem runs, but eventually switch to speedier transports of the colony’s passive majority. Later transports grow faster still, as ants improve their speed with experience. An ant’s choice of recruitment type is governed by a quorum rule, such that her likelihood of starting to transport increases with the population of the new site. The size of the quorum depends on experience, with ants demanding a larger population to launch immediately into transport than they do to switch to transport after first leading a few tandem runs. Perception of quorum attainment requires direct contact between ants. The ants’ behavior qualitatively matches that of T. albipennis, where models have shown that decentralized choice of the best site depends on quality-dependent recruitment delays, amplified by a quorum rule for initiating transport. Parameter estimates for an agent-based model show significant quantitative differences between the species, and suggest that T. albipennis may place relatively greater emphasis on emigration speed. Received 11 February 2005; revised 10 May 2005; accepted 20 May 2005.     

Subsistence hunting and conservation issues in the game reserve of Gile, Mozambique

Ethnozoological research was conducted to gather information on the hunting activities and their relevance for the subsistence of local people in 8 villages around the game reserve of Gile, Mozambique. Two series of data were gathered by questionnaires to: (a) 510 householders from eight villages located in the outskirts of the Reserve; (b) 10 hunters from the village of Gile, the main centre of the study area. Several hunting techniques were recorded: spears, nets, traps (including gin-traps) and wildfires, while the use of guns did not appear relevant. The importance of subsistence hunting for local people was underlined by the high percentage of respondents who declared that they usually conduct this activity and sell bushmeat. The proportion of hunters per village was related to the village size but not to its geographical location of villages and the household composition. A positive relationship existed between the proportion of hunters, crop production and fishing activities, indicating that hunting is part of an integrated system of subsistence activities. Most animals harvested were mammals (89.5%, of which 46.7% were ungulates) and most were captured within the Reserve (96%). A higher percentage of animals was sold (56%), representing a relevant income source for the villagers. Small animals were mainly captured by traps during solitary hunting, medium-sized animals in collective net hunting; larger prey were captured by gin-traps adopted by both solitary and collective hunting. In the diet of the local people wild animals represented a higher protein source than domestic animals.     

Two historical weapon fragments as an aid to estimating the longevity and movements of bowhead whales

The age of bowhead whales captured by Native Alaskan hunters in the Bering, Chukchi and Beaufort Seas has been estimated via chemical analyses of the eye lenses, and other techniques. The racemization-age estimates indicate that bowhead whales (Balaena mysticetus) have a lifespan of more than a century. Stone and ivory weapon fragments recovered from bowhead whales hunted in Wainwright and Barrow (Alaska) in 1981, 1992, 1993 and 1997, provided rough but independent assessments of the whales’ longevity; however, their date of manufacture was unknown. Adding further confirmation of these age estimates, this note describes bomb lance fragments recovered recently (2007) and about 30 years ago (1980) from bowhead whales harvested by Eskimo hunters that were “dateable” and likely manufactured between 1879 and 1885.     

Polyethism within hunters of the ponerine ant,Ectatomma ruidum Roger (Formicidae,Ponerinae)

Summary During laboratory experiments, two categories of prey-foraging workers were found inEctatomma ruidum: stingers and transporters. When numerous live drosophila were offered to the ants, one group of hunters specialized in killing the prey and another in transporting simultaneously the dead drosophila to the nest. Sometimes, there was a transfer of prey by a stinger towards a transporter, after an active soliciting of the transporter by antennation or by using the forelegs. We found high positive correlations between the colony size and the number of ants in each subcaste. A negative correlation existed between the colony size and the proportion of hunters. However, the proportion of workers in the two behavioral subcastes of hunters was stable in spite of differences in colony size. The phylogenetic interest of this type of cooperative predation is discussed.     

Temporal and ontogenetic variation in the diet of squid (<Emphasis Type="Italic">Loligo forbesii</Emphasis> Streenstrup) in Scottish waters

The squid Loligo forbesii is the only cephalopod species currently targeted by fisheries in the northern NE Atlantic. An active predator, it feeds primarily on fish, crustaceans and cephalopods. During 15 years since the only previous large-scale study of the diet of this species in Scottish waters, there have been substantial changes in marine fish abundances. The present study evaluates sources of variation (temporal, ontogenetic) in diet composition and prey size preferences of L. forbesii, including a comparison of contemporary (July 2006–June 2007) and historical (1990–1992) dietary datasets. Results revealed significant size-related and seasonal variation in diet composition and prey size. Teleost fish of the families Ammodytidae and Gobiidae were eaten by squid of all sampled sizes, although occurrence of gobies was generally more frequent in smaller squids, while Gadidae were eaten more frequently by larger squids. Cannibalism was also more frequent in larger squids. Compared to the 1990–1992 dataset, clupeid fish were less important in the diet of squid in 2006–2007, while the importance of gobies increased, and the size of gobies eaten also increased. The trend in gadoids differed according to the index used: their frequency of occurrence was considerably higher in 2006–2007 than in 1990–1992, but their numerical importance was slightly lower. In general, results provided little evidence that changes in the diet of L. forbesii correspond with changes in fish abundance, at least at the scales at which these are measured.     

