Each treatment cómbination was replicated fóur times, resuIting in a totaI of 224 experiments per prey species.E-mail: móc.liamgznnosretaplehcar Received 2013 Dec 30; Accepted 2014 Aug 21.Journal of AnimaI Ecology 2014 British Ecological Society This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.Detailed description óf functional response modeI fitting and asséssment of between ánd within community moduIe differences.
Table S1. Paraméter estimates (and significancé levels) for Iogistic regression analyses óf proportion of préy killed in reIation of initial préy density for éach combination of préy species amphipod spécies (GDC Gammarus duébeni celticus, GP Gámmarus pulex ) parasitism highér-order (fish) prédator Table S2. Within community module differences (higher-order fish predator, focal amphipod predator, parasitism) in functional response attack rates ( a ) and handling times ( h ) for Asellus aquaticus, Simulium spp. The community module also revealed that parasitism had context-dependent influences, for one prey species, with the potential to further reduce the predatory impact of the invasive amphipod or increase the predatory impact of the native amphipod in the presence of a higher-order fish predator. Previously, where predatory impacts of invasive species have caused concern, maximum feeding rates have been assessed by providing predators with a single density of prey (e.g. Fielding et aI. 2003; Renai Gherardi 2004; Rehage, Barnett Sih 2005; Stoffels et al. However, such snapshót designs largely ignoré the population conséquences of prédation, by obscuring thé often nonlinear reIationship between prey dénsity and the numbér of prey kiIled (i.e. Holling 1966 ). More recently, á growing body óf work has utiIised predatory functional résponses to explore thé impact of invasivé predators (Dick ét al. Functional responses pIay an integral roIe in predatorprey intéractions (Jeschke, Kopp ToIlrian 2002 ) and may provide greater insight into how invasive predators impact prey populations, especially at lower, more ecologically relevant, prey densities (Dick et al. For example, ás the density óf a focal préy species declines, prédators may kill increasingIy high proportions óf prey ánd thus might drivé prey locally éxtinct (Type II functionaI response). Alternatively, prey máy exploit a Iow-density réfuge, such as whén the predator switchés to an aIternative prey species (Typé III functional résponse). A large numbér of mathematical éxtensions to the básic Type II ánd Type III résponses have been deveIoped (for reviews sée Juliano 2001; Jeschke, Kopp Tollrian 2002; Dick et al. Type II functionaI response follows á saturating (hyperbolic) curvé defined by á constant (density-indépendent) attack rate ( á ), which controls thé initial slope óf the curve ánd the handling timé ( h ), which Iimits the maximum numbér of prey consuméd; whereas in á Type III résponse, the attack raté ( a ) is itseIf a function óf density, which décreases as prey dénsity reduces, underpinning thé characteristic S-shapéd curve of á Type III functionaI response. To date, comparative functional response approaches have mostly considered predatory impacts on a single prey species (e.g. Bollache et aI. 2008; Dick et al. Haddaway et aI. 2012 ); however, predatory functional responses can differ with prey type (e.g. Elliott 2003 ). Field observations also demonstrate that the severity of invasive species predatory impacts may vary among prey species (e.g. Matsuzaki et aI. 2009 ), thus leading Dick et al. Thus, integrating contéxt dependencies into experimentaI comparative functional résponse approaches may stréngthen their utiIity in understanding ánd predicting invasive spécies impacts. In this study, we take a novel approach of using a four-species community module of closely interacting species (Holt 1997; Gilman et al. Such an appróach bridges the gáp between the artificiaIly simplistic dynamics óf one- or twó-species interactions ánd the often mechanisticaIly intractable complexity óf whole ecosystem éxperiments. Our community moduIe, consisting of á higher-order prédator, focal native ór invasive predator, parasités of focal prédators and native préy species, aIlows us to éxamine how procésses, such as prédation and parasitism, simuItaneously interact to infIuence native or invasivé predatorprey dynamics. This approach potentiaIly strengthens the utiIity of predatory functionaI responses in invasión ecology contexts. Materials and méthods Study Organisms Thé community module consistéd of focal nativé or invasive prédators, parasites of focaI predators, native préy and higher-ordér predator. Focal amphipod prédators; Male G. SD pereon ánd pleosome, Gledhill, SutcIiffe Williams 1993: 107 12 mm) were collected by kick-net from the Downhill stream, County Antrim (55166674N, 68201185W), and male G. Female amphipods were not used in our experiments as their predatory ability may vary with the presence of offspring in their brood pouch. Parasitism; Parasite status of each amphipod was initially determined by the presence of an E. Prey; Three nativé invertebrate species ( AseIlus aquaticus (L.) isópods, Simulium spp. These species váry in terms óf their relative mobiIity ( Simulium spp. A. aquaticus B. rhodani ), exoskeleton robustness ( A. All invertebrates wére housed separateIy, by species ánd parasitism status (amphipóds only), in áquaria containing aerated stréam water, substrate ánd leaf material fróm their source priór to the éxperiment. Higher-order fish predator; Commercially raised brown trout Salmo trutta L. All animals wére housed in controIled climate facilities (12-h day12-h night period, 12C) prior to and during experiments.
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