Eggs for breakfast: The demographic consequences of cannibalism and harsh environments

Background/Question/Methods

Resource quality can shape population dynamics through multiple pathways. At the population level, core demographic parameters such as births, deaths, and transitions between life stages change based on the quality of the resource environment. While modeling methods built around these parameters have been used for decades to understand stage-structured population growth, more work is needed to understand the biological underpinnings (e.g., specific traits) of life history transitions, particularly across environments. Separately, traits that underlie these life history transitions have been measured in controlled experiments under different treatments, but studies rarely connect those traits to their net effect on population dynamics. However, in doing so, we might identify the emergence of multiple pathways to the same overall demographic parameters via differentially interacting traits across environments. Here, we combine both approaches: examining how and why resource environments affect behavioral traits that mediate transitions between life stages (e.g., cannibalism), and measuring the cascading effect of trait differences on stage-structured population dynamics of the flour beetle Tribolium confusum across eight resource environments varying in quality and toxicity. We then use these data to build a Larvae-Pupae-Adult model to further explore the consequences of varying fecundity, mortality, and cannibalism across the different environments.

Results/Conclusions

We found that the stage-structured population dynamics of Tribolium confusum differ substantially across resource environments of varying quality and toxicity, but for different reasons in each environment. Harsher flour mixtures resulted in higher extinction and lower overall population growth rates than more favorable flours (F = 4.7, p < .001). The abundance of each life stage (larva, pupa, or adult) at any given time was also heavily influenced by the flour environment (𝜒2 = 144.3, p < .001). Preliminary results from our Larvae-Pupae-Adult model indicate that fecundity, juvenile mortality, and which life stage is the greatest victim or perpetrator of cannibalism all depend strongly on the resource environment. Cannibalism in particular plays an important role in structuring population dynamics in harsh resource environments by inflating survival of the cannibalizing stage and thus maintaining population growth. This study provides early insight into how the traits of individuals (especially behavioral ones; e.g., cannibalism) can scale up to affect population dynamics in stage-structured systems, in different ways depending on the environmental context.