Predictions Of Optimal Foraging Theory Research Articles

Seasonal variation of population and individual dietary niche in the avivorous bat, Ia io

The variation in niche breadth can affect how species respond to environmental and resource changes. However, there is still no clear understanding of how seasonal variability in food resources impacts the variation of individual dietary diversity, thereby affecting the dynamics of a population's dietary niche breadth. Optimal foraging theory (OFT) and the niche variation hypothesis (NVH) predict that when food resources are limited, the population niche breadth will widen or narrow due to increased within-individual dietary diversity and individual specialization or reduced within-individual dietary diversity, respectively. Here, we used DNA metabarcoding to examine the composition and seasonality of diets of the avivorous bat Ia io. Furthermore, we investigated how the dietary niches changed among seasons and how the population niche breadth changed when the availability of insect resources was reduced in autumn. We found that there was differentiation in dietary niches among seasons and a low degree of overlap, and the decrease of insect resource availability and the emergence of ecological opportunities of nocturnal migratory birds might drive dietary niche shifts toward birds in I. io. However, the population's dietary niche breadth did not broaden by increasing the within-individual dietary diversity or individual specialization, but rather became narrower by reducing dietary diversity via predation on bird resources that served as an ecological opportunity when insect resources were scarce in autumn. Our findings were consistent with the predictions of OFT, because birds as prey for bats provided extremely different resources from those of insects in size and nutritional value. Our work highlights the importance of size and quality of prey resources along with other factors (i.e., physiological, behavioral, and life-history traits) in dietary niche variation.

Juggling options: Manipulation ease determines primate optimal fruit‐size choice

AbstractOptimal foraging theory predicts that animals will seek simultaneously to minimize food processing time and maximize energetic gain. To test this hypothesis, we evaluated whether a specialist seed‐predator primate forages optimally when choosing among variable‐sized thick‐husked fruits. Our objects of study were the golden‐backed uacari (Cacajao ouakary, Pitheciidae) and single‐seeded pods of the macucu tree (Aldina latifolia, Fabaceae). We predict that golden‐backed uacari will consume fruits of the size class that requires the least time to obtain, handle, and ingest. We used scan sampling, ad libitum to record feeding observations, and measured fruits, their penetrability, and the size of taxidermized C. ouakary hands. To test whether uacaris selected for optimal characteristics, we compared 8 metrics from 75 eaten and 105 uneaten seeds/fruits collected. Uacaris selected fruits of medium size and weight disproportionately to their abundance. Processing large fruits took six times longer than did medium‐sized fruits, but seeds were only four times as large, that is, for energetic yield per unit time, thus choosing medium‐sized pods was optimal. Disproportionate selection by C. ouakary of fruits of medium size and mass in relation to their abundance suggests active sub‐sampling of the available weight–size continuum. This selectivity probably maximizes trade‐offs between the energy derived from a seed, and time and energy expended in processing fruit to access this, so following optimal foraging theory predictions. The greater time spent processing large pods is attributed to difficulties manipulating objects five to seven times the size of the animal's palm and one‐sixth its own body weight.

What seeds tell us about birds: a multi-year analysis of acorn woodpecker foraging movements

BackgroundForaging movements of animals shape their efficiency in finding food and their exposure to the environment while doing so. Our goal was to test the optimal foraging theory prediction that territorial acorn woodpeckers (Melanerpes formicivorus) should forage closer to their ‘central place’ in years of high resource availability and further afield when resources are less available. We used genetic data on acorns stored in caching sites (granaries) and adult trees for two oak species (Quercus lobata and Quercus agrifolia) to track acorn movements across oak savanna habitat in central California. We also compared the patterns of trees these territorial bird groups foraged upon, examining the effective numbers of source trees represented within single granaries (α), the effective number of granaries (β), the diversity across all granaries (γ), and the overlap (ω) in source trees among different granaries, both within and across years.ResultsIn line with optimal foraging theory predictions, most bird groups foraged shorter distances in years with higher acorn abundance, although we found some exceptionally long distance foraging movements in high acorn crop years. The α-diversity values were significantly higher for Quercus lobata, but not for Quercus agrifolia, in years of high acorn production. We also found that different woodpecker family groups visited almost completely non-overlapping sets of source trees, and each particular group visited largely the same set of source trees from year to year, indicating strong territorial site fidelity.ConclusionsAcorn woodpeckers forage in a pattern consistent with optimal foraging theory, with a few fascinating exceptions of long distance movement. The number of trees they visit increases in years of high acorn availability, but the extra trees visited are mostly local. The territorial social behavior of the birds also restricts their movement patterns to a minimally overlapping subsets of trees, but the median movement distance appears to be shaped more by the availability of trees with acorns than by rigid territorial boundaries.

