Hard-bodied Prey Research Articles

FUNCTIONAL LINKAGES AMONG MORPHOLOGY, FEEDING PERFORMANCE, DIET, AND COMPETITIVE ABILITY IN MOLLUSCIVOROUS SUNFISH

Pumpkinseed (Lepomis gibbosus) and redear (Lepomis microlophus) sunfish are phylogenetic sister species that are specialized for molluscivory. The native ranges of these two sunfishes are allopatric, except for a small region of overlap in the Carolinas. However, for purposes of sport fishery enhancement, redear have been introduced into many northern lakes where pumpkinseed populations were native. As a result, a large zone of artificial sympatry of pumpkinseed and redear populations has been created in the last decade in lakes of southern Michigan. In this study I examined the feeding performance and diets of co-occurring redear and pumpkinseed both in Michigan lakes and in laboratory studies of these sunfish species from those lakes. Previous research on these species suggests that redear are morphologically and behaviorally more specialized for molluscivory than pumpkinseed, and results from the present study showed that at a given size, the crushing capacity of redear was -2X greater than that of pumpkinseed. For at least the smaller size classes of sunfish, the extent' of molluscivory was constrained by crushing strength. Therefore, greater crushing strength of redear allowed them to undergo an ontogenetic niche shift from a diet of predominantly soft-bodied invertebrates to a diet of snails at a smaller size than co-occurring pumpkinseed. Once molluscivorous, redear consumed larger snails than did pumpkinseed. Diet analysis also showed that following their earlier niche shift, redear were significantly more mol- luscivorous than sympatric pumpkinseed. Summing the effects of greater individual con- sumption of snails by redear and the effects of a greater proportion of a redear population being molluscivorous due to their earlier niche shift, redear were predicted to be more proficient competitors for snails. It appeared, however, that the superior feeding ability of redear on hard-bodied prey may have come at the cost of reduced efficiency at feeding on soft-bodied invertebrates.

Functional Linkages Among Morphology, Feeding Performance, Diet, and Competitive Ability in Molluscivorous Sunfish

Pumpkinseed (Lepomis gibbosus) and redear (Lepomis microlophus) sunfish are phylogenetic sister species that are specialized for molluscivory. The native ranges of these two sunfishes are allopatric, except for a small region of overlap in the Carolinas. However, for purposes of sport fishery enhancement, redear have been introduced into many northern lakes where pumpkinseed populations were native. As a result, a large zone of artificial sympatry of pumpkinseed and redear populations has been created in the last decade in lakes of southern Michigan. In this study I examined the feeding performance and diets of co-occurring redear and pumpkinseed both in Michigan lakes and in laboratory studies of these sunfish species from those lakes. Previous research on these species suggests that redear are morphologically and behaviorally more specialized for molluscivory than pumpkinseed, and results from the present study showed that at a given size, the crushing capacity of redear was ∼2× greater than that of pumpkinseed. For at least the smaller size classes of sunfish, the extent of molluscivory was constrained by crushing strength. Therefore, greater crushing strength of redear allowed them to undergo an ontogenetic niche shift from a diet of predominantly soft-bodied invertebrates to a diet of snails at a smaller size than co-occurring pumpkinseed. Once molluscivorous, redear consumed larger snails than did pumpkinseed. Diet analysis also showed that following their earlier niche shift, redear were significantly more molluscivorous than sympatric pumpkinseed. Summing the effects of greater individual consumption of snails by redear and the effects of a greater proportion of a redear population being molluscivorous due to their earlier niche shift, redear were predicted to be more proficient competitors for snails. It appeared, however, that the superior feeding ability of redear on hard-bodied prey may have come at the cost of reduced efficiency at feeding on soft-bodied invertebrates.

