Priority effects among young-of-the-year fish: Reduced growth of bluegill sunfish (Lepomis macrochirus) caused by yellow perch (Perca flavescens)?

Abstract

When available, Daphnia spp. are often preferred by age-0 yellow perch and bluegill sunfish because of energetic profitability. We hypothesised that predation by age-0 yellow perch could lead to a midsummer decline (MSD) of Daphnia spp. and that priority effects may favour yellow perch because they hatch before bluegill, allowing them to capitalise on Daphnia spp. prior to bluegill emergence. Data were collected from 2004 to 2010 in Pelican Lake, Nebraska, U.S.A. The lake experienced a prolonged MSD in all but 1year (2005), generally occurring within the first 2weeks of June except in 2008 and 2010 when it occurred at the end of June. MSD timing is not solely related to seasonal patterns of age-0 yellow perch consumption. Nevertheless, when Daphnia spp. biomass was low during 2004 and 2006-2010 (<4mgwet weightL -1), predation by age-0 yellow perch seems to have suppressed Daphnia spp. biomass (i.e. <1.0mgwet weightL -1). The exception was 2005 when age-0 yellow perch were absent. Growth of age-0 bluegill was significantly faster in 2005, when Daphnia spp. were available in greater densities (>4mgwet weightL -1) compared with the other years (<0.2mgwet weightL -1). We conclude that age-0 yellow perch are capable of reducing Daphnia biomass prior to the arrival of age-0 bluegill, ultimately slowing bluegill growth. Thus, priority effects favour age-0 yellow perch when competing with age-0 bluegill for Daphnia. However, these effects may be minimised if there is a shorter time between hatching of the two species, higher Daphnia spp. densities or lower age-0 yellow perch densities. © 2012 Blackwell Publishing Ltd.