Geology topics

Bryan Richards

Publications and source records attributed to Bryan Richards.

3 recordsLinked to original sources

USGS2025

A system dynamics model to understand the integrated ecological and human dimension aspects of wildlife health and disease management

Chronic wasting disease (CWD) presents an ongoing challenge for the management of deer populations and sustaining harvest opportunities across North America. Existing disease models often fail to fully capture the complex interplay between disease dynamics, host ecology, and socio-economic factors. We developed a comprehensive system dynamics (SD) model that integrates demographic, epidemiological, ecological, and socio-economic processes within a single model to more fully characterize the complex network of causal feedbacks throughout the system. The model was calibrated using a Bayesian approach that incorporates prior knowledge to generate biologically interpretable outcomes, even with sparse data. For estimating the joint posterior distribution of model parameters, we leveraged time series of deer abundance, harvest composition, genetic profiles, CWD surveillance, and hunter demographics and behavior. Model outputs reproduced key system behaviors, including observed CWD prevalence trends, deer population dynamics, and hunter license purchasing patterns. Model predictions were most sensitive to parameters governing initial deer population size and recruitment. While model predictions generally aligned with observed data, discrepancies in early CWD detection and overestimation of the reactivation of long-inactive hunters reflect data limitations and modeling challenges. Key results suggest that indirect transmission is necessary to explain observed prevalence, that transmission is moderately density-dependent, and that observed population-level genetic shifts driven by CWD may play a role in transmission and progression. The SD modelling approach enabled estimation of difficult-to-measure parameters and identified potential leverage points for management—such as prioritizing increasing participation in antlerless harvest of existing hunters over the recruitment of new hunters. This integrated modeling approach offers a flexible foundation for adaptive wildlife disease management and emphasizes the value of unifying biological and human dimension processes to better inform effective, evidence-based policy.

BioRxiv↗

USGS2007

Chronic Wasting Disease

Chronic wasting disease (CWD) is an always-fatal, neurological illness occurring in North American cervids (members of the deer family), including white-tailed deer, mule deer, elk and moose. Since its discovery in 1967, CWD has spread geographically and increased in prevalence locally. CWD is contagious; it can be transmitted freely within and among free-ranging populations. It is likely that diseased animals can transmit CWD to healthy animals long before they become clinically ill. Managing CWD in free-ranging populations is extremely difficult, therefore preventative measures designed to reduce the chance for disease spread are critically important.

Fact Sheet↗

USGS2004

Chronic wasting disease risk analysis workshop: An integrative approach

Risk analysis tools have been successfully used to determine the potential hazard associated with disease introductions and have facilitated management decisions designed to limit the potential for disease introduction. Chronic Wasting Disease (CWD) poses significant challenges for resource managers due to an incomplete understanding of disease etiology and epidemiology and the complexity of management and political jurisdictions. Tools designed specifically to assess the risk of CWD introduction would be of great value to policy makers in areas where CWD has not been detected. To this end, the U.S. Geological Survey (USGS) created a steering committee representing states, native communities, federal, academic, and non-government entities. This committee formulated a collaborative process for the development of CWD risk assessment tools applicable to both free-ranging and captive populations. The committee recommended a workshop be held on the topic and suggested the format, content, and potential participants. Identified objectives of the workshop included: 1. Identify and discuss the needs of various government and non-government groups involved with assessing, managing, and/or preventing CWD. 2. Identify current gaps in CWD research specifically in relation to information applicable to the risk analysis process. 3. Construct a general, consensual, framework model (Figure 1) that incorporates all factors identified as potentially associated with the presence or absence of CWD (Table 1). The resulting CWD Risk Analysis Workshop was held May 11–13, 2004 in Fort Collins, Colorado. The workshop was attended by 28 individuals representing a cross-section of management, research, and nongovernment organizations. Experts with experience in a variety of risk analysis approaches and representatives from public and private user groups presented in the plenary session. The remainder of the workshop consisted of facilitated breakout sessions and all-group discussions. The framework model (Figure 1) reflects the workshop discussions and subsequent review and comments from workshop participants and steering committee members.

Open-File Report↗