Which portion of the natural panorama is used for view-based navigation in the Australian desert ant?

Ants that forage in visually rich environments often develop idiosyncratic routes between their nest and a profitable foraging ground. Such route knowledge is underpinned by an ability to use visual landmarks for guidance and place recognition. Here we ask which portions of natural visual scenes are essential for visually guided navigation in the Australian desert ant Melophorus bagoti whose foragers navigate through a habitat containing grass tussocks, shrubs and trees. We captured M. bagoti foragers after they had returned to their nest from a feeder, but before they had entered their nest, and tested their ability to home accurately from a series of release locations. We used this simple release paradigm to investigate visually guided navigation by monitoring the accuracy of nestwards orientation when parts of the ants’ visual field were obscured. Results show that the lower portion of the visual panorama is more important for visually guided homing than upper portions. Analysis of panoramic images captured from the release and nest locations support the hypothesis that the important visual information is provided by the panoramic contour, where terrestrial objects contrast against sky, rather than by a limited number of salient landmarks such as tall trees.     

Traveling in clutter: Navigation in the Central Australian desert ant Melophorus bagoti

The Central Australian desert ant Melophorus bagoti is the most thermophilic ant on the continent. It comes out to forage during the hottest part of the day in the summer months. The ant shares a cluttered, plant-filled habitat with other arthropods and uses a range of navigational strategies. We review recent studies on this species concerning its use of habitual routes, distant landmarks, landmarks around the nest, and path integration, which is keeping track of the distance and direction traveled from one's starting point. Functional predictions concerning the acquisition, retention, and integration of memories of distances and of landmarks are also reviewed, illuminating the behavioral ecology of spatial cognition.     

The role of competition by dominants and temperature in the foraging of subordinate species in Mediterranean ant communities

In this paper we test the influence of temperature and interference competition by dominant species on the foraging of subordinate species in Mediterranean ant communities. We have analyzed the changes in resource use by subordinate species in plots with different abundances of dominant ants, and in different periods of the day and the year, i.e., at different temperatures. The expected effects of competition by dominant species on foraging of subordinates were only detected for two species in the number of baits occupied per day, and for one species in the number of foragers at pitfall traps. In all three cases, subordinate species were less represented at baits or in traps in plots with a high density of dominants than in plots with a medium or low density of dominants. The number of workers per bait, and the foraging efficiency of subordinate species did not differ in plots differing in dominant abundance. Daily activity rhythms and curves of temperature versus foraging activity of subordinate species were also similar in plots with different abundance of dominant species, indicating no effect of dominants on the foraging times of subordinates. Instead, temperature had a considerable effect on the foraging of subordinate species. A significant relationship was found between maximum daily temperature and several variables related to foraging (the number of foragers at pitfall traps, the number of baits occupied per day, and the number of workers per bait) of a number subordinate species, both in summer and autumn. These results suggest that the foraging of subordinate ant species in open Mediterranean habitats is influenced more by temperature than by competition of dominants, although an effect of dominants on subordinates has been shown in a few cases. In ant communities living in these severe and variable environments, thermal tolerance reduces the importance of competition, and the mutual exclusion usually found between dominant and subordinate species appears to be the result of physiological specialization to different temperature ranges. Received: 8 May 1998 / Accepted: 30 July 1998     

