Should I stay or should I go now? Patch use by African army ant colonies in relation to food availability and predation

Army ant colonies do not have permanent nests but frequently move to new patches. Local food depletion is considered the ultimate cause of this nomadic behaviour, but the proximate causes are not well understood. We tested if and how patch departure time of the aboveground-hunting army ant Dorylus molestus under field conditions is influenced by food availability and nest attacks by predators. In the first food supplement experiment, colonies receiving additional food throughout an entire nest stay did not reside in their nests for longer periods than control colonies. However, the distances travelled by colonies after nest stays during which colonies obtained food were shorter than those before these nest stays, indicating that colonies do assess food availability and avoid moving too far away from patches of high food availability. In the second food supplement experiment, in which colonies were given even larger amounts of food in the second half of their nest stay to mimic a rich unpredictable food source that these highly polyphagous predators are likely to encounter sometimes, patch departure times likewise did not differ between treated and control colonies. Either patch departure time is independent of food availability or there is another, as yet unappreciated proximate cause of colony movements in this species which we were unable to control for in our field experiments. One possibility is that encounters between neighbouring colonies influence patch departure time. In the experiment on the effect of predation, colonies responded to simulated nest attacks by mammals by leaving nests almost instantaneously and thus much earlier than control colonies. Rapid nest evacuation is likely a response to minimize the probability of repeat attacks by predators which cannot be repelled in other ways. Future studies will be necessary to definitively determine whether food availability influences patch departure times and to elucidate the consequences of colony encounters.     

Anti-predator behaviour in the ant Pheidole desertorum: The importance of multiple nests

The relationship between emigrations and anti-predator behaviour in the ant Pheidole desertorum was investigated in the field. Frequent emigrations in P. desertorum result in the colony having multiple nests, of which only one is occupied at a time. A field procedure demonstrated that the ants quickly find and enter the unoccupied nests after a nest evacuation caused by the army ant Neivamyrmex nigrescens. When colonies were denied access to their unoccupied nests after an evacuation, survival of the brood and alates was significantly lower than in colonies allowed access to all their nests. These results suggest that emigrations in P. desertorum are part of a defence strategy against army ants.     

Size and composition of swarming colonies in Provespa anomala (Hymenoptera, Vespidae), a nocturnal social wasp

Summary: Ninety-eight nests of various growing stages of Provespa anomala were found in the lowlands of Sumatra, Indonesia, from August to January. Its colony cycle is considered to be annual, with nests built throughout the year. There were two types of early nests before the emergence of workers, one with a worker number of less than 63 and the other of more than 231. The former were new nests, each containing a new queen and were built by reproductive swarming, whereas each of the latter was possibly re-built by an old queen and an absconding swarm. Ten swarming colonies were attracted by an oil-lamp light; these consisted of a copulated queen with immature oocytes in the ovary and 55 workers on average. No males, or workers stylopized by Xenos provesparum were observed either in colonies before worker emergence or in swarms coming flying into the light. Differences between swarming in Provespa, polygyny and nest relocation in Vespa, and those in swarm-founding Polistinae are discussed.     

An alternative strategy for maintenance of eusociality after nest destruction: new nest construction in a primitively eusocial wasp

Although nests are central to colonial life in social insects, nests are sometimes damaged by predators or natural disasters. After nest destruction, individuals usually construct new nests. In this case, a sophisticated mechanism like the scent trail pheromone used in large insect colonies that recruit individuals to new nest sites would be important for the maintenance of eusociality. In independent-founding Polistes wasps, it is well known that queens enforce workers physiologically on the natal nests even if evidence of trail pheromone use has not been exhibited. We investigated the effect of the queen on an alternative strategy for the maintenance of eusociality by first females after nest destruction in the primitively eusocial wasp Polistes chinensis. We predicted that the first females in queen-absent colonies have various behavioral options after nest destruction. Even if the females construct new nests cooperatively with other individuals, the new nest construction should be conducted more smoothly in queen-present colonies because the queens regulate the behavior of wasps. We made wasps construct new nests by removing the entire brood from existing nests. The presence of the queen did not cause variation in the alternative strategy of the first females, as the first females (workers) usually constructed new nests cooperatively irrespective of the queen-presence. Thus, the workers in the queenpresent colonies affiliated to the new nest construction more smoothly and constructed new nests more efficiently than workers in the queen-absent colonies. Our results suggest that the presence of the queen is important for maintaining eusociality in primitively eusocial wasps after nest destruction. Received 8 February 2005; revised 5 October 2005; accepted 17 October 2005.     

