Biotic interactions could control colonization success during stream restoration

Biotic interactions involved in colonization are likely important if tolerant aquatic taxa, which have settled first, prevent desired taxa from colonizing when conditions improve. These interactions could be particularly influential during restoration but are poorly understood in streams. We investigated the interactions between 3 stream macroinvertebrate taxa, the snail Potamopyrgus antipodarum (Gray, 1843), mayfly nymphs in the genus Deleatidium, and caddisfly larvae in the family Conoesucidae, to assess whether order of arrival and competitor identity influence colonization success. In a replicated (n = 5) mesocosm experiment, we added an early colonist—either snails, mayflies, or caddisflies—then added 1 of the other 2 invertebrates and measured colonization success. Snails were competitively dominant over mayflies, reducing their colonization regardless of arrival order. Caddisflies, in comparison, had an inhibitory priority effect on both mayflies and snails, whereas mayflies had an inhibitory priority effect on caddisfly colonization. Last, snails had a facilitative priority effect on caddisfly colonization. These results indicate that competitive dominance and multiple types of priority effects could shape freshwater macroinvertebrate assemblages and, therefore, could inhibit desired taxa from colonizing during restoration efforts. Thus, stream restoration strategies should consider the effects of biotic interactions, including priority effects, on restoration outcomes.