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The red-eared slider turtle (Trachemys scripta elegans; RES) is often considered one of the world’s most invasive species. Results from laboratory and mesocosm experiments suggest that introduced RES outcompete native turtles for key ecological resources, but such experiments can overestimate the strength of competition. We report on the first field experiment with a wild turtle community, involving introduced RES and a declining native species of conservation concern, the western pond turtle (Emys marmorata; WPT). Using a before/after experimental design, we show that after removing most of an introduced RES population, the remaining RES dramatically shifted their spatial basking distribution in a manner consistent with strong intraspecific competition. WPT also altered their spatial basking distribution after the RES removal, but in ways inconsistent with strong interspecific competition. However, we documented reduced levels of WPT basking post-removal, which may reflect a behavioral shift attributable to the lower density of the turtle community. WPT body condition also increased after we removed RES, consistent with either indirect or direct competition between WPT and RES and providing the first evidence that RES can compete with a native turtle in the wild. We conclude that the negative impacts on WPT basking by RES in natural contexts are more limited than suggested by experiments with captive turtles, although wild WPT do appear to compete for food with introduced RES. Our results highlight the importance of manipulative field experiments when studying biological invasions, and the potential value of RES removal as a management strategy for WPT.

Globally endangered ecosystems, such as ephemeral wetlands, are often critical habitat for multiple interacting imperilled species. To conserve this biodiversity, managers must consider both species‐specific resource requirements and mechanisms for endangered species coexistence under variable habitat conditions. We examined communities native to California playa pools, ephemeral wetlands that have declined by >90% from their historic extent. Specifically, we describe the diet of a federally Threatened amphibian (Ambystoma californiense), and characterise interactions between this amphibian and two federally Endangered macrocrustaceans (Branchinecta conservatio and Lepidurus packardi) across three rain years to understand how these imperilled species coexist. We examined the dietary preferences of A. californiense larvae, metamorphs, juveniles, and breeding adults, and determined how prey electivity by larval A. californiense differs between natural playa pools and human‐modified stock ponds. Within playa pools, both breeding adult and larval A. californiense preyed extensively on L. packardi, whereas fully terrestrial juveniles had relatively empty stomachs. We provide evidence for size‐moderated optimal foraging by larval A. californiense, and show that larval prey differed dramatically between playa pools and stock ponds. Additionally, an ontogenetic progression from smaller to larger prey gave the relatively large, endangered macrocrustaceans an early‐season temporal refuge, during which they reached maturity in all three rain years. Consistent with complex life cycle theory, our results suggest that ephemeral wetland habitat offers abundant food resources for A. californiense relative to terrestrial habitat. Our findings also suggest that diet flexibility facilitates the persistence of this imperilled amphibian in human‐modified stock ponds. Temporal offsets in prey maturation rates and ontogenetic shifts in predator diets are likely to facilitate coexistence among the focal endangered species. We highlight the importance of accounting for spatial and temporal variation in interspecific interactions when predicting the effects of environmental change on biodiversity, particularly in highly threatened ecosystems.

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

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Plastic pollution, and especially plastic ingestion by animals, is a serious global issue. This problem is well documented in marine systems, but it is relatively understudied in freshwater systems. For turtles, it is unknown how plastic ingestion compares between marine and non-marine species. We review the relevant turtle dietary literature, and find that plastic ingestion is reported for all 7 marine turtle species, but only 5 of 352 non-marine turtle species. In the last 10 years, despite marine turtles representing just 2% of all turtle species, almost 50% of relevant turtle dietary studies involved only marine turtles. These results suggest that the potential threat of plastic ingestion is poorly studied in non-marine turtles. We also examine plastic ingestion frequency in a freshwater turtle population, finding that 7.7% of 65 turtles had ingested plastic. However, plastic-resembling organic material would have inflated our frequency results up to 40% higher were it not for verification using Raman spectroscopy. Additionally, we showcase how non-native turtles can be used as a proxy for understanding the potential for plastic ingestion by co-occurring native turtles of conservation concern. We conclude with recommendations for how scientists studying non-marine turtles can improve the implementation, quality, and discoverability of plastic ingestion research.

The snake Mastigodryas dorsalis (Bocourt, 1890) is generally considered absent from Mexico, but a few sources indicate otherwise. Herein we resolve this issue by re-examining a historical specimen and by reporting new records for M. dorsalis in Chiapas, Mexico. These records extend the known distribution of the species 87 km northwest of the nearest pre-existing record in Guatemala. Additionally, based on these new records and an exhaustive literature review, we present an updated distribution for the species and revise its known elevational range to 300–2110 m. A complete Spanish translation of this paper is available in the Supplemental Data. Una traducción completa al español de este artículo está disponible en los Datos Suplementarios.