Cameron W. Barrows

A FRAMEWORK FOR MONITORING MULTIPLE-SPECIES CONSERVATION PLANS

Abstract The shift from single species conservation initiatives to multiple-species conservation plans has not been accompanied by parallel changes in methods to evaluate the success of these efforts, nor to provide managers critical information to employ adaptive management strategies. Layering single species approaches for monitoring multiple-species conservation plans is inefficient and may lead to management strategies that have unintended detrimental impacts on target and nontarget organisms. Alternative approaches, such as ecosystem monitoring, can also fail to provide adequate protection for listed species and so may not fulfill regulatory requirements. We propose a hybrid approach that employs conceptual and spatial data in an iterative process to create niche models for species and species associations within natural communities. Niche models are composed of testable hypotheses linking species occurrences to environmental parameters over multiple scales. During an initial data gathering period these hypotheses are evaluated, accepted or rejected, and modified as indicated by new data. Once niche models are corroborated, the focus of monitoring shifts to a greater emphasis on identified anthropogenic and natural environmental drivers of species occurrence and abundance. The focus on environmental drivers supplies managers with direct information as to how, when, and where to employ adaptive management strategies when natural variance in those drivers is compromised by anthropogenic stressors. We provide a specific example on the conceptualization, development, and implementation of our hybrid approach from a new Multiple-species Habitat Conservation Plan for the Coachella Valley, in the Colorado desert of southern California.

POPULATION DYNAMICS OF A THREATENED SAND DUNE LIZARD

Abstract Understanding how and why the abundance of a species changes in space and time is an essential component to effective endangered species conservation. Key to this understanding is being able to distinguish natural population dynamics from a downward trajectory of a species at risk of extinction. For many species in arid environments, rainfall drives population changes. This is the case for Coachella Valley fringe-toed lizards (Uma inornata), a species listed as threatened under the U.S. Endangered Species Act. At low rainfall levels, the lizards exhibit negative population growth until annual precipitation exceeds 40 to 50 mm. Fluctuation in the population growth of the lizards is also correlated with changes in their diet. A regression model using rainfall and diet to explain lizard population dynamics resulted in a significant R2 value of 0.956. Because drought is common in their arid environment, it is not unusual for this lizard species to endure consecutive years of population declines. Fringe-toed lizard population counts during extended droughts often approach zero, yet the populations quickly rebound during periods of near average rainfall. If counts approaching zero are not reliable thresholds for when remedial management actions are warranted, then monitoring based management decisions need to use criteria that are more heuristic. Departures from the rainfall-diet-population growth model might provide the signal needed for management actions.

Biological Monitoring and Bridging the Gap Between Land Management and Science

Abstract Traditional monitoring approaches may have the objective of gathering data to estimate population size for a given species, but often lack the context of hypothesis testing. As such, many natural areas managers (responsible for ecological monitoring) and scientists have shared little common ground. The goal of monitoring should be to inform managers so that they can insure that the species, communities, and ecosystems under their charge are able to persist in the face of stressors, often from anthropogenic sources. The inherent complexity of natural systems makes this a daunting task, a task that requires a renewed partnership between managers and conservation biologists. The non-equilibrium paradigm of population dynamics establishes a theoretical framework for shifting monitoring objectives from only population estimates to understanding the processes that drive the dynamics of those populations. Using a hypothesis-driven scientific approach, monitoring designs can embrace the scientific method, provide insights into the ecological processes at work within natural systems, and importantly, point directly to if, when, and how active management may need to be employed in order to prevent the loss of biodiversity. This approach provides a common ground for conservation biologists and natural areas managers to forge partnerships to better understand the complexity of ecological systems and our ability to sustain those systems for future generations.

Identifying Habitat Linkages to Maintain Connectivity for Corridor Dwellers in a Fragmented Landscape

