Abstract
Intraguild predation interactions make fish communities prone to exhibit alternative stable states with either piscivore or prey fish dominance. In the Baltic Sea, local declines of coastal piscivores like perch (Perca fluviatilis) have been observed to coincide with high densities of sticklebacks (Gasterosteus aculeatus). Mechanisms behind this shift between piscivore and stickleback dominance were studied both experimentally and in field. Results showed that predation by sticklebacks has a strong negative effect on perch larvae survival, but this effect rapidly decreases with increasing perch size, likely due to gape limitations and digestion constraints in sticklebacks. Large spatial and temporal variations in patterns of stickleback migration into perch spawning sites were observed. Whether or not high density of sticklebacks will cause declines in coastal piscivore populations is suggested to depend on the availability of spawning sites in which sticklebacks do not migrate into or arrive late in the reproduction season of coastal piscivores.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-015-0665-5) contains supplementary material, which is available to authorized users.
Highlights
Life history omnivory is common in fish and may involve both habitat shifts and interactions where species both prey on and compete with each other, i.e., intraguildElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.predation (IGP) (Werner and Gilliam 1984; Irigoien and de Roos 2011)
We have only studied the performance of the smallest stages of YOY perch, the strong negative effects on perch larval survival suggest that the negative effects of sticklebacks most likely operate on the earliest life stages
Competition for zooplankton from sticklebacks has previously been suggested to be the main reason for observed patterns of low recruitment in coastal piscivores (Ljunggren et al 2010)
Summary
Life history omnivory (shifts in resource use from invertebrates to fish over ontogeny) is common in fish and may involve both habitat shifts and interactions where species both prey on and compete with each other, i.e., intraguild. The collapse of cod (Gadus morhua) has resulted in predation release of small planktivores, and a planktivore dominated offshore ecosystem (Casini et al 2009; Eriksson et al 2011) Along with this shift in the offshore ecosystem, local declines in the Baltic Proper have been observed of the coastal keystone piscivorous fish species: perch (Perca fluviatilis) and pike (Esox lucius) (Ljunggren et al 2010; Eriksson et al 2011). In a coastal area with high densities of stickleback we estimated (a) the number of perch migrating from the sea up to a small freshwater lake for spawning, (b) the YOY perch densities in that lake, and (c) the proportion of perch that have been recruited from freshwater systems in that area
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