The effects of phenological mismatches on demography

Abstract

Climate change is altering the phenology of species across the world, but what are the consequences of these phenological changes for the demography and population dynamics of species? Time-sensitive relationships, such as migration, breeding and predation, may be disrupted or altered, which may in turn alter the rates of reproduction and survival, leading some populations to decline and others to increase in abundance. However, finding evidence for disrupted relationships, or lack thereof, and their demographic effects, is difficult because the necessary detailed observational data are rare. Moreover, we do not know how sensitive species will generally be to phenological mismatches when they occur. Existing long-term studies provide preliminary data for analysing the phenology and demography of species in several locations. In many instances, though, observational protocols may need to be optimized to characterize timing-based multi-trophic interactions. As a basis for future research, we outline some of the key questions and approaches to improving our understanding of the relationships among phenology, demography and climate in a multi-trophic context. There are many challenges associated with this line of research, not the least of which is the need for detailed, long-term data on many organisms in a single system. However, we identify key questions that can be addressed with data that already exist and propose approaches that could guide future research.

Figure 1.

Examples illustrating differing degrees and types of phenological mismatch. The left panel (a–f) illustrates how the synchrony (or degree of overlap) between a focal species (solid line) and its environment (broken line) diminishes as the species' phenology advances. The distribution of suitable environmental conditions can be wide (a,b) or narrow (c,d). The distribution could also be asymmetrical (e,f). The curves could represent relationships between phenological phases of individuals or populations of the same or different species—e.g. flowering and pollinator activity, or predator and prey activity. The curves could also represent the relationship between an individual or population and appropriate abiotic conditions—e.g. leaf development and frost-free conditions, or tadpole development and water level. The right panel (g) illustrates how the synchrony between a species and its environment varies in response to increasing differences in the timing of activity of a species and its environment for the three cases shown in the left panel (a–f). Here, we measure synchrony as the area of overlap between the focal species and environment curves. The vertical line indicates the degree of synchrony when the focal species' phenology is advanced relative to its environment (b,d,f). The dash and dot pattern in each curve in (g) matches the environmental curve (left panel) that it represents—dashed (a,b), dotted (c,d), and dot-dash (e,f).

Figure 2.

Conceptual model of various levels of interaction that might be affected by phenological mismatch: (a) organism–abiotic environment, (b) within organism and intraspecific, (c) intraguild and (d) intertrophic. Arrows represent relationships among abiotic conditions and species at various trophic levels, relationships that depend on the phenology of the species involved.

Figure 3.

A schematic outline of how climate change may affect reproduction. Changes in the environment at the time of decision-making may affect the timing of reproduction via the response mechanism. For example, changes in temperature might affect the timing of breeding or flowering. However, changes in the environment at the time of selection (e.g. egg hatching or fruit maturation) will affect the fitness consequences of breeding at a particular date. Conditions at the time of decision-making may have historically provided reliable cues of conditions at the time of selection. Changes in climate may change the historical relationship and lead to maladaptive decisions. Adapted from Visser et al. (2004).