Local thermal extremes shape the nature of herbivore plasticity that controls plant communities
Data files
Nov 26, 2025 version files 81.07 KB
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Baker_2022_All_Ambient_Loggers_CSV.csv
3.26 KB
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Baker_2022_Behavior_CSV.csv
5.22 KB
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Baker_2022_Behavior_Delta_CSV.csv
2.22 KB
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Baker_2022_Behavior_Loggers_CSV.csv
1.97 KB
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Baker_2022_Community_Data_CSV.csv
9.69 KB
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Baker_2022_Experimental_Warming_Loggers_CSV.csv
2.54 KB
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Baker_2022_Physiology_CSV.csv
18.23 KB
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Baker_2022_Physiology_Delta_CSV.csv
8.07 KB
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Baker_2022_PRISM_Precipitation_CSV.csv
231 B
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Baker_2022_Survival_CSV.csv
5.91 KB
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Baker_2022_Survival_Delta_CSV.csv
2.58 KB
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Baker_2024_Vegetation_Warming_CSV.csv
2.87 KB
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README.md
18.28 KB
Abstract
Prevailing views hold that species’ physiological plasticity may confer resilience to warming, but its importance varies across climatic gradients (e.g., latitude). Yet, along such gradients local species populations may experience fine-scale spatially heterogeneous variation in extreme temperatures and other ecological stressors. We show that at four Cool (mean diel maximum 29.83°C) and four Warm (mean diel maximum 31.51°C) sites, interspersed as a spatial mosaic throughout a 26,200 km2 area, local herbivore populations responded differently to stress from experimental warming (ambient, warmed) and predation (presence, absence). Cool and Warm site herbivore populations utilized different combinations of behavioral and physiological plasticity to cope with the dual stressors that were contingent on local temperature extremes. These unique plastic responses had divergent cascading effects on the plant community. Our results suggest that paying attention to local population variation can enhance the ability to predict the fate of natural communities under environmental change.
https://doi.org/10.5061/dryad.v15dv427d
Description of the data and file structure
The dataset contains 12 comma separated value files which encompass all of the data used in the statistical analyses for this manuscript. These files consist of climate data, measures of grasshopper (Melanoplus femurrubrum) plasticity, and plant community biomass. The climate data consists of in situ temperature measurements and remotely sensed precipitation data used to (1) characterize sites, (2) determine the influence of experimental warming on thermal regimes, and (3) record weather during behavioral assays. The grasshopper plasticity data measures how experimental warming altered (1) grasshopper canopy height, (2) grasshopper respiration rates, and (3) grasshopper survival. The plant community impact data consists of measures of initial conditions and end season plant biomass to quantify how grasshopper plasticity may have altered the plant surrounding community. File descriptions and column definitions are provided below.
Files and variables
File: Baker_2022_All_Ambient_Loggers_CSV.csv
Description: Includes the daily maximum temperature, daily mean temperature, daily minimum temperature, daily coefficient of variation in temperature, and daily range in temperature recorded by each temperature logger in all ambient cages at a site (MX2201, Onset Corporation, Bourne, MA, USA). We included data from temperature loggers deployed in cages for the present study and those deployed in a parallel field experiment that utilized the same 8 populations in identical cages to better resolve thermal regimes within local population sites.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Logger: Denotes each unique temperature logger used in field cages.
- Latitude: Denotes the latitude of the site.
- Longitude: Denotes the longitude of the site.
- Daily Max: The daily maximum temperature (°C) over the course of the field experiment.
- Daily Mean: The daily mean temperature (°C) over the course of the field experiment
- Daily Min: The daily minimum temperature (°C) over the course of the field experiment.
- Daily Coeff: The daily coefficient of variation in temperature over the course of the field experiment.
- Daily Range: The daily range in temperature (°C) over the course of the field experiment.
File: Baker_2022_PRISM_Precipitation_CSV.csv
Description: The mean daily precipitation at sites throughout the field experiment.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Precipitation: The mean daily precipitation (mm) at each site at an 800m2 resolution provided by PRISM Climate Group (URL: http://www.prism.oregonstate.edu)
- Elevation: The elevation of each site (m asl)
File: Baker_2022_Experimental_Warming_Loggers_CSV.csv
Description: Includes the daily maximum temperature, daily mean temperature, daily minimum temperature, daily coefficient of variation in temperature, and daily range in temperature recorded by each temperature logger during the field experiment under either ambient or experimentally warmed conditions (MX2201, Onset Corporation, Bourne, MA, USA).
