Small Prey Items Research Articles

Gluttonous predators: how to estimate prey size when there are too many prey

Prey size is an important factor in food consumption. In studies of feeding ecology, prey items are usually measured individually using calipers or ocular micrometers. Among amphibians and reptiles, there are species that feed on large numbers of small prey items (e.g. ants, termites). This high intake makes it difficult to estimate prey size consumed by these animals. We addressed this problem by developing and evaluating a procedure for subsampling the stomach contents of such predators in order to estimate prey size. Specifically, we developed a protocol based on a bootstrap procedure to obtain a subsample with a precision error of at the most 5%, with a confidence level of at least 95%. This guideline should reduce the sampling effort and facilitate future studies on the feeding habits of amphibians and reptiles, and also provide a means of obtaining precise estimates of prey size.

Size-specific predation by dominant consumers maintains a ‘trophic cul-de-sac’

Manipulations of fully grown (>60.0 mm) detritivorous Sydney mud whelks Pyrazus ebeninus Brugiere 1972 suggest that the species serves as a 'trophic cul-de-sac', limiting flow of car- bon from producers to top consumers. However, although large P. ebeninus individuals experience negligible predation, smaller individuals that do not cause the same depletion of primary and sec- ondary producers may suffer predatory losses. To assess the role that predation on the small whelks might play in weakening the trophic cul-de-sac provided by larger conspecifics, we investigated size- and habitat-specific patterns of predation on P. ebeninus through a series of field and laboratory ex- periments. Field tethering of 3 size classes of snail indicated that irrespective of seasonal differences in predation intensity, small (30.1 to 40.0 mm shell height, SH) individuals experienced significantly greater predatory mortality (25% over 7 wk) than medium (50.1 to 60.0 mm SH: 7.5%) or large (70.1 to 80.0 mm SH: 2%) conspecifics. Predatory mortality was largely attributable to naticid predators, al- though several tethered snails were crushed, perhaps by elasmobranchs, toadfish or crabs. For some size classes there were differences in predatory mortality between low shore mudflats and higher shore mangrove forests, but the direction of these differences varied between autumn and spring, and the differences disappeared altogether when densities of predators were held constant, indicating that they were not driven by habitat per se. In laboratory experiments, the relative contributions of small, medium and large P. ebeninus individuals to the total prey consumed by the naticid gastropod Conu- ber sordidus Swainson 1821 were similar between choice and no-choice experiments, and even in the absence of small prey items, large P. ebeninus snails were not consumed. Thus, even when there is de- pletion of small size classes of P. ebeninus, it is unlikely that common benthic predators would con- sume sufficient numbers of large snails to prevent deleterious effects of this species on primary and secondary production. To the contrary, predatory mortality of small P. ebeninus individuals may en- sure that its populations continue to be dominated by the large, damage-causing size classes.

Trophic ecology of bullet tuna Auxis rochei larvae and ontogeny of feeding-related organs

The bullet tuna Auxis rochei, Risso 1810, is a small tuna widely distributed in tropical and temperate Seas. The present study reports on the first attempt to jointly monitor diet and food selection in larvae of this species and to assess the influence of the ontogenetic development of feed- ing-related organs on the diet. A. rochei larvae from 2 to 7 mm long are diurnal feeders and highly active predators, with high values of feeding incidence, gut fullness and number of ingested prey items. The rate of change in prey item size in relation to larval size was higher than in other species. Only small, non-motile prey items are eaten at the onset of feeding. Rapid mouth development and the early appearance of teeth allow larvae from 3 to 5 mm long to ingest a wide range of prey. How- ever, niche breadth decreases at 5 mm, when larvae avoid small prey items in favour of larger ones with a higher carbon content. Chesson's selectivity index indicated that small larvae (from 2 to 3 mm long) selected a variety of small prey items, mainly copepod nauplii. Larvae measuring 3 to 5 mm selectively ate cladocerans and appendicularians, and larvae with lengths ≥5 mm preferred appen- dicularians and fish larvae. Precocious body development (mouth, teeth, and onset of stomach and caudal fin development) and improved visual acuity (larger lens diameter and angular cone density) are factors that contribute to the feeding success of larvae of this species.

