Understanding how abiotic conditions influence dispersal patterns of organisms is important for understanding the degree to which species can track and persist in the face of changing climate. The goal of this study was to understand how weather conditions (temperature, precipitation and wind patterns) influence the dispersal patterns of multiple non-migratory grasshopper species from lower elevation grassland habitats in which they ­­complete their life-cycles to higher elevations that extend beyond their range limits. The study also explored the role of weather factors (temperature and precipitation) in influencing the population sizes of species found at lower elevations. 

Field sites and grasshopper surveys

Grasshoppers were sampled from four sites along an elevational gradient within Boulder County, Colorado, USA. These sites, running along the 40th parallel, are Chautauqua Mesa (1752 m; 39.999 -105.283), A1 (2195 m; 40.015 N -105.377 W), meadow west of B1 (2591 m; 40.023 -105.430), and C1 (3048 m; 40.036 -105.547) and they reflect grassy clearings associated with the foothills, premontane, montane and sub-alpine life zones, respectively.  The grasshopper data used were collected via weekly surveys beginning in June and extending into mid-September during two time periods constituting a historic 1959-60 survey by G. Alexander, and a contemporary 2007-15 survey by C. Nufio.  Each survey consisted of systematic 1.5-person-hours of sweep-netting (divided among 1 to 3 surveyors) and 0.75 person-hours of time spent searching for adults  that may have been missed by sweep netting.  

Weather data

To explore how weather conditions influence grasshopper dispersal patterns, temperature, precipitation, and wind data from 2007-15, obtained from the National Renewable Energy Laboratory’s National Wind Technology Center’s (NWTC) M2 Tower (1855m. 39.9106 -105.2348), were correlated with the number of dispersers collected at the sites from June to mid-September. To explore the role of weather variables in influencing grasshopper populations sizes,  temperature and precipitation data from May 1 to September 7 from the United States Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) weather station data (Cooperative ID 050848; 39.9919  -105.2667), were correlated with the population sizes of resident grasshoppers at the lowest site during the 1959-60 and 2007-12 surveys.  

See manuscript for further details.