Abstract

Climate change and invasive species threaten many ecosystems, including surface freshwater systems. Increasing temperatures and reduced hydroperiod due to climate change may promote the persistence of invasive species and facilitate new invasions due to potentially higher tolerance to environmental stress in successful invaders. Amphibians demonstrate high levels of plasticity in life history characteristics, particularly those species which inhabit both ephemeral and permanent water bodies. We tested the influence of two projected effects of climate change (increased temperature and reduced hydroperiod) on Pacific chorus frog (Pseudacris regilla) tadpoles alone and in combination with the presence of tadpoles of a wide-spread invasive amphibian, the American bullfrog (Lithobates catesbeianus). Specifically, we explored the effects of projected climate change and invasion on survival, growth, mass at stage 42, and development rate of Pacific chorus frogs. Direct and indirect interactions between the invasive tadpole and the native tadpole were controlled via a cage treatment and were included to account for differences in presence of the bullfrog compared to competition for food resources and other direct effects. Overall, bullfrogs had larger negative effects on Pacific chorus frogs than climate conditions. Under future climate conditions, Pacific chorus frogs developed faster and emerged heavier. Pacific chorus frog tadpoles developing in the presence of American bullfrogs, regardless of cage treatment, emerged lighter. When future climate conditions and presence of invasive American bullfrog tadpoles were combined, tadpoles grew less. However, no interaction was detected between climate conditions and bullfrog presence for mass, suggesting that tadpoles allocated energy towards mass rather than length under the combined stress treatment. The maintenance of overall body condition (smaller but heavier metamorphs) when future climate conditions overlap with bullfrog presence suggests that Pacific chorus frogs may be partially compensating for the negative effects of bullfrogs via increased allocation of energy towards mass. Strong plasticity, as demonstrated by Pacific chorus frog larvae in our study, may allow species to match the demands of new environments, including under future climate change.

Highlights

  • Human impacts have dramatically altered many ecosystems, including surface freshwater habitats [1]

  • Four Pacific chorus frog tadpoles died before reaching stage 42

  • Overwintered bullfrogs may counterintuitively have a smaller effect on competitors than first year bullfrog tadpoles [43, 60], suggesting that larger negative effects of bullfrog tadpoles may be seen if the experiment were repeated with first year tadpoles of a more similar size to the Pacific chorus frog tadpoles in this experiment

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Summary

Introduction

Human impacts have dramatically altered many ecosystems, including surface freshwater habitats [1]. Freshwater systems are influenced by climate change in multiple ways, including increased rate of surface evaporation, reduced hydroperiods, alteration of chemical and biological processes, and increased temperatures [2]. Invasive species can demonstrate high levels of phenotypic plasticity and adaptation potential, allowing them to respond to environmental change and successfully invade new ranges [3]. Invasive species may have higher tolerance to environmental stress than native species [4, 5]. This plasticity and ability to tolerate changes in environmental conditions suggest that invasive species may flourish under future climate conditions. Climate change and invasive species can interact to negatively affect native species

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