Search

UK farming is at a crossroads. Its continued dependency on decoupled direct payments, shortage of investment finance, difficulties in changing cost structure and the reduced scope to differentiate and diversity sources of farm revenue, exacerbated by the unprecedented increases in the price of key inputs, means farmers face stark choices with fewer remaining effective management options. This study reviews two previous crossroads moments in UK agriculture and considers how the current crossroads moment is different from those. It then provides an estimate of the impacts of the current challenges on the size of the future farming population, based on the methodology used by McInerney. The inter-farm distribution of assets, debts and earnings, differences in farm specialisation, availability of finance and farm-succession arrangements mean it is not easy to identify which individual farms are most likely to fail. Nevertheless, upland grazing, lowland grazing and mixed farm-types seem to be the most vulnerable. Assuming low but realistic returns to fixed and working capital and income/farm, the future farming population is estimated to be 138,000: a 23% reduction from the number of 2019 farming population. The population falls to 15,000 if all subsidies paid in 2021 are removed from the calculation. The actual fall will be smaller than this because farmers will develop new revenue streams and farming systems. But a reduction even approaching 23% is likely to result in more generous assistance being made available, and perhaps even a reversal of some key elements of the new policies.

In Guyana, the coastal plains dominate agricultural production, while the hinterland is an emerging agricultural frontier. The coastal and hinterland regions have differing agro-climatic conditions, but share immediate climate change and environmental degradation pressures, including soil degradation. Even though climate change adaptation is prioritized over greenhouse gas mitigation in Guyana, soil-focused farming, otherwise known as sustainable soil management (SSM), can provide a system that creates synergies between these two facets of climate-smart agriculture and, also, promotes soil security. This article proposes a bottom-up planning process for SSM in Guyana by assessing its underlying psycho-social and physical facilitators and barriers. The main questions addressed are: what are the attitudes of Guyanese farmers to climate change? What are their capabilities for SSM, in terms of education, technology and government support? In answering these questions, inductive-derived thematic analysis of transcripts derived from in-depth telephone interviews with seventeen (17) farmers, from coastal and hinterland regions, provides an initial basis for ground truthing on the local appropriateness of SSM. Results show that hinterland farmers are more emotive and value-driven about their environment, while coastal farmers, instead, prioritize access to markets and gaining favorable prices for their commodities. Additionally, the lack of education and training are identified as severe limitations to the capabilities of farmers to practice SSM. In conclusion, a weak marketing environment is seen as a binding constraint of sustainable intensification as surplus goods attract low prices. Stronger linkages to dynamic markets, as well as increased investment opportunities are needed for sustainable farming to become economically feasible. Therefore, psychosocial capital must be strengthened before any natural capital is improved under Guyana's various agro-environmental policies.

Understanding how mobile, marine predators use three-dimensional space over time is central to inform management and conservation actions. Combining tracking technologies can yield powerful datasets over multiple spatio-temporal scales to provide critical information for these purposes. For the white shark (Carcharodon carcharias), detailed movement and migration information over ontogeny, including inter- and intra-annual variation in timing of movement phases, is largely unknown in the western North Atlantic (WNA), a relatively understudied area for this species. To address this need, we tracked 48 large juvenile to adult white sharks between 2012 and 2020, using a combination of satellite-linked and acoustic telemetry. Overall, WNA white sharks showed repeatable and predictable patterns in horizontal movements, although there was variation in these movements related to sex and size. While most sharks undertook an annual migratory cycle with the majority of time spent over the continental shelf, some individuals, particularly adult females, made extensive forays into the open ocean as far east as beyond the Mid-Atlantic Ridge. Moreover, increased off-shelf use occurred with body size even though migration and residency phases were conserved. Summer residency areas included coastal Massachusetts and portions of Atlantic Canada, with individuals showing fidelity to specific regions over multiple years. An autumn/winter migration occurred with sharks moving rapidly south to overwintering residency areas in the southeastern United States Atlantic and Gulf of Mexico, where they remained until the following spring/summer. While broad residency and migration periods were consistent, migratory timing varied among years and among individuals within years. White sharks monitored with pop-up satellite-linked archival tags made extensive use of the water column (0–872 m) and experienced a broad range of temperatures (−0.9 – 30.5°C), with evidence for differential vertical use based on migration and residency phases. Overall, results show dynamic inter- and intra-annual three-dimensional patterns of movements conserved within discrete phases. These results demonstrate the value of using multiple tag types to track long-term movements of large mobile species. Our findings expand knowledge of the movements and migration of the WNA white shark population and comprise critically important information to inform sound management strategies for the species.

Sharks serve as key predators in coastal areas, with several species using near shore habitats as nursery refuges. With many shark species threatened or endangered, it is now critical to increase the knowledge of how anthropogenic activities impact these populations. This study is the first attempt at characterizing epigenetic modifications in elasmobranchs, and their potential as biomarkers of stress and disease using a dredging event episode in the early 2000′s in Bimini, Bahamas, as a model system. Lemon shark fin samples were selected from a historic archive (1995–2012) of Bimini’s North (impacted) and South (control) shark nurseries, and classified as before (1995–2000), during (2001–2006), and after (2007–2012) the dredging event. Genome-wide DNA methylation was analyzed in these samples, along with the quantification of trace metals to investigate temporal and spatial patterns of metal concentrations. The obtained results revealed differential DNA methylation patterns in sharks from the North nursery (closest to the dredging site). While low concentrations of metals were found for all nursery sites and time frames, one trace metal (Manganese) was significantly correlated with the observed differences in DNA methylation. Overall, the findings of this study support DNA methylation as a potential stress biomarker for sharks, even in the absence of a reference genome. Furthermore, the identification of genomic regions differentially methylated in response to stress provides a basis for future analyses aimed at identifying gene networks and subsequent physiological responses to these events. Collectively, these analyses will help improve shark population monitoring, management, and conservation in impacted areas.

To understand why an animal might gain by playing dead, or more precisely, exhibit post-contact immobility (PCI), we consider the context in which this behaviour occurs. Is it, for example, a method by which a potential victim encourages a predator to direct its attention elsewhere? We investigate this possibility by using the marginal value theorem to analyse predator behaviour in the context of this defence strategy by potential prey. We consider two models. In the first, (random revisiting) the predator may return to sites it has already depleted within the patch. In the second, (systematic search) the predator goes only to new sites within the patch. The results of the two models are qualitatively extremely similar. We show that when prey occur in patches, PCI favours prey survival. Indeed, certain antlion larvae have PCI durations characterized by very long half-lives. These appear to be of such long durations that further increases would convey no substantial benefits in redirecting potential predators to other antlions within the patch and subsequently to other patches.

Early independence from parents is a critical period where social information acquired vertically may become outdated, or conflict with new information. However, across natural populations, it is unclear if newly independent young persist in using information from parents, or if group-level effects of conformity override previous behaviours. Here, we test if wild juvenile hihi ( Notiomystis cincta , a New Zealand passerine) retain a foraging behaviour from parents, or if they change in response to the behaviour of peers. We provided feeding stations to parents during chick-rearing to seed alternative access routes, and then tracked their offspring's behaviour. Once independent, juveniles formed mixed-treatment social groups, where they did not retain preferences from their time with parents. Instead, juvenile groups converged over time to use one access route­ per group, and juveniles that moved between groups switched to copy the locally favoured option. Juvenile hihi did not copy specific individuals, even if they were more familiar with the preceding bird. Our study shows that early social experiences with parents affect initial foraging decisions, but social environments encountered later on can update transmission of arbitrary behaviours. This suggests that conformity may be widespread in animal groups, with potential cultural, ecological and evolutionary consequences.

Reintroductions are essential to many conservation programmes, and thus much research has focussed on understanding what determines the success of these translocation interventions. However, while reintroductions disrupt both the abiotic and social environments, there has been less focus on the consequences of social disruption. Therefore, here we investigate if moving familiar social groups may help animals (particularly naive juveniles) adjust to their new environment and increase the chances of population establishment. We used social network analysis to study changes in group composition and individual sociality across a reintroduction of 40 juvenile hihi (Notiomystis cincta), a threatened New Zealand passerine. We collected observations of groups before a translocation to explore whether social behaviour before the reintroduction predicted associations after, and whether reintroduction influenced individual sociality (degree). We also assessed whether grouping familiar birds during temporary captivity in aviaries maintained group structure and individual sociality, compared to our normal translocation method (aviaries of random familiarity). Following release, we measured if survival depended on how individual sociality had changed. By comparing these analyses with birds that remained at the source site, we found that translocation lead to re-assortment of groups: non-translocated birds maintained their groups, but translocated juveniles formed groups with both familiar and unfamiliar birds. Aviary holding did not improve group cohesion; instead, juveniles were less likely to associate with aviary-mates. Finally, we found that translocated juveniles that lost the most associates experienced a small but significant tendency for higher mortality. This suggests sociality loss may have represented a disruption that affected their ability to adapt to a new site.

Most animal traps are constructed from self-secreted silk, so antlions are rare among trap builders because they use only materials found in the environment. We show how antlions exploit the properties of the substrate to produce very effective structures in the minimum amount of time. Our modelling demonstrates how antlions: (i) exploit self-stratification in granular media differentially to expose deleterious large grains at the bottom of the construction trench where they can be ejected preferentially, and (ii) minimize completion time by spiral rather than central digging. Both phenomena are confirmed by our experiments. Spiral digging saves time because it enables the antlion to eject material initially from the periphery of the pit where it is less likely to topple back into the centre. As a result, antlions can produce their pits—lined almost exclusively with small slippery grains to maximize powerful avalanches and hence prey capture—much more quickly than if they simply dig at the pit's centre. Our demonstration, for the first time to our knowledge, of an animal using self-stratification in granular media exemplifies the sophistication of extended phenotypes even if they are only formed from material found in the animal's environment.

Aim Determining the causes of range size variation in the distributions of alien species is important for understanding the spread of invasive species. Factors influencing alien range size have been explored for some species at a regional level, but to date there has been no global analysis of an entire class. Here, we present such an analysis for birds, testing for the effects of introduction event, location and species-level variables on alien range sizes. Location Global. Methods We used a novel dataset on the global distributions of alien bird species to test for relationships between alien range size and colonization pressure, residence time, extent of the global climatic niche, native range size, body mass and specialization, using a statistical approach based on phylogenetic generalized least squares models. We performed this analysis globally, and for separate biogeographical realms. Results Approximately half of the variation in alien bird range size is explained by colonization pressure in univariate analysis. We identified consistent effects of higher colonization pressure at global and realm levels, as well as support for effects of native range size and residence time. We found less support for effects of body mass, specialization or extent of the global climatic niche on alien range size. Main conclusions Alien bird range sizes are generally small relative to their native range sizes, and many are continuing to expand. Nevertheless, current variation is predictable, most strongly by the event-level factor of colonization pressure. Whether a species is widespread is a better predictor of alien range size than whether a species could be widespread (estimated by global climatic niche extent), while we also find effects of residence time on alien range size. These relationships may help to identify those alien species that are more likely to spread and hence have greater environmental and economic impacts where they have been introduced.

This study documents and discusses recent (2002-2015) sightings and captures of smalltooth sawfish Pristis pectinata in the Bahamas. Movement patterns and habitat preferences of five P. pectinata are examined: two tracked with acoustic telemetry in Bimini and three tagged with pop-up archival transmitting tags in Andros. Historically, P. pectinata may have been distributed throughout the Bahamas; however, since 2002 only 61 encounters were recorded including: Andros (30), Bimini (19) and a handful across other Islands (12). In Bimini, all P. pectinata were >225 cm (stretched total length, LST) suggesting that it is not used as a nursery area. Pristis pectinata in Andros ranged from c. 80 to 450 cm (LST) indicating that this island might be an important nursery and breeding habitat. Pristis pectinata tracked in both islands remained at depths

Colonies of neotropical army ants of the genus Eciton Latreille offer some of the most captivating examples of intricate interactions between species, with hundreds of associated species already described in colonies of Eciton burchellii Westwood. Among this plethora of species found with Eciton colonies, two genera of staphylinid beetles, Ecitomorpha Wasmann, and Ecitophya Wasmann, have evolved to mimic the appearance and parallel the colouration of the most abundant ant worker cast. Here, we study for the first time the association of these ant-mimicking beetles with their ant host in an evolutionary and population genetics framework. The central emphasis is on colonies of E. burchellii, the only Eciton species that harbours both genera of ant-mimicking beetles. Phylogenetic and population structure analyses using the same mtDNA COI region (802 bp) for ants and beetles indicated that speciation patterns of the myrmecophiles were congruent with specialization to a particular Eciton (sub)species. Therefore, current taxonomic treatments of Eciton and its Ecitomorpha and Ecitophya associates need revision. Molecular clock analyses suggested that diversification of the Eciton hosts pre-date that of their guests, with a possible earlier association of Ecitophya (found with a large number of Eciton species) than with Ecitomorpha (found only with E. burchellii colonies). Population-level analyses revealed that patterns of diversification for the myrmecophiles are also consistent with specialisation to a particular host across broad geographical areas but not at small geographical scales, with gene flow within each species found between host colonies, even across landscape features that are strong barriers for Eciton female-mediated gene flow.

We study the plasticity of collective decision-making in ants by blocking key aspects of pheromone communication across entire colonies. To achieve this, droplets of paint were applied over the gaster tips of entire worker populations within colonies of the rock ant, Temnothorax albipennis. This treatment should prevent pheromone release potentially from each ant’s Dufour’s, poison, and pygidial glands in addition to the hindgut. We then examined the collective decision-making abilities of treatment and control colonies over alternative new nest sites in binary choice experiments. The performance of treatment colonies was compared with that of control colonies that had also been marked with paint but in such a way as not to disrupt their pheromone excretions from the gaster tip. Our results reveal the importance of “gaster-tip” pheromones during colony emigrations. Treatment-colony emigrations were significantly less successful than those of the controls, as the quality of their nest site assessments was reduced. However, treatment ants presented an extraordinary example of behavioral plasticity as they reduced their quorum thresholds in order to maintain normal emigration completion times. Hence, the ants whose communication systems have been compromised can still emigrate swiftly and maintain low levels of colony exposure.

Mechanisms driving selection of body size and growth rate in wild marine vertebrates are poorly understood, thus limiting knowledge of their fitness costs at ecological, physiological and genetic scales. Here, we indirectly tested whether selection for size-related traits of juvenile sharks that inhabit a nursery hosting two dichotomous habitats, protected mangroves (low predation risk) and exposed seagrass beds (high predation risk), is influenced by their foraging behaviour. Juvenile sharks displayed a continuum of foraging strategies between mangrove and seagrass areas, with some individuals preferentially feeding in one habitat over another. Foraging habitat was correlated with growth rate, whereby slower growing, smaller individuals fed predominantly in sheltered mangroves, whereas larger, faster growing animals fed over exposed seagrass. Concomitantly, tracked juveniles undertook variable movement behaviours across both the low and high predation risk habitat. These data provide supporting evidence for the hypothesis that directional selection favouring smaller size and slower growth rate, both heritable traits in this shark population, may be driven by variability in foraging behaviour and predation risk. Such evolutionary pathways may be critical to adaptation within predator-driven marine ecosystems.

Understanding how and why animals are distributed through time and space has always been a fundamental component of ecology and is an essential prerequisite for effective conservation/management. However, for highly-mobile k-selected species, behavioural predictability is rarely considered over appropriate scales relative to life-history. To address this point, a multidisciplinary approach combining telemetry, external tagging, physical assessment, environmental monitoring and genetic analysis was adopted to determine a spatial framework for the movements of adult lemon sharks, Negaprion brevirostris, at multiple spatial and temporal scales from 2007 to 2011. Lemon sharks (n=83) were tracked with passive acoustic telemetry revealing a winter residency in the southeast Florida region. Detections from individuals recorded within the core winter habitat for > 20 days (n = 56) were incorporated into a generalized linear mixed-effects model (GLMM) to investigate the influence of water temperature, photoperiod, moon phase, month and year on presence. The findings of this study suggest a temperature driven “migration-residency” model for mature lemon shark distribution across the U.S. eastern seaboard. Lemon sharks are distributed across a wide geographical area in the summer months and migrate south concentrating off southeast Florida in the winter, with this pattern repeated each year. From comparative genetic analysis and the absence of any evidence of mating behaviour during the winter residency period, mating and parturition are most probably occur in May/June between northern Florida and the Carolinas. This study highlights the importance of determining the specific dynamics and proximate causes of animal movement and distribution over appropriate spatial and temporal scales relative to life-history.

Tandem running is a recruitment strategy whereby one ant leads a single naïve nest mate to a resource. While tandem running progresses towards the goal, the leader ant and the follower ant maintain contact mainly by tactile signals. In this paper, we investigated whether they also deposit chemical signals on the ground during tandem running. We filmed tandem-running ants and analysed the position of the gasters of leaders and followers. Our results show that leader ants are more likely to press their gasters down to the substrate compared to follower ants, single ants and transporter ants. Forward tandem-run leaders (those moving towards a new nest site) performed such trail-marking procedures three times more often than reverse tandem leaders (those moving towards an old nest site). That leader ants marked the trails more often during forward tandem runs may suggest that it is more important to maintain the bond with the follower ant on forward tandem runs than on reverse tandem runs. Marked trails on the ground may serve as a safety line that improves both the efficiency of tandem runs and their completion rates.

We investigated excavation and nest site choice across sediment-filled cavities in the ant Temnothorax albipennis. Colonies were presented with sediment-filled cavities, covering a spectrum from ones that should be quick to excavate but will form a weak enclosing wall to those that should be slow to excavate but form a strong wall. Overall, colonies only showed a significant preference for cavities that were fastest to excavate over those that were slowest. The speed of decision making and moving appears paramount over the suitability of the sediment for forming an enclosing wall. The mechanism behind the choice is the differential between the rates at which alternatives are excavated and accumulate ants. The rates for a particular type of cavity were unaffected by the type with which it was paired. This suggests that there is no significant competition between sites during the decision-making process. Certain colonies were able consistently to discriminate across more closely matched alternatives. These colonies required a greater number of ants to be present and took longer before beginning to move. A race is run between alternatives to become habitable but the process may be tuned across colonies such that it may run for longer and an incorrect or split decision is less likely.

Large ant colonies invariably use effective scent trails to guide copious ant numbers to food sources. The success of mass recruitment hinges on the involvement of many colony members to lay powerful trails. However, many ant colonies start off as single queens. How do these same colonies forage efficiently when small, thereby overcoming the hurdles to grow large? In this paper, we study the case of combined group and mass recruitment displayed by some ant species. Using mathematical models, we explore to what extent early group recruitment may aid deployment of scent trails, making such trails available at much smaller colony sizes. We show that a competition between group and mass recruitment may cause oscillatory behaviour mediated by scent trails. This results in a further reduction of colony size to establish trails successfully. © 2013 Society for Mathematical Biology.

Migratory behaviour forms an intrinsic part of the life histories of many organisms but is often a high-risk process. Consequently, varied strategies have evolved to negate such risks, but empirical data relating to their functioning are limited. In this study, we use the model system of the house-hunting ant Temnothorax albipennis to demonstrate a key strategy that can shorten migration exposure times in a group of social insects. Colonies of these ants frequently migrate to new nest sites, and due to the nature of their habitat, the distances over which they do so are variable, leading to fluctuating potential costs dependent on migration parameters. We show that colonies of this species facultatively alter the dynamics of a migration and so compensate for the distance over which a given migration occurs. Specifically, they achieve this by modulating the rate of ‘tandem running’, in which workers teach each other the route to a new nest site. Using this method, colonies are able to engage a larger number of individuals in the migration process when the distance to be traversed is greater, and furthermore, the system appears to be based on perceived encounter rate at the individual level. This form of decentralised control highlights the adaptive nature of a behaviour of ecological importance, and indicates that the key to its robustness lies in the use of simple rules. Additionally, our results suggest that such coordinated group reactions are central to achieving the high levels of ecological success seen in many eusocial organisms. Electronic supplementary material The online version of this article (doi:10.1007/s00114-016-1386-8) contains supplementary material, which is available to authorized users.

Social behaviour may enable organisms to occupy ecological niches that would otherwise be unavailable to them. Here, we test this major evolutionary principle by demonstrating self-organizing social behaviour in the plant-animal, Symsagittifera roscoffensis . These marine aceol flat worms rely for all of their nutrition on the algae within their bodies: hence their common name. We show that individual worms interact with one another to coordinate their movements so that even at low densities they begin to swim in small polarized groups and at increasing densities such flotillas turn into circular mills. We use computer simulations to: (i) determine if real worms interact socially by comparing them with virtual worms that do not interact and (ii) show that the social phase transitions of the real worms can occur based only on local interactions between and among them. We hypothesize that such social behaviour helps the worms to form the dense biofilms or mats observed on certain sun-exposed sandy beaches in the upper intertidal of the East Atlantic and to become in effect a super-organismic seaweed in a habitat where macro-algal seaweeds cannot anchor themselves. Symsagittifera roscoffensis , a model organism in many other areas in biology (including stem cell regeneration), also seems to be an ideal model for understanding how individual behaviours can lead, through collective movement, to social assemblages.

Coastal biodiversity is threatened worldwide by both direct and indirect anthropogenic activities. To more effectively manage and protect coastal biodiversity, accurate assessments of genetic, species, and ecosystem level diversity are required. We present the results from an assessment of the aquatic species diversity of a small (3 km2), shallow, mangrove-fringed Bahamian lagoon (the North Sound) subject to ongoing anthropogenic development. The assessment was conducted through a collation of field observations and data in published literature. We found that eight angiosperm species, 30 macroalgal species, and 370 animal species (including 95 fishes, 69 arthropods, 56 birds, and 45 mollusks) were documented within the lagoon. At least 11 of these species are of conservation concern, such as the critically endangered smalltooth sawfish (Pristis pectinata) and hawksbill turtle (Eretmochelys imbricata). Comparisons of community similarity indicated that the North Sound has a relatively distinct fauna and flora, but available data suggest that the species found there are most similar to those found in nearby habitats in Cuba. The lagoon forms a key nursery habitat for many species, including lemon sharks (Negaprion brevirostris), Caribbean spiny lobsters (Panulirus argus), and queen conch (Strombas gigas). Recently, the lagoon was included as part of a new marine protected area (MPA), but much of the habitat has already experienced considerable anthropogenic disturbance and the MPA boundaries have yet to be established. We have therefore analyzed the lagoon biodiversity and expect the data presented here to serve as a baseline for future comparisons.

Non-consumptive or risk effects imposed by predators can influence prey behaviour over different spatio-temporal scales. Prey vulnerability to predation can also be dependent on abiotic conditions, such as tidal height. We conducted direct field observations of juvenile lemon sharks Negaprion brevirostris in a tidally influenced mangrove-inlet. We also used acoustic tracking to determine the movement patterns of juvenile lemon sharks and their predators (sub-adult lemon sharks) across the tidal cycle. Results showed that greater numbers of juvenile lemon sharks used the mangrove-inlet for longer time periods at deeper and warmer high tide depths. This coincided with an increased presence of potential predators (sub-adult lemon sharks) in the surrounding areas. Furthermore, in accordance with body-size dependent anti-predatory investment, smaller juvenile lemon sharks visited the mangrove inlet more often, spent longer there and left latest on average. Our acoustic tracking data also revealed a tidally-influenced pattern, with both juvenile and sub-adult lemon sharks detected at locations inshore over the high tide and offshore during the low tide. We concluded that the mangrove lake served as a 'refuge' for juvenile lemon sharks over the high tide, providing safe habitat when inshore areas become accessible to large predators, such as sub-adult lemon sharks. We suggest that these decisions are updated through ontogeny and also with daily fluctuations in abiotic factors, such as water depth. This study provides evidence for how intra-specific predatorprey interactions in a top predator species influence juvenile habitat selection, with potential implications for population structure and regulation.

Radio telemetry of 29 desert tortoises Gopherus agassizii in 2000 and 60 in 2001 at 4 sites in the Mojave Desert of California, USA, revealed that males had larger home ranges and moved greater distances than females, but that tortoises at sites with more rainfall did not always have larger home ranges or move greater distances. The Ivanpah Valley received more rainfall than the Fort Irwin area, Superior Valley, and Fremont, but differences between home range size and rain- fall were not consistent. Within the Ivanpah Valley, the plot at the highest elevation received more rainfall than the lower plots. However, within the Ivanpah Valley, tortoises at the 3 locations did not differ in home range and movement. In the wetter year (2001), female tortoises moved greater dis- tances each day at Ivanpah than female tortoises at Superior and Fremont, which were drier sites. Males moved farther per day than females in both years. In 2001, female tortoises in the Ivanpah Val- ley used more burrows than tortoises at Fremont and Superior, but similar numbers as tortoises at Fort Irwin. There was no mortality of tortoises in 2000 and a 5% mortality in 2001.

Many purely physical complex systems, in which there are both stochasticity and local interactions between the components, exhibit record dynamics. The temporal statistics of record dynamics is a Poisson process operating on a logarithmic rather than a linear time scale (i.e. a log-Poisson process). Record dynamics often drive substantial changes in complex systems when new high water marks in partially stochastic processes trigger new events. Social insect colonies are exemplary complex biological systems in which many of the local interactions of the components have been moulded by natural selection for the common good. Here, we combine experimental manipulation of ant colony demography with modelling to test the hypothesis that social interactions are the mechanism underlying the record dynamics. We found that compared with the control, log-Poisson statistics were disrupted in colonies in which the pattern of interactions was modified by the removal of the brood, and disappeared completely in ‘callow’ colonies composed entirely of very young workers from the same age cohort. We conclude that a subtle interplay between the demography of the society and the pattern of the interactions between the ants is crucial for the emergence of record dynamics. This could help identify what makes an ant colony a cohesive society.

Resource distribution is fundamental to social organization, but it poses a dilemma. How to facilitate the spread of useful resources but restrict harmful substances? This dilemma reaches a zenith in famine relief. Survival depends on distributing food fast but that could increase vulnerability to poisons. We tested how Temnothorax albipennis ants solve this dilemma in the distribution of honey solution after 48 h of starvation in four colonies with individually marked workers. We constructed the complete network of liquid food transmission (trophallaxis) between individuals. Within the first 30 min of famine relief, 95% of the workers received food and the distribution rate was an order of magnitude faster compared to the controls. We tested the assumptions of a simple analytical model that best fitted our data. Good mixing during famine relief was facilitated by the movement of internal workers away from the brood pile and the movement of foragers with food away from the nest entrance. This is intriguing because T. albipennis workers have spatial fidelity zones and in the controls internal and external workers were segregated. We discovered that colony vulnerability to poisons during famine relief might be mitigated by: (1) the dilution of food from the same source through mixing, (2) the concentration of food in workers positioned midway between the colony centre and its periphery and (3) the existence of living 'silos'. The latter are expendable foragers, who stay inside the nest and store food during famine relief, thus acting as potential disposable testers for food toxicity. © 2009 The Association for the Study of Animal Behaviour.

Social insects are distinguished by their extraordinary degree of cooperation and the complexity of their group organization. However, a high proportion of individuals (often .50% at any one time) in a social insect colony tend to be inactive. It has been hypothesized that larger colonies can afford such inactivity because of efficiencies gained through stronger division of labor. We quantify the degree to which colonies of different sizes exhibit division of labor, and what proportion tends to be inactive, in the ant Temnothorax albipennis. Colony size neither influenced individual specialization nor overall division of labor in this species and larger colonies did not show a higher proportion of inactive workers. Interestingly, small colonies seemed to rely more on a small number of high-performance workers: the proportion of work performed by the single most active worker is significantly higher in smaller colonies for several tasks. More research is needed to resolve when and how colony size affects collective organization and division of labor in insect colonies. Key words: colony size, division of labor, scaling, self-organization, social insects, specialization, task allocation. [Behav Ecol]

Ant colonies are factories within fortresses (Oster and Wilson 1978). They run on resources foraged from an outside world fraught with danger. On what basis do individual ants decide to leave the safety of the nest? We investigated the relative roles of social information (returning nestmates), individual experience and physiology (lipid stores/corpulence) in predicting which ants leave the nest and when. We monitored Temnothorax albipennis workers individually using passive radio-frequency identification technology, a novel procedure as applied to ants. This method allowed the matching of individual corpulence measurements to activity patterns of large numbers of individuals over several days. Social information and physiology are both good predictors of when an ant leaves the nest. Positive feedback from social information causes bouts of activity at the colony level. When certain social information is removed from the system by preventing ants returning, physiology best predicts which ants leave the nest and when. Individual experience is strongly related to physiology. A small number of lean individuals are responsible for most external trips. An individual’s nutrient status could be a useful cue in division of labour, especially when public information from other ants is unavailable.

Compromises between speed and accuracy are seemingly inevitable in decision-making when accuracy depends on time-consuming information gathering. In collective decision-making, such compromises are especially likely because information is shared to determine corporate policy. This political process will also take time. Speed–accuracy trade-offs occur among house-hunting rock ants, Temnothorax albipennis . A key aspect of their decision-making is quorum sensing in a potential new nest. Finding a sufficient number of nest-mates, i.e. a quorum threshold (QT), in a potential nest site indicates that many ants find it suitable. Quorum sensing collates information. However, the QT is also used as a switch, from recruitment of nest-mates to their new home by slow tandem running, to recruitment by carrying, which is three times faster. Although tandem running is slow, it effectively enables one successful ant to lead and teach another the route between the nests. Tandem running creates positive feedback; more and more ants are shown the way, as tandem followers become, in turn, tandem leaders. The resulting corps of trained ants can then quickly carry their nest-mates; but carried ants do not learn the route. Therefore, the QT seems to set both the amount of information gathered and the speed of the emigration. Low QTs might cause more errors and a slower emigration—the worst possible outcome. This possible paradox of quick decisions leading to slow implementation might be resolved if the ants could deploy another positive-feedback recruitment process when they have used a low QT. Reverse tandem runs occur after carrying has begun and lead ants back from the new nest to the old one. Here we show experimentally that reverse tandem runs can bring lost scouts into an active role in emigrations and can help to maintain high-speed emigrations. Thus, in rock ants, although quick decision-making and rapid implementation of choices are initially in opposition, a third recruitment method can restore rapid implementation after a snap decision. This work reveals a principle of widespread importance: the dynamics of collective decision-making (i.e. the politics) and the dynamics of policy implementation are sometimes intertwined, and only by analysing the mechanisms of both can we understand certain forms of adaptive organization.

Here, we study distribution of workload and its relationship to colony size among worker ants of Temnothorax albipennis, in the context of colony emigrations. We find that one major aspect of workload, number of items transported by each worker, was more evenly distributed in larger colonies. By contrast, in small colonies, a small number of individuals perform most of the work in this task (in one colony, a single ant transported 57% of all items moved in the emigration). Transporters in small colonies carried more items to the new nest per individual and achieved a higher overall efficiency in transport (more items moved per transporter and unit time). Our results suggest that small colonies may be extremely dependent on a few key individuals. In studying colony organisation and division of labour, the amount of work performed by each individual, not just task repertoire (which tasks are performed at all), should be taken into account.

Colonies of the ant Temnothorax albipennis improve their collective performance over successive emigrations (Langridge et al. Behav Ecol Sociobiol 56:523–529, 2004, Behav Ecol Sociobiol 62:447–456, 2008). Here, by analysing the performance of individual transporters (workers that carry the brood, queen and a proportion of adults), we investigate whether they spend less time at the old and new nests during repeated emigrations. Transporters expedited choosing and picking up brood items at the old nest and depositing them in the new nest. Such improvements were not associated with adult transport. Generally, when carrying brood items, but not when carrying adults, transporters visited several locations in the new nest before depositing them. Transporters did not interact with other adults when depositing brood items. Consequently, reductions in depositing times are the sum of time savings made by individual transporters. By contrast, transporters spent most time interacting with other adults before picking up brood items at the old nest. As the frequency of these interactions did not decline, we suggest the behaviours of interacting adults were modified in a way that hastened their completion. Thus, reductions in picking-up times probably occur because of time saved during interactions.

Decision making is of crucial importance in the lives of both animals and humans. How decisions of group members scale up to group decisions is of great interest. Accordingly, we gave homeless ant colonies (n = 67) in three experiments a choice between two nest sites (with small, big or mixed sand grains), each of which had to be excavated to be habitable. Among the colonies that chose only one of the new nest sites, all preferred the ones that could be excavated most easily and quickly. There are interesting parallels between the collective choice of mining sites and the ability of certain ants to select short cuts; both involve positive feedback. However, in this paper, we discuss a mechanism whereby collective co-ordination in the production of social infrastructure can occur in the absence of signalling.

We showed how super-organisms, here ant colonies, modify their home according to their increasing or decreasing space requirements. The ontogeny of wall building by colonies of the ant Temnothorax albipennis involves discontinuous rebuilding events that are reminiscent of moulting in insects. Here for the first time we manipulated worker density by changing nest cavity size instead of worker number, thus avoiding accidentally shifting the balance of workers with different propensities for building tasks. Our results suggest for the first time that history influences wall building in ants when worker density decreases (e.g. with colony diminution) as well as when it increases (e.g. with colony growth) as shown by earlier work. Furthermore, we found that ants used a greater number of the larger building blocks (big sand grains) both after cavity expansion and, more surprisingly, also after cavity contraction. The pattern of nest ‘moulting’ we experimentally manipulated and analysed should provide insights into possible trade-offs between the various functions and structural properties of the nest that these animals may have to optimize.

Animal groups can gather disproportionately more information and often outperform solitary individuals in ecologically important activities. Collective decisions, however, may involve costly mechanisms for reaching a consensus. Nest building is a prime example. In a previous study on foraging for building materials by the ant Temnothorax albipennis, we showed that colonies prefer larger building blocks (bigger sand grains) at all distances but always collect some smaller building blocks too. Walls made of mixtures of big and small grains are stronger and more compact. Here we study colonies with marked individuals to look at the foraging decisions of individuals that underlie the collective outcome for the colony. We found that at short distances some foragers preferred big grains and others small grains. However, at longer distances the proportion of foragers preferring big grains increased, whereas no foragers preferred small grains at the greatest distance. We found no evidence of an effect of individual morphology or foraging experience on preference. At all three distances foragers assessed grains before making a choice and were more likely to choose a big grain as a consequence. This likelihood increased with increasing distance. However, even at the greatest distance ants included small grains in the final wall after their initial preference for big grains. Therefore, we conclude that individual decisions to retrieve small grains are not simply errors. Instead, the construction itself may provide cues for the organization of the foraging activity of individuals into the collective building of an approximately optimal mixed wall by the colony.

We investigated an extreme behavioural specialization in the army ant Eciton burchellii. The spectacular group raids of these ants, which can contain up to 200 000 workers, always remain connected to the nest by a ‘principal trail’ of forager traffic. Remarkably, some workers use their bodies to plug potholes in the natural surfaces that the principal trail travels over, to provide a partly living surface for their nestmates to use. We found that this highly specialized behaviour results in a clear net benefit to the colony. Our experiments show that foragers do not discriminate against surfaces that force all individuals to run as slowly as the smallest workers, but that this prompts some ants to plug neighbouring low-quality surfaces. Individuals size-match to the hole they plug and cooperate to plug larger holes. The resulting modified surface allows prey-laden foragers to attain maximum speed. Overall, this results in a strong positive relationship between ant size and speed and an increase in the mean speed of prey-laden traffic. Moreover, calculations suggest that under a range of realistic scenarios, plugging behaviour results in a clear increase in daily prey intake. Broadly, our study provides rare quantitative evidence that extreme specialization by a minority can significantly improve the performance of a majority, and benefit the group as a whole. It also suggests, however, that these benefits are a consequence of the unusual and derived foraging strategy of E. burchellii. This highlights the importance of considering ecology and evolutionary history in the study of social organization in animal societies.

Building by ants often involves excavation, but Temnothorax albipennis colonies build walls in preformed cavities. To do this they need to choose and retrieve building material. Thus, building in T. albipennis can be analysed, in part, from the perspective of a foraging strategy. We gave ant colonies a choice between large and small sand grains that were available at three different distances. From theoretical considerations, we expected ant colonies to maximize the amount of material collected per unit time and therefore to choose large grains exclusively. Instead, they always chose grains of both sizes. Such partial preferences can be explained in terms of the mechanical benefits of constructing walls as a mixture of two grain sizes. Barricades composed of two grain sizes can be more resilient than walls made from a single grain size, as estimated in terms of angles of maximum stability and packing densities. Thus, foraging decisions need to be analysed in the broader context of how collected material is utilized. Here partial foraging preferences can have direct benefits: different choices by different foragers and even individual ‘error’ proneness might contribute to the collective good.

Conspecific ant colonies are often overdispersed, i.e. they are further apart than they would be if they were distributed randomly. This overdispersion might be driven by competition for food resources or nest sites and may result from established colonies preventing incipient colonies from settling too close to them. We investigated another possible mechanism for overdispersion: active nest choice by emigrating colonies. Colonies may be influenced by the presence of conspecifics when they are emigrating from a nest that has become uninhabitable. In the laboratory, we presented Temnothorax albipennis ant colonies with a choice of three new nests, which were equidistant from their old nest site. The new nests were identical except that one was near to an established conspecific colony. The emigrating colonies significantly preferred the new nest site that was furthest from the resident colony. This selection was not just the result of access to the other nests being blocked by aggression from the resident colony; emigrating colonies thus made active choices. Odour cues may influence nest selection: odours left around nest sites by foreign colonies deterred nest occupancy. There was more aggression near the resident colony, but this appeared to be caused by the greater density of resident ants there rather than those ants being more aggressive per capita. We also observed a relatively high proportion of fusions between colonies. Possible reasons for this are considered together with their implications.

Some organisms maintain a battery of defensive strategies against their exploiters (predators, parasites or parasitoids), while others fail to employ a defence that seems obvious. In this paper, we shall investigate the circumstances under which defence strategies might be expected to evolve. Brood parasites and their hosts provide our main motivation, and we shall discuss why the reed warbler Acrocephalus scirpaceus has evolved an egg-rejection but not a chick-rejection strategy as a defence against the common (Eurasian) cuckoo Cuculus canorus, while the superb fairy-wren Malurus cyaneus has evolved a chick-rejection but not an egg-rejection strategy as a defence against Horsfield's bronze-cuckoo Chrysococcyx basalis. We suggest that the answers lie in strategy-blocking, where one strategy (the blocking strategy) prevents the appearance of another (the blocked strategy) that would be adaptive in its absence. This may be common in exploiter-victim systems. © 2006 Springer Science+Business Media, Inc.

We show that one of the advantages of quorum-based decision-making is an ability to estimate the average value of a resource that fluctuates in quality. By using a quorum threshold, namely the number of ants within a new nest site, to determine their choice, the ants are in effect voting with their feet. Our results show that such quorum sensing is compatible with homogenization theory such that the average value of a new nest site is determined by ants accumulating within it when the nest site is of high quality and leaving when it is poor. Hence, the ants can estimate a surprisingly accurate running average quality of a complex resource through the use of extraordinarily simple procedures.

Summary 1Certain ants have considerable morphological diversity within the workforce, with individuals physically specialized for particular jobs. The ecological conditions that select for this phenomenon are still poorly understood. 2We use a comparative analysis to address the hypothesis that prey type has selected for greater morphological diversity in the small, monophyletic army ant genus Eciton. These ants are nomadic group-predators and transport loads in the limited space below the body, so bulkier prey types should select for more diverse worker morphology. 3We show that five Eciton species differ in the presence or absence of a distinct ‘submajor caste’, the morphological exaggeration of submajors when present, and the allometric scaling of standard workers over a broad size range. Crucially, the presence and morphological exaggeration of submajors is associated with the variety of awkwardly shaped prey types that the species takes, and this caste specializes in prey transport. 4Our findings support the importance of dietary composition in the evolution of worker morphological diversity in Eciton and demonstrate the utility of our general approach. Future critical tests of this hypothesis are discussed, as well as how our approach can contribute to a broader understanding of the relationship between ecology and the evolution of worker morphological diversity.

Social insects are well-known for their ability to achieve robust collective behaviours even when individuals have limited information. It is often assumed that such behaviours rely on very large group sizes, but many insect colonies start out with only a few workers. Here we investigate the influence of colony size on collective decision-making in the house-hunting of the ant Temnothorax albipennis. In experiments where colony size was manipulated by splitting colonies, we show that worker number has an influence on the speed with which colonies discover new nest sites, but not on the time needed to make a decision (achieve a quorum threshold) or total emigration time. This occurred because split colonies adopted a lower quorum threshold, in fact they adopted the same threshold in proportion to their size as full-size colonies. This indicates that ants may be measuring relative quorum, i.e. population in the new nest relative to that of the old nest, rather than the absolute number. Experimentally reduced colonies also seemed to gain more from experience through repeated emigrations, as they could then reduce nest discovery times to those of larger colonies. In colonies of different sizes collected from the field, total emigration time was also not correlated with colony size. However, quorum threshold was not correlated with colony size, meaning that individuals in larger colonies adopted relatively lower quorum thresholds. Since this is a different result to that from size-manipulated colonies, it strongly suggests that the differences between natural small and large colonies were not caused by worker number alone. Individual ants may have adjusted their behaviour to their colony’s size, or other factors may correlate with colony size in the field. Our study thus shows the importance of experimentally manipulating colony size if the effect of worker number on the emergence of collective behaviour is to be studied.

Animals searching for food, mates, or a home often need to decide when to stop looking and choose the best option found so far. By re-analyzing experimental data from experiments by Mallon et al. (Behav Ecol Sociobiol 50:352–359, 2001), we demonstrate that house-hunting ant colonies are gradually more committed to new nests during the emigration. Early in house-hunting, individual ants were flexibly committed to new nest sites. However, when carrying to a new nest had started, ants hardly ever switched preference. Using a theoretical model based on experimental data, we test at which stage flexible commitment influences speed and accuracy most. We demonstrate that ant colonies have found a good compromise between impatience and procrastination. Early flexibility combined with later rigidity is identically effective as other strategies that include flexible commitment, but it is particularly good when emigration conditions are harsh.

11 pages; International audience; Information about food sources can be crucial to the success of a foraging animal. We predict that this will influence foraging decisions by group-living foragers, which may sacrifice short-term foraging efficiency to collect information more frequently. This result emerges from a model of a central-place forager that can potentially receive information on newly available superior food sources at the central place. Such foragers are expected to return early from food sources, even with just partial loads, if information about the presence of sufficiently valuable food sources is likely to become available. Returning with an incomplete load implies that the forager is at that point not achieving the maximum possible food delivery rate. However, such partial loading can be more than compensated for by an earlier exploitation of a superior food source. Our model does not assume cooperative foraging and could thus be used to investigate this effect for any social central-place forager. We illustrate the approach using numerical calculations for honeybees and leafcutter ants, which do forage cooperatively. For these examples, however, our results indicate that reducing load confers minimal benefits in terms of receiving information. Moreover, the hypothesis that foragers reduce load to give information more quickly (rather than to receive it) fits empirical data from social insects better. Thus, we can conclude that in these two cases of social-insect foraging, efficient distribution of information by successful foragers may be more important than efficient collection of information by unsuccessful ones.

Selfish gene and self-organisation approaches have revolutionised the study of social insects and have provided unparalleled insights into the highly sophisticated nature of insect social evolution. Here, we briefly review the core programs and interfaces with communication and recognition studies that characterise these fields today, and offer an interdisciplinary future perspective for the study of social insect evolutionary biology.

Colonies of the ant Temnothorax (formerly Leptothorax) albipennis can collectively choose the best of several nest sites, even when many of the active ants who organize the move visit only one site ...

The worker caste of polymorphic ant species consists of individuals of strikingly different morphologies. Most studies of polymorphic species have focused on intracolonial allometries and their association with division of labour and task performance of workers of different physical subcastes. However, the factors driving the evolution of these allometries are poorly understood. Here, we analyse the importance of life-style (hypogaeic vs intermediate vs epigaeic) as a factor in the evolution of allometries of functionally important body traits in Dorylus army ants in the context of an evolutionary scenario according to which a hypogaeic life-style is the ancestral state in this group. To this end, we conducted a detailed comparative analysis of the allometries of nine characters for ten species belonging to all six currently recognized subgenera and showing different life-styles. Eight of the nine traits under consideration show a clear increase in relative size from hypogaeic to intermediate to epigaeic life-style. These results strongly suggest that shifts in ecological niche are linked with adaptations in these traits. The degree of overall differentiation among species is more pronounced in larger than in smaller workers. The pattern of division of labour in the epigaeic D. molestus indicates that two factors that may have caused this phenomenon are new food habits and an increased need for colony defence.

Leptothorax ant colonies sort their brood in concentric annuli with the smallest items in the middle and the largest on the periphery. Such brood sorting is a prime example of collective structure formation by social insects. Its underlying mechanism, however, is still not understood. We tested the hypothesis that brood sorting has two phases: the phase of clustering, proposed earlier, is followed by a phase of spacing, when ants move brood items away in a random direction but in a type-specific way so that items of different brood types spread out to a different extent. We hypothesized that in phase 2, spacing, items of the smallest brood type spread out the least and end up in the centre, whereas items of the largest brood type spread out the most and end up on the periphery. We found two distinct phases in the direction of brood movement during brood sorting associated with nest emigration. In phase 1, ants moved brood items in the direction away from the nest entrance. This was the clustering phase. In phase 2, ants moved brood items in a random direction. This was the spacing phase. Ants moved smaller items for longer than larger items. This is consistent with the hypothesis that ants put down brood items as a function of their weight. The diffusion coefficient and the frequency of movement were different for different brood types. The measure of the average spread (root-mean-square displacement) for each brood type was consistent with their order from the centre to the periphery of the sorted brood structure. The process underlying this spread, however, could not be simple diffusion since the movements of different brood types are interdependent. We discuss the mechanisms that could underlie the switch between the two phases.

We considered how ant, Tapinoma simrothi, colonies dispose of the material generated by their nest excavations in nest entrance craters. We developed a model for optimum crater formation on both flat and sloping ground (although we have not solved it in full generality for sloping ground). We found that the ants, when working on flat ground, show a close approximation to this least costly waste disposal. Craters on slopes may not be optimal even though they will be cheaper to make than ones of a similar volume on level ground. We further tested the model with a manipulative experiment, which also suggested the simple rule of thumb that ants might use. In response to having one-quarter of their crater removed, the ants focused most of their further waste disposal in that quarter. This suggests that their rule of thumb may be to deposit material at the nearest point with an angle of elevation less than that of the optimal angle. This should generate symmetrical craters on flat ground. The model also makes certain additional and testable predictions about the fine structure of craters.

A high-quality home can be a major factor determining fitness. However, when house hunting becomes necessary, animals might often face a speed-versus-accuracy trade-off and therefore be unable to survey their environment extensively for the optimum site. We found that the ant Leptothorax albipennis was able to correct errors made in such a hurried decision by continuing to survey even after a colony had settled in a nest site. Colonies moved from intact undisturbed nests to another nest site whenever the new nest site presented a sufficient improvement in nest quality. Thus, scout ants must be able to judge and compare the quality of the new, empty nest site with the one currently inhabited by the colony. Emigrations from intact nests were initiated by high numbers of ants recruited by tandem runs. This evidence may explain how a small number of scouts can motivate an entire colony to move when there is no immediate need to do so. Compared with their behaviour in emigrations from destroyed nests, the ants favoured even more strongly accuracy over speed, because they waited for a larger number of scouts to agree on one site before starting the emigration. They could do this without increased risk because the rest of the colony remained safely in the old nest.

We tested the decision-making abilities of emigrating ant colonies. The colonies had to choose a new nest site when presented with two or more potential nest sites, each with different attributes or different combinations of attributes. For Leptothorax albipennis colonies in the laboratory, darkness of the nest cavity, internal height of the cavity and width of the entrance were all important attributes. The colonies ranked these attributes: darkness of the nest site was more important than internal cavity height, which in turn was more important than entrance width. These choices conform to the logic of transitivity. In addition, the colonies used a sophisticated decision-making strategy in which they took all alternatives and all attributes into consideration. Furthermore, the ants, in effect, weighed the different values of different attributes. They also chose the best nest when presented with only one excellent nest among four mediocre ones or one excellent nest in an array of one excellent, one good and one mediocre. Altogether, our results suggest that these ant colonies, in deciding upon a new home, used a weighted additive strategy, one of the most computationally expensive and thorough decision-making strategies. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.