Investigating Predation in the Fossil Record: Modern Analogs

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Virginia Tech

Predation is considered a powerful ecological force influencing community structure, diversity, and abundance. Paleoecology offers a unique perspective, allowing us to examine ecological processes such as predation over evolutionary timescales. The three studies summarized below include two case studies testing the role of predation in evolution and one method-oriented project, which explores new tools with which to examine predator-prey interactions in the fossil record. Considering the importance of community interactions in the current global biodiversity crisis, understanding ecological and evolutionary dimensions of predation is critical to conservation biology and ecology, as predators are thought to play a vital role in maintaining ecosystem health and biodiversity.

Predation has been dismissed as a causal mechanism for some major prey groups. For example, the evolutionary decline and cryptic or antitropical distribution of brachiopods is often explained as due to the potentially low energetic value and suspected non-palatability or toxicity of brachiopod tissues. Here we demonstrate that multiple invertebrate marine predators (crustaceans, echinoderms, and gastropods) are willing and able to consume brachiopods, and that predation pressure on the living brachiopod population may be consequential. Examination of the fossil record is consistent with this interpretation: evidence for drilling and repair of brachiopod shells is found throughout the fossil record in multiple orders. This suggests that although brachiopods may be unwanted prey in the presence of energetically more desirable targets, they do appear to be edible and are subject to intense predator-prey interactions.

Limpets are important prey for some crab species, yet little is known about the role of durophagy in the evolution of the limpet shell. Feeding trials using three common species of Pacific Northwest limpets (Lottia digitalis, L. pelta and Tectura scutum) were conducted to assess how different shell morphologies affect mortality and handling time. We predicted that large size, shell ornament, and low-spires would result in either increased survivorship, and/or longer handling times. Contrary to our expectation that ridges resist predation, individuals with smooth morphologies experienced significantly lower mortality, as did those with low-spires. As species possessing high-spires and ridges typically occur high in the intertidal where predation risk due to crabs is relatively low, these morphologies are likely adaptions to physical factors such as thermal stress.

One of the major caveats of using gastropod drill holes to assess predator-prey interactions in both the modern and the ancient is the correct identification of drill holes of predatory origin. By examining known predatory drill holes using environmental scanning electron microscopy, we aim to refine the development of a novel technique for augmenting their identification, and to explore the relationship between predator body size, predatory radula dentition, and radular microrasping marks observed on the shells of prey organisms. Electron micrographs were used to measure the spacing of microrasping marks produced by the radula, and the intercusp spacing of the radula dentition. A relationship between predator body size and microrasping marks makes it possible to infer predator size from these microtraces in both modern and fossil specimens, augmenting our ability to examine predator-prey interactions throughout the history of this important ecological interaction.

Proxies for predation intensity such as predation traces or antipredatory morphologies provide an invaluable method to examine predation in both modern communities, and the fossil record. Our understanding of the importance of predation in regulating biodiversity and in evolution will continue to grow with the development of new methodologies, and a comprehensive understanding of predatory defenses.

Morphology, Toxicity, Predation Traces, Durophagy