Community Dynamics of Prairie Grasshoppers Subjected to Periodic Fire: Predictable Trajectories or Random Walks in Time?

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Abstract
Grasshopper communities were sampled by sweep net at 6 sites in native tallgrass prairie at Konza Prairie, Kansas, USA, in 1982-86 to assess community change from year to year in prairie burned once every 4 years. Species richness, diversity, and composition of grasshoppers did not vary in regular fashion with the 4 year fire cycle. Furthermore, the ratio of grass- to forb-feeding grasshoppers generally did not change consistently during the fire cycle at individual sites, although for all sites combined, the relative abundance of grass feeders initially increased after a fire and subsequently declined in succeeding years without fire. Observed year to year changes in grasshopper communities were tested against those predicted by a random walk model of community change using ordination (DCA) results for species composition at individual sites in individual years. This analysis revealed that local communities varied in restricted, compensatory fashion such that they tended to return towards some central or characteristic species composition when displaced. Thus while fire itself imparts relatively little predictability to grasshopper community dynamics in periodically burned prairie, such dynamics are nevertheless to a limited degree predictable.