Reduction of adaptive genetic diversity radically alters eco‐evolutionary community dynamics

Abstract

Adaptive variation in the traits determining ecological interactions can lead to evolution so rapid that ecological dynamics change course while in progress (i.e., 'eco-evolutionary dynamics'). However, little is known about how the qualitative properties of eco-evolutionary dynamics (e.g., cycling, equilibrium, etc.) are affected by the amount of heritable variation present. Here, we show that a change in the range of variation in a heritable prey defense trait determines what dynamics are observed in an experimental predator-prey system. We combine modelling and laboratory experiments to show that initial defense trait variation determines whether populations exhibit eco-evolutionary cycles in which heritable variation is maintained, or converge to an equilibrium at which the prey population becomes monomorphic. Our results show how small changes in the amount of adaptive genetic variance initially present can radically alter eco-evolutionary dynamics, and can ultimately determine whether heritable variation is maintained or lost.

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

“…The Monod equation is equivalent to a Holling type II functional response but is not restricted to predator—prey interactions and has been applied also to autotrophic organisms taking up nutrients (e.g., Becks et al., 2010; Raatz, Gaedke, & Wacker, 2017; Yoshida et al., 2003). The per capita growth rate of A i in dependence of N is described by…”

“…The parameter χ P describes the efficiency with which consumed prey individuals are converted into predator individuals. To reach a suitable parametrization, we refer our model to an empirically well‐studied rotifer‐algae system with Brachionus calyciflorus as a predator and different genotypes of Chlamydomonas reinhardtii as prey (Becks, Ellner, Jones, & Hairston, 2012; Becks et al., 2010). For details on the values and units of the parameters and the state variables, see Table 2.…”

“…TVC, Typical values used in chemostat experiments with rotifers and algae as they enable sufficient rotifer densities but avoid light limitation (e.g., Becks et al., 2010; Yoshida et al., 2003); NM, No measurements available. For simplicity, we assume that the fraction of T spent for attacking and manipulating the prey is equal, that is, c a  = 0.5 (sensitivity analysis in Appendix S3).…”

“…Furthermore, the type of defense costs regarding competitiveness (resource uptake affinity or growth rate) plays an important role for coexistence. Theory already showed that predator‐mediated coexistence crucially depends on the environmental conditions (Chase et al., 2002), for example, the enrichment level (Genkai‐Kato & Yamamura, 1999; Leibold, 1996; Proulx & Mazumder, 1998), the prey switching behavior of the predator (Abrams & Matsuda, 1993; Fryxell & Lundberg, 1994; Murdoch, 1969), the magnitude of the trade‐off between defense and competitiveness (Abrams, 1999; Kasada, Yamamichi, & Yoshida, 2014; Tirok & Gaedke, 2010), and the difference in both the defense level and the competitiveness between the prey types (Becks, Ellner, Jones, & Hairston, 2010; Ehrlich, Becks, & Gaedke, 2017; Jones & Ellner, 2007). However, the role of different defense mechanisms and competition costs in prey communities remains unclear but holds promise to be decisive for their coexistence and the occurring population dynamics.…”

“…Previous studies on predator‐mediated coexistence in diamond‐shaped food web models often implicitly assumed pre‐attack defenses (Abrams, 1999; Fryxell & Lundberg, 1994; Yamauchi & Yamamura, 2005) and considered either a higher half‐saturation constant (Becks et al., 2010; Jones & Ellner, 2007; Yoshida, Jones, Ellner, Fussmann, & Hairston, 2003) or a lower maximum growth rate as costs (Abrams, 1999; Kasada et al., 2014; Yoshida et al., 2007). In this study, we explicitly model pre‐attack and post‐attack defenses and both cost types.…”