• Changes in food web structure and functioning
  • Processes governing the distribution, paleoecology, and evolution of marine invertebrates
  • The fidelity of the fossil record
  • The application and development of quantitative paleontological methods

Global climate change and human activities continue to create an urgent need for effective conservation and management strategies, which require a thorough understanding of how and why ecosystems respond to extreme structural changes. Yet there are no precedents in human experience to guide us. The use of the fossil record to understand the fate of today’s ecosystems is imperative, as anthropogenic disturbances and climate change threaten all biologic processes, and are occurring at unprecedented rates, yielding shifting baselines that create a moving target for conservation scientists and resource managers. My research on marine invertebrate communities, therefore, includes two main themes: (1) taphonomic investigations assessing the quality of the fossil record and identifying the limits of its applicability to paleoecology and conservation, and (2) understanding processes driving ecosystem structure and functioning, and community response to perturbation.

Ordovician food webs across the Richmondian Invasion

Invasive species cause many extinctions today, but there is still a lot we don’t know about how new species can change the way an ecosystem works. This project uses the fossil record to look at what happened when new species arrived in ancient marine ecosystems. We ask questions about what happened after invasions in the past by making computer models of fossil food webs. We can then use what we learn to see what could happen in some similar invasions today. These fossil food web models will also help us understand the connection between the number of species in ecosystems, and how stable they are. This knowledge can then help us understand how and why ecosystems have changed over the last 500 million years.

Mesozoic marine food webs from the western Tethys

Increasing ecospace utilization, predation intensity, motility, infaunality, and disturbance suggest that ecological complexity has increased through geologic time as specialized morphologies and functions have evolved. Throughout the Phanerozoic, several fundamental changes in trophic structure are thought to have occurred as a result of notable shifts in faunal dominance in benthic marine communities . While these patterns of taxonomic richness, ecological diversity, and evolution are well established, interpreting their meaning remains challenging .

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Three western Tethys marine food webs from the Anisian (left), Bathonian (center), and Aptian (right). Filled circles (nodes) are guilds, and lines between nodes show consumer-resource interactions. The networks are arranged by trophic position, and the colours indicate sub-communities (modules). Here the size of the nodes has been log scaled relative to the mean body size of species within that guild. Notice that guilds containing species that have very large body sizes occur at higher trophic levels, and that body sizes increase through time.

Modeling of ecological networks based on these evolutionary faunas suggest that increasing Phanerozoic diversity and ecological complexity, and increasing intensity of biotic interactions result in increasing network complexity. However, it has been suggested that early Paleozoic community structure may be remarkably similar to that of modern communities, and that trophic organization may not have undergone any significant changes since the Cambrian.

This project aims to test whether Mesozoic escalatory trends affected ecosystem structure and function, using marine food webs from the Jurassic and Cretaceous. Differences in community dynamics among these ecosystems will be quantified using food web structure, models of community stability dynamics, and a mathematical model of secondary extinction that accounts for the uncertainty associated with paleontological data.

Food webs are being reconstructed using the Paleobiology Database and published literature, and numerous museum collections. Trophic interactions are inferred from relevant autecological literature, functional morphology, habitat, species associations, or living analog species. Changes in ecosystem dynamics will be measured as community stability after minor perturbation, and resistance to the propagation of secondary extinctions in stochastically generated species level food web networks.

Traces of biotic interactions found on fossil echinoids

The evolutionary importance of biotic interactions remains controversial. Moreover, our current paleontological knowledge is molluskocentric and relies largely on one type of interaction (predation). To expand our understanding of the eco-evolutionary role of biotic interactions, we are working to quantify parasitism and predation patterns for post-Paleozoic echinoids. Using the literature and neontological museum collections we also hope to codify characteristics of various types of interactions (predation, parasitism, commensalism, etc.) that affect modern echinoids.

Images of the eight different trace morphotypes found on fossil echinoids. (A) Circular; (B) Subcircular; (C) Elongated; (D) Irregular; (E) Rectangular; (F) Figure-Eight; (G) Notched; (H) Linear.

The project will establish a permanent database for studying biotic interactions on present-day and fossil echinoids, thus enabling researchers to quantify traces recorded in echinoid tests with greater accuracy.

The resulting Echinoid-Associated Traces (EAT) database will include data on the identity/ecology of trace makers, identity/ecology/phylogeny of affected echinoids, and morphology, frequency, and distribution of EATs. This will enhance the cognitive value of ichnological data in studies of biotic interactions. The EAT database will represent a lasting resource for ecologists and paleontologists, an evolving interdisciplinary repository of knowledge.

The EAT database will also be used to identify fossil traces attributable to parasitic (eulimid) and predatory (cassid) gastropods on Triassic-to-Recent echinoids. Surveys of the literature and museum collections - augmented by field sampling and preexisting ecological and phylogenetic knowledge - can then be used to compile fossil data on EATs to test multiple hypotheses regarding the importance of biotic interactions.

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Repair scars preserve decadal-scale patterns of predation intensity despite short-term ecological disturbances

The severity of local community alteration after recent disturbances. Photographs of the rocky intertidal on Dixon Island, ~ 1 mile north of the Bamfield Marine Sciences Centre. (Left) The rocky intertidal on the wave exposed shore of Dixon Island in 2010, before the onset of sea star wasting disease and other short-term disturbances. (Right) The same channel in 2015, after regional disturbances. Both sea stars and live mussels are entirely absent from the channel in 2015.
Repair scar morphology. An example of a repair scar on T. funebralis from Barkley Sound. The arrows indicate the repair scar and the resultant characteristic disruption of growth lines.

Recent ecological disturbances have dramatically altered the composition of rocky intertidal Pacific coast communities of North America, particularly top invertebrate predators. Predation is an important regulatory force on intertidal gastropod communities, and the depletion or loss of predators is therefore likely to have a considerable community-wide short-term impact. However, assessing the magnitude and nature of the resulting ecological changes may be problematic in the absence of data recording pre-disturbance conditions. Here the effectiveness of traces of unsuccessful crab predation on gastropod shells at providing along-term, decadal record of predation intensity in Barkley Sound (Vancouver Island, British Columbia) was evaluated subsequent to multiple large-scale ecological disturbances, including sea star wasting disease, abnormally high sea surface temperatures, and harmful algal blooms. The frequency of failed crab attacks recorded by repair scars on six populations of the intertidal gastropod Tegula funebralis were surveyed to compare spatial patterns in predation intensity before and after disturbance (2013 and 2015 respectively). The repair frequency gradient observed in 2013 was also recorded by repair scars in 2015 (Spearman’s Rho = 1, p = 0.002), and repair frequency was not affected by gastropod size in either 2013 (Spearman’s Rho = 0.14, p = 0.80) or 2015 (Spearman’s Rho = 0.66, p = 0.18). These findings are consistent with the hypothesis that repair frequency provides decadal records of predation intensity, and may be effective to establish persistent levels of predation intensity prior to disturbances in rocky intertidal habitats.