ABSTRACT Anthropogenic habitat fragmentation typically precedes conservation planning; maintaining remaining linkages among core habitat areas can thus become a key conservation objective. Identifying linkages for dispersal and ensuring those linkages have long-term protection and management are challenging tasks for wildlife managers. These tasks can be especially daunting for smaller species with low mobility, termed corridor dwellers, which must maintain sustainable populations within corridors. Between May 2007 and June 2009, we collected occurrence locations for a corridor dweller, the Palm Springs pocket mouse (Perognathus longimembris bangsii), from museums, previous research, and our own field sampling. We used those data to model their suitable niche space and then identify suitable linkages between proposed conservation areas. We used a partitioned Mahalanobis D2 statistic to create a spatially explicit niche model describing the distribution of a suitable niche space, and we validated the model statistically, with live trapping and with burrowing owl (Athene cunnicularia) diets. Our model identified soil characteristics, topographic ruggedness, and vegetation as variables delimiting Palm Springs pocket mouse habitat; sand content of the soils was an especially important characteristic. Our historic distribution model identified 120,000–90,000 ha as historically potential Palm Springs pocket mouse habitat; roughly 39% of that has been lost to more recent development. Most of the remaining suitable habitat occurred in the northwestern portion of the valley. We modeled habitat within core reserves as well as within proposed linkages between those reserves as having high similarity to known occupied habitats. Live trapping in areas with high (≥0.95) Habitat Suitability Index (HSI) values resulted in captures at 66% of those locations and, along with burrowing owl diets, refined a qualitative model as to what constituted a suitable Palm Springs pocket mouse corridor. While most corridor analyses have focused on mobile species which may traverse corridors in hours, days, or weeks, linkages for corridor dwellers must include habitat for sustaining multi-generational populations. This requires evaluating whether continuous suitable habitat exists within proposed corridors. Our research demonstrates how niche modeling can provide a landscape-scale view of the distribution of suitable habitat to evaluate conservation objectives for connectivity.

Conserving Species in Fragmented Habitats: Population Dynamics of the Flat-Tailed Horned Lizard, Phrynosoma mcallii

Abstract Understanding what drives population dynamics is a key tool for conserving species in fragmented habitats. We evaluate hypotheses explaining fluctuations in populations of flat-tailed horned lizards, Phrynosoma mcallii, in the Coachella Valley, California. This species has the smallest range of any horned lizard in the United States. Within portions of its range, there are potentially conflicting activities, such as suburban development, agriculture, off-road recreation, and activities along the international border. We analyzed fluctuations in populations with respect to resource variables during 2001–2007. Unlike results for other desert lizards, population dynamics of horned lizards did not correlate positively with rainfall. Compaction of sand, abundance of harvester ants, annual rainfall, and annual cover of plants all contributed to parsimonious models, but contributions of these variables varied between year and criteria for the dependent variable (occurrence of horned lizard). We also examined demographic characteristics of increasing and decreasing populations. Rates of growth of hatchlings and age at sexual maturity provided a mechanistic explanation for the observed population dynamics, and were consistent with a food-limiting hypothesis.

IS THE COACHELLA VALLEY FRINGE-TOED LIZARD (UMA INORNATA) ON THE EDGE OF EXTINCTION AT THOUSAND PALMS PRESERVE IN CALIFORNIA?

Abstract Reliable estimates of extinction time for small populations of threatened and endangered species based on long-term field surveys provide crucial information for species conservation. We estimated population parameters and extinction times for Coachella Valley fringe-toed lizard (Uma inornata), which is listed as a federally threatened species and a California state endangered species. We used field survey data from 2 transects (TPP1 and TPP2) at Thousand Palms Preserve, California, from 1986 to 2003. We also used data from another subpopulation (TPP3) of this species 6 km from TPP1 and TPP2, where this species became extinct in 2001, to estimate uncertainty of extinction time. Our results indicated that the difference between modeled extinction time and the real extinction time of the subpopulation on TPP3 was about 2 y. The extinction times for U. inornata at TPP1 and TPP2 would be about 23 to 50 y. The extinction time estimate has good relationship with the habitat area; thus, in larger effective habitat area, there will be an increase in the estimated time to extinction. Assuming all available habitats have population connectivity, the estimated extinction time would be about 78 y. There was a trend toward a decrease in the mean reproductive productivity of the lizard during the study. Although there were cycles in population dynamics, the population density trajectories on phase diagram became close to 0. For fragmented sand-dune habitats <100 to 200 ha, the persistence of subpopulations of U. inornata is doubtful. The main cause for the decrease of this subpopulation might be the shortage of food resources during the frequent, severe droughts.

