Tadpole swimming near plant stem. Image credit: Alan Emery (CC0)
Biodiversity is declining, and many species may face extinction in the future. Some species are more vulnerable to human-driven threats than others, but limited resources make it impossible to assess the extinction risk of every species in detail. Certain traits, such as body size, are known to be associated with extinction risk, so understanding these relationships can help predict which species may be most threatened.
However, many animal species have complex life cycles. Frogs, beetles and butterflies, for example, undergo dramatic changes in body form, behaviour and habitat as they develop from larvae to adults. Yet conservation assessments focus almost exclusively on adult traits, largely overlooking the distinctive threats faced by younger life stages. This could lead to underestimating a species’ overall extinction risk.
Song et al. asked whether traits of both adults and larvae are associated with extinction risk and, if so, whether these relationships are consistent across life stages. This is important because if threats differ between stages, an adult-centred approach could overlook vulnerabilities earlier in life. For amphibians, for example, protecting adult habitats while neglecting the specific needs of tadpoles could lead to ineffective conservation strategies.
Studying nearly 300 Chinese amphibian species, Song et al. found that extinction risk was associated with traits from both adult and tadpole stages. Some associations were shared across life stages: larger body size was linked to higher extinction risk in both tadpoles and adults. They also identified stage-specific associations. Habitats used by tadpoles were related to extinction risk, whereas they did not find the same relationship for adult habitat.
Because most described animal species, including many insects, crustaceans and other invertebrates, have complex life cycles, comparing trait-threat relationships across life stages could be widely applicable. The findings of Song et al. highlight the importance of considering vulnerabilities at all stages of the life cycle when assessing extinction risk and developing conservation strategies.
To make conservation planning more effective, we need better data on the functional traits and ecological requirements of non-adult life stages, formal integration of information from multiple life stages into conservation assessments, and habitat protection that accounts for the needs of all life stages, particularly habitats that are critical for larvae.
