Legacy effects of fish but not elevation influence lake ecosystem response to environmental change

Abstract

How communities reorganize during climate change depends on the distribution of diversity within ecosystems and across landscapes. Understanding how environmental and evolutionary history constrain community resilience is critical to predicting shifts in future ecosystem function. The goal of our study was to understand how communities with different histories respond to environmental change with regard to shifts in elevation (temperature, nutrients) and introduced predators. We hypothesized that community responses to the environment would differ in ways consistent with local adaptation and initial trait structure. We transplanted plankton communities from lakes at different elevations with and without fish in the Sierra Nevada Mountains in California to mesocosms at different elevations with and without fish. We examined the relative importance of the historical and experimental environment on functional (size structure, effects on lower trophic levels), community (zooplankton composition, abundance and biomass) and population (individual species abundance and biomass) responses. Communities originating from different elevations produced similar biomass at each elevation despite differences in species composition; that is, the experimental elevation, but not the elevation of origin, had a strong effect on biomass. Conversely, we detected a legacy effect of predators on plankton in the fishless environment. Daphnia pulicaria that historically coexisted with fish reached greater biomass under fishless conditions than those from fishless lakes, resulting in greater zooplankton community biomass and larger average size. Therefore, trait variation among lake populations determined the top‐down effects of fish predators. In contrast, phenotypic plasticity and local diversity were sufficient to maintain food web structure in response to changing environmental conditions associated with elevation.

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

“…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). Another recent mesocosm experiment from our study region tested the response of trout‐experienced versus trout‐naive zooplankton to fish predation and shifts in elevation (Symons et al 2020). In contrast to our design, Symons et al (2020) used a combined inoculum of zooplankton from three lakes for each treatment condition and found that the effects of prior exposure to trout far exceeded those of elevation of origin on zooplankton community biomass.…”

“…Another recent mesocosm experiment from our study region tested the response of trout‐experienced versus trout‐naive zooplankton to fish predation and shifts in elevation (Symons et al 2020). In contrast to our design, Symons et al (2020) used a combined inoculum of zooplankton from three lakes for each treatment condition and found that the effects of prior exposure to trout far exceeded those of elevation of origin on zooplankton community biomass. Together these results support our contention that thousands of generations of zooplankton exposure to trout predators is a significant source of variation between our two zooplankton communities.…”