Abstract
Constraints on evolutionary adaptation and range shifts mean that phenotypic plasticity, which includes physiological, developmental or behavioural responses to environmental conditions, could be an important mode of adaptation to a changing climate for many species with small insular populations. While there is evidence to suggest adaptive plasticity to climate in some island populations, little is known about this capacity in species that have experienced a severe population bottleneck. In a changing climate, plasticity in the timing of life-history events, such as in breeding phenology, is adaptive if timing is optimised in seasonal environments, although these processes are poorly understood for tropical species. Here, we quantify the effects of climate on the breeding phenology and success of the Mauritius kestrel (Falco punctatus), a tropical raptor whose extinction has been averted by conservation management. We show that the timing of egg-laying is advancing in response to warming, at rates similar to temperate bird populations. Individual females show plasticity to temperature, although there is limited variation among individual responses. We show that advances in breeding phenology are likely to be adaptive, as they track changes in a seasonal climate window of favourable conditions, defined by late winter-early spring temperatures and the onset of the summer rainy season. Our results provide a rare example of a small and bottlenecked insular population that has adjusted to recent climate change through phenotypic plasticity. Furthermore, seasonal climate windows and their dynamics may be widespread mechanisms through which tropical species are impacted by and respond to climate change.
Highlights
The vulnerability of species to climate change can be assessed through a framework of exposure, sensitivity and adaptive capacity (Williams et al 2008; Dawson et al 2011)
We carried out exploratory analyses to identify the presence of climate impacts on breeding phenology and success, and we investigated whether there have been any interannual trends in the timing of breeding
The results of our analyses, taken together, demonstrate three important observations: (1) that a tropical bird species shows phenological advances driven by plasticity primarily in response to warming temperatures, as has already been documented for many temperate species; (2) that this tropical bird species synchronises its breeding season with a seasonal climate window, defined by late winter-early spring temperatures and the onset of the rainy season (RS), and tracks changes in this window in an adaptive manner; and, (3) that phenotypic plasticity contributes to the adaptive capacity of a small insular population recovering from a severe population bottleneck
Summary
The vulnerability of species to climate change can be assessed through a framework of exposure, sensitivity and adaptive capacity (Williams et al 2008; Dawson et al 2011). Adaptive responses to a changing climate may involve physiological and behavioural (phenotypic) plasticity, spatial or elevational range shifts or evolutionary changes, without which local extirpation or complete extinction are increasingly likely (Williams et al 2008; Dawson et al 2011) and management interventions become necessary Island-endemic species are generally regarded as vulnerable to climate change. Their limited distributions increase population-level exposure to climate risks and limit the scope for dispersal and spatial shifts (Foden et al 2013). Small population size can limit genetic diversity and the potential for evolutionary adaptation to new pressures (Parmesan et al 2000), and adaptive capacity may be compromised in species that have experienced a population bottleneck (Nicotra et al 2015)
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