Colony Foraging Activity Research Articles

Conditional indirect genetic effects of caregivers on brood in the clonal raider ant.

Caregivers shape the rearing environment of their young. Consequently, offspring traits are influenced by the genes of their caregivers via indirect genetic effects (IGEs). However, the extent to which IGEs are modulated by environmental factors, other than the genotype of social partners (i.e., intergenomic epistasis), remains an open question. Here we investigate how brood are influenced by the genotype of their caregivers in the clonal raider ant, Ooceraea biroi, a species in which the genotype, age and number of both caregivers and brood can be experimentally controlled. First, we used four clonal lines to establish colonies that differed only in the genotype of caregivers and measured effects on foraging activity, as well as IGEs on brood phenotypes. In a second experiment, we tested whether these IGEs are conditional on the age and number of caregivers. We found that caregiver genotype affected the feeding and foraging activity of colonies, and influenced the rate of development, survival, body size, and caste fate of brood. Caregiver genotype interacted with other factors to influence the rate of development and survival of brood, demonstrating that IGEs can be conditional. Thus, we provide an empirical example of phenotypes being influenced by IGE-by-environment interactions beyond intergenomic epistasis, highlighting that IGEs of caregivers/parents are alterable by factors other than their brood's/offspring's genotype.

Annual flowers strips benefit bumble bee colony growth and reproduction

Bumble bees are important crop pollinators but are negatively impacted by agricultural intensification and concomitant loss of floral resources. Flower strips can increase the abundance and sometimes the diversity of bumble bees at local scales, but the importance of flower strips for bumble bee populations at larger scales remains poorly understood. We investigated the effect of flower strips on bumble bee colony growth and reproduction at landscape scales. Commercial bumble bee colonies of a native species (Bombus terrestris) were placed and monitored at different distances from flower strips that were sown on existing ecological focus areas (European Common Agricultural Policy) in southern Sweden. Both the average colony growth (weight) and the production of reproductives (drones and queens) were highest for colonies adjacent to flower strips and declined with increasing distance. Colonies close to the flower strip also produced more reproductives per colony weight. Colony foraging activity was negatively related to the distance to flower strips whereas worker size was not affected. Annual flower strips in ecological focus areas benefit bumble bee colonies by increasing foraging success, colony growth and finally boosting sexual reproduction, demonstrating potential benefits for pollination within and between seasons. These effects were spatially limited but extended to foraging ranges of bumble bees. However, effects of increased colony growth on the abundance of foraging bees in the landscape may extend to larger distances because of forager movements within seasons and queen dispersal between seasons, suggesting that voluntary or incentivised collaboration between farmers may be needed to achieve optimal implementation of flower strips.

Nectar source profitability influences individual foraging preferences for pollen and pollen-foraging activity of honeybee colonies

Abstract: Most foraging honeybees specialize in either pollen or nectar collection, although some do alternate between both resources. Little is known about this behavioral plasticity and the factors that control it. We studied how the profitability of nectar sources influences the transition of bees between nectar and pollen collection at the individual response level, by measuring the number of switches when the productivity of a sugar source (either sugar concentration or solution flow rate) was experimentally decreased or increased. At the social level, we studied whether the quality of the nectar that circulates inside a hive alters the rate of incoming pollen foragers. We then calculated the ratio between pollen and non-pollen foragers, before and after the hives were fed either a 3 or a 50% w/w sugar solution. In the first experiment, we showed that bees that persisted in visiting the feeder when offered low-quality solutions were more likely to switch to pollen than those foraging only on highly concentrated solutions. Looking at the collective responses, the ratio of pollen over non-pollen foragers increased after the input of a low-quality sugar solution and decreased after the input of a high-quality sugar solution. We conclude that the profitability of nectar sources interacts with the sugar responsiveness of bees, thus driving foraging preferences for pollen and modifying the pollen foraging activity of the colony. The results also show that bees integrate gustatory information from both rewarding resources based on local cues available either at the foraging site or inside the hive. Significance statement: Switching between resource types could be adaptive for honeybees that specialize in either nectar or pollen foraging. This would allow them to react to changes in the foraging environment. Although we observed that switching behavior is constrained by the responsiveness of bees to sugar, the switch from nectar to pollen (and vice versa) is an active decision of the bees in response to the decreasing or increasing profitability of pollen versus nectar sources. Given the ability of some bees to switch between foraging tasks based solely on gustatory cues available at the foraging site, we investigated whether source-related information conveyed inside the hive also affects colony foraging activity towards nectar and pollen resources. We observed that behavioral plasticity of individuals can be integrated into a social response by colonies reallocating their foraging forces according to the food-related information available inside the hive. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