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether the field cage and associated temperature logger was subjected to natural (ambient) or experimental warming (warmed) conditions.
- Logger: Denotes each unique temperature logger used in field cages.
- Daily Max: The daily maximum temperature (°C) over the course of the field experiment.
- Daily Mean: The daily mean temperature (°C) over the course of the field experiment
- Daily Min: The daily minimum temperature (°C) over the course of the field experiment.
- Daily Coeff: The daily coefficient of variation in temperature over the course of the field experiment.
- Daily Range: The daily range in temperature (°C) over the course of the field experiment.
File: Baker_2022_Behavior_Loggers_CSV.csv
Description: Includes the maximum temperature, minimum temperature, mean temperature, coefficient of variation in temperature, and range in temperature recorded by each temperature logger during behavioral assays of grasshopper populations (MX2202, Onset Corporation, Bourne, MA, USA).
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether the behavioral terrarium and associated logger was subjected to natural (ambient) or experimental warming (warmed) conditions during behavioral assays.
- Logger: Denotes each unique temperature logger used in terrarium.
- Max: The maximum temperature (°C) recorded during the behavioral assay.
- Mean: The mean temperature (°C) recorded during the behavioral assay.
- Min: The minimum temperature (°C) recorded during the behavioral assay.
- Coeff: The coefficient of variation in temperature during the behavioral assay.
- Range: The range in temperature (°C) during the behavioral assay.
File: Baker_2022_Behavior_Delta_CSV.csv
Description: Includes the percent change in canopy height induced by experimental warming relative to baseline ambient conditions.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment and during behavioral assays.
- Terrarium: Denotes the terrarium within which grasshopper behavior was assessed.
- Delta Behavior: The percent change in canopy height caused by experimental warming relative to baseline ambient conditions.
File: Baker_2022_Behavior_CSV.csv
Description: Includes the mean daily canopy height (cm) of grasshoppers reared under different experimental treatments.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether grasshoppers were reared under natural (ambient) or experimental warming (warmed) conditions throughout the experiment and during behavioral assays.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment and during behavioral assays.
- Terrarium: Denotes the terrarium within which grasshopper behavior was assessed.
- Mean Height: The mean height (cm) of all grasshoppers within a single terrarium.
File: Baker_2022_Physiology_Delta_CSV.csv
Description: Includes the percent change in mass specific respiration rate induced by an experimentally warmed rearing environment relative to baseline ambient conditions at 25°C, 30°C, and 35°C.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment.
- Temperature: Denotes the assay temperature at which grasshopper mass specific respiration rate was measured (25°C, 30°C, or 35°C).
- Cage: Denotes the field cage from which the grasshopper was collected.
- Individual: Denotes each unique grasshopper measured.
- Delta Respiration: The percent change in mass specific respiration rate induced by an experimentally warmed rearing environment relative to baseline ambient conditions.
File: Baker_2022_Physiology_CSV.csv
Description: Includes the mass specific respiration rate (µl of CO2 min-1g-1) at 25°C, 30°C, and 35°C for grasshoppers reared in the field under different experimental treatments.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether grasshoppers were reared under natural (ambient) or experimental warming (warmed) conditions throughout the experiment.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment.
- Temperature: Denotes the assay temperature at which grasshopper mass specific respiration rate was measured (25°C, 30°C, or 35°C).
- Cage: Denotes the field cage from which the grasshopper was collected.
- Individual: Denotes each unique grasshopper measured.
- Mass Specific Respiration: The mass specific respiration rate (µl of CO2 min-1g-1) of each grasshopper at a given assay temperature.
File: Baker_2022_Survival_Delta_CSV.csv
Description: Includes the percent change in grasshopper survival induced by experimental warming relative to baseline ambient conditions.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment.
- Cage: Denotes the field cage in which grasshoppers were reared.
- Delta Survival: The percent change in survival caused by experimental warming relative to baseline ambient conditions.
- Notes: In one instance, a *Pisaurina spp. *was found in a cage assigned to receive no predators. Therefore, we treated this cage as a predator cage for our analyses.
