Frequent nest relocation in the ant Aphaenogaster araneoides: resources, competition, and natural enemies

Sessile and vagile organisms differ from one another in some fundamental ways, including methods of resource acquisition and competition. Ant colonies are typically studied as sessile entities, even though a large fraction of ant species frequently relocate their nests in the course of their life history. Little is known about the causes and consequences of nest relocation, but it is likely that the costs and benefits of relocation are driven by nest quality, neighborhood competition, or resource availability. In this paper, we document several cycles of nest relocation in a population of the Central American ant Aphaenogaster araneoides . In our first experiment, we tracked the pattern of relocation, testing whether environmental characteristics and colony demography were associated with relocation behavior. In our second experiment, we manipulated resource availability by adding or subtracting leaf litter, which is known to predict colony growth. We found that colonies relocated their nests once per week on average and colonies often reoccupied nests from which they had once emigrated. Larger colonies relocated more frequently than smaller colonies, and quickly growing colonies utilized a greater number of nests within their home range compared to slowly growing colonies. Relocation events were most likely to occur in periods when vapor pressure deficits were greatest. Nearest neighbor distance and other measures of environmental conditions were not associated with relocation behavior and there was no significant effect of litter removal or supplementation. We found evidence that multiple natural enemies attacked A. araneoides colonies. Based on the demographic correlates of relocation and our rejection of other plausible hypotheses, we propose that nest relocation is driven by the escape from natural enemies.     

Intraspecific Thievery in the Ant Ectatomma ruidum is Mediated by Food Availability

Animals modify their foraging strategies in response to environmental changes that affect foraging performance. In some species, cleptobiosis represents an alternative strategy for resource access. The environmental factors that favor the incidence or prevalence of cleptobiosis, however, are poorly described. The cleptobiotic Neotropical ant Ectatomma ruidum is characterized by a high frequency of thievery behavior, a specific type of intraspecific cleptobiosis, in which specialized thief workers insinuate themselves into nests of neighboring colonies and intercept food items brought into these nests. Here, we evaluate how colonies adjust thievery behavior in response to food availability. We supplemented food availability and measured how the incidence and intensity of thievery responded to resource availability. We found that the incidence and intensity of thievery decline in response to supplemental food, suggesting that thievery behavior is a response to resource limitation at the population scale. This finding indicates that the phenomenon of intraspecific thievery, although a rare strategy in among colonies of social animals, is a viable alternative foraging tactic in the context of competition and food limitation.     

Colony structure and spatial distribution of food resources in the polydomous meat ant <Emphasis Type="Italic">Iridomyrmex purpureus</Emphasis>

Polydomous social insects may reduce the costs of foraging by the strategic distribution of nests throughout their territory or home-range. This efficiency may most likely be achieved if the resources are relatively stable in place and time, and the colonies and nests are distributed in response to the location of the resources. However, no study has investigated how the distribution of food sources influences the spatial patterns of nests within polydomous colonies under natural conditions. Our two year study of 140 colonies of the Australian ant Iridomyrmex purpureus revealed that the decentralization of nests within colonies is associated with the distribution of trees containing honey-dew producing hemiptera. We show there is a positive correlation between the maximum distance between trees containing hemiptera and the maximum distance between nests within a colony. In addition, we demonstrate the mechanism by which this pattern may arise; new nests are built nearer to trees containing hemiptera than existing nests. Further, the distance between trees containing hemiptera and the nearest nests was negatively correlated with the length of exploitation of that tree. Finally, we show that most food is delivered to the nearest nest after which other ants redistribute it between the nests. Combined, these data suggest that foraging efficiency may be an important selection pressure favouring polydomy in I. purpureus. Received 6 April 2006; revised 29 September; accepted 4 October 2006.     

Field study on the foraging characteristics of a ponerine ant,Hagensia havilandi Forel

Summary A field study of the foraging strategy used by the ponerine ant,Hagensia havilandi is reported. They have permanent nests in the leaf litter of coastal forests.H. havilandi is a diurnal forager and collects a variety of live and dead arthropods. These predatory ants exhibit individual foraging with no cooperation in the search for or retrieval of food items. Three colonies were observed and showed similar temporal and spatial foraging patterns. The paths of individual ants were followed and the results showed that the foragers exhibit area fidelity, and return to the nest via a direct route on finding on prey item. Several foragers did not return to the nest at dusk but returned the following morning. Occasionally a limited amount of tandem recruitment was displayed.     

