Combining functional and taxonomic approaches allows a deeper understanding of community assembly processes following disturbance. We examined how insect community composition shifted and then recovered in small Colorado streams in response to catastrophic flooding in 2013 using samples collected in 2011, 2014 and 2015. We sampled 14 streams along a gradient of flood intensity and collected community composition samples from different habitat types. Flood intensity was determined using a disturbance metric we developed that incorporates hydraulic stress during peak runoff and channel disturbance. We calculated taxonomic diversity indices, including species richness and temporal beta diversity, and functional diversity metrics, including functional richness, functional dispersion, and functional distance. Our goal was to examine the effect of flood disturbance on 10 response traits related to life history and movement ability and on trophic traits, using previously published trait matrices of stream insects and expert information about the presence of a terrestrial adult life stage during the flood. In addition to measuring community response in the year immediately following the flood event, we also collected an additional year of data to determine whether stream insect communities would recover within two years following severe flood disturbance.
Results/Conclusions
Taxonomic richness declined with increasing disturbance intensity one year after the floods, but showed no significant relationship with disturbance intensity two years following the floods. The change in functional richness one and two years post-flood was not significantly predicted by disturbance intensity. Functional distance between years at the same site was positively predicted by the intensity of flood disturbance experienced both one and two years post-flood. The positive relationship between disturbance intensity and functional distance between pre- and post-flood communities suggests that the disturbance resulted in functional turnover of response traits. Temporal beta diversity at sites was also positively related to disturbance intensity one and two years post-flood. The percent change in predator abundance was negatively related to disturbance intensity one year post-flood compared to pre-flood, but was not related to disturbance intensity two years post-flood. No other trophic guilds’ change in abundance had a relationship with disturbance intensity one or two years post-flood. Overall, our functional analysis suggests that the flood event acted as an acute, but strong filter on trophic, mobility, and life history traits and resulted in both taxonomic and functional turnover in stream insect communities.