Introduction
Research on among individual variation in behavior has increased rapidly
in recent years, offering a more nuanced perspective on how populations
are composed and may respond to the environment. Animal personality,
when individuals consistently differ from each other in the expression
of behavioral traits across time or contexts, has been frequently
observed across taxa (Dingemanse et al., 2003; Sih, Bell and Johnson,
2004; Réale et al., 2007; Bell, Hankison and Laskowski, 2009). However,
the average expression of any behavioral trait only partially reflects
the personality of the individual and it is also important to consider
how variable behavioral expression is within the individual (Nussey,
Wilson and Brommer, 2007; Dingemanse et al., 2010; Mathot et al., 2012).
Within individual variability in behavior can be directional, for
example, habituation to a novel environment (Brown, 2001; Allan, Bailey
and Hill, 2020), change in behavior appropriate to context, such as the
level of risk (Steinhoff et al., 2020), but also random or unpredictable
(Stamps, Briffa and Biro, 2012; O’Dea, Noble and Nakagawa, 2020).
Furthermore, recent research has shown that even the expression of
similar traits can have different underlying mechanism depending on the
context (Mouchet & Dingemanse, 2021).
Nevertheless, it is expected that among individual variation in behavior
has ecological consequences (Bolnick et al., 2003; Bolnick et al.,
2011). Individual trophic specialization and its connection to foraging
behavior is well known (Araújo, Bolnick and Layman, 2011; Bolnick et
al., 2003), but has been researched mostly independently from animal
personality. It is intuitively appealing that animal personality could
result in both consistent differences in diet and trophic niche breath.
For example, bold stickleback have been found to be less likely to alter
their foraging behavior across contexts (Ólafsdóttir & Magellan, 2016).
Boldness was found to affect multiple foraging decisions in deer mice,
but the effect of personality traits was also context dependent (Boone,
Brehm and Mortelliti, 2021). Correlations between animal personality and
trophic niche could have significant implications for ecosystems as many
current environmental impacts or stressor are expected to favor specific
behavioral types, for example, bolder fish are more likely to disperse
and form invasive populations (Cote et al., 2010; Myles-Gonzalez et al.,
2015), fishing may be more likely to remove bolder (Biro & Post, 2008)
and more sociable (Crespel et al., 2021) fish. Boldness has been shown
to correlate positively with juvenile survival in damselfish (McCormick,
Fakan and Allan, 2018).
Stable isotopes are a useful tool to retrospectively estimate ecological
niche as they reflect the diet and environment of the individual over
the past days to months and, by combining tissue types, can reflect
within individual variation in resource use (MacNeil, Skomal and Fisk,
2005, Gratton & Forbes, 2006). Measures of both behavior and stable
isotope values could therefore offer an important on the ecological
consequences of animal personality. The stable isotopes
δ13C and δ15N are commonly used in
conjunction to examine trophic niche variation within and between groups
(Post, 2002). δ13C reflects local primary production
and commonly differs along the axis of benthic – pelagic production and
δ15N is consistently enriched as it passes through the
food web allowing its use as a metric of trophic level (Post, 2002;
Cherel & Hobson, 2007). Studies combining laboratory measures of
personality and stable isotope estimates of trophic niche are not
common. Dhellemmes et al., (2021) found that exploratory behavior in
juvenile lemon sharks (measured in a controlled test) correlates to
δ13C values representing sheltered or unsheltered
foraging habitats but only when predators were abundant. A recent study
on red knots found that observations of foraging behavior correlated to
personality (exploratory behavior) but this was supported by stable
isotope values suggesting a long-term effect of personality (Ersoy et
al., 2021). Conversely, no effect was observed between dominance and
stable isotope values of crayfish across different contexts (Glon,
Larson and Pangle, 2016; Adey & Larson, 2020).
Much of animal personality research has been laboratory based and it is
now pressing to further examine the ecological or evolutionary relevance
of personality. However, laboratory measures of behavior are easily
applied and controlled, for example, allowing measures of plasticity
across controlled contexts and measures of subjects of known origin,
such as, individuals of known relatedness. Because of the convenience
and flexibility of laboratory measures it is valuable to understand how,
or if, they have relevance for ecological traits in the wild. For this
purpose, stable isotopes can be a useful as they retrospectively
represent trophic niche in the wild over timeframes that are often
unfeasible for direct observation in nature and can be as easily applied
to aquatic species when field observations are difficult.
My objective was to examine if behavioral traits measured in the
laboratory correlated to ecological niche in the wild, supporting that
behavioral variation among individuals could have ecological or
ecosystem consequences. For this aim we used a rapid behavioral assay to
assess latency to explore and activity of individually identifiable
threespine stickleback (Gasterosteus aculeatus ). We then assessed
if either individual intercept or slope for these traits, estimated
across three trials, correlated to ecological niche or temporal change
in ecological niche (as estimated by δ13C and
δ15N stable isotopes). We hypothesized that bolder and
more active individuals may have higher δ15N values,
reflecting higher trophic levels, and lower δ13C
values reflecting less benthic foraging. Moreover, we expected bolder
individuals to have less change in stable isotope niche over time,
indicative of more consistent and generalist foraging. Finally, we
expected that behavior would have only moderate effects on stable
isotope values.