Patch Choice Research Articles

Shellfish Gathering and Conservation on Low Coral Islands: Kiribati Perspectives

ABSTRACTLow coral island societies in the Pacific have always lived in a precarious environment. Consequently, some writers have stated that people living on atolls and table reefs must have devised effective conservation strategies. Predictions from three optimal foraging models in ethnographic contexts (patch choice, patch sampling, and risk) applied to shellfish gathering in Kiribati, Micronesia, do not support the assumption that human foragers are motivated by a desire to conserve resources. While historical ecology data are sparse, there is little to indicate that coral islanders in the past needed to practice conservation of marine resources, including shellfish.

Logging‐induced changes in habitat network connectivity shape behavioral interactions in the wolf–caribou–moose system

Habitat connectivity influences the distribution dynamics of animals. Connectivity can therefore shape trophic interactions, but little empirical evidence is available, especially for large mammals. In forest ecosystems, logging alters functional connectivity among habitat patches, and such activities can affect the spatial game between large herbivores and their predators. We used graph theory to evaluate how harvesting‐induced changes in habitat connectivity influence patch choice and residency time of GPS‐collared caribou (Rangifer tarandus caribou) and moose (Alces alces) in winter in the boreal forest. We then investigated the predator–prey game by assessing how GPS‐collared wolves (Canis lupus) adjusted their movements to changes in landscape properties and in the networks of their prey species. We built prey habitat networks using minimum planar graphs organized around species‐specific, highly selected habitat patches (i.e., network nodes). We found that spatial dynamics of large herbivores were influenced not only by the intrinsic quality of habitat patches, but also by the connectivity of those network nodes. Caribou and moose selected nodes that were connected by a high number of links, and moose also spent relatively more time in those nodes. By limiting node accessibility, human disturbances influenced travel decisions. Caribou and moose avoided nodes that were surrounded by a high proportion of cuts and roads, but once within these nodes, moose stayed longer than in other nodes. Caribou selectively moved among nodes with low distance costs, and their residency time increased with distance costs required to reach the nodes. Wolves selected their prey's nodes, where vegetation consumed by caribou and moose was highly abundant. Furthermore, wolves discriminated among those nodes by selecting the most connected ones. In fact, selection by wolves was stronger for their prey's nodes than for the prey's utilization distribution per se, a difference that increased with the level of human disturbance. Considering the difficulty of keeping track of highly mobile prey, predators may benefit by targeting not only their prey's resource patches, but also the most highly connected patches. Matrix quality and connectivity are therefore key elements shaping the predator–prey spatial game in human‐altered landscapes because of their impact on the spatial dynamics of the interacting species.

Small-scale bee patch use is affected equally by flower availability and local habitat configuration

Bee foraging is complex and observed patterns often deviate from predictions. Much of this deviation can be explained through differences in the characteristics of the flower patch, but not all. We suggest that the position of the flower patch within the landscape can have strong effects on bee patch use, independent of the characteristics of the flower patch, through changes in access to nesting resources and the microclimate. Further, the effects of different habitat configurations are likely to vary among bee groups, depending on flight distances and resource requirements. We surveyed local habitat and plant community characteristics around 100 observation plots in native grassland within temperate savannah and recorded bee patch use by direct observation. Using structural equation modeling, we quantified the direct and indirect effect of plant community and habitat configuration on patch use for all bees, only bumblebees, and only non-bumblebees. Our models explained nearly 50% of the variation in bee patch use, with equal importance assigned to local habitat configuration and the plant community. Flower abundance was the best indicator of patch use, followed by distance to forest edge, site productivity and proportion forest cover. Contrary to previous findings, flower diversity had weak, yet negative effects on patch use after accounting for covariance with other factors. Although all bees most frequently visited plots with high flower densities, bumblebees preferentially used edge habitats, while non-bumblebees were mostly found in productive grassland areas with access to forest habitat. Our results show that small-scale habitat configuration can have direct effects on bee patch use as strong as or stronger than those of the flower patch itself. Further, the exact habitat configuration that drives bee patch choices is likely to vary among groups. This suggests that habitat configuration should be considered in bee conservation efforts.