Colony size does not predict foraging distance in the ant Temnothorax rugatulus: a puzzle for standard scaling models

Body size is often positively correlated with ecologically relevant traits such as fecundity, survival, resource requirements, and home range size. Ant colonies, in some respects, behave like organisms, and their colony size is thought to be a significant predictor of many behavioral and ecological traits similar to body size in unitary organisms. In this study, we test the relationship between colony size and field foraging distance in the ant species Temnothorax rugatulus. These ants forage in the leaf litter presumably for small arthropod prey. We found colonies did not differ significantly in their foraging distances, and colony size is not a significant predictor of foraging distance. This suggests that large colonies may not exhaust local resources or that foraging trips are not optimized for minimal distance, and thus that food may not be the limiting resource in this species. This study shows T. rugatulus are behaving in ways that differ from existing models of scaling.     

Nest demographics and foraging behavior of <Emphasis Type="Italic">Apterostigma collare</Emphasis> Emery (Hymenoptera,Formicidae) provide evidence of colony independence

Apterostigma collare Emery is a highly derived fungus-growing ant within the Tribe Attini whose small, fungal nests are found in tropical rain forests. This study focuses on determining the colony structure of A. collare, specifically searching for evidence of polydomy or independence. We surveyed and observed nests in the field, and performed foraging bioassays and dissected nests in the laboratory. We determined the size and contents of nests in field populations. Nests found near other nests were not statistically different in size compared to nests found alone. There was also no statistical difference between near and lone nests regarding the presence of a queen in the nest. Most nests contained one queen with brood and workers, regardless of their proximity to other nests. Observations also were made of foraging and trail-marking behaviors. Foraging activity observed in the field revealed that workers left the nest area and followed trails upwards into the canopy, but they did not interact with foragers from other nearby nests. In a laboratory foraging arena, foragers marked a trail to a food source by dragging the gaster. Bioassays showed that A. collare workers preferred their own foraging trails, but not those of other conspecific colonies. All results suggest that each nest represents an independent colony, supporting a previous report that nests found in close proximity do not constitute a polydomous colony. Received 19 July 2006; revised 23 March 2007; accepted 6 June 2007.     

The Role of Non-Foraging Nests in Polydomous Wood Ant Colonies

A colony of red wood ants can inhabit more than one spatially separated nest, in a strategy called polydomy. Some nests within these polydomous colonies have no foraging trails to aphid colonies in the canopy. In this study we identify and investigate the possible roles of non-foraging nests in polydomous colonies of the wood ant Formica lugubris. To investigate the role of non-foraging nests we: (i) monitored colonies for three years; (ii) observed the resources being transported between non-foraging nests and the rest of the colony; (iii) measured the amount of extra-nest activity around non-foraging and foraging nests. We used these datasets to investigate the extent to which non-foraging nests within polydomous colonies are acting as: part of the colony expansion process; hunting and scavenging specialists; brood-development specialists; seasonal foragers; or a selfish strategy exploiting the foraging effort of the rest of the colony. We found that, rather than having a specialised role, non-foraging nests are part of the process of colony expansion. Polydomous colonies expand by founding new nests in the area surrounding the existing nests. Nests founded near food begin foraging and become part of the colony; other nests are not founded near food sources and do not initially forage. Some of these non-foraging nests eventually begin foraging; others do not and are abandoned. This is a method of colony growth not available to colonies inhabiting a single nest, and may be an important advantage of the polydomous nesting strategy, allowing the colony to expand into profitable areas.     

