Competition during early ontogeny: Effects of native and invasive planktivores on the growth, survival, and habitat use of bluegill

Abstract

Early life stages of fishes are sensitive to ecological and environmental disturbances and experience very high mortality rates. During early ontogeny, the growth and survival of larval fish often depends on food availability. Because habitat and diet shifts are strongly tied to individual body size, factors that influence the growth rates of individuals (e.g. resource limitation, competition) also affect other aspects of ontogeny including the timing of habitat or diet shifts. In the context of biological invasions, non‐native species can potentially disrupt the interaction of larval fish with their food via competition for shared prey, reducing growth and survival during a vulnerable period of an organism's life history. We hypothesised that invasive planktivores negatively affect native species through the vulnerable larval life stage via competition for zooplankton resources. To test this hypothesis, we conducted a series of experiments to assess and contrast the effects of invasive (bighead carp, Hypophthalmichthys nobilis) and native (golden shiners, Notemigonus crysoleucas) planktivores on zooplankton densities, and their effects on the growth, survival, abundance, and habitat use of larval bluegill (Lepomis macrochirus). Overall, the effects of the invasive planktivore were consistently greater than the native planktivore in terms of reduced prey densities, reduced bluegill growth rates, and delays to the timing of ontogenetic habitat shifts. Growth rates of bluegill larvae were reduced by 58–87% in the presence of bighead carp and 37% in the presence of golden shiners (relative to controls), but such reductions did not consistently lead to reduced survival (in mesocosm experiment) or relative abundance (in pond experiment). However, we estimated that bighead carp and golden shiners delayed ontogenetic habitat shifts in bluegill by 9–24 and 1–3 days, respectively. Although we did not detect an effect of planktivores on the numbers of larval bluegill, our findings suggest that bighead carp may still affect bluegill ontogeny and freshwater food webs by disrupting the timing of ontogenetic habitat shifts. By affecting the coupling of habitats via organism movements during early ontogeny, bighead carp may indirectly disrupt predator–prey interactions of native taxa.

Dynamic competition and resource partitioning during the early life of two widespread, abundant and ecologically similar fishes

“…A number of studies have demonstrated that competition can have negative impacts on fish growth, survival or fitness (e.g. Werner & Gilliam, 1984;Persson, 1983aPersson, , 1987Byström et al, 1998;Britton et al, 2018;Fletcher et al, 2019). In spite of the differences in foraging ecology observed in this study, there were no significant differences in the growth or condition of roach or bream larvae in allopatry and sympatry (cf., Britton et al, 2018), suggesting that the strength of competition and/or the duration of the experiment were insufficient to have a measurable effect.…”

“…Other possible explanations include that the fish density was too low, but this also seems unlikely as it was more than an order-of-magnitude higher than in some successful experiments of density-dependent growth (e.g. Byström et al, 1998;Byström & García-Berthou, 1999;Fletcher et al, 2019). However, although absolute density was constant, and comparable with those observed in the wild (e.g.…”

“…Despite this, few studies have examined competition and resource partitioning in young fishes, especially the consequences of temporal variations in resource availability, and our understanding of the mechanisms and implications is incomplete. This is important because early ontogeny is invariably the critical period in the life cycle of fishes, with competition-induced changes in individual growth rates, condition or survival having direct implications for adult cohort size and population and community dynamics (Beaugrand et al, 2003;Fletcher et al, 2019). Furthermore, as fish are key predators in the majority of aquatic environments, competition and resource partitioning can have tangible impacts on energy pathways, foodweb dynamics and ecosystem functioning (Miller & Rudolf, 2011;Nakazawa, 2015).…”

Developmental ecomorphology of the epibranchial organ of the silver carp, Hypophthalmichthys molitrix

“…Widespread invasion of silver carp has had substantial ecological and economic effects on freshwater ecosystems in the United States (Fletcher et al ., 2019; Freedman et al ., 2012; Solomon et al ., 2016; Zhang et al ., 2015). Larval silver carp compete with juvenile sport fishes for resources, creating an upstream effect on their population and ultimately the economy that is supported by such fisheries (Fletcher et al ., 2019; Solomon et al ., 2016).…”

“…Widespread invasion of silver carp has had substantial ecological and economic effects on freshwater ecosystems in the United States (Fletcher et al ., 2019; Freedman et al ., 2012; Solomon et al ., 2016; Zhang et al ., 2015). Larval silver carp compete with juvenile sport fishes for resources, creating an upstream effect on their population and ultimately the economy that is supported by such fisheries (Fletcher et al ., 2019; Solomon et al ., 2016). Later in ontogeny, silver carp can consume particles as small as 5 μm, but also regularly consume those as large as 100 μm and compete with fish species across the entire trophic hierarchy (Battonyai et al ., 2015; Cremer & Smitherman, 1980; Smith, 1989; Zhou et al ., 2009).…”