Patterns Of Prey Use Research Articles

Repeated dietary shifts in elapid snakes (Squamata: Elapidae) revealed by ancestral state reconstruction

Abstract Identifying the traits of ancestral organisms can reveal patterns and drivers of organismal diversification. Unfortunately, reconstructing complex multistate traits (such as diet) remains challenging. Adopting a ‘reconstruct, then aggregate’ approach in a maximum likelihood framework, we reconstructed ancestral diets for 298 species of elapid snakes. We tested whether different prey types were correlated with one another, tested for one-way contingency between prey type pairs, and examined the relationship between snake body size and dietary composition. We demonstrate that the evolution of diet was characterized by niche conservation punctuated by repeated dietary shifts. The ancestor of elapids most likely fed on reptiles and possibly amphibians, with deviations from this ancestral diet occurring repeatedly due to shifts into marine environments and changes in body size. Moreover, we demonstrate important patterns of prey use, including one-way dependency—most obviously the inclusion of eggs being dependent on a diet that already included the producers of those eggs. Despite imperfect dietary data, our approach produced a robust overview of dietary evolution. Given the paucity of natural history information for many organisms, our approach has the potential to increase the number of lineages to which ancestral state reconstructions of multistate traits can be robustly applied.

Morphological traits correlated with resource partitioning among small characin fish species coexisting in a Neotropical river

AbstractBody shape variation should play a central role in determining the feeding ability of a fish species. We tested whether variations in feeding resource use of sympatric and closely related fish species could be explained by differences in ecologically relevant metrics, such as body morphology, trophic apparatus or combinations thereof. Fish were sampled at 14 sampling sites from Pelotas River and tributaries, Upper Uruguay, Brazil. The stomach contents of five species of Characidae (Astyanax and Bryconamericus) were analysed by the volumetric method. A geometric morphometric approach was used together with internal morphological traits to predict their patterns of prey use. Significant differences in body depth, snout and caudal peduncle lengths were found. Concomitant pronounced variations were verified to occur among species in structures related to digestion and absorption. Increased numbers of cusps, more pyloric caeca and higher intestinal coefficient values were observed in species that consumed greater proportions of plants. The opposite trends occurred in species that consumed greater proportions of insects. Mixed linear models indicated that the characin species differed significantly in the use of algae, aquatic insects, terrestrial insects, plant remains/seeds and detritus. Dietary differences reflected in low trophic niche overlap. Partial least squares regression results indicated strong correlations between morphological divergences and the corresponding variations in species diet. These outcomes combined confirm that the morphological traits that best enables the exploration of certain resource were an important factor in the resource‐related divergence and were the underlying reasons for these species' respective feeding modes.

Foraging connections: Patterns of prey use linked to invasive predator diel movement.

Invasive predators can profoundly impact native communities, especially in insular ecosystems where functionally equivalent predators were evolutionarily absent. Beyond direct consumption, predators can affect communities indirectly by creating or altering food web linkages among existing species. Where invasive predators consume prey from multiple distinct resource channels, novel links may couple the dynamics of disjunct modules and create indirect interactions between them. Our study focuses on invasive populations of Eleutherodactylus coqui (Anura: Leptodactylidae) on Hawaii Island. Coqui actively forage in the understory and lower canopy at night but return to the forest floor and belowground retreats by day. Recent dietary studies using gut contents and naturally occurring stable isotopes indicate higher than expected consumption of litter arthropods, which in these Hawaiian forests are primarily non-native species. We used laboratory studies to observe diurnal and nocturnal foraging behavior, and experimental field additions of C4 vegetation as a litter tracer to distinguish epigaeic sources from food web pools in the C3 canopy. Lab trials revealed that prey consumption during diurnal foraging was half that consumed during nocturnal foraging. Analysis of δ13C isotopes showed incorporation of C4 carbon into litter arthropods within one month, and Bayesian mixing models estimated that 15–25% of the carbon in coqui tissue was derived from litter sources. These results support recent findings that E. coqui are not quiescent diurnally but instead actively forage. Such activity by a mobile invasive predator may introduce a novel linkage that integrates detrital and foliar resource pools, potentially distributing influences of invasive litter arthropods through the broader system to amplify impacts on native species.

