Environmental change impacts on population size and life history
Life history and population size impact both ecological dynamics and
evolutionary trajectories[76,77], In turn, population size is
inherently linked to adaptive potential, as larger populations have more
standing genetic variation available for natural selection, [38,78]
(see section 2). Thus, the importance of phenotypic plasticity in
adaptive evolution depends on changes in population size, which also
influences the likelihood of local extinctions[79–82]. Such impacts
of population size depend on life history; long-lived species can
persist longer at small population sizes than short-lived species, which
can collapse quickly[83,84].
Much evidence shows that higher rates of environmental change lead to
decreases in population size[85], suggesting that rates of local
extinction rates of many bird and mammal species will increase as the
rate of climate warming exceeds the rate of adaptive responses[86].
However, population size can increase in some species under higher rates
of environmental change. For instance, bird species adapted to drier
climates can utilize agricultural land and are predicted to persist in
and colonize into drier habitats under climate change[87].
Mechanistically, however, the explicit links between increasing rate of
environmental change and population dynamics remains largely unresolved.
The interplay between increasing environmental variability and
population size has now been intensively studied both theoretically and
empirically[88]. Despite the usual assumption that a more variable
environment is detrimental for populations, recent syntheses across
systems show that the effect of environmental variability is highly
context-dependent and can have positive as well as negative effects on
population growth rates[24,89]. Demographically-explicit theories
have made important progress in elucidating the mechanisms for why
increased environmental variability can have different influences on
population size[90]. The mechanisms that produce the disparities in
demographic responses to variable environments usually depend on
system-specific density-dependent effects, which influence transient dynamics of population trends[91].
Temporal autocorrelation in the environment has gained much attention in
population biology and climate change research[31,34]. Here too, the
emerging message is that autocorrelated environments can have
positive[92,93] or negative[93] impacts on population size and
extinction risk, depending on life history strategies[94], and
phylogenetic history[95]. For example, annual plants have lower
extinction risks when the environment is more positively temporally
autocorrelated compared to perennial plants[93]. Moreover, in some
cases, population size itself can become more variable through time
under positive environmental autocorrelations, thereby increasing
extinction risk[34].