Ground dwelling invertebrate community responses to bison and prescribed fire management in tallgrass prairies

Background/Question/Methods

Disturbance events are important drivers of ecosystem function and can play consequential roles in shaping ecological communities. In the central U.S., fire and grazing by bison are disturbance events which historically shaped tallgrass prairies. These disturbances have been greatly disrupted but remain important management tools in restored prairie and the little remnant prairie habitat that remains. Fire and grazing effects on plant communities are well studied, but less is known about their effects on invertebrates. The little research that exists has focused on invertebrates inhabiting vegetation. We sought to understand how bison grazing and prescribed fire affect abundance, diversity, and community composition of ground-dwelling invertebrate groups. Our study was conducted in Illinois at the Nachusa Grasslands, which is composed of restored and remnant prairies differing in the presence and absence of bison and prescribed fire schedule. We collected ground-dwelling invertebrates using pitfall traps in May and June of 2017 and 2018 and identified them to order or family. We analyzed Shannon diversity and density of invertebrate groups using linear mixed models and assessed community composition using principal coordinates analysis.

Results/Conclusions

Surprisingly, invertebrate diversity was decreased when bison were present and was unaffected by fire or the fire–bison interaction. Bison, and to a lesser extent fire, caused differences in community composition. Individual invertebrate groups differed in their responses to both disturbances. Prescribed fire generally increased beetles but caused declines in several ecologically diverse groups, including lepidopterans, snails and slugs, arachnids, and true bugs. Bison presence may amplify the abundances of predominant groups, such as common beetles and orthopteran species, that outcompete other invertebrates leading to lower diversity. These invertebrates may have responded positively to increased dung, new habitat created by wallowing, and changes in plant species composition. Understanding these effects may help land managers choose management strategies that promote desirable invertebrate-driven ecosystem processes.