Wolves, white‐tailed deer, and beaver: implications of seasonal prey switching for woodland caribou declines

Population increases of primary prey can negatively impact alternate prey populations via demographic and behavioural responses of a shared predator through apparent competition. Seasonal variation in prey selection patterns by predators also can affect secondary and incidental prey by reducing spatial separation. Global warming and landscape changes in Alberta's bitumen sands have resulted in prey enrichment, which is changing the large mammal predator–prey system and causing declines in woodland caribou Rangifer tarandus caribou populations. We assessed seasonal patterns of prey use and spatial selection by wolves Canis lupus in two woodland caribou ranges in northeastern Alberta, Canada, that have undergone prey enrichment following recent white‐tailed deer Odocoileus virginianus invasion. We determined whether risk of predation for caribou (incidental prey) and the proportion of wolf‐caused‐caribou mortalities varied with season. We found that wolves showed seasonal variation in primary prey use, with deer and beaver Castor canadensis being the most common prey items in wolf diet in winter and summer, respectively. These seasonal dietary patterns were reflected in seasonal wolf spatial resource selection and resulted in contrasting spatial relationships between wolves and caribou. During winter, wolf selection for areas used by deer maintained strong spatial separation between wolves and caribou, whereas wolf selection for areas used by beaver in summer increased the overlap with caribou. Changing patterns in wolf resource selection were reflected by caribou mortality patterns, with 76.2% of 42 adult female caribou mortalities occurring in summer. Understanding seasonal patterns of predation following prey enrichment in a multiprey system is essential when assessing the effect of predation on an incidental prey species. Our results support the conclusion that wolves are proximately responsible for woodland caribou population declines throughout much of their range.

Plant production and alternate prey channels impact the abundance of top predators

While numerous studies have examined the effects of increased primary production on higher trophic levels, most studies have focused primarily on the grazing food web and have not considered the importance of alternate prey channels. This has happened despite the fact that fertilization not only increases grazing herbivore abundance, but other types of consumers such as detritivores that serve as alternate prey for generalist predators. Alternate prey channels can sustain generalist predators at times when prey abundance in the grazing food web is low, thus increasing predator densities and the potential for trophic cascades. Using arthropod data from a fertilization experiment, we constructed a hierarchical Bayesian model to examine the direct and indirect effects of plant production and alternate prey channels on predators in a salt marsh. We found that increased plant production positively affected the density of top predators via effects on lower trophic level herbivores and mesopredators. Additionally, while the abundance of algivores and detritivores positively affected mesopredators and top predators, respectively, the effects of alternate prey were relatively weak. Because previous studies in the same system have found that mesopredators and top predators rely on alternate prey such as algivores and detritivores, future studies should examine whether fertilization shifts patterns of prey use by predators from alternate channels to the grazing channel. Finally, the hierarchical Bayesian model used in this study provided a useful method for exploring trophic relationships in the salt marsh food web, especially where causal relationships among trophic groups were unknown.

Predator hunting mode influences patterns of prey use from grazing and epigeic food webs

Multichannel omnivory by generalist predators, especially the use of both grazing and epigeic prey, has the potential to increase predator abundance and decrease herbivore populations. However, predator use of the epigeic web (soil surface detritus/microbe/algae consumers) varies considerably for reasons that are poorly understood. We therefore used a stable isotope approach to determine whether prey availability and predator hunting style (active hunting vs. passive web-building) impacted the degree of multichannel omnivory by the two most abundant predators on an intertidal salt marsh, both spiders. We found that carbon isotopic values of herbivores remained constant during the growing season, while values for epigeic feeders became dramatically more enriched such that values for the two webs converged in August. Carbon isotopic values for both spider species remained midway between the two webs as values for epigeic feeders shifted, indicating substantial use of prey from both food webs by both spider species. As the season progressed, prey abundance in the grazing food web increased while prey abundance in the epigeic web remained constant or declined. In response, prey consumption by the web-building spider shifted toward the grazing web to a much greater extent than did consumption by the hunting spider, possibly because passive web-capture is more responsive to changes in prey availability. Although both generalist predator species engaged in multichannel omnivory, hunting mode influenced the extent to which these predators used prey from the grazing and epigeic food webs, and could thereby influence the strength of trophic cascades in both food webs.

