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Revisiting a Paradox of Increased Cannibalism Among Juvenile Wolf Spiders with an Individual-Based Model
thesisposted on 01.08.2021, 00:00 by Noah B Lemke
To resolve an observed paradox by Wagner & Wise (1996) where similar or increased rates of cannibalism were observed among juvenile wolf spiders (Lycosidae) despite an increase in habitat complexity and the presence of alternative prey, I developed a series of individual-based models within the modeling environment NetLogo to test several hypotheses that could potentially replicate the phenomenon. I calibrated my models with real-world spider data and scaled the dimensions of the simulations to match that of Wagner & Wise’s 1996 mesocosm experiment (0.35 m2). Instead of replicating their 2x2 factorial design, however, I modeled habitat complexity along a gradient of increasing leaf litter cover which captured potential non-linearities that may have been missed along this gradient. Failing to reproduce the paradox with the first set of mechanisms I tested, I adjusted the model to incorporate an additional range of cannibalistic propensities within the modeled spider population. Some spiders would starve before attacking conspecifics, others would attack conspecifics only if hungry, and another group would readily attack conspecifics without any physiological constraints. This trait was also plastic, meaning spiders which were normally reluctant to engage in cannibalism shifted their behavior to become more aggressive while within leaf litter. Following these adjustments, I successfully demonstrated multiple sets of circumstances under which the paradox could be replicated, namely when the spider population was initialized to be heterogenous regarding their affinity towards cannibalism, and when leaf litter induced a behavioral shift towards the most aggressive cannibalistic morph. Although my model may not replicate the exact set of circumstances that produced the original paradox, this research revealed several in which it could, increasing the likelihood that the pattern Wagner & Wise observed in their mesocosm study is a naturally occurring phenomenon. Additionally, because of NetLogo's ease of use in exploring speculative hypotheses, this research provides a scaffold for alternative theories to be proposed and tested. If future empirical studies can successfully demonstrate these patterns, then this might shift the paradigm of how ecologists envision “highly cannibalistic” species, leading population and community models to consider incorporating an innate propensity to cannibalize within their framework.