Coupling instantaneous energy-budget models and behavioural mode analysis to estimate optimal foraging strategy: an example with wandering albatrosses.

BackgroundHow foragers move across the landscape to search for resources and obtain energy is a central issue in ecology. Direct energetic quantification of animal movements allows for testing optimal foraging theory predictions which assumes that animals forage so as to maximise net energy gain. Thanks to biologging advances, we coupled instantaneous energy-budget models and behavioural mode analysis to test optimal foraging theory predictions on wandering albatross Diomedea exulans during the brooding period. Specifically, the instantaneous energy-budget model considered the energetic balance (i.e., the difference between empirical energy gain data and modelled energy expenditure via heart rate values) along the trajectory of a given individual. Four stereotypic instantaneous behavioural modes were identified based on trajectory properties (e.g., speed and turning angle) by applying a new algorithm called Expectation Maximization Binary Clustering. Previous studies on this species have shown that foraging-in-flight is the optimal foraging strategy during the incubation period when albatrosses undertake long-distance movements but no specific foraging strategy has been determined for shorter foraging movements (e.g., brooding period).ResultsThe output of our energy-budget model (measured as net energy gain) highlighted the potential optimality of alternative search strategies (e.g., sit-and-wait) during brooding, when birds may be subjected to specific energetic trade-offs and have to adapt their foraging strategies accordingly. However, not all birds showed this pattern, revealing the importance of considering individual variability in foraging strategies, as well as any switching among strategies, before drawing population-level generalizations. Finally, our study unveils the importance of considering fine scale activities to make realistic estimates of trip energy expenditure for flying birds at sea.ConclusionsThe up-scaling of accurately measured fine-scale energy patterns is essential to quantify energy balances, and their fluctuations by season of different activities among individuals or populations. In particular, we offer new insights for the energetic quantification of the effect of changing oceanic winds on the biology of pelagic predators in the southern oceans.Electronic supplementary materialThe online version of this article (doi:10.1186/2051-3933-2-8) contains supplementary material, which is available to authorized users.

Using diel movement behavior to infer foraging strategies related to ecological and social factors in elephants.

BackgroundAdaptive movement behaviors allow individuals to respond to fluctuations in resource quality and distribution in order to maintain fitness. Classically, studies of the interaction between ecological conditions and movement behavior have focused on such metrics as travel distance, velocity, home range size or patch occupancy time as the salient metrics of behavior. Driven by the emergence of very regular high frequency data, more recently the importance of interpreting the autocorrelation structure of movement as a behavioral metric has become apparent. Studying movement of a free ranging African savannah elephant population, we evaluated how two movement metrics, diel displacement (DD) and movement predictability (MP - the degree of autocorrelated movement activity at diel time scales), changed in response to variation in resource availability as measured by the Normalized Difference Vegetation Index. We were able to capitalize on long term (multi-year) yet high resolution (hourly) global positioning system tracking datasets, the sample size of which allows robust analysis of complex models. We use optimal foraging theory predictions as a framework to interpret our results, in particular contrasting the behaviors across changes in social rank and resource availability to infer which movement behaviors at diel time scales may be optimal in this highly social species.ResultsBoth DD and MP increased with increasing forage availability, irrespective of rank, reflecting increased energy expenditure and movement predictability during time periods of overall high resource availability. However, significant interactions between forage availability and social rank indicated a stronger response in DD, and a weaker response in MP, with increasing social status.ConclusionsRelative to high ranking individuals, low ranking individuals expended more energy and exhibited less behavioral movement autocorrelation during lower forage availability conditions, likely reflecting sub-optimal movement behavior. Beyond situations of contest competition, rank status appears to influence the extent to which individuals can modify their movement strategies across periods with differing forage availability. Large-scale spatiotemporal resource complexity not only impacts fine scale movement and optimal foraging strategies directly, but likely impacts rates of inter- and intra-specific interactions and competition resulting in socially based movement responses to ecological dynamics.

