Abstract
Consequences of human actions like global warming, spread of exotic species or resource consumption are pushing species to extinction. Even species considered to be at low extinction risk often show signs of local declines. Here, we evaluate the impact of eucalypt plantations, the best-known exotic tree species worldwide and its interaction with temperature and predators on amphibian development, growth, antipredator responses and physiology. For this purpose, we applied a fully factorial experiment crossing two types of leaf litter (native oak or eucalypt), two temperatures (15 and 20°C) and presence/absence of native predators. We found that leachates of eucalypt leaf litter reduced amphibian development and growth, compromised their antipredator responses and altered their metabolic rate. Increased temperature itself also posed serious alterations on development, growth, antioxidant ability and the immune status of tadpoles. However, the combined effects of eucalypt leaf litter and increased temperature were additive, not synergistic. Therefore, we show that non-lethal levels of a globally spread disruptor such as leachates from eucalypt leaf litter can seriously impact the life history and physiology of native amphibian populations. This study highlights the need to evaluate the status of wild populations exposed to human activities even if not at an obvious immediate risk of extinction, based on reliable stress markers, in order to anticipate demographic declines that may be hard to reverse once started. Replacing eucalypt plantations with native trees in protected areas would help improving the health of local amphibian larvae. In zones of economic interest, we would recommend providing patches of native vegetation around ponds and removing eucalypt leaf litter from pond basins during their dry phase.
Highlights
Human activities over the last three centuries have caused grave perturbations worldwide resulting in temperature increase, desertification, forest plantations, urbanization and diminished water resources (Brook et al, 2008; Eisenhauer et al, 2012; Haddeland et al, 2014)
We found that leachates of eucalypt leaf litter reduced amphibian development and growth, compromised their antipredator responses and altered their metabolic rate
We measured the activity of four antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR)
Summary
Human activities over the last three centuries have caused grave perturbations worldwide resulting in temperature increase, desertification, forest plantations, urbanization and diminished water resources (Brook et al, 2008; Eisenhauer et al, 2012; Haddeland et al, 2014). Such transformations have pushed so many species to the brink of extinction that they can be considered to be causing the sixth mass extinction (Leakey and Lewin, 1996; Ceballos et al, 2017). In response to these changes, local species with high mobility can migrate to more suitable habitats, but species with high phylopatry or little vagility will necessarily rely on plastic adjustments of their phenotype, like behavioral shifts or physiological adjustments to respond to the environmental modifications (Scheiner, 2016; Edelaar et al, 2017)
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