Background/Question/Methods
Recent studies have prompted a widespread debate on the existence and magnitude of temporal changes in insect abundance. Our understanding of long term trends in insect abundance has been complicated by a lack of time series data that is collected in a consistent manner, at large spatial scale and across taxa. We demonstrate that this gap can be filled by quantifying aerial insect abundance through use of historic data from NEXRAD weather stations. This data source is particularly valuable as it furthers our understanding of macro scale patterns in insect abundance and biomass under influence of global change.
In this study, we analyzed weather surveillance radar observations for the period 2013-2020 from 155 weather radars across the continental US. Radar remote sensing has been used to quantify long term patterns in bird and bat abundances. We accessed dual-polarization radar measurements at noon for each day in the time period. We calculated circular depolarization ratio from the radar products differential reflectivity and correlation coefficient, and used this to filter out weather and large (vertebrate) animals. We removed all scans containing precipitation to prevent masking of insect signals, and corrected abundance estimates for the number of scans removed from the analysis. We calculated scattering area for every radar image and assumed radar cross section based on a subset of likely taxa to estimate absolute insect abundance.
Results/Conclusions
Preliminary results show no overall pattern of decline in insect aerial abundance during the period 2012-2020. Instead, there is significant variation between years in insect abundance, without a clear temporal trend. Abundance also varies greatly between regions. Aerial insect abundance is greater at lower latitudes in the US than at more northern latitudes, and greater along migratory flyways. Variation in aerial insect abundance is not correlated with change in local temperature or precipitation across the time span of our study, suggesting limited effects of climate change on overall abundance of aerial insects in the past 8 years.
These results suggest that while anthropogenic change has resulted in declines in insect biodiversity and services, overall abundance may not be similarly affected. It is likely that anthropogenic change has resulted in changes in species composition rather than overall declines. However, our study is preliminary and should be extended to longer time series before definitive conclusions can be drawn.
This approach demonstrates the potential of weather surveillance radar observations for tracking ecological patterns at large scales.