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1.
Several glandular sources of trail pheromones have been discovered in army ants in general. Nevertheless, at present the understanding of the highly coordinated behavior of these ants is far from complete. The importance of trail pheromone communication for the coordination of raids and emigrations in the ponerine army ant Leptogenys distinguenda was examined, and its ecological function is discussed. The secretions of at least two glands organize the swarming activities of L. distinguenda. The pygidial gland is the source of an orientation pheromone holding the group of raiding workers together. The same pheromone guides emigrations to new nest sites. In addition, the poison sac contains two further components: one with a weak orientation effect and another which produces strong, but short-term attraction and excitement. The latter component is important in prey recruitment and characterizes raid trails. This highly volatile recruitment pheromone allows the extreme swarm dynamic characteristic of this species. Emigration trails lack the poison gland secretion. Due to their different chemical compositions, the ants are thus able to distinguish between raid and emigration trails. Nest emigration is not induced chemically, but mechanically, by the jerking movements of stimulating workers.  相似文献   

2.
A typical colony of Neotropical army ants (subfamily Ecitoninae) regularly raids a large area around their bivouac by forming a narrow directional column that can reach up to one hundred meters in length. The raid is finished and then relaunched 12–17 times, each time toward different orientation. After completing all bouts the colony relocates to a new area. A hypothetical alternative to this foraging mode is raiding radially and symmetrically by expanding the search front in every direction like a circular bubble. Using an existing agent-based modeling software that simulates army ants’ behavior, we compared the two possible modes of foraging in different food distributions. Regardless of the food patch abundance, the radial raiding was superior to the directional raiding when food patches had low quality, and the directional raiding was favorable when the patches were rich. In terms of energy efficiency, the radial raiding was the better strategy in a wide range of conditions. In contrast, the directional raiding tended to yield more food per coverage area. Based on our model, we suggest that the directional raiding by army ants is an adaptation to the habitats with abundance of high-quality food patches. This conclusion fits well with the ecology of army ants.  相似文献   

3.
Slave-making ants are social parasites that exploit the labor of workers from their host species by keeping them captive in the slave-maker nest. Slave-makers vary in their degree of specialization, ranging from obligate slave-makers that cannot survive without captives, to facultative slave-makers, which are often found living independently. Our study system included one obligate slave-maker, Polyergus breviceps, two facultative slave-makers, Formica puberula and F. gynocrates, and two hosts, F. occulta and F. sp. cf. argentea. We observed all raids conducted during two raiding seasons by seven P. breviceps colonies, two F. puberula colonies, and two F. gynocrates colonies. We report on raiding frequency, average raid distances, and then compare the probability of being raided multiple times in a single raiding season for the two host species. We also report on the spatial distribution of slave raids, which suggests that slave-makers avoid raiding in areas used by other slave-maker colonies. This is the first report of raiding activity for P. breviceps in this location, and the first report of raiding activity of any kind for F. puberula and F. gynocrates.  相似文献   

4.
J. Zee  D. Holway 《Insectes Sociaux》2006,53(2):161-167
Invasive ants often displace native ants, and published studies that focus on these interactions usually emphasize interspecific competition for food resources as a key mechanism responsible for the demise of native ants. Although less well documented, nest raiding by invasive ants may also contribute to the extirpation of native ants. In coastal southern California, for example, invasive Argentine ants (Linepithema humile) commonly raid colonies of the harvester ant, Pogonomyrmex subnitidus. On a seasonal basis the frequency and intensity of raids vary, but raids occur only when abiotic conditions are suitable for both species. In the short term these organized attacks cause harvester ants to cease foraging and to plug their nest entrances. In unstaged, one-on-one interactions between P. subnitidus and L. humile workers, Argentine ants behaved aggressively in over two thirds of all pair-wise interactions, despite the much larger size of P. subnitidus. The short-term introduction of experimental Argentine ant colonies outside of P. subnitidus nest entrances stimulated behaviors similar to those observed in raids: P. subnitidus decreased its foraging activity and increased the number of nest entrance workers (many of which labored to plug their nest entrances). Raids are not likely to be the result of competition for food. As expected, P. subnitidus foraged primarily on plant material (85% of food items obtained from returning foragers), but also collected some dead insects (7% of food items). In buffet-style choice tests in which we offered Argentine ants food items obtained from P. subnitidus, L. humile only showed interest in dead insects. In other feeding trials L. humile consistently moved harvester ant brood into their nests (where they were presumably consumed) but showed little interest in freshly dead workers. The raiding behavior described here obscures the distinction between interspecific competition and predation, and may well play an important role in the displacement of native ants, especially those that are ecologically dissimilar to L. humile with respect to diet. Received 15 July 2005; revised 19 October 2005; accepted 26 October 2005.  相似文献   

5.
We present field experiments and analyses that test both the assumptions and the predictions of a model that showed how the swarm raids of the army ant Eciton burchellimight be self-organizing, i.e., based on hundreds of thousands of interactions among the foraging workers rather than a central administration or hierarchical control. We use circular mill experiments to show that the running velocity of the ants is a sigmoidal function of the strength of their trail pheromones and provide evidence that the swarm raid is structured by the interaction between outbound and inbound forager traffic mediated by the pheromones produced by both of these sets of ants. Inbound traffic is also affected by the distribution of prey, and hence, sites of prey capture alter the geometry of the raid. By manipulating the prey distributions for E. burchelliswarms, we have made them raid in a form more typical of other army ant species. Such self-organization of raids based on an interaction between the ants and their environment has profound consequences for interpretations of the evolution of army ant species.  相似文献   

