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Size Refuge (size + refuge)
Selected AbstractsAbrupt community change on a rocky shore , biological mechanisms contributing to the potential formation of an alternative stateECOLOGY LETTERS, Issue 6 2004Robert T. Paine Abstract The 1997/1998 El Niño initiated a major shift in the intertidal assemblage on the Washington State outer coast. A 25 year time series (1978,2003) shows stands of dominant canopy algae replaced by mussel beds. A prior experiment had indicated that mussels can become too large to be eaten by starfish; newly initiated starfish removals predict mussel attainment of a size refuge. Such escapes inhibit recovery towards prior community composition and enhance development of alternative community states which may persist long after the originating forcing has lessened or disappeared. [source] Pike predation on hatchery-reared Atlantic salmon smolts in a northern Baltic riverECOLOGY OF FRESHWATER FISH, Issue 1 2008J. Kekäläinen Abstract,,, The effect of pike Esox lucius predation on the mortality of newly stocked Atlantic salmon Salmo salar smolts was investigated in the Pyhäjoki River, Finland. The number of smolts eaten by pike was assessed by estimating the size of the pike population (mark,recapture experiment) and studying the stomach contents of pike. Before recapturing the pike, approximately 39,700 smolts were stocked upstream of the 2.5-km-long (89-ha) research area. The estimated size of the >40-cm pike population was 1507 (95% CL 1012,4731) individuals (17 pike and 29.8 kg·ha,1). Pike were estimated to eat 29% of the released smolts during 1 week. The diet of the pike in the research area consisted almost entirely of smolts, whereas in the reference area with no stocked smolts, the meal sizes were significantly smaller and the importance of smolts as prey was substantially lower. Pike <40 cm had not eaten any smolts, probably indicating a size refuge for the smolts, or alternatively fear of intraspecific interactions or cannibalism of pike. [source] Effect of brown trout body size on post-stocking survival and pike predationECOLOGY OF FRESHWATER FISH, Issue 2 2004P. Hyvärinen Abstract,,, A total of 40 (20 age-3 + 20 age-4) radio-tagged hatchery-reared brown trout (Salmo trutta L.) and 40 wild radio-tagged northern pike (Esox lucius L.) were released into a regulated river. Age-3 brown trout were predicted and observed to be highly vulnerable to predation by pike (50% mortality), whereas age-4 brown trout were predicted and observed to enjoy an almost absolute size refuge from predation (5% mortality). Almost half of the fish from both age groups similarly emigrated and survived from the river within 3 days of the release. However, there was a considerable difference in survival between age groups for fish that remained in the river for a longer period. Of these, all except one age-3 brown trout were eaten by pike, whereas all but one age-4 fish survived predation. Resumen 1. Un total de 40 individuos de Salmo trutta (20 de edad-3 y 20 de edad-4) procedentes de piscifactoría fueron marcados con radio-transmisores y 40 individuos de Esox lucius también marcados con radio-transmisores, fueron soltados en un río regulado. Predecimos y observamos que los individuos de edad-3 de S. trutta fueron altamente vulnerables a la predación por Esox lucius (50 % de mortalidad) mientras que los individuos de edad-4 gozaron de refugio de tamaño casi absoluto de la predación (5% de mortalidad). 2. Casi la mitad de los peces de ambos grupos de edad sobrevivieron y emigraron del río durante los tres días siguientes a la suelta. Sin embargo, hubo una considerable diferencia en la supervivencia entre grupos de edad para los peces que permanecieron en el río por un período mayor de tiempo. De estos, todos excepto 1 individuo de S. trutta de edad-3 fueron comidos por E. lucius mientras que todos excepto un individuo de edad-4 sobrevivieron a la predación. [source] THE ROLE OF SIZE-SPECIFIC PREDATION IN THE EVOLUTION AND DIVERSIFICATION OF PREY LIFE HISTORIESEVOLUTION, Issue 5 2002Troy Day Abstract Some of the best empirical examples of life-history evolution involve responses to predation. Nevertheless, most life-history theory dealing with responses to predation has not been formulated within an explicit dynamic food-web context. In particular, most previous theory does not explicitly consider the coupled population dynamics of the focal species and its predators and resources. Here we present a model of life-history evolution that explores the evolutionary consequences of size-specific predation on small individuals when there is a trade-off between growth and reproduction. The model explicitly describes the population dynamics of a predator, the prey of interest, and its resource. The selective forces that cause life-history evolution in the prey species emerge from the ecological interactions embodied by this model and can involve important elements of frequency dependence. Our results demonstrate that the strength of the coupling between predator and prey in the community determines many aspects of life-history evolution. If the coupling is weak (as is implicitly assumed in many previous models), differences in resource productivity have no effect on the nature of life-history evolution. A single life-history strategy is favored that minimizes the equilibrium resource density (if possible). If the coupling is strong, then higher resource productivities select for faster growth into the predation size refuge. Moreover, under strong coupling it is also possible for natural selection to favor an evolutionary diversification of life histories, possibly resulting in two coexisting species with divergent life-history strategies. [source] Impact of a native predatory whelk on cultivated oysters (Crassostrea gigas) crops in San Quintin Bay, MexicoAQUACULTURE RESEARCH, Issue 4 2009Laura F Rodriguez Abstract San Quintin Bay (Baja, California, Mexico) is extensively utilized by artisanal farmers to cultivate Pacific oysters (Crassostrea gigas) using a rope/rack system. A large juvenile oyster mortality event was significantly correlated with the presence of native predatory whelks, Macron trochlea. Surveys, field and lab experiments were performed to identify the predatory behaviour of the whelk, determine factors affecting oyster mortality, and quantify the impact on oyster farmers. Macron trochlea was found to be a voracious, active predator, which can consume ,4 juvenile oysters day,1. Juvenile oysters suffer significantly higher mortality in the presence of whelks. Macron trochlea has the largest impact on small oysters. Once oysters grow to >30 mm they reach a size refuge above which there is much lower mortality. At average growth rates, an oyster can escape predation after ,3 months. But, in areas of highest whelk densities, at average predation rates, whelks could consume the standing crop of juvenile oysters in approximately 43 days. For the artisanal oyster farmers of San Quintin this represents a substantial economic loss, which was unaccounted for previously. Farmers can reduce loss to whelk predation by seeding juvenile oysters in low whelk density areas until oysters reach the size refuge. [source] | ||||||||||