James R. Dixon

Feeding Ecology of the Concho Water Snake, Nerodia harteri paucimaculata

The diet of the Concho water snake Nerodia harteri paucimaculata was investigated from 1987 to 1990 by palpation of stomach contents. Prey remains representing 304 prey items were recovered from 192 individual snakes. Concho water snakes were almost completely piscivorous, feeding on 19 species of fish from nine families with minnows (Cyprinidae) dominating numerically. Cricket frogs (Acris crepitans) represented the only non-piscine prey. Diet diversity increased ontogenetically according to snake body size. Observations of foraging snakes suggest an ontogenetic change in foraging sites concurrent with a change in diet composition. Prey size was positively correlated with snake body size although some snakes occasionally ingested numerous small prey, possibly due to opportunistic feeding on small prey aggregations. Snakes occasionally attempted to handle prey too large to be ingested. Feeding occurred from mid-March to early November. Gravid females fed throughout the spring into mid-July and resumed feeding after parturition. Neonate and juvenile riverine snakes ingested prey in proportion to apparent availability while adults consumed a disproportionate amount of larger prey species. Lacustrine snakes primarily consumed prey associated with benthic or shallow water habitats. However, few individuals of open water and top water species were ingested, suggesting that prey habitat preference strongly influences catchability in lake systems.

APPARENT HYBRIDIZATION BETWEEN CNEMIDOPHORUS GULARIS AND CNEMIDOPHORUS SEPTEMVITTATUS FROM AN AREA OF SYMPATRY IN SOUTHWEST TEXAS

A potential area of sympatry for Cnemidophorus gularis and C. septemvittatus in Texas was identified from fine-mapping of museum locality records. The area was investigated and these two taxa were found to occur together at a single locality. Variation in the phenotypes of specimens observed and collected from this locality suggested hybridization between gularis and septemvittatus. Subsequent examination of several characters across the range for gularis and septemvittatus revealed considerable intraspecific vari- ability in phenotypes. DNA sequences for 932 base pairs of the ND4 to tRNALeu region of the mitochondrial genome were analyzed by a variety of phylogenetic and distance methods to determine the relationship between gularis and septemvittatus collected at this locality and samples collected away from the area of sympatry. Data are also included for the outgroup taxa Teius teyou, Cnemidophorus inornatus, C. laredoensis, C. lemniscatus, C. sexlineatus, and C. tigris. Results from all analyses indicate extremely low levels of se- quence divergence between gularis and septemvittatus relative to the divergence among the species of Cnemidophorus examined. The variation between the species gularis and septemvittatus is of a similar mag- nitude to that found within the species tigris, inornatus, and sexlineatus. Among the gularis collected in sympatry with septemvittatus, two have DNA sequences which unambiguously place them within the sep- temvittatus clade. The parthenoform C. laredoensis (female gularis x male sexlineatus), (1) provides addi- tional cladistic resolution within gularis, (2) is equidistant in divergence from gularis and septemvittatus, and (3) is basal to both species. As both gularis and septemvittatus represent diagnosable taxa by both phenotypic and genetic data, we conclude that hybridization between gularis and septemvittatus in sym- patry is the most likely explanation of the results.

A New Dendrobatid Frog (Colostethus) from Venezuela with Notes on its Natural History and that of Related Species

A new species of Colostethus (C. guatopoensis), described from north central Vene- zuela, is unique by having fully webbed hind feet. Natural history notes on it, C. herminae, and C. bromelicola are presented. In 1979 the Venezuelan government asked us to conduct a survey of the her- petofauna of the Parque Nacional Guato- po in the states of Guarico and Miranda, Venezuela. One of us (Rivero-Blanco) resides in Caracas, Venezuela, and the other (Dixon) surveyed the park from 17 June to 11 December 1980. Our work was concentrated along the major roads that bisect the park, but principally between the north and south boundaries of the park beginning 23 km north and ending 58 km north of Al- tagracia de Orituco. The park contains 96,640 ha of premontane rainforest that varies from 200 m to 1450 m in eleva- tion (see Ewel, Madriz and Tosi, 1976, for a description of the forest). Several major streams are found in the park and

Spatial Ecology of the Concho Water Snake (Nerodia harteri paucimaculata) in a Large Lake System