The Regulation of Ant Colony Foraging Activity without Spatial Information

Many dynamical networks, such as the ones that produce the collective behavior of social insects, operate without any central control, instead arising from local interactions among individuals. A well-studied example is the formation of recruitment trails in ant colonies, but many ant species do not use pheromone trails. We present a model of the regulation of foraging by harvester ant (Pogonomyrmex barbatus) colonies. This species forages for scattered seeds that one ant can retrieve on its own, so there is no need for spatial information such as pheromone trails that lead ants to specific locations. Previous work shows that colony foraging activity, the rate at which ants go out to search individually for seeds, is regulated in response to current food availability throughout the colony's foraging area. Ants use the rate of brief antennal contacts inside the nest between foragers returning with food and outgoing foragers available to leave the nest on the next foraging trip. Here we present a feedback-based algorithm that captures the main features of data from field experiments in which the rate of returning foragers was manipulated. The algorithm draws on our finding that the distribution of intervals between successive ants returning to the nest is a Poisson process. We fitted the parameter that estimates the effect of each returning forager on the rate at which outgoing foragers leave the nest. We found that correlations between observed rates of returning foragers and simulated rates of outgoing foragers, using our model, were similar to those in the data. Our simple stochastic model shows how the regulation of ant colony foraging can operate without spatial information, describing a process at the level of individual ants that predicts the overall foraging activity of the colony.     

Foraging strategy quick response to temperature of Messor barbarus (Hymenoptera: Formicidae) in Mediterranean environments

Animals principally forage to try to maximize energy intake per unit of feeding time, developing different foraging strategies. Temperature effects on foraging have been observed in diverse ant species; these effects are limited to the duration of foraging or the number of foragers involved. The harvester ant Messor barbarus L. 1767 has a specialized foraging strategy that consists in the formation of worker trails. Because of the high permeability of their body integument, we presume that the length, shape, and type of foraging trails of M. barbarus must be affected by temperature conditions. From mid-June to mid-August 1999, we tested the effect on these trail characteristics in a Mediterranean forest. We found that thermal stress force ants to use a foraging pattern based on the variation of the workers trail structure. Ants exploit earlier well-known sources using long physical trails, but as temperatures increases throughout the morning, foragers reduce the length of the foraging column gradually, looking for alternative food sources in nonphysical trails. This study shows that animal forage can be highly adaptable and versatile in environments with high daily variations.     

华南地区桑园和荒地两种生境中红火蚁觅食工蚁的食物组成

【目的】红火蚁Solenopsis invicta Buren是世界最危险的有害入侵生物之一,2004年入侵我国华南地区,并给农林业安全、生态安全带来极大危害。调查并明确田间红火蚁觅食工蚁的食物种类及数量,不仅为评估红火蚁猎食对生态环境中节肢动物群落的影响,而且为红火蚁防治饵剂的改进提供科学依据。【方法】本研究采用蚁道剖析法,对华南地区桑园和荒地两种生境中红火蚁觅食工蚁搬运的固体残片取样和鉴定;依搬运工蚁及其固体残片尺寸进行测量分级并称重,以分析工蚁多态性与固体食物大小的关系;采用薄层色谱法和氨基酸分析法测定嗉囊液体样品的营养成分及含量。【结果】在华南地区桑园和荒地中,红火蚁觅食工蚁搬运回巢的固体食物包括固体的动物残片和植物种子,其中动物残片属于3门7纲21个类群(包括14个昆虫目),昆虫纲动物所占比例为总固体食物的45.53%~46.10%。工蚁偏好搬运长1.400±0.043 mm~2.306±0.063 mm和宽0.723±0.028 mm~1.261±0.051 mm的固体残片,其重量在0.203~0.413 mg之间。红火蚁觅食工蚁嗉囊液体由多种氨基酸、果糖和葡萄糖组成,在桑园和荒地采集到的红火蚁嗉囊液体样本中的氨基酸总含量分别为1 544.31 mg/L和861.48 mg/L,氨基酸种类分别为33种和32种,其中31种氨基酸为共有的。【结论】华南地区桑园和荒地中,红火蚁固体食物组成均以昆虫纲动物为主;参与固体残片搬运觅食蚁的80%属于中型工蚁,搬运较大型固体残片的大型工蚁仅占5%;红火蚁工蚁嗉囊液体含有丰富的氨基酸和单糖。     

