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Keystone predation can be a determinant of community structure, including species diversity, but factors underlying "keystoneness" have been minimally explored. Using the system in which the original keystone, the sea star Pisaster ochraceus, was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H1) predation rates and effects will vary in space but not time; (H2) per population predation rates will vary primarily with individual traits and population variables; (HJHH3) per capita predation rates will vary only with individual traits; (H4) predation effects will vary with traits, variables, and external drivers; and (H5) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H1), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H4). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H2, per population), or only with extrinsic (H3, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contra H4). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling, H5). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness. [ABSTRACT FROM AUTHOR]

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Abstract Predatory behavior of the crab Eriphia verrucosa (Forskål, 1775) on the oyster Magallana angulata (Lamarck, 1819), the mussel Mytilus galloprovincialis Lamarck, 1819, the limpet Patella depressa Pennant, 1777, the hermit crab Clibanarius erythropus (Latreille, 1818), the gastropod Phorcus lineatus (da Costa, 1778) and the sea urchin Paracentrotus lividus (Lamarck, 1816) was experimentally studied. Taken into account that the sampled population of E. verrucosa was infected with the parasitic barnacle Sacculina eriphiae Smith, 1906, four predator categories were established regarding crab sex and parasite presence: uninfected and infected males and females, respectively. These four crab categories were fed on the six preys offered, but prey remains suggest that the crab obtains the flesh of each prey using different methods of attack. Irrespective of the prey species, uninfected females consistently presented lower percentages of crab feeding and total consumption. On average, it was found that a significantly higher percentage of crabs feed on M. galloprovincialis, P. depressa and Ph. lineatus than on the other three prey species (chi-squared test, p < 0.05). In terms of mean eaten biomass, the preys most eaten were P. lividus and P. depressa and the least eaten was C. erythropus (ANOVA test, p < 0.05). For crabs feeding on M. galloprovincialis and Ph. lineatus there was a significant positive correlation (p < 0.05) between the predator size and prey size, as well as between the predator size and total prey consumption. According to these results, potential effects of this top predator on intertidal communities are also discussed.

Bilberry (Vaccinium myrtillus L.) is one of the dominant plants of the Fennoscandian boreal coniferous forest and constitutes a major food source for many insect herbivores. A common ant species in these forests is the wood ant Formica (Formica) aquilonia Yarrow, which preys heavily on other invertebrates within its territories. The aim of this study was to investigate whether aquilonia's predation on the insect herbivores may have indirect positive or negative effects on bilberry. Damage to the bilberry, its vegetative growth and reproduction were quantified in order to contrast localities close to (2 m) and far away from (50 m) ant nests.Close to ant nests, herbivore damage to the bilberry was significantly lower and reproductive success, i.e. proportion of flowers succeeding to berries, significantly higher. The results of this study therefore suggest that distance to aquilonia nests, and thus predation from ants, can significantly affect herbivore damage to the bilberry and its reproductive success (supporting the hypothesis of a top down effect in this three-trophic-level system). Vegetative growth, i.e., density and biomass of current year shoots, and reproductive investment, i.e., proportion of current year shoots with flower, of the bilberry was, however, not affected by distance to ant nests, indicating that the bilberry can also compensate for losses due to herbivory.

Whilst consumption by rodents is often invoked as a major mortality factor for large-seed species of trees, its relative importance compared with other mortality factors is poorly known. We investigated experimentally the fate of post-dispersal seeds of Quercus glauca under different understorey environments (areas covered by (i) a pteridophyte Pyrrosia lingua, (ii) a ground-vine, Trachelospermum asiaticum and (iii) no vegetation) from the germination stage to seedling emergence and establishment stages in humid maritime woodland. We employed a pair of caged and uncaged treatments to evaluate the impact of seed removal/predation by rodents, which allowed us to separate seed removal/predation mortality from mortality due to other factors. Effects by rodents were greater in the no-understorey habitat than in the Pyrrosia and Trachelospermum habitats at early stages of development, whilst non-rodent-associated mortality was relatively more important towards the seedling establishment stages in all habitats. In the absence of predation/removal by rodents (i.e. the caged treatment), more seedlings survived in the no-understorey habitat whilst seedlings were significantly taller in the Pyrrosia habitat. In contrast, no significant difference was observed in either seed/seedling survivorship or seedling height amongst habitats where seeds/seedlings were exposed to rodent predation/removal. Overall, this study in a humid maritime woodland has revealed the temporally variable influence of mortality factors and the context-dependent survival of oak seeds/seedlings, making a contrast to observations in drier woodlands; in the no-understorey environment predation/removal effect was heavier but later survivorship was higher, whilst in vegetated environments, predation/removal was reduced but survivorship was not high. [ABSTRACT FROM AUTHOR]

A new integrated Bayesian framework for making quantitative assessments, predictions, and risk analyses of shrimp (Pandalus borealis) stock development is constructed. A biomass dynamic model, based on the logistic function but including an explicit term for cod predation, suggests that the quantity of shrimp consumed by cod could equal that taken by the fishery. The model proved superior to an alternative model in its ability to estimate parameters central to the assessment; the alternative model subsumed cod predation as part of an overall population growth effect without a time trend. Two series of shrimp biomass indices, catch, cod biomass estimates, cod consumption estimates, and prior distributions of model parameters provided information to the models. Process and observation errors were incorporated simultaneously using a state-space modelling framework. A Bayesian approach was used to construct posterior probability distributions of model parameters and derived variables relevant for management advice, including quantification of future risk of transgressing reference points in relation to alternative management options. [Copyright &y& Elsevier]

Feral cats are directly responsible for a large percentage of global extinctions, particularly on islands. We reviewed feral cat eradication programs with the intent of providing information for future island conservation actions. Most insular cat introductions date from the nineteenth and twentieth centuries, whereas successful eradication programs have been carried out in the last 30 years, most in the last decade. Globally, feral cats have been removed from at least 48 islands: 16 in Baja California (Mexico), 10 in New Zealand, 5 in Australia, 4 in the Pacific Ocean, 4 in Seychelles, 3 in the sub-Antarctic, 3 in Macaronesia (Atlantic Ocean), 2 in Mauritius, and 1 in the Caribbean. The majority of these islands (75%; = 36) are small (≤5 km2). The largest successful eradication campaign took place on Marion Island (290 km2), but cats have been successfully removed from only 10 islands (21%) of ≥10 km2. On Cousine Island (Seychelles) cat density reached 243 cats/km2, but on most islands densities did not exceed 79.2 cats/km2 ( = 22; 81%). The most common methods in successful eradication programs were trapping and hunting (often with dogs; 91% from a total of 43 islands). Frequently, these methods were used together. Other methods included poisoning (1080; monofluoracetate in fish baits; = 13; 31%), secondary poisoning from poisoned rats ( = 4; 10%), and introduction of viral disease (feline panleucopaenia; = 2; 5%). Impacts from cat predation and, more recently, the benefits of cat eradications have been increasingly documented. These impacts and benefits, combined with the continued success of eradication campaigns on larger islands, show the value and role of feral cat eradications in biodiversity conservation. However, new and more efficient techniques used in combination with current techniques will likely be needed for success on larger islands. [ABSTRACT FROM AUTHOR]