DOI: 10.5061/dryad.prr4xgxgz
title: Data from: Migrating bison engineer the green wave

description: Newly emerging plants provide the best forage for herbivores. To exploit
 this fleeting resource, migrating herbivores align
 their movements to surf the wave of spring green-up. With new
 technology to track migrating animals, the Green Wave Hypothesis has
 steadily gained empirical support across a diversity of migratory taxa.
 This hypothesis assumes the green wave is controlled by variation in
 climate, weather, and topography, and its progression dictates the timing,
 pace, and extent of migrations. However, aggregate grazers that are also
 capable of engineering grassland ecosystems make some of the
 world’s most impressive migrations, and it is unclear how the green wave
 determines their movements. Here we show that Yellowstone’s bison
 (Bison bison) do not choreograph their migratory movements to the wave of
 spring green-up. Instead, bison modify the green wave as
 they migrate and graze. While most bison surfed during early
 spring, they eventually slowed and let the green wave pass them
 by. However, small-scale experiments indicated that feedback from
 grazing sustained forage quality. Most importantly, a 6-fold decadal shift
 in bison density revealed that intense grazing caused grasslands to green
 up faster, more intensely, and for a longer duration. Our finding broadens
 our understanding of the ways in which animal movements underpin the
 foraging benefit of migration. The widely accepted Green Wave Hypothesis
 needs to be revised to include large aggregate grazers that not only move
 to find forage, but also engineer plant phenology through grazing, thereby
 shaping their own migratory movements.
description: Details of how these data were collected can be found in the
 Methods and Supplementary Materials of Geremia et al. 2019, Migrating
 bison engineer the green wave (Proceedings of the National Academy of
 Science). A brief summary of each dataset follows:
 bisonsurfdata.csv - Data to replicate analysis of green-wave
 surfing in bison. See Methods and Text S1 in Supplementary text for
 details. Columns: id = animal id; year = year of day of animal location;
 jul = julian date of animal location; maxIRGdate = julian date of max IRG
 for the location.  fecaldata.csv - Data to replicate
 analysis of bison diet quality over time. See Methods for details.
 Columns: year = year fecal sample was collected; julianday = julian day
 fecal sample was collected; CP = crude protien of sample; DOM = digestible
 organic matter of sample. leafdata.csv - Data to
 replicate anlaysis of plant-forage quality as it relates to days from peak
 IRG. See Methods and Text S1 for details. Columns: year = year plant
 tissue sample was collected; julianday = julian day plant tissue sample
 was collected; leafN = N of sample; leafC = C of sample; NETDFPIRG =
 absolute value of the number of days between the julian date the sample
 was collected and the julian day of peak IRG for the pixel where the
 sample was collected. functionalNDVIdata.csv - Data to
 replicate functional NDVI analysis. See Methods and Text S3, S4, S5, and
 S6 for details. Columns: site = name of grazing experiment site; year =
 year of NDVI data; bisonuseindex = grazing intensity index; swe = Snow
 Water Equivelant value; precip = precipitation value; temp = temperature
 value; slope = slope of site in degrees; aspect = aspect of site in
 degrees; elev = elevation of site; columns 10 through 42 = NDVI values for
 julian dates 57 through 313 at 8 day intervals.
 grazingexperimentdata.csv - Data to replicate grazing experiment
 analysis. See Methods and Text S3 and S5 for details. Columns: siteyrid =
 site and year combined; site = name of grazing experiment site; year =
 year of data collection; julianday = julian day of data collection;
 plottype = type of plot, control (for plots within fenced exclosure) or
 experimental (plots outside in grazed areas); plotnumber = both control
 and experimental plots were replicated with up to 6 replicates each;
 shootbiomass = shoot biomass of sample; leafN = N of sample; leafC = C of
 sample; SiteAnnualgrazingintensity = grazing intensity index for the year.
 Note that site grazing intensity can be slightly less than 0 due to
 sampling variation. See Text S3 in regards to "adding positive and
 negative increments." grazingintensitydata.csv -
 Data to to build the linear relationship between field measured grazing
 intensity and landscape modeled grazing intensity. See Text S3 and S5 for
 details. Columns: siteyrid = site and year combined; site = name of
 grazing experiment site; year = year; grazingintensity = is field measured
 grazing intensity using the plot data; bisonuseindex = the averaged value
 for bison use from scaled Brownian Bridge Movement Models for the larger
 areas around each grazing experiment site.  fullspringbisonsurfdata.csv –
 Additional data to replicate analysis of green-wave surfing in bison
 described in Geremia et al. 2020 Response to Craine: Bison redefine what
 it means to move to find food. Columns are the same as described in
 bisonsurfdata.csv. Data file includes locations as described in the
 response letter. Run analyses.R – Native R code to
 replicate analyses in Geremia et al. 2019 and Geremia et al. 2020. Run by
 downloading and unzipping files to a user defined working directory and
 specifying the working directory in the code header.
  
description: Details of how these data were collected can be found in the
 Methods and Supplementary Materials of Geremia et al. 2019, Migrating
 bison engineer the green wave (Proceedings of the National Academy of
 Science). Please contact the bison project at Yellowstone National Park if
 you plan to use these data for any purpose. Thank you.