Grasshopper community responses to bison grazing and fire frequency

The primary evolutionary and ecological drivers of grassland ecosystems are climate, fire, and grazing.  These factors interact in complex ways to affect structure and function of grassland ecosystems.  At Konza Prairie Biological Station (KS, USA), bison act as a keystone species increasing habitat heterogeneity and diversity of many taxonomic groups such as plants, small mammals, and invertebrates, including grasshoppers. Here we report on an ongoing field experiment examining how fire and food quality influence bison foraging and how this in turn mediates grasshopper community composition and density.  

The Konza Prairie is divided into watersheds with treatments that manipulate fire frequency and grazing.  Our experiment was run in two watersheds (N2A and N2B) that are open to bison grazing.  N2A was burned in spring 2012 and 2014, while N2B was burned in spring 2011 and 2013.  In each watershed, we set up sixteen 15m x 15m plots in which we varied forage quality (fertilized, unfertilized) and bison grazing (bison exclosures, control plots).  We measured bison use of the plots, plant height, plant foliar quality, percent cover, and grasshopper density and community composition in each plot from 2011 - 2014.

While grasshoppers have been found to be more abundant in grazed vs. ungrazed watersheds, we find that within grazed watersheds, grasshoppers are more abundant in ungrazed patches compared to grazed patches.  We also find that grasshopper abundance was higher overall in the watershed that had been burned that year compared the watershed that had been burned the year before, indicating that grasshoppers, like bison, are responding to burn history.