Food resource use in a tropical eastern Pacific tidepool fish assemblage

An understanding of the trophic organization patterns of tropical littoral fish assemblages can contribute to the knowledge of key ecosystem processes while simultaneously assisting to validate large-scale biogeographic patterns (i.e. latitudinal patterns in fish herbivory). In the present study, the diets of eight fish species inhabiting the tide pools of a rocky shore on the western coast of Colombia (tropical eastern Pacific) are documented. A total of 17 prey items were identified, with a major representation (average percent by weight) of crabs and macroalgae items in the guts of all species. Small crustacean prey items (crabs, shrimps, copepods and amphipods) dominated the diets of most species, but consumption of macroalgae and diatoms by a significant number of species was also observed. We identified four significant trophic guilds within the assemblage using multivariate techniques (cluster analysis and nMDS): an omnivorous guild, consisting of Malacoctenus zonifer and the smallest size class of Bathygobius ramosus; a small-prey carnivorous guild, consisting of the intermediate size classes of B. ramosus and the smallest size class of Gobiesox adustus; a large-prey carnivorous guild, consisting of both largest size classes of B. ramosus and G. adustus; and an herbivorous guild consisting of Abudefduf concolor, A. troschelii and Chaenomugil proboscideus. The diet of two species slightly overlapped those of the rest of the assemblage and did not conform to any guild (Echidna nocturna and Halichoeres aestuaricola). It is hypothesised that guild formation may be a consequence of aggregation of species at abundant resources in the intertidal zone rather than a direct consequence of inter-specific competition. Ontogenetic changes in diets were observed in two resident species of the assemblage (B. ramosus and G. adustus). The latitudinal trend for herbivory inside this tropical assemblage is discussed in comparison with similar temperate studies in the eastern Pacific.

Independent evolutionary origins of landlocked alewife populations and rapid parallel evolution of phenotypic traits

Alewife, Alosa pseudoharengus, populations occur in two discrete life-history variants, an anadromous form and a landlocked (freshwater resident) form. Landlocked populations display a consistent pattern of life-history divergence from anadromous populations, including earlier age at maturity, smaller adult body size, and reduced fecundity. In Connecticut (USA), dams constructed on coastal streams separate anadromous spawning runs from lake-resident landlocked populations. Here, we used sequence data from the mtDNA control region and allele frequency data from five microsatellite loci to ask whether coastal Connecticut landlocked alewife populations are independently evolved from anadromous populations or whether they share a common freshwater ancestor. We then used microsatellite data to estimate the timing of the divergence between anadromous and landlocked populations. Finally, we examined anadromous and landlocked populations for divergence in foraging morphology and used divergence time estimates to calculate the rate of evolution for foraging traits. Our results indicate that landlocked populations have evolved multiple times independently. Tests of population divergence and estimates of gene flow show that landlocked populations are genetically isolated, whereas anadromous populations exchange genes. These results support a 'phylogenetic raceme' model of landlocked alewife divergence, with anadromous populations forming an ancestral core from which landlocked populations independently diverged. Divergence time estimates suggest that landlocked populations diverged from a common anadromous ancestor no longer than 5000 years ago and perhaps as recently as 300 years ago, depending on the microsatellite mutation rate assumed. Examination of foraging traits reveals landlocked populations to have significantly narrower gapes and smaller gill raker spacings than anadromous populations, suggesting that they are adapted to foraging on smaller prey items. Estimates of evolutionary rates (in haldanes) indicate rapid evolution of foraging traits, possibly in response to changes in available resources.

