Cecil R. Schwalbe

Implications of anthropogenic landscape change on inter-population movements of the desert tortoise (Gopherus agassizii)

In the Sonoran Desert of North America, populations of the desert tortoise (Gopherus agassizii) occur in rocky foothills throughout southwestern Arizona and northwestern Mexico. Although tortoise populations appear to be isolated from each other by low desert valleys, individuals occasionally move long distances between populations. Increasingly, these movements are hindered by habitat fragmentation due to anthropogenic landscape changes. We used molecular techniques and radiotelemetry to examine movement patterns of desert tortoises in southern Arizona. We collected blood samples from 170 individuals in nine mountain ranges and analyzed variability in seven microsatellite loci to determine genetic differentiation among populations. Gene flow estimates between populations indicate that populations exchanged individuals historically at a rate greater than one migrant per generation, and positive correlation between genetic and geographic distance of population pairs suggests that the limiting factor for gene flow among populations is isolation by distance. Life history traits of the desert tortoise, a long-lived species with delayed sexual maturity, may severely constrain the ability of small populations to respond to disturbances that increase adult mortality. Historic gene flow estimates among populations suggests that recovery of declining populations may rely heavily on the immigration of new individuals from adjacent mountain ranges. Management strategies compatible with the evolutionary history of gene flow among disjunct populations will help ensure the long-term persistence of Sonoran desert tortoise populations.

Distance sampling for Sonoran Desert tortoises

We used line transects and distance sampling in combination with radiotelemetry to estimate density of a desert tortoise (Gopherus agassizii) population in the Rincon Mountains near Tucson, Arizona, USA, as part of a long-term study evaluating the impact of urban development on tortoises. During 2000, 34 1-km transects were each sampled twice in the 368.5-ha study area. We observed 46 tortoises with midline carapace lengths ≥150 mm (subadults and adults) plus 7 juveniles on transects. For subadults and adults, the encounter rate was 0.63 tortoises/km, and the mean proportion of tortoises observable during radiotelemetry, conducted concurrently with transect sampling, was 82%. Corrected mean density based on line transects and radiotelemetry was 0.523 tortoises/ha (CV = 22.99, 95% CI = 0.29-0.79), and absolute abundance in the study area was estimated to be 193 (CV = 23.0%, Cl = 107-291). Using the 2 independent coverages of transects as separate samples, the Lincoln-Petersen mark-recapture estimator produced an abundance estimate of 224 subadult and adult tortoises (CV = 53.9%, CI = 72-440). Transects measured on the ground over uneven topography resulted in 3% smaller estimates of density when compared to analysis with transect lengths determined from coordinates plotted on a map. Distance sampling appears to be a feasible method of estimating density of Sonoran Desert populations of the desert tortoise, but transect lengths should be based on mapped rather than measured distances to prevent biases caused by uneven topography.

NASAL AND CLOACAL BACTERIA IN FREE-RANGING DESERT TORTOISES FROM THE WESTERN UNITED STATES

Aerobic bacteria were collected from three free-ranging desert tortoise (Gopherus agassizii) populations in the eastern Mojave Desert (Arizona, Utah; USA) from 1989 to 1993, and from two free-ranging populations in the central Sonoran Desert (Arizona, USA) from 1990 to 1994. Six species of nasal bacteria and 18 species of cloacal bacteria were identified. At least one potential pathogen was found in the nasal cavity (Pasteurella testudinis), and at least two potential pathogens in the cloaca (Pseudomonas spp., Salmonella spp.).

