Patch Choice Research Articles

Density-dependent predation by blue crabs Callinectes sapidus on natural prey populations of infaunal bivalves

We used field and laboratory mesocosm experiments to examine the effects of the func- tional response of the blue crab Callinectes sapidus foraging on Balthic clams Macoma balthica in the upper Chesapeake Bay. Field experiments measured the density-dependent effect of blue crabs on clam patches in both mud and sand substrates at multiple sites spanning the natural range of clam densities, allowing us to examine the effects of larger-scale variation in prey abundance on prey mortality patterns. We compared the results of our field experiments to mesocosm experiments with 1 and 2 blue crabs to determine differences in the effects of single and multiple predators on the den- sity-dependence of clam mortality. We observed predator behavior to identify mechanisms responsi- ble for differences in prey mortality patterns. In the field, M. balthica mortality was not significantly density dependent, but the natural density of prey surrounding experimental patches had a negative density-dependent effect on clam mortality in mud. In the mesocosms, 1 or 2 blue crabs caused den- sity-dependent mortality. Density dependence was weaker in mesocosms with 2 crabs. Agonistic behaviors were not significantly affected by clam density, but the presence of a conspecific increased a crab's foraging time at the lowest clam density. Changes in behavior when multiple crabs forage together may partly account for the reduction in density dependence of clam mortality. Predator responses such as the effects of conspecifics on foraging and patch choice that were lacking in the laboratory appear to be key in determining prey mortality patterns in the field. Larger-scale patterns of prey density variation were more important in determining prey mortality rates than the small- scale variation represented by the experimentally manipulated patches.

Site Reconnaissance in the Kipsing and Tol River Watersheds of Central Kenya: Implications for Middle and Later Stone Age Land-Use Patterns

Two seasons of archaeological site reconnaissance and geo-archaeological fieldwork in the Kipsing and Tol river valleys of central Kenya have resulted in (1) the location of 58 surface sites and 13 spot finds and (2) the excavation and dating of 11 alluvial stratigraphic profiles. These data are incorporated with our previous work in the study area to yield a preliminary interpretation of Middle and Later Stone Age tool technologies and land-use strategies during the Late Pleistocene period there. Specifically, the nature of the lithic inventories and observed distribution of archaeological sites suggests that people in the Middle Stone Age employed a “patch choice” resource and land-use strategy while those in the subsequent Later Stone Age period utilized a “logistical” strategy.

Balancing variable patch quality with predation risk.

Patch choice is almost always under the influence of multiple factors. Patch quality and the threat of predation are two such factors that have been shown to influence the foraging decisions of animals. In addition, aspects of patch quality may also vary with time, and consequently animals should incorporate temporal information to reduce their uncertainty about current patch conditions. The temporal weighting rule (TWR), which has been validated in previous studies, describes how animals should choose among variable options with the passage of time. In this study, we varied an additional factor, predation risk, along with certainty about patch yields in a field experiment, utilizing individually marked, free-ranging least chipmunks, Tamias minimus. We gave the animals in each condition experience at our experimental patches and then recorded patch choices a few minutes or one to 2 days later. The results show that animals combined perceived predation risk with a progressively shifting assessment of patch quality to form estimates of overall patch value as modeled by TWR. Based on the information available, the animals' patch choices were, arguably, the most adaptive choices.

Prospecting in the collared flycatcher: gathering public information for future breeding habitat selection?

Visiting breeding patches can allow prospecting individuals to gather information on local patch quality to make optimal decisions about selecting a breeding habitat in the following year. This prospecting behaviour has been described in many bird species. However, the nature of the information gathered by prospectors often remains unknown. We collected data on prospecting behaviour in the collared flycatcher, Ficedula albicollis, a small hole-nesting passerine bird, to investigate whether prospectors could gather information on their conspecifics' reproductive success, that is, ‘public information’. If they could, they would be expected to inspect conspecific nests, prospect at the time when public information is reliable, and be attracted to, and spend time at, successful sites. Prospecting at conspecific nests was frequent. Prospectors were mainly males, and prospecting activity closely matched the peak of nesting activity. The probability of observing a prospector at a nest increased with parental activity, measured by feeding rate and vigilance behaviour, but did not depend on direct measures of success of the inspected nest (nestling number and condition), or on female characteristics. Because feeding rate and vigilance behaviour were predictors of breeding success at fledging, prospectors were attracted to the most successful nests when cueing on conspicuous parental activity. Therefore, prospectors could gather accurate information on local conspecific reproductive success that may be used for breeding patch choice in the following year. We discuss alternative explanations for our results, and the need to test experimentally whether prospectors gather public information. We also discuss the role of breeding constraints on, and the origin of sex differences in, prospecting.