The use of distal rhynchokinesis by birds feeding in water

The use of distal rhynchokinesis, which consists of the movement of the distal part of the upper jaw with respect to the cranium, is well documented in long-billed shorebirds (Scolopacidae), commonly being associated with the deep probing feeding method. However, the functional and evolutionary significance of distal rhynchokinesis and other cranial kinesis is unclear. We report for the first time the use and occurrence of distal rhynchokinesis in wild long-billed shorebirds feeding on small prey items suspended in water. We tested whether prey size in captive dunlins Calidris alpina influences the occurrence of distal rhynchokinesis during feeding and also whether its use affects foraging efficiency. We found that wild dunlin, curlew sandpiper Calidris ferruginea, sanderling Calidris alba and little stint Calidris minuta commonly use distal rhynchokinesis to strike, capture and transport small prey items. Prey size influenced the occurrence of distal rhynchokinesis during the transport phase, with this type of cranial kinesis being more frequently used with larger prey. The rhynchokinesis protraction angle (a measure of bill tip elevation) during prey strike and transport was affected by prey size, and bill gape was modulated through the use of distal rhynchokinesis in relation to prey size. Finally, the use of distal rhynchokinesis throughout intra-oral prey transport was related to shorter transport times, which improved foraging efficiency. We conclude that distal rhynchokinesis is a mechanism that could contribute to the flexible feeding behaviour of long-distance migratory shorebirds, enhancing small prey profitability and so improving foraging efficiency, and may have played a role in the evolutionary radiation of Scolopacidae (Charadrii).

Variation in Paleoindian fauna use on the Great Plains and Rocky Mountains of North America

Drawing on data from 69 zooarchaeological assemblages from Paleoindian sites in the Great Plains and Rocky Mountains, this paper explores factors underlying changes in prehistoric diet breadth. Results indicate that different site types provide different perspectives on Paleoindian faunal use. Kill assemblages can only inform on the exploitation of large game, while the full variety of prey used by foragers is represented at camps. In contrast to prior claims, however, the inclusion of kill site assemblages in zooarchaeological analyses does not appear to bias our perspective of Paleoindian subsistence. Rather, there is strong indication that Paleoindian foragers targeted different types of prey depending on which habitat they occupied. In more-diverse environments of alluvial valleys and foothill/mountains, foragers exploited large game whenever possible, but they also targeted a suite of smaller prey items. In more uniform grassland environments, subsistence strategies focused almost exclusively on hunting large prey, such as bison and mammoth. These results also provide limited support for prior studies that argue for intensified resource use and increased diet breadth in response to early Holocene environmental changes, at least in certain settings.

Small-Prey Profitability: Field Analysis of Shorebirds’ use of Surface Tension of Water to Transport Prey

AbstractPrevious laboratory studies have shown that Red-necked Phalarope (Phalaropus lobatus), Wilson’s Phalarope (P. tricolor), Western Sandpiper (Calidris mauri), and Least Sandpiper (C. minutilla) use the surface tension of water surrounding a prey item to transport it from bill tip to mouth. Although such experimental work suggests that many species of shorebird may be capable of surface-tension feeding, no field studies have been done that examine this possibility. We studied the occurrence and interspecific variation in the performance of surface-tension transport (STT) in wild shorebirds feeding on identical prey items in shallow water. All shorebirds videotaped—Little Stint (C. minuta), Dunlin (C. alpina), Sanderling (C. alba), Curlew Sandpiper (C. ferruginea), Common Redshank (Tringa totanus), and Black-winged Stilt (Himantopus himantopus)—used STT to feed on small prey items. Individuals employing STT used one or several cycles of jaw spreading to transport the prey contained in a drop of water upward along the bill cavity, an action indicative of STT. Two distinct types of prey transport were observed: (1) use of STT in isolation by calidridine species following the description given in previous studies (i.e., an absence of other feeding mechanisms such as tongue movements, suction, or inertial transport), and (2) STT aided by inertial transport (head jerks) as seen in Common Redshank and Black-winged Stilt. Measured prey-transport variables (number of cycles, total time, and speed of transport) varied among species. The absence of significant relationships between these variables and measures of external morphology (bill length, bill length-to-width ratio, and bill length-to-depth ratio) suggests that some interspecific variations in STT performance may be attributable to differences in internal bill morphology. We show that STT is a common feeding mechanism in small or medium- sized shorebird species that feed on small prey items in shallow water. Birds using STT transported ≤3.6× faster than the theoretical value predicted by a previous model and can achieve high intake rates when foraging on high densities of available small prey items.Ventajas de las Presas Pequeñas: Análisis de Campo del Uso de la Tensión Superficial del Agua por las Aves Playeras para Transportar las Presas

