Environmental change impact role of within-generational plasticity
Plasticity and population dynamics are known to impact the ability of populations to evolutionarily track a moving optimum[39,96]. While selection works to decrease the phenotypic lag, plasticity can also reduce the size of this lag[40] (but see [10]). However, this impact of plasticity on lag size is complex, for plasticity itself can evolve, has different forms depending on the life history strategies of the population[97,98], and can be considered at the level of genes, individuals, populations, or species[99,100]. Even within these levels, there is disagreement about how different environments alter the ability of plasticity to affect lag in populations of different size[100]. How we judge the efficacy of plasticity to affect population dynamics depends on assumptions about its inherent costs and limitations[101] and how they interact with the three environmental parameters.
Often plasticity is assumed to buffer decreases in population size due to increasing rates of environmental change, although it is increasingly clear that this relationship is context dependent[100]. A key implicit assumption in moving optimum theory is that plasticity incurs some energetic cost[48,102] which depends on the type of trait (e.g., morphology, phenology, physiology, behaviour) and the rate of environmental change. The cost of plasticity thus adjusts the critical limit of environmental change, producing a complex interaction between rate of environmental change and net benefit of plasticity[103,104].
Environmental variability also impacts the ability of plasticity to benefit population size and persistence. Although plasticity can mitigate the detrimental effects of environmental variability in some cases[105,106], individual-based simulations have shown that the magnitude of environmental fluctuations has surprisingly limited effects on population persistence[107]. The limitation of their results is in part because increased variation can decrease survival[108] without much effect on the amount of plasticity or amount of phenotypic lag.
Environmental temporal autocorrelation seems to have a clearer effect on the benefit of plasticity to population persistence than environmental variability. Both the theoretical and empirical literatures suggest that unreliable environmental cues, or low temporal autocorrelation, decrease the ability of plasticity to reduce extinction risk[101,109]. Here, we consider within-generational plasticity, but note that there is increasing interest in the evolution of plasticity over multiple generations[9]. More predictable fluctuations select for increased plasticity, suggesting that plasticity has a beneficial role for tracking moving optima[110].