Morphological Divergence in an Insular Bat, Lasiurus cinereus semotus

1. Bats are the only terrestrial mammals to have reached isolated oceanic islands without human assistance. Despite the fact that the greatest evolutionary divergence would be expected on such islands, very few studies on the divergence of oceanic island fauna from their mainland counterparts have focused on bats. This study investigated divergence of the insular Hawaiian Hoary Bat, Lasiurus cinereus semotus, from its North American subspecies, L. c. cinereus. 2. Divergence in the Hawaiian Hoary Bat involved characters related to flight and feeding. 3. The Hawaiian bat has undergone a 45% reduction in body size with allometric responses in the size of its wings. These changes resulted in a combination of low wing loading (ratio of weight to wing area) with relatively long, narrow wings. The low wing loading permits slower and more manoeuvrable flight near vegetation, while the relatively long, narrow wings enable enduring flight in open areas. This increased flexibility in flight behaviour has allowed the Hawaiian bat to expand its foraging habitat to include open habitats similar to those of L. c. cinereus, and closed habitats that are not used by L. c. cinereus. 4. Divergence in characters related to feeding involved relative increases in size of the gape, size of the masseter muscle and the height of the coronoid process. These changes give the jaw more crushing power for more efficient processing of large and hard-bodied prey. This has enabled the Hawaiian bat to include large, and hard-bodied insects (not taken by L. c. cinereus) in its diet despite a marked reduction in body size.

Evolution of coloration, urotomy and coral snake mimicry in the snake genusScaphiodontophis(Serpentes: Colubridae)

The Neotropical hinged-tooth, coral snake mimics of the genus Scaphiodontophis are characterized by extremely long and disproportionately thick tails that are extremely fragile. Both the coloration and tail structure are putative antipredator devices. While all examples have components of the coloration that match those of the venomous coral snakes (family Elapidae), the range of variation is extreme, leading to controversy on the status of various populations, including nine named taxa. Individual, ontogenetic and geographic variation in scutellation and head, body and tail coloration were analysed to evaluate population status and possible evolutionary trends based on a sample of 183 examples from Mexico, Central America and Colombia. Variation in subcaudal counts show population differences (higher in Mexico and upper Central America) but are not congruent with geographic variation in coloration. Generally snakes from north of Nicaragua and from central and eastern Panama have a pattern of dyads (black-light-black bands separating red bands), those from Atlantic slope Nicaragua to western Panama a pattern of monads (light-black-light bands separating the red ones) and those from Colombia have both pattern types on the same snake. The dyads and/or monads may be present the length of the body and tail, restricted to the anterior part of the body or on the entire body or on the anterior part of the body and on the tail. Two or more of these variants may occur at a single geographic locality or only a single one may be present. Head and nuchal colour patterns (Z, A, V, and Du) are relatively consistent geographically. The Atlantic slope Guatemala, Belize and Honduras population have the A pattern, those of Nicaragua, Costa Rica and western Panama the V pattern, and those in Colombia a Du pattern. Other populations have the Z coloration. Intermediate conditions in coloration of the body and tail and head and neck are found at localities intermediate between the main pattern types, indicating intergradation among adjacent populations. Consequently, we regard these snakes as representative of a single species, Scaphiodontophis annulatus Duméril and Bibron and the eight other names applied to various populations and individuals as synonyms. Analysis of colour pattern leads us to the conclusion that the tricolour pattern evolved from a uniform one through a lineate-spotted condition (usually present on the non-tricolour portions of the snake) through a bicolour red and black pattern to the dyadal condition. The monadal pattern in turn was derived from the dyadal one. The data further indicates that tricolour components first appeared anteriorly and progressively expanded posteriorly. The evolutionary sequence for the head and nuchal pattern appears to be A → Z → V → Du S. annulatus has a series of jaw and tooth specializations designed for rapid processing of hard-bodied prey found during diurnal foraging in the leaf-litter. Urotomy in this species involves intervertebral tail-breakage (pseudoautotomy) without regeneration. Evidence is presented supporting the long-tail multiple break hypothesis as applicable to Scaphiodontophis and other snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to Coniophanes and other snakes with a high incidence of urotomy having long but unspecialized tails (unspecialized pseudoautotomy) without multiple breaks over time. All Scaphiodontophis colour patterns have a general resemblance to that of venomous coral snakes and offer protection from generalizing predators having innate or other triggered responses to coral snake colours. The aposematic effect is enhanced by tail thrashing and head twitching behaviours. The characteristic foraging pose of S. annulatus , which tends to expose the head and anterior body, makes even the incomplete tricolour pattern effective as an antipredator defense. No evidence supports the idea that tail thrashing or the incomplete tricolour pattern directs the predator attacks to the tail to expedite pseudoautotomy. Coral snake mimicry and specialized pseudoautotomy are shown not to be co-evolved and pseudautotomy seems to have evolved long before mimetic coloration in this genus.

