Phenotypic plasticity increases exposure to extreme climatic events that reduce individual fitness

Abstract

Climate models, and empirical observations, suggest that anthropogenic climate change is leading to changes in the occurrence and severity of extreme climatic events (ECEs). Effects of changes in mean climate on phenology, movement, and demography in animal and plant populations are well documented. In contrast, work exploring the impacts of ECEs on natural populations is less common, at least partially due to the challenges of obtaining sufficient data to study such rare events. Here, we assess the effect of changes in ECE patterns in a long-term study of great tits, near Oxford, over a 56-year period between 1965 and 2020. We document marked changes in the frequency of temperature ECEs, with cold ECEs being twice as frequent in the 1960s than at present, and hot ECEs being ~three times more frequent between 2010 and 2020 than in the 1960s. While the effect of single ECEs was generally quite small, we show that increased exposure to ECEs often reduces reproductive output, and that in some cases the effect of different types of ECE is synergistic. We further show that long-term temporal changes in phenology, resulting from phenotypic plasticity, lead to an elevated risk of exposure to low temperature ECEs early in reproduction, and hence suggest that changes in ECE exposure may act as a cost of plasticity. Overall, our analyses reveal a complex set of risks of exposure and effects as ECE patterns change and highlight the importance of considering responses to changes in both mean climate and extreme events. Patterns in exposure and effects of ECEs on natural populations remain underexplored and continued work will be vital to establish the impacts of ECEs on populations in a changing climate.

Keywords: Wytham woods; extreme climatic event; great tit; laying date; rainfall; reproductive success; temperature.

FIGURE 1

Fitted values for change in the number of hot (yellow) and cold (blue) extreme climatic events experienced by great tits between 1 April and 30 June, for Wytham, near Oxford UK, between 1965 and 2020 (N = 56 years). Whilst the number of cold extreme climatic events (ECEs) over the breeding season (April–June) has decreased over time, the number of hot ECEs in the same period has increased.

FIGURE 2

Shown are temporal trends in the probability of exposure of great tits to hot extreme climatic events (ECEs) across different periods of the breeding cycle (N = 12,219 breeding attempts). Grey bars correspond to the proportion of birds in each year that did (top) or did not (bottom) encounter a hot ECE. Coloured lines represent temporal trends before laying date was accounted for in the model, whilst grey lines correspond to model predictions when individual laying dates were included as fixed effect.

FIGURE 3

Shown are temporal trends in the probability of exposure of great tits to cold extreme climatic events (ECEs) across different periods of the breeding cycle (N = 12,219 breeding attempts). Grey bars correspond to the proportion of birds in each year that did (top) or did not (bottom) encounter a cold ECE. Coloured lines represent temporal trends before laying date was accounted for in the model, whilst grey lines correspond to model predictions when individual laying dates were included as fixed effect.

FIGURE 4

The proportion of great tit eggs that hatched declined as (a) the number of cold extreme climatic events (ECEs) and (b) the number of high rainfall ECEs increased (N = 11,339 breeding attempts). Shown are model predictions and associated 95% credible intervals.

FIGURE 5

(a) The probability of great tit pairs fledging at least one chick declined as the number of cold extreme climatic events (ECEs) experienced from hatching to Day 7 post‐hatch increased. (b) In contrast, pairs were more likely to fledged at least one chick if they experienced multiple hot ECEs during the period of peak food requirement (Days 8–15 post‐hatch) (N = 11,264 breeding attempts). Shown are model predictions and associated credible intervals.

FIGURE 6

The proportion of great tit chicks that successfully survived to fledging declined as the number of cold extreme climatic events (ECEs) in the first week post‐hatching increased. In contrast, experiencing multiple hot ECEs during the period of peak chick food requirements (Days 8–15 post‐hatch) was associated with higher fledging success (N = 11,264 breeding attempts). Shown are model predictions and associated credible intervals.

FIGURE 7

Encountering both a cold/hot extreme climatic event (ECE) and a high rainfall ECE during incubation had a larger negative impact on hatching success than encountering either a temperature ECE or a high rainfall ECE in isolation (N = 11,339 breeding attempts). Shown are model predictions and associated credible intervals.

FIGURE 8

Encountering high rainfall extreme climatic events (ECEs) was beneficial to fledging success when combined with a cold ECE between days 16 and 21 (N = 11,264 breeding attempts). Shown are model predictions and associated credible intervals.