Swarms of swift scavengers: ecological role of marine intertidal hermit crabs in California

This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s00227-015-2639-3While marine hermit crabs are well known for being omnivorous filter feeders, less is known about the role they may play as active carrion scavengers in intertidal ecosystems. Prior studies have revealed that intertidal hermit crabs can be attracted to chemical cues from predated gastropods. Yet their attraction is usually assumed to be driven primarily by the availability of new shells rather than by food. We conducted field experiments to assess hermit crabs’ potential role as generalist carrion scavengers on the California Coast, examining their speed of attraction and the size of the aggregations they formed in response to chemical cues from freshly smashed gastropods and mussels, both of which indicated available carrion. Compared to all other marine species, hermit crabs (Pagurus samuelis, P. hirsutiusculus, and P. granosimanus) were the fastest to arrive at the provisioning sites. Hermit crabs also dominated the provisioning sites, accumulating in the largest numbers, with aggregations of up to 20 individuals, which outcompeted all other scavengers for carrion. Notably, hermit crabs arrived equally quickly for both smashed gastropod and mussel, even though the latter does not offer suitable shells for hermit crabs and even though the former only yields shell-related chemical cues over time frames longer than our experiments. These results thus suggest that shell availability is not the only, or even the primary, reason marine intertidal hermit crabs aggregate at carrion sites; they also aggregate to forage, thereby playing an important role as active carrion scavengers in intertidal ecosystems.Research was supported by funding from the Miller Institute at Berkeley to M.L

Meaningful Gesture in Monkeys? Investigating whether Mandrills Create Social Culture

BACKGROUND: Human societies exhibit a rich array of gestures with cultural origins. Often these gestures are found exclusively in local populations, where their meaning has been crafted by a community into a shared convention. In nonhuman primates like African monkeys, little evidence exists for such culturally-conventionalized gestures. METHODOLOGY/PRINCIPAL FINDINGS: Here I report a striking gesture unique to a single community of mandrills (Mandrillus sphinx) among nineteen studied across North America, Africa, and Europe. The gesture was found within a community of 23 mandrills where individuals old and young, female and male covered their eyes with their hands for periods which could exceed 30 min, often while simultaneously raising their elbow prominently into the air. This 'Eye covering' gesture has been performed within the community for a decade, enduring deaths, removals, and births, and it persists into the present. Differential responses to Eye covering versus controls suggested that the gesture might have a locally-respected meaning, potentially functioning over a distance to inhibit interruptions as a 'do not disturb' sign operates. CONCLUSIONS/SIGNIFICANCE: The creation of this gesture by monkeys suggests that the ability to cultivate shared meanings using novel manual acts may be distributed more broadly beyond the human species. Although logistically difficult with primates, the translocation of gesturers between communities remains critical to experimentally establishing the possible cultural origin and transmission of nonhuman gestures

Food fights: aggregations of marine hermit crabs (<I>Pagurus samuelis</I>) compete equally for food- and shell-related carrion

This is the author accepted manuscript. The final version is available from Rosenstiel School of Marine & Atmospheric Science at http://dx.doi.org/10.5343/bms.2015.1054.Competition for limiting resources drives animal aggression. Aggression in hermit crabs has been well studied in shell acquisition circumstances, yet less is known about hermit crabs' competitive behavior in other contexts, especially as they relate to feeding. As active foragers, competition for food resources may be a major determinant of hermit crab aggression and fighting behavior, particularly in intertidal marine environments, where protein-rich carrion may be limiting. Here, we measured aggressive, competitive interactions between hermit crabs [Pagurus samuelis (Stimpson, 1857)] that were presented with carrion in the laboratory, immediately after they were collected from the field. Aggregations of three crabs were provided with either mussel or gastropod flesh. Both forms of carrion naturally indicate food availability, though only the latter may correlate with potential shell availability. We found that levels of aggression rose significantly in response to both carrion conditions, but not in response to a control condition involving the introduction of a non-eatable object. Larger individuals displayed the highest levels of aggressive behavior, but levels of aggression did not differ between crabs provided with the gastropod and the mussel flesh. These results reveal that food—independent of a shell resource—can be a powerful motivator for competitive behavior in hermit crabs. Further studies of food-related aggression between different hermit crab species could shed light on how interspecific competition might lead to potential specializations on different carrion or prey resources.Research was supported by funding from the Miller Institute at Berkeley to M.L

Which States Matter? An Application of an Intelligent Discretization Method to Solve a Continuous POMDP in Conservation Biology

When managing populations of threatened species, conservation managers seek to make the best conservation decisions to avoid extinction. Making the best decision is difficult because the true population size and the effects of management are uncertain. Managers must allocate limited resources between actively protecting the species and monitoring. Resources spent on monitoring reduce expenditure on management that could be used to directly improve species persistence. However monitoring may prevent sub-optimal management actions being taken as a result of observation error. Partially observable Markov decision processes (POMDPs) can optimize management for populations with partial detectability, but the solution methods can only be applied when there are few discrete states. We use the Continuous U-Tree (CU-Tree) algorithm to discretely represent a continuous state space by using only the states that are necessary to maintain an optimal management policy. We exploit the compact discretization created by CU-Tree to solve a POMDP on the original continuous state space. We apply our method to a population of sea otters and explore the trade-off between allocating resources to management and monitoring. We show that accurately discovering the population size is less important than management for the long term survival of our otter population

Scent of death_Ecology and Evolution_all raw Excel data (uploaded 2018-12-28 to Dryad)

All data for both experiments in the paper (Experiments 1 and 2)

Data from: Scent of death: evolution from sea to land of an extreme collective attraction to conspecific death

All living organisms must eventually die, though in some cases their death can bring life-giving opportunities. Few studies, however, have experimentally tested how animals capitalize on conspecific death and why this specialization would evolve. Here we conducted experiments on the phylogenetically most closely-related marine and terrestrial hermit crabs to investigate the evolution of responses to death during the sea-to-land transition. In the sea, death of both conspecifics and heterospecifics generates unremodeled shells needed by marine hermit crabs. In contrast, on land, terrestrial hermit crabs are specialized to live in architecturally remodeled shells, and the sole opportunity to acquire these essential resources is conspecific death. We experimentally tested these different species’ responsiveness to the scent of conspecific versus heterospecific death, predicting that conspecific death would have special attractive value for the terrestrial species. We found the terrestrial species was overwhelmingly attracted to conspecific death, rapidly approaching and forming social groupings around conspecific death sites that dwarfed those around heterospecific death sites. This differential responsiveness to conspecific versus heterospecific death was absent in marine species. Our results thus reveal that on land a reliance on resources associated exclusively with conspecifics has favored the evolution of an extreme collective attraction to conspecific death