Influence of seasonality and gestation on habitat selection by northern Mexican gartersnakes (Thamnophis eques megalops)

PLOS ONE, Nov 2019

Species conservation requires a thorough understanding of habitat requirements. The northern Mexican gartersnake (Thamnophis eques megalops) was listed as threatened under the U.S. Endangered Species Act in 2014. Natural resource managers are interested in understanding the ecology of this subspecies to guide management decisions and to determine what features are necessary for habitat creation and restoration. Our objective was to identify habitat selection of northern Mexican gartersnakes in a highly managed, constructed wetland hatchery. We deployed transmitters on 42 individual gartersnakes and documented use of habitat types and selection of specific habitat features. Habitat selection was similar between males and females and varied seasonally. During the active season (March–October), gartersnakes primarily selected wetland edge habitat with abundant cover. Gestating females selected similar locations but with less dense cover. During the inactive season (November–February), gartersnakes selected upland habitats, including rocky slopes with abundant vegetation. These results of this study can help inform management of the subspecies, particularly in human-influenced habitats. Conservation of this subspecies should incorporate a landscape-level approach that includes abundant wetland edge habitat with a mosaic of dense cover for protection and sparsely vegetated areas for basking connected to terrestrial uplands for overwintering.

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Influence of seasonality and gestation on habitat selection by northern Mexican gartersnakes (Thamnophis eques megalops)

January Influence of seasonality and gestation on habitat selection by northern Mexican gartersnakes (Thamnophis eques megalops) Tiffany A. Sprague 0 1 Heather L. Bateman 0 1 0 College of Integrative Sciences and Arts, Arizona State University , Mesa, Arizona , United States of America 1 Editor: Christopher M. Somers, University of Regina , CANADA Species conservation requires a thorough understanding of habitat requirements. The northern Mexican gartersnake (Thamnophis eques megalops) was listed as threatened under the U.S. Endangered Species Act in 2014. Natural resource managers are interested in understanding the ecology of this subspecies to guide management decisions and to determine what features are necessary for habitat creation and restoration. Our objective was to identify habitat selection of northern Mexican gartersnakes in a highly managed, constructed wetland hatchery. We deployed transmitters on 42 individual gartersnakes and documented use of habitat types and selection of specific habitat features. Habitat selection was similar between males and females and varied seasonally. During the active season (March±October), gartersnakes primarily selected wetland edge habitat with abundant cover. Gestating females selected similar locations but with less dense cover. During the inactive season (November±February), gartersnakes selected upland habitats, including rocky slopes with abundant vegetation. These results of this study can help inform management of the subspecies, particularly in human-influenced habitats. Conservation of this subspecies should incorporate a landscape-level approach that includes abundant wetland edge habitat with a mosaic of dense cover for protection and sparsely vegetated areas for basking connected to terrestrial uplands for overwintering. - Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: Funding was provided by Arizona Game and Fish Department from the Heritage Fund, IIAPM I15001, and the CAMP Fund (Conservation and Mitigation Program) (to HLB), www.azgfd. com/wildlife/heritagefund/program/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Introduction One of the most important elements of species management and conservation is knowledge of habitat requirements [ 1,2 ]. Understanding habitat selection at multiple spatial scales is vital for effective species management [ 3,4 ]. Habitat selection in ectothermic animals can be driven by intrinsic factors, such as body size and reproductive condition [5±7], and extrinsic factors, such as distribution of resources, temperature, predators, and prey [8±10]. Selection of habitat features is not static because animals can alter selection based on daily or seasonal variation [ 11,12 ]. In snake species, behaviors such as hibernating, breeding, and foraging can strongly influence habitat selection [ 1,13,14 ]. Habitat modification and loss can restrict the ability of animal species to move about the landscape to preferentially select required resources [ 15,16 ]. Many species of snakes have experienced dramatic population declines because of habitat loss and degradation [ 17,18 ], including species that rely on wetland areas [ 13,19 ]. Rivers and wetlands around the world have been disrupted and fragmented, affecting the rich biodiversity that depends on them [20±22]. Many species of aquatic and semi-aquatic snakes have declined due to drought and human-caused impacts to their habitat [ 18,23,24 ]. In the semiarid southwestern United States, riparian areas are imperiled habitat [ 25,26 ] and occupy less than 3% of the total land area [27]. However, riparian areas provide a mosaic of productive habitats and support many species [ 19,28 ]. Numerous aquatic and semi-aquatic animal species have declined due to damming and diversion of surface water and pumping of groundwater [ 29,30 ]. One hallmark subspecies that has experienced such declines is the northern Mexican gartersnake (Thamnophis eques megalops; S1 Fig). Substantial portions of the historical range of the northern Mexican gartersnake have been dewatered, resulting in local extirpations [ 31,32 ]. Many sites where this gartersnake persists have been reduced in size or have become isolated [31±33]. Historically, the northern Mexican gartersnake ranged throughout much of central and southern Arizona, into southwestern New Mexico and Mexico, and may have occurred in California and Nevada along the Colorado River [32]. The subspecies now occurs at low densities and may be extirpated from as much as 90% of its historical range in Arizona and New Mexico [31±33]. The northern Mexican gartersnake is state-listed and federally listed as threatened [ 32,34,35 ]. The few studies on this subspecies have described home ranges and general habitat associations (second and third-order habitat selection based o (...truncated)


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Tiffany A. Sprague, Heather L. Bateman. Influence of seasonality and gestation on habitat selection by northern Mexican gartersnakes (Thamnophis eques megalops), PLOS ONE, 2018, Volume 13, Issue 1, DOI: 10.1371/journal.pone.0191829