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].