An integrative modeling approach to elucidate suction-feeding performance

Research on suction-feeding performance has mostly focused on measuring individual underlying components such as suction pressure, flow velocity, ram or the effects of suction-induced forces on prey movement during feeding. Although this body of work has advanced our understanding of aquatic feeding, no consensus has yet emerged on how to combine all of these variables to predict prey-capture performance. Here, we treated the aquatic predator-prey encounter as a hydrodynamic interaction between a solid particle (representing the prey) and the unsteady suction flows around it, to integrate the effects of morphology, physiology, skull kinematics, ram and fluid mechanics on suction-feeding performance. We developed the suction-induced force-field (SIFF) model to study suction-feeding performance in 18 species of centrarchid fishes, and asked what morphological and functional traits underlie the evolution of feeding performance on three types of prey. Performance gradients obtained using SIFF revealed that different trait combinations contribute to the ability to feed on attached, evasive and (strain-sensitive) zooplanktonic prey because these prey types impose different challenges on the predator. The low overlap in the importance of different traits in determining performance also indicated that the evolution of suction-feeding ability along different ecological axes is largely unconstrained. SIFF also yielded estimates of feeding ability that performed better than kinematic traits in explaining natural patterns of prey use. When compared with principal components describing variation in the kinematics of suction-feeding events, SIFF output explained significantly more variation in centrarchid diets, suggesting that the inclusion of more mechanistic hydrodynamic models holds promise for gaining insight into the evolution of aquatic feeding performance.

Prey selection in the trap-nesting wasp Trypoxylon (Trypargilum) opacum Brèthes (Hymenprtera; Crabronidae)

The purpose of our research was to document and discuss the temporal patterns of prey use shown by the trap-nesting wasp Trypoxylon opacum in two different habitats in Southern Brazil. It was carried out from December 2001 to December 2004. Twenty nine species belonging to five families of spiders were captured by T. opacum. Araneidae was the most captured family and has been strongly represented by the genus Eustala. Through Bray-Curtis s coefficient and the unweighted pair group method average (UPGMA), the spiders can be divided into three groups: the smaller group includes the most abundant species (Alpaida sp2, Bertrana rufostriata, Eustala sp1, Eustala sp2, Eustala sp3 and Eustala sp4), the second group includes species with intermediate abundance (Alpaida, Alpaida gracia and Mangora sp2), and the third and largest group includes the less abundant species, (Acacesia villalobosi, Alpaida argenata, Alpaida sp1, Araneus blumenau, Araneus sicki, Crysometa boraceia, Crysometa sp3, Eustala sp8, Eustala sp11, Larinia t-notata, Mangora sp1, Ocrepeira aff gnomo, Sanogasta sp., Sanogasta sp2, Sanogasta sp3, Salticidae sp2, Theridion sp1, Theridion sp2, Wagneriana eupalaestris, Wagneriana iguape). Of 1,053 identified spiders, 362 were captured in the grassland areas and 691 in the swamp, since T. opacum built nests only in these two habitats. The diversity, richness and evenness of spiders in T. opacum nests were higher in grassland than in the swamp.