File: Baker_2022_Survival_CSV.csv
Description: Includes the grasshopper survival within each experimental cage at the end of the field season.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether grasshoppers were reared under natural (ambient) or experimental warming (warmed) conditions throughout the experiment.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment.
- Cage: Denotes the field cage in which grasshoppers were reared.
- Grasshopper Survival Count: The number of surviving grasshoppers at the end of the field experiment
- Grasshopper Survival Proportion: The proportion of grasshoppers surviving at the end of the field experiment.
- Notes: In one instance, a Pisaurina spp. was found in a cage assigned to receive no predators. Therefore, we treated this cage as a predator cage for our analyses.
File: Baker_2022_Community_Data_CSV.csv
Description: Includes initial conditions and end season plant biomass of field cages stocked with grasshoppers under experimental warming (ambient, warmed) and predation risk (absent, present) treatments.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, HF= Harvard Forest, MC= Middlebury College, SC= Smith College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether grasshoppers were reared under natural (ambient) or experimental warming (warmed) conditions throughout the experiment.
- Predation: Denotes whether grasshoppers were reared in the presence (Predator) or absence (No Predator) of Pisaurina spp. throughout the experiment.
- Cage: Denotes the field cage from which plant biomass was collected.
- Initial Solidago Cover: Initial percent cover of Solidago within a cage prior the application of experimental treatments.
- Solidago Biomass: End season Solidago biomass (g).
- log(Solidago Biomass): Log10 transformed end season Solidago biomass (g).
- Initial Grass Cover: Initial percent cover of grass (primarily Poa spp.) within a cage prior to the application of experimental treatments.
- Grass Biomass: End season grass (primarily Poa spp.) biomass (g).
- Notes: In one instance, a Pisaurina spp. was found in a cage assigned to receive no predators. Therefore, we treated this cage as a predator cage for our analyses.
File: Baker_2024_Vegetation_Warming_CSV
Description: Includes initial conditions and end season plant biomass of field cages without any grasshoppers under experimental warming (ambient, warmed) treatments.
Variables
- Site Type: Denotes whether the local population’s field site experienced high daily maximum temperatures (Warm sites) or low daily maximum temperatures (Cool sites).
- Population: Denotes the source population and rearing site of grasshoppers. Population codes are abbreviated names of each site: DC= Dartmouth College, FN= Flanders Nature Center, MC= Middlebury College, SP= Saint Paul’s School, UP = Upland Park, YM= Yale-Myers Forest.
- Warming: Denotes whether grasshoppers were reared under natural (ambient) or experimental warming (warmed) conditions throughout the experiment.
- Cage: Denotes the field cage from which plant biomass was collected.
- Initial Solidago Cover: Initial percent cover of Solidago within a cage prior the application of experimental treatments.
- Solidago Biomass: End season Solidago biomass (g).
- log(Solidago Biomass): Log10 transformed end season Solidago biomass (g).
- Initial Grass Cover: Initial percent cover of grass (primarily Poa spp.) within a cage prior to the application of experimental treatments.
- Grass Biomass: End season grass (primarily Poa spp.) biomass (g).
Access information
Precipitation data was derived from the following source:
- Precipitation data from the PRISM Climate Group, Oregon State University (2022) http://www.prism.oregonstate.edu
Field experiment design
For each grasshopper population, we factorially crossed spider predation risk (present, absent) and experimental warming (warming, ambient) using experimental mesocosm cages in the field. Each cylindrical cage (0.25 m2 × 1.0 m H) was constructed using vinyl-coated garden wire fencing; the sides and tops of each cage were covered with insect screening. We deployed 20 cages (each separated by at least 1 m) within each field over naturally growing vegetation. We selected cage locations to ensure they all contained a similar initial composition of grass and Solidago, which was verified by measuring initial percent cover of grass and Solidago.
