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Selective Predation (selective + predation)
Selected AbstractsASYMMETRY IN STRUCTURAL DEFENSES: INSIGHTS INTO SELECTIVE PREDATION IN THE WILDEVOLUTION, Issue 9 2003C. A. Bergstrom Abstract Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations. [source] Selective predation on the broad-toothed rat, Mastacomys fuscus (Rodentia: Muridae), by the introduced red fox, Vulpes vulpes (Carnivora: Canidae), in the Snowy Mountains, AustraliaAUSTRAL ECOLOGY, Issue 4 2002K. Green Abstract Since 1981 there has been debate over whether foxes (Vulpes vulpes Linnaeus) selectively prey on the broad-toothed rat (Mastacomys fuscus Thomas) relative to the bush rat (Rattus fuscipes (Waterhouse)). In the present study, three areas of the argument are examined. (i) In a study of fox diet over 3 years at both alpine and subalpine altitudes, M. fuscus outnumbered R. fuscipes in faecal remains in all seasons, in all years, and at both altitudes. Overall, M. fuscus occurred in scats five times as frequently as did R. fuscipes in the alpine zone and twice as often in the subalpine zone. (ii) Data from population studies of M. fuscus and R. fuscipes showed no evidence that M. fuscus is trap shy; neither the pattern of captures of individuals caught once, twice and so on, nor the proportion of the estimated population of each species captured during trapping sessions was significantly different. (iii) The suitable habitat for M. fuscus within the potential home ranges of foxes contributing to the subalpine fox scat collection constituted approximately 50% of the total area. However, there was no significant difference between the numbers of fox trails encountered in habitat suitable or unsuitable for M. fuscus in 19 paired transects skied in winter, indicating no preferential foraging in either habitat. Selective feeding on M. fuscus was therefore established, but how that choice is exercised was not determined. [source] Quality matters: resource quality for hosts and the timing of epidemicsECOLOGY LETTERS, Issue 2 2009Spencer R. Hall Abstract Epidemiologists increasingly realize that species interactions (e.g. selective predation) can determine when epidemics start and end. We hypothesize here that resource quality can also strongly influence disease dynamics: epidemics can be inhibited when resource quality for hosts is too poor and too good. In three lakes, resource quality for the zooplankton host (Daphnia dentifera) was poor when fungal epidemics (Metschnikowia bicuspidata) commenced and increased as epidemics waned. Experiments using variation in algal food showed that resource quality had conflicting effects on underlying epidemiology: high-quality food induced large production of infective propagules (spores) and high birth rate but also reduced transmission. A model then illustrated how these underlying correlations can inhibit the start of epidemics (when spore production/birth rate are too low) but also catalyse their end (when transmission becomes too low). This resource quality mechanism is likely to interface with other ones controlling disease dynamics and warrants closer evaluation. [source] Diversity and functional importance of coral-feeding fishes on tropical coral reefsFISH AND FISHERIES, Issue 3 2008Andrew J. Cole Abstract Fishes that feed from live corals (corallivores) are a conspicuous component of healthy coral reef environments. However, knowledge of the occurrence and ecological significance of this feeding mode is fragmentary. Historically, very few fish were considered capable of feeding from live coral, and those few that did were considered ecologically insignificant. More recently, the role of corallivores has been re-evaluated; published records document 128 corallivorous fish species from 11 different families, with 69 of these belonging to the family Chaetodontidae. Other families, including the Labridae, Tetraodontidae, Balistidae, Monacanthidae, Pomacentridae and Scaridae, all have between seven and ten coral-feeding species. One-third of coral-feeding fishes feed almost exclusively on corals, with more than 80% of their diet based on coral. Corallivorous fish show distinct prey preferences and consume only a small subset of available corals, usually the genera Acropora, Pocillopora and Porites. This selective predation by corallivores can limit abundance and distribution of preferred corals. Chronic predation by corallivores may also exacerbate effects of coral disturbance (e.g. climate-induced coral bleaching), impeding reef recovery and causing further coral loss. Conversely, the cover of preferred corals can be a primary determinant of corallivore abundance and physiological condition. Owing to this close association, obligate corallivores invariably decline in response to loss of coral cover. Increased knowledge of the number of corallivores and their diets suggest that this feeding mode is more important to coral reef food webs than