Biodiversity loss and the simplification of trophic webs: Lessons from cephalopods in deep time

Anthropogenic global change and environmental degradation lead to not only declines in biodiversity but also the simplification of trophic webs and fundamental changes in biotic interactions as taxa are removed from ecosystems. These changes are currently playing out over time scales of decades and centuries. Still, it would be instructional to understand the relationships between biotic interactions, diversity, and environmental change through deep time. Here, focusing on cephalopods, we quantify the relationships between antagonistic interactions and estimates of diversity, origination rates, and extinction rates. We have compiled a database of antagonistic biotic interactions preserved on fossil cephalopods composed of 279 species occurrences and 148,846 specimens ranging in age from Silurian to Quaternary. Predation occurrences were sparse in the Paleozoic, with peaks in the Jurassic and Cretaceous. We constructed a Generalized Linear Model comparing predation frequency and parasitism prevalence (for samples whose n ≥ 10) to mean standing genus diversity and three-timer origination and extinction rates using data from the Paleobiology Database and the Shareholder Quorum Subsampling methodology available on the FossilWorks website. A significant positive relationship exists between the frequency/prevalence of antagonistic interactions and mean standing diversity. Origination and extinction rates both have significant negative relationships with antagonistic interactions with much higher coefficients than mean standing diversity. We interpret this to mean that the intensity of antagonistic biotic interactions is higher when diversity is elevated but, more importantly, stable. We think this reflects that many of these interactions are obligate and taxon-specific. Ongoing work will include proxy data for temperature and CO2 concentration. As with modern ecosystems, we see evidence for links between diversity loss and the simplification of trophic webs in deep time.