Friday, August 7, 2009

PS 78-28: Effects of dragonfly colonization history on the biodiversity of aquatic communities

Natalie A. Amoroso and David R. Chalcraft. East Carolina University


It is clear that current interactions among species in a system can have an important role in controlling the biodiversity of that system.  Some studies, however, have shown that the timing of species arrival to a community could influence 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 larval dragonflies but their presence is dependent, in part, on the timing in which adult dragonflies find and oviposit in the pond.  We tested the hypothesis that the biodiversity of aquatic invertebrates present in temporary ponds is influenced by the arrival time of larval dragonflies.  Specifically, we hypothesize that ponds with early-arriving dragonflies will have a lower biodiversity of aquatic insects compared to ponds where dragonfly colonization is continuously inhibited or where dragonflies arrive late in the summer.  To test this hypothesis, we experimentally altered the timing in which dragonflies could oviposit eggs into artificial ponds (modified stock tanks).  After a four month period, the insect biodiversity of each pond was sub-sampled and quantified.


We found that ponds allowing early dragonfly colonization produced more metamorphosed dragonflies than ponds preventing early dragonfly colonization.  Preliminary results suggest that ponds with only late-arriving dragonflies had more late-instar dragonflies than ponds always allowing dragonfly colonization.  The fewest late-instar dragonflies were found in ponds with only early-arriving dragonflies.  Hence, early-arriving dragonflies appear to inhibit late-arriving individuals.  In addition, dragonfly oviposition caused differences in insect communities among ponds, yet dragonfly arrival time does not influence total insect species richness in ponds.  We found that ponds which prevented dragonfly colonization had greater beetle species richness than ponds allowing dragonfly colonization but dragonfly arrival time did not influence beetle richness.  Total abundance of beetles did not vary among treatments.  Trends indicate that chironomid abundance is greatest in ponds with only late-arriving dragonflies and least in ponds where dragonflies can continuously oviposit.  These results suggest predatory dragonflies have important effects on insect assemblages in ponds.  The timing of dragonfly arrival, however, seems to play an important role in influencing the abundance of some taxa (e.g., dragonflies or flies) but did not affect the abundance or biodiversity within other taxa (e.g., beetles) or in the number of insect species found.