Ground beetle response to forest disturbance: A test of the competition-colonization trade-off model

Understanding the role of natural and anthropogenic disturbances in the maintenance of species diversity and community dynamics remains a focal area of research as humans continue to threaten natural habitat and biodiversity.  Ecological theory predicts species diversity is maximized at intermediate levels of disturbance, resulting in a peaked diversity-disturbance relationship.  One mechanism that could produce this pattern is the competition-colonization trade-off model, which states intermediate levels of disturbance result in high species diversity due to a trade-off in traits for competition and colonization ability.  The objective was to test the competition-colonization trade-off model by assessing the response of ground beetle assemblages before and after forest disturbance at Powdermill Nature Reserve in Pennsylvania.  Carabidae are considered indicators of environmental and successional change, and their dispersal strategies can be categorized based on wing development.  Baseline pre-disturbance assemblage data were collected in 2013, and then a randomized factorial experiment with two disturbance treatments, forest canopy and understory vegetation, was initiated in June 2014 creating a disturbance intensity gradient.  Two blowdowns created by a tornado in June 2012 were used as an additional high intensity disturbance treatment.  Preliminary results of carabid assemblages from pre-disturbance and tornado blowdown sites sampled in 2013 support the competition-colonization trade-off model.  Carabid species diversity was similar in control (low disturbance) and tornado blowdown (high disturbance) sites, but carabid species composition differed between the two disturbance treatments.  The proportion of carabids capable of flight was higher in the blowdowns.