Geology topics

Tom L. Dudley

Publications and source records attributed to Tom L. Dudley.

7 recordsLinked to original sources

USGS2020

Calibrating environmental DNA metabarcoding to conventional surveys for measuring fish species richness

The ability to properly identify species present in a landscape is foundational to ecology and essential for natural resource management and conservation. However, many species are often unaccounted for due to ineffective direct capture and visual surveys, especially in aquatic environments. Environmental DNA metabarcoding is an approach that overcomes low detection probabilities and should consequently enhance estimates of biodiversity and its proxy, species richness. Here, we synthesize 37 studies in natural aquatic systems to compare species richness estimates for bony fish between eDNA metabarcoding and conventional methods, such as nets, visual census, and electrofishing. In freshwater systems with fewer than 100 species, we found eDNA metabarcoding detected more species than conventional methods. Using multiple genetic markers further increased species richness estimates with eDNA metabarcoding. For more diverse freshwater systems and across marine systems, eDNA metabarcoding reported similar values of species richness to conventional methods; however, more studies are needed in these environments to better evaluate relative performance. In systems with greater biodiversity, eDNA metabarcoding will require more populated reference databases, increased sampling effort, and multi-marker assays to ensure robust species richness estimates to further validate the approach. eDNA metabarcoding is reliable and provides a path for broader biodiversity assessments that can outperform conventional methods for estimating species richness.

Frontiers in Ecology and Evolution↗

USGS2020

Looking where it’s hard to see: A case study documenting rare Eucyclogobius newberryi presence in a California lagoon

Environmental DNA (eDNA) analysis is increasingly used for biomonitoring and research of fish populations and communities by environmental resource managers and academic researchers. Although managers are much interested in expanding the use of eDNA as a survey technique, they are sceptical about both its utility (given that information is often limited to presence/absence of a species) and feasibility (given the need for proper laboratory facilities for sample processing). Nonetheless, under the right circumstances, eDNA analysis is cost‐effective compared to many traditional aquatic survey methods and does not disturb habitat or harm the animals being surveyed. This article presents a case study in which eDNA analysis was successfully used to document the presence of a rare fish species in a waterway earmarked for restoration. The authors discuss the conditions that allowed this study to occur quickly and smoothly and speculate on how the goals of researchers and managers can be integrated for efficient and informative use of this tool.

California↗

USGS2020

Final report: Southwestern Willow Flycatcher (Empidonax traillii extimus) and Western Yellow-billed Cuckoo (Coccyzus americanus occidentalis) surveys and habitat availability modeling on the Santa Clara River, California, 26 March 2020

Our project aimed to conduct population surveys for Southwestern Willow Flycatcher (Empidonax trailii extimus; SWFL) and Yellow-billed Cuckoo (Coccyzus americanus; YBCU) in 2018 and 2019, apply existing habitat models to illustrate and predict past, current, and future habitat suitabilities for these two species, and update and standardize classification and mapping of riparian vegetation to reflect recent conditions along the lower 50 miles of the Santa Clara River. Models developed by Hatten and Paradzick (2003), Hatten, et al. (2010), Hatten (2016), and Johnson et al. (2016) were applied to the SCR to provide California Department of Fish and Wildlife (CDFW) and the U.S. Fish and Wildlife Service (USFWS) with useful tools for management of resources for SWFL and YBCU.

California↗

USGS2014

Synergistic interactions between leaf beetle herbivory and fire enhance tamarisk ( Tamarix spp.) mortality

The combined effects of herbivory and fire on plant mortality were investigated using prescribed burns of tamarisk ( Tamarix ramosissima Lebed) exposed to herbivory by the saltcedar leaf beetle (Chrysomelidae: Diorhabda carinulata Desbrocher). Tamarix stands in the Humboldt Sink (NV, USA) were divided into three treatments: summer burn (August 2006), fall burn (October 2006) and control (unburned), and litter depth was manipulated to vary fire intensity within burn seasons. A gradient of existing herbivory impact was described with three plant condition metrics prior to fire: reduced proportions of green canopy, percent root crown starch sampled at the height of the growing season (August 2006), and percent root crown starch measured during dormancy (December 2006). August root crown starch concentration and proportion green canopy were strongly correlated, although the proportion green canopy predicted mortality better than August root crown starch. December root crown starch concentration was more depleted in unburned trees and in trees burned during the summer than in fall burn trees. Mortality in summer burned trees was higher than fall burned trees due to higher fire intensity, but December root crown starch available for resprouting in the spring was also lower in summer burned trees. The greatest mortality was observed in trees with the lowest December root crown starch concentration which were exposed to high fire intensity. Disproportionate changes in the slope and curvature of prediction traces as fire intensity and December starch reach reciprocal maximum and minimum levels indicate that beetle herbivory and fire intensity are synergistic.

