Is one of your dogs more shy than the other? One of your cats more sociable? Have you ever noticed that your pets seem to have their own distinct personalities? Well, as it turns out, personalities go well beyond us humans and our pets. Research has revealed that individual behavioral differences are taxonomically ubiquitous: the vast majority of animal species exhibit some degree of among-individual behavioral variation. Even individual bacteria can differ in fundamental behavioral traits like activity level. Furthermore, and importantly, these individual-level behavioral differences commonly persist over time and across environmental situations. This combination of among-individual behavioral differences and the persistence of these differences within populations of non-human animals has been dubbed “animal personality”.
While personality has been established as widespread feature of animal populations, it remains unclear whether population and community ecologists should care about this variation. As population and community ecologists, we are mostly concerned with births and deaths because these are the processes that influence population persistence and community structure. On one hand, if personality has weak effects on births and deaths relative to other factors (e.g., climate, habitat change), then we probably don’t need to worry about it. But, if an individual’s personality alters how it interacts with other members of it’s population or other species and these effects feedback to influence its fitness, then quantifying personality and understanding its consequences might enhance our predictive capacity for ecological dynamics. In this latter situation, it would serve us well to get a better handle on the ecological effects of animal personality. Does an individual’s personality influence where it forages? It’s susceptibility to predation? How much it eats? It’s competitive interactions with other individuals? A major goal of our research is to explore such pathways. Because interactions have fitness consequences, our hypothesis is that personality effects should scale to affect population and community dynamics (Toscano et al. 2016).
One particular trait we study is boldness, defined as the behavioral reaction to a risky situation. Bold individuals should maintain their normal behaviors in the presence of risk. For example, bold individuals might feed at a higher rate than shy individuals in the presence of a predator (Toscano and Griffen 2014). Yet, there are consequences to such an action. For example, bold individuals might also be more susceptible to being eaten, producing a energy gain/mortality risk tradeoff (Toscano 2017). Our lab is currently exploring these hyotheses as well as others relating animal personality to the strength and outcomes of species interactions. We are particularly interested in making a direct link between animal personality traits and parameters in species interaction models that predict community dynamics.
Size- and stage-structured species interactions
Big fish eats little fish; right? Seems simple enough. While this is often the case (but don’t tell that to the parasites in the room), the story gets a bit more complex. Body size influences ecological interactions in myriad ways, and we’re just beginning to grasp the full extent of these effects.
Our lab is concerned with developmental change in a broad sense, which includes both continuous growth in size (think us humans) but also more abrupt transitions between different life-history stages (think about a caterpillar turning into a butterfly). The latter scenario is particularly interesting because juveniles totally remodel their morphology and behavior in response to the different selection pressures they will face as adults. Because of these different selection pressures, many species undergo ontogenetic niche shifts where their interactions with the abiotic environment and other organisms change dramatically as they develop.
A major focus of our lab is to understand how the effects of size- or stage-variation within populations, including ontogenetic niche shifts, extend to the community level. Our previous work has shown that size variation within intertidal crab populations dictates their top-down control of bivalve prey communities in oyster reefs, highlighting size diversity as a crucial but underappreciated component of biological diversity (Toscano and Griffen 2012). We also demonstrated that oyster reef habitat structure uniquely limits the feeding rates of large crabs, reducing their prey consumption below that of smaller individuals (Toscano and Griffen 2013). Such an interaction between predator size and habitat structure, likely widespread in nature, reverses the presumed positive relationship between predator size and feeding rate.
We are currently testing a relatively new body of theory that considers both maturation and reproduction as food-dependent processes. This means that both maturation and reproduction respond to changing food consumption (the more you eat, the more you grow and the more babies you make). This simple assumption, which is always upheld in natural systems, has some counterintuitive consequence for community dynamics. For example, we have shown that food-dependent maturation can drive alternative stable community states (Toscano et al. 2016) and causes predator extinction when predators are cannibalistic (Toscano et al. 2017). This body of work relies on the tight coupling of theory and experiments, where each research approach is used to inform and advance the other. We use freshwater zooplankton to test theory due to their fast generation times and small size, making them ideal for answering big questions at a manageable scale.