Michael A. Patten, Emily A. Hjalmarson, Brenda D. Smith-Patten, and Jason T. Bried

Ecological Indicators 106(2019) DOI: https://doi.org/10.1016/j.ecolind.2019.105460

Numerous interacting abiotic and biotic factors shape an organism’s spatial distribution, and these factors vary
spatially and temporally, such that habitat used for breeding may differ from habitat used at other times of the
life cycle. We address this complex issue in the context of citizen science and opportunistic species occurrence
records, a valuable data source for biogeography and conservation. We focus on the insect order Odonata, the
dragonflies and damselflies, which as adults are popular in citizen science programs. Our goal was to devise a
means to estimate with high confidence whether a site supports a breeding population if only opportunistic data
are available. Our approach fitted logistic curves from occupancy models of observations of tenerals (newly
emerged adults that cannot yet disperse from a natal site) against counts of all adults, adult females only, and
incidence of breeding behaviors (ovipositing, mate guarding, tandem pairs). Models included median body size
and abundance class as covariates of detectability. We subjected logistic curves to a Bayesian two-segment
piecewise regression to obtain best estimates of the threshold (with associated credible intervals as an estimate of
uncertainty) to assess if a given predictor (e.g., adult count) or combination of predictors was associated with
breeding occurrence. We found that no single threshold fit all odonates: thresholds of varying precision were
identified for the suborders (dragonflies, damselflies) and for families and select genera in each suborder. Counts
of females greatly reduced the required threshold, whereas breeding behavior data reduced the threshold in
some cases. Our study shows it is possible to identify breeding occurrences in opportunistic adult Odonata
records. It also highlights how citizen scientists should record not only a sound species list with rudimentary
counts of adults but also note the sex and breeding behavior. The identification of breeding occurrences in
extensive opportunistic data is pertinent to understanding species’ distributions and habitat requirements along
with their ecological sensitivity and value as bioindicators.

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