Evolutionary and demographic consequences of phenological mismatches

Abstract

Climate change has often led to unequal shifts in the seasonal timing (phenology) of interacting species, such as consumers and their resource, leading to phenological 'mismatches'. Mismatches occur when the time at which a consumer species's demands for a resource are high does not match with the period when this resource is abundant. Here, we review the evolutionary and population-level consequences of such mismatches and how these depend on other ecological factors, such as additional drivers of selection and density-dependent recruitment. This review puts the research on phenological mismatches into a conceptual framework, applies this framework beyond consumer-resource interactions and illustrates this framework using examples drawn from the vast body of literature on mismatches. Finally, we point out priority questions for research on this key impact of climate change.

Fig. 1

Definitions of mismatch and mistiming. (A) Mismatch occurs when the time in the annual cycle where resource demands of the consumer species are highest does not match with the period where this resource is most abundant. (B) Mistiming occurs when the phenology (of either the individual (dots) or the population (vertical line)) deviates from the date at which fitness peaks, which will then lead to directional selection for either earlier (as depicted here) or later consumer phenology. Individual (a) is well-timed with the fitness optimum, while individuals (b) and (c) are too late and hence mistimed.

Fig. 2

Optimal mismatches caused by multiple fitness components of phenology. Total fitness (black solid line) is the product of fitness determined by resource phenology (green solid line) and another fitness component (blue solid line). In (A) the later fitness optima of the blue fitness component, e.g. fledgling survival probability due to predation, leads to a later optimal fitness and hence an optimal mismatch (difference between green and black dashed vertical lines). In (B) also the shape of the blue fitness component, e.g. adult pre-breeding survival, leads not only to a later peak of total fitness but also to an asymmetric total fitness curve, which will shift the optimal phenotype to an even later date when the environment varies through time (black dotted line). The overall outcome is an optimal mismatch (difference between green and black dashed vertical lines).

Fig. 3

Relationships between mismatch and reproductive success at the individual and population level. The coloured lines depict fitness curves in relation to individual mismatch for three different scenarios of mismatch (green: too early, blue: well matched, red: too late) indicated by the three frequency distributions of individual mismatch. The dots on the fitness functions indicate population mean fitness for each scenario. In (A) the height of the fitness curves of three scenarios is similar. This means that population mean reproductive success is only a function of population mean mismatch: If the population is on average too early (frequency distribution of phenology in green) or too late (red) it has a reduced population mean reproductive success (cf. dots on fitness curves). In (B) the height of the fitness curves differ: It is lowest when the population is too early (green curve and green frequency distribution) and highest when the population is too late (red curve and red frequency distribution). This leads to an increase of population mean reproductive success with mismatch (cf. dots on fitness curves), because mean mismatch covaries positively with the height of the resource peak. Note that the units of mismatch and the relationship between population mean mismatch and the height of the fitness curve have been chosen arbitrarily (this works the other way around too, i.e. a negative covariance between mean mismatch and the height of the resource peak).

Fig. 4

Examples for mismatch affecting reproductive success: In common murres (Uria aalge, top left), great tits (Parus major, top right), caribou (Rangifer tarandus, bottom left) and roe deer (Capreolus capreolus, bottom right) mean breeding success is reduced in years with an increased population-level mismatch between breeding phenology and the phenology of the main food resource. Picture credits and licenses: Melissa McMasters CC-BY, Luc Viatour CC-BY-SA, Andreas Eichler CC-BY-SA, Alexandre Buisse CC-BY-SA (clockwise from top left).