6.
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.  相似文献   

7.
Most of what we know about the moving behaviour of the nomadic army ant Eciton burchellii comes from Barro Colorado Island (BCI) in Panama. Nomadic colonies raid roughly in straight line during the day and relocate their nests along this path in the evening. At BCI, nomadic colonies raid roughly in the same compass bearing of the previous day, presumably using their pheromone-marked raiding trails as cues to pick directions. Deviations from this direction occur when a nomadic colony fails to move, possibly due to environmental conditions. The generality of these results has been questioned. We studied nomadic colonies of E. burchellii at La Selva Biological Station, Costa Rica to evaluate the generality of the results obtained from BCI. We measured the angle between consecutive raids, manipulated the distribution of previous day’s raid pheromones around nests to evaluate the effect of raid pheromone on foraging direction, and evaluated the effect of rainfall on the probability of moving and on deviation from the previous day’s raid. Colonies did not follow the same compass bearing of the previous day and formed new raids on areas with previous day’s raid pheromones or without them. Rainfall can explain when nomadic colonies move, but did not explain deviation from the previous day’s raid direction. Our results suggest that caution should be taken when generalizing the insightful results obtained from the BCI population.  相似文献   

8.
New World army ants (Ecitoninae) are nomadic group-predators that are widely thought to have a substantial impact on their prey. Nevertheless, quantitative data on prey intake by army ants is scarce and mostly limited to chance encounters. Here, I quantify the prey intake of the army ant Eciton hamatum at the contrasting scales of raid, colony (sum of simultaneous raids), and population. Like most army ants, E. hamatum conducts narrow ‘column raids’ and has a specialized diet of ant prey. I show that individual raids often had periods of no prey intake, and raid intake rates, calculated in g/min, differed significantly among colonies. Moreover, neither mean nor peak raid intake rates were correlated with colony size. Similarly, colony intake rates differed significantly among colonies, and mean colony intake rates were not correlated with colony size. However, mean colony intake rates were significantly higher than mean raid intake rates, and peak colony intake rate was correlated with colony size. Having multiple raids thus improves colony-level intake rates, and larger colonies can harvest more prey per unit time. Mean colony intake rate across colonies was 0.067 g/min dry weight and mean daily colony intake was calculated at 38.2 g. This intake is comparable to that of Eciton burchellii, which has a more generalized diet and conducts spectacular ‘swarm raids’ that are seen as having a greater impact on prey than column raids. Population size on Barro Colorado Island, Panama, was estimated to be 57 colonies, which extrapolates to a daily population intake of nearly 2 kg of prey dry weight, or 120 g/km2. Broadly, these findings demonstrate that column raiding army ants experience considerable variation in prey intake for individual raids, but can still achieve notable impact at the larger scales of colony and population. Furthermore, they challenge the idea that swarm-raiding species necessarily have greater intake and thus impact on prey. Instead, I suggest that conducting multiple column raids may be a strategy that allows for comparable intake from a more specialized diet.  相似文献   

9.
In this paper we report the results of a detailed study on the behavioural ecology of slave raiding in the European amazon ant, Polyergus rufescens Latr. The field study, supported also by a video-tape recording technique, was conducted over an unbroken period of 53 days, during which observations of the activity of the residents (both slave-makers and slaves) were made for 10 h each day. It was possible to observe 38 slave raids distributed over 32 days, among which 27 were followed by the sack of 10 different nests of Formica cunicularia Latr., whereas 11 failed because of various reasons. Simple, compound and multiple raids occurred. We recorded the timing, frequency, distance, and direction of slave raids, including the number of participants and the type of captured brood. Moreover, particular attention was paid to the atmospheric conditions present at the moment of the raid onset. Information was also collected about the behaviour of the “activators” and the scouts before and during the movement of the storming column. Both dealate and winged P. rufescens queens, having emerged from the mixed colony during 6 sexual flights, were seen following the outbound raiding column during 4 raids. Finally, some peculiar behaviour, such as digging out the soil near the target nest to facilitate the entry of the raiding swarm, and the pillage of adult ants (eudulosis) was recorded and described. Data have been compared with what is known about the other species of the genus Polyergus.  相似文献   

10.
Summary: Field and laboratory observations demonstrate that Leptogenys distinguenda is characterized by typical army ant behavior. Like in the "classical" army ants from the subfamilies Ecitoninae, Dorylinae and Aenictinae, raiding and emigration behavior are closely linked. The direction of raids can be altered in field experiments to a wide extent by offering ample food, suggesting it is highly influenced by the patchiness of prey. The sum of recruitments coming from one direction and the recruitment overrun are primarily responsible for the spatial development and the extension of raids. Emigration frequency can be suppressed by overfeeding a colony in the field. This result is interpreted as a secondary effect of reduced swarming activity, which gets suppressed as well in the same experiment. The discovery of a suitable nest site is considered the proximate stimulus for emigration, and the best explored areas are those that have been most thoroughly raided. As a result, emigrations are likely to lead into areas with high prey densities.  相似文献   

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