Rowan Lockwood

Extinctions in ancient and modern seas

In the coming century, life in the ocean will be confronted with a suite of environmental conditions that have no analog in human history. Thus, there is an urgent need to determine which marine species will adapt and which will go extinct. Here, we review the growing literature on marine extinctions and extinction risk in the fossil, historical, and modern records to compare the patterns, drivers, and biological correlates of marine extinctions at different times in the past. Characterized by markedly different environmental states, some past periods share common features with predicted future scenarios. We highlight how the different records can be integrated to better understand and predict the impact of current and projected future environmental changes on extinction risk in the ocean.

Integrating Paleobiology, Archeology, and History to Inform Biological Conservation

The search for novel approaches to establishing ecological baselines (reference conditions) is constrained by the fact that most ecological studies span the past few decades, at most, and investigate ecosystems that have been substantially altered by human activities for decades, centuries, or more. Paleobiology, archeology, and history provide historical ecological context for biological conservation, remediation, and restoration. We argue that linking historical ecology explicitly with conservation can help unify related disciplines of conservation paleobiology, conservation archeobiology, and environmental history. Differences in the spatial and temporal resolution and extent (scale) of prehistoric, historic, and modern ecological data remain obstacles to integrating historical ecology and conservation biology, but the prolonged temporal extents of historical ecological data can help establish more complete baselines for restoration, document a historical range of ecological variability, and assist in determining desired future conditions. We used the eastern oyster (Crassostrea virginica) fishery of the Chesapeake Bay (U.S.A.) to demonstrate the utility of historical ecological data for elucidating oyster conservation and the need for an approach to conservation that transcends disciplinary boundaries. Historical ecological studies from the Chesapeake have documented dramatic declines (as much as 99%) in oyster abundance since the early to mid-1800 s, changes in oyster size in response to different nutrient levels from the sixteenth to nineteenth centuries, and substantial reductions in oyster accretion rates (from 10 mm/year to effectively 0 mm/year) from the Late Holocene to modern times. Better integration of different historical ecological data sets and increased collaboration between paleobiologists, geologists, archeologists, environmental historians, and ecologists to create standardized research designs and methodologies will help unify prehistoric, historic, and modern time perspectives on biological conservation.

Abundance not linked to survival across the end-Cretaceous mass extinction: Patterns in North American bivalves

Ecological studies suggest that rare taxa are more likely to go extinct than abundant ones, but the influence of abundance on survivorship in the fossil record has received little attention. An analysis of Late Maastrichtian bivalve subgenera from the North American Coastal Plain found no evidence that survivorship is tied to abundance across the end-Cretaceous mass extinction (65 million years ago), regardless of abundance metric or spatial scale examined. The fact that abundance does not promote survivorship in end-Cretaceous bivalves suggests that the factors influencing survivorship during mass extinctions in the fossil record may differ from those operating during intervals of background extinction.

Morphological Adaptations to Predation Risk in Passerines

Avoiding predation is an important factor in avian life-history strategies and there are many examples of adaptations that appear to decrease predation risk. However, we are not aware of any studies of structural morphological adaptations to reduce predation risk in any avian species. Here, we have compared published indices of relative predation risk for passerine species with two size-constrained measures of wingtip shape and relative hind limb morphology. Our analyses indicate that species with rounded wingtips and those with relatively short femora compared with tarsi are at a lower relative predation risk than those with more pointed wingtips and relatively longer femora. These relations are discussed in terms of the functional morphology of wingtip shape and hind limb morphology and suggestions for further experimental investigations are made.