Diet of the invasive piscivorous fish <Emphasis Type="Italic">Fistularia commersonii</Emphasis> in a recently colonized area of the eastern Mediterranean

The composition of the diet of the Indo-Pacific cornetfish Fistularia commersonii from the SE Aegean Sea is described. The stomach contents of 245 specimens collected between September 2004 and March 2005 were examined. Dietary comparisons were made reflecting the relationship between diet composition, time of year, and fish size. Correlation between predator length and prey length was significant. The diet of the blue cornetfish consists of 96% by number and 99.95% by weight of fish. Size classification and habitat of prey groups (benthic, supra-benthic, and pelagic) showed that with increased body length the blue cornetfish extended its diet to larger prey and more generalist feeding. Spicara smaris, Boops boops, and Mullidae spp. were the most abundant prey by weight whereas a variety of small benthic fish (especially gobiids) and newly hatched fish constituted the largest number of prey items. Length–weight relationships for the cornetfish were investigated.     

Is Meat Flavor a Factor in Hunters’ Prey Choice Decisions?

By focusing on the caloric composition of hunted prey species, optimal foraging research has shown that hunters usually make economically rational prey choice decisions. However, research by meat scientists suggests that the gustatory appeal of wildlife meats may vary dramatically. In this study, behavioral research indicates that Mayangna and Miskito hunters in Nicaragua inconsistently pursue multiple prey types in the optimal diet set. We use cognitive methods, including unconstrained pile sorts and cultural consensus analysis, to investigate the hypothesis that these partial preferences are influenced by considerations of meat flavor. Native informants exhibit high agreement on the relative appeal of different meats. Given the absence of other noteworthy differences between spider monkeys (Ateles geoffroyi) and howler monkeys (Alouatta palliata), the unappealing flavor of howler monkeys seems to be a factor in the partial preference for this species.     

Conservation by native peoples

Native peoples have often been portrayed as natural conservationists, living a “balanced” existence with nature. It is argued that this perspective is a result of an imprecise operational definition of conservation. Conservation is defined here in contrast to the predictions of foraging theory, which assumes that foragers will behave to maximize their short-term harvesting rate. A behavior is deemed conservation when a short-term cost is paid by the resource harvester in exchange for long-term benefits in the form of sustainable harvests. An example of the usefulness of such an operational definition is presented using data on patch and prey choice decisions of a group of subsistence hunters, the Piro of Amazonian Peru. Results indicate that the area around the Piro village is depleted of prey, and that hunters allocate more time to patches where return rates are highest. This response is consistent with both a conservation strategy and foraging theory. Contrary to the expectation of the conservation strategy, however, hunters do not restrain from pursing opportunistically encountered prey in the depleted areas. The implications for conservation policy are briefly discussed. Michael Alvard received his Ph.D. at the University of New Mexico in 1993 and is currently an assistant professor of anthropology at Dickinson College. His interests include the impact of traditional hunting on prey species and the evolution of conservation. He is currently pursuing research opportunities with the Wana, a group of subsistence hunters living in the rain forests of Sulawesi, Indonesia.     

Age and sex-specific variation in detectability of moose (<Emphasis Type="Italic">Alces alces</Emphasis>) during the hunting season: implications for population monitoring

The sustainability of wild ungulate harvests can be greatly enhanced if monitoring data are available to permit an adaptive management approach. Utilising data provided by hunters is potentially the most cost-effective approach. In Scandinavia, observations recorded by moose (Alces alces) hunters provide a range of indices of population density, composition and reproductive performance. These are routinely used in practical management, but there are still many questions about their accuracy and precision. In this study, we availed of the fact that virtually all individual moose on the island of Vega in central Norway were marked during the period 1992–2005. Thus, we were able to compare the observation indices provided by hunters to the known size and composition of the population. The results indicate that the hunter observation indices provided accurate estimates of variation in moose cow recruitment and twinning rates. The estimates of sex ratio closely followed the pattern of annual variation but showed a consistent pattern of over-estimating the proportion of males. Thus, males seem to visually expose themselves more often for hunters than do females. The density index, measured as number of moose seen per hunter day did not to the same extent follow the variation in population density, possibly because moose were more naive in the first years after hunting was introduced or because of reduced detection conditions due to increasing scrub and tree encroachment during the study period. The results are discussed in light of their application to management and the evolutionary pressures in moose anti-predator behaviour.     

