docComparing the predatory impact of invasive and native crabs
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Comparing the predatory impact of invasive and native crabs
Comparing the predatory impact of invasive and native crabs Brett Howard Simon Fraser University Earth to Ocean Research Group Isabelle Côté (SFU) & Thomas Therriault (DFO) Global invaders Carcinus maenas Global invaders Carcinus maenas Charybdis hellerii wildsingapore.com Global invaders Carcinus maenas Charybdis hellerii Hemigrapsus takanoi Hemigrapsus sanguineus H. sangineus (c) B. Whitman H. takanoi (c) Decleer Misjel Global invaders Carcinus maenas Charybdis hellerii Hemigrapsus takanoi Hemigrapsus sanguineus Eriocheir sinensis E. sinensis Wikimedia Commons Global invaders Carcinus maenas Charybdis hellerii Hemigrapsus takanoi Hemigrapsus sanguineus Eriocheir sinensis Rhithropanopeus harrisii R. harrisii (c) D.E. Keith Global invaders Carcinus maenas Charybdis hellerii Hemigrapsus takanoi Hemigrapsus sanguineus Eriocheir sinensis Rhithropanopeus harrisii Interactions with native species non-native Interactions with native species non-native native Interactions with native species non-native native Differences in design Experimental Spatial Temporal Are invasive crabs better predators? Global invasions Design differences Meta-analysis Species interactions Literature search WOS and ASFA (3,222 results) 3,108 excluded (crab + marine + predat* + compet*) Marine, near-shore, adult crabs With and without crab treatments Consumptive interaction Response = measure of abundance 114 included (729 experiments) Moderators Moderators Crab species Native Non-native Moderators Crab species Native Non-native Prey functional group Mobile infauna Mobile epifauna Vertebrates Sessile epifauna Primary producers Moderators Crab species Native Non-native Prey functional group Mobile infauna Mobile epifauna Vertebrates Sessile epifauna Primary producers Interaction Direct Indirect Moderators Crab species Native Non-native Prey functional group Mobile infauna Mobile epifauna Vertebrates Sessile epifauna Primary producers Interaction Direct Indirect Experimental design Natural field experiments Unstocked enclosures Stocked enclosures Lab mesocosms Predation experiments Measuring effect sizes • Effect size metric = standardized mean difference (Hedges g) • X = mean abundance of responding species g = Xwithout - Xwith g= Spooled • Spooled • is the pooled standard deviation across groups Effect sizes weighted by the inverse of the sampling variance Interpreting effect sizes 0 Standardized Mean Difference (g) Interpreting effect sizes abundance increased 0 Standardized Mean Difference (g) Interpreting effect sizes abundance decreased abundance increased 0 Standardized Mean Difference (g) Interpreting effect sizes abundance decreased abundance increased 0 Standardized Mean Difference (g) Direct vs. indirect n Direct abundance 588 Indirect abundance 141 -2 -1 0 1 Standardized Mean Difference (g) 2 Prey functional g roup Direct abundance n abundance Mobile infauna 222 Mobile epifauna 166 Primary producers 44 Sessile invertebrates 150 Vertebrates 6 -3 -2 -1 0 1 2 Standardized Mean Difference (g) 3 Prey functional g roup Indirect Direct abundance n abundance Mobile infauna 222 Mobile epifauna 166 Primary producers 44 Sessile invertebrates 150 Vertebrates 6 Mobile infauna 6 Mobile epifauna 2 Primary producers 60 Sessile invertebrates 67 Vertebrates 6 -3 -2 -1 0 1 2 Standardized Mean Difference (g) 3 Experimental design Direct abundance n abundance Natural experiments 15 Unstocked enclosures 187 Stocked enclosures 116 Mesocosms 92 Predation experiments 178 -3 -2 -1 0 1 2 Standardized Mean Difference (g) 3 Experimental design Indirect Direct abundance n abundance Natural experiments 15 Unstocked enclosures 187 Stocked enclosures 116 Mesocosms 92 Predation experiments 178 Natural experiments 7 Unstocked enclosures 16 Stocked enclosures 33 Mesocosms 85 -3 -2 -1 0 1 2 Standardized Mean Difference (g) 3 Are invasive crabs better predators? abundance -2 -1 n abundance 0 1 Standardized Mean Difference (g) 2 Are invasive crabs better predators? n Direct abundance Non-native crabs 166 Native crabs 422 Indirect abundance Non-native crabs 75 Native crabs 66 -3 -2 -1 0 1 2 Standardized Mean Difference (g) 3 Functionally novel predators Interspecific competition Population vs. per capita effects Functionally novel predators Cumulative impacts on native biodiversity Interspecific competition Population vs. per capita effects Conclusions Global invasions Design differences Meta-analysis Species interactions Conclusions Global invasions Design differences Meta-analysis Species interactions All crabs have negative direct effects Indirect effects generally positive Future research: emphasis on interspecific competition Conclusions Global invasions Design differences No significant difference between designs Meta-analysis Future research: focus on population and ecosystem effects Species interactions All crabs have negative direct effects Indirect effects generally positive Future research: emphasis on interspecific competition Conclusions Global invasions Design differences No significant difference between designs Non-native and native crabs are equally effective predators Future research: compare native and non-native in situ to determine functional redundancy Meta-analysis Future research: focus on population and ecosystem effects Species interactions All crabs have negative direct effects Indirect effects generally positive Future research: emphasis on interspecific competition Acknowledgements