Male and female voles do not differ in their assessments of predation risk

A forager's willingness to trade off safety for food varies with its energetic state. Animals in a low energetic state should accept higher risk than animals with larger energy reserves. In mammals, energy expenditure by females on gestation and lactation may exceed the relatively low cost of sperm production by males. It follows, if reproductive costs are indeed higher for females than for males, that reproductive females may be more likely than males to trade safety for food. Thus, we evaluated the use of safe versus risky foraging patches by male and female meadow voles using putatively safe and risky habitats. We also used behavioural trials to assess whether sexual differences in personality could account for any differences in patch use. Voles preferred to forage in safe patches over risky ones. There was no difference between male and female voles, or between reproductive and non-reproductive individuals, in their respective use of safe versus risky foraging patches. Personality also had no effect on patch choice. The results are consistent with recent studies on other species that have failed to find differences in reproductive costs between the sexes. Experiments on foraging behaviour might thus provide simple and repeatable tests for sexual differences and similarities in reproductive costs.

Pelagic movements of pacific leatherback turtles (dermochelys coriacea) highlight the role of prey and ocean currents

Leatherback turtles are renowned for their trans-oceanic migrations. However, despite numerous movement studies, the precise drivers of movement patterns in leatherbacks remain elusive. Many previous studies of leatherback turtles as well as other diving marine predators have analyzed surface movement patterns using only surface covariates. Since turtles and other marine predators spend the vast majority of their time diving under water, an analysis of movement patterns at depth should yield insight into what drives their movements. We analyzed the movement paths of 15 post-nesting adult female Pacific leatherback turtles, which were caught and tagged on three nesting beaches in Mexico. The temporal length of the tracks ranged from 32 to 436 days, and the spatial distance covered ranged from 1,532 km to 13,097 km. We analyzed these tracks using a movement model designed to yield inference on the parameters driving movement. Because the telemetry data included diving depths, we extended an earlier version of the model that examined surface only movements, and here analyze movements in 3-dimensions. We tested the effect of dynamic environmental covariates from a coupled biophysical oceanographic model on patch choice in diving leatherback turtles, and compared the effects of parameters measured at the surface and at depth. The covariates included distance to future patch, temperature, salinity, meridional current velocity (current in the north–south direction), zonal current velocity (current in the east–west direction), phytoplankton density, diatom density, micro-plankton density, and meso-zooplankton density. We found significant, i.e. non-zero, correlation between movement and the parameters for oceanic covariates in 8 of the tracks. Of particular note, for one turtle we observed a lack of correlation between movements and a modeled index of zooplankton at the surface, but a significant correlation between movements and zooplankton at depth. Two of the turtles express a preference for patches at depth with elevated diatoms, and 2 turtles prefer patches with higher mezozooplankton values at depth. In contrast, 4 turtles expressed a preference for elevated zooplankton patches at the surface, but not at depth. We suggest that our understanding of a marine predator’s response to the environment may change significantly depending upon the analytical frame of reference, i.e. whether relationships are examined at the surface, at depth, or at different temporal resolutions. Lastly, we tested the effects of accounting for ocean currents on the movement patterns and found that for 13 of the 15 turtles, the parameter governing distance to the next patch decreased. Our results suggest that relationships derived from the analysis of surface tracks may not entirely explain movement patterns of this highly migratory species. Accounting for choices in the water column has shown that for certain individual turtles, what appears to be favourable habitat at depth is quantitatively different from that at the surface. This has implications for the analysis of the movements and diving behaviour of any top marine predator. The leatherback turtle is a deep diving reptile, and it is important to understand the subsurface variables that influence their movements if we are to precisely map the spatial dimensions of favorable leatherback habitat. These results present a new view into the drivers of diving patterns in turtles, and in particular represent a way of analyzing movements at depth that can be extended to other diving species.

