Priority effects in the assembly of macroinvertebrate communities after disturbance

Community assembly—or reassembly—occurs frequently in stream systems following both natural and anthropogenic disturbance events. Stream communities must reassemble following flooding, drought, and even restoration projects. Priority effects during community assembly occur when early colonists change the process of assembly through direct or indirect effects, or through modification of the abiotic environment.  Using a 2x4 full-factorial experiment in 16 artificial stream channels, we tested whether early colonization of target macroinvertebrate functional groups would alter the structure of a developing macroinvertebrate community, and whether simulated drought conditions would change the influence of such priority effects. Initial colonists of channels were either filter-feeders (C. fluminea), grazers (Physa sp.), a combination of the two, or no early colonists, followed by subsequent colonization by an all natural assemblage as was found in an adjacent stream. Samples were collected over a trajectory of 11 weeks in the fall of 2008 in the Clemson University Experimental Forest. Here we discuss the differences in community structure and stability produced by priority effects, as well as how early colonization interacted with drought to alter the effect of early colonists.