Behavioural Plasticity in Foraging Mode of Typical Plovers

The foraging behaviour of typical plovers is highly stereotyped, and short-billed plovers all forage visually in a run—stop—search manner. To date, the use of a sandpiper-like foraging method by typical plovers is considered anecdotal in non-breeding plovers, since only one study has described Grey Plovers Pluvialis squatarola foraging as sandpipers do, striding slowly and pecking at the water surface during short periods. We studied the behaviour and intake rate of Grey and Ringed Plovers Charadrius hiaticula foraging like sandpipers on suspended prey items in the water column of hypersaline pans, and investigated factors that may influence their occurrence. The feeding rate was 48.9 ± 18.0 (SD) and 19.1 ± 6.3 prey min-1 for Ringed and Grey Plover, respectively. For Ringed Plovers, the net intake rate was 0.23 ±0.05 kJ min-1, and for Grey Plovers 0.09 ± 0.01 kJ min-1. The sandpiper-like foraging method was particularly important for Ringed Plovers, since up to 24% of the population foraged in this way at high tide. We found that the sandpiper-like foraging method is a common foraging method in Ringed Plover feeding in prey-abundant pans and is occasionally used by Grey Plovers as well. We showed that behavioural plasticity in foraging methods of typical plovers may be greater than has been assumed previously. These results suggest that typical plovers can successfully locate and capture small prey items while walking continuously and without the need to stop to improve visual acuity.

Foraging specialisms, prey size and life‐history patterns: a test of predictions using sympatric polymorphic Arctic charr (Salvelinus alpinus)

Abstract – We use arguments based on optimal foraging theory to predict body size constraints and the consequences of these on a range of life‐history traits in three trophic specialist morphs of Arctic charr, Salvelinus alpinus, living in sympatry in Loch Rannoch, Scotland. As predicted, foraging specialists feeding on small prey items with a narrow size range showed evidence of deterministic growth; the ultimate body size of macrobenthos feeders being larger (L∞ = 238 mm) than that of planktivores (L∞ = 216 mm). In contrast, the piscivorous morph showed no evidence of reaching a maximal body size.The two size‐constrained morphs (benthivores and planktivores) matured earlier and died younger (living for up to 11 and 7 years, respectively, in this study) than did the piscivorous charr which showed continuous growth up to at least 17 years.The pattern of annual reproductive investment in maturing individuals was complex. Planktivores invested in larger eggs than the other two forms, but benthivores produced a greater number of eggs than planktivores, which in turn produced more than piscivores. Planktivorous males had a greater investment in mean testis weight than the other two forms.Lifetime reproductive output was the greatest in the benthivorous charr, intermediate in planktivorous and the lowest in the piscivorous charr when measured either as fecundity or as gonadal weight. We conclude that constraints imposed upon foraging specialists by foraging efficiency is a significant driver of body size and ultimately reproductive investment in gape‐limited foraging salmonids.

Prey Size Selection under Simultaneous Choice by the Broad‐Headed Skink (Eumeces laticeps)

AbstractDiet selection among several prey types present in a dense aggregation, permitting a predator to become satiated without changing patches, may be important for predators that can eat many small prey items in a single bout. Choice in this scenario differs from that in optimal foraging models for sequential diet choice model and simultaneous choice models when travel time between patches is needed. Furthermore, satiation and depletion effects may be important in dense prey aggregations. We predicted that in dense prey aggregations, predators should eat the most profitable prey first, switching to smaller prey as larger ones become depleted and predators become satiated, and that prey below some minimum profitability should be rejected. When large numbers of prey of varying sizes were presented simultaneously, broad‐headed skinks (Eumeces laticeps) preferentially consumed large crickets, ate some medium‐sized crickets late in ingestion sequences, but ate no small crickets. Prey depletion, with selection of the currently most profitable prey type, appears to account for much of observed prey switching, and satiation may contribute. When four crickets of each of four sizes were presented, lizards ate largest first, then medium‐sized. Some then ate small crickets, but none ate very small crickets. These observations and exclusion of small crickets from the diet by many lizards when larger ones were unavailable support the predictions. In tests with three sizes of juvenile mice presented singly, the smallest were attacked at shortest latency and eaten, medium‐sized mice were attacked at greater latency but could not be subdued, and large mice were not attacked. These data suggest that as prey become too large to subdue and eat readily, profitability declines until they are excluded from the diet. Unsuccessful attacks on medium‐sized mice suggest that lizards had to learn their own capabilities with respect to a novel prey type.

