Robert M Dorazio, Ph.D. (Former Employee)
Science and Products
Statistical Models for the Design and Analysis of Environmental DNA (eDNA) Surveys of Invasive and Imperiled Species
Detecting invasive species at low densities or prior to population establishment is critical for successful control and eradication. For example, Burmese pythons occupy thousands of square kilometers of mostly inaccessible habitats.
USGS is working to develop hierarchical models that will help analyze population-level surveys and sampling protocols, including presence-absence, point-count, multiple observer, removal, and capture-recapture.
Hierarchical Models for Computing Inferences About Species Assemblages Subject to Imperfect Detection
USGS is developing strategies to model species assemblages to allow inferences to be made about individual species, local communities of species, or for an entire metacommunity of species - while accounting for errors in species detection during sampling.
Surveys of environmental DNA (eDNA): a new approach to estimate occurrence in Vulnerable manatee populations
Environmental DNA (eDNA) detection is a technique used to non-invasively detect cryptic, low density, or logistically difficult-to-study species, such as imperiled manatees. For eDNA measurement, genetic material shed into the environment is concentrated from water samples and analyzed for the presence of target species. Cytochrome...Hunter, Margaret; Meigs-Friend, Gaia; Ferrante, Jason A.; Takoukam Kamla, Aristide; Dorazio, Robert; Keith Diagne, Lucy; Luna, Fabia; Lanyon, Janet M.; Reid, James P.
Time series sightability modeling of animal populations
Logistic regression models—or “sightability models”—fit to detection/non-detection data from marked individuals are often used to adjust for visibility bias in later detection-only surveys, with population abundance estimated using a modified Horvitz-Thompson (mHT) estimator. More recently, a model-based alternative for analyzing combined...ArchMiller, Althea A.; Dorazio, Robert; St. Clair, Katherine; Fieberg, John R.
Concepts and practices: Estimating abundance of prey species using hierarchical model-based approaches
Tigers predominantly prey on large ungulate species, such as sambar (Cervus unicolor), red deer (Cervus elaphus), gaur (Bos gaurus), banteng (Bos javanicus), chital (Axis axis), muntjac (Muntiacus muntjak), wild pig (Sus scrofa), and bearded pig (Sus barbatus). The density of a tiger population is strongly correlated with the density of such prey...Dorazio, Robert; Kumar, N. Samba; Royle, Andy; Gopalaswamy, Arjun M.
Field practices: Assessing tiger population dynamics using photographic captures
From these histories, capture frequency statistics and estimates of capture probabilities can be derived.Karanth, K. Ullas; Nichols, James D.; Harihar, Abishek; Miquelle, Dale; Kumar, N. Samba; Dorazio, Robert
Concepts: Integrating population survey data from different spatial scales, sampling methods, and species
Conservationists and managers are continually under pressure from the public, the media, and political policy makers to provide “tiger numbers,” not just for protected reserves, but also for large spatial scales, including landscapes, regions, states, nations, and even globally. Estimating the abundance of tigers within relatively small areas (e.g...Karanth, K. Ullas; Nichols, James D.; Dorazio, Robert; Delampady, Mohan; Dey, Soumen; Gopalaswamy, Arjun M.
eDNAoccupancy: An R package for multi-scale occupancy modeling of environmental DNA data
In this article we describe eDNAoccupancy, an R package for fitting Bayesian, multi-scale occupancy models. These models are appropriate for occupancy surveys that include three, nested levels of sampling: primary sample units within a study area, secondary sample units collected from each primary unit, and replicates of each secondary sample unit...Dorazio, Robert; Erickson, Richard A.
Concepts: Assessing tiger population dynamics using capture–recapture sampling
Capture-recapture can be viewed as an animal survey method in which the count statistic is the total number of animals caught, and the associated detection probability is the probability of capture.Royle, J. Andrew; Gopalaswamy, Arjun M.; Dorazio, Robert; Nichols, James D.; Jathanna, Devcharan; Parameshwaran, Ravishankar
A hierarchical model for estimating the spatial distribution and abundance of animals detected by continuous-time recorders
MotivationSeveral spatial capture-recapture (SCR) models have been developed to estimate animal abundance by analyzing the detections of individuals in a spatial array of traps. Most of these models do not use the actual dates and times of detection, even though this information is readily available when using continuous-time recorders, such as...Dorazio, Robert; Karanth, K. Ullas
Integrated species distribution models: combining presence-background data and site-occupancy data with imperfect detection
Two main sources of data for species distribution models (SDMs) are site-occupancy (SO) data from planned surveys, and presence-background (PB) data from opportunistic surveys and other sources. SO surveys give high quality data about presences and absences of the species in a particular area. However, due to their high cost, they often cover a...Koshkina, Vira; Wang, Yang; Gordon, Ascelin; Dorazio, Robert; White, Matthew; Stone, Lewi
Detection limits of quantitative and digital PCR assays and their influence in presence-absence surveys of environmental DNA
A set of universal guidelines is needed to determine the limit of detection (LOD) in PCR-based analyses of low concentration DNA. In particular, environmental DNA (eDNA) studies require sensitive and reliable methods to detect rare and cryptic species through shed genetic material in environmental samples. Current strategies for assessing...Hunter, Margaret; Dorazio, Robert M.; Butterfield, John S.; Meigs-Friend, Gaia; Nico, Leo; Ferrante, Jason A.
Incorporating imperfect detection into joint models of communites: A response to Warton et al.
Warton et al.  advance community ecology by describing a statistical framework that can jointly model abundances (or distributions) across many taxa to quantify how community properties respond to environmental variables. This framework specifies the effects of both measured and unmeasured (latent) variables on the abundance (or occurrence) of...Beissinger, Steven R.; Iknayan, Kelly J.; Guillera-Arroita, Gurutzeta; Zipkin, Elise; Dorazio, Robert; Royle, Andy; Kery, Marc
State-dependent resource harvesting with lagged information about system states
Markov decision processes (MDPs), which involve a temporal sequence of actions conditioned on the state of the managed system, are increasingly being applied in natural resource management. This study focuses on the modification of a traditional MDP to account for those cases in which an action must be chosen after a significant time lag in...Johnson, Fred A.; Fackler, Paul L.; Boomer, G Scott; Zimmerman, Guthrie S.; Williams, Byron K.; Nichols, James D.; Dorazio, Robert
eDNAoccupancy allows users to specify and fit multi-scale occupancy models with or without covariates, to estimate posterior summaries of occurrence and detection probabilities, and to compare different models using Bayesian model-selection criteria.
Environmental DNA picks up traces of the elusive mammals’ saliva, skin, waste, or exhaled breaths.