The Role of Dopamine in the Collective Regulation of Foraging in Harvester Ants

SummaryColonies of the red harvester ant (Pogonomyrmex barbatus) differ in how they regulate collective foraging activity in response to changes in humidity. We used transcriptomic, physiological, and pharmacological experiments to investigate the molecular basis of this ecologically important variation in collective behavior among colonies. RNA sequencing of forager brain tissue showed an association between colony foraging activity and differential expression of transcripts related to biogenic amine and neurohormonal metabolism and signaling. In field experiments, pharmacological increases in forager brain dopamine titer caused significant increases in foraging activity. Colonies that were naturally most sensitive to humidity were significantly more responsive to the stimulatory effect of exogenous dopamine. In addition, forager brain tissue significantly varied among colonies in biogenic amine content. Neurophysiological variation among colonies associated with individual forager sensitivity to humidity may reflect the heritable molecular variation on which natural selection acts to shape the collective regulation of foraging.

Busier bees: increasing nest traffic in commercial bumblebee colonies

Commercially-reared bumblebee colonies contribute to the pollination of crops globally. If the efficiency of commercial colonies at providing pollination services could be increased, it would have implications for agricultural outputs. Commercial colonies are sold with an internal nectar reservoir on which bees can forage from within the nest. Nectar stores in naturally-produced nectar pots of colonies can affect forager recruitment and activity outside the nest. Thus, it is possible that artificial nectar reservoirs could impact the foraging activity of colonies. To investigate this, commercial Bombus terrestris audax colonies were placed in a university parkland campus. Colonies were split into three treatment groups: those with (1) access to an unaltered nectar reservoir; (2) access to a diluted reservoir; and (3) no reservoir access. Foraging observations were made for all colonies over a 19-day period. The mass of each colony was measured and demographic data were collected. Colonies with diluted reservoirs had 131% and 39% more bees entering and leaving than colonies with no reservoir access and unaltered reservoirs respectively. Both treatments with access to a nectar reservoir gained more mass, had a higher proportion of pollen foraging bees, and had more workers, males, larvae and pupae, than colonies with no access to a reservoir. These results demonstrate that manipulating the availability and concentration of internal nectar reservoirs of commercial B. terrestris colonies significantly affects the number of bees entering and leaving the colony. Dilution of the nectar reservoir could be a strategy for increasing the pollination services commercial colonies provide to crops. Further research in commercial crops is required before such a strategy could be implemented on farms.

Sexual castes of Trachymyrmex fuscus (Formicidae: Attini) performing worker tasks

ABSTRACT: The main of this research was to report an atypical foraging behavior in a colony of Trachymyrmex fuscus, situated in "Cerrado" (savanna ecoregion of Goiás, Brazil). The colony foraging activity was performed only by sexual caste. Comparison of the foraging rhythm of this colony with another of the same specie where foraging was performed only by worker caste, showed that working time hours were very similar. After observations on the foraging behavior, both colonies were excavated in order to characterize them (nest size, population composition and estimating of the symbiotic fungus volume). Besides the foraging activity performed only by sexual females, other important observations were highlighted in that colony: low number of workers, presence of worker larvae and pupae (45 and 43 respectively) and apparently normal growth of the symbiotic fungus. Our hypothesis is that sexual females were in charge of the entire colony maintenance. This could be a strategy of colony survival when the worker caste is reduced.

