Interactions among body size, trophic level, and dispersal traits predict beetle detectability and occurrence responses to fire

© 2019 The Royal Entomological Society 1. Testing the extent to which traits act alone or in combination with other traits to influence responses to fire informs the trade-off between increased generalisation using single traits and increased predictive power using interactions. This study investigated the following question: do four traits (body size, trophic group, dispersal ability, and stratum of the ecosystem), alone or in combination, best explain changes in beetle occurrence with time since fire?. 2. The data from 4 years and 15 independent fires in southern Australia were analysed using generalised linear mixed models. The study also assessed whether detectability depends on time since fire using multi-year detection models, because detectability has the potential to confound occurrence patterns. 3. The best model included the three-way combination of size, flight, and trophic level interacting with time since fire and with year. The relationship between detectability and time since fire was similar to the occurrence relationship in six of the 10 trait–combination groups, with flightless species generally showing reduced detection probability as time since fire increased. Detectability did not confound occurrence responses for four trait groups, with three increasing with time since fire and one decreasing. 4. Generalisation using main effects of traits risks oversimplifying animal responses to fire, because combinations of traits influence the direction and magnitude of the response. Also, taking detectability into account is critical to correctly interpretating occupancy data. Three-way trait combinations that differ by just one trait, particularly dispersal ability, can result in either negligible effects of disturbance on detectability or strong effects that influence observed occurrence.