The structure and dynamics of Pleistocene food-webs in Beringia: Using stable isotopes to inform ecological networks across the last glacial period

Background/Question/Methods

The effects of long-term climatic drivers on the structure and dynamics of megafaunal food-webs are poorly understood, primarily due to the time-scale on which these processes operate. In the Fairbanks, AK region of Beringia, a series of extinctions and species introductions coincided with increasing aridity and decreasing temperatures during the Full-Glacial, and decreasing aridity, increasing temperatures, and encroachment of boreal forests during the Post-Glacial. The impact of these changes on the structural properties of Beringian food-webs is unknown. Ratios of stable isotopes can be used to investigate both modern and paleontological food-webs, such that comparisons of trophic relationships across space and time can be made. Here we introduce a method by which isotopic data from predators and prey can be used to directly inform the strengths of interactions within food-webs, and investigate three temporally resolved mammalian communities that span the last glacial cycle (Pre-, Full-, and Post-Glacial) to assess changes in network structure over time. In addition, we used techniques from generalized modeling to quantify the dynamics of each Pleistocene system, thus enabling an assessment of the impact of each species on food-web stability across the last glacial cycle.

Results/Conclusions

Preliminary results of our analyses reveal that the occurrence of Bison is strongly stabilizing across the Pre-, Full-, and Post-Glacial time periods, whereas the local extinction of woodland muskox Symbos, in addition to the replacement of the nimravid cat Homotherium with the American lion Panthera resulted in a more stable food-web configuration during the Full-Glacial. Our analysis of network structure reveals that the Post-Glacial Beringian food-web was structurally more similar to modern African food-webs than the Pre- or Full-Glacial (lower nestedness and higher compartmentalization). In addition, the Post-Glacial food-web had a much higher proportion of asymmetrical network structures than the Pre- or Full-Glacial, particularly among strongly interacting species, suggesting that there was a greater potential for oscillatory dynamics than in previous time-periods. Our analysis of Beringian food-web structure and dynamics as a response to long-term climatic drivers may contribute to a more comprehensive understanding of modern megafaunal communities.