One of the 100 worst world invaders 34 is a red-eared slider ( Trachemys scripta elegans), which is also among the most widespread animal species outside its native range 35, 36. In others, no such responses have been documented 32, 33. Some species innately detect and elicit adaptive responses to stimuli of novel predators in the absence of a common evolutionary history 29, 30, 31. Tadpoles of various frog species respond differently to novel predators. For example, the relatively early seasonal appearance (or accelerated developmental rate) of a prey species may decrease its predation risk early in life, but increase the negative effects of competition with its former predator later in life 28. The fitness consequences of phenological shifts that appear early in the ontogeny of a species can also be fundamentally different from the effects observed at later ontogenetic stages. Specifically, predation during early life-history stages, when organisms are particularly susceptible to both biotic and abiotic factors, is likely to have pervasive effects on community development 27. These responses can, inter alia, consist of changes in body morphology 18, 19, behaviour 20, or timing of life-history switch points, such as hatching 21, 22, 23 or metamorphosis 24, 25, 26. In addition to these predators causing direct mortality, current theoretical and empirical studies of trophic cascades suggest that the indirect effect of the "landscape of fear" created by predators may be more important than direct killing 13, 14, 15, 16.Īmphibians are a particularly good model for studying morphological, physiological, and behavioural responses to changes in community composition 17. Globally, many native communities are currently increasingly forced to face new alien predators 10, which, in extreme cases, can lead to the extinction of whole prey populations 11, 12. Any change in species composition can have consequences on interacting species, both within and among trophic levels 3, 4, 5, the result of which depends on the timing of presence/activity of individual species 6, 7, 8, 9. The coexistence of species in a given community depends on the set of species involved 1, 2. In conclusion, the predator had the effect on metamorphosis traits only if it was present in the early development of tadpoles. The presence of a predator in late tadpole development influenced neither the time to metamorphosis nor size/body mass at metamorphosis. However, these growth rates did not exceed the growth rates of equally sized tadpoles in the other treatments and therefore were not sufficient to compensate for the growth slowdown in the first part of development. After the removal of the predator, growth accelerated above the level measured under the conditions of both the late predator and no predator. The early presence of a predator conspicuously reduced the growth increments of the tadpoles at early development. We found that the tadpoles had a longer larval period and were smaller in size at metamorphosis and lower in body mass when the predator was present in early development than when the tadpoles developed without a predator. In this study, we examine the dynamics of the ontogeny of common frog ( Rana temporaria) tadpoles under different time patterns of an alien predator-the red-eared slider ( Trachemys scripta elegans) presence. Many native communities are increasingly forced to face both direct and indirect pressures from new alien predators, which, in extreme cases, can lead to the extinction of prey populations. The coexistence of species in a given community depends on the set of species involved and the timing of their interactions.
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