Conservation reliance of a threatened snake on rice agriculture

Abstract

Conservation-reliant species require perpetual management by humans to persist. But do species that persist largely in human-dominated landscapes actually require conditions maintained by humans? Because most extant populations of giant gartersnakes (Thamnophis gigas) inhabit the highly modified rice agricultural regions of the Sacramento Valley, we sought to evaluate whether giant gartersnakes are indeed a conservation-reliant species dependent on maintenance of rice agriculture and its infrastructure for their continued existence. Specifically, we examined the extent to which giant gartersnakes use rice fields themselves, and whether survival of adult giant gartersnakes was influenced by the amount of rice grown near their home ranges and daily movements. We found that although giant gartersnakes only use rice fields minimally and then only between mid-June and early September, their survival was lower when less rice agriculture was available near the areas they inhabited. Survival was particularly low in early spring, when giant gartersnakes emerge from brumation but rice fields are not yet flooded. The incongruity between the phenology of rice growing and giant gartersnake foraging requirements suggests that although giant gartersnakes are reliant on the rice agroecosystem, rice agriculture is likely suboptimal habitat for giant gartersnakes. Giant gartersnakes’ reliance on the rice agroecosystem challenges the notion of preservation-based conservation, but provides opportunities for win-win scenarios benefitting both rice farmers and giant gartersnakes. Our study highlights that in addition to land use, the timing of land management might be crucial for conservation-reliant species. Keywords: Agroecology, California, Giant gartersnake, Mortality, Survival, Thamnophis gigas