Josh B. Pierce

Landscape-level influences of terrestrial snake occupancy within the southeastern United States.

Habitat loss and degradation are thought to be the primary drivers of species extirpations, but for many species we have little information regarding specific habitats that influence occupancy. Snakes are of conservation concern throughout North America, but effective management and conservation are hindered by a lack of basic natural history information and the small number of large-scale studies designed to assess general population trends. To address this information gap, we compiled detection/nondetection data for 13 large terrestrial species from 449 traps located across the southeastern United States, and we characterized the land cover surrounding each trap at multiple spatial scales (250-, 500-, and 1000-m buffers). We used occupancy modeling, while accounting for heterogeneity in detection probability, to identify habitat variables that were influential in determining the presence of a particular species. We evaluated 12 competing models for each species, representing various hypotheses pertaining to important habitat features for terrestrial snakes. Overall, considerable interspecific variation existed in important habitat variables and relevant spatial scales. For example, kingsnakes (Lampropeltis getula) were negatively associated with evergreen forests, whereas Louisiana pinesnake (Pituophis ruthveni) occupancy increased with increasing coverage of this forest type. Some species were positively associated with grassland and scrub/shrub (e.g., Slowinskis cornsnake, Elaphe slowinskii) whereas others, (e.g., copperhead, Agkistrodon contortrix, and eastern diamond-backed rattlesnake, Crotalus adamanteus) were positively associated with forested habitats. Although the species that we studied may persist in varied landscapes other than those we identified as important, our data were collected in relatively undeveloped areas. Thus, our findings may be relevant when generating conservation plans or restoration goals. Maintaining or restoring landscapes that are most consistent with the ancestral habitat preferences of terrestrial snake assemblages will require a diverse habitat matrix over large spatial scales.

Snake co‐occurrence patterns are best explained by habitat and hypothesized effects of interspecific interactions

Snakes often occur in species-rich assemblages, and sympatry is thought to be facilitated primarily by low diet overlap, not interspecific interactions. We selected, a priori, three species pairs consisting of species that are morphologically and taxonomically similar and may therefore be likely to engage in interspecific, consumptive competition. We then examined a large-scale database of snake detection/nondetection data and used occupancy modelling to determine whether these species occur together more or less frequently than expected by chance while accounting for variation in detection probability among species and incorporating important habitat categories in the models. For some snakes, we obtained evidence that the probabilities that habitat patches are used are influenced by the presence of potentially competing congeneric species. Specifically, timber rattlesnakes (Crotalus horridus) were less likely than expected by chance to use areas that also contained eastern diamond-backed rattlesnakes (Crotalus adamanteus) when the proportion of evergreen forest was relatively high. Otherwise, they occurred together more often than expected by chance. Complex relationships were revealed between habitat use, detection probabilities and occupancy probabilities of North American racers (Coluber constrictor) and coachwhips (Coluber flagellum) that indicated the probability of competitive exclusion increased with increasing area of grassland habitat, although there was some model uncertainty. Cornsnakes (Pantherophis guttatus or Pantherophis slowinskii) and ratsnakes (Pantherophis alleghaniensis, Pantherophis spiloides, or Pantherophis obsoletus) exhibited differences in habitat selection, but we obtained no evidence that patterns of use for this species pair were influenced by current interspecific interactions. Overall, our results are consistent with the hypothesis that competitive interactions influence snake assemblage composition; the strength of these effects was affected by landscape-scale habitat features. Furthermore, we suggest that current interspecific interactions may influence snake occupancy, challenging the paradigm that contemporary patterns of snake co-occurrence are largely a function of diet partitioning that arose over evolutionary time.

