Population and Community Dynamics of Lizards and Rodents in Organ Pipe Cactus National Monument 1989-2006 and Implications for Future Monitoring


Flesch, A. D.

Ecological monitoring is built on a foundation of repeatedly measuring resources over time so that the presence, magnitude, and direction of trends can be detected in sufficient time to make informed management decisions (Thompson et al. 1998, Yoccoz et al. 2001, Pollock et al 2002). For agencies charged with protecting and preserving natural resources, such as the National Park Service (NPS Organic Act, 1916), monitoring provides a critical feedback mechanism for guiding management and for assessing and revising the status of natural resources over time. At Organ Pipe Cactus National Monument (ORPI) in southern Arizona, an Ecological Monitoring Program (EMP) was initiated in the 1980s with help from the Cooperative Parks Studies Unit (CPSU) and associated scientists, including those at the University of Arizona. In the early and mid-1990s, several new sites and components were added to the EMP and oversight by an advisory committee of managers and researchers began. Throughout this process, researchers and ORPI staff were tasked with presenting relevant information from the program to both guide management and to allow periodic reviews and modifications. Most recently, these efforts culminated in a comprehensive report on trends in vegetation, wildlife, and other environmental factors (e.g., weather and air and water quality) (ORPI 2006). Currently, the EMP is in the midst of a thorough evaluation to determine its relevance, efficiency, and application to management. Because the EMP is likely the longest standing monitoring program in the National Park System (A. Hubbard, Sonoran Desert Network, pers. comm.) these data have great potential to guide management and monitoring. Furthermore, they may also provide valuable information to educators, policy makers, scientists, resource managers, and non-governmental organizations that are interested in the status and trends of natural resources on public lands.

Periodic reviews are an essential component of long-term monitoring efforts because they ensure that methods are appropriate and that objectives are both relevant and being efficiently met. Most importantly, frequent reviews of monitoring data enable managers to identify and respond to current threats so that appropriate actions can be taken. In recent years, ORPI and other areas along the international boundary have experienced marked increases in human migration and illegal smuggling from the south and in law enforcement associated with these activities. These activities have made monitoring more difficult and costly and pose potential threats to biological and cultural resources. Because the EMP was not explicitly designed to address these new and developing stressors, review and modification of the program are especially relevant.

Because appropriate management actions often depend on detecting changes in relevant resource conditions, ability to detect temporal trends in these conditions is often the most important attribute of a monitoring program. In ORPI, a partial internal review of the EMP was accomplished between 1997 and 1999 by Petterson (1998) who recommended modified protocols and objectives to better meet NPS standards. For example, it was recommended that lizard monitoring be designed to detect a 15% annual change in populations of western whiptail (Aspidoscelis tigris) over a ten-year period (α = 0.10, β = 0.20). With support from the Desert Southwest Cooperative Ecosystem Studies Unit, a panel of scientists met to review the EMP in March 2006. Early in the workshop, it was evident that thorough analyses were needed before the program could be properly evaluated. During follow-up discussions, the panel determined that beginning the review process with the rodent and lizard data was most appropriate.

Data analyses require large investments of time and although recent efforts have been informative (ORPI 2006), information from the EMP has not been thoroughly analyzed since 1998 (Rosen 2000). Because existing data span a broad temporal frame during which weather conditions have varied markedly and sites vary widely across topographic, vegetation, and hydrologic gradients, they have great potential to elucidate population and community dynamics of vertebrates and the factors that drive these dynamics. Further, evaluation and enhancement of existing protocols have applications throughout the park system, to inventory and monitoring networks throughout NPS, and to other entities that are now developing monitoring programs in the Sonoran Desert and elsewhere.

Published Date

Publication Type

Technical Reports