How stable are communities in the context of a rapidly changing environment? Assessing the stability of ecological communities requires long-term data on community composition, data which are often lacking. To address this question we conducted larval dragonfly sampling in 2017-2019, repeating an original survey conducted in 2000-2002. In both time periods we sampled dragonfly larvae from lakes and ponds in southeast Michigan which span a range of hydroperiods and top predator communities. We used the original survey methods in both time periods to collect larval dragonflies in 18 of the originally surveyed 22 lakes and ponds. Sampling occurred in May and August for 2.5 years in both surveys, with three May sampling periods and two August sampling periods for both time periods. We assessed the extent of change observed in abundance, richness, and composition in these communities across the 15+ year time gap.
Results/Conclusions
We collected over 6400 dragonfly larvae representing a total of 37 species. Community composition was largely stable across the two time periods. While rare species were not recorded in each survey, there was no clear pattern of loss or gain in species and common species in 2000-2002 were also common species in 2017-2019. Richness also remained relatively stable with a trend towards lower richness in August in the 2017-2019 surveys compared with the earlier survey. Larval abundance was lower in 2017-2019 than in the earlier survey with most of this decline being detected in the August samples, possibly explaining the observed decline in richness in this time period as well. Given the relatively stability of abundance in the May samples across the two time periods this decline may be related to shifts in phenology rather than declines in absolute larval numbers. Our findings suggest a generally high level of community stasis in these lakes and ponds across this time period. However, declines in larval abundance across these time periods may either signal genuine declines in these important insect populations, or as appears more likely, shifts in their phenology that change the timing of when larvae are present in these habitats.
