Predator Cannibalism Research Articles

THE INFLUENCE OF SIZE-SPECIFIC INDIRECT INTERACTIONS IN PREDATOR–PREY SYSTEMS

Nonlethal indirect interactions between predators often lead to nonadditive effects of predator number on prey survival and growth. Previous studies have focused on systems with at least two different predator species and one prey species. However, most predators undergo extreme ontological changes in phenotype such that interactions between different-sized cohorts of a predator and its prey could lead to nonadditive effects in systems with only two species. This may be important since different-sized individuals of the same species can differ more in their ecology than similar-sized individuals of different species. This study examined trait-mediated indirect effects in a two-species system including a cannibalistic predator with different-sized cohorts and its prey. I tested for these effects using larvae of two stream salamanders, Gyrinophilus porphyriticus (predator) and Eurycea cirrigera (prey), by altering the densities and combinations of predator size classes in experimental streams. Results showed that the presence of large individuals can significantly reduce the impact of density changes of smaller conspecifics on prey survival through nonlethal means. In the absence of large conspecifics, an increase in the relative frequency of small predators significantly increased predation rates, thereby reducing prey survival. However, with large conspecifics present, increasing the density of small predators did not decrease prey survival, resulting in a 14.3% lower prey mortality than predicted from the independent effects of both predator size classes. Small predators changed their microhabitat use in the presence of larger conspecifics. Prey individuals reduced activity in response to large predators but did not respond to small predators. Both predators reduced prey growth. These results demonstrate that the impact of a predator can be significantly altered by two different types of trait-mediated indirect effects in two-species systems: between different-sized cohorts and between different cohorts and prey. This study demonstrates that predictions based on simple numerical changes that assume independent effects of different size classes or ignore size structure can be strongly misleading. We need to account for the size structure within predator populations in order to predict how changes in predator abundance will affect predator-prey dynamics.

Kinship Influences Cannibalism in the Wolf Spider, Pardosa milvina

Recent studies have called into question the role of Wright's coefficient of relatedness (r) in the interactions among relatives. Kin selection theory predicts a positive relationship between relatedness and frequency of “altruistic” acts, but a number of researchers have reported the opposite relationship. I used a lycosid spider (Pardosa milvina) to test the hypothesis that genetic relatedness would affect the propensity of a cannibalistic species to prey on genetic relatives. I considered lack of predation to be a form of “altruism” where the predator incurs a cost (loss of a meal) that benefits potential prey. Specifically, I questioned whether direct genetic offspring would be avoided as prey items and whether the sex or reproductive condition of a cannibalistic predator would affect the likelihood of predation on conspecific juveniles. As predicted by kin selection theory, spiderling mothers ate significantly fewer of their own offspring than they did of nonkin spiderlings of the same age. Adult virgin female and adult male spiders ate significantly more spiders than females that had recently carried spiderlings. Females with egg sacs consumed significantly fewer spiderlings than did virgin female spiders. These findings support Hamilton's rule and suggest that, in some systems, genetic relatedness plays a strong role in governing altruistic behavior toward relatives.

Predator behaviour and prey density: evaluating density‐dependent intraspecific interactions on predator functional responses

Abstract In models of size‐structured predator–prey systems, the effects are evaluated of gape‐size limited predation on prey population growth and density when predators are non‐interacting, cannibalistic, interfering, and cannibalistic and interfering. Predation from non‐interacting predators markedly reduces prey density, compared with prey densities in the absence of predation. When density‐dependent cannibalism between predators is introduced, predator density and therefore total functional response decrease, resulting in a decrease in predation pressure and higher prey densities. Size‐ and density‐dependent interference between predators substantially decreases functional responses in the predators, and the prey population is thus allowed to grow more dense. Allowing for cannibalism between interfering predators also decreases predator density, but here the decreased number of predators does not have the releasing effect seen in solely cannibalistic predators. The interference between predators decreases with predator density, and per capita functional responses increase and compensate for the decrease in predator density. These theoretical results are compared with results from natural systems with pikeperch and northern pike. Both species are cannibalistic, and pike are also kleptoparasitic, mirroring the models. Results from introductions of the different piscivores into natural systems corroborate the outcome of the models, since introduction or increased densities of pikeperch have shown to have severe and long‐lasting effects on prey, while pike have only initial, decreasing over time effects on prey stock. Thus, predator behaviour may seriously affect predator impact on prey, and size‐ and density‐dependent interactions between predators may be a major key to the understanding of predator–prey dynamics and community composition in lakes.

