Prey Capture

Carnivorous plants trap and utilize animals in order to improve their supply with mineral nutrients. One strategy for prey capture is the use of adhesive traps, i.e., leaves that produce sticky substances. Sticky shoots are widespread in the plant kingdom and serve to protect the plant, especially flowers and seeds. In some taxa, mechanisms have been developed to absorb nutrients from the decaying carcasses of animals killed by the glue. In carnivorous plants sensu stricto, additional digestive enzymes are secreted into the glue to accelerate degradation of prey organisms. The glues are secreted by glands that are remarkably uniform throughout all taxa producing adhesive traps. They follow the general scheme of plant glandular organs: the glands consist of a stalk, a neck equipped with a suberin layer that separates the gland from the rest of the plant, and the glandular cells producing sticky secretions. This glue always forms droplets at the tip of the glandular hairs. In most genera, these glands produce only glue whereas enzymes for prey digestion are secreted by a second type of gland. Two types of glue can be distinguished, polysaccharide mucilage in Droseraceae, Lentibulariaceae and their relatives, and terpenoid resins in Roridulaceae. On the ultrastructural level, mucilage is produced by the Golgi apparatus. Resins can be expected to be produced by the endoplasmic reticulum and by leucoplasts. Adhesive traps are suitable not only for the capture of small animals but also for the collection of organic particles like pollen grains. The glue may contain toxic compounds but the prey usually dies from suffocation by clogging of its tracheae. In Pinguicula and Drosera, the performance of the traps is improved by a slow movement, i.e., the folding of the leaf around the prey animal upon stimulation. In some species of Nepenthes, a pitcher with smooth walls is filled with a sticky digestive fluid. Some organisms, however, have developed strategies to survive on the deadly traps. Several species of Hemiptera are able to walk on the sticky traps and nourish on the prey; their faeces are absorbed by the plant. In Roridula, this relationship is highly specialized and essential for both the plant and the insect. Mutualistic fungi and bacteria are common in many adhesive traps where they degrade and dissolve the plant’s prey. The traps of Drosera, on the other hand, are virtually sterile. In spite of the extensive literature on adhesive traps, numerous questions still remain. Only a small percentage of “sticky” plants have actually been tested for carnivory. The properties and composition of their glues are widely unknown. In advanced adhesive traps, the mechanisms regulating secretion and absorption are poorly understood. Thereby, some glues may be applicable for human as they are non-toxic, quite stable under environmental conditions, and partly exhibit mildly antibiotic properties. Some carnivorous plants with adhesive traps have been used by humans for the capture of insects as well as for food processing.

Male–male fighting (MMF) in snakes is a sexually dimorphic trait in adults that is expressed during breeding periods and confers reproductive advantages to winners. This trait, however, is not ubiquitous among the approximately 2,700 species of extant snakes, and past research shows evidence of taxonomic trends. We evaluated the phylogenetic distribution of MMF in extant snakes using two previously published estimates of snake evolutionary history. We clearly identified multiple independent gains and losses of MMF in snakes and phylogenetically important taxa for which information on MMF is lacking. We followed this with two tests of the association of MMF with mode of prey capture using the concentrated-changes test (CCT) of Maddison (1990), and a third test using the subtree decomposition method of Read and Nee (1995). In the CCT analyses, first we tested whether MMF was randomly distributed with respect to mode of prey subjugation in snake lineages. This hypothesis was rejected, with MMF being significantly more concentrated in taxa that subjugate prey by constriction and/or envenomation. Second, we tested a more temporally exact hypothesis: whether changes in state of MMF were randomly distributed with respect to occurrences of state changes in mode of prey subjugation. Results of this test depended on the exact test parameters used. In general, however, this hypothesis also was rejected, suggesting that loss of constriction and/or envenomation typically results in loss of MMF, or vice versa. Last, the subtree decomposition test indicated a significant correlation between evolution of MMF and evolution of constriction and/or envenomation as the primary mode of prey subjugation. We propose that the relationship between these states is not causal but results from both characters being independent adaptations to energy resource scarcity.

In Las Banos in the Philippines (Laguna, Luzon), Scytodes sp. indet. is a web-building spitting spider (Scytodidae) that preys primarily on jumping spiders (Salticidae) and Portia labiata is an aggressive-mimic jumping spider that preys especially frequently on Scytodes. Tactics ...

Echolocating bats can be divided into guilds according to their preferred habitat and foraging behaviour, which coincide with distinct adaptations in wing morphology and structure of echolocation signals. Although coarse structuring of niche space between different guilds is generally accepted, it is not clear how niches differ within guilds, or whether there is fine-grained niche differentiation reflected in echolocation signal structure. Using a standardized performance test, here we show clutter-dependent differences in prey-capture success for bats from five species of European Myotis. These species are morphologically similar, sympatric, and all belong to the guild labelled "edge space aerial/trawling foragers". We further demonstrate a strong correlation between the prey-detection ability of the species and the respective search-call bandwidth. Our findings indicate that differences in echolocation signals contribute to within-guild niche differentiation. This is the first study relating sensory abilities of a set of potentially competing animal species to a direct measure of their respective foraging performance, suggesting an important role of sensory ecology in the structuring of animal communities.