Evolution of coloration, urotomy and coral snake mimicry in the snake genus Scaphiodontophis (Serpentes: Colubridae)

The Neotropical hinged-tooth, coral snake mimics of the genusScaphiodontophisare characterized by extremely long and disproportionately thick tails that are extremely fragile. Both the coloration and tail structure are putative antipredator devices. While all examples have components of the coloration that match those of the venomous coral snakes (family Elapidae), the range of variation is extreme, leading to controversy on the status of various populations, including nine named taxa. Individual, ontogenetic and geographic variation in scutellation and head, body and tail coloration were analysed to evaluate population status and possible evolutionary trends based on a sample of 183 examples from Mexico, Central America and Colombia. Variation in subcaudal counts show population differences (higher in Mexico and upper Central America) but are not congruent with geographic variation in coloration. Generally snakes from north of Nicaragua and from central and eastern Panama have a pattern of dyads (black-light-black bands separating red bands), those from Atlantic slope Nicaragua to western Panama a pattern of monads (light-black-light bands separating the red ones) and those from Colombia have both pattern types on the same snake. The dyads and/or monads may be present the length of the body and tail, restricted to the anterior part of the body or on the entire body or on the anterior part of the body and on the tail. Two or more of these variants may occur at a single geographic locality or only a single one may be present. Head and nuchal colour patterns (Z, A, V, and Du) are relatively consistent geographically. The Atlantic slope Guatemala, Belize and Honduras population have the A pattern, those of Nicaragua, Costa Rica and western Panama the V pattern, and those in Colombia a Du pattern. Other populations have the Z coloration. Intermediate conditions in coloration of the body and tail and head and neck are found at localities intermediate between the main pattern types, indicating intergradation among adjacent populations. Consequently, we regard these snakes as representative of a single species,Scaphiodontophis annulatusDumeril and Bibron and the eight other names applied to various populations and individuals as synonyms. Analysis of colour pattern leads us to the conclusion that the tricolour pattern evolved from a uniform one through a lineate-spotted condition (usually present on the non-tricolour portions of the snake) through a bicolour red and black pattern to the dyadal condition. The monadal pattern in turn was derived from the dyadal one. The data further indicates that tricolour components first appeared anteriorly and progressively expanded posteriorly. The evolutionary sequence for the head and nuchal pattern appears to be A → Z → V → DuS. annulatushas a series of jaw and tooth specializations designed for rapid processing of hard-bodied prey found during diurnal foraging in the leaf-litter. Urotomy in this species involves intervertebral tail-breakage (pseudoautotomy) without regeneration. Evidence is presented supporting the long-tail multiple break hypothesis as applicable toScaphiodontophisand other snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast toConiophanesand other snakes with a high incidence of urotomy having long but unspecialized tails (unspecialized pseudoautotomy) without multiple breaks over time. AllScaphiodontophiscolour patterns have a general resemblance to that of venomous coral snakes and offer protection from generalizing predators having innate or other triggered responses to coral snake colours. The aposematic effect is enhanced by tail thrashing and head twitching behaviours. The characteristic foraging pose ofS. annulatus, which tends to expose the head and anterior body, makes even the incomplete tricolour pattern effective as an antipredator defense. No evidence supports the idea that tail thrashing or the incomplete tricolour pattern directs the predator attacks to the tail to expedite pseudoautotomy. Coral snake mimicry and specialized pseudoautotomy are shown not to be co-evolved and pseudautotomy seems to have evolved long before mimetic coloration in this genus.