Patterns of prey use by lesser scaup Aythya affinis (Aves) and diet overlap with fishes during spring migration

Recent decline in the lesser scaup Aythya affinis population has been linked to changes in wetland conditions along their spring migration routes. In particular, the use of amphipod prey by lesser scaup has declined in many regions of the upper Midwest U.S.A. and has been linked to expanded fisheries, although empirical data on diet overlap are lacking. To explore patterns of prey use by lesser scaup and diet overlap with fishes, we quantified diets of scaup and fishes during the 2003 and 2004 spring migration in eastern South Dakota, U.S.A. We compared diet overlap between lesser scaup and fishes collected from Twin Lakes, South Dakota—an important stopover location for spring-migrating scaup. Plant seeds occurred in >95% of lesser scaup diets (n = 118) and represented an appreciable amount of consumed biomass (>70%). Gastropods, amphipods, and chironomids were the most abundant invertebrate prey taxa and occurred in 29–34% of lesser scaup diets. Although relatively frequent, these taxa each contributed only 4–27% of the diet by weight. Percent dry mass of amphipods, a preferred prey by lesser scaup, was low (4%) indicating that amphipod availability may be reduced during spring migration. Analysis of fish diets showed that black bullhead Ameiurus melas and yellow perch Perca flavescens had the highest diet overlap with lesser scaup at 94% and 92%, respectively. Moreover, mean size of amphipods and chironomids found in fish diets were significantly larger than that consumed by lesser scaup. Our findings support the notion that amphipod use by spring-migrating lesser scaup has declined and that size-selective predation by fishes may influence prey availability for lesser scaup.

Understanding biodiversity effects on prey in multi‐enemy systems

Biodiversity-ecosystem functioning theory would predict that increasing natural enemy richness should enhance prey consumption rate due to functional complementarity of enemy species. However, several studies show that ecological interactions among natural enemies may result in complex effects of enemy diversity on prey consumption. Therefore, the challenge in understanding natural enemy diversity effects is to predict consumption rates of multiple enemies taking into account effects arising from patterns of prey use together with species interactions. Here, we show how complementary and redundant prey use patterns result in additive and saturating effects, respectively, and how ecological interactions such as phenotypic niche shifts, synergy and intraguild predation enlarge the range of outcomes to include null, synergistic and antagonistic effects. This study provides a simple theoretical framework that can be applied to experimental studies to infer the biological mechanisms underlying natural enemy diversity effects on prey.

Prey-switching by Cassin’s auklet Ptychoramphus aleuticus reveals seasonal climate-related cycles of Euphausia pacifica and Thysanoessa spinifera

Euphausia pacifica and Thysanoessa spinifera comprise a substantial proportion of the diet of Cassin's auklet Ptychoramphus aleuticus in the Gulf of the Farallones, California. Ocean climate variability has been linked to fluctuations in euphausiid abundance and life-history parame- ters. We tested the hypothesis that seasonal patterns of prey use by auklets correspond to within- season variation in upwelling and sea surface temperature (SST), by comparing the proportion (by number) of E. pacifica and T. spinifera in auklet diet samples obtained during the chick-rearing period to SST and an upwelling index (UI) over 11 years. We found that the proportion of E. pacifica adults in auklet diet decreased over the chick-rearing period, and increased with increasing UI and decreasing SST. We detected curvature in the relationship between adult E. pacifica and UI, with E. pacifica increasing to a point and decreasing thereafter. T. spinifera in auklet diet showed an increase over the chick-rearing period, but no relationships were detected with UI or SST. Mass of individual adult E. pacifica increased with increasing UI and decreasing SST. We detected moderate curvature in the relationship between mass of individual adult T. spinifera and SST. The proportion of E. paci- fica juveniles in auklet diet did not change seasonally and was not related to UI or SST, while the pro- portion of T. spinifera juveniles in auklet diet increased seasonally and with increases in UI. Seasonal changes in the ingestion of euphausiids by auklets appeared to be affected by ocean climate variabil- ity; however, prey-selection via a shift in foraging location or competition with other marine preda- tors are alternative valid explanations. This study highlighted the utility of using top marine preda- tors to sample prey availability, thereby complementing traditional net sampling procedures for determining the distribution and abundance of euphausiids in marine systems.