Genetic and morphometric assessment of an unusual tortoise (Gopherus agassizii) population in the Black Mountains of Arizona

Under recent regulatory designation of the U.S. Fish and Wildlife Service, desert tortoises (Gopherus agassizii) occurring east and south of the Colorado River constitute the Sonoran population, whereas those to the west and north form the Mojave population. These management units, distinguished by significant genetic, morphometric, and ecological differences, represent deep phylogenetic subdivisions within G. agassizii and are of high conservation value. We provide genetic and morphological profiles for an unusual tortoise population inhabiting the Black Mountains of Arizona, some 40 km east of the Colorado River. Both mitochondrial (mt) DNA and morphometric analyses revealed predominately Mojavean features: ten of eleven Black Mountain tortoises possessed Mojave mtDNA markers, and 24 of 37 animals exhibited Mojave morphometric phenotypes. Our results indicate west-to-east movement of tortoises across the Col- orado River, though how or when a Mojave lineage became established in the Black Mountains is difficult to ascertain. Active dispersal, river meander, and human transport (early or modem peoples) serve as plau- sible explanations. Future management of the Black Mountain tortoises should emphasize the populations Mojavean affinities.

Natural History of a Northern Population of Twin-Spotted Rattlesnakes, Crotalus pricei

Abstract The twin-spotted rattlesnake (Crotalus pricei) is a small-bodied pitviper that has received little attention in the literature to date. The species reaches the northern limit of its range in southeastern Arizona, where it inhabits higher elevations than any of the states 10 other rattlesnake species. During 1997–2000, we captured, measured, and marked 127 C. pricei in Arizonas Chiricahua Mountains between 2530 and 2900 m elevation. We also used radiotelemetry to track the movements of 16 C. pricei in the study area during 1997–1998. Mean (± SE) snout–vent length of C. pricei was 387.8 ± 8.3 mm (range = 168–572), and mean mass was 53.5 ± 3.3 g (range = 3.6–188.5). Based on fecal analyses, lizards constituted the bulk of prey (74%), but the diet of C. pricei also included mammals, birds, and a conspecific. Mating was concentrated in August and early September and parturition took place during late July and August. Mean number of embryos was 3.94 ± 0.34 (range = 1–6) and female reproduction appeared biennial or less frequent. Based on shed and growth rates, female C. pricei develop embryos at 4–5 years of age. Gravid females maintained warmer body temperatures relative to substrate temperature than nongravid females or males, presumably by spending more time basking than other snakes. Radiotelemetry revealed that movement patterns varied from year to year, as males moved over six times farther per week during the 1998 monsoon season (July to September) than during the 1997 monsoon season. Additionally, use of talus slopes by males decreased during 1998. During dry years, such as 1998, males may be forced off talus into cooler microclimates where resources are less concentrated than on talus.

Spatial occupancy models for predicting metapopulation dynamics and viability following reintroduction

Summary 1. The reintroduction of a species into its historic range is a critical component of conservation programmes designed to restore extirpated metapopulations. However, many reintroduction efforts fail, and the lack of rigorous monitoring programmes and statistical models have prevented a general understanding of the factors affecting metapopulation viability following reintroduction. 2. Spatially explicit metapopulation theory provides the basis for understanding the dynamics of fragmented populations linked by dispersal, but the theory has rarely been used to guide reintroduction programmes because most spatial metapopulation models require presence– absence data from every site in the network, and they do not allow for observation error such as imperfect detection. 3. We develop a spatial occupancy model that relaxes these restrictive assumptions and allows for inference about metapopulation extinction risk and connectivity. We demonstrate the utility of the model using six years of data on the Chiricahua leopard frog Lithobates chiricahuensis, a threatened desert-breeding amphibian that was reintroduced to a network of sites in Arizona USA in 2003. 4. Our results indicate that the model can generate precise predictions of extinction risk and produce connectivity maps that can guide conservation efforts following reintroduction. In the case of L. chiricahuensis, many sites were functionally isolated, and 82% of sites were characterized by intermittent water availability and high local extinction probabilities (0� 84, 95% CI: 0� 64–0� 99). However, under the current hydrological conditions and spatial arrangement of sites, the risk of metapopulation extinction is estimated to be <3% over a 50-year time horizon. 5. Low metapopulation extinction risk appears to result from the high dispersal capability of the species, the high density of sites in the region and the existence of predator-free permanent wetlands with low local extinction probabilities. Should management be required, extinction risk can be reduced by either increasing the hydroperiod of existing sites or by creating new sites to increase connectivity. 6. Synthesis and applications. This work demonstrates how spatio-temporal statistical models based on ecological theory can be applied to forecast the outcomes of conservation actions such as reintroduction. Our spatial occupancy model should be particularly useful when management agencies lack the funds to collect intensive individual-level data.

