Validating dispersal distances inferred from autoregressive occupancy models with genetic parentage assignments

Abstract

Dispersal distances are commonly inferred from occupancy data but have rarely been validated. Estimating dispersal from occupancy data is further complicated by imperfect detection and the presence of unsurveyed patches. We compared dispersal distances inferred from seven years of occupancy data for 212 wetlands in a metapopulation of the secretive and threatened California black rail (Laterallus jamaicensis coturniculus) to distances between parent-offspring dyads identified with 16 microsatellites. We used a novel autoregressive multi-season occupancy model that accounted for both unsurveyed patches and imperfect detection to quantify patch isolation using buffer radius (BRM) and incidence function (IFM) connectivity measures at 15 scales (1-10, 15, 20, 25, and 30 km). Connectivity measures were then fit as colonization covariates in occupancy models to estimate a model-averaged dispersal distance. As predicted, colonization was more strongly related to connectivity at small spatial scales (<10 km). AIC weights were greatest at 7 km for BRM and at 4 km for IFM. Model-averaged dispersal distances (BRM = 7.46 km; IFM = 5.48 km) showed good agreement with the mean M(±SE) dispersal distance from 23 parent-offspring dyads (5.58 ± 1.92 km), indicating reasonably accurate mean dispersal distances can be inferred from occupancy data when isolation strongly affects colonization.

Integrating social and ecological data to model metapopulation dynamics in coupled human and natural systems

“…In the foothills of the California Sierra Nevada, irrigation by landowners has greatly increased the size and number of small wetlands (mean area = 0.37 ha; Richmond et al 2010a). These wetlands support metapopulations of two closely related, secretive marsh birds, the smaller, dispersal-limited black rail (Laterallus jamaicensis) and the larger, more vagile Virginia rail (Rallus limicola; Richmond et al 2010b, Hall et al 2018. The California subspecies of black rail (L. j. corturniculus) is listed as a California State Threatened Species because of habitat loss (Eddleman et al 1988), and the other U.S. subspecies (L. j. jamaicensis) is proposed to be listed as Threatened under the Endangered Species Act.…”

“…, Hall et al. ). The California subspecies of black rail ( L. j. corturniculus ) is listed as a California State Threatened Species because of habitat loss (Eddleman et al.…”

“…Previous studies found no evidence of competition between black and Virginia rails, so we simulated their dynamics separately (Risk et al 2011). Connectivity was modeled with an autoregressive buffer radius metric (Appendix S1) that had previously been found to fit best for black rails and was validated with genetic data (Hall et al 2018). This connectivity metric incorporated occupancy probability at sites within the buffer radius that were unsurveyed or had nondetections.…”

The rescue effect and inference from isolation–extinction relationships

“…The study area was the zone III Sierra Nevada Foothills ecoregion (US Environmental Protection Agency ) in Nevada, Yuba, and southern Butte counties, plus a 1 km buffer to quantify isolation for sites near the study area boundary (see Richmond et al for a description, and appendix of Hall et al for a map). Patchy wetlands are found throughout this rangeland landscape.…”

“…Because our model assumed no false positive detections, for sites where the species was detected. For unsurveyed sites (all wetlands were mapped; Hall et al ), was equal to the unconditional occupancy probability in the first year (Ψ i ) and in the remaining years was calculated as follows:where γ i,t and ε i,t are colonisation and extinction probabilities in the subsequent years (MacKenzie et al ).…”