Thermal controls of insect emergence in some high arctic ponds
Climate change is disproportionately warming the Arctic, with potentially important ecological consequences. Insects emerging from the myriad tundra ponds on Alaska’s Arctic Coastal Plain are a primary prey resource for many tundra-nesting birds. Synchronization of this pulse of emerging prey biomass with avian nesting activity is crucial for breeding success. Arctic warming may stimulate invertebrate development and result in earlier adult emergence. A dozen chironomid species comprised over 95% of insect emergence from ponds near Barrow, Alaska both in 1975-77 and in 2009-12. These midge populations show highly synchronous emergence, with most individuals of a species emerging from a given pond within a 3-5 day span. A succession of synchronously-emerging individual species produces a 3-4 week long pulse of adult insect biomass, an ephemeral but highly-available food resource for recently hatched waterbirds. A shift in this window of adult insect availability may disrupt the synchronization of this predator/prey interaction and result in lowered waterbird fitness.
The phenological sequence of emerging chironomids in 2009-12 closely resembled that observed in the 1970s. Tundra ponds at Barrow, AK have thawed earlier and experienced warmer water temperatures in recent years, relative to the 1970s. The median date of chironomid emergence was earlier by more than 4 days in the recent decade, and 14 of 15 dominant midge species exhibited significantly earlier emergence timing. Date of thaw is a good predictor of the onset of midge community emergence, but emergence duration in a given pond depends on species composition each year. Pupal development in the common species Trichotanypus alaskensis conforms well to a thermal-time model, and cumulative degree-hours post thaw is a good predictor of peak emergence for many, but not all, midge species. A range of life-history strategies among different species contributes to variation in the onset and duration of midge community emergence and species may differ in their response to a warming climate.