Host‐dependent differences in prey acquisition between populations of a kleptoparasitic spider Argyrodes kumadai (Araneae: Theridiidae)

Abstract 1. A kleptoparasitic spider, Argyrodes kumadai, is known to use phylogenetically unrelated host species in different regions –Cyrtophora moluccensis (Araneidae) in south‐west Japan and Agelena silvatica (Agelenidae) in north‐east Japan. The work reported here examined whether differences in host characters affect prey acquisition of A. kumadai.2. Field surveys showed that prey‐biomass capture rate of Argyrodes was significantly higher in populations parasitising Cyrtophora than in populations parasitising Agelena. Although Argyrodes appeared to catch fewer prey within Cyrtophora webs, they were able to feed upon substantially larger prey.3. Differences in prey‐biomass capture rate were found to reflect differences in host traits rather than regional differences in potential prey availability. Individuals in populations parasitising Cyrtophora were observed to acquire prey via a number of foraging tactics that included stealing wrapped food bundles, feeding upon prey remains and, in the case of large prey items, feeding together with the host. In contrast, individuals in populations parasitising Agelena were only ever observed to feed upon small prey items ignored by its host.4. This variability in prey acquisition between kleptoparasite populations reflected different opportunities for feeding within their respective host webs – opportunities that were primarily determined by the foraging behaviour of the host. One key trait associated with host foraging behaviour was host‐web structure, namely the presence/absence of a retreat.

Mouthing off about fish capture: Jaw movement in pinnipeds reveals the real secrets of ingestion

Determination of when and where animals feed and how much they consume is fundamental to understand their ecology and role in ecosystems. However, the lack of reliable data on feeding habits of wild animals, and particularly in marine endotherms, attests to the difficulty in doing this. A promising recent development proposes using a Hall sensor-magnet system, the inter-mandibular angle sensor (IMASEN) attached to animals’ jaws to elucidate feeding events. We conducted trials on captive pinnipeds by feeding IMASEN-equipped animals with prey to examine the utility of this system. Most feeding events were clearly distinguishable from other jaw movements; only small prey items might not be resolved adequately. Based on the results of this study we examined feeding events from free-ranging pinnipeds fitted with IMASENs and dead-reckoners and present data on prey capture and ingestion in relation to the three-dimensional movement patterns of the seals.

FOOD AND FEEDING HABITS OF THE EGYPTIAN SOLE SOLEA AEGYPTIACA (CHABANAUAD, 1972), FROM PORT SAID, MEDITERRANEAN SEA, EGYPT

ABSTABCT T food and feeding habits of the Egyptian Sole, Solea aegyptiaca (Chabanauad, 1972) were studied in Port Said area, Mediterranean Sea during the period from October 2004 to September 2005. The annual composition of the diet, the intensity of feeding, seasonal variation of diet composition and variation of diet with length, showed a low-intensity of feeding activity of S. aegyptiaca, and indicated that they feed on a wide variety of prey types (polychaetes, mollusks, amphipods, sediments and small quantities of crustacean fragments, Ascidia, fish parts, sea grasses, brittlestars, unknown medusae and algae), with a limited variation in diet among seasons. The prey types and size differed from juvenile to adults, juvenile ingested only 5 small prey items; while adult had eaten about 11 of large sized prey items. The diet composition of Egyptian sole is indicative of a generalist feeding strategy.