Importance of the habitat choice behavior assumed when modeling the effects of food and temperature on fish populations

Various mechanisms of habitat choice in fishes based on food and/or temperature have been proposed: optimal foraging for food alone; behavioral thermoregulation for temperature alone; and behavioral energetics and discounted matching for food and temperature combined. Along with development of habitat choice mechanisms, there has been a major push to develop and apply to fish populations individual-based models that incorporate various forms of these mechanisms. However, it is not known how the wide variation in observed and hypothesized mechanisms of fish habitat choice could alter fish population predictions (e.g. growth, size distributions, etc.). We used spatially explicit, individual-based modeling to compare predicted fish populations using different submodels of patch choice behavior under various food and temperature distributions. We compared predicted growth, temperature experience, food consumption, and final spatial distribution using the different models. Our results demonstrated that the habitat choice mechanism assumed in fish population modeling simulations was critical to predictions of fish distribution and growth rates. Hence, resource managers who use modeling results to predict fish population trends should be very aware of and understand the underlying patch choice mechanisms used in their models to assure that those mechanisms correctly represent the fish populations being modeled.

When to use public information for breeding habitat selection? The role of environmental predictability and density dependence

To select their future breeding site, individuals usually have to assess local quality by using environmental cues. One optimal cue may be ‘public information’, the local reproductive success of conspecifics in a breeding patch (patch reproductive success) because it integrates the effect of all environmental factors on breeding success. However, the quality of information conveyed by patch reproductive success is likely to depend on (1) environmental predictability and (2) interactions between individuals. We investigated how these two factors, ignored by previous models, affect the performance of individuals using patch reproductive success for breeding habitat selection compared with other information. We built a two-patch, game-theoretical model to compare the success of a strategy of breeding habitat selection based on patch reproductive success relative to four other strategies: (1) random patch choice; (2) philopatry; (3) choice based on the presence of conspecifics the previous year (conspecific attraction); and (4) choice based on intrinsic patch quality the previous year. The results illustrate how the efficiency of strategies in tracking variations in patch quality depend on environmental predictability and costs linked to density dependence, themselves linked to the dynamics of spatial aggregation of individuals. In particular, strategies based on measures of patch reproductive success perform the best for intermediate and high temporal predictability of patch quality, whereas philopatry and conspecific attraction then perform poorly. The ‘conspecific attraction’ strategy always coexists with other strategies by efficiently parasitizing the information they use. We discuss the implications of a better understanding of breeding habitat selection behaviours for evolutionary and conservation biology. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Ideal free distributions when resources undergo population dynamics

This study examines the influence of optimal patch choice by consumers on resource population dynamics and on consumer distribution in a two patch environment. The evolutionarily stable strategy which describes animal distributions across habitat patches is called the ideal free distribution (IFD) strategy. Two mechanisms that lead to the IFD are: (1) direct consumer competition such as interference, and (2) exploitative competition for resources. This article focuses on the second mechanism by assuming that resources undergo population dynamics while consumer abundance is fixed. Two models of resource growth are considered in detail: the exponential and the logistic. The corresponding consumer IFD is derived for each of these two models, assuming that consumers behave adaptively by moving to the patch which provides them with the highest fitness. This derivation does not require that resources are at an equilibrium, and it provides, for each resource density, the corresponding distribution of consumers. The article suggests that adaptive patch choice by consumers decreases between patch heterogeneity in resource levels and weakens the apparent competition between resources. The results for a single consumer population are extended for two competing consumer populations. The corresponding IFD is computed as a function of the two consumer densities. This allows for the analytical description of isolegs which are the boundary lines, in the two consumer density phase space, separating regions where qualitatively different habitat preferences are predicted.

