Environmental variability affects flexibility in activity onset at large geographic scales

Timing is an essential component of the phenotype, influencing organism
fitness and fundamentally shaping ecological interactions. Although
variation in the timing of activity can be substantial, the degree to
which this variation stems from behavioral flexibility (within-individual
variation) vs. consistent behavioral differences (among-individual
variation) is poorly understood and represents a key knowledge gap as
these have different ecological and evolutionary implications. Whereas
flexibility in timing may be advantageous in novel circumstances,
individuals could also make mistakes. Alternatively, consistent
among-individual differences in timing may lead certain individuals to
exhibit maladaptive behavior when confronting novel conditions (e.g.,
light pollution or novel predators). We estimated activity onset from 1050
captures of 483 individual white-footed mice, Peromyscus leucopus, across
the upper Midwest, Northeast, Mid-Atlantic, and southern Appalachia
regions of the United States. In each locale, we quantified the total
phenotypic variation in activity onset and partitioned this into its
within- and among-individual components. We then examined whether mice at
locations experiencing more variable climate or residing in more
structurally variable habitats exhibited differences in within- or
among-individual variation in timing. We found that timing flexibility was
always greater than consistency, and individuals from populations at
cooler, drier sites with variable seasonal precipitation and temperature
were more flexible than mice at warmer, wetter sites with less seasonal
change in precipitation and temperature. Behavioral flexibility was not
significantly associated with habitat structure heterogeneity. Our results
reveal that most variation in timing across the range of this species
derives from within-individual variation.