McKee A.M.,U.S. Geological Survey |
Spear S.F.,The Orianne Society |
Pierson T.W.,University of Georgia
Biological Conservation | Year: 2015
Isolation of environmental DNA (eDNA) is an increasingly common method for detecting presence and assessing relative abundance of rare or elusive species in aquatic systems via the isolation of DNA from environmental samples and the amplification of species-specific sequences using quantitative PCR (qPCR). Co-extracted substances that inhibit qPCR can lead to inaccurate results and subsequent misinterpretation about a species' status in the tested system. We tested three treatments (5-fold and 10-fold dilutions, and spin-column purification) for reducing qPCR inhibition from 21 partially and fully inhibited eDNA samples collected from coastal plain wetlands and mountain headwater streams in the southeastern USA. All treatments reduced the concentration of DNA in the samples. However, column purified samples retained the greatest sensitivity. For stream samples, all three treatments effectively reduced qPCR inhibition. However, for wetland samples, the 5-fold dilution was less effective than other treatments. Quantitative PCR results for column purified samples were more precise than the 5-fold and 10-fold dilutions by 2.2× and 3.7×, respectively. Column purified samples consistently underestimated qPCR-based DNA concentrations by approximately 25%, whereas the directional bias in qPCR-based DNA concentration estimates differed between stream and wetland samples for both dilution treatments. While the directional bias of qPCR-based DNA concentration estimates differed among treatments and locations, the magnitude of inaccuracy did not. Our results suggest that 10-fold dilution and column purification effectively reduce qPCR inhibition in mountain headwater stream and coastal plain wetland eDNA samples, and if applied to all samples in a study, column purification may provide the most accurate relative qPCR-based DNA concentrations estimates while retaining the greatest assay sensitivity. © 2014.
Rahman S.C.,Independent University, Bangladesh |
Rahman S.C.,Lawachara Snake Research and Conservation Project |
Rashid S.M.A.,Lawachara Snake Research and Conservation Project |
Rashid S.M.A.,Center for Advanced Research in Natural Resources and Management |
And 2 more authors.
Herpetological Journal | Year: 2013
During the last decades annual activity patterns of temperate snake species have received considerably more attention than those of tropical snakes. In this study, we document the monthly activity patterns of a species-rich assemblage of snakes from a tropical forest-plantation mosaic in Bangladesh based on specimens collected by a systematic road kill survey for 14 months, and relate them to the climatic characteristics of the study area with special reference to monsoon regimes. We recorded 503 Dead-On-Road (DOR) snakes, belonging to 30 different species, with a mean DOR/km rate of 0.247. Overall, snake activity was uneven throughout the year, being particularly intense during July, August and October, and significantly reduced in December, January and February. Five out of nine species with considerably robust sample sizes showed consistently uneven monthly activity patterns. Monsoon seasonality deeply influenced the phenology of several Asian-tropical snakes, with some species being active especially at the middle or end of the monsoon period while others are active throughout the monsoon period.
Steen D.A.,Joseph W. Jones Ecological Research Center |
Steen D.A.,Auburn University |
Steen D.A.,Virginia Polytechnic Institute and State University |
Mcclure C.J.W.,Auburn University |
And 10 more authors.
Journal of Animal Ecology | Year: 2014
Summary: 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. © 2013 British Ecological Society.
Rahman S.C.,Independent University, Bangladesh |
Reza A.A.,Delta State University |
Data R.,Independent University, Bangladesh |
Jenkins C.L.,The Orianne Society
Herpetological Journal | Year: 2014
Despite the greatest diversity of snakes being in the tropics, detailed ecological studies are rare, especially in tropical Asia. We studied the ecology of a coastal marine homalopsid (rear-fanged, aquatic snakes) assemblage in southeastern Bangladesh. Data were collected on community structure, resource partitioning (diet and habitat), body size and sexual size dimorphism. A total of 653 specimens belonging to three species were collected: Cerberus rynchops (81% of total capture), a medium-sized piscivorous snake, found to be the most abundant species in the study site followed by two crustacean eaters, Gerada prevostana (13%) and Fordonia leucobalia (6%). The three species were relatively similar in terms of body size but were inconsistent with each other both in terms of morphological patterns and demography characteristcs, with sex-rato being equal in two species but female-biased in G. prevostana. There was no apparent non-random resource partitioning along the microhabitat axis but a clear pattern of niche partitioning was observed along the food axis. Despite the very unusual evolutionary history of the Homalopsidae inside the group of the Colubroidea, our snake assemblage very closely resembled other communites of snakes worldwide.
Enge K.M.,Florida Fish And Wildlife Conservation Commission |
Stevenson D.J.,The Orianne Society |
Elliott M.J.,Nongame Conservation Section |
Bauder J.M.,The Orianne Society
Herpetological Conservation and Biology | Year: 2013
The Eastern Indigo Snake (Drymarchon couperi) historically occurred in southern Mississippi and Alabama, Georgia, and Florida. Old reports from South Carolina are not thought to be credible. Naturally occurring populations likely no longer occur in Mississippi and Alabama, and populations elsewhere are of conservation concern. However, there have been no large-scale efforts to determine the historical and current distributions of the eastern indigo snake across its entire range. Toward this end, we obtained records of eastern indigo snakes by: (1) searching databases, the literature, and U.S. museum collections; (2) soliciting sightings from qualified individuals via e-mail and questionnaires; and (3) conducting visual-encounter surveys in Georgia. In Southeastern and South-Central Georgia, we documented 379 recent (2001-2012) records from 29 counties and from 26 public or conservation lands (≥ 100 ha in area) in 18 counties. In Florida, we documented 595 recent (2001-2012) records from 46 counties and from 154 public or conservation lands ≥ 100 ha in area in 44 counties. The species still occurs throughout most of peninsular Florida except in urban areas and some agricultural regions, but recent records are scarce or absent in the panhandle and Florida Keys. habitat loss, degradation, and fragmentation probably have impacted eastern indigo snake populations over much of their range, and a severe decline of gopher Tortoise (Gopherus polyphemus) populations in the Florida panhandle may account for the scarcity of eastern indigo snakes in this region because tortoise burrows are important overwintering refugia. © 2013. Kevin Enge. All Rights Reserved.