Cooperative food transport in the Neotropical ant, <Emphasis Type="Italic">Pheidole oxyops</Emphasis>

Cooperation in foraging through information sharing is widespread in social insects and has been much studied. In contrast, cooperative transport of food items by groups of workers is less common and has received comparatively little attention. We investigated collective food retrieval in the Neotropical ant Pheidole oxyops, a ground-nesting species in which minor workers (mean body weight 0.6 mg) collectively transport larger dead insects back to the nest entrance. In total, 29% of items and 78% of total mass is transported collectively. We examined the configurations of ants carrying single experimental food items (weight 119 mg, size 10 × 10 × 1 mm) and found it to be non-random, with twice as many carrying ants at the corners as expected. This arrangement is achieved by preferential joining of corners and leaving of sides by carriers. Corner carrying increased carrying speed by up to 29%. Ants also preferentially carried food items from the front and back, versus the middle.     

Mechanisms of selectivity in a nocturnal fish: a lack of active prey choice

Fish that feed on individual zooplankton usually exhibit strong selectivity for large prey. Such selectivity can result from the predator’s active choice of larger prey or from differential encounter rate due to lower detectability of small prey, or both. In diurnal fishes, selectivity is thought to be determined mostly by active choice. In spite of a lack of direct observations, active choice is also considered the prevailing mechanism of prey selectivity in nocturnal fishes. Our objective was to resolve this mechanism in the highly selective, nocturnal zooplanktivorous fish Apogon annularis. Laboratory experiments indicated that the fish’s encounter rate with small prey was lower than that with large prey and that its selectivity became stronger with decreasing light intensity. Feeding efficiency, defined as the ratio between feeding and encounter rates, ranged 41–89% and was positively correlated with prey size. When feeding on a mixture of prey sizes, the fish fed on each size group at a rate similar to that of its feeding on the respective size alone, indicating that selectivity in A. annularis was due to size-dependent encounter rate and differential feeding efficiency. A low visual acuity in A. annularis, as inferred from its inability to detect small prey (<0.9 mm in length), together with the low abundance of large zooplankton in situ, can explain the dominance of differential encounter over active choice in this nocturnal coral-reef fish.     

An unusual case of cooperative hunting in a solitary carnivore

Cooperative hunting has been documented for several group-living carnivores and had been invoked as either the cause or the consequence of sociality. We report the first detailed observation of cooperative hunting for a solitary species, the Malagasy fossa (Cryptoprocta ferox). We observed a 45 min hunt of a 3 kg arboreal primate by three male fossas. The hunters changed roles during the hunt and subsequently shared the prey. We hypothesize that social hunting in fossas could have either evolved to take down recently extinct larger lemur prey, or that it could be a by-product of male sociality that is beneficial for other reasons.     

Scanning pattern of greater rheas,<Emphasis Type="Italic"> Rhea americana</Emphasis>: collective vigilance would increase the probability of detecting a predator

Many models using vigilance to predict the probability of detecting an approaching predator assumes that prey scanning events should be produced at random. Consequently, the length of intervals among successive scans must follow a negative exponential distribution. We analyzed the scanning behavior of the greater rhea, Rhea americana, which is a gregarious, flightless bird, in eastern Argentina. We investigated whether individual and/or collective scanning departed from random and whether this departure varied with group size. We used two simulation models based on observed scanning sequences to assess the effectiveness of vigilance on the individual and collective level when faced with an opportunistic or stalking predator. The analysis of 59 behavioral sequences of wild greater rheas foraging solitary or in groups of two to six or more individuals revealed that the inter-scan length of individual sequences significantly departed from random. In contrast, inter-scan intervals for collective vigilance were shorter than individual ones, but only fit the random expectation for groups of two and five individuals. Models showed that collective vigilance could increase the probability of detecting a predator, thereby reducing their vulnerability, independent of whether the predator uses a stalking or opportunistic approaching strategy.     

Aquatic feeding in a terrestrial turtle: a functional-morphological study of the feeding apparatus in the Indochinese box turtle Cuora galbinifrons (Testudines, Geoemydidae)

The Indochinese box turtle Cuora galbinifrons is regarded as a purely terrestrial species, but our results demonstrate that it can feed both on land and in water. The inverse relationship between the relative development of the hyoid apparatus and the tongue found in the most investigated chelonians is not valid in the Indochinese box turtle. Our morphological analysis of the feeding apparatus reveals that the palate shape and the design of the tongue are consistent with terrestrial feeders, but the construction of the hyoid complex is more characteristic of aquatic feeders. Previous studies have demonstrated that tongue enlargement negatively impacts the capacity of the turtles to suction feed. The present study focuses on the aquatic intraoral prey transport kinematic patterns. Our analysis is based on high-speed films with 250 fr/s and high-speed cineradiography with 50 fr/s. The aquatic intraoral food transport mechanisms differ depending on prey size: small items are transported predominantly by “inertial suction”, whereas larger items are moved by the tongue—normally a clear terrestrial strategy. As the genus Cuora is ancestrally aquatic, the use of lingual food transport in the aquatic environment is presumably an aberrant modus typical only for the most terrestrial among the Asian box turtles.