Nevada↗

USGS2014

Riparian restoration framework for the Upper Gila River, Arizona

This technical report summarizes the methods and results of a comprehensive riparian restoration planning effort for the Gila Valley Restoration Planning Area, an approximately 53-mile portion of the upper Gila River in Arizona (Figure 1-1). This planning effort has developed a Restoration Framework intended to deliver science-based guidance on suitable riparian restoration actions within the ecologically sensitive river corridor. The framework development was conducted by a restoration science team, led by Stillwater Sciences with contributions from researchers at the Desert Botanical Garden (DBG), Northern Arizona University (NAU), University of California at Santa Barbara (UCSB), and U.S. Geological Survey (USGS). All work was coordinated by the Gila Watershed Partnership of Arizona (GWP), whose broader Upper Gila River Project Area is depicted in Figure 1-1, with funding from the Walton Family Foundation’s Freshwater Initiative Program.

Arizona↗

USGS2012

The effect of leaf beetle herbivory on the fire behaviour of tamarisk (Tamarix ramosissima Lebed.)

The non-native tree, Tamarix spp. has invaded desert riparian ecosystems in the south-western United States. Fire hazard has increased, as typically fire-resistant native vegetation is replaced by Tamarix. The tamarisk leaf beetle, Diorhabda carinulata Desbrochers, introduced for biological control, may affect fire behaviour by converting hydrated live Tamarix leaves and twigs into desiccated and dead fuels. This potentially increases fire hazard in the short term before native vegetation can be re-established. This study investigates how fire behaviour is altered in Tamarix fuels desiccated by Diorhabda herbivory at a Great Basin site, and by herbivory simulated by foliar herbicide at a Mojave Desert site. It also evaluates the influence of litter depth on fire intensity. Fire behaviour was measured with a fire intensity index that integrates temperature and duration (degree-minutes above 70°C), and with maximum temperature, duration, flame lengths, rates of spread and vegetation removal. Maximum temperature, flame length and rate of spread were enhanced by foliar desiccation of Tamarix at both sites. At only the Mojave site, there was a trend for desiccated trees to burn with greater fire intensity. At both sites, fire behaviour parameters were influenced to a greater degree by litter depth, vegetation density and drier and windier conditions than by foliar desiccation.

International Journal of Wildland Fire↗

USGS2010

A river system to watch: documenting the effects of saltcedar ( Tamarix spp.) biocontrol in the Virgin River valley

Throughout riparian areas of the southwestern United States, non-native saltcedar (also known as tamarisk; Tamarix spp.) can form dense, monotypic stands and is often reported to have detrimental effects on native plants and habitat quality (Everitt 1980; Shafroth et al. 2005). Natural resource managers of these riparian areas spend considerable time and resources controlling saltcedar using a variety of techniques, including chemical (Duncan and McDaniel 1998), mechanical, and burning methods (Shafroth et al. 2005). Approximately one billion dollars are spent each year on river restoration projects nationally (Bernhardt et al. 2005), and a majority of these projects focus on invasive species control in the Southwest (Follstad Shah et al. 2007). A technique that has drawn much attention is the use of the saltcedar leaf beetle ( Diorhabda spp.), a specialist herbivore, as biological control of saltcedar (Lewis et al. 2003). Research testing was conducted with beetles housed in secure enclosures in six states in 1998 and 1999 (Dudley et al. 2001), followed by open release at some of those sites starting in 2001 (DeLoach et al. 2004). By 2005, full-scale saltcedar biocontrol was implemented in 13 states, led by the USDA Animal and Plant Health Inspection Service (APHIS), the agency that oversees biological control programs, and with the participation and support of the U.S. Fish and Wildlife Service (USFWS). Despite the widespread application of Diorhabda , however, only limited research has quantified the consequences (benefits and costs) on biotic communities and ecosystem services. Alterations to riparian areas caused by various non-native species control activities have the potential to affect a variety of habitat types used by wildlife (Bateman et al. 2008a); processes like water availability, fluvial deposition, and erosion; and the establishment of other non-native species (Carruthers and D'Antonio 2005, Shafroth et al. 2005, DeLoach et al. 2006). Similarly, biocontrol is expected to modify riparian ecosystems, and it is imperative to document and evaluate both the environmental benefits and the potential costs of this tamarisk management method.

Virgin River↗