Colony variation in the collective regulation of foraging by harvester ants

This study investigates variation in collective behavior in a natural population of colonies of the harvester ant, Pogonomyrmex barbatus. Harvester ant colonies regulate foraging activity to adjust to current food availability; the rate at which inactive foragers leave the nest on the next trip depends on the rate at which successful foragers return with food. This study investigates differences among colonies in foraging activity and how these differences are associated with variation among colonies in the regulation of foraging. Colonies differ in the baseline rate at which patrollers leave the nest, without stimulation from returning ants. This baseline rate predicts a colony's foraging activity, suggesting there is a colony-specific activity level that influences how quickly any ant leaves the nest. When a colony's foraging activity is high, the colony is more likely to regulate foraging. Moreover, colonies differ in the propensity to adjust the rate of outgoing foragers to the rate of forager return. Naturally occurring variation in the regulation of foraging may lead to variation in colony survival and reproductive success.     

Search strategies of ants in landmark-rich habitats

Search is an important tool in an ant’s navigational toolbox to relocate food sources and find the inconspicuous nest entrance. In habitats where landmark information is sparse, homing ants travel their entire home vector before searching systematically with ever increasing loops. Search strategies have not been previously investigated in ants that inhabit landmark-rich habitats where they typically establish stereotypical routes. Here we examine the search strategy in one such ant, Melophorus bagoti, by confining their foraging in one-dimensional channels to determine if their search pattern changes with experience, location of distant cues and altered distance on the homebound journey. Irrespective of conditions, we found ants exhibit a progressive search that drifted towards the fictive nest and beyond. Segments moving away from the start of the homeward journey were longer than segments heading back towards the start. The right tail distribution of segment lengths was well fitted by a power function, but slopes less than −3 on a log-log plot indicate that the process cannot be characterized as Lévy searches that have optimal slopes near –2. A double exponential function fits the distribution of segment lengths better, supporting another theoretically optimal search pattern, the composite Brownian walk.     

The short-term regulation of foraging in harvester ants

In the seed-eating ant Pogonomyrmex barbatus, the return ofsuccessful foragers stimulates inactive foragers to leave thenest. The rate at which successful foragers return to the nestdepends on food availability; the more food available, the morequickly foragers will find it and bring it back. Field experimentsexamined how quickly a colony can adjust to a decline in therate of forager return, and thus to a decline in food availability,by slowing down foraging activity. In response to a brief, 3-to 5-min reduction in the forager return rate, foraging activityusually decreased within 2–3 min and then recovered within5 min. This indicates that whether an inactive forager leavesthe nest on its next trip depends on its very recent experienceof the rate of forager return. On some days, colonies respondedmore to a change in forager return rate. The rapid colony responseto fluctuations in forager return rate, enabling colonies toact as risk-averse foragers, may arise from the limited intervalover which an ant can track its encounters with returning foragers.     

Intra- and interspecific dominance hierarchies and variation in foraging tactics of two species of stream-dwelling chars

Aggressive interactions, foraging behavior, habitat use and diet were studied in sympatric populations of white-sported char,Salvelinus leucomaenis, and Dolly Varden,Salvelinus malma, in a Japanese mountain stream. Underwater observations on individuals of both species revealed two distinct behavioral regimes: aggressive drift foragers and non-aggressive benthos foragers. Aggressive drift foragers defended partial territories around focal points from which they made forays to capture invertebrates drifting in the water column. Non-aggressive benthos foragers cruised around and beneath cobble in large foraging ranges that overlapped each other. Intra- and interspecific, size-dependent dominance hierarchies were recognized among aggressive drift foragers, whereas non-aggressive benthos foragers showed no such relationships. Terrestrial invertebrates were the most abundant prey in the diets of drift foragers, whereas a very small proportion of the diet of benthos foragers was made up of these taxa. Benthos foragers showed more complex diet composition than drift foragers. These results suggest that non-aggressive benthos foragers may avoid not only interference but also exploitative competition by using alternative foraging tactics. The proportion of drift foragers to benthos foragers among white-spotted char was more than 35 times that among Dolly Varden. The significant difference in the proportion of each species using the two types of foraging strategy results in interspecific food segregation in sympatric populations.     

