DOI: 10.5061/dryad.4b8gthtbd
title: Legacy effects of fish but not elevation influence lake ecosystem response to environmental change

description: 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. 
description: <strong>Experiment overview</strong>
 We collected communities of plankton and micro-organisms from
 lakes that varied in their environment due to elevation, and history of
 fish stocking. We transplanted them to different elevations with and
 without fish (Figure 1). Thus, the treatments were: (1) History of
 elevation (HElev): source community elevation (2 levels, sub-alpine
 [average of 2591m] and alpine [average of 3252m]) (2) History of fish
 (HFish): source community fish presence (2 levels, +/-) (3) Experimental
 elevation treatment (EElev): transplant elevation (3 levels, montane
 [1200m], sub-alpine [2149m] and alpine [3093m]) and (4) Experimental fish
 treatment (EFish): fish presence in the transplant environment (2 levels,
 +/-). We used three transplant elevations (EElev) so that communities from
 each elevation were exposed to a lower elevation to simulate the
 directional environmental change these communities are predicted to
 experience. This results in a total of 24 treatments, each replicated five
 times for a total of 120 mesocosms, 40 at each experimental
 elevation. <strong>Mesocosm
 Sampling</strong> We sampled the mesocosms
 monthly for four months following the introduction of fish to quantify
 water chemistry, zooplankton community composition and abundance, and
 chlorophyll-a (a proxy for phytoplankton biomass). We sampled the
 zooplankton community using an integrated tube sampler. We collected 20L
 from haphazardly chosen locations from each mesocosm, condensed the sample
 on a 63μm mesh filter, and preserved it with 70% ethanol. We counted
 zooplankton samples using a protocol designed to estimate the abundance of
 common species and detect rare species: we identified two hundred
 individuals to the lowest taxonomic resolution possible (generally to
 species for crustaceans and genus for rotifers) without counting more than
 50 individuals of each species toward the total. We scanned the remainder
 of the sample to detect rare species. While Miner et al. (B. E. Miner,
 Knapp, Colbourne, & Pfrender, 2013) showed that large-bodied
 unmelanized Daphnia “pulex-type” species is Daphnia melanica using mtDNA
 sequencing, we classified unmelanized “pulex-types” as D. pulicaria
 following (Fisk et al., 2007; Knapp & Sarnelle, 2008; Latta et
 al., 2007).  To calculate zooplankton community
 biomass, we measured the body length of 15 individuals of the three most
 common species in each sample. For rare species, we used the average body
 length of all measured individuals of that species. Body size measurements
 were done only on the final set of samples (September); for these samples,
 we used the mesocosm-specific measurements to calculate biomass and mean
 body length, but for all other sample dates, we used the average length of
 each species across all treatments. We then used published length-weight
 regressions to estimate zooplankton biomass (Dumont, Van de Velda,
 & Dumont, 1975; McCauley, 1984). To calculate the average body
 size, we used an abundance-weighted mean length. Community biomass was
 determined by summing the population biomasses of each species.
 To characterize the environment in our mesocosms, we measured a
 series of water chemistry variables. First, total nitrogen (TN) and total
 phosphorus (TP) were measured by filtering water through 63μm-mesh,
 collecting it in triple-rinsed 20mL high-density polyethylene (HDPE)
 bottles, then preserving it with H2SO4 to a pH&lt;2 and storing it at
 ~4°C until later analysis. TN and TP (mg L-1) were measured using an
 auto-analyzer (LaChat QuikChem 8500, persulfate digestions, LaChat,
 Colorado, USA). We collected DOC samples by filtering water through
 precombusted glass fiber filters (Whatman GF/F, pore size 0.45um, Whatman,
 Maidstone, UK) into triple-rinsed 20mL glass vials and preserved with HCl
 to a pH&lt;2. DOC (mg L-1) was measured using a total organic carbon
 analyzer (TOC-V CSN, Shimadzu Scientific Instruments, Kyoto, Japan).
 Chlorophyll-a concentration (chl-a, μg L-1), a proxy for phytoplankton
 biomass, was measured in a known volume of water filtered through a GF/F
 that we froze before processing. Chl-a concentration was measured using a
 Turner Trilogy fluorometer (Turner, San Jose, USA) following a 24 hour
 ~4°C methanol extraction. We added water (~200 L) to each mesocosm after
 sampling to replenish evaporated water. The evaporation rate was similar
 between the three locations.  
description: Please see the ReadMe file for units.