Blowing in the wind:: a field test of overland dispersal and colonization by aquatic invertebrates

Despite the importance of dispersal to ecology, accurate estimates of dispersal rates are often difficult to obtain, especially for organisms that rely on passive dispersal of propagules to colonize new sites. To investigate potential dispersal vectors and relative colonization rates of zooplankton, we conducted a field experiment in which we restricted potential dispersal vectors (insects, birds, amphibians) from transporting zooplankton to mesocosms. Twenty-six non-insect invertebrate taxa invaded our array during 2 years. Colonization rates of organisms varied considerably, with some species appearing several weeks after the experiment began and others appearing after a year. We observed no difference in colonization rates among treatments, suggesting that species were transported to our experiment primarily by wind or rain, rather than by animal vectors. The absence of an additional 13 zooplankton species common in ponds immediately adjacent to the array either occurred because of dispersal limitation or an inability to invade the existing communities. Ecologists generally assume that all zooplankton are rapidly dispersed hence the potential for dispersal limitation is generally ignored. Our results suggest that zooplankton vary in Their dispersal and colonization ability. Hence, increased attention should be focused on the potential role of dispersal limitation and its importance for understanding the structure and function of aquatic communities.