The influence of sward canopy structure on foraging decisions by grazing cattle. I. Patch selection

AbstractPatch selection by grazing dairy cows in response to simultaneous variation in combinations of sward structural characteristics was examined in three experiments in which four mature dairy cows were offered a choice of patches (typically 0.9 m × 0.9 m) of perennial ryegrass (Lolium perenne) presented in a linear arrangement. Treatments involved combinations of variations in sward height, stubble height and/or depth of regrowth, prepared by preliminary cutting treatments. They were arranged in balanced sets of four to nine treatments, which were arranged in linear sequences of eighteen to twenty‐seven patches. Within experiments, sequences were balanced across replicate sets of patches, which were grazed separately by individual cows. The number of bites removed and the residence time for each patch were highly correlated in all three experiments, and the results are reported using number of bites per patch as an estimator of foraging behaviour. In the first experiment, with vegetative swards, cows preferentially selected the tallest swards. When swards comprising reproductive stem were offered in Experiment 2, cows selectively grazed short‐stubble swards rather than tall‐stubble swards, although both offered a similar depth of regrowth. Cows did not exhibit preference for swards comprising the greatest quantity of leaf mass, indicating that the spatial distribution of plant components assumed greater importance. In the third experiment, the number of bites removed increased with increasing depth of regrowth, and was negatively correlated with sward height. The three patch‐appraisal cues investigated were broadly ranked in order of importance as (i) depth of regrowth, (ii) sward maturity and (iii) sward height. There was no evidence, at least at a short temporal scale, that patch behaviour was influenced by conditions in adjacent patches, suggesting that the cows assessed grazing opportunities on a patch‐by‐patch basis.

Herbivory and plant resource competition: a review of two interacting interactions

This review discusses the prevalence and potential for interactive effects between herbivory and competition on plant growth and biomass, and it is apparent that such effects typically arise when there is a mismatch between the spatial scale of herbivore behaviour (food or patch choice) and the spatial heterogeneity of the plant community. Historically, such interactive effects have been examined using two approaches. Studies using the first approach have excluded plant neighbors and herbivores in a factorial experiment, and scored effects on plant biomass. Studies using the second approach have observed herbivore abundance or herbivory on plants with or without plant neighbors, and have identified a large number of mechanisms underlying such interactive effects. The two types of studies have produced somewhat conflicting results, where interactive effects have been commonly observed in studies using the second approach and only rarely in studies using the first approach. This is most likely a consequence of a biased choice of study systems, where studies using the first approach have primarily studied mammalian herbivory while studies using the second approach have been more focussed on insect herbivory. Moreover, studies using the first approach have typically been very small‐scale manipulations and this probably precludes most possible interactive effects in systems with mammalian herbivory. This points to the fact that studies examining interactive effects of herbivory and plant competition should more carefully consider the behaviour and life history of herbivores included in the study prior to the design of removal experiments.

Linking foraging behavior to lifetime reproductive success for an insect parasitoid: adaptation to host distributions

European and American populations of the parasitoid Cotesia glomerata show pronounced differences in foraging behavior across plants and leaves. This variation in spatial aspects of foraging behavior was observed about 350 generations after the introduction of C glomerata from Europe to North America. We used a simulation model to study how these behavioral differences affect lifetime reproductive success in environments that differ in the-spatial distribution of hosts. The preferred gregarious host Pieris brassicae occurs in rare large clusters in Europe but-is absent in North America. The solitary caterpillars of Pieris rapae are negative binomially distributed across plants during summer in North America, whereas they are Poisson-distributed in Europe, and early and late in the season in North America. Simulations showed that the foraging strategy of American C. glomerata resulted in a higher lifetime reproductive success than did the strategy of European C. glomerata on a Poisson R rapae distribution, but did not differ on the more clustered negative binomial distribution. American parasitoids spend less time on exploration flights, focusing on the exploitation of P rapae patches. This suggests that C. glomerata has adapted to the North American environment through the loss of exploration traits necessary for the location of rare clusters of P brassicae. Lifetime reproductive success of the European strategy was most sensitive to art increase in the giving up time on infested leaves. This behavioral parameter was more than twice as high in the American parasitoids compared with their European conspecifics. [KEYWORDS: fitness; hierarchical patches; information use; patch choice; patch leaving; spatial foraging behavior]