SMALL-PREY PROFITABILITY: FIELD ANALYSIS OF SHOREBIRDS’ USE OF SURFACE TENSION OF WATER TO TRANSPORT PREY

Abstract Previous laboratory studies have shown that Red-necked Phalarope (Phalaropus lobatus), Wilson’s Phalarope (P. tricolor), Western Sandpiper (Calidris mauri), and Least Sandpiper (C. minutilla) use the surface tension of water surrounding a prey item to transport it from bill tip to mouth. Although such experimental work suggests that many species of shorebird may be capable of surface-tension feeding, no field studies have been done that examine this possibility. We studied the occurrence and interspecific variation in the performance of surface-tension transport (STT) in wild shorebirds feeding on identical prey items in shallow water. All shorebirds videotaped—Little Stint (C. minuta), Dunlin (C. alpina), Sanderling (C. alba), Curlew Sandpiper (C. ferruginea), Common Redshank (Tringa totanus), and Black-winged Stilt (Himantopus himantopus)—used STT to feed on small prey items. Individuals employing STT used one or several cycles of jaw spreading to transport the prey contained in a drop of water...

The Evolutionary Basis for the Feeding Behavior of Domestic Dogs (Canis familiaris) and Cats (Felis catus)1–3

The dentition, sense of taste and meal patterning of domestic dogs and cats can be interpreted in terms of their descent from members of the order Carnivora. The dog is typical of its genus, Canis, in its relatively unspecialized dentition, and a taste system that is rather insensitive to salt. The preference of many dogs for large infrequent meals reflects the competitive feeding behavior of its pack-hunting ancestor, the wolf Canis lupus. However, its long history of domestication, possibly 100,000 years, has resulted in great intraspecific diversity of conformation and behavior, including feeding. Morphologically and physiologically domestic cats are highly specialized carnivores, as indicated by their dentition, nutritional requirements, and sense of taste, which is insensitive to both salt and sugars. Their preference for several small meals each day reflects a daily pattern of multiple kills of small prey items in their ancestor, the solitary territorial predator Felis silvestris. Although in the wild much of their food selection behavior must focus on what to hunt, rather than what to eat, cats do modify their food preferences based on experience. For example, the "monotony effect" reduces the perceived palatability of foods that have recently formed a large proportion of the diet, in favor of foods with contrasting sensory characteristics, thereby tending to compensate for any incipient nutritional deficiencies. Food preferences in kittens during weaning are strongly influenced by those of their mother, but can change considerably during at least the first year of life.

Energy content and digestibility of brine shrimp ( Artemia franciscana) and other prey items of eared grebes ( Podiceps nigricollis) on the Great Salt Lake, Utah

We measured the gross energy of brine shrimp ( Artemia franciscana), brine shrimp cysts, brine flies ( Ephydra spp.), brine fly larva, and corixids ( Trichocorixa verticalis) from the Great Salt Lake (GSL). We estimated the apparent and true digestible energy in eared grebes ( Podiceps nigricollis) for these prey items through feeding trials. We found no difference in energy concentration (kJ/g) between any of the invertebrates except for brine fly larva. Invertebrates from the GSL have a relatively high mean energy concentration ranging from 18.8 kJ/g to 23.9 kJ/g. Eared grebes are able to use 82.2–94.9% of the dry mass and 87.4–89.7% of the gross energy (true digestibility) content of their prey items. The high energy content and digestibility partially explain how an eared grebe can successfully forage on such small prey items on the GSL. In contrast, brine shrimp cysts had a high-energy concentration (23.5 kJ/g), but had the lowest amount of true digestible energy (34% of dry mass and 51% of energy), which helps explain why grebes are rarely observed foraging on them.

Burbot Consumption and Relative Abundance in the Apostle Islands Region of Lake Superior

Burbot ( Lota lota), are native Lake Superior piscivores that share similar habitat and food resources with other predators including lean and siscowet lake trout ( Salvelinus namaycush). To better understand their ecological role in the fish community, we combined fisheries assessment information from 1970 to 2002 with a bioenergetics model to estimate their predatory impact in the Apostle Islands region of Lake Superior. Relative abundance declined in the Apostle Islands region from 3.41 fish/1,000 m in 1978 to 0.27 fish/1,000 m in 1998. Fishing mortality was minimal based on creel estimates and observed bycatch in the commercial fishery. Burbot < 400 mm consumed a higher fraction of small prey items such as Mysis relicta, fish eggs and sculpins ( Cottidae) while larger burbot were almost exclusively piscivorous. Overall diet composition ( by mass) was represented primarily by Coregonus spp. (64%) and rainbow smelt ( Osmerus mordax) (17%). We estimated the burbot population size in the Apostle Islands between 1970 and 2000 at 56,541 to 1,585,035 age 1+ fish. This population consumed between 56 and 1,584 metric tonnes (0.13 to 3.54 kg/ha) of prey. Increases in both lean and siscowet lake trout abundance have likely contributed to the decline in burbot abundance through predation and/or competition for food resources. Given the current burbot population in the Apostle Islands, this species is unlikely to control production of prey fish or invertebrate taxa.