Intraspecific interactions in a community of arboreal nesting termites (Isoptera: Termitidae)

In coconut plantations of northern New Guinea, the arboreal nesting termite community comprises three species:Nasutitermes princeps, N. novarumhebridarum, andMicrocerotermes biroi. In orde to assess the importance of intraspecific interactions in this community, we conducted pairwise encounters between batches of individuals in the laboratory and between entire nest populations in seminantural conditions. Three levels of agonism were defined in laboratory bioassays: anagonism, moderate agonism, and strong agonism. Anagonism was observed during all control tests with homocolonical groups and in some tests with allocolonial groups of all species. Moderate agonism included initial aggressiveness that subsequently faded out, and initially passive encounters where aggression progressively built up and led to fighting. Strong agonism corresponded to initial aggressiveness and fighting. Results obtained in alboratory bioassays were consistent with bioassays in seminatural conditions. WhenNasutitermes colonies were anagonists in laboratory bioassays, their foraging trails merged without aggression in field tests.N. princeps nests that were moderately agonistic in laboratory tests fought and either continued to avoid each other or finally joined after elimination of the most aggressive individuals. The most aggressiveM. biroi andN. princeps colonies fought and their foraging trails diverged afterward. Direct attacks on alien nests were winnessed inM. biroi. In all species, anagonism occurred in 21–34% of the combinations tested, between either geographically close or distantcolonies. An exeption was a group of 112 anagonist nests ofN. princeps, which most probably constituted a supercolony. The level of agonism betweenNasutitermes colonies was constant during the wet and dry season. Termite colonies excluded each other, both intra- and interspecifically, from the coconut trees, and their territories seem distributed in a mosaic pattern. Agonism between colonies may result in the elimination of the weakest colonies or in trail divergence, maintaining this mosaic. In cotrast, lack of agonism between some colonies suggests the possibility of colony fusion and gene exchanges without nuptial flights.     

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.     

The influence of intraspecific competition on resource allocation during dependent colony foundation in a social insect

Organisms face a trade-off between investment in fewer, larger offspring, or more, smaller offspring. Most organisms can adjust investment through variation in the size and number of offspring in response to factors such as resource availability and competition. In some social animals, established colonies divide into groups of individuals that become autonomous, a process known as colony fission (also dependent colony foundation in social insects). Resource allocation under fission can be fine-tuned by adjusting the number of new groups (offspring number) and the number of individuals in each new group (offspring size). We assessed the influence of competition on resource allocation during fission in the ant Cataglyphis cursor, by allowing colonies to fission in experimental enclosures of high or low conspecific colony density. The pattern of colony fission was similar to that observed in the field: each fissioning colony produced a few new nests comprising a highly variable number of workers and a single queen, the old queen was often replaced, and new queens were produced in excess. The number of new nests produced depended on the available workforce in the parent colony but was not affected by differences in colony density. Comparison with data from fission under natural field conditions, however, indicates that colonies in enclosures produced fewer, larger new nests, suggesting that resource investment patterns during fission are indeed subject to extrinsic factors. The density of conspecific colonies in the immediate surroundings may be an unreliable estimate of competition intensity and other factors should be considered.     

Effects of non-uniform static magnetic fields on the rate of myosin phosphorylation

The effect on myosin phosphorylation from exposure to a magnetic field generated by an array of four permanent magnets was investigated. Two lateral positions in the non-uniform field over the array were explored, each at four vertical distances over the surface of the device. The rate of myosin phosphorylation was found to depend on the position laterally over the array as well as the distance from the device surface. The square magnet array was comprised of axially magnetized, cylindrical NdFeB permanent magnets arranged with poles of alternating polarity in a plane (MagnaBloc trade mark therapeutic device). Detailed dosimetry of the magnet array was compiled: the magnetic flux density averaged over the exposure volume spanned the range 0.7-86 mT for the eight different exposure positions. The corresponding range for the absolute field gradient was 0.4-20 T/m. Comparing the dosimetry to the experimental outcome, our results imply that magnetic field amplitude alone is not sufficient to describe the influence of the field in this preparation.     

Orientation in the wandering albatross: interfering with magnetic perception does not affect orientation performance

After making foraging flights of several thousands of kilometers, wandering albatrosses (Diomedea exulans) are able to pinpoint a specific remote island where their nests are located. This impressive navigation ability is highly precise but its nature is mysterious. Here we examined whether albatrosses rely on the perception of the Earth's magnetic field to accomplish this task. We disturbed the perception of the magnetic field using mobile magnets glued to the head of nine albatrosses and compared their performances with those of 11 control birds. We then used satellite telemetry to monitor their behavior. We found that the ability of birds to home specific nest sites was unimpaired by this manipulation. In particular, experimental and control birds did not show significant differences with respect to either foraging trip duration, or length, or with respect to homing straightness index. Our data suggest that wandering albatrosses do not require magnetic cues to navigate back to their nesting birds.     

NESTING OF THE VILLAGE WEAVER PLOCEUS CUCULLATUS

From August to October 1975, 31 nesting colonies of Village Weavers were identified within an area of 3000 km², south of Lake Chad in Africa. The number of nests and the productivity of each colony were estimated by means of several samplings made during the course of the nesting season. Differences between bush colonies and village colonies are not relevant. The average length of the nesting season is 70 days. In each colony the number of nests increases during the first month and then decreases. The average number of fledging attempts is four per colony, with a period of about ten days from one to another. On a regional scale, breeding periods and fledging attempts are well synchronized. Each nest carries an average of 2.4 eggs and 1.9 young, the difference occurring only at hatching. Due to regional synchronism, the period of most intensive reproductive activity, at which the number of nests reaches its maximum, can be determined.     

Brood reduction in temperate and sub-tropical ospreys

Summary In an effort to understand patterns and causes of nestling loss in Ospreys (Pandion haliaetus), I studied brood reduction in three eastern U.S. Osprey colonies during 1978 and 1979. The colonies, located in Florida Bay (1) and on coastal Long Island, N.Y. (2), differed in the average daily amount of food delivered to nestlings; Florida nests received 43% and 11% less fish per day than nests in the two N.Y. colonies, largely because latitude and season restricted day length and thus foraging time for the winter-breeding Florida Ospreys. Increased distance from stable food sources accounted for the lower rate of feeding at one of the N.Y. colonies. Variation in clutch size in the three colonies reflected differences in latitude more than in food availability; average clutch sizes in Long Island were larger than Florida clutches by 0.5 of an egg, but were similar to each other and to those in other northeastern U.S. Osprey populations.Increased nestling loss coincided with reduced food delivery rates and, in food stressed colonies, this loss was 2–3 times greater than any recorded for Ospreys. Starvation was the primary cause of nestling death, with mortality concentrated on third chicks, which hatched on average 3.9 d later and from eggs 5.6% smaller than chicks hatching first. Sibling aggression accounted for the preferential feeding of older nestmates,but only in colonies or nests where food was limited. Aggressive chicks nearly always stopped fighting after being fed. This behavior provided a reversible mechanism for controling brood reduction that was based on nutrition. Growth rates of young measured during the first half of the growth period were more variable between colonies than within nests. This is interpreted as reflecting both the differences in colony food delivery rates as well as the evolutionary pressures of sibling competition to equalize the growth of nestmates.     

Restricted effective queen dispersal at a microgeographic scale in polygynous populations of the ant Formica exsecta

Ecological constraints on effective dispersal have been suggested to be a key factor influencing social evolution in animal societies as well as the shift from single queen colonies (monogyny) to multiple queen colonies (polygyny) in ants. However, little is known about the effective dispersal patterns of ant queens. Here we investigate the microgeographic genetic structure of mitochondrial haplotypes in polygynous populations of the ant Formica exsecta, both between pastures and among nests within pastures. An analysis of molecular variance revealed a very high genetic differentiation (phiST = 0.72) between pastures, indicating that queens rarely disperse successfully between pastures, despite the fact that pastures were sometimes as close as 1 km. Most of the pastures contained only a single haplotype, and haplotypes were frequently distinct between nearby pastures and even between groups of nests within the same pasture. In the three pastures that contained several haplotypes, haplotypes were not randomly distributed, the genetic differentiation between nests being phiST = 0.17, 0.52, and 0.69. This indicates that most queens are recruited within their parental colonies. However, a large proportion of nests contained more than one haplotype, demonstrating that colonies will sometimes accept foreign queens. The relatedness of mitochondrial genes among nestmates varied between 0.62 and 0.75 when relatedness was measured within each pasture and ranged between 0.72 and 1.0 when relatedness was assessed with all pastures as a reference population. Neighboring nests were more genetically similar than distant ones, and there was significant isolation by distance. This pattern may be due to new nests being formed by budding or by limited effective queen dispersal, probably on foot between neighboring nests. These results show that effective queen dispersal is extremely restricted even at a small geographical scale, a pattern consistent with the idea that ecological constraints are an important selective force leading to the evolution and maintenance of polygyny.     

Conspecific nest parasitism in the Pied Avocet Recurvirostra avosetta

Evidence for the occurrence of conspecific nest parasitism (CNP) in Pied Avocets Recurvirostra avosetta is presented. Clutches of more than four eggs had obviously been produced by more than one female but were incubated by only one pair each. Minimum estimates for the frequencies of parasitized clutches and parasitic eggs were 3.3% and 1.3% respectively. CNP increased in frequency in colonies with higher nest densities. The frequency of CNP was unaffected by the rate of nest failures early in the season. On average, parasitic eggs were laid earlier in the season than the majority of non-parasitic eggs. Parasitic Avocets usually deposited their eggs during the laying period of host nests. Parasitized nests had significantly longer incubation periods than unparasitized nests. Hatching success in supernormal clutches was insignificantly reduced compared with four-egg clutches. The annual breeding success of individuals with parasitized clutches was considerably (but not significantly) higher than those of non-parasitized individuals. This was probably due to the fact that parasites chose to deposit their eggs in dense colonies whose members had significantly higher breeding success than the individuals in loose colonies. In colonies with a high rate of CNP, the frequency of clutches of more than five eggs increased. These clutches had little chance of survival.     

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.     

Seasonal patterns of egg production in field colonies of the termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera: Rhinotermitidae)

This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May, soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days.     

Spatial patterns, temporal variability, and the role of multi-nest colonies in a monogynous Spanish desert ant

Abstract 1. The colonies of the Spanish desert ant Cataglyphis iberica are polydomous. This study describes the temporal and spatial patterns of the polydomy in this species at two different sites, and presents analyses of its role in reducing the attacks of the queen over sexual brood, and in allowing better habitat exploitation.
2. The spatial distribution of nests was clumped while colonies were distributed randomly. Mean nearest neighbour distance ranged from 3.4 to 7.0 m for nests and from 12.3 to 14.1 m for colonies. Distance of foragers searching for food varied among nests: mean values were between 6.1 and 12.6 m.
3. At both sites, the maximum number of nests per colony occurred in summer, during the maximum activity period of the species. Colonies regrouped at the end of this period but overwintered in several nests.
4. Nest renewal in C. iberica colonies was high and showed great temporal variability: nests changed (open, close, re-open) continuously through the activity season and/or among years. The lifetime of up to 55% of nests was only 1–3 months.
5. Polydomy in C. iberica might decrease the interactions between the queen and the sexual brood. In all colonies excavated just before the mating period, the nest containing the queen did not contain any virgin female. Females were in the queenless nests of the colony.
6. The results also suggest that polydomous C. iberica colonies may enhance habitat exploitation because foraging activity per colony increases with nest number. The relationship between total prey input and foraging efficiency and number of nests per colony attains a plateau or even decreases after a certain colony size (four to six nests). This value agrees with the observed mean number of nests per colony in C. iberica .     

Fitness consequences of ecological constraints and implications for the evolution of sociality in an incipiently social bee

Ecological constraints such as resource limitation, unfavourable weather conditions, and parasite pressure have long been considered some of the most important selective pressures for the evolution of sociality. In the present study, we assess the fitness consequences of these three ecological factors on reproductive success of solitary nests and social colonies in the socially polymorphic small carpenter bee, Ceratina australensis, based on 982 nests collected over four reproductive periods. Nest site limitation was predicted to decrease opportunities for independent nest initiation and increase the frequency of social nesting. Nest sites were not limiting in this species and the frequency of social nesting was consistent across the four brood‐rearing periods studied. Unfavourable weather was predicted to lower the frequency of female dispersal from their natal nests and to limit the brood‐rearing season; this would increase the frequency and fitness of social colonies. Daily temperature and precipitation accumulation varied between seasons but were not correlated with reproductive success in this bee. Increased parasite pressure is predicted to increase the frequency and fitness of social colonies because solitary bees must leave the nest unattended during foraging bouts and are less able to defend the nest against parasites. Severe parasitism by a chalcid wasp (Eurytoma sp.) resulted in low reproductive success and total nest failure in solitary nests. Social colonies had higher reproductive success and were never extirpated by parasites. The high frequency of solitary nests suggests that this is the optimal strategy. However, social colonies have a selective advantage over solitary nesting females during periods of extreme parasite pressure, and we suggest that social nesting represents a form of bet‐hedging against unpredictable fluctuations in parasite number. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 57–67.     

Reproductive mechanisms and dynamics of habitat colonization in Microcerotermes biroi (Isoptera: Termitidae)

Abstract. 1. Previous studies on the arboreal termite community in coconut plantations of northern New Guinea showed that Microcerotermes biroi is the most abundant species, despite the fighting superiority of two competitor species Nasutitermes princeps and N.novarumhebridarum. In this study we tested the hypothesis that the success of M.biroi is due to its efficiency at colonizing new habitats following nuptial flights.
2. We demonstrated experimentally the ability of M.biroi colonies to replace their reproductives when removed, or to produce reproductives in satellite nests when isolated from the remainder of the colony. Replacement reproductives were always neotenics, derived from nymphs or workers.
3. Despite the ability of neotenics to differentiate within their home colonies, 84% of field colonies were headed by dealated imagos. This value constitutes a minimum estimate of the proportion of field colonies founded independently by imagos after the nuptial flight.
4. The monitoring of a young plantation during the first 31/2 years of its colonization by arboreal nesting termites revealed its invasion by M.biroi , which colonized 63% of the trees while neither Nasutitermes species appeared.
5. Our results demonstrate that M.biroi is actually a pioneer species, able to invade a new habitat by means of nuptial flights. They outline the importance of each species' reproductive strategy in shaping the arboreal-nesting termite community.     

Clumping versus spacing out: Experiments on nest predation in fieldfares (Turdus pilaris)

Fieldfares (Turdus pilaris), which nest solitarily as well as in colonies, offer an opportunity to assess within one species the relative advantages of clumping versus spacing out. An experiment with artificial, egg-baited nests showed that predation in the absence of fieldfares was higher on clumped than on scattered nests. In another experiment, we tested whether artificial nests run a higher risk of predation near solitary fieldfare pairs than near fieldfare colonies. Nest predation was higher near solitary fieldfare pairs than outside and inside fieldfare colonies. The risk probably was higher outside than inside colonies. Communal antipredator attacks is the likely cause of reduced predation near colonies. Even solitary fieldfare pairs confer some degree of protection, because predation was lower at artificial nests near solitary fieldfare pairs than at nests without neighbouring fieldfares.