Does history matter? : An experimental assessment of whether dragonfly colonization history affects insect biodiversity within ephemeral ponds

Current interactions among species could have an important role in controlling biodiversity. Some studies however have shown that the particular time a species arrives at a site during the process of community assembly could alter the strength of species interactions within ecological communities. Such priority effects should be important in frequently disrupted environments such as temporary ponds which provide opportunities for new collections of species to colonize the refilled pond. In temporary ponds the top predators are often dragonfly naiads. The particular time that dragonflies arrive at a pond is dependent in part on dragonfly breeding phenology and pond isolation. I tested the hypothesis that the arrival time of dragonfly naiads to ephemeral ponds influences the biodiversity of aquatic insects present in the pond. To test this hypothesis I experimentally altered the time dragonflies could oviposit eggs into artificial ponds (modified stock tanks) and quantified insect biodiversity within each pond after four months of community assembly. I found that early-arriving dragonflies inhibited the successful recruitment of late-arriving dragonflies. The dragonfly colonization history of a pond affected the total number of insect species in a pond by altering the number of coleopteran and heteropteran species present. Coleopterans were less diverse in ponds where dragonflies colonized at any point in time during the process of community assembly. However heteropterans were more diverse in ponds that had only early-arriving dragonflies compared to ponds with continuous dragonfly colonization. The presence of dragonflies during any time of colonization decreased the abundance of adult insects. Alternatively dragonfly arrival time did not influence the species richness abundance or species evenness of juvenile insects. The results indicate the timing at which key species arrive to a community can substantially alter the biodiversity of an ephemeral pond. Dragonfly colonization history most impacted aquatic obligates such as coleopterans and heteropterans. Changes in adult species richness and abundance of aquatic insects were likely because of a combination of two factors: (i) coleopterans and heteropterans preferentially selecting ponds with low abundances of dragonfly naiads for increased success of offspring; (ii) dragonfly predation on juvenile insects which reduced the abundance of individuals able to complete metamorphosis.