Dietary overlap among coral-feeding butterflyfishes (Chaetodontidae) at Lizard Island, northern Great Barrier Reef

This study documented the range of corals, and other prey types, consumed by 20 species of butterflyfishes, which co-occur at Lizard Island, northern Great Barrier Reef, Australia. Six species (Chaetodon aureofasciatus, C. baronessa, C. lunulatus, C. plebius, C. rainfordi and C. trifascialis) fed almost exclusively on scleractinian corals, and a further eight species (C. citrinellus, C. kleinii, C. lunula, C. melannotus, C. rafflesi, C. speculum, C. ulietensis, and C. unimaculatus) took a significant proportion of their bites from corals. The other six species (C. auriga, C. ephippium, C. lineolatus, C. semeion, C. vagabundus, and Chelmon rostratus) rarely consumed coral, but fed on small discrete prey items from non-coral substrates. Coral-feeding butterflyfishes consumed a wide range of corals. Chaetodon lunulatus, for example, consumed 51 coral species from 24 different genera. However, there was up to 72% dietary overlap between coral-feeding butterflyfishes, with 11/14 species feeding predominantly on Acropora hyacinthus or Pocillopora damicornis. The most specialised corallivore, C. trifascialis, took 88% of bites from A. hyacinthus. Chaetodon trifascialis defend territories encompassing one or more colonies of A. hyacinthus, and may have prevented other species such as C. lunulatus from feeding even more extensively on this coral. This study has shown that coexistence of coral-feeding butterflyfishes occurs despite an apparent lack of partitioning of prey resources. While different coral-feeding butterflyfishes were more or less selective in their use of different coral prey, virtually all species fed predominantly on A. hyacinthus or P. damicornis.

An Invasion of CheatsThe Evolution of Worthless Nuptial Gifts

Nuptial gifts are food items or inedible tokens that are transferred to females during courtship or copulation [1Vahed K. The function of nuptial feeding in insects A review of empirical studies.Biol. Rev. 1998; 73: 43-78Crossref Scopus (464) Google Scholar, 2Pizzari T. Food, vigilance, and sperm The role of male direct benefits in the evolution of female preference in a polygamous bird.Behav. Ecol. 2003; 14: 593-601Crossref Scopus (51) Google Scholar, 3Thornhill R. Alcock J. The Evolution of Insect Mating Systems. Harvard University Press, Cambridge, MA1983Google Scholar]. Tokens are of no direct value to females, and it is unknown why females require such worthless gifts as a precondition of mating. One hypothesis is that token giving arose in species that gave nutritious gifts and males exploited female preferences for nutritional gifts by substituting more easily obtainable but worthless items [4Sakaluk S.K. Sensory exploitation as an evolutionary origin to nuptial food gifts in insects.Proc. R. Soc. Lond. B. Biol. Sci. 2000; 267: 339-343Crossref Scopus (97) Google Scholar]. An invasion of such behavior would require that females accept the substitute gift and copulate for a period of time similar to that with genuine gifts. We show that both these prerequisites are met in the dance fly Rhamphomyia sulcata, in which females normally accept a nutritious gift. We removed the gift from copulating pairs and replaced it with either a large or small prey item or inedible token. We found that although pairs copulated longest with a large genuine gift, the tokens resulted in copula durations equivalent to those with a small genuine gift. We also observed that males that returned to the lek with tokens re-paired successfully. These findings suggest that female behavior in genuine gift-giving species is susceptible to the invasion of male cheating on reproductive investment.