Diel feeding of the chaetognath Sagitta enflata in the Zanzibar Channel, western Indian Ocean

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 193:117-123 (2000) - doi:10.3354/meps193117 Diel feeding of the chaetognath Sagitta enflata in the Zanzibar Channel, western Indian Ocean Vidar Øresland* Institute of Marine Research, National Board of Fisheries, PO Box 4, 453 21 Lysekil, Sweden *E-mail: v.oresland@imr.se ABSTRACT: The diel feeding cycle of Sagitta enflata, the dominant chaetognath in the Indian Ocean, was investigated, using gut content analyses, between the monsoon periods on 2 occasions, October 1995 and May 1996. Zooplankton samples were collected every second hour during a 24 h period close to a drifting buoy in the middle of the Zanzibar Channel. S. enflata made up 64% (October) and 77% (May) of all chaetognaths in this study. S. enflata and all chaetognaths contributed as much as 30 and 33%, respectively, of the total 90 µm net zooplankton wet weight in October (May samples could not be weighed due to occurrence of phytoplankton). S. enflata fed most actively at night. Small copepods with a mandible width <0.07 mm (prosome length <1 mm) were its predominant prey. Feeding rate and mean number of small copepods found in S. enflata were 3 times higher in October than in May. In contrast, the estimated daily predation impact on the standing stock of small copepods (by number) was around 1% for both periods. This may be a negligible predation effect considering the short life-span of tropical copepods. It is suggested that predation effects are related to temperature, since a similar predation impact may be important in cold polar waters where copepod life-spans are much longer. Daily cannibalistic predation impact (by number) was estimated to be between 1 and 4% (October) and between 2 and 9% (May) using assumed maximum and minimum digestion times of 8 and 2 h. Cannibalism, therefore, may be an important source of mortality in S. enflata populations. KEY WORDS: Zooplankton · Chaetognatha · Sagitta enflata · Flacisagitta enflata · Copepods · Feeding · Predation · Cannibalism · Indian Ocean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 193. Publication date: February 28, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Survivorship and Cannibalism in Lyctocoris campestris (Hemiptera: Anthocoridae): Effects of Density, Prey Availability, and Temperature1

Availability of prey was an important factor for cannibalism in Lyctocoris campestris (F.). Cannibalistic predation in L. campestris nymphs was density dependent irrespective of prey level or space provided. Mean adult longevity varied under different prey, water, and temperature regimes. Adults survived for more than 2 wks when no prey or free water was provided, and survivorship increased slightly when bugs had access to free water. Females survived longer than males (P = 0.03) when only water was provided. Under a no-prey regime, lower rearing temperatures yielded significantly higher adult survivorship. Lyctocoris campestris adults survived for 23.5 d without prey or water at 17°C. The cannibalistic predation among nymphs and the ability of adults to survive for an extended period of time without prey or water may enable bug populations to persist until prey populations rebound in a stored-product ecosystem.

Cannibalistic phenomena in salamandra salamandra larvae in certain water bodies and under experimental conditions

Salamandra salamandra larvae originating from a single batch (layed by one female) were raised at different temperatures and on ion-rich or distilled water. Temperature, but not the presence or absence of ions affected growth. Larvae originating from one batch or from several batches born on the same day, were kept without food for long periods of several months in order to observe cannibalistic predation under such conditions. This phenomenon is known in natural populations of salamanders inhabitating either rain pools in rocks or permanent springs poor in aquatic life. It was found that cannibalism increased under experimental conditions proportionally to the increase in size between the larvae.

A Technique for Rearing Larvae of Medetera aldrichii (Diptera: Dolichopodidae)1

In studies to develop a suitable technique for rearing the larval stages of the predator Medetera aldrichii Wheeler on its host, the Douglas-fir beetle, Dendroctomus pseudotsugae Hopkins, 4 media were plated in glass “sandwiches”: agar, Douglas-fir sawdust, Douglas-fir beetle frass, and Douglas-fir phloem (modified). Prey and predator larvae were introduced into these sandwiches and kept at 22°C in darkened, controlled-temperature cabinets. Predator cannibalism occurred in all media. Only the phloem mixture was a successful rearing medium, with larvae surviving to the third (ultimate) instar in all tests.

Cannibalistic Predation in Populations of Flour Beetles

Cannibalistic Predation in Populations of Flour Beetles