We created experimental warming treatments by wrapping the sides of assigned cages with translucent plastic sheeting (4 mm Film-Gard, Covalence Plastics, Minneapolis, MN, USA); the bottom 10 cm of the cages was left unwrapped to permit airflow. Experimental warming does not increase temperatures consistently over 24 hours: warming occurred during the day and dissipated at night, resulting in the simultaneous change of mean diel mean temperature (+0.67 °C), mean diel maximum temperature (+2.79 °C), mean diel minimum temperature (-0.27 °C), and mean diel coefficient of variation in temperature (+15%; P < 0.05 in all cases). While wrapping could influence plant growth and development by altering wind and humidity, prior work indicates that end-of-season plant biomass was unaffected directly by such experimental warming treatments.
From late June to early July, we cleared cages of all arthropods before randomly assigning spider predators and grasshoppers to the various treatment cages. We then stocked predator treatment cages with local spiders at natural field densities (1 spider per cage). In mid-July, we stocked all cages with local third-instar grasshoppers at natural field densities (5 grasshoppers per cage). One week after stocking, we replaced any grasshoppers that experienced mortality due to handling stress. Thereafter, we allowed grasshoppers to grow and develop under their respective treatment combinations until late September to early October.
Geographic variation in climatic conditions among local populations
Populations were selected to encompass a range of the thermal regimes (mean temperature, variability, and extremes) present in New England. Remotely sensed data may not capture fine spatial-scale thermal regimes experienced by grasshoppers within a local field site, therefore we recorded temperature hourly within the vegetation canopy at 60 cm above the soil with temperature loggers placed within multiple* *experimental field cages at every site (MX2201, Onset Corporation, Bourne, MA, USA). We included data from temperature loggers deployed in cages for the present study and those deployed in a parallel field experiment that utilized the same 8 populations in identical cages to better resolve and quantify variation in thermal regimes within local population sites. We calculated mean diel mean temperature, mean diel coefficient of variation in temperature, and mean diel temperature extremes for each logger at a population’s field site. We then used GLMs to compare metrics with Site type as a fixed effect and population as a random effect nested within Site type (all conducted in R v.4.2.2 with lme4 v.1.1.31 , lmerTest v.3.1.3, DHARMa v.0.4.6, and MuMIn v.1.48.4 packages).
We tested the effect of experimental warming treatments on cage temperatures for each local population by analyzing temperature data from loggers deployed in ‘warmed’ and ‘ambient’ treatments with GLMs that compared the mean diel maximum, mean and minimum temperature, and mean diel coefficient of variation in temperature among populations and between Site types. Site type and experimental warming were considered fixed effects, and population was considered a random effect nested within Site type.
Behavioral Plasticity
During sunny days in mid-August, we assayed how grasshoppers from different populations responded behaviorally to predation risk and experimental warming by recording their habitat use within benchtop terraria in their native fields. Terraria (30 cm W × 40 cm L × 90 cm H) had a rectangular plywood base with sides and tops enclosed with fiberglass insect screening. Terraria were planted with 1-2 Solidago (60 cm H) and grasses grown in a greenhouse. We superimposed a 4 × 4 cm measurement grid on one face (84 cm × 40 cm) of each terrarium to allow measurement of the vertical position of grasshoppers in the canopy at each sampling time. We wrapped terraria assigned to experimental warming treatments with clear, thin plastic sheeting to generate warming. We recorded the temperature in a subset of the terraria every 5 minutes (MX2202 loggers from Onset Corporation, Bourne, MA, USA) at a canopy height of 60 cm.
At each field site, we transferred 2-3 grasshoppers from our previously established field experiment cages to a benchtop terrarium with the same experimental warming and predation risk treatments of sourced grasshoppers. For the predation risk treatment, we caught spiders from each respective field; however, due to a spider population crash in one of our VT populations, we sourced spiders from our second VT population. After stocking, we allowed the grasshoppers and spiders to acclimate to the terraria overnight and resume normal behaviors. Every 20 minutes between 09:00-17:40, we recorded the vertical position of each grasshopper within each terrarium. After completing habitat use measurements, grasshoppers were returned to their respective field experiment cages and spiders were confirmed to be alive and mobile in every predation risk terrarium.
During the behavioral assays in field terraria, experimental warming raised mean temperatures by 5.99 °C, maximum temperature by 7.25 °C, and minimum temperatures by 3.17 °C (P < 0.05 in all cases). Experimental warming also increased the coefficient of variation in temperature by 13%, but this trend was not significant (P = 0.0831). The influence of experimental warming on temperatures did not differ significantly among Site types (P > 0.05 in all cases). The effects of experimental warming were larger in the terraria than those in our field cages because we only assessed behavior on clear, sunny days, whereas field loggers within experimental cages integrated weather conditions over the whole season. We tested for behavioral plasticity by analyzing the percent change in mean daily vertical position within benchtop terraria from ambient baseline conditions with GLMs that considered predation risk and Site type as fixed effects with population as a random effect nested within Site type.