QUANTIFYING TAPHONOMIC BIAS OF COMPOSITIONAL FIDELITY, SPECIES RICHNESS, AND RANK ABUNDANCE IN MOLLUSCAN DEATH ASSEMBLAGES FROM THE UPPER CHESAPEAKE BAY

Abstract Years of over-fishing combined with increased nutrient pollution have had a catastrophic effect on the ecology of the Chesapeake Bay. The Holocene record of bay mollusks may provide a baseline for ecological restoration, but the effects of taphonomic bias on these assemblages first must be assessed. In this study, a live-dead comparison was carried out on four sites distributed in the main channel of the upper bay. Molluscan death-assemblage data were obtained from replicate box-core samples from which whole specimens and fragments were sorted, identified, and counted. Data on live communities at the same sites, sampled over the past twenty years, were provided by the Chesapeake Bay Program, making it possible to examine the degree to which death assemblages reflect long-term changes in the live community. Traditional live-dead metrics document a strong agreement between live-community and death-assemblage estimates of species composition, richness, and abundance—77% of the species in the live community are found in the death assemblage, and 99% of the individuals of species found in the death assemblage are found in the live community. Correlations between live and dead estimates of species richness are not statistically significant, although they do improve with longer-term sampling of the live community. Rank abundance of taxa in the death assemblage is correlated strongly and significantly with live rank abundance regardless of the duration of live sampling. These results suggest that Holocene molluscan assemblages may provide useful estimates of richness and abundance for Chesapeake Bay restoration.

Paleontological baselines for evaluating extinction risk in the modern oceans

Recognizing the threat of additive risk Humans are accelerating the extinction rates of species in both terrestrial and marine environments. However, species extinctions have occurred across time for a variety of other reasons. Finnegan et al. looked at the extinction rates across marine genera (groups of species) over the past 23 million years to determine intrinsic extinction rates and what traits or regions correspond to the highest rates. Combining patterns of intrinsic extinction with regions of high anthropogenic threat revealed taxa and areas, particularly in the tropics, where the risk of extinction will be especially high. Science, this issue p. 567 Fossils reveal patterns of extinction in marine species, past and present. Marine taxa are threatened by anthropogenic impacts, but knowledge of their extinction vulnerabilities is limited. The fossil record provides rich information on past extinctions that can help predict biotic responses. We show that over 23 million years, taxonomic membership and geographic range size consistently explain a large proportion of extinction risk variation in six major taxonomic groups. We assess intrinsic risk—extinction risk predicted by paleontologically calibrated models—for modern genera in these groups. Mapping the geographic distribution of these genera identifies coastal biogeographic provinces where fauna with high intrinsic risk are strongly affected by human activity or climate change. Such regions are disproportionately in the tropics, raising the possibility that these ecosystems may be particularly vulnerable to future extinctions. Intrinsic risk provides a prehuman baseline for considering current threats to marine biodiversity.

Body size, extinction events, and the early Cenozoic record of veneroid bivalves: a new role for recoveries?

Mass extinctions can play a role in shaping macroevolutionary trends through time, but the contribution of recoveries to this process has yet to be examined in detail. This study focuses on the effects of three extinction events, the end-Cretaceous (K/T), mid-Eocene (mid-E), and end- Eocene (E/O), on long-term patterns of body size in veneroid bivalves. Systematic data were col- lected for 719 species and 140 subgenera of veneroids from the Late Cretaceous through Oligocene of North America and Europe. Centroid size measures were calculated for 101 subgenera and glob- al stratigraphic ranges were used to assess extinction selectivity and preferential recovery. Vene- roids underwent a substantial extinction at the K/T boundary, although diversity recovered to pre- extinction levels by the early Eocene. The mid-E and E/O events were considerably smaller and their recovery intervals much shorter. None of these events were characterized by significant ex- tinction selectivity according to body size at the subgenus level; however, all three recoveries were strongly size biased. The K/T recovery was biased toward smaller veneroids, whereas both the mid-E and E/O recoveries were biased toward larger ones. The decrease in veneroid size across the K/T recovery actually reinforced a Late Cretaceous trend toward smaller sizes, whereas the increase in size resulting from the Eocene recoveries was relatively short-lived. Early Cenozoic changes in predation, temperature, and/or productivity may explain these shifts.