Ecological and morphological differentiation of pumpkinseed sunfish in lakes without bluegill sunfish

Over the last three decades, sunfish of the familyCentrarchidae have become recognized as a model system in which the ecological consequences of species interactions can be observed and tested. The evolutionary consequences of species interactions in sunfish have received less attention. Bluegill (Lepomis machrochirus) and pumpkinseed (Lepomis gibbosus) sunfish are two common and well-studied species that occupy separate ecological niches. Adult bluegill are generalists that feed in the open water on zooplankton during much of the year, while adult pumpkinseeds specialize on crushing hard-bodied prey such as snails. These species coexist over much of their geographical ranges, but bluegill are historically absent from several large drainage basins in the northeastern US. Here we show that pumpkinseeds from an Adirondack lake without bluegills have differentiated into two morphological forms, one of which is planktivorous. Differentiation is independent of sex and occurs over a broad range of sizes. Thus, the ecological diversity that exists between the bluegill and pumpkinseeds in sympatry has been replaced by a comparable degree of diversity within pumpkinseeds in allopatry.

Foraging ecology in the lizard Anolis oculatus (Iguanidae) from Dominica, West Indies

In general, populations of Anolis lizards on West Indian islands face few predators, are at high density and are thought to be limited by food. This paper describes how the foraging ecology of Anolis oculatus, a solitary species confined to the island of Dominica, Lesser Antilles, varies with habitat and season in relation to the quantity and quality of available food.Availability of invertebrate food (determined using pitfall traps and sticky traps) was greater in a dry scrub woodland site, Cabrits National Park (CNP), compared with a montane rainforest site, Palmiste Ridge. In the former, there were general increases in abundance, volumes of softbodied prey and sizes of invertebrates from dry season to wet season. Concomitant dietary changes, as determined principally by stomach flushing, included an increase (by volume) in the proportion of soft‐bodied prey. Dietary analyses confirmed the importance of ants (Formicidae) in the diet of A. oculatus, although for large individuals (mainly adult males) at the rainforest site, soft‐bodied prey such as Oligochaeta and Orthoptera were, in volumetric terms, more important. Prey capture observations showed that large A. oculatus fed mainly above ground. Anolis oculatus at the montane rainforest site used higher perch heights than those in dry scrub woodland, although in both habitats, small individuals (mainly juveniles) fed mainly at ground level on ants. In the dry season in CNP, the diet (in volumetric terms) of smaller Anolis was dominated by hardbodied prey such as ants, springtails (Collembola), barklice (Psocoptera) and beetles (Coleoptera). large Anolis used springtails and barklice to a lesser extent, resulting in relatively low food niche overlap values between size classes and a reduced potential for intraspecific competition compared with the wet season.

Growth-related changes in diet and foraging behavior of the yellow wrasseThalassoma lutescens at Kuchierabu Island

Ontogenetic changes in diet and foraging behavior ofThalassoma lutescens were examined in shallow reef habitats around Kuchierabu Island, southern Japan. This species mainly took small benthic invertebrates, including gammarids, polychaetes, sipunculids, chitons, crabs, gastropods, pelecypods and urchins from algal mats. Larger fish consumed correspondingly larger prey, although most of the latter were armored with hard exoskeletons, shells or body plates (e.g., crabs, gastropods, pelecypods and urchins). Such hard parts were crushed with the molar-like, pharyngeal teeth which develop with fish growth, allowing exploitation of such larger, hard-bodied prey. Because the densities of larger prey species were relatively low in the initial habitats foraged, larger fish shifted their foraging attention to rock and coral crevices, where the prey species dwelt in greater numbers, as well as foraging over larger areas. Such behavioral changes maintained high foraging efficiency in larger fish.