Designing a sustainable monitoring framework for assessing impacts of climate change at Joshua Tree National Park, USA

Predicting species’ responses to a warming and drying (for North America’s desert southwest region) climate provides focus for monitoring to track shifts in species’ occupancy, and ultimately identifying management options to stem losses to biodiversity. Here we describe a monitoring framework to achieve that objective. A first step is to identify which species to monitor; which species will provide the greatest information for discerning the effects of climate change versus the myriad of other stressors that may impact their distributions and abundance. To select focal species we employed two complimentary approaches. One tool, vulnerability assessments (VAs), use available scientific literature to assess exposure to environmental stressors and adaptive capacity or resilience to climate change. Another approach is habitat suitability modeling (HSM) coupled with simulated temperature shifts. This method statistically combines environmental variables at known species’ locations, such as climate and terrain, to model the complex interaction of factors that constrain a species’ distribution. All other variables held constant, simulated temperature shifts can identify species’ sensitivities to those shifts and identify potential refugia. We used these tools to assess risk of local extinction due to predicted levels of climate change, as well as to identify where to locate monitoring plots to best capture the shifts in species distributions over time. A challenge in developing a monitoring program to document the effects of climate change on biodiversity is program sustainability. One way to support and enhance the sustainability of such a program will be to couple trained biologists with volunteer citizen scientists.

Temporal Patterns of Abundance of Arthropods on Sand Dunes

Abstract During >1 decade, I surveyed arthropods on a desert sand-dune system in the Coachella Valley, Riverside County, California. The most abundant of these arthropods were Coachella Valley giant sand-treader crickets Macrobaenetes valgum (Orthoptera: Rhapidophoridae), beetles Asbolus laevis and Edrotes ventricosus (Coleoptera: Tenebrionidae), and California harvester ants Pogonomyrmex californicus (Hymenoptera: Formicidae). While dynamics of M. valgum closely tracked precipitation, the other three species had complex fluctuations that often lacked correlations to annual rainfall. Beyond identifying departures from expected rainfall-driven relationships, an important outcome was an understanding of how long-term datasets are essential for understanding dynamics of populations. Resumen Durante >1 década, he monitoreado artrópodos en un sistema desértico de dunas de arena en el Valle de Coachella, condado de Riverside, California. Los artrópodos más abundantes fueron el grillo de arena gigante , Macrobaenetes valgum (Ortóptera: Rhapidophoridae), los escarabajos Asbolus laevis y Edrotes ventricosus (Coleóptera: Tenebrionidae) y la hormiga granívora roja Pogonomyrmex californicus (Hymenóptera: Formicidae). Mientras que la dinámica de M. valgum coincidió bien con la precipitación, las otras tres especies mostraron fluctuaciones complejas que con frecuencia carecían de correlaciones con las lluvias anuales. Más allá de la identificación de desvíos de las relaciones esperadas de la dinámica y la precipitación, un resultado importante fue la comprensión de la manera en que los conjuntos de datos a largo plazo son esenciales para entender la dinámica de poblaciones.

Native Wildlife Use Of Highway Underpasses In A Desert Environment

Abstract While highway underpasses and culverts are often identified in conservation planning as wildlife corridors, their success at facilitating connectivity in deserts has rarely been tested. We evaluated wildlife use of seven, pre-existing highway underpass structures and four associated canyon sites over 29 mo to identify spatial and temporal wildlife use patterns and to assess factors that may constrain wildlife use, particularly for native carnivore species. Our results indicate that a wide diversity of wildlife species utilize the underpass structures including rodents, lagomorphs, deer, and carnivores. Structural attributes of the underpasses have a minor influence on use by most observed species, although structural characteristics and human activity both contributed to determining bobcat (Lynx rufus) usage. Wildlife and human diel patterns differed between the underpass sites and their associated canyons. We suggest that providing a range of underpass structures to support use by a diversity of wildlife, as well as development or modification of underpasses to minimize human disturbance, will enhance landscape connectivity in desert systems.

Occupancy patterns of western yellow bats (Lasiurus xanthinus) in palm oases in the lower Colorado Desert

Abstract Where their ranges overlap, western yellow bats (Lasiurus xanthinus) often select roost sites in the fronds of native desert fan palms (Washingtonia filifera) as well as in other palm species. Roost occupancy patterns and characteristics of palm trees or palm oases important for roost selection across the Colorado Desert are unknown. We surveyed 41 palm oasis sites throughout the Colorado Desert and found 33 of those locations to have western yellow bat activity, and we confirmed day roosts at 19 sites. Compared to unoccupied palm sites, bats were found roosting in palm oases that were at higher elevations, had evidence of new palm growth, and where palms had a full range of skirt lengths. Our findings have implications for managing palm oases for western yellow bats.