Selection between Densities of Artificial Vegetation by Young Bluegills Avoiding Predation

Abstract

Young (35–50 mm, standard length) bluegills Lepomis macrochirus are restricted to vegetated habitats by predation pressure. Vegetation provides refuge by hindering predator foraging success. In this study, we tested the ability of bluegills to actively perceive and select densities of vegetation where they are safe from predation. Bluegills were presented with two plots of artificial vegetation (cover plots) of different densities (1,000, 250, 100, and 50 stems/m2) in an experimental arena and then confronted with a predator, a largemouth bass Micropterus salmoides. Prey distribution in the arena before, during, and after exposure to the predator, as well as the predatorˈs foraging activities, were recorded for each trial. Before predator introduction, bluegills in all combinations of cover plots spent most of their time in or around the thicker plot of vegetation in the arena. With the predator present in combinations with cover plot 1,000, prey chose this plot as a refuge when attacked. Cover plot 250 was selected as often as positions at the water‐air interface, and plots 100 and 50 were ignored as refuges. After removal of the predator, only in combinations with cover plot 1,000 did prey remain around the thicker cover plot present. Predator success (number of prey caught/total number of attacks) was lowest in trials with cover plot 1,000 present. When confronted with a predator, young bluegills appear capable of perceiving and selecting plots of vegetation offering safety from predation.

The influence of a severe reservoir drawdown on springtime zooplankton and larval fish assemblages in Red Willow Reservoir, Nebraska

“…Bluegill and green sunfish (L. cyanellus), two species present in many reservoirs in this region, are phytophyllic at multiple life stages (Crowder and Cooper 1982;Werner and Hall 1977), particularly early life stages (Gotceitas and Colgan 1987;Werner and Hall 1988). Thus, they may also be negatively affected by the loss of aquatic macrophytes as a consequence of extreme reservoir drawdown (Martin et al 1981;Bettoli et al 1993).…”

“…Low water levels can reduce the availability of adequate spawning (Ploskey 1986;Kallemeyn 1987) and nursery (Edwards and Twomey 1982;Werner et al 1983;Gotceitas and Colgan 1987;Werner and Hall 1988) habitat for fish. Seasonal changes in reservoir flushing rate can cause changes in zooplankton and phytoplankton abundance; a high flushing rate can lead to low zooplankton abundance (Watson et al 1996;Kalff 2003), which could reduce food availability for larval fish at a critical stage.…”

Habitat structure influences the survival and predator–prey interactions of early juvenile red king crab Paralithodes camtschaticus

“…When predators are absent, prey habitat choice should maximize foraging (Werner et al 1983). Under perceived predator threat, prey should respond with behaviors that maximize immediate survival (Stein & Magnuson 1976), including retreat to refuge structure, reduced activity, reduced foraging, and direct defense (Stein & Magnuson 1976, Gilliam & Fraser 1987, Gotceitas & Colgan 1987, Laurel & Brown 2006. This trade-off results in reduced growth rates (Werner et al 1983, Werner 1991, 1992, Tupper & Boutilier 1995, with population-level consequences such as reduced reproductive potential.…”

The effect of vegetation density on juvenile bluegill diet and growth

“…Yet juveniles often forage suboptimally in structurally complex habitats, such as dense vegetation, to avoid pelagic predation risk (Mittelbach 1981), which can be a major factor determining recruitment to age-1 (Santucci and Wahl 2003). Studies of bluegill behavior in the laboratory (Gotceitas and Colgan 1987;Savino and Stein 1989;Shoup et al 2003) and in ponds (Werner et al 1983a) both show that bluegill spend more time in structurally complex habitats when predators are present. Furthermore, structurally complex habitats can negatively affect foraging returns of juvenile bluegill (Mittelbach 1981;Gotceitas 1990a;Pothoven et al 1999), and vegetation density negatively correlates with bluegill growth (Shoup et al 2007).…”

“…Foraging by fishes can be affected in many ways by habitat, which can influence prey abundance (Gerking 1957;Savino et al 1992;Barwick 2004), behavior patterns (Savino and Stein 1989), predator attack success (Savino and Stein 1982;Gotceitas and Colgan 1987), and ultimately prey selection (Schramm and Zale 1985;Dibble and Harrel 1997;Shoup and Wahl 2009) and competitive interactions (Abrahams 1994;Wellenreuther et al 2007;Robertson et al 2008). Therefore, changes in vegetation abundance could cause changes in diet and growth rate of juvenile bluegill that are independent of the effects of predation risk.…”