DIET OF THE BIG BROWN BAT, EPTESICUS FUSCUS, FROM PENNSYLVANIA AND WESTERN MARYLAND

Abstract We used fecal analysis to describe the diet of Eptesicus fuscus in Pennsylvania and western Maryland. We examined spatial variation in diet composition among three populations and temporal variation within a maternity colony. Temporal patterns of prey use were compared with similar data collected previously from a maternity colony in Indiana. Overall, Coleoptera (58–82%), especially Scarabaeidae (14–31%), were the dominant prey items. Hemiptera, primarily Acrosternum hilare (5–19%), were also major prey, and Tettigoniidae (not previously reported) were prey of two populations (6%, 17%). Significant spatial and temporal variation existed in diet composition among populations and use of major prey types, respectively. Comparison of temporal data collected in this study and in Indiana indicated a nearly identical pattern in the use of Scarabaeidae. These insects are abundant in the spring, and the data suggest widespread specialization on Scarabaeidae in April and May. Several insects preyed on by E...

Effect of intra- and interspecific interactions on the feeding behavior of two subtidal sea stars

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 232:149-162 (2002) - doi:10.3354/meps232149 Effect of intra- and interspecific interactions on the feeding behavior of two subtidal sea stars Carlos F. Gaymer*, John H. Himmelman*, Ladd E. Johnson Département de Biologie and GIROQ (Groupe Interuniversitaire de Recherches Océanographiques du Québec), Université Laval, Québec G1K 7P4, Canada *Corresponding author. E-mail: john.himmelman@bio.ulaval.ca ABSTRACT: Competition and its effects are difficult to demonstrate, as they vary depending on the species present and the environmental conditions in each community. We conducted laboratory and field experiments to evaluate the effects of intra- and interspecific interactions on the use of food resources and behavior of the sea stars Leptasterias polaris and Asterias vulgaris, 2 major predators in subtidal communities of the northern Gulf of St. Lawrence. We demonstrate interference (encounter) competition between the two. For both species, the presence of the other (as detected by both contact and chemical signals) decreased feeding activity and provoked behavioral changes (avoidance, decrease in percentage feeding). These effects were reversible and short-lived, and were more pronounced when there was a shortage of food and when sea stars were exposed to simulated attacks by the other species (involving pedicellarial pinching). L. polaris seemed to be the inferior competitor as (1) it switched to less profitable prey size (smaller mussels, Mytilus edulis) when A. vulgaris was present, and (2) it avoided A. vulgaris and reduced its feeding activity when food was scarce. The dominance of A. vulgaris is possibly attenuated at our study site (near its northern distributional limit) by the reduction of its fitness when water temperatures are low (most of the year) and during the winter when it migrates to deeper water. Competition for food resources seems to occur periodically (mainly summer), in localized areas (patches and beds of mussels) or when sea stars form dense aggregations in which they are likely to interact frequently. Interactions, and thus the chance of competition, are less likely at greater depths. Coexistence seems to be permitted by both the attenuation of the dominance of A. vulgaris and by the great variations in how L. polaris and A. vulgaris interact (strongly affected by variations in prey availability, sea star abundance, and in the patterns of prey use by both sea stars). KEY WORDS: Sea stars · Feeding ecology · Prey preference · Feeding experiments · Behavior · Interference · Competition · Avoidance Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 232. Online publication date: May 03, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Ecological Explanation through Functional Morphology: The Feeding Biology of Sunfishes

Researchers have been using simple morphological measures as indicators of ecological features for some time. The utility of morphological variables as ecological indicators depends upon our understanding of how the variable effects the ability of the organism to perform a particular task. Functional morphological analyses identify those features that can be directly related to behavioral performance and help to distinguish causal functional relationships from spurious correlations. The behavioral abilities of the individual, in turn, shape patterns of resource use and fitness by placing limits on the range of resources that can be utilized and by shaping the cost/benefit curve for resource choices. Examples from research on the feeding biology of North American sunfishes are discussed to illustrate how functional morphology can be used to provide explanations for differences between species in patterns of prey use, patterns of habitat use, ontogenetic diet switches, and population size. Trends from analyses of the evolution of fish feeding mechanisms suggest specific functional features that are most likely to vary among taxa and underlie differences in feeding performance and diet. Included in this group of predictive variables are the organization of lever arms in the jaw opening and closing systems, the size of the mouth, and the size of muscles used in prey—crushing behaviors. The link between morphology and ecology will be made most firmly when variables are chosen that clearly reflect the ability of the organism to perform relevant behaviors.

