title: Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators.
abstract: Occurrence of cannibalism and inferior competitive ability of predators compared to their prey have been suggested to promote coexistence in size-structured intraguild predation (IGP) systems. The intrinsic size-structure of fish provides the necessary prerequisites to test whether the above mechanisms are general features of species interactions in fish communities where IGP is common. We first experimentally tested whether Arctic char (Salvelinus alpinus) were more efficient as a cannibal than as an interspecific predator on the prey fish ninespine stickleback (Pungitius pungitius) and whether ninespine stickleback were a more efficient competitor on the shared zooplankton prey than its predator, Arctic char. Secondly, we performed a literature survey to evaluate if piscivores in general are more efficient as cannibals than as interspecific predators and whether piscivores are inferior competitors on shared resources compared to their prey fish species. Both controlled pool experiments and outdoor pond experiments showed that char imposed a higher mortality on YOY char than on ninespine sticklebacks, suggesting that piscivorous char is a more efficient cannibal than interspecific predator. Estimates of size dependent attack rates on zooplankton further showed a consistently higher attack rate of ninespine sticklebacks compared to similar sized char on zooplankton, suggesting that ninespine stickleback is a more efficient competitor than char on zooplankton resources. The literature survey showed that piscivorous top consumers generally selected conspecifics over interspecific prey, and that prey species are competitively superior compared to juvenile piscivorous species in the zooplankton niche. We suggest that the observed selectivity for cannibal prey over interspecific prey and the competitive advantage of prey species over juvenile piscivores are common features in fish communities and that the observed selectivity for cannibalism over interspecific prey has the potential to mediate coexistence in size structured intraguild predation systems.
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden. par.bystrom@emg.umu.se
authors.forename: Pär
authors.initials: P
authors.lastname: Byström
authors.forename: Per
authors.initials: P
authors.lastname: Ask
authors.forename: Jens
authors.initials: J
authors.lastname: Andersson
authors.forename: Lennart
authors.initials: L
authors.lastname: Persson
mesh_terms: D000818:Animals; D002190:Cannibalism; D005399:Fishes / Q000502:physiology*; D020387:Food Chain; D011235:Predatory Behavior
references.citation: Am Nat. 2001 Sep;158(3):259-76
references.pmid: 18707323
references.citation: Ecology. 2008 Jun;89(6):1650-60
references.pmid: 18589529
references.citation: Am Nat. 2000 Feb;155(2):200-218
references.pmid: 10686161
references.citation: J Anim Ecol. 2006 Mar;75(2):434-44
references.pmid: 16637996
references.citation: Am Nat. 2011 Dec;178(6):701-14
references.pmid: 22089866
references.citation: Zh Obshch Biol. 2000 Nov-Dec;61(6):601-15
references.pmid: 11190562
references.citation: Am Nat. 2012 Dec;180(6):791-801
references.pmid: 23149403
references.citation: Oecologia. 1987 Sep;73(2):170-177
references.pmid: 28312284
references.citation: Ecology. 2007 Nov;88(11):2697-705
references.pmid: 18051636
references.citation: Am Nat. 2000 Feb;155(2):219-237
references.pmid: 10686162
references.citation: Proc Biol Sci. 2004 Feb 22;271(1537):333-40
references.pmid: 15101690