Harvester ants use interactions to regulate forager activation and availability

Social groups balance flexibility and robustness in their collective response to environmental changes using feedback between behavioural processes that operate at different timescales. Here we examine how behavioural processes operating at two timescales regulate the foraging activity of colonies of the harvester ant, Pogonomyrmex barbatus, allowing them to balance their response to food availability and predation. Previous work showed that the rate at which foragers return to the nest with food influences the rate at which foragers leave the nest. To investigate how interactions inside the nest link the rates of returning and outgoing foragers, we observed outgoing foragers inside the nest in field colonies using a novel observation method. We found that the interaction rate experienced by outgoing foragers inside the nest corresponded to forager return rate, and that the interactions of outgoing foragers were spatially clustered. Activation of a forager occurred on the timescale of seconds: a forager left the nest 3-8 s after a substantial increase in interactions with returning foragers. The availability of outgoing foragers to become activated was adjusted on the timescale of minutes: when forager return was interrupted for more than 4-5 min, available foragers waiting near the nest entrance went deeper into the nest. Thus, forager activation and forager availability both increased with the rate at which foragers returned to the nest. This process was checked by negative feedback between forager activation and forager availability. Regulation of foraging activation on the timescale of seconds provides flexibility in response to fluctuations in food abundance, whereas regulation of forager availability on the timescale of minutes provides robustness in response to sustained disturbance such as predation.

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.

Hydrocarbons emitted by waggle-dancing honey bees stimulate colony foraging activity by causing experienced foragers to exploit known food sources

Two hypotheses concerning the function of the hydrocarbons emitted by waggle-dancing bees are investigated in this study. First, we test the hypothesis that the waggle-dance compounds stimulate foraging behavior. In support of this hypothesis, the number of bee departures from a hive increased as much as 46% and the number of forager visits to a feeder station increased as much as 106% when the dance compounds were introduced into the hive. Second, we test the hypothesis that the waggle-dance compounds stimulate foraging by causing experienced foragers to depart the hive to exploit known food sources. In support of this hypothesis, individually marked foragers visited an empty feeder station both more often and in greater numbers following exposure to the waggle-dance compounds than following exposure to a control substance. The results of these experiments suggest that the waggle-dance compounds function as a foraging semiochemical, operating in synergy with the waggle dance itself.

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.

Mating for variety increases foraging activity in the harvester ant, Pogonomyrmex occidentalis

Multiple mating by females characterizes most insect species, but is relatively uncommon in social insects. Females may mate with multiple mates because they experience the direct benefits of increased survival or fecundity, to acquire high quality mates, or to lower the risk of reduced fecundity by mating with incompatible males. We used the extensive natural variation in mating frequency in the western harvester ant, Pogonomyrmex occidentalis, to test the hypothesis that increased mating by the queen leads to an increase in colony performance. Colonies with greater genetic diversity began to forage earlier in the day and foraged for longer time periods. The workers which initiated foraging were a nonrandom subset of the genotypes present in the colony. We used a statistical approach to correctly predict the direction and magnitude of the correlation between genetic diversity and colony foraging activity.

A scientific note on the directional accuracy of the waggle dance over the course of a day

Honey bees communicate information about distance and direction to a food source with a waggle dance (von Frisch, 1993). During the waggle phase see (Tautz et al., 1996), a bee walks forward an angle with respect to vertical while waggling her abdomen. This angle matches, on average, the angle between food source and sun azimuth. For a given food location, there is variation both within dances of the same bee and between different bees. Lindauer (1961) reported that when the sun is at the zenith (which only occurs in the tropics), dancing either ceases or is disoriented 10 minutes before and after solar noon. No directional information can be communicated when the sun is directly overhead. In temperate regions, colony foraging activity declines around noon, a phenomenon von Frisch (1993) called “noontime laziness”. He argued that this effect could not be explained in terms of food profitability, and attributed it to a diurnal periodicity in activity, although this was not directly tested. An alternative explanation of noontime laziness links these two phenomena: perhaps foragers experience greater difficulty orienting their dances when the sun is higher in the sky, and are less inclined to dance, which in turn reduces foraging activity. This study tests one component of this hypothesis: the effect of the sun’s position on the accuracy of the information within the dance. Three unrelated colonies, A, B, and C, were housed in observation hives (see Seeley, 1995, Chap. 4). Colonies were housed at two locations (A

Information flow and regulation of foraging activity in bumble bees (Bombus spp.)