Predicting patterns of prey use from morphology of fishes

Predicting patterns of prey use from morphology of fishes

Ecomorphological relationships among Caribbean tetraodontiform fishes

The anatomy of the oral jaw apparatus, lever‐arm mechanics and the diet of six species of Caribbean fishes in the order Tetraodontiformes were investigated to explore the relationships between trophic morphology and feeding habit in these fishes. Tetraodontiforms use their oral jaw apparatus to capture and reduce a broad range of prey types such as plankton, polychaete worms, holothuroids, sea urchins, crabs, molluscs, gorgonians and algae. The different feeding habits of tetraodontiforms are reflected by differences in the morphological and biomechanical features of their oral jaw apparatus that appear to enhance their abilities to feed on hard prey organisms. Species that bite and crush hard, benthic prey organisms had more massive bones and muscles, longer jaw‐opening in‐levers, and higher jaw‐closing lever ratios than the planktivorous, suction‐feeding species. Masses of the jaw and suspensorium bones and lower jaw adductor muscles as well as the jaw‐opening in‐levers and jaw‐closing lever ratios of crushers were greater than those of biters. In contrast, the mass of the adductor muscle of the upper jaw did not vary among species with different diets, indicating that this muscle may not be central to the factors that determine patterns of prey use in these fishes. The diversity of feeding behaviours and the wide range of feeding habits among fishes in the order Tetraodontiformes illustrate the versatility of the oral jaw apparatus as a single functional feeding system in fishes.

Food-niche relationships and guild structure of diurnal birds of prey: competition versus opportunism

Food-niche relationships of diurnal raptors have been claimed to be shaped by either competitive interactions or opportunistic feeding. We confront these alternatives by analyzing the patterns of prey use of five assemblages of falconiforms. Our results show that food-niche breadth is not a species property but is determined by the food resources locally available; neither does it become narrower in larger assemblages nor is it correlated with raptor size. Food-niche overlaps are frequently very high and do not become smaller in larger assemblages. Mean weight of prey taken is positively correlated with raptor weight within assemblages, but varies widely across assemblages, with a single species showing manyfold differences. Weight ratios between raptors contiguous in the size axis fall well below the 2.2–3.4 expected figures, nor are they negatively correlated with the amount of food-niche overlap. Normalized distance ratios (d/w) of spacing between raptors along the food-size axis are usually smaller than the expected 1. The five assemblages are organized in feeding guilds whose size is larger where fewer prey categories are available per raptor species. In most cases we found little support for predictions based on competition-structured assemblages. This is probably because of the opportunistic feeding behavior of raptors, and perhaps also because food might not be a limiting resource for them.

Patterns of prey use in four sympatric species ofPhilanthus(Hymenoptera: Sphecidae) with a review of prey selection in the genus

Summary Observations were made on four sympatric species of sphecid wasps of the genus Philanthus that nest in late summer and prey upon Hymenoptera. All four species nest in a restricted locale, but with little overlap in nesting areas. Comparison of nest contents of females demonstrated limited overlap in prey utilization among the four species, but only when both size and taxonomic category of prey were considered. The ultimate cause of this resource partitioning is unknown. Review of 30 populations of 16 species of North American Philanthus reveals varying degrees of specialization on prey types. Although populations of one species, separated in either time or space, tend to have similar niche breadths, this is not always the case. Intra-and inter-populational comparisons of prey records suggest behavioural plasticity allowing response to variations in prey availability. Some of the divergence in prey use among species is due to differences in predator size.