The Reliability of Fecal Analysis as a Method for Determining the Diet of Insectivorous Mammals

The reliability of fecal analysis for dietary assessment was evaluted in four species of insectivorous mammals. In separate experiments, invertebrates were fed to captive animals by one author, and feces were analyzed, without prior knowledge of diet composition, by the other author. There was overall agreement between ranked frequencies of different taxa of invertebrates consumed and recovered in feces. However, underestimation of numbers of invertebrates in feces was more evident (1) as increasing numbers of the same type of invertebrate were ingested, (2) for soft-bodied than for hard-bodied invertebrates, (3) for small than for large invertebrates, and (4) for well-fed than for hungry insectivores. We conclude that fecal analysis is a relatively reliable method for determining the diet of generalist insectivores that eat hard-bodied prey, especially if the results are expressed as the number of animals in which a prey item is found rather than as the minimum number of prey eaten per animal. However, we caution that there are more potential sources of bias in fecal analysis than realized previously.

Form and function of the tooth crown structure in gekkonid lizards (Reptilia, Squamata, Gekkonidae)

The shapes of gekkonid teeth are examined in detail using scanning electron microscopy. The teeth are found to have lingually tilted cusps similar to those reported in caecilians and extinct dissorophoid amphibians. In most species, teeth possess two cusps separated by a concave sulcus, but in (at least) one species, teeth have four well-developed cusps. Because the cusps are weakly developed or absent in large or noninsectivorous geckos, we suggest that the observed arrangement of cusps aids smaller species in grasping hard-bodied prey. The cusps of most gekkonid teeth possess well-developed median tips which are more pronounced than those of amphibians with bicuspid teeth. The shapes of these teeth may be of value in phylogenetic investigations.

A quantitative analysis of ferric iron in butterflyfish teeth (Chaetodontidae, Perciformes) and the relationship to feeding ecology

Despite much work on the iron compounds found on invertebrate and vertebrate teeth, no interspecific quantitative analyses of iron compounds in fish teeth have ever been conducted, nor in any vertebrate has such a study related the iron concentrations to the feeding ecology. This study reveals that ferric iron exists on the tooth cap of eight species of chaetodontid butterflyfishes. The iron layer appears early in tooth development and is darkest, and presumably more concentrated, towards the tooth tip. There are significant differences among the eight species, with those that feed on harder prey having more iron than those that feed on softer-bodied prey. Furthermore, there exist differences among the species that correlate with the degree of morphological specialization for feeding on hard-bodied prey. The iron layer, which has been shown by others to be harder than the underlying enameloid, probably represents a specialization to harden the teeth, resisting abrasion and cracking.

THE FUNCTIONS OF NEMATOCYSTS IN PREY CAPTURE BY EPIPELAGIC SIPHONOPHORES (COELENTERATA, HYDROZOA)

The nematocysts of 24 siphonophore species were examined by light and scanning electron microscopy (SEM) for differences that could relate to differences in the sizes and types of prey captured. The siphonophore species in the suborder Calycophorae had 4-30 microbasic mastigophores (0.7-18.0 µl volume), and 50-2000 smaller homotrichous anisorhizas in uncoiled nematocyst batteries. The physonect siphonophore species had 4-120 stenoteles or microbasic mastigophores (1.8-40.7 µl volume), and 150-20,500 smaller homotrichous anisorhizas in coiled nematocyst batteries. The sizes of crustacean prey (primarily copepods) captured by species in both suborders increased with increasing nematocyst size and numbers. Examination by SEM of captured, but uningested prey showed that the heavily-spined threads of these nematocysts adhered to the prey surface, and primarily entangled the prey. In contrast, the tentacles of siphonophores in the suborder Cystonectae, which includes Physalia physalis, have only isorhizas of 1.0-18.0 µl volume with and without small spines on the threads. These nematocysts penetrate the soft-bodied prey (mostly fish larvae) of these siphonophores, but apparently do not penetrate or entangle hard-bodied prey. Thus prey capture by siphonophores differs with the sizes, numbers, and types of nematocysts present in each species. The possible functions of nematocyst batteries in tentacle spreading, and luring of large zooplankton prey are discussed.

Hinged Teeth in Snakes: An Adaptation for Swallowing Hard-Bodied Prey

Six genera of snakes, representing at least three lineages, possess teeth that fold backward against the jaws rather than being firmly ankylosed. This condition, effected by a connective tissue hinge at the base of each tooth, is associated with suites of cephalic modifications that enable the snakes to grasp and to swallow hard-bodied prey.