The distribution, movements, activity range, and habitat use of the Concho water snake, Nerodia harteri paucirnaculata, were studied by mark-recapture and radio telemetry in a large lake system, in central Texas, USA. Concho water snake emigration and distribution were largely driven by alteration of habitat availability caused by fluctuating water levels. Habitat characteristics associated with the presence of snakes at the study area were turbid water, minimal wave action, a gentle shoreline gradient, a silt substrate, and a rocky shoreline. Males and gravid females were equally vagile, and the likelihood of a snake undertaking an emigrational movement was independent of age andlor reproductive condition. However, males had significantly more movement days than gravid females. Radio-tagged males had detectable move- ments on 64% of monitored days, compared to 43% of monitored days for gravid females. Mean activity range length was 278 m for males, 219 m for gravid females, and 210 m for juveniles. Concho water snakes generally selected retreat sites within 3 m of water, although gravid females selected sites as far as 15 m from water. As a management procedure for lake populations, we advocate increasing the vertical distri- bution of rocky shoreline. habitat, densities are greatly reduced (pers. Little is known about the spatial ecology of obs.), which may increase the likelihood of local snakes occurring in temporally volatile habitats. extirpations. With the impending construction Houston and Shine (1994) reported high dis- of Ivie Reservoir and the subsequent inundation persal rates for filesnakes (Acrochordus arafurae) of a significant portion of Concho water snake among billabongs, attributable to fluctuating habitat, assessment of the ecological attributes water levels. They also cite extensive wet season of lake populations became imperative. Of spe- movements for water pythons (Liasis fuscus) cial interest was a population persisting in E. V. (Madsen and Shne, unpubl. data). The above Spence Reservoir, constructed in 1969. Data ob- studies illustrate the importance of environmen- tained from the Spence Reservoir population tal variables on snake spatial ecology in natural may be applied to the future management of the systems. The present study deals with a popu- Ivie Reservoir population. lation of Concho water snakes in an artificial en-

The central and south American anomalepid snakes of the genus Liotyphlops

The essential characters of the anomalepid snake genus Liotyphlops are found in its osteology, scale rows, numbers of dorsals, size, and head scale arrangements. The twelve currently recognized species of Liotyphlops are reduced to five through the analyses of variation of all available specimens in the Genus. Liotyphlops caracasensis, L. cucutae, L. guentheri, L. incertus, L. metae, L. petersi, and L. rowani, are placed in the synonomy of other species. One currently recognized synonym, L. beui, is removed from synonomy and recognized as a separate species. A new species is described from the Rio Magdalena basin of Colombia, and one individual from Brazil represents an apparent new species, but is not formally described in this paper. Other species of Liotyphlops recognized by us areL. albirostris, L. anops, L. schubarti, L. ternetzii, and L. wilderi. Variation in lateral head scale arrangements is documented for a large series of L. albirostris from Panama. Head scale variations, variations in numbers of scale rows about the body, and absence ofan unified method of labeling head scales has produced an excessive number of synonyms for the species of the genus. A new method for labeling lateral head scales of Liotyphlops is proposed, the entire distribution ofthe genus is clarified, and a key to the species is presented.

Freshwater Turtle Conservation in Texas: Harvest Effects and Efficacy of the Current Management Regime

ABSTRACT The collapse of Asian turtle populations led to the creation of a worldwide freshwater turtle market in the 1990s. Texas is one of several states in the United States that has capitalized on this market. The Texas Parks and Wildlife Department (TPWD) recently instituted regulations designed to protect turtles from commercial harvest in public waters. Two counties in the Lower Rio Grande Valley (LRGV) accounted for 66.1% of known wild turtle harvest in 1999, with no reported harvest in subsequent years. We sampled 60 sites in the LRGV to determine if we could detect harvest effects. We also investigated the potential for sustainable harvest under the new harvest guidelines using source-sink dynamics implemented in a Geographic Information System (GIS) approach. We detected differences congruent with harvest effects for red-eared sliders (Trachemys scripta) and Texas spiny softshells (Apalone spinifera). Based on a GIS analysis of water bodies throughout the entire state, we estimated that only 2.2% of water bodies are protected under the current commercial harvest regulations. We determined source water bodies could supply 30.5% of sink water bodies in the LRGV, and we concluded that long-term sustainable turtle harvest is unlikely under the current management regime due to the intensity of commercial harvests, the low number of protected water bodies, and non-robust or non-interactive protected populations. One solution to this would be modification of the regulations to include season and bag limits, a management strategy currently implemented in various forms by 14 states in the eastern half of the United States.

