Foraging activity of leaf-cutter ants is affected by barometric pressure

Among all activities displayed by ant colonies, searching for food is essential for all individuals survival. However, many external activities are hazardous or restrictive for the entire society. Even though leaf-cutter ants are highly successful insects, they are subject to extreme aspects of foraging, as raindrops and wind. Although recruitment and food exploitation are known to change with temperature and humidity, barometric pressure changes and how they affect ant behavior remain unknown. We aimed to determine how an increase or decrease in barometric pressure might modify foraging strategies of the leaf-cutter ant Atta sexdens compared to steady pressure. The first modification observed in the workers behavior was the scouts greater promptness in leaving the nest when the barometric pressure decreased. Regard to the foragers, there was no difference in the number of individuals recruited for collecting leaves. However, it was cut and brought into the nest 1.5 and 2 times more leaves during the pressure drop, respectively. The reason for this foraging efficiency as a whole was ultimately the sum of the efficiency of each forager. The shifts in behavior, therefore, could be related to the indirect consequences of a pressure decrease, such as rainfall and strong winds, both strong constraints on ants on a trail. This is the first report of barometric pressure affecting the behavior of a social insect under controlled conditions.     

The nutritional consequences of rejecting food in the Ituri Forest of Zaire

Based on a representative sample of 449 different individuals, food avoidances are shown to be nutritionally insignificant on average for a population of horticulturalists and foragers living in the Ituri Forest of northeastern Zaire. However, due to variability in food-related beliefs, nutritional costs may be biologically significant for a few individuals. Less than 2% of potential dietary calories are restricted to horticulturalists on average due to food avoidances, while less than 1% is the average cost of these beliefs among foragers. When nutritional costs are calculated from reported avoidance rules rather than consumption practice, estimated costs are significantly inflated. These lower actual costs arise because individuals make use of rules that permit them to eat otherwise restricted foods. For example, eating specific plants is believed to prevent the illness that would otherwise follow the consumption of a tabooed food. Use of such exception rules significantly reduces the nutritional cost of food avoidances for many individuals in this population.     

Relationships between densities of previous and simultaneous foragers and the foraging behaviour of three bumblebee species

1. The local insect composition may be as important as the local floral composition for bumblebees' foraging behaviour. However, little is known about how the local abundance of insects affects the foraging patterns of individuals. 2. Using field observations, we studied the relationships between the local density of previous and simultaneous foragers and the local foraging behaviour of Bombus pascuorum, Bombus lucorum/B. terrestris and Bombus lapidarius while pollinating Centaurea jacea. 3. The number of bumblebees foraging in the plots was positively related to the number of new individuals arriving at these plots. The number of inflorescences contacted and the duration of visits were negatively related to the number of simultaneous foragers, but only in B. lucorum/B. terrestris. The effects of previous foragers on the behaviour of other bumblebees were species‐specific and variable in their direction. Such contrasting effects can be explained in terms of bumblebee species' abundances and functional similarity. In some cases, the effect of previous foragers increased with Centaurea density. 4. The local abundance of previous and simultaneous foragers affected the foraging behaviour of particular bumblebee individuals in complex ways. Future studies on local foraging behaviour might benefit from including the abundance of co‐foragers.     

Scramble or contest competition over food in solitarily foraging mouse lemurs (Microcebus spp.): New insights from stable isotopes

The relationships between resource distribution, type of competition, and consequences for social organization have been formalized in the socioecological model (SEM) which predicts that ecological factors are the main determinants of female distribution. We tested this basic prediction in two solitary primates (Microcebus berthae and M. murinus) which differ in female association patterns. Using stable nitrogen and carbon isotope data of hair samples and food sources we quantified inter‐specific differences in diet. δ¹³C in M. berthae reflected a diet composed mainly of insect secretions. Higher within‐species as well as seasonal variation in δ¹³C of M. murinus indicated a wider trophic niche including plant and animal source food. Constantly elevated δ¹⁵N in M. murinus most likely reflected extended torpor during the lean season. This energy‐saving strategy together with a wider, more opportunistic feeding niche might reduce female competition in this species, facilitating smaller female ranges, and a higher association potential. In contrast, δ¹⁵N fluctuated seasonally in M. berthae, most likely indicating varying amounts of arthropod food in the diet. Intense scramble competition over small and seasonally limited resources might lead to female spatial avoidance and a reduced association potential in M. berthae. Thus, differences in female association patterns between these two solitary foragers are due to different types of competition and overall intensities of intra‐specific competition. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Testing predictions of foraging theory for a sit-and-wait forager, Anolis gingivinus

Research in foraging theory has been dominated by studies ofactive foragers choosing among patches and among prey withina patch. Studies of central-place foraging have mainly focusedon loading decisions of an animal provisioning a central place.The problem faced by a sit-and-wait forager that encountersprey at a distance has received little attention. In this studywe tested foraging theory predictions for such foragers, Anolisgingivinus females in the West Indies island of Anguilla. Wepresented lizards with antlion larvae at various distances.Experiment 1 showed that an individual's probability of pursuingprey decreases with the prey's distance and is best describedby a sigmoidal function (which may be as steep as a step function).This function's inflection point defines a cutoff distance.Experiment 3 tested how cutoff distance changes as a functionof prey size. Cutoff distances were greater for larger prey,as predicted for an energy-maximizing forager. Experiments 2and 4 tested how cutoff distance changes as a function of preyabundance. As predicted, cutoff distance were greater at a sitewhere prey abundance was lower. Furthermore, cutoff distancesdecreased immediately following prey augmentation and returnedto previous values within one day of ending augmentation. Thus,moles' foraging behavior is a dynamic process, consistent withthe qualitative predictions of foraging theory. We attributethe success of this study in supporting fundamental foragingtheory predictions to the lizards exhibiting natural behaviorunder field conditions and to particular advantages of studyingsit-and-wait foragers.     

Correlation between octopaminergic signalling and foraging task specialisation in honeybees

Regulation of pollen and nectar foraging in honeybees is linked to differences in the sensitivity to the reward. Octopamine (OA) participates in the processing of reward-related information in the bee brain, being a candidate to mediate and modulate the division of labour among pollen and nectar foragers. Here we tested the hypothesis that OA affects the resource preferences of foragers. We first investigated whether oral administration of OA is involved in the transition from nectar to pollen foraging. We quantified the percentage of OA-treated bees that switched from a sucrose solution to a pollen feeder when the sugar concentration was decreased experimentally. We also evaluated if feeding the colonies sucrose solution containing OA increases the rate of bees collecting pollen. Finally, we quantified OA and tyramine (TYR) receptor genes expression of pollen and nectar foragers in different parts of the brain, as a putative mechanism that affects the decision-making process regarding the resource type collected. Adding OA in the food modified the probability that foragers switch from nectar to pollen collection. The proportion of pollen foragers also increased after feeding colonies with OA-containing food. Furthermore, the expression level of the AmoctαR1 was upregulated in foragers arriving at pollen sources compared with those arriving at sugar-water feeders. Using age-matched pollen and nectar foragers that returned to the hive, we detected an upregulated expression of a TYR receptor gene in the suboesophageal ganglia. These findings support our prediction that OA signalling affects the decision in honeybee foragers to collect pollen or nectar.     

Human consumption of large herbivore digesta and its implications for foraging theory

Vegetal matter undergoing digestion in herbivores' stomachs and intestines, digesta, can be an important source of dietary carbohydrates for human foragers. Digesta significantly increases large herbivores' total caloric yield and broadens their nutritional profile to include three key macronutrients (protein, fat, and carbohydrates) in amounts sufficient to sustain small foraging groups for multiple days without supplementation. Ethnographic reports of routine digesta consumption are limited to high latitudes, but the practice may have had a wider distribution prehistorically. Including this underappreciated resource in our foraging hypotheses and models can substantively change their predictions. Assessing the explanatory power of kilocalorie-centered models relative to ones that attend to humans' other nutritional requirements can help us better address major questions in evolutionary anthropology. This paper explores the foraging implications of digesta in two contexts—sex-divided subsistence labor and archaeologically observed increases in plant use and sedentism—using estimates of available protein and carbohydrates in the native tissues and digesta, respectively, of a large ruminant herbivore (Bison bison).     

The adaptive value of inactive foragers and the scout-recruit system in honey bee (Apis mellifera) colonies

In honey bee (Apis mellifera) colonies, scouts search for productiveforage sites and then recruit other workers to those locations using a waggle dance. A simple and tractable mathematical modelof the honey bee scout-recruit system was developed to studythe relationship between nectar availability, the efficiencyof the honey bee's recruitment system, and the optimal proportionof scouts that maximizes net gain (benefit - cost), or, energeticefficiency (benefit/cost - 1). The models consider both the energetic costs and benefits of active scouts and recruits aswell as the cost of an inactive forager reserve. They predictconditions when individual foraging is favored over the honeybee's recruitment system, when the colony should abandon foragingaltogether, and the optimal proportion of scouts (when thescout-recruit system is favored). The models' predictions qualitatively match empirical data. Surprisingly, previous empirical datafrom the honey bee suggest that recruits' costs are greaterthan scouts'—recruits spend significantly longer searchingfor a forage patch than do scouts—thereby causing researchersto rethink how the scout-recruit system might be adaptive. Using average returns, the models demonstrate how the scout-recruitsystem is adaptive despite these apparent higher recruit costsrelative to the scouts'. A sensitivity analysis demonstratesthat the results are robust to a broad range of relative costsof active workers, inactive workers, and the energetic benefitsof the forage. Consequently, the model is demonstrated to berelevant to many insect societies that employ a scout-recruitsystem.