There have been a number of studies on the claws of Mesozoic birds, largely driven by interest in the habitat of Archaeopteryx. Many Mesozoic avians have large, well formed manual claws, largely absent in contemporary birds. Juvenile hoatzins are the only living birds with claws that are large enough to be generally functional, but not equivalent to those of Mesozoic birds. When birds developed an effective backstroke permitting easy ascent from flat surfaces, the need for manual claws disappeared, which would suggest that they were primarily used for climbing tree trunks and had little function in prey capture. This hypothesis has both phylogenetic and functional implications. The numerous claw studies to date are based primarily on measurements taken of the bony core, all that is usually preserved in fossils. Examination of contemporary birds shows that this is a poor estimator of the size and shape of the horny sheath that actually forms the functional claw. The discovery of vast numbers of exceptionally preserved fossil birds from the Late Jurassic and Early Cretaceous of China means that we now have an opportunity to compare actual horny claw data from the earliest birds with that of modern birds and test hypotheses on climbing, terrestrial activity, and predation.

Pitcher plants of the genusNepenthesattract and trap invertebrate prey using nectar-secreting pitchers. Pitcher morphology and spectral reflectance characteristics were investigated for sixNepenthesspecies from northwest Borneo (N. albomarginata, N. ampullaria, N. bicalcarata, N. gracilis, N. mirabilisvar.echinostomaandN. rafflesiana). Morphological measurements focused on the size of the pitcher rim (or peristome, the site of the major nectaries) in relation to pitcher length. The results show considerable interspecific variation in morphology. Spectral reflectance measurements quantified the degree of colour contrast between the peristome and pitcher body, from ultraviolet (UV) to red wavelengths. The contrast maxima for each species were compared with insect visual sensitivity maxima. The six species showed a wide range of reflectance patterns, with pitchers ofN. rafflesianapossessing the greatest degree of ‘fit’ between contrast maxima and insect sensitivity maxima, in the UV, blue and green regions of the spectrum. Based on the morphological and reflectance analyses, we hypothesized that pitchers ofN. rafflesianawould be more attractive to anthophilous (flower-visiting) invertebrates than the sympatricN. gracilis. Analysis of prey contents generally supported the hypothesis, suggesting possible interspecific resource partitioning. Morphological and spectral characteristics of the other species are discussed in relation to published studies on prey capture by those species.

Morphological divergence resulting from differences in resource and habitat use is common in many fishes inhabiting postglacial ecosystems. We tested whether young yellow perch Perca flavescens differ in morphology, genetic composition, or diet in the nearshore (deep open-water) versus wetland and littoral habitats (shallow zones) of Lake Michigan and Saginaw Bay, Lake Huron. Twenty-one morphological measurements and six meristic counts were compared for 132 age-1 yellow perch, and the genetic variation at 12 nuclear DNA microsatellite loci was assessed for a subset of age-1 individuals across habitats and adults from nearshore zones. The results showed morphological and genetic divergence in yellow perch between Lake Michigan and Lake Huron and among those in nearshore versus wetland habitats in Lake Michigan (but not Lake Huron). Lake Huron yellow perch had deeper, longer bodies and larger dorsal fins than those from Lake Michigan. Those in nearshore habitats from both lakes had deeper, longer bodies and larger dorsal fins than did those occupying wetlands, which may reflect an adaptive response to predators and open-water cruising. In Lake Michigan, these differences may have a genetic basis that is not apparent in Lake Huron, suggesting a role for phenotypic plasticity. Piscivorous and zooplanktivorous individuals had similar morphologies, with larger body depths than insectivores, which may be useful for fast-starts during prey capture and provide protection from predation in open water. Comparisons of morphology, population structure, and diet thus reveal that the morphological diversity of yellow perch between habitats and lake basins reflects an interplay between phenotypic plasticity and genetic divergence.

Human impacts on water transparency may affect plunge-diving seabirds. We studied prey capture success of Sandwich Terns Sterna sandvicensis as a function of six environmental variables during the breeding season. We observed diving terns in the south eastern North Sea and found a non-linear optimum curve for the relationship between Secchi transparency and prey capture probability. High capture probability was found at 1.5–2.0 m, with an optimum of 63% at 1.74 m. At a minimum transparency of 0.4 m and at a maximum transparency of 3.2 m, capture probabilities were about halved. Conversion of transparency to total suspended matter (TSM) concentration showed that the optimum concentration for foraging terns would be 5–10 mg/L under mean summer conditions for chlorophyll-a. However, the summer-averaged TSM concentrations in the nearshore Dutch coastal waters range between 10 and 30 mg/L, which implies that foraging Terns in the breeding season do not encounter optimal foraging conditions. The Full Plunge Dive, with which the largest diving depth can be achieved, was applied dominantly in clear water, while the Partial Plunge Dive and Contact Dip were applied more frequently in turbid water, thus showing that Sandwich Terns adjust their diving technique in response to water transparency.