Patch Choice Decisions Research Articles

Odour information enables patch choice by mammalian herbivores from afar, leading to predictable plant associational effects

Abstract Neighbouring plants can alter the susceptibility of high‐quality focal plants to herbivores by affecting herbivore patch choice. Herbivores can use plant odour to make patch‐scale foraging decisions from afar, but the actual information they rely on within complex plant odours is rarely defined. Revealing the information enabling patch choice by herbivores will provide the mechanistic link underpinning associational effects of plant neighbours arising from these foraging decisions. Here, our first aim was to test whether odour cues alone enable a mammalian herbivore to make patch choice decisions leading to predictable associational effects of neighbours on high‐quality focal plants. Our second aim was then to test whether artificial odour, designed to mimic the informative odour component within the whole odour profile of low‐quality neighbours, is as effective as real plants in influencing patch choice and associational refuge. We tested patch choice by African elephants, Loxodonta africana using a giant Y‐maze and real or artificial plant odours as the only cues for the neighbours of a high‐quality focal plant. We quantified the probability of various odour treatments being chosen in comparison with the odour of a focal plant alone. Compared with focal plants alone, we found that elephants were more likely to choose patches with the focal plant plus high‐quality neighbours of the same or different species, but less likely to choose patches with the focal plant plus low‐quality neighbours. We also demonstrated that an artificial subset of odours, designed to be informative, were as effective as real low‐quality neighbours in influencing patch choice and hence associational refuge to the focal plant. Our results demonstrate a key role of plant odour—and specifically informative components within complex odour profiles—in patch choice decisions by a mammalian herbivore, leading to plant associational effects on high‐quality focal plants. Understanding what olfactory information herbivores use when deciding which patches to visit or avoid, and how it affects focal plant susceptibility is important ecologically. Non‐random patch choice will not only affect individual fitness of herbivores, but also shape plant community dynamics through impacting plant survival and recruitment. Furthermore, artificially re‐creating odour information could offer a new tool to influence herbivore foraging decisions, with implications for wildlife management and conservation, including plant protection. Read the free Plain Language Summary for this article on the Journal blog.

Patch choice decisions by a fission–fusion forager as a test of the ecological constraints model

Chapman et al.’s (Behav Ecol Sociobiol 36:59–70, 1995) ecological constraints model posits that the size and distribution of food patches place restrictions upon foraging group size. Larger groups incur increased travel costs for any given array of patches, and thus, to fulfil individual energetic and nutritional requirements, foragers should adjust group sizes to balance energy obtained against that spent on travelling. Support for this model comes from both comparative and species-specific studies but findings are contradictory, and the utility of the model has been questioned. This study provides a rigorous test, analysing measurements from distinct food patches and individual inter-patch movements, on an appropriately shorter temporal scale. Using data drawn from two social groups of a species characterised by a high degree of fission–fusion dynamics, the chimpanzee (Pan troglodytes), we show that larger parties foraged in larger food patches and for longer durations, and that larger parties were associated with further travel between patches. Overt contest competition over food increased with party size. We found no evidence of distinct sex differences in either party size or travel distances: the predictive power of forager sex was low compared to that of ecological variables. We propose that analysis at the patch level is more appropriate than a daily averaging approach that may smooth out the very variation being investigated. Our findings suggest that, despite certain limitations, Chapman et al.’s (Behav Ecol Sociobiol 36:59–70, 1995) model of ecological constraints remains a useful tool. Ecology does indeed constrain grouping patterns, and the impact of this is not necessarily differentiated by sex.Significance statementForaging animals face the ‘more mouths to feed’ problem: as the numbers in a group increase, the group must travel further to find enough food, using up energy. Hence, foragers should adjust numbers to minimise these costs, but tests of this idea have proved inconclusive. We investigated the foraging behaviour of chimpanzees, a species with highly flexible grouping, considering their travel between specific patches of food. We found clear support for this proposition, with larger patches of food hosting larger numbers of foragers, and such groups having to travel further to find food. Although it is often thought that female animals should respond more strongly to foraging costs, we found little evidence of sex differences. Our results show that ecology does indeed constrain grouping patterns, and that the impact is felt equally by males and females.

To follow or not? How animals in fusion-fission societies handle conflicting information during group decision-making.

When group members possess differing information about the environment, they may disagree on the best movement decision. Such conflicts result in group break-ups, and are therefore a fundamental driver of fusion-fission group dynamics. Yet, a paucity of empirical work hampers our understanding of how adaptive evolution has shaped plasticity in collective behaviours that promote and maintain fusion-fission dynamics. Using movement data from GPS-collared bison, we found that individuals constantly associated with other animals possessing different spatial knowledge, and both personal and conspecific information influenced an individual's patch choice decisions. During conflict situations, bison used group familiarity coupled with their knowledge of local foraging options and recently sampled resource quality when deciding to follow or leave a group - a tactic that led to energy-rewarding movements. Natural selection has shaped collective behaviours for coping with social conflicts and resource heterogeneity, which maintain fusion-fission dynamics and play an essential role in animal distribution.