Communication in the context of foraging in bumble bees has received less attention than in other social bees. Yet, recent studies have revealed that information flow mediates colony foraging activity. The species studied do not recruit to specific locations, but bees can learn the scent of food sources at the nest, which may reduce their search time. Location communication may not confer high benefits to bumble bees. But bees react to nectar influx with increased foraging activity, with high quality food eliciting more activity. This shows that bees recognize and sample freshly collected nectar. If the colony has no demand for food, foraging activity does not increase. Successful foragers distribute a tergal gland pheromone in the nest that also elicits higher foraging activity. Information exchange in the nest thus enables bumble bees to base their decision to forage on demand and the presence and profitability of food. Bombus terrestris / recruitment / social insect / collective foraging / communication

A scientific note on food alert in Bombus transversalis

Bumble bees (Bombini), stingless bees (Meliponini) and honey bees (Apini), the three major groups of eusocial bees, have very different systems of organizing colony foraging activity, sometimes involving sophisticated mechanisms of recruitment. Honey bees, as the most well known example, perform “waggle dances”, highly stereotyped motor patterns, which contain information about coordinates and properties of newly discovered food sources (von Frisch, 1967). In the stingless bees (Meliponini), mechanisms and information content of communication about food sources vary among species from mere alerting systems (no communication of location, only of presence of food sources) to, at the other extreme, communication about location and distance of a food source via scent marks and acoustic signals (Lindauer and Kerr, 1960; Nieh, 1998). In bumble bees, an alerting system which involves communicating presence and odor, but not location of food sources, was found in Bombus terrestris L. (Dornhaus and Chittka, 1999, 2001). However, before concluding that this alerting system is a plesiomorphic character retained in the bumble bees and not solely an invention of B. terrestris, its presence in other bumble bees should be demonstrated. This is what we report here. We examined recruitment behavior of the Amazonian bumble bee, Bombus transversalis (Olivier). This is one of the few bumble bee species adapted to living in the wet tropics (Cameron et al., 1999, Taylor and Cameron, in press). As B. transversalis is in the subgenus Fervidobombus, it is only distantly related to B. terrestris (Williams, 1994). If the same alerting effect can be found in B. transversalis as in B. terrestris, that would suggest that an alerting mechanism could be broadly distributed across bumble bees. 2. EXPERIMENTS

Simulation of Topographic and Daily Variation in Colony Activity ofPogonomyrmex occidentalis(Hymenoptera: Formicidae) Using a Soil Temperature Model

The relationships between soil temperature and foraging activity of ground-dwelling ants have been widely studied, but variation in activity among ant colonies has hindered the integration of foraging activity across time and space. We developed time-integrated simulations of colony foraging activity by linking estimates of the temperature–activity responses of ant colonies to a soil temperature model. In the field, we measured the relationship between soil surface temperature and foraging activity by 29 colonies of the western harvester ant, Pogonomyrmex occidentalis Cresson, located at 3 topographic positions within a shortgrass steppe ecosystem. The temperature–activity relationships estimated by logistic regression were then coupled with a soil temperature model to predict the number of foraging hours per day during June and July 1996. Soil temperature was a significant predictor of colony foraging probability, whereas topographic position affected overall foraging probability or shifted peak activity to higher or lower temperatures. These temperature-activity relationships resulted in greater simulated foraging times for colonies on slopes than on uplands during June, but upland colonies had greater foraging times during July. Simulated foraging times for ant colonies on uplands also were the least sensitive to changes in soil temperature because of variation in vegetation cover, air temperature, and solar radiation. We suggest that greater densities of ant colonies on uplands are partly because of a favorable microclimate for P. occidentalis in addition to soil characteristics, nest maintenance, or proximity to mating sites.

