Differential responses to warming and increased precipitation among three contrasting grasshopper species

We conducted a field manipulation experiment to investigate developmental and demographic responses to warming and increased precipitation in three Inner Mongolian grasshopper species that differ in phenology (an early-season species Dasyhippus barbipes, a mid-season species Oedaleus asiaticus, and a late-season species Chorthippus fallax). Infrared heaters were used for warming the ground surface by 1-2 degrees C above the ambient condition and periodic irrigations were applied to simulate a 50% increase in annual precipitation. We found that warming advanced the timing for egg hatching and grasshopper eclosion in each of the three species. However, grasshopper diapause and increased precipitation appeared to offset the effect of warming on egg development. Hatching and development were more strongly affected by warming in the mid-season O. asiaticus and the late-season C. fallax relative to the early-season D. barbipes. Warming by similar to 1.5 degrees C advanced the occurrence of the mid-season O. asiaticus by an average of 4.96 days; while warming and increased precipitation interactively affected the occurrence of the late-season C. fallax, which advanced by 5.53 days. Our data and those of others suggest that most grasshopper species in the Inner Mongolian grassland are likely to extend their distribution northward with climate change. However, because of the differential response to warming we demonstrate for these species, the different grasshopper species are predicted to aggregate toward the middle period of the growing season, potentially increasing interspecific competition and grazing pressure on grasslands.