Feeding Site Selection by Frog-Biting Midges (Diptera: Corethrellidae) on Anuran Hosts

A critical challenge of obtaining a blood meal resides in selecting a feeding site at the host. We investigate the feeding sites of species of frog-biting midges (Corethrella spp) on tungara frogs, Engystomops pustulosus (Cope), and two species of treefrogs, Dendropsophus ebraccatus (Cope) and Dendropsophus microcephalus (Cope). To investigate the differences in midge feeding sites, we performed field observations, histological sections of the frogs and examined the mouthparts of the midges. Feeding sites are predicted by the vascular properties of the skin in different body areas of the frogs. According to optimal foraging theory, the midges should feed on host body areas that maximize blood intake. Contrary to optimal foraging theory predictions, however, their feeding sites correspond to body areas with high intensity host defensive behavior.

Morphological correlates of prey consumed by Podarcis melisellensis (Braun, 1877) and P. siculus (Rafinesque, 1810) (Sauria, Lacertidae) from two mainland regions in the eastern Adriatic area

The correlation between trophic utilization and morphology was studied for two lizard species (Podarcis melisellensis and P. siculus) from two mainland localities in the eastern Adriatic area; this is the first report of trophic and morphometric data for P. melisellensis from mainland populations. Variance partitioning showed that most of the variation in morphological traits for the analyzed lizards was the result of differences between species, and to a lesser extent between sexes. Locality did not have a strong effect on the variation of morphological traits. Prey weight is the only characteristic of prey that generally exhibits correlations with morphological characteristics rather than prey size. The pattern of correlations is generally weaker for P. melisellensis than for P. siculus. Optimal foraging theory predictions were generally confirmed: P. siculus is more constrained by trophic resource availability, with a premium on larger and heavier prey consumed in the less productive locality (SM), which can be relaxed in more productive regions (KL). P. melisellensis shows such constraints only for males in the less productive region (SM). Females of both species consume heavier prey.

Stomach fullness modulates prey size choice in the frillfin goby, Bathygobius soporator

Behaviours related to foraging and feeding in predator–prey systems are fundamental to our understanding of food webs. From the perspective of a predator, the selection of prey size depends upon a number of factors including prey vulnerability, prey size, and the predator's motivation to eat. Thus, feeding motivation and prey visual cues are supposed to influence predator decisions and it is predicted that prey selection by visual cues is modulated by the predator's stomach fullness prior to attacking a prey. This study was conducted using an animal model from the rocky shores ecosystem, a predatory fish, the frillfin goby Bathygobius soporator, and a benthic prey, the mottled shore crab Pachygrapsus transversus. Our results demonstrate that frillfin gobies are capable of visually evaluating prey size and that the size evaluation process is modulated by the level of stomach fullness. Predators with an empty stomach (0% fullness) attacked prey that was larger than the predicted optimal size. Partially satiated predators (50% stomach fullness) selected prey close to the optimal size, while fully satiated predators (100% stomach fullness) showed no preference for size. This finding indicates an integrative response of the predator that depends on the input of both internal and external sensory information when choosing prey. Predator perceptions of visual cues (prey size) and stomach fullness modulate foraging decisions. As a result, a flexible feeding behaviour emerges, evidencing a clearly adaptive response in line with optimal foraging theory predictions.

Foraging behaviour of Brazilian riverine and coastal fishers: How much is explained by the optimal foraging theory?

Optimal Foraging Theory (OFT) is here applied to analyse the foraging behaviour of Brazilian artisanal fishers of the Atlantic coast (Itacuruca and Sao Paulo Bagre villages) and of the inland Amazonian region (Jaraua and Ebenezer villages). Two OFT predictions are tested. Hypotheis1: A fisher who travels to more distant sites should return with more fish, and Hypothesis 2: The further a fisher goes, the longer s/he should stay fishing in a patch. OFT did not explain fishers' behaviour (non-significant regressions for coastal villages) or explain it in specific seasons (low water season for one Amazonian village: H1 r 2 =24.1; H2 r 2 =37.2) and in specific habitats (e.g., lakes and backwaters in Jaraua village, Lakes: H1 r 2 =13.5; H2 r 2 =24.0; Backwaters: H1 r 2 =34.4; H2 r 2 =46.5). The findings can indicate areas or seasons that are under higher fishing pressure, when fishers try to get the best out of a situation without any concern about resource conservation. By knowing the variables that influence fishers' decision-making processes, management initiatives may be more fine-tuned to the local reality and are thus more likely to succeed.