Factors influencing seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

This study investigated the effects of colony growth and development, food storage, foraging activity and weather on the migration behavior of African honey bees in the Okavango River Delta, Botswana. Four observation colonies were studied during the honey bee migration season (November–May), at which time the availability of blooming species was reduced. Two of the colonies (colonies 1 & 2) migrated during the study period, while the remaining two (colonies 3 & 4) did not. During the 4–6 weeks preceding the onset of migration preparations, colonies 1 & 2 exhibited increasing population sizes, high levels of brood production with low brood mortality, relatively large stores of food, and increasing mass. In contrast, the populations of colonies 3 & 4 did not increase, brood-rearing activity was erratic and lower, brood mortality was higher, food stores became depleted and colony mass declined. Both colonies 3 & 4 ceased rearing brood, and colony 3 died of starvation. Colony foraging activity was examined by monitoring waggle-dance activity 2–3 days each week. For 4–6 weeks before the onset of migration in colonies 1 & 2, daily foraging areas and mean daily foraging distances became increasingly large and variable. Colonies 3 & 4 exhibited foraging patterns similar to those observed for colonies 1 & 2 preceding migration. There was no clear association between 7 weather parameters examined and migration behavior. These data suggest that migration is influenced by an interaction of intra-colony demographics, food reserves and foraging patterns. Migration may be feasible only for those colonies that possess (1) a population of appropriate size and age structure to compensate for the natural attrition of older workers during the emigration process, and (2) sufficient food reserves for long-distance travel and the establishment of a new nest. Changing foraging patterns may reflect a deteriorating foraging environment, which may trigger the onset of migration preparations, provided that colony demographics and food reserves are conducive. Colonies that show decreased brood production, higher brood mortality and reduced food stores may be incapable of migrating, even when experiencing deteriorating foraging conditions. Rather, such colonies may have a greater chance of survival if they attempt to persist in a given area.

Effects of stress, age, season, and source colony on levels of octopamine, dopamine and serotonin in the honey bee ( Apis mellifera L.) brain

The effects of environmental and genetic factors on levels of octopamine, dopamine and serotonin in brains from worker honey bees ( Apis mellifera L.) were measured using high-performance liquid chromatography with electrochemical detection. Exiting foragers were stressed by clamping their legs, which resulted in peak elevation of octopamine and serotonin after 10 min. Significant seasonal differences in levels of all three biogenic amines were found for bees sampled from an observation colony during the spring, summer and autumn of 1990. Levels of the amines were highest during June–September, corresponding to high levels of colony foraging activity. These differences may reflect seasonal changes in colony nutrition, population size, or brood-rearing activity. The levels of all three amines were significantly lower in the brains of newly emerged bees than in brains from randomly aged worker bees from the same colony. Since the total protein content in bee brains was not different for bees from these two groups, age-related differences were not related to brain growth. Significantly different levels of octopamine, dopamine and serotonin were detected among workers in colonies that contained unrelated queens.

Microclimatic factors influencing foraging patterns and success of the thermophilic desert ant,Ocymyrmex barbiger

Ocymyrmex barbiger is a diurnal scavenger of arthropods in which the number of successful foraging excursions per colony per day increases with daily vapour pressure deficit. It appears that the ants make use of prey items which succumb to thermal and desiccation stress. Running speed is a function of surface temperature but progressively less time is spent searching for prey beyond a critical surface temperature with the result that the optimal search temperature for individual foragers is about 52°C. Maximal foraging activity of colonies occurs at surface temperatures corresponding to this optimal search temperature.

Nectar selection by Melipona and Apis mellifera (Hymenoptera: Apidae) and the ecology of nectar intake by bee colonies in a tropical forest.