Mechanisms of dispersed central-place foraging in polydomous colonies of the Argentine ant

Many species of ants occupy multiple nests, a condition known as polydomy. Because of their decentralized structure, polydomous colonies may be removed from some of the constraints associated with classic central-place foraging. We used laboratory and field experiments to assess the mechanisms involved in dispersed central-place foraging in polydomous colonies of the Argentine ant Linepithema humile, a widespread invasive species. Both in the laboratory and in the field, Argentine ants established new nests at sites located near food. Laboratory colonies of L. humile redistributed workers, brood and resources among nests in response to the spatial heterogeneity of food resources. In addition, laboratory colonies formed recruitment trails between nests in the context of foraging, providing a mechanism for the transport of material between nests. This highly flexible system of allocating nests, workers and brood throughout a colony's foraging area potentially increases foraging efficiency and competitive ability. The importance of polydomy as a determinant of competitive ability is underscored by its prevalence among ecologically dominant ants, including most, if not all, highly invasive species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Foraging preferences of ants on a heterogeneous Brazilian sandy shore habitat

1. Ants may select their food in response to nutritional needs of the colony and forage in a way that optimises a complementary nutrition. Even though resource availability is known to affect ant colony and individual health, there is still no study that has investigated the plastic preferences of ants according to spatial resource availability in naturally heterogeneous conditions. 2. Beaches are great biomes to test spatial foraging preference because a complete absence of nectaries can be found. Dorymyrmex nigra Pergande 1896 was found inhabiting a beach in southeastern Brazil, in which nectar sources are heterogeneously distributed. This study tested whether the foraging preference to sugar baits depended on the availability of nectar sources surrounding the nests. 3. We found that more D. nigra workers foraged on sugar baits when the colonies lacked naturally occurring nectar in their vicinity compared with colonies with abundant nectar nearby. 4. These results show that the foraging preference of ants depends upon resource availability. This is the first study to use a natural mosaic of resource availability to show that resource preference of ants is plastic and varies spatially.     

Determinants of reproductive success in voles: space use in relation to food and litter size manipulation

Spacing behaviour of female mammals is suggested to depend on the distribution and abundance of food. In addition, food limitation has been found to constrain the reproductive success of females. However, whether females maximize their reproductive success by adjusting space use in relation to current food availability and reproductive effort (e.g. litter size) has not been experimentally studied. We examined these questions by manipulating simultaneously food resources (control vs. food supplementation) and litter sizes (control vs. plus two pups) of territorial female bank voles (Clethrionomys glareolus) in large outdoor enclosures. Females with supplementary food had smaller home ranges (foraging area) and home range overlaps than control females, whereas litter size manipulation had no effect on space use. In contrast, the size of territory (exclusive area) was not affected by food supplementation or litter size manipulation. As we have previously shown elsewhere, extra food increases the reproductive success of bank vole females in terms of size and proportion of weaned offspring. According to the present data, greater overlap of female home ranges had a negative effect on reproductive success of females, particularly on survival of offspring. We conclude that higher food availability increases the reproductive success of bank vole females, and this effect may be mediated through lower vulnerability of offspring to direct killing and/or detrimental effects from other females in the population. Moreover, it seems that when density of conspecifics is controlled for, home range sizes of females, but not territoriality, is related to food resources in Clethrionomys voles.     

Scratching beneath the surface: Bandicoot bioturbation contributes to ecosystem processes

Animals that forage for food or dig burrows by biopedturbation can alter the biotic and abiotic characteristics of their habitat. The digging activities of such ecosystem engineers, although small at a local scale, may be important for broader scale landscape processes by influencing soil and litter properties, trapping organic matter and seeds, and subsequently altering seedling recruitment. We examined environmental characteristics (soil moisture content, hydrophobicity and litter composition) of foraging pits created by the southern brown bandicoot (Isoodon obesulus; Peramelidae), a digging Australian marsupial, over a 6‐month period. Fresh diggings typically contained a higher moisture content and lower hydrophobicity than undisturbed soil. A month later, foraging pits contained greater amounts of fine litter and lower amounts of coarse litter than adjacent undug surfaces, indicating that foraging pits may provide a conducive microhabitat for litter decomposition, potentially reducing litter loads and enhancing nutrient decomposition. We tested whether diggings might affect seedling recruitment (seed removal by seed harvesters and seed germination rates) by artificially mimicking diggings. Although there were no differences in the removal of seeds, seedling recruitment for three native plant species (Acacia saligna, Kennedia prostrata and Eucalyptus gomphocephala) was higher in plots containing artificial diggings compared with undug sites. The digging actions of bandicoots influenced soil moisture and hydrophobicity, the size distribution of litter and seedling recruitment at a local scale. The majority of Australian digging mammals are threatened, with many suffering substantial population and range contraction. However, their persistence in landscapes plays an important role in maintaining the health and function of ecosystems.     