Physiological Plasticity
From late September to early October, we randomly selected one grasshopper from every treatment cage that had surviving grasshoppers and grouped them according to their treatment of origin (i.e., each factorial combination of experimental warming and predation risk). Grasshoppers were immediately transported to the laboratory at Yale University where their thermal performance was measured as mass specific respiration rate at 25°C, 30°C, and 35°C.
We evaluated the thermal performance of grasshoppers from different populations and rearing treatments, by measuring the mass specific CO2 respiration of grasshoppers across a 10°C gradient in temperature. We measured the respiration rates of grasshoppers at 25°C, 30°C, and 35°C as a metric of physiological stress because respiration integrates stress induced by both temperature and predation risk. After being collected in the field, grasshoppers were kept in an environmental control chamber (Percival Scientific, Inc., Perry, IA) at ~ 22°C with constant light levels and 50% relative humidity. Grasshoppers were given an ad libitum supply of water and no food for at least 24 hours after collection to put them in a post absorptive state. Just before beginning respiration rate measurements, we weighed (g) each grasshopper to allow calculation of their mass-specific respiration rate. We measured respiration as the volume of CO2 exhaled by grasshoppers with a Qubit S-151 infrared CO2 analyzer (Q-S151 model, 1 ppm resolution: Qubit Biology Inc., Kingston, Ontario, Canada) after scrubbing the air of water vapor. We used an incurrent flow rate of ~ 110mL/min. We measured respiration at 25°C and increased temperature sequentially to 30°C and then 35°C with the Qubit gas switching system in the 8 tube stop flow arrangement. In this arrangement, we used the following parameters: Stop Time = 14 minutes, Dwell Time = 2 minutes, Delay Short = 0.2 minutes, Delay Long = 1.5 minutes, Event Time = 0.5 minutes. We decided on these intervals to avoid saturating the CO2 analyzer, to produce repeatable results for an individual grasshopper, and to manage flow constraints of the system. In order to avoid saturating the system when assessing respiration, we used Airgas Ultra Zero Grade Air. Working with air of a known CO2 concentration improved the accuracy of our measurements and allowed us to extend dwell times without the risk of saturating the CO2 analyzer. We allowed grasshoppers to acclimate to each temperature for 32 minutes prior to measurement.
We tested for physiological plasticity by analyzing the percent change in the mass specific respiration rates of grasshoppers relative to baseline ambient conditions using GLMs that considered predation risk, Site type (i.e., Cool vs Warm), and assay temperature (25°C, 30°C, or 35°C) as fixed effects and population as a random effect nested within Site type. To account for repeated measures on individual grasshopper across all three temperature treatments, we also included ‘individual’ as a random effect nested within each unique combination of population, predation risk, and Site type.
Survival
At the end of the season, we tested for survival differences among grasshopper populations by analyzing the percent change in grasshopper counts from baseline ambient conditions with GLMs that considered predation risk and Site type as fixed effects and population as a random effect nested within Site type.
Geographic variation in the link between grasshopper trait plasticity and community-level impacts
At each field site, we removed all above-ground plant biomass within each experimental cage. Because grasshopper herbivory can reduce the biomass of grass and Solidago, we sorted all plant biomass from each cage by Solidago and grass. Solidago and grass samples were weighed after drying for 48 hours at 60°C. Cool sites and Warm sites did not differ with respect to initial Solidago cover, initial grass cover, or precipitation during the experiment (P>0.05 in all cases; 800 m2 resolution precipitation from the PRISM Climate Group; http://www.prism.oregonstate.edu).
We evaluated the impacts of grasshoppers on their local plant community by testing for treatment effects on end-of-season Solidago biomass and grass biomass using GLMs that considered experimental warming, predation risk, and Site type as fixed effects and population as a random effect nested within Site type. To meet the assumptions of GLMs, Solidago biomass data was log(10) transformed before analysis.