Conspecific Avoidance During Foraging in Venturia canescens (Hymenoptera: Ichneumonidae): The Roles of Host Presence and Conspecific Densities

We explored the effects of the presence of conspecifics on host patch choice decisions made by the parasitoid Venturia canescens. Different odor sources were located in plastic boxes at the end of each arm of a glass Y-tube olfactometer. In a set of experiments, odor sources were either (a) host kairomone patches with or without conspecifics (5 or 20) or (b) two odor sources located in successive boxes (a host kairomone patch and a patch with 20 conspecifics in one arm versus a host patch and an empty patch in the other). Our results indicate that V. canescens avoids competition only at high conspecific densities. Avoidance occurs only when foraging wasps perceive the combined odors from host kairomones and conspecific females. Separating the host patch from conspecific parasitoids does not perturb avoidance behavior.

The effects of resource depression on foraging efficiency, diet breadth, and patch use in southern New Zealand

While many studies have examined human impacts on prehistoric environments, few have explicitly examined how foragers adapt to the changing environmental situations that they have created. The goal of this analysis is to study the relationship between human foraging economies and human-related environmental change in southern New Zealand. Foraging theory is used to generate predictions about subsistence change resulting from the declining abundance of important resources such as moas and seals. In particular, these predictions examine changes in (1) the kind of resources exploited (foraging efficiency), (2) the number of resources utilized (diet breadth), and (3) the habitats exploited (patch choice). The predictions are tested using the large assemblage of vertebrate faunal remains from the well-stratified and well-dated Shag River Mouth site. This study shows that using foraging theory models to structure analysis provides a more fine-grained spatial and temporal resolution of subsistence change in southern New Zealand than has been previously achieved.

Group foraging sensitivity to predictable and unpredictable changes in food distribution: past experience or present circumstances?

The ideal free distribution theory (Fretwell & Lucas, 1970) predicts that the ratio of foragers at two patches will equal the ratio of food resources obtained at the two patches. The theory assumes that foragers have "perfect knowledge" of patch profitability and that patch choice maximizes fitness. How foragers assess patch profitability has been debated extensively. One assessment strategy may be the use of past experience with a patch. Under stable environmental conditions, this strategy enhances fitness. However, in a highly unpredictable environment, past experience may provide inaccurate information about current conditions. Thus, in a nonstable environment, a strategy that allows rapid adjustment to present circumstances may be more beneficial. Evidence for this type of strategy has been found in individual choice. In the present experiments, a flock of pigeons foraged at two patches for food items and demonstrated results similar to those found in individual choice. Experiment 1 utilized predictable and unpredictable sequences of resource ratios presented across days or within a single session. Current foraging decisions depended on past experience, but that dependence diminished when the current foraging environment became more unpredictable. Experiment 2 repeated Experiment I with a different flock of pigeons under more controlled circumstances in an indoor coop and produced similar results.

Patch Choice Decisions among Ifaluk Fishers

Studies of patch choice decisions among human foragers have failed to explain why foragers do not exclusively exploit the patch with the highest mean profitability. One possible explanation is that profitability rankings are likely to vary daily; however, this instability is not captured when profitabilities are calculated as a sampled average over a longer time span. Here I present data on the patch choice decisions of Ifaluk fishers to evaluate whether men are responding to daily variation in the profitability of their primary fishing patch. Results show that men choose to fish most frequently in the patch with the highest mean profitability. Men fish in alternative patches (alternative from the most profitable patch) when, on that morning or the previous day, return rates in the most profitable patch are lower than the overall mean per capita return rate of alternative patches. Results also indicate that when fishers pursue alternative patches after fishing in the patch with the highest profitability, their mean per capita return rates are generally higher in the alternative patches exploited. However, variance in the profitability of the most profitable patch cannot explain why men exploit two patches, the Nine‐mile reef and the dogtoothed tuna patch, which on average have very low profitability. These results and directions for future research are discussed. [Keywords: human behavioral ecology, patch choice decisions, Micronesia]

Patch Choice and Foraging Behavior of Nonbreeding American Flamingos in Yucatán, Mexico

Abstract We studied nonbreeding American Flamingos (Phoenicopterus ruber ruber) using the Celestún Lagoon, Yucatán, Mexico, to characterize feeding patches and to describe factors influencing patch choice. Four invertebrate taxa (polychaetes, molluscs, chironomids, crustaceans) and two plant foods (seeds of widgeongrass [Ruppia maritima] and tubercles of muskgrass [Chara fibrosa]) comprised 99% of potential food items in 76 patches we sampled. Patches tended to be dominated either by invertebrates or plant foods; only 12% of patches had 50:50 ratios of plant and invertebrate foods. Food was more abundant in invertebrate versus plant-dominated patches (157 vs. 67 items patch−1), but flamingo flock size was smaller in invertebrate-dominated patches (60 vs. 147 birds patch−1). More individuals walk-fed as invertebrates increased in the patch, and more birds stamp-fed as plant foods increased. We argue that groups of foraging flamingos apparently indicate location of food for conspecifics (local enhancement), and may also provide information about patch quality through feeding behavior. Selección de Parches y Comportamiento de Forrajeo en Phoenicopterus ruber ruber en la Época No-Reproductiva en Yucatán, México Resumen. Estudiamos el comportamiento de forrajeo en un grupo de flamencos (Phoenicopterus ruber ruber) durante la época no-reproductiva en la Laguna de Celestún, Yucatán, México, para caracterizar a los parches de forrajeo y describir los factores que influyen en la selección del parche. Cuatro taxa de invertebrados (poliquetos, moluscos, quironómidos y crustáceos) y dos alimentos vegetales (semillas de Ruppia maritima y tubérculos de Chara fibrosa) conformaron el 99% de los elementos alimenticios potenciales para los flamencos en los 76 parches que muestreamos. Los parches tendieron a ser dominados por invertebrados o por alimento vegetal. Sólo el 8% de los parches tuvieron proporciones de 50:50% de invertebrados y alimentos vegetales. El alimento fue más abundante en parches dominados por invertebrados que en los dominados por alimentos vegetales (157 vs. 67 elementos por parche), pero el tamaño del grupo de flamencos fue más pequeño en parches dominados por invertebrados (60 vs. 147 individuos). La cantidad de individuos que se alimentaban caminando aumentó a medida que aumentaban los invertebrados en el parche, y la cantidad de individuos que se alimentaban parados aumentó a medida que aumentaban los alimentos vegetales. Sugerimos que los grupos de flamencos que forrajean aparentemente no sólo indican a los coespecíficos la ubicación del alimento (mejoramiento local), sino que también podrían proveen información sobre la calidad del parche a través del comportamiento de alimentación.

NEST SITE SELECTION AND NEST SUCCESS IN A SONG SPARROW POPULATION: THE SIGNIFICANCE OF SPATIAL VARIATION

Abstract I tested the hypothesis that individual Song Sparrows (Melospiza melodia) choose nesting microhabitat that reduces their risk of nest predation, using two years of data (n = 196 nests) from two adjacent sites in California coastal scrub, one grazed and one ungrazed. Nesting habitat was compared between nest patches and random locations, and between successful and unsuccessful nests. In both sites, nest patch habitat differed significantly in structure and plant species composition from habitat available within territories. However, of six habitat characteristics associated with nest patch choice, only two were related to nest success, and that relationship differed between the two study sites. Only in the grazed site was the amount of coyote bush (Baccharis pilularis) in the nest patch positively associated with both nest site selection and nest success. In contrast, coyote bush was unrelated to nest site choice and had a nonlinear relationship with nest success in the ungrazed site, such that ne...

PATCH CHOICE AND FORAGING BEHAVIOR OF NONBREEDING AMERICAN FLAMINGOS IN YUCATÁN, MEXICO

Abstract We studied nonbreeding American Flamingos (Phoenicopterus ruber ruber) using the Celestun Lagoon, Yucatan, Mexico, to characterize feeding patches and to describe factors influencing patch choice. Four invertebrate taxa (polychaetes, molluscs, chironomids, crustaceans) and two plant foods (seeds of widgeongrass [Ruppia maritima] and tubercles of muskgrass [Chara fibrosa]) comprised 99% of potential food items in 76 patches we sampled. Patches tended to be dominated either by invertebrates or plant foods; only 12% of patches had 50:50 ratios of plant and invertebrate foods. Food was more abundant in invertebrate versus plant-dominated patches (157 vs. 67 items patch−1), but flamingo flock size was smaller in invertebrate-dominated patches (60 vs. 147 birds patch−1). More individuals walk-fed as invertebrates increased in the patch, and more birds stamp-fed as plant foods increased. We argue that groups of foraging flamingos apparently indicate location of food for conspecifics (local enhancement),...

Choice of foraging patches by hill sheep given different opportunities to seek shelter and food

AbstractA patch choice experiment was conducted in which sheep were offered choices between patches of upland pasture which differed in their sward height and degree of shelter from the wind. Experimental plots (48 m ✕ 4 m) were divided into 4 m ✕ 4 m patches. Alternate patches were mown in advance of the experiment to create nominal sward heights of 4 and 6 cm. Portable shelters were erected on the windward side of alternate patches to reduce wind speed on sheltered patches by half. The four treatment combinations used to test the influence of sward height, shelter and their interaction on patch use were: patchy swards with and without shelters and uniform swards with and without shelters. Five adult sheep per treatment were observed while grazing the plots for 6 h/day on five occasions (days) in autumn. Patch choice was measured by video observation and using a patch marker technique. On none of the observation days was the weather condition sufficiently severe that animals were outside their thermoneutral zone. There was a strong influence of sward height on patch use with sheep spending 0·382 of their time on short swards when patchy swards were offered compared with 0·503 of their time on equivalent areas when swards were uniform. Thermal conditions did not influence patch choice with sheep spending an average of 0·442 of their time on equivalent patches whether they were sheltered or not. There was no interaction between sward conditions and thermal conditions on the amount of time spent on different patches. Data from the patch marker method supported observation data. The results confirm that sheep are resilient to extremes of cold weather commonly occurring at temperate latitudes and suggest that thermal constraints have minimal influence on the small-scale foraging movements of sheep, as long as they remain within their thermoneutral zone.

Sharing, consumption, and patch choice on Ifaluk atoll : Evaluating an explanatory hypothesis.

Anthropological tests of patch choice models from optimal foraging theory have primarily employed acquisition rates as the currency of the model. Where foragers share their returns, acquisition rates may not be similar to consumption rates and thus may not be an appropriate currency to use when modeling foraging decisions. Indeed, on Ifaluk Atoll the distribution patterns of fish vary by fishing method and location. Previous analyses of Ifaluk patch choice decisions suggested that if Ifaluk fishers are trying to maximize their production rates they should rarely torch fish for dogtoothed tuna. However, some men do spend considerable time and energy exploiting the dogtoothed tuna patch. To improve our understanding of the constraints and motivations influencing men's decisions to exploit this patch, here I use per capita consumption rates as a currency, rather than production rates, to evaluate predictions generated from a patch choice model. Results indicate that although fish caught in other patches are more widely distributed than fish caught in the dogtoothed tuna patch, the consumption rates of torch fishers and their kin are still considerably lower than the consumption rates of men pursuing fish in other patches. Although these results are unable to explain why Ifaluk men exploit the dogtoothed tuna patch, an important explanatory hypothesis is eliminated.

Towards a cognitive niche: divergent foraging strategies resulting from limited cognitive ability of foraging herbivores in a spatially complex environment

A model was developed to explain one mechanism whereby differential optimal foraging strategies can occur between species as a result of selection for competition avoidance. This is the primary requirement for niche differentiation to evolve without a difference in the underlying foraging ability or morphology. The model used an individual-based patch choice mechanism, whereby herbivores move from patch to patch seeking food with the highest nutrient intake characteristics. The choice of patch was governed by a parameter, μ, which determined to what extent information in the landscape at different distances from the herbivore was used by it to make foraging decisions. A genetic algorithm was used to optimise the value, μ, in a complex landscape. The value of μ quickly converged to a single value with stabilising selection occurring when there was only a single species foraging. When there was a competing species with a fixed value of μ, the value of μ evolved to be above or below the mean for the single species mean depending on whether the value of μ for the competitor was below, or above the single-species mean, respectively. This was indicative of niche segregation. However μ tended to vary unstably over time when allowed to vary simultaneously in both species, although there was evidence for interaction between the two values. These results indicate that there can be a competitive advantage in choosing a cognitive strategy that is complementary to that used by other species.