Effect of harvester ants of the genus Pogonomyrmex on the soil seed bank around their nests in the central Monte desert,Argentina

1. The abundance and composition of soil seed banks is a key determinant of plant community structure. Harvester ants can remove huge quantities of preferred seeds close to the nest affecting composition and spatial distribution of plants. 2. In the central Monte desert (Argentina) ants of the genus Pogonomyrmex have high seed removal rates, especially of the five main grasses. The aim of this study was to establish if their foraging activity affects spatial patterns of the soil seed bank around their nests. Our hypotheses were: (1) removal by ants decreases seed abundance of preferred species in the soil; and (2) the effect varies in time. 3. Soil seed abundance was assessed at different distances from Pogonomyrmex nests in the litter and in bare soil at the beginning, the middle, and the end of the season (late spring‐early autumn). 4. A lower seed abundance of preferred species was observed close to the nest in the litter at the end of the season. Non‐preferred species showed no distance gradient. 5. The lower foraging activity and seed consumption at the beginning of the season could explain the temporal variation of the spatial effect. This was only observed in the litter, probably because of the higher removal frequency in this substrate. 6. Colonies of Pogonomyrmex spp. could enhance the heterogeneity of soil seed banks in the central Monte desert from the summer to the beginning of the autumn. Implications for vegetation dynamics depend on the degree to which seed density limits perennial grasses recruitment after ant activity season.     

Group hunting in a ponerine ant,Leptogenys nitida Smith

Field observations on the emigration and foraging behaviours of the southern African ponerine ant, Leptogenys nitida, were undertaken at Mtunzini, Natal, South Africa. These colonies have a single ergatoid queen and 200–1000 workers. The nest sites are found in the leaf litter and these nests are moved frequently over distances ranging from 0.5 to 5 m. Leptogenys nitida is a diurnal predator of arthropods dwelling in the leaf litter. Up to 500 workers participate in each foraging trail, and are not led by definite scouts. Ants form clear trunk trails and fan out at various intervals to search for prey. The prey is searched for and retrieved cooperatively. From laboratory tests it was determined that ants will follow pygidial gland extracts, with the poison gland extract eliciting a limited response. The type of army ant behaviour observed in L. nitida seems to be different to that observed in other ponerine ants.     

Ecology of spiders inhabiting abandoned mammal burrows in South African savanna

Summary We marked the sites chosen by 338 foundress queens of two desert ant species (Veromessor pergandei and Myrmecocystus flaviceps) and monitored changes in the spacing of both species and the foraging activity at V. pergandei young nests. Although the long established colonies of both species tend intraspecifically toward regular dispersion, queens of both species were intraspecifically clumped. After 3 months, when the first workers emerged, the young colonies (reduced to a total of 42 colonies) were randomly spaced intraspecifically. We also followed the spatial patter of queens with respect to established colonies of both species. Queens founded nests away from the nests of all established colonies on the site. After three months, the young colonies were dispersed away from conspecifics only. During June through August 1986, we censused the number of foragers at the surviving V. pergandei nests. Young colonies that were more active also tended to be far from established conspecifics in July and August. There was no correlation of forating activity with distance to heterospecific established colonies in any month. These results indicate that established conspecifics may reduce the survivorship of young ant colonies.     

Ants distinguish neighbors from strangers

Summary Ants are known to distinguish their own nests and nestmates from all others, using colony-specific odors. Here I show that harvester ants (Pogonomyrmex barbatus) can further distinguish between two kinds of non-nestmates of the same species: neighbors and strangers. Interactions between colonies were thought to depend on the numbers of alien ants that each colony encounters on its territory. The results described here show that such interactions also depend on information about colony identity. Encounters on foraging trails with ants from neighboring colonies, deter foraging more than encounters with ants from distant ones. The history of interactions between particular pairs of colonies may have important effects on intraspecific competition for food.     