Foraging Patch Selection in Winter: A Balance between Predation Risk and Thermoregulation Benefit

In winter, foraging activity is intended to optimize food search while minimizing both thermoregulation costs and predation risk. Here we quantify the relative importance of thermoregulation and predation in foraging patch selection of woodland birds wintering in a Mediterranean montane forest. Specifically, we account for thermoregulation benefits related to temperature, and predation risk associated with both illumination of the feeding patch and distance to the nearest refuge provided by vegetation. We measured the amount of time that 38 marked individual birds belonging to five small passerine species spent foraging at artificial feeders. Feeders were located in forest patches that vary in distance to protective cover and exposure to sun radiation; temperature and illumination were registered locally by data loggers. Our results support the influence of both thermoregulation benefits and predation costs on feeding patch choice. The influence of distance to refuge (negative relationship) was nearly three times higher than that of temperature (positive relationship) in determining total foraging time spent at a patch. Light intensity had a negligible and no significant effect. This pattern was generalizable among species and individuals within species, and highlights the preponderance of latent predation risk over thermoregulation benefits on foraging decisions of birds wintering in temperate Mediterranean forests.

Paleoindian technological provisioning strategies in the northwestern Great Basin

Great Basin populations during the Pleistocene–Holocene Transition (PHT) are often characterized as being mobile and focused on wetlands; however, the factors that influenced where Paleoindians selected residential campsites are poorly understood. Using predictions derived from optimal foraging-based patch choice models and GIS reconstructions of the PHT landscape, some researchers have argued that occupations in smaller wetlands should have been shorter than occupations in larger wetlands but such arguments have rarely been evaluated using empirical data. The PHT lithic record provides an opportunity to evaluate the relationship between wetland size and occupation span by applying Kuhn's (1995) concept of technological provisioning. Kuhn expects more mobile populations to provision individuals and more sedentary populations to provision places and suggests that: (1) a strategy of provisioning individuals should be reflected by a high proportion of more extensively used artifacts made on non-local raw materials; and (2) a strategy of provisioning places should be reflected by a high proportion of less extensively used artifacts made on local raw materials. We apply the technological provisioning concept to lithic assemblages from two of the Parman localities, extensive PHT sites in the northwestern Great Basin, and compare local and nonlocal artifacts to determine if Paleoindians shifted from provisioning individuals while moving to/from the sites to provisioning the place while occupying them. There is no relationship between artifact transport distance and artifact use intensity. We interpret these findings as evidence that Paleoindians did not alter their provisioning strategies while occupying the Parman localities, likely because occupations were brief within a small wetland poorly-suited to support groups for long periods.

The learning mechanism underlying public information use in ninespine sticklebacks (Pungitius pungitius).

Elucidating the mechanisms by which animals learn from others is central to understanding the evolution of behavioral adaptations and the constraints that limit options when gathering information about the environment. Here we present findings from three experiments that investigated the psychological mechanisms underlying public-information use in ninespine sticklebacks (Pungitius pungitius). Using a prey patch choice assay we compared two candidate processes, local enhancement and stimulus enhancement. These experiments revealed (a) that fish only selected socially demonstrated prey patches via local enhancement, (b) that even in the absence of any confounding influence of local enhancement there was no evidence for stimulus enhancement in patch choice, and (c) sensitization rather than associative learning underlies the observed public information use. Our findings suggest that local and stimulus enhancement are distinct processes, and that local enhancement is not merely a subcategory of stimulus enhancement, as has previously been argued in the literature. We offer several reasons why learning via stimulus enhancement may not have arisen in ninespine sticklebacks, and speculate that the evolution of this learning mechanism may be favored by specific properties of social structure.

Towards an anomaly-free quantum dynamics for a weak coupling limit of Euclidean gravity: Diffeomorphism covariance

The G-->0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)xU(1)xU(1) gauge theory. In an earlier paper, Tomlin and Varadarajan constructed the quantum Hamiltonian constraint of density weight 4/3 for this U(1)xU(1)xU(1) theory so as to produce a non-trivial anomaly free LQG-type representation of the Poisson bracket between a pair of Hamiltonian constraints. These constructions involved a choice of regulating coordinate patches. The use of these coordinate patches is in apparent conflict with spatial diffeomorphism covariance. In this work we show how an appropriate choice of coordinate patches together with suitable modifications of these constructions results in the diffeomorphism covariance of the continuum limit action of the Hamiltonian constraint operator, while preserving the anomaly free property of the continuum limit action of its commutator.

Adult fruit fly attraction to larvae biases experience and mediates social learning

We investigated whether adult fruit flies (Drosophila melanogaster) use cues of larvae as social information in their food patch choice decisions. Adult male and female fruit flies showed attraction to odours emanating from foraging larvae, and females preferred to lay eggs on food patches occupied by larvae over similar unoccupied patches. Females learned and subsequently preferred to lay eggs at patches with novel flavours previously associated with feeding larvae over patches with novel flavours previously associated with no larvae. However, when we controlled for the duration of exposure to each flavoured patch, females no longer preferred the flavour previously associated with feeding larvae. This suggests that social learning in this context is indirect, as a result of strong social attraction biasing experience.

Limited feeding on bacteria by two intertidal benthic copepod species as revealed by trophic biomarkers

Harpacticoids can discriminate between biofilms of different bacterial strains. We investigated whether assimilation of bacteria is selective and whether harpacticoids select for the most nutritional bacteria. We specifically focused on the role of bacterial characteristics in copepod food selection. Trophic biomarkers (stable isotopes, fatty acids) were used to test selective assimilation of three bacteria by the harpacticoids Platychelipus littoralis and Delavalia palustris, all isolated from a salt marsh. The bacteria Gramella sp., Jannaschia sp. and Photobacterium sp. with contrasting ribosomal protein and fatty acid contents were (13)C-labelled and offered in a food patch choice experiment with monospecific and combination treatments (single and two strains per microcosm respectively). Low assimilation of bacterial carbon and lack of significant fatty acid transfer proved that bacteria were a poor food source for the harpacticoids. Assimilation was copepod species-specific and bacteria strain-specific (preference for Photobacterium). However, only a low degree of selective feeding occurred; it can partly be explained by bacterial extracellular metabolites rather than by biochemical content and densities. Finally, the energetic cost of differential bacterivory resulted in a negative fatty acid balance for Platychelipus, while Delavalia showed an improved fatty acid profile and thus a positive response to the low-quality bacterial food.

Hierarchical patch choice by an insectivorous bat through prey availability components

Food availability does not only refer to the abundance of edible items; accessibility and detectability of food are also essential components of the availability concept. Constraints imposed by a habitat’s physical structure on the accessibility and detectability of food have been seldom treated simultaneously to the abundance of prey at the foraging patch level in observational studies. We designed a research that allowed decoupling the effects of microhabitat structure and prey abundance on foraging patch selection of the trawling insectivorous long-fingered bat (Myotis capaccinii). The use of different patches of river was surveyed by radiotelemetry during three periods of the bat’s annual cycle, and prey abundance was accordingly measured in and out of the hunting grounds of the tracked bats by insect traps emulating the species’ foraging. Bats preferentially used river stretches characterised by an open course and smooth water surfaces, i.e. they used the most suitable patches in terms of prey accessibility and detectability, respectively. In addition, prey abundance in the selected river stretches was higher than in others where bat activity was not recorded, although the latter also offered good access and prey detection possibilities. Bats also shifted foraging stretches seasonally, likely following the spatiotemporal dynamics of prey production over the watershed. We suggest that the decisions of bats during the patch choice process fitted a hierarchical sequence driven first by the species’ morphological specialisations and ability to hunt in unobstructed spaces, then by the detectability of prey on water surfaces and, finally, by the relative abundance of prey.

Cattle use protein as a currency in patch choice on tropical grass swards

Patch choice by large herbivores is a major impact on grasslands and has consequences to both animals and vegetation in grazing systems. Previous studies have performed controlled experiments using artificially created patches to approach the mechanisms by which herbivores choose and use vegetation patches. However, the number of patch types offered to animals and the method of patch creation are limited, compared with diverse patch structure of actual grasslands. Furthermore, patch choice on tropical grasslands and the effect of hunger on patch preference remain relatively unexplored. We conducted six experiments to examine the effects of external (vegetation quantity and quality) and internal (hunger) environments on patch choice by cattle (Bos taurus) on tropical grass (Paspalum notatum) swards. In each experiment, three cows were allowed to graze three plots in sequence after a fast. The plots comprised 16, 36 or 9 patches of 4, 6 or 9 types created by defoliation treatments alone or in combination with fertilizer treatments. Fertilized patches were richer in protein but similar in digestibility compared with non-fertilized ones. Animals always showed highest preference for a fertilizer-treated, protein-rich patch when fertilizer treatments were incorporated into patch preparation. Among dry matter, digestible dry matter (as a surrogate to digestible energy) and protein, the allocation of grazing time to patch types best matched the predicted potential intake on a protein basis. Results showed usefulness of fertilizer for better simulating patchy vegetation of grasslands and overcoming the difficulty in discriminating between digestibility and protein as a currency for patch choice. Facing quantitative and qualitative patchiness in vegetation, animals were sensitive to protein concentration in the diet and perceived protein intake as a currency for patch selection. As a response to the internal environment, animals traded forage quality for quantity with increasing levels of hunger.

Patch choice from a distance and use of habitat information during foraging by the parasitoid Ibalia leucospoides

1. In environments in which resources are distributed heterogeneously, patch choice and the length of time spent on a patch by foragers are subject to strong selective pressures. This is particularly true for parasitoids because their host foraging success translates directly into individual fitness.2. The aim of this study was to test whether: (i) females of the parasitoid Ibalia leucospoides (Hymenoptera: Ibaliidae) can discriminate among patches according to host numbers; (ii) the surrounding context affects the initial choice of patch, as well as time spent on patch; and (iii) the perceived quality of a given patch is affected by the quality of the surrounding patches.3. Each female was randomly exposed to one of three different three‐patch environments which differed in host number per patch, mean environment host number and host distribution among patches. For each treatment level, the first patch chosen and the time allocated to each patch visited by the female were recorded.4. Females of I. leucospoides were able to discriminate different levels of host numbers among patches from a distance. The patch bearing the highest number of hosts was, predominantly, the first choice. Patch host number in association with mean habitat profitability influenced the length of time spent on the first patch visited. By contrast, variance in habitat profitability did not influence time allocation decisions. Contrary to the study prediction, there were no significant habitat‐dependent time allocation differences among patches holding the same number of hosts.5. The results indicate that, for I. leucospoides, patch exploitation decisions are partially influenced by information obtained from the habitat as a whole, a behaviour that may prove to indicate adaptive ability in highly patchy environments, as well as suggesting the presence of good cognitive abilities in this parasitoid species.

Spatial and temporal predictions of moose winter distribution

Herbivores are usually distributed unevenly across the landscape often because of variation in resource availability. We used zero-inflated generalised additive models (to account for data with a high number of zeros) that include georeferences to predict winter distribution of a large herbivore (moose Alces alces). Moose distribution was analysed in relation to forage availability and distance to neighbouring sites. Our results showed that the ability to explain moose distribution indexed by pellet count data at a local scale increased when spatial information (longitude and latitude) was added to the model compared to the model only including food availability. By using the relationship between moose and forage distribution, and the spatial information, we predicted patch choice by moose reasonably well in 2 out of 4 years. However, the distribution of moose was also influenced by weather conditions, as it was most clumped in the year with most snow. In conclusion, our study lends support for a non-linear approach using georeferences for a comprehensive understanding of herbivore distribution at a small scale. This result also indicates that the use of a certain patch by moose not only depends on the selected patch itself but is also influenced by the neighbouring patch and factors at a larger spatial scale, such as moose management influencing the density above moose home range level. The relatively high proportion of unexplained variation suggests that the use of a certain patch is also influenced by other factors such as topography, predation, competition, weather conditions, and wildlife management strategies.

Testing the Ideal Free Distribution Hypothesis: Moose Response to Changes in Habitat Amount

According to the ideal free distribution hypothesis, the density of organisms is expected to remain constant across a range of habitat availability, provided that organisms are ideal, selecting habitat patches that maximize resource access, and free, implying no constraints associated with patch choice. The influence of the amount of habitat on moose (Alces alces) pellet group density as an index of moose occurrence was assessed within the Foothills Natural Region, Alberta, Canada, using a binary patch-matrix approach. Fecal pellet density was compared across 45 sites representing a gradient in habitat amount. Pellet density in moose habitat increased in a linear or quadratic relationship with mean moose habitat patch size. Moose pellet density decreased faster thanwhatwould be expected from a decrease in habitat amount alone. This change in pellet group density with habitat amount may be because one or both of the assumptions of the ideal free distribution hypothesis were violated.

Effects of anti-predator defence through toxin sequestration on use of alternative food microhabitats by small herbivores

Many invertebrate herbivores sequester plant toxins from their food, and the availability of toxins and the costs and benefits of sequestering toxins may influence food patch choice. In many plants, young leaves contain higher concentrations of toxins than old leaves and so can be preferred by sequestering herbivores, even if herbivores are more readily detected by predators when on them. We modelled patch use and sequestration strategies for the growth period of herbivores, assuming that the effectiveness of a toxin against predators is positively related to its cost of sequestration and that high-reward patches have higher predation risk. We show that the empirically commonly-observed strategy of moving from a low-reward patch to a high-reward patch can be optimal in a range of circumstances, but especially those that are common in nature. Body size when herbivores are predicted to switch increases with increasing size of maturation under most conditions, whilst use of the high-reward patch increases. Our predictions about how the proportion of time spent in the high-reward patch changes with the distribution and potency of toxins indicate a reason for plant toxins to be relatively mild. We provide further testable predictions about the role of the plant's defence strategy and herbivore behaviour in tritrophic interactions.

Boldness affects foraging decisions in barnacle geese: an experimental approach

Individuals foraging in groups constantly need to make decisions, such as when to leave a group, when to join a group, and when to move collectively to another feeding site. In recent years, it has become evident that personality may affect these foraging decisions, but studies where individuals are experimentally forced into different roles are still absent. Here, we forced individual barnacle geese, Branta leucopsis, differing in boldness scores, either in a joining or in a leaving role in a feeding context. We placed a food patch at the far end of a test arena and measured the arrival latency and number of visits of individuals to the patch either in the presence of a companion that was confined near the food patch (“joining context”) or in the presence of a companion that was confined away from the food patch (“leaving context”). We also ran trials without a companion (“nonsocial context”). Bolder individuals arrived more quickly than shyer individuals in the “leaving” context, but there was no effect of boldness in the “joining” context, suggesting that boldness differences are important in explaining variation in leaving behavior but not in joining behavior. The difference in arrival latency between the “joining” and non-social context increased with decreasing boldness score, suggesting that shyer individuals are more responsive to the presence of other individuals (i.e., social facilitation). These results indicate that individual differences in boldness play a role in patch choice decisions of group-living animals, such as when to leave a flock and when to join others at a patch.

The spatial distribution of flocking foragers: disentangling the effects of food availability, interference and conspecific attraction by means of spatial autoregressive modeling

Patch choice of foraging animals is typically assumed to depend positively on food availability and negatively on interference while benefits of the co‐occurrence of conspecifics tend to be ignored. In this paper we integrate a classical functional response model based on resource availability and interference with a conspecific attraction model and use it to simulate spatial distributions of animals in their continuous resource landscapes. We consider both equilibrium and non‐equilibrium distributions. We show that the integrated model produces distributions of foraging animals that closely match the distributions observed in nature. The simulations also show that under information uncertainty the locations of flocks are highly variable when conspecific attraction is strong. We furthermore explain how we can estimate the impacts of conspecific attraction and interference on the distribution of foraging animals by spatial autoregression. On the basis of simulated data we show that the separate impacts of interference and conspecific attraction can be disentangled when prior information on either is available, in addition to information on resource density and predator density, and that the total food effect is given by the spatial multiplier.

Last Trip Return Rate Influence Patch Choice Decisions of Small-Scale Shrimp Trawlers: Optimal Foraging in São Francisco, Coastal Brazil

Studies using Optimal Foraging Theory to understand human behavior have stated that daily variation in patch profitability could explain mismatches between theoretical predictions and actual behavior. In this paper, we tested whether the return rate of the last fishing trip could predict fishers’ choices to return or choose a different fishing ground for their next trip. We collected data on fishing trips using interviews and direct observation of fishers’ activities at the main landing point in Sao Francisco, a small-scale shrimp fishing community on Brazil’s southern coast. We found that fishers returned more often to fishing grounds where the return rate of the previous fishing trip was above the average gross return of the environment. Daily variations in patch quality accounted for fishers’ decisions, but other factors may also influence the observed behavior, such as scale of analysis, information exchange, environmental conditions, and economic variables.