Timing is everything: priority effects alter community invasibility after disturbance

Theory suggests that communities should be more open to the establishment of regional species following disturbance because disturbance may make more resources available to dispersers. However, after an initial period of high invasibility, growth of the resident community may lead to the monopolization of local resources and decreased probability of successful colonist establishment. During press disturbances (i.e., directional environmental change), it remains unclear what effect regional dispersal will have on local community structure if the establishment of later arriving species is affected by early arriving species (i.e., if priority effects are important). To determine the relationship between time‐since‐disturbance and invasibility, we conducted a fully factorial field mesocosm experiment that exposed tundra zooplankton communities to two emerging stressors – nutrient and salt addition, and manipulated the arrival timing of regional dispersers. Our results demonstrate that invasibility decreases with increasing time‐since‐disturbance as abundance (nutrient treatments) or species richness (salt treatments) increases in the resident community. Results suggest that the relative timing of dispersal and environmental change will modify the importance of priority effects in determining species composition after a press disturbance. Dispersing species often have increased establishment success after environmental change; however, after an initial period of high invasibility, the resident community may exert priority effects over the dispersing species, reducing invasibility through time. Using an aquatic mesocosm experiment, we found that disturbed communities were more invasible when dispersers were added shortly after disturbance, but invasibility quickly declined through time as the resident community increased in abundance and richness. Additionally, invasibility decreased faster in the stressor that increased resource availability (i.e., nutrients) than the lethal stressor (i.e., salt). Our results suggest that the type and the relative timing of disturbance and dispersal will affect the establishment of new species into communities.