Colony foraging activity of four Melipona species (Apidae: Meliponinae, tribe Meliponini) was studied during the dry season, when many plants flower in central Panama. The efficiency of sucrose solution uptake by Melipona was compared to that of domesticated European Apis mellifera. Dynamics of nectar foraging were also recorded for 3 of the Melipona visiting the forest shrub, Hybanthus prunifolius (Violaceae). 1. Sugar concentration in nectar brought to nests averaged from 21 to 60% sugar for 15 colonies of M. fasciata, M. compressipes triplaridis, M. fuliginosa and M. marginata micheneri. Concentrations ranged from 19 to 72%, and all species collected nectars ranging at least between 24 and 63% sugar. However, M. compressipes and M. marginata preferred higher concentrations and foraged less on dilute nectars. Peak colony nectar harvest occured in late morning or early afternoon; peak pollen harvest was in early morning. 2. Imbibing rates of bees given 20, 30, 45, 60 or 70% sucrose solutions were highest at ≦45% sucrose, but caloric intake was most rapid at 60% sucrose for all species. All but M. marginata displayed greater net intake rates than domesticated European Apis mellifera. A foraging choice model incorporating caloric reward and imbibing rates of bees suggests M. compressipes and M. marginata should specialize on richer nectars. Rate of caloric intake per forager weight was higher for all Melipona (0.03-0.13g) than for A. mellifera (0.10 g). 3. The nectar of Hybanthus prunifolius (Violaceae), a shrub pollinated exclusively by Melipona, progressed from 35 to 60% sugar during the day. Bees foraged most when nectar was below 60% concentration, a pattern best explained as the result of intercolony competition and greater availability of lower quality nectar. 4. Sugar concentration in nectar harvested by colonies rose from lower to higher values through the day for Melipona. The increasing caloric reward of nectar is adaptive in exploiting foraging preferences of such bees. As standing nectar crop is depleted by competing bees, a gradual shift to more rewarding nectar should promote increased bee foraging range, more flower visits during a foraging trip, floral constancy, and genetic outcrossing. 5. The nectar load capacity of A. mellifera is greater than that of Melipona. Other factors being equal, Africanized A. mellifera, now a permanent resident of neotropical forests, should visit more flowers during a foraging trip. Additional species differences in foraging behavior are analyzed.

Foraging and spatiotemporal territories in the honey ant Myrmecocystus mimicus wheeler (Hymenoptera: Formicidae)

The honey ant Myrmecocystus mimicus is a scavenger, forages extensively on termites, collects floral nectar, and tends homoptera. Individual foragers of M. mimicus usually disperse in all directions when leaving the nest, but there are also groups of foragers that tend to swarm out of the nest primarily in one direction. Such massive departues are usually at irregular intervals, which may last several hours. The results of field and laboratory experiments suggest that these swarms of foragers are organized by a group recruitment process, during which recruiting scout ants lay chemical orientation trails with hindgut contents and simultaneously stimulate nestmates with a motor display and secretions from the poison gland. Usually these columns travel considerable distances (4–48 m) away from the nest, frequently interfering with the foraging activity of conspecific neighboring colonies. To prevent a neighboring colony from access to temporal food sources or to defend spatiotemporal borders, opposing colonies engage in elaborate display tournaments. Although hundreds of ants are often involved during these tournaments almost no physical fights occur. Instead, individual ants confront each other in highly sterotyped aggressive displays, during which they walk on stilt legs while raising the gaster and head. Some of the ants even seem to inflate their gasters so that the tergites are raised and the whole gaster appears to be larger. In addition, ants involved in tournament activities are on average larger than foragers. The dynamics of the tournament interactions were observed in several colonies over several weeks-mapping each day the locations of the tournaments, the major directions of worker routes away from the nest, and recording the general foraging activities of the colonies. The results indicate that a kind of dominance order can occur among neighboring colonies. On the other hand, often no aggressive interactions among neighboring colonies can be observed, even though the colonies are actively foraging. In those cases the masses of foragers of each colony depart in one major direction that does not bring them into conflict with the masses of foragers of a neighboring colony. This stability, however, can be disturbed by offering a new rich food source to be exploited by two neighboring colonies. This invariably leads to tournament interactions. When a colony is considerably stronger than the other, i.e., with a much larger worker force, the tournaments end quickly and the weaker colony is raided. The foreign workers invade the nest, the queen of the resident colony is killed or dirven off, while the larvae, pupae, callow workers, and honey pot workers are carried or dragged to the nest of the raiders. From these and other observations we conclude that young M. mimicus queens are unlikely to succeed in founding a colony within approximately 3 m of a mature M. mimicus colony because they are discovered and killed, or driven off by workers of the resident colony. Within approximately 3–15 m queens are more likely to start colonies, but these incipient groups run a high risk of being raided and exterminated by the mature colony. Although populations of M. mimicus and M. depilis tend to replace each other, there are areas where both species overlap marginally. Foraging areas and foraging habitats of both species also overlap broadly, but we never observed tournament interactions between M. mimicus and M. depilis. The adaptive significance of the spatiotemporal territories in M. mimicus is discussed.