Use of trees by the Texas ratsnake (Elaphe obsoleta) in eastern Texas

Abstract We present information on the use of trees by Elaphe obsoleta (Texas Ratsnake) in a mesic pine-hardwood forest in eastern Texas. Using radiotelemetry, seven snakes (3 females, 4 males) were relocated a total of 363 times from April 2004 to May 2005, resulting in 201 unique locations. Snakes selected trees containing cavities and used hardwoods and snags for a combined 95% of arboreal locations. Texas Ratsnake arboreal activity peaked during July and August, well after the peak of avian breeding activity, suggesting arboreal activity involves factors other than avian predation.

COPPERHEADS ARE COMMON WHEN KINGSNAKES ARE NOT: RELATIONSHIPS BETWEEN THE ABUNDANCES OF A PREDATOR AND ONE OF THEIR PREY

Abstract:  Common Kingsnakes (formerly known collectively as Lampropeltis getula) are experiencing localized declines throughout the southeastern United States. Because there have been limited studies to determine how snakes regulate prey populations, and because Kingsnake declines may result in ecosystem impacts, we evaluated the hypothesis that Kingsnakes regulate the abundance of one of their prey, the venomous Copperhead (Agkistrodon contortrix). We generated a database of captures of the two species across the southeastern United States and, while controlling for large-scale habitat preferences, identified a negative relationship between the relative abundance of Kingsnakes and the relative abundance of Copperheads. Our results are correlative but consistent with the hypothesis that Copperhead populations experience a release from predation pressure where Kingsnake abundances are low. We suggest that Kingsnake declines, which are occurring for unknown reasons, are having ecological effects in affected ecosystems. We further highlight the potential role that snakes play in influencing the population dynamics of their prey.

Resolving Questionable Records of Pituophis ruthveni (Louisiana Pinesnake)

Abstract Pituophis ruthveni (Louisiana Pinesnake) is considered one of the rarest snakes in North America. For that reason, P. ruthveni is not well represented in scientific collections, and each existing specimen is very important. Some museum records for the species are considered questionable or unverified, especially those that represent extralimital records or those from habitats not normally utilized by Louisiana Pinesnake. Clarifying these questionable Louisiana Pinesnake records will ultimately provide a better understanding of its historic and current distribution, which is necessary for listing decisions, critical-habitat designation, and overall conservation efforts for the species. To resolve this uncertainty, we performed a multivariate analysis using 13 morphological characters on 50 specimens representing 3 snake groups: (1) P. ruthveni (n = 23), (2) P. catenifer sayi (Bullsnake; n = 23), and (3) questionable or unverified snakes (n = 4). We included Bullsnake because they are sister to Louisiana Pinesnake genetically and also most morphologically similar. We identified all questionable records of Louisiana Pinesnake examined as Bullsnake. Blotch count, ventral-scale number, and scale-row number at mid-body were the most reliable characters for distinguishing between groups. These results have potential conservation implications for the species. The influence of these erroneous records could be substantial in future research and conservation of the species due to the relatively few known specimens of Louisiana Pinesnake. We recommend that the specimens we identified be annotated and considered erroneous records.

Winter movements of Louisiana pine snakes (Pituophis ruthveni) in Texas and Louisiana

Abstract Despite concerns that the Louisiana Pine Snake (Pituophis ruthveni) has been extirpated from large portions of its historic range, only a limited number of studies on their movement patterns have been published. Winter movement patterns are of particular interest since it has been hypothesized that impacts of management practices would be reduced during the winter. Using radiotelemetry, we determined winter movement patterns of Louisiana Pine Snakes (11 males, 8 females) in 5 study areas (2 in Louisiana and 3 in Texas). Movements during winter (November—February) were greatly curtailed compared to the remainder of the year; however, snakes occasionally undertook substantial movements. Relocations were typically within the snakes previous active-season home range, and movements were more frequent in the early portion of winter. All hibernation sites were within Bairds Pocket Gopher (Geomys breviceps) burrow systems at depths ranging from 13–25 cm. Louisiana Pine Snakes did not use communal hibernacula, nor did individual snakes return to previously used sites in successive years.