Reintroduced grazers and prescribed fire effects on beetle assemblage structure and function in restored grasslands

Ecological restoration seeks to re-establish functioning ecosystems, but
planning and evaluation often focus on taxonomic community structure and
neglect consumers and their functional roles. The functional trait
composition of insect assemblages, which make up the majority of animal
diversity in many systems, can reveal how they are affected by restoration
management and the consequences for ecosystem function. We sampled ground
beetle (Coleoptera: Carabidae) assemblages in restored tallgrass prairies
varying in management with prescribed fire and reintroduced American bison
(Bison bison) to describe their taxonomic and functional trait structure.
We also measured seed and arthropod predation to relate management, beetle
assemblage characteristics, and function, and to test if function is
maximized by trait diversity, dominant trait values, or beetle abundance.
Beetle assemblages primarily varied with restoration age, declining over
time in richness and both taxonomic and functional diversity, but bison
presence also influenced taxonomic composition. Prescribed fire reduced
seed predation in summer and arthropod predation in fall. Although seed
predation was unrelated to beetle assemblages, arthropod predation was
greater in sites with higher abundances of carnivorous ground beetles. The
relatively weak impacts of fire and bison on functional assemblage
structure is a promising sign that these management disturbances, aimed at
supporting a diverse native plant community, are not detrimental to beetle
assemblages. The significance of reduced predator function following
prescribed fire will depend on the restoration context and whether seed or
arthropod predation relates to management goals.