Consequences of the size structure of fish populations for their effects on a generalist avian predator

Abstract

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-010-1862-3) contains supplementary material, which is available to authorized users.

Habitat selection and reproductive success of coot Fulica atra on ponds under different fish size and density conditions

“…The competitive impact of carp on birds can be increased to a large degree by non-trophic (trait-mediated) interactions, since vagile adult insects and breeding amphibians avoid ponds with fish that pose a predation threat to their eggs and larvae (e.g. Resetaris & Wilbur, 1989;Trekels & Vanschoenwinkel, 2017), and these effects may be contingent on fish size and density (Kloskowski, 2011). Overall, we did not find differences in coot breeding parameters or food availability between 1?…”

“…Here we used separate stocking of ponds with carp age cohorts as the context for a natural experiment to investigate coot habitat selection and breeding success in relation to the age structure of fish. Carp effects on aquatic ecosystems are size-dependent, as prey capture and ingestion are limited by gape size and because larger individuals tend to penetrate deeper into the sediments and to mobilise phosphorus through sediment suspension (Lammens & Hoogenboezem, 1991;Driver et al, 2005;Kloskowski, 2011). The species has been reported to increase phytoplankton production and decrease water transparency and macrophyte coverage, with effects generally increasing with fish density (Weber & Brown, 2015).…”

Management practices to enhance wildlife diversity of man-made fish ponds: the importance of the hydroperiod

“…Carp-mediated eutrophication due to resuspension of nutrient-laden sediments or mobilization of nutrients from excretion (Lougheed et al, 1998;Matsuzaki et al, 2009;Weber and Brown, 2015) may have different effects on amphibians and waterbirds. Some amphibian species are reported to avoid habitats dominated by fish that pose a predatory threat to their eggs and larvae (Binckley and Resetarits, 2007;Kloskowski, 2011). By contrast, many waterbirds prey on fish, although carp vulnerability declines with body growth (Moser, 1986) and larger-size carp can diminish food availability for waterbirds through competition or deterioration of water clarity (Santoul and Mastrorillo, 2003;Broyer and Calenge, 2010).…”

Fish reduce habitat coupling by a waterbird: evidence from combined stable isotope and conventional dietary approaches

“…Such habitat coupling is likely to be affected by fishes, which can influence migratory movements of insect and amphibian populations (Baxter et al 2004;Wesner 2010;Greig et al 2012). Fish influence on connectors across ecosystems adds a new dimension to the complex network of trophic and nontrophic interactions between fishes and birds (LeBourdais et al 2009;Kloskowski 2011). Their understanding may require reconstruction of multiple food-web linkages, including those among ecosystems and communities.…”

“…Although grebes, as pursuit divers, can extensively feed upon fishes, they are generalist predators well adapted to foraging on invertebrates by gleaning them from the bottom and from aquatic vegetation (Fjeldså 1982;reviewed in Vlug 2002), and may even avoid fish-dominated habitats to reduce competition for shared food (Wagner and Hansson 1998). Here, we compared the dietary sources of grebes nesting on fishless ponds and ponds stocked with common carp Cyprinus carpio, an omnivorous fish capable of a strong impact on the prey resources of waterbirds (Haas et al 2007;Kloskowski 2011). We estimated prelaying diet composition of grebes through observations of foraging birds and gut content analyses.…”