traditionally thought. [source] Predation and the persistence of melanic male mosquitofish (Gambusia holbrooki)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2004L. Horth Abstract The empirical reasons for the persistent rarity of a genotype are typically complex and tedious to identify, particularly in nature. Yet rare morphs occur in a substantial fraction of phenotypic polymorphisms. A colour polymorphism has persisted for decades in the eastern mosquitofish, yet why this is so remains obscure. Here, I report the results of (1) intensive sampling at 45 natural sites to obtain the frequency distribution of the melanic (black) mosquitofish morph in Florida, (2) predation trials, conducted independently in mesocosms, with three different predatory species and (3) two mark-recapture studies, conducted in nature. This work (1) documents the rarity of melanic mosquitofish in nature, (2) demonstrates that melanic males experience a selective advantage over silver males in the presence of predators, (3) indicates no difference in the colour morphs, survival at a natural site essentially devoid of these predators, although suggesting a higher rate of recapture for melanic males at a site rife with predators. Overall, selective predation appears to contribute to the persistence of the melanic morph, despite its rarity in nature. [source] Changes in survivorship, behavior, and morphology in native soft-shell clams induced by invasive green crab predatorsMARINE ECOLOGY, Issue 3 2010W. Lindsay Whitlow Abstract Many studies on invasive species show reduced native densities, but few studies measure trait-mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft-shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait-mediated effects to investigate predator,prey dynamics. [source] Coping with third parties in a nursery pollination mutualism: Hadena bicruris avoids oviposition on pathogen-infected, less rewarding Silene latifoliaNEW PHYTOLOGIST, Issue 4 2006Arjen Biere Summary ,,In nursery pollination systems, pollinator offspring usually feed on pollinated fruits or seeds. Costs and benefits of the interaction for plant and pollinator, and hence its local outcome (antagonism,mutualism), can be affected by the presence of ,third-party' species. Infection of Silene latifolia plants by the fungus Microbotryum violaceum halts the development of fruits that provide shelter and food for larvae of the pollinating moth Hadena bicruris. We investigated whether the moth secures its benefit by selective oviposition on uninfected flowers. ,,Oviposition was recorded in eight natural populations as a function of plant infection status, local neighbourhood, plant and flower characteristics. ,,Oviposition was six times lower on flowers from infected than on those from uninfected plants. Oviposition decreased with decreasing flower and ovary size. Moths could use the latter to discriminate against diseased flowers. ,,Although moths show an adaptive oviposition response, they reduce the future potential of healthy hosts because they still visit infected plants for nectar, vectoring the disease, and they reduce any fitness advantage gained by disease-resistant plants through selective predation of those plants. [source] Energetic costs, underlying resource allocation patterns, and adaptive value of predator-induced life-history shiftsOIKOS, Issue 2 2008Karsten Rinke We studied costs and benefits of life history shifts of water fleas (genus Daphnia) in response to infochemicals from planktivorous fish. We applied a dynamic energy budget model to investigate the resource allocation patterns underlying the observed life history shifts and their adaptive value under size selective predation in one coherent analysis. Using a published data set of life history shifts in response to fish infochemicals we show that Daphnia invests less energy in somatic growth in the fish treatment. This observation complies with theoretical predictions on optimal resource allocation. However, the observed patterns of phenotypic plasticity cannot be explained by changes in resource allocation patterns alone because our model-based analysis of the empirical data clearly identified additional bioenergetic costs in the fish treatments. Consequently, the response to fish kairomone only becomes adaptive if the intensity of size selective predation surpasses a certain critical level. We believe that this is the first study that puts resource allocation, energetic costs, and adaptive value of predator induced life-history shifts , using empirical data , into one theoretical framework. [source] Linkage disequilibrium and natural selection for mimicry in the Batesian mimic Hypolimnas misippus (L.) (Lepidoptera: Nymphalidae) in the AfrotropicsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010IAN J. GORDON On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore- and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 180,194. [source] | ||||||||||||||||||||||