Ghost of habitat past: historic habitat affects the contemporary distribution of giant garter snakes in a modified landscape

Abstract

Historic habitat conditions can affect contemporary communities and populations, but most studies of historic habitat are based on the reduction in habitat extent or connectivity. Little is known about the effects of historic habitat on contemporary species distributions when historic habitat has been nearly completely removed, but species persist in a highly altered landscape. More than 93% of the historic wetlands in the Central Valley of California, USA, have been drained and converted to agricultural and other uses, but agricultural wetlands, such as rice and its supporting infrastructure of canals, allow some species to persist. Little is known about the distribution of giant garter snakes Thamnophis gigas, a rare aquatic snake species inhabiting this predominantly agricultural landscape, or the variables that affect where this species occurs. We used occupancy modeling to examine the distribution of giant garter snakes at the landscape scale in the Sacramento Valley (northern portion of the Central Valley) of California, with an emphasis on the relative strength of historic and contemporary variables (landscape-scale habitat, local microhabitat, vegetation composition and relative prey counts) for predicting giant garter snake occurrence. Proximity to historic marsh best explained variation in the probability of occurrence of giant garter snakes at the landscape scale, with greater probability of occurrence near historic marsh. We suspect that the importance of distance to historic marsh represents dispersal limitations of giant garter snakes. These results suggest that preserving and restoring areas near historic marsh, and minimizing activities that reduce the extent of marsh or marsh-like (e.g. rice agriculture, canal) habitats near historic marsh may be advantageous to giant garter snakes. bs_bs_banner Animal Conservation. Print

Integrating growth and capture–mark–recapture models reveals size‐dependent survival in an elusive species

“…Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016. Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016.…”

“…In addition to the relationship between survival and snake size, we also found survival of giant gartersnakes was positively related to the cover of emergent and floating vegetation. Radiotelemetry studies show that giant gartersnakes select areas with higher cover of emergent vegetation, and occupancy studies show that snakes primarily occur in or near areas that were historically tule marsh (Halstead et al 2014(Halstead et al , 2016. Thus, it is intuitive that snakes survive at a higher rate in habitats that have more emergent vegetation cover, which better replicate the tule marshes these snakes inhabited before widespread land use change.…”

Private Landowner Conservation Behavior Following Participation in Voluntary Incentive Programs: Recommendations to Facilitate Behavioral Persistence

“…If the system is less dynamic or if its dynamism is on longer time scales (e.g., fire regimes), the relatively short length of conservation contracts may not provide enough time to meet specific conservation goals. In addition, if target species are not highly mobile (e.g., small, terrestrial species such as giant garter snake [Thamnophis gigas; Halstead et al 2013]) and appropriate connectivity to existing habitat does not exist, these species may have a harder time taking advantage of short-term habitat. Even worse, short-term habitat could become an ecological trap (Hale & Swearer 2016) if individuals settle in habitat that disappears as land reverts, rather than persists, when payments end.…”

Better late than never: a synthesis of strategic land retirement and restoration in California

“…We identified four flagship studies that best captured the evidence and approaches to use data at these scales. Field surveys of animal occurrence frequencies and percentage cover of vegetation types have been used in factor analysis to assess whether distance to historic preferred vegetation type significantly predicted probability of occurrence (Halstead et al 2014). The approaches included aggregated historic vegetation maps, proxy vegetation studies, historic range maps, and survey records to explore species-centric habitat assessments.…”

“…Agricultural and retired lands with former land use histories were also included in the vegetation maps. Field surveys of animal occurrence frequencies and percentage cover of vegetation types have been used in factor analysis to assess whether distance to historic preferred vegetation type significantly predicted probability of occurrence (Halstead et al 2014). In this instance, increasing distances from historic habitat that included preferred vegetation decreased the likelihood of occupancy.…”