Amphibian Research and Monitoring Initiative (ARMI): a successful start to a national program in the United States

Most research to assess amphibian declines has focused on local-scale projects on one or a few species. The Amphibian Research and Monitoring Initiative (ARMI) is a national program in the United States mandated by congressional directive and implemented by the U.S. Department of the Interior (specifically the U.S. Geological Survey, USGS). Program goals are to monitor changes in populations of amphibians across U.S. Department of the Interior lands and to address research questions related to amphibian declines using a hierarchical framework of base-, mid- and apex-level monitoring sites. ARMI is currently monitoring 83 amphibian species (29% of species in the U.S.) at mid- and apex-level areas. We chart the progress of this 5-year-old program and provide an example of mid-level monitoring from 1 of the 7 ARMI regions.

Diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake)

Abstract We describe the diet of Crotalus lepidus klauberi (Banded Rock Rattlesnake) using samples collected in the field and from museum specimens, as well as several records from unpublished reports. Most records (approximately 91%) were from the northern Sierra Madrean Archipelago. Diet consisted of 55.4% lizards, 28.3% scolopendromorph centipedes, 13.8% mammals, 1.9% birds, and 0.6% snakes. Sceloporus spp. comprised 92.4% of lizards. Extrapolation suggests that Sceloporus jarrovii represents 82.3% of lizard records. Diet was independent of geographic distribution (mountain range), sex, source of sample (stomach vs. intestine/feces), and age class. However, predator snout–vent length differed significantly among prey types; snakes that ate birds were longest, followed in turn by those that ate mammals, lizards, and centipedes. Collection date also differed significantly among prey classes; the mean date for centipede records was later than the mean date for squamate, bird, or mammal records. We found no difference in the elevation of collection sites among prey classes.

Mycoplasmosis in Free-ranging Desert Tortoises in Utah and Arizona

Upper respiratory tract disease (URTD) has been associated with major losses of free-ranging desert tortoises (Gopherus agassizii) in the southwestern United States. This prompted a clinical examination of 63 free-ranging desert tortoises for signs of URTD and sampling for Mycoplasma agassizii, the causative agent of URTD. Tortoises were sampled from three sites in the eastern Mojave Desert (1992–93), and from three sites in the Sonoran Desert (1992–94). Plasma samples were tested for antibodies to M. agassizii using an enzyme-linked immunosorbent assay (ELISA). Nasal aspirate samples from 12 Sonoran tortoises were tested using polymerase chain reaction (PCR) test directed at the 16S rRNA gene of M. agassizii. Nasal aspirate samples from all tortoises were cultured for M. agassizii. In the Mojave Desert, nine tortoises had clinical signs of URTD and eight were seropositive for M. agassizii. In the Sonoran Desert, there were no clinical signs of URTD, but two tortoises were seropositive, and two tortoises had positive PCR results.

EFFECTS OF DESTRUCTIVE COLLECTING PRACTICES ON REPTILES: A FIELD EXPERIMENT

Abstract A basic tenet of wildlife management is that acceptable harvest methods should have little impact on populations other than eliminating or reducing the number of surplus individuals. We evaluated whether collectors who use destructive methods to harvest individual animals threaten reptile populations in Arizona, USA. Destructive methods usually involve permanent damage to cracks and crevices in rock outcrops that provide moist, cool shelter sites for reptiles. We surveyed 80 rock outcrops in an area slated for development. We treated half of the rock outcrops by imitating the activities of collectors using pry bars to overturn rocks and break open cracks, and we then resurveyed the rock outcrops. Multivariate repeated-measures analysis revealed that damaged rock outcrops support fewer reptiles than undamaged outcrops. We also observed species, sex, age-class, and seasonal effects due to treatment. To combat the growing problem of habitat destruction from reptile harvest, we recommend protection of rock outcrops and education of reptile collectors.