PS 44-143
Variable effects of spiders on trophic cascades in a northern mixed grass prairie
Trophic cascades have been documented in a numerous systems where predators reduce herbivore numbers or feeding behavior, and indirectly affect plant biomass or composition. Grasshoppers are typically the dominant insect herbivore in North American grasslands and spider-grasshopper trophic cascades have been documented in some North American grasslands. However, the strength of these spider-grasshopper trophic cascades appears to vary between grassland ecosystems. In addition, trophic cascades have not been examined in northern mixed prairie. Experiments were conducted in 2012 and 2013 in a northern mixed prairie in eastern Montana to examine 1) if trophic cascades are evident in a grass dominated lower productivity system, and 2) if grasshopper density modifies trophic cascades.
Results/Conclusions
In 2012, no trophic cascade was evident in high or low grasshopper treatments using the mixed grass and forb feeding grasshopper Melanoplus sanguinipes. However, a trophic cascade was evident at the higher grasshopper density in 2013 with the smaller bodied grass feeding species Ageneotettix deorum. The trophic cascade was observed even though biomass production was much higher than in 2012. The results indicate that grasshopper functional composition may influence whether trophic cascades are observed in low productivity grass dominated prairie.