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.