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Background/Question/Methods Intraguild predation (IGP) has been suggested to be common in nature although theory suggests that the room for coexistence of intraguild consumer and intraguild predator is limited. Size-dependent interactions and refuges have been identified as important factors affecting the community dynamics of IGP systems. In a recent study investigating the invasion success of juvenile and adult guppies (Poecilus reticulata) into a resident population of the least killifish (Heterandria formosa) without refuges, we showed that invasion success depended on invader body size where adults succeeded while juveniles failed to invade. Here we tested whether the inclusion of refuges would affect the ability of differently sized guppies to invade a resident least killifish population. We tested for the effects of refuges on invasion success of differently sized invading guppies in laboratory experiments scaling from long-term community dynamics to short-term individual experiments. Species abundances, species’ size-spectra and invader growth were measured. Results/Conclusions In contrast to the results without refuges, we found that invasion success in both small and large guppies with refuges was 50% (i.e. random), successful invasion always followed by H. formosa extinction. Invasion experiments with intermediately sized guppies showed the same effect of refuges: small invader increased their invasion success whereas larger individuals decreased their invasion success in the presence of refuges. Furthermore, we observed an increase of invasion success with increasing invader size in the absence of refuges while invasion success was size-independent in the presence of refuges. Individual and short-term experiments on the size-dependent predatory capture rate of large P. reticulata on H. formosa juveniles and on juvenile competition within and between the two species provided explanations for the change in size-dependent invader success as observed in the long-term invasion experiments. Large female invaders acted as IG predators on small H. formosa in the absence of refuges but not in the presence of refuges. Juvenile competition experiments showed that if only considering the mean growth rate of juvenile invaders no effect of density, refuges, or H. formosa presence on P. reticulata was present. However, analysis of the size-spectra of P. reticulata showed a significant interaction between competitive condition and refuges resulting from that P. reticulata exhibited extreme left-skewed size distributions with interspecific competition and refuges. Hence refuges are not advantageous for the “mean-sized”-invader but only for some individuals that succeed to grow fast into less vulnerable sizes.

Refuges randomize the invasion success of small and large predators in an intraguild predation system. Available from: https://www.researchgate.net/publication/267280200_Refuges_randomize_the... [accessed Sep 26, 2017].