The K/T event and infaunality: morphological and ecological patterns of extinction and recovery in veneroid bivalves

Abstract Although the causes of mass extinctions have been studied in detail, recoveries have received little attention until recently. In this study, I examine the influence of extinction versus recovery intervals on ecological patterns across the end-Cretaceous (K/T) event in veneroid bivalves. Systematic and stratigraphic data were collected for 140 subgenera of veneroids, ranging from the Late Cretaceous through Oligocene of North America and Europe. Morphological data were collected for 1236 specimens representing 101 subgenera. Extinction selectivity and differential recovery were assessed with respect to morphology, and by extension, burrowing ecology in these bivalves. Eighty-one percent of veneroid subgenera went extinct at the K/T and diversity did not return to preextinction levels until 12 million years later. Despite the severity of the K/T extinction, I found little evidence of morphological or ecological selectivity. The K/T recovery, in contrast, was strongly biased toward taxa with deep pallial sinuses (i.e., toward deeper burrowers). For veneroids, the morphological and ecological effects of the K/T event are not tied to the extinction itself, but to the recovery that followed. The K/T recovery initiated a trend toward deeper burrowing that helped to establish veneroids as one of the most abundant and successful groups of modern marine bivalves.

Millennial-scale sustainability of the Chesapeake Bay Native American oyster fishery

Significance Oysters are important organisms in estuaries around the world, influencing water quality, constructing habitat, and providing food for humans and wildlife. Following over a century of overfishing, pollution, disease, and habitat degradation, oyster populations in the Chesapeake Bay and elsewhere have declined dramatically. Despite providing food for humans for millennia, we know little about Chesapeake Bay oyster populations prior to historical fishing in the late 1800s. Using fossil, archaeological, and modern biological data, we reconstruct changes in oyster size from the Pleistocene and prior to human harvest through prehistoric Native American occupation and modern times. These data demonstrate sustainability in the Native American oyster fishery, providing insight into the future management of oysters in the Chesapeake Bay and around the world. Estuaries around the world are in a state of decline following decades or more of overfishing, pollution, and climate change. Oysters (Ostreidae), ecosystem engineers in many estuaries, influence water quality, construct habitat, and provide food for humans and wildlife. In North America’s Chesapeake Bay, once-thriving eastern oyster (Crassostrea virginica) populations have declined dramatically, making their restoration and conservation extremely challenging. Here we present data on oyster size and human harvest from Chesapeake Bay archaeological sites spanning ∼3,500 y of Native American, colonial, and historical occupation. We compare oysters from archaeological sites with Pleistocene oyster reefs that existed before human harvest, modern oyster reefs, and other records of human oyster harvest from around the world. Native American fisheries were focused on nearshore oysters and were likely harvested at a rate that was sustainable over centuries to millennia, despite changing Holocene climatic conditions and sea-level rise. These data document resilience in oyster populations under long-term Native American harvest, sea-level rise, and climate change; provide context for managing modern oyster fisheries in the Chesapeake Bay and elsewhere around the world; and demonstrate an interdisciplinary approach that can be applied broadly to other fisheries.

Does morphological variation buffer against extinction? A test using veneroid bivalves from the Plio-Pleistocene of Florida

Abstract Although morphological variation is known to influence the evolutionary fates of species, the relationship between morphological variation and survivorship in the face of extinction-inducing perturbations is poorly understood. Here, we investigate this relationship for veneroid bivalves in association with the Plio-Pleistocene extinction in Florida. Fourteen pairs of related species were selected for analysis, with each pair including one species that survived the Plio-Pleistocene extinction and another that became extinct during the interval. Morphological landmark data were acquired for more than 1500 museum specimens, representing 19 localities that encompass four well-known Plio-Pleistocene units in the study region. Procrustes superimposition was applied to each sample, and overall multivariate variation was calculated as the mean squared partial Procrustes distance between specimens and their mean form. Morphological variation was calculated at three geographic scales for each species, and differences in variation between survivors and victims were examined within each species pair. Results indicate that species surviving the Plio-Pleistocene extinