A fungus infected environment does not alter the behaviour of foraging ants

Eusocial insects are exposed to a wide range of pathogens while foraging outside their nest. We know that opportunistic scavenging ants are able to assess the sanitary state of food and to discriminate a prey which died from infection by the entomopathogenic fungus Metarhizium brunneum. Here, we investigate whether a contamination of the environment can also influence the behaviour of foragers, both at the individual and collective level. In a Y-maze, Myrmica rubra ants had the choice to forage on two prey patches, one of which containing sporulating items. Unexpectedly, the nearby presence of sporulating bodies did not deter foragers nor prevent them from retrieving palatable prey. Ant colonies exploited both prey patches equally, without further mortality resulting from foraging on the contaminated area. Thus, a contamination of the environment did not prompt an active avoidance by foragers of which the activity depended primarily on the food characteristics. Generalist entomopathogenic fungi such as M. brunneum in the area around the nest appear more to be of a nuisance to ant foragers than a major selective force driving them to adopt avoidance strategies. We discuss the cost–benefit balance derived from the fine-tuning of strategies of pathogen avoidance in ants.

Migration and foraging strategies at varying spatial scales in western North Atlantic right whales: a review of hypotheses

Western North Atlantic right whales (Eubalaena glacialis) utilise several important foraging habitats off the northeastern United States andeastern Canada, where they feed on dense patches of zooplankton. At a fundamental level, a right whale’s optimal strategy should be tolocate and exploit the prey patches with the highest net energetic return from foraging. There remain many questions, however, concerningtheir migration and foraging strategies and the environmental cues and sensory modalities involved in migration and foraging, all of whichare likely to vary at different spatial scales. For example, a right whale most likely uses different mechanisms and strategies for locationof primary feeding grounds than those used for detection of optimum prey patches within a feeding area. This paper proposes a multi-scaled,hierarchical, conceptual model of right whale migratory and foraging strategies and presents a variety of hypotheses concerning themechanisms involved. Right whales may return to the general area of their feeding grounds based on prior experience. The locations ofsuccessful foraging in the immediately preceding years are likely to be re-visited, as are habitats to which an animal was exposed whileaccompanying its mother during its first year of life. It is also possible that the whales utilise large- or medium-scale environmental cues,such as currents, temperature discontinuities, or salinity signals indicating coastal plumes, to locate likely areas of high zooplankton patchdensity. Whilst on their feeding grounds, right whales tend to be aggregated, but there are usually outliers which may represent occasionalexcursions in search of other prey patches, though there is currently no evidence to address whether they communicate information aboutprey to other individuals. Their behaviour whilst actively feeding indicates that they can detect differences in patch density and adjust theirbehaviour accordingly. A likely sensory mechanism for quantification of patch density and triggering of feeding behaviour would be thevibrissae around the anterior opening of the mouth.

Multiple-stage decisions in a marine central-place forager

Air-breathing marine animals face a complex set of physical challenges associated with diving that affect the decisions of how to optimize feeding. Baleen whales (Mysticeti) have evolved bulk-filter feeding mechanisms to efficiently feed on dense prey patches. Baleen whales are central place foragers where oxygen at the surface represents the central place and depth acts as the distance to prey. Although hypothesized that baleen whales will target the densest prey patches anywhere in the water column, how depth and density interact to influence foraging behaviour is poorly understood. We used multi-sensor archival tags and active acoustics to quantify Antarctic humpback whale foraging behaviour relative to prey. Our analyses reveal multi-stage foraging decisions driven by both krill depth and density. During daylight hours when whales did not feed, krill were found in deep high-density patches. As krill migrated vertically into larger and less dense patches near the surface, whales began to forage. During foraging bouts, we found that feeding rates (number of feeding lunges per hour) were greatest when prey was shallowest, and feeding rates decreased with increasing dive depth. This strategy is consistent with previous models of how air-breathing diving animals optimize foraging efficiency. Thus, humpback whales forage mainly when prey is more broadly distributed and shallower, presumably to minimize diving and searching costs and to increase feeding rates overall and thus foraging efficiency. Using direct measurements of feeding behaviour from animal-borne tags and prey availability from echosounders, our study demonstrates a multi-stage foraging process in a central place forager that we suggest acts to optimize overall efficiency by maximizing net energy gain over time. These data reveal a previously unrecognized level of complexity in predator–prey interactions and underscores the need to simultaneously measure prey distribution in marine central place forager studies.