Search in External and Internal Spaces

There is compelling molecular and behavioral evidence that goal-directed cognition is an evolutionary descendant of spatial-foraging behavior. Across animal species, similar dopaminergic processes modulate between exploratory and exploitative foraging behaviors and control attention. Consequently, we hypothesized that spatial-foraging activity could prime attentional cognitive activity. We examined how searching in physical space influences subsequent search in abstract cognitive space by presenting participants with a spatial-foraging task followed by a repeated Scrabble task involving search for words that could be made from letter sets. Participants who searched through clumpier distributions in space behaved as if words were more densely clumped in the Scrabble task. This was not a function of arousal, but was consistent with predictions of optimal-foraging theory. Furthermore, individual differences in exploratory search were conserved across the two types of tasks. Along with the biological evidence, our results support the idea that there are generalized cognitive search processes.

The assumption of optimality in foraging models: A simulated experiment with dairy cows grazing grass pasture

The “patch model” of optimal foraging theory (OFT) assumes that animals choose and exploit patches of food in order to maximise their food intake rate and derives the foraging rules (patch selection and exploitation) to achieve this. While evidence from field studies has been found to be broadly consistent with the predictions of OFT, this does not imply that animals actually forage using OFT rules, however, as the same observations could possibly arise as the result of non‐optimising foraging rules (e.g., avoidance of low food intake rate). Because OFT is potentially very useful for the purpose of managing animal production systems (e.g., for predicting and manipulating the intake of grazing dairy cows), it is of interest to know to what extent OFT remains useful if animals actually behave sub‐optimally. This paper examines this question by simulating animals foraging in a two‐dimensional spatially heterogeneous environment (New Zealand dairy cows grazing grass pasture) using six different foraging rules with varying degrees of optimality. The results showed that both optimal patch selection and optimal patch residence time rules significantly increase intake rate in this type of environment, but differences resulting from use of different variations of the patch selection rules are small. Therefore, although OFT is highly simplified, and animals’ senses and knowledge are imperfect, this need not preclude the use of OFT in practical applications, as the predictions of OFT are likely to be similar to the predictions of other, more realistic, foraging strategies, even when these are quite sub‐optimal in formulation.

Feeding behaviour and diet choices and diet choices of cattle with physical and temporal constraints on forage accessibility: an indoor experiment

AbstractAn indoor choice experiment was conducted to assess the extent to which heifers offered two forages of different quality will attempt to consume the better quality forage when the weight/number of constraints applied on its harvesting increase. The experiment involved six Salers heifers, a leafy (L) and a coarse (C) hay, and two combined or single accessibility constraints. A physical constraint consisted of reducing the prehensibility of L by covering the trough with a steel grid of either 4 cm or 6 cm mesh size (L4 or L6 v. L ∞ for no grid). A temporal constraint limited the daily access time to both hays to 4 v. 24 h. The hays were either offered alone or together over 2-week periods. Dry-matter intake and feeding time were recorded daily.As expected, the physical constraint (only L4 was efficient) made the heifers decrease their choice (proportion of feeding time or intake) for L regardless of access time, whereas the temporal constraint had no significant effect on choice. The heifers greatly modulated their intake rate of L even under strong physical constraint (L4), and then unexpectedly managed to ingest L faster than C. This emphasizes their motivation to keep ingesting the better quality forage, and underlines the difficulties in comparing diet choices with the optimal foraging theory predictions based on the relative values of a behavioural component subject to large variation, i.e. intake rate. In a very constraining situation (L4 and 4-h access), heifers made a choice that allowed them to increase their total daily digestible organic matter (DOM) intake compared with L4 or C offered alone because of an inverse relationship between feeding time and intake rate on L4. They did not however maximize their total daily DOM intake in a less constraining situation (L ∞ or L6 and C, with 4-h access), since they did not consume L exclusively and showed a marked preference for a mixed diet.

The Ecology of the Dingo in Northeastern New-South-Wales .4. Prey Selection by Dingoes, and Its Effect on the Major Prey Species, the Swamp Wallaby, Wallabia-Bicolor (Desmarest)

Prey selection and its effect on the major prey species was examined between 1979 and 1980 by comparing the diet of dingoes and the biology of the swamp wallaby at two sites where the relative numbers of dingoes and wallabies differed. Selection of prey by dingoes was not opportunistic but demonstrated a preference for larger native species, and was similar to that found in the same area between 1972 and 1974. In particular, dingoes had a strong preference for swamp wallaby, the occurrence of which in the diet was disproportionate to its observed numbers; and switching was not observed even when numbers of swamp wallaby were reduced and alternative macropod prey present. Contrary to Optimal Foraging Theory predictions that the predator should become more catholic in prey selection, this species was more frequent in the diet when its availability was lower. At one site the major effect of this predation was the disruption of the breeding cycle, as a result of the loss of large pouch young because of the harassment of their mothers.