Predators drive community reorganization during experimental range shifts

Abstract

1. Increased global temperatures caused by climate change are causing species to shift their ranges and colonize new sites, creating novel assemblages that have historically not interacted. Species interactions play a central role in the response of ecosystems to climate change, but the role of trophic interactions in facilitating or preventing range expansions is largely unknown. 2. The goal of our study was to understand how predators influence the ability of range-shifting prey to successfully establish in newly available habitat following climate warming. We hypothesized that fish predation facilitates the establishment of colonizing zooplankton populations, because fish preferentially consume larger species that would otherwise competitively exclude smaller-bodied colonists. 3. We conducted a mesocosm experiment with zooplankton communities and their fish predators from lakes of the Sierra Nevada Mountains in California, USA. We tested the effect of fish predation on the establishment and persistence of a zooplankton community when introduced in the presence of higher-and lowerelevation communities at two experimental temperatures in field mesocosms. 4. We found that predators reduce the abundance of larger-bodied residents from the alpine and facilitate the establishment of new lower-elevation species. In addition, fish predation and warming independently reduced the average body size of zooplankton by up to 30%. This reduction in body size offset the direct effect of warming-induced increases in population growth rates, leading to no net change in zooplankton biomass or trophic cascade strength. 5. We found support for a shift to smaller species with climate change through two mechanisms: (a) the direct effects of warming on developmental rates and (b) sizeselective predation that altered the identity of species' that could colonize new higher elevation habitat. Our results suggest that predators can amplify the rate of range shifts by consuming larger-bodied residents and facilitating the establishment of new species. However, the effects of climate warming were dampened by reducing the average body size of community members, leading to no net change in ecosystem function, despite higher growth rates. This work suggests that trophic interactions play a role in the reorganization of regional communities under climate warming.

Patch size drives colonization by aquatic insects, with minor priority effects of a cohabitant

“…These priority effects can either positively or negatively impact species richness within a metacommunity, depending on local adaptation and generation times of early colonists, as well as dispersal rates of later colonists (Vanoverbeke et al, 2016). If early colonists acclimate quickly to local conditions or late colonists have low dispersal rates, then the early colonists will dominate the metacommunity and decrease overall diversity (Grainger & Gilbert, 2016;Jones et al, 2020;Lawler & Morin, 1993;Shurin, 2001). If the reverse is true, or if early colonists are predators that relieve competitive exclusion effects, then early colonists can cause a net increase in species diversity (Beisner, 2001;McCauley & Briand, 1979;Sarnelle, 2005).…”

Prey naiveté alters the balance of consumptive and non‐consumptive predator effects and shapes trophic cascades in freshwater plankton

“…The communities shifted to smaller body sizes with predation, resulting in reduced community biomass despite increased zooplankton abundance. Intraspecific reductions in body size and increased population sizes indicate that smaller body sizes may be adaptive for many taxa in the presence of size‐selective predators (Brooks and Dodson 1965, Fisk et al 2007, Jones et al 2020). The intraspecific shifts that we observed may have driven by adaptive reductions in adult body size or by demographic shifts toward juvenile life stages.…”

“…Convict Lake, the source of our experienced zooplankton community, is larger, deeper and lower elevation than Eastern Brook, our fishless lake. A considerable body of work shows that the presence/absence of fish is a significant selective pressure on zooplankton communities in lakes of the Sierra Nevada (Knapp 1996, Knapp et al 2001, Sarnelle and Knapp 2005, Symons and Shurin 2016, Jones et al 2020). Prior experiments from the region demonstrated intraspecific differences in adaptive constitutive and plastic anti‐predator traits in zooplankton from several lakes with fish, relative to trout‐naive zooplankton (Fisk et al 2007, Latta et al 2007).…”

“…Convict Lake, the source of our experienced zooplankton community, is larger, deeper and lower elevation than Eastern Brook, our fishless lake. A considerable body of work shows that the presence/absence of fish is a significant selective pressure on zooplankton communities in lakes of the Sierra Nevada (Knapp 1996, Knapp et al 2001, Sarnelle and Knapp 2005, Symons and Shurin 2016, Jones et al 2020.…”

Predators balance consequences of climate‐change‐induced habitat shifts for range‐shifting and resident species

“…The outcome of any such shift will depend on the balance of these interactions (Lurgi et al, 2012). For example, resident predators may play important roles in altering competitive or other intraguild interactions between resident and shifting species of lower trophic levels (Chase et al, 2002;Chesson & Kuang, 2008;Jones et al, 2020). Disentangling the roles that these various, simultaneous, interactions play in the outcomes of shifts in habitat use should be one of the primary objectives of studies seeking to understand the outcomes of species responses to climate change.…”