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.

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.

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.

Dredging for edible cockles (Cerastoderma edule) on intertidal flats: short-term consequences of fisher patch-choice decisions for target and non-target benthic fauna

AbstractKraan, C., Piersma, T., Dekinga, A., Koolhaas, A. and van der Meer, J., 2007. Dredging for edible cockles (Cerastoderma edule) on intertidal flats: short-term consequences of fisher patch-choice decisions for target and non-target benthic fauna. – ICES Journal of Marine Science, 64. Intertidal flats in the Dutch Wadden Sea are protected by national and international treaties. Still, mechanical dredging for edible cockles Cerastoderma edule was allowed in 74% of 1200 km2 of intertidal flats. Cumulatively, between 1992 and 2001, 19% of the intertidal area was affected by mechanical cockle-dredging at least once. On the basis of a grid of 2650 stations sampled annually, we evaluate the extent to which cockle-dredging from 1998 to 2003 was selective with respect to non-target macrozoobenthic intertidal fauna. In all 4 years that comparisons could be made, to-be-dredged areas contained greater diversity of macrobenthic animals than areas that remained undredged. Targeted cockles were 2.5 times more abundant in areas that were to be dredged shortly, but other species also occurred in higher densities in these areas. Small amphipods and some bivalves occurred less in to-be-dredged areas than elsewhere. In terms of short-term responses to dredging, four non-target species showed a significant decrease in abundance 1 year after dredging. Only Tellina tenuis showed an increase a year after dredging.

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.

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]

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.

Patch choice decisions of wild blackbirds: the role of preharvest public information

Although group foragers have the potential to enhance their patch choice decisions by observing the sampling behaviour of competitors (i.e. using ‘public information’), empirical support for such an ability is sparse and conflicting. We examined whether wild blackbirds, Turdus merula, were more likely to choose the richer (20-fold) of two seminatural food patches if they had seen other blackbirds (demonstrators) feeding in them beforehand. There was no evidence that birds having such preharvest public information preferentially selected the richer patch, even if their choice was not limited by the continuing presence of dominant demonstrators. Nor did patch selectors favour the patch occupied by a demonstrator (or just vacated by one) despite an above-average probability that these patches were the richer. Instead, our birds often showed preferences for one or other of the otherwise identical patch locations, were more likely to select the rich patch if it had not changed location since their last visit, and avoided dominant conspecifics. We conclude that preharvest public information has little or no influence on blackbird patch choice decisions.

Flower choice by naı̈ve young crab spiders and the effect of subsequent experience

Initial responses of naı̈ve individuals to critical environmental stimuli provide important information about the innate contribution to behaviour, and subsequent responses to the same stimuli may show the role of experience in mediating those initial responses. To test the role of these factors, I measured initial patch choices and giving-up responses of just-emerged, naı̈ve, second-instar crab spiders, Misumena vatia, on several hunting sites they encountered after leaving their natal nests. In follow-up tests I measured the effects of these experiences on subsequent patch choice decisions. The choice of hunting sites is a vital decision at all stages of the life cycle for sit-and-wait predators such as Misumena. In their initial tests these spiderlings remained more frequently on goldenrod (Solidago spp.) flowers than on green or yellow goldenrod buds, a preference they retained through tests run on 5 consecutive days. Individuals on green and yellow buds shifted sites more quickly and frequently than those from flowers, and made most of these moves to flowers, which attracted many more prey than did buds. These differences were not affected by age, energetic condition, or loss of information over the period of the experiment. Once spiderlings moved from buds, they showed a high, increasing tendency to move from buds in subsequent runs, those from flowers showed a consistently low tendency. These results suggest that spiderlings retain their innate behavioural patterns through the second instar, but that experience also plays a modest role in patch choice at this stage.

Choice of hunting site as a consequence of experience in late-instar crab spiders.

Earlier experiences may play an important role in the choice of hunting sites, but their effects on the foraging repertoire of most animals remain poorly understood. I tested the role of previous flower choices (hunting sites) by penultimate-instar female crab spiders Misumena vatia in making subsequent patch-choice decisions. M. vatia is a sit-and-wait predator, and the two flower species used, ox-eye daisy Chrysanthemum leucanthemum and common buttercup Ranunculus acris, are important hunting sites. Spiders with different immediate experience showed similar short-term (<1 day) giving-up times on the two flower species, independent of their previous substrate. However, four-fifths of the individuals that remained a day or longer tended to leave buttercups sooner than daisies, especially if they had previously occupied daisies. Thus they may directly assess the quality of a potential hunting site, perhaps in response to prey abundance, but previous experience may play a minor role as well. Of spiders that made several consecutive choices of hunting sites, those on daisies often confined these runs to daisies (one of two years); those on buttercups did not exhibit comparable fidelity. Spiders molting into the adult stage almost always subsequently chose the same flower species (either daisy or buttercup) as the one on which they molted. Thus, juvenile experiences may influence adults, the critical stage when virtually all of the spiders' reproductive resources are gathered, even if this resulted from imprinting on their molt sites rather than carrying information over the molt.

The value of titration experiments: a reply to Moody et al. (1996)

Behavioural ecology has been remarkably successful as a discipline, in part because much of the theory that has been developed is readily testable through manipulative experiments in the laboratory and the ®eld. Although the preferred currency for most theories is ®tness, it has usually been possible to incorporate modi®cations or simplifying assumptions that allow the use of more readily observed, surrogate measures of ®tness. Admittedly this does require some compromise, but in the grand tradition of behavioural ecology this trade-o€ is easy to solve: the bene®ts outweigh the costs. Moody et al. (1996) (henceforth referred to as MHM), explored the role that risk dilution will have on the results of experiments that investigate predation risk ± foraging trade-o€s. Assuming that the probability of being killed by a predator is inversely related to the number of animals feeding at a site, they developed a model that incorporates risk dilution into ideal free distributions (IFDs) under predation risk. Due to risk dilution, their model suggests that patch choice decisions will be a€ected not only by the presence of predators and relative food availability, but also by the total number of animals. Their suggestions are very useful in advancing our theoretical understanding of this problem. However, we disagree with their critical assessment of the use of the IFDs as an experimental tool to quantify decisions involving con icting demands. In 1989, Abrahams and Dill (henceforth referred to as AD) published a paper that described an experimental technique that could be used to quantify the energetic equivalence of the risk of predation and, more importantly, presented the results of experiments that tested its validity. The approach is based upon a continuous-input IFD. With this type of IFD, when food is the only parameter that describes patch quality, the spatial distribution of the foragers will match the spatial distribution of their food. A large number of authors have demonstrated that under experimental conditions, animals closely conform to an IFD (for a review see Milinski and Parker 1991). Incorporation of an additional patch parameter (i.e. the risk of predation) should result in a change in the spatial distribution of animals that re ects the relative change in patch quality. Di€erences in individual intake rates will then provide a measure of the assessed value of this parameter from the animals' perspective, and can be determined empirically. This approach describes our ®rst experiment. Our second experiment then tested a prediction (derived from the results of the ®rst experiment) concerning how much additional food must be added to the dangerous patch in order for the foragers to consider it equivalent to the safe patch. To make this prediction, we assumed a linear relationship between energy and ®tness. This was not intended to describe the actual relationship between these two parameters, but to make it possible to interpret deviations in the spatial distribution with respect to the relationship between energy and ®tness. For example, if more animals than we predicted used the dangerous location after the addition of extra food, then we concluded that the ®tness bene®ts of the patch increased by more than the manipulated energy bene®ts. Conversely, if the addition of extra food resulted in fewer animals than predicted using the dangerous location, then we concluded that the ®tness bene®ts of the patch increased by less than the manipulated energy bene®ts. These experiments demonstrated that even with the linearity assumption, we could fairly accurately predict the amount of additional food that must be added to a dangerous patch to o€set the risk of predation. MHM were critical of this approach for three reasons: (1) our calculations did not incorporate risk dilution; (2) the relationship between ®tness and energy should have no in uence on the calculations necessary to Behav Ecol Sociobiol (1998) 44: 147±148 O Springer-Verlag 1998

Cues Associated With Patch-Choice Decisions By Foraging Crab Spiders Misumena Vatia

I tested the roles of insect prey presence, abundance, and distance in the selection of hunting sites by crab spiders Misumena vatia (Thomisidae) on milkweed inflorescences. Since the inflorescences on a single plant differ in numbers of prey attracted, one can also assess the effect of relative prey abundance on patch choice as overall prey abundance in an area changes. About three-fourths of the spiders chose the inflorescence attracting the most insects on a plant at densities from half to twice the normal prey, and in tests with additional prey presented at close range. Thus they appear to respond to relative prey densities in patch choice, and their accuracy of choice remains constant over a wide range of prey abundance. However, spiders without prey, and ones that had just fed, selected sites randomly. Individuals from all the other experiments left inflorescences, especially high-quality ones, more often as overall prey density increased. This result closely fits a risk-sensitivity model that predicts mobility in choice of hunting site if average prey availability exceeds that required to produce a clutch of eggs.