Apparent Dear-enemy Phenomenon and Environment-based Recognition Cues in the Ant Leptothorax nylanderi

Inter- and intraspecific competition was investigated in ants of the myrmicine genus leptothorax in a deciduous woodland near Würzburg, Germany. The most common species, A. (Myrafant) nylanderi, lives in rotting pine, oak, and elder sticks and may locally reach densities of 10 nests per m². In the studied sites, only a small fraction of colonies were polydomous, i.e. single colonies typically did not inhabit several nest sites. The home ranges of nylanderi colonies overlap the ranges of other conspecific colonies and colonies of other species, especially L. (s.str.) gredleri. Foragers from different colonies encountering one another in the field back off without exhibiting strong aggression, suggesting that colonies do not defend absolute foraging territories. In laboratory experiments, the frequency and severity of agonistic interactions among workers from different colonies, all living in pine sticks, increased significantly with the distance between their nests. Workers from colonies nesting in different types of wood exhibited significantly more aggression. Experiments in which we transferred colonies from pine sticks into artificial pine or oak nests corroborate the hypothesis that nesting material strongly influences colony odour in L. nylanderi. The evolutionary significance of this apparent dear-enemy phenomenon is discussed.     

Colony foraging allocation is finely tuned to food distance and sweetness even close to a bee colony

Social bee colonies can allocate their foraging resources over a large spatial scale, but how they allocate foraging on a small scale near the colony is unclear and can have implications for understanding colony decision‐making and the pollination services provided. Using a mass‐foraging stingless bee, Scaptotrigona pectoralis (Dalla Torre) (Hymenoptera: Apidae: Meliponini), we show that colonies will forage near their nests and allocate their foraging labor on a very fine spatial scale at an array of food sources placed close to the colony. We counted the foragers that a colony allocated to each of nine feeders containing 1.0, 1.5, or 2.0 M sucrose solution [31, 43, and 55% sucrose (wt/wt), respectively] at distances of 10, 15, and 20 m from the nest. A significantly greater number of foragers (2.6–5.3 fold greater) visited feeders placed 10 vs. 20 m away from the colony. Foraging allocation also corresponded to food quality. At the 10‐m feeders, 4.9‐fold more foragers visited 2.0 M as compared to 1.0 M sucrose feeders. Colony forager allocation thus responded to both differences in food distance and quality even when the travel cost was negligible compared to normal colony foraging distances (10 m vs. an estimated 800–1 710 m). For a nearby floral patch, this could result in unequal floral visitation and pollination.     

Survival of transplanted nests of the red wood ant Formica aquilonia （Hymenoptera： Formicidae）： The effects of intraspecific competition and forest clear-cutting

The fitness and survival of ant colonies depend on the resources near their nests. These resources may be limited due to poor habitat quality or by intra- and interspecific competitions, which in extreme cases may cause the ant colony to perish. We tested the effect of intraspecific competition and habitat degradation （forest clear-cutting） on colony survival by transplanting 26 nests of the red wood ant （Formica aquilonia Yarrow, 1955） in 26 different forest areas that contained 0-11 conspecific alien nests per hectare. F. aquilonia is highly dependent on canopy-dwelling aphids, thus the removal of trees should cause food limitation. During the course of the 4-year experiment, 9 of the forests were partially clear- cut. We found that while forest clear-cutting significantly decreased the colonies＇ survival, intraspecific competition did not. As a highly polygynous and polydomous species, E aquilonia seems to tolerate the presence of alien conspecific colonies to a certain extent.     

Soldier diterpene patterns in relation with aggressive behaviour,spatial distribution and reproduction of colonies in Nasutitermes princeps

The territorial organization of the colonies of N. princeps (Desneux) (Isoptera: Temitidae) was studied by four methods: maps of nest systems, tests of aggressiveness, comparison of soldier diterpene patterns, and determination of the reproductive status of the nests. The diterpene patterns are rather variable among sympatric colonies, and allow the tracing of soldiers from their respective colonies throughout their foraging range. Soldiers from neighbouring nests display in some instances closely resembling diterpene patterns, suggesting close genetic relatedness and polycalic colonies, i.e. composed of several linked nests spread over large territories. Most likely, N, princeps colonies reproduce by budding. The number and type of reproductives found in the nests are consistent with this hypothesis. Tests of aggressiveness supported the above conclusions, but absence of aggression did not always indicate that the termites belonged to the same colony.     

Observations onApoica pallens,a nocturnal neotropical social wasp (Hymenoptera: Vespidae,Polistinae, Epiponini)

Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos.