Resurvey

Clarence H. Kennedy surveyed sites throughout central California and Nevada while based at Stanford University in 1914 and 1915. He then published comprehensive lists of every species found at these locations, along with some notes on habitat conditions and species behavior in the Proceedings of the National Museum (Kennedy, 1917). While many details are missing in this document (like specific collection dates!!), I tracked down this information from his collection of dragonflies, which are now scattered in museums throughout California, the University of Michigan, and the Florida State Collection of Arthropods. I have resurveyed Kennedy’s original sites to determine how communities have changed at these specific locations.

During the summers of 2011-2013, I surveyed 81 locations for adult Odonata throughout central California and Nevada, 45 of which were directly comparable to Kennedy’s sites. I compared community metrics and occurrence rates for the two time periods. Using multispecies linear mixed models, I have identified land use and climatic factors associated with significant changes in Odonata communities.

The next step in this research is to estimate species detection and occurrence probabilities of several species that have expanded (e.g. Enallagma civile, Libellula luctuosa, Tramea lacerata) or contracted (e.g. Hetaerina americana, Ophiogomphus morrisoni, Sympetrum danae) since Kennedy’s survey. Occupancy modeling incorporates data from multiple surveys to estimate detection probability in addition to occurrence. These hierarchical models can also incorporate both survey-level (e.g. effort or visit temperature) and habitat (e.g. canopy cover and elevation) covariates in estimates of detection and/or occupancy. I am using the same modeling approach to estimate historical detection and occupancy in relation to environmental conditions during Kennedy’s time. The ultimate goal of this work is to determine if detection and occupancy rates of Odonata species has changed significantly between the two time periods.

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