Diet and Feeding Behavior of Teiid Lizards from Trans-Pecos, Texas

Diet and feeding behavior of six species of Cnemidophorus occurring in Trans-Pecos Texas were studied over a three-year period. Comparative food data revealed that similar food items were utilized by all six species, but minor differences did occur that could be significant during adverse times. A dramatic shift in items consumed was documented for Cnemidophorus gularis as the activity season of 1968 progressed from the dry season into the wet season. Foraging behavior among sympatric species often represented a difference in methods of obtaining food which allowed species to exploit items, which although of the same general category, represented distinct differences in prey. A 3-year study was conducted on sympatric species of teiid lizards (Cnemidophorus) in the Trans-Pecos Region of Texas from June 1968 to August 1970. The study compared various aspects of competition and niche relationships in an effort to determine what factors are operating to preserve or break down species integrity within the genus. Natural hybridization between species of Cnemidophorus have been well documented (Wright and Lowe, 1967a) with the result sometimes giving rise to all-female parthenogenetic populations (Lowe and Wright, 1966; Wright and Lowe, 1967b). Part of the study involved dietary habits, including feeding behavior of sympatric species. Previous field studies indicate that two and often as many as four sympatric species of Cnemidophorus occur in the Trans-Pecos Region of Texas (Milstead, 1957, 1965; Degenhardt, 1966; Duellman and Zweifel, 1962). Milstead (1957, 1965) reported on the diet of three species of Cnemidophorus in the Black Gap area of Brewster County, Texas, and Medica (1967) compared the diet of four sympatric species of Cnemidophorus near Las Cruces, New Mexico. Two species, C. tigris marmoratus and C. inornatus heptagrammus, were present in both 1 Contribution No. 10058, of the Texas Agricultural Experiment Station.

Population Dynamics of the Concho Water Snake in Rivers and Reservoirs

Abstract The Concho Water Snake (Nerodia harteri paucimaculata) is confined to the Concho–Colorado River valley of central Texas, thereby occupying one of the smallest geographic ranges of any North American snake. In 1986, N. h. paucimaculata was designated as a federally threatened species, in large part because of reservoir projects that were perceived to adversely affect the amount of habitat available to the snake. During a ten-year period (1987–1996), we conducted capture–recapture field studies to assess dynamics of five subpopulations of snakes in both natural (river) and man-made (reservoir) habitats. Because of differential sampling of subpopulations, we present separate results for all five subpopulations combined (including large reservoirs) and three of the five subpopulations (excluding large reservoirs). We used multistate capture–recapture models to deal with stochastic transitions between pre-reproductive and reproductive size classes and to allow for the possibility of different survival and capture probabilities for the two classes. We also estimated both the finite rate of increase (λ) for a deterministic, stage-based, female-only matrix model using the average litter size, and the average rate of adult population change, λ ˆ, which describes changes in numbers of adult snakes, using a direct capture–recapture approach to estimation. Average annual adult survival was about 0.23 and similar for males and females. Average annual survival for subadults was about 0.14. The parameter estimates from the stage-based projection matrix analysis all yielded asymptotic values of λ < 1, suggesting populations that are not viable. However, the direct estimates of average adult λ for the three subpopulations excluding major reservoirs were λ ˆ  =  1.26, SE ˆ(λ ˆ)  =  0.18 and λ ˆ  =  0.99, SE ˆ(λ ˆ)  =  0.79, based on two different models. Thus, the direct estimation approach did not provide strong evidence of population declines of the riverine subpopulations, but the estimates are characterized by substantial uncertainty.

Geographic Variation in the Kentropyx calcarata Species Group (Sauria: Teiidae): A Possible Example of Morphological Character Displacement

Morphological variation of the South American lizard genus Kentropyxis discussed, with particular emphasis on the Amazonian distributed calcarata species group. Ecological and zoogeographical data are analyzed. Analysis of geographic variation of meristic characters, in con- junction with color and striping pattern variation, supports the recognition of three Amazonian species of Kentropyx with small dorsal scales. A dramatic morphological change is noted for Ken- tropyx calcarata, and it is suggested that the morphological divergence might be an example of character displacement.

A New Subspecies of the Iguanid Lizard, Sceloporus grammicus, from Northeastern Mexico, with Comments on its Evolutionary Implications and the Status of S. g. disparilis.

Sceloporus grammicus tamaulipensis is described from the isolated Sierra de Tamaulipas mountain range in southern Tamaulipas, Mexico, where it is apparently restricted to oak and pine-oak habitats of high elevations. It is distinguished from other adjacent races of S. grammicus by its larger scales and, consequently, a much lower number of dorsal scales, and to a lesser extent, scales around mid-body. Males of S. g. tamaulipensis are separated from males of S. g. grammicus, some of which have low numbers of dorsals, by ventral color patterns. This new race is also distinct at two allozyme loci (esterase-1, IDH). Morphometric, color pattern, and chromosome data suggest that S. g. tamaulipensis is most closely related to S. grammicus populations inhabiting the Sierra San Carlos and lowland thorn scrub habitats of northern Tamauli- pas and southern Texas. Sceloporus grammicus disparilis is not clearly differentiated from S. g. microlepidotus and is placed in synonymy with it.