CHANGES IN THE STRUCTURE AND ORGANIZATION OF MESOZOIC MARINE FOOD WEBS

The use of the fossil record to understand the role of biodiversity in ecosystem structure and functioning is imperative, as anthropogenic disturbances and climate change threaten biologic processes and are occurring at unprecedented rates. Here we compare three marine food webs from the M. Triassic (Anisian), M. Jurassic (Bathonian), and E. Cretaceous (Aptian) of the western Tethys to identify changes in marine food web structure across the Mesozoic, during an extended interval of biodiversification. Modularity and connectance were calculated for each food web, two metrics quantifying ecological network structure that are dependent on the density of interactions between organisms. Modules are groups of organisms more densely connected among themselves than to the rest of the network, forming subcommunities within the network, and connectance measures the density of interactions (the proportion of possible interactions that are realized) and is believed to increase as networks increase in size. It is unclear how an increase in modularity and connectance are associated with stability. The number of subcommunities decreased notably from the Anisian (33) to the Bathonian (12) and Aptian (9), and the strength of the division of the network into subcommunities increased from the Anisian (0.24) to the Bathonian and Aptian (0.32). This suggests that increasing proportions of generalist species may have led to a fusion of modules and a more cohesive network, reducing the number of modules. Increasing modularity may have resulted from an increase in the strength of interactions, i.e., greater predation pressure. Connectance was consistent from the Anisian (0.09) to the Bathonian (0.07) and Aptian (0.08). These changes in subcommunities suggest restructuring in trophic organization possibly associated with changes in energetics or predation intensity during the Mesozoic Marine Revolution. In modern food webs, human activities are causing a restructuring of trophic organization due to the predation pressures from activities such as over-fishing. A better understanding of changes in ancient food web structure and functioning can provide insight into how communities respond to and recover from disturbances and can be used to aid in present day conservation efforts.