Spatial organization in ants’ nests: does starvation modify the aggregative behaviour of Lasius niger species?

Ant colonies that undergo long starvation periods have to tune their exploratory and foraging responses to face their food needs. Although the number of foragers is known to increase with food deprivation in the ant Lasius niger, such enhanced food exploitation is not related to a more intense recruitment by successful scouts. We thus suggest that the colony’s response to a food shortage could result from changes at the level of the ant recruits, in particular from changes in their spatial organization inside the nest. Since aggregation plays a key role in the social organization of ants, we assume that the colony’s response to starvation could be due to changes in the aggregative behaviour of L. niger nestmates.We thus compared the aggregation dynamics of inner-nest workers and foragers having undergone either a short or a long-lasting starvation period. Whatever the ethological group (foragers or inner-nest workers), there was no significant influence of starvation on the aggregation dynamics nor on any feature of the observed clusters. This result shows that an increased foraging response to food shortage cannot be explained by changes in the tendency of nestmates to aggregate within the nest. Finally, we discuss other behavioural mechanisms, in particular changes in behavioural thresholds that could underlie the adaptive changes seen in colony foraging after long starvation periods. Received 25 June 2007; revised 21 January 2008; accepted 24 January 2008.     

Influence of environmental and colony factors on the initial commodity choice of foragers of the stingless bee Plebeia tobagoensis (Hymenoptera, Meliponini)

Novice foragers of social bees have to decide what food commodity to collect when they start foraging for the first time. In this decision making process two types of factors are involved: internal factors (the response threshold) and external factors (environmental and colony conditions). In this study we will focus on the importance of two external factors, pollen storage level and information from experienced foragers about food availability in the field, on the initial commodity choice of foragers of the stingless bee species Plebeia tobagoensis. We also studied the effect of the initial choice of individuals on their subsequent foraging career. This study was performed in a closed greenhouse compartment, where food availability and colony condition could be controlled. Information on food availability in the field from experienced foragers and pollen storage level both greatly influenced the initial commodity choice of individuals, with more choices for the commodity communicated by experienced foragers or lacking in storage. The initial choice of foragers is of importance for their future foraging career, although a substantial proportion of foragers did switch between food commodities. Because of the ability of novice foragers to become flexibly distributed over foraging tasks, social bees are able to react to changes in their environment without directly having to decrease foraging effort devoted to other foraging tasks. This, in combination with individual flexibility during foraging careers makes it possible for colonies of P. tobagoensis to forage efficiently in an ever-changing environment. Received 7 November 2005; revised 12 January 2006; accepted 16 February 2006.     

Phorid parasitoids affect foraging activity of Solenopsis richteri under different availability of food in Argentina

1. In Argentina, six species of Pseudacteon parasitoids (Phoridae) attack Solenopsis richteri, one of the two species of South American fire ant that are exotic pests in North America. 2. The presence of these Pseudacteon species significantly reduces the number of ants at food resources in the field, as well as foraging activity generally. 3. Some Pseudacteon not only attack ants walking on trails or at feeding sites, but also at mound entrances, inhibiting workers from leaving to forage. 4. The average size of foraging ants (which prescribes their suitability as hosts) decreased in the presence of phorids. 5. The number of attacking phorids was correlated positively with the number of ants walking towards the food on the trail before the attack. 6. Solenopsis richteri workers responded to manipulations of food size and presence or absence of parasitoids in a risk-adjusting way, i.e. although more foragers were recruited to larger food items, attacking phorids reduced ant foraging activity by the same factor regardless of the size of the food offered. 7. The data suggest that S. richteri colonies juggle the needs to harvest food efficiently, reduce competition, and avoid excess risks from parasitoids in complex ways.     

Foraging decisions of individual workers vary with colony size in the greenhead ant Rhytidoponera metallica (Formicidae, Ectatomminae)

Summary. The ability of worker ants to adapt their behaviour depending on the social environment of the colony is imperative for colony growth and survival. In this study we use the greenhead ant Rhytidoponera metallica to test for a relationship between colony size and foraging behaviour. We controlled for possible confounding ontogenetic and age effects by splitting large colonies into small and large colony fragments. Large and small colonies differed in worker number but not worker relatedness or worker/brood ratios. Differences in foraging activity were tested in the context of single foraging cycles with and without the opportunity to retrieve food. We found that workers from large colonies foraged for longer distances and spent more time outside the nest than foragers from small colonies. However, foragers from large and small colonies retrieved the first prey item they contacted, irrespective of prey size. Our results show that in R. metallica, foraging decisions made outside the nest by individual workers are related to the size of their colony.Received 23 March 2004; revised 3 June 2004; accepted 4 June 2004.     

Dispersed central-place foraging in the polydomous odorous house ant, Tapinoma sessile as revealed by a protein marker

The odorous house ant, Tapinoma sessile, is a native ant species common throughout North America. In urban areas, this ant is classified a pest species and exhibits several attributes characteristic of invasive “tramp” ants (sensu Passera, 1994). These include: extreme polygyny, colony reproduction by budding, reduced internest aggression, generalist diet, and polydomy. Here we explore the organization of foraging and the pathways of food distribution in polydomous colonies of T. sessile in the laboratory and field using a novel marking technique (rabbit IgG protein) and enzyme linked immunosorbent assay (ELISA). Laboratory assays revealed patterns of food allocation from foragers to other castes and developmental stages. Foragers distributed the IgG- labelled sucrose to the majority of workers within 24 h, and workers retained significantly more sucrose than either queens or larvae. Approximately 50% of queens tested positive for the IgG marker and some queens received significantly more sucrose than others, indicating a possible reproductive dominance hierarchy. Larvae received little sucrose demonstrating their minor reliance on carbohydrates. The results of field experiments showed that odorous house ants are dispersed central-place foragers whereby ants from individual nests exhibit high foraging site fidelity, travel along well-established trails, and forage on a local scale. Dispersed central-place foraging most likely allows the odorous house ant to more efficiently secure both clumped and dispersed food sources and possibly increases its competitive ability. As a result, colonies become numerically large and ecologically dominant. The results of our study contribute to our understanding of the social behavior and colony organization in T. sessile. In addition, they provide a framework for designing more effective ant control programs based on liquid baits. Received 13 December 2005; revised 28 February 2006; accepted 3 March 2006.     

Context-dependent navigation in a collectively foraging species of ant, Messor cephalotes

More than 100 years of scientific research has provided evidence for sophisticated navigational mechanisms in social insects. One key role for navigation in ants is the orientation of workers between food sources and the nest. The focus of recent work has been restricted to navigation in individually foraging ant species, yet many species do not forage entirely independently, instead relying on collectively maintained information such as persistent trail networks and/or pheromones. Harvester ants use such networks, but additionally, foragers often search individually for food either side of trails. In the absence of a trail, these ‘off-trail’ foragers must navigate independently to relocate the trail and return to the nest. To investigate the strategies used by ants on and off the main trails, we conducted field experiments with a harvester ant species, Messor cephalotes, by transferring on-trail and off-trail foragers to an experimental arena. We employed custom-built software to track and analyse ant trajectories in the arena and to quantitatively compare behaviour. Our results indicate that foragers navigate using different cues depending on whether they are travelling on or off the main trails. We argue that navigation in collectively foraging ants deserves more attention due to the potential for behavioural flexibility arising from the relative complexity of journeys between food and the nest.     

Mortality risk versus food quality trade-offs in ants: patch use over time

Abstract.

• 1 Foragers of the ant species Lasius pallitarsis (Provancher) and Myrmica incompleta Provancher were given access to two food patches that differed in nutritive quality. In about half of the trials, the higher quality patch also had a mortality risk for the foragers in the form of a large Formica subnuda Emery ant located along the trail. Colonies were given access to the food for 4 or 24 h, every second day.
• 2 Use of the higher quality patch by L.pallitarsis foragers was depressed by the mortality risk. In contrast to the predictions of a food stress hypothesis, foragers used the risky patch more in the longer access trials. This appears due to a decline in the activity level of the F.subnuda, which results in a significantly lower mortality risk per trip.
• 3 M.incompfeta also significantly decreased their use of the higher quality patch when a F.subnuda was present. However, the length of time a colony had access to the patches had no effect on the use of the risky patch. M.incompleta foraging behaviour seems relatively insensitive to short-term food stress or changing levels of mortality risk.
• 4 The differences between species in their exploitation of patches and reactions to F.subnuda are discussed in terms of the species’natural history.

     

Forager abundance and its relationship with colony activity level in three species of South American Pogonomyrmex harvester ants

The proportion of foragers in ant colonies is a fairly constant species-specific characteristic that could be determined by intrinsic or extrinsic factors. If intrinsic factors are relevant, species with similar life history characteristics (e.g., colony size and foraging strategies) would be expected to have a similar proportion of foragers in their colonies. Within the genus Pogonomyrmex, North American species can vary largely in their colony size, whereas only species with small colonies are known in South America. We studied the characteristics of the foraging subcaste in three sympatric South American species of Pogonomyrmex harvester ants, and compared it with the available information on other species of the same genus. We used two mark-recapture methods and colony excavations to estimate the number and proportion of foragers in the colonies of P. mendozanus, P. inermis, and P. rastratus, and to test the relationship between forager external activity levels and abundance per colony. Forager abundance in the three studied species was lower than in most North American species. The percentage of foragers in their colonies ranged 7–15 %, more similar to North American species with large colonies than to those with small colony size. Foraging activity was positively correlated with forager abundance in all three species, implying that colony allocation to number of foragers allows for higher food acquisition. Further comparative studies involving a wider range of traits in South and North American species would allow to unveil the role of environmental factors in shaping each species’ particular traits.     

Desert ants (Melophorus bagoti) navigating with robustness to distortions of the natural panorama

Many insects are known to use the terrestrial visual panorama for navigation. Research suggests that large-scale panoramic properties are often used for orientation rather than individual objects, usually called landmarks. We degraded the natural panorama encountered by Australian red honey ants, Melophorus bagoti, to test how robust their orientation based on the terrestrial panorama is. Foraging ants were lured to a feeder at a constant location. Trained ants were allowed to run home individually with food, but were captured just before they entered their nest. The tested ant was brought back to the location of the feeder, now covered, and allowed to run home again under different distortions of the natural panorama. In one experiment, a large tract of the view on one side of the feeder was obstructed by a tall plastic sheet. In a second experiment, the visual heights of terrestrial objects were altered by raising or lowering the ant by 80 cm. Under both kinds of distortions, the ants continued to be well oriented in the homeward direction. Navigation based on the natural terrestrial panorama proved robust to large distortions.     

The regulation of foraging activity in red harvester ant colonies

Behavioral plasticity in social insects is intriguing because colonies adjust to environmental change through the aggregated responses of individuals. Without central control, colonies adjust numbers of workers allocated to various tasks. Individual decisions are based on local information from the environment and other workers. This study examines how colonies of the seed-eating ant Pogonomyrmex barbatus adjust the intensity of foraging in an arid environment where conspecific neighbors compete for foraging area. The main question is how foragers decide whether to leave the nest. Patrollers search the area before foragers emerge. Removal experiments show that the return of the patrollers stimulates the onset of foraging, and later, the rate at which foragers return affects the rate at which foragers continue to leave the nest. Foraging activity is less sensitive to changes in the rate of returning foragers than to changes in the rate of returning patrollers. These results suggest that whether a colony forages at all on a given day depends on conditions detected early by patrollers but that once foraging begins, the intensity of foraging does not track, on an hourly timescale, how quickly foragers can find food.