DO PHYLOGENETIC RELATIONSHIPS PREDICT ECOLOGICAL SIMILARITY?

A fundamental question in paleobiology is whether ecology is correlated with evolutionary history. This question is central to evaluating niche conservatism in the fossil record and has implications for understanding how diversity is partitioned throughout the Phanerozoic. Answering this big question requires first addressing the relationship between ecology and phylogeny within a well-resolved clade.

We focus on Strophomenida, an order of brachiopods that was abundant, diverse, geographically widespread, and geologically long ranging. We combine time-calibrated phylogenetic trees with genus occurrence data through time to determine how environmental preferences are distributed on a tree and evaluate support for models of ecological similarity. To do this, we calculated phylogenetic distance and ecological difference between species pairs for 83 taxa used in recent phylogenetic revisions of the order. Phylogenetic distance was calculated as the pairwise branch length between tips of the tree of an equal time calibration model. Ecological difference was calculated as the pairwise distance along gradients of water depth, carbonate, and latitudinal affinity.

Results show no relationship between environmental affinity and position within the phylogenetic tree, such that similarity between closely related genera is not greater than similarity between distantly related genera. Instead, long-lived groups preserved only a pruned subset of the initial ecological burst that occurred during the radiation of Strophomenida. This pattern reflects processes at the largest macroevolutionary and macroecological scales. For fossil groups, expected ecological and evolutionary patterns are scaled up beyond what is addressed by theories built from studying modern ecology. This hierarchical scaling is complex, but the combined phylogenetic and paleoecological methods used in this study demonstrate an avenue for understanding it. Expanding this approach to other groups will improve our understanding of how ecological and evolutionary processes are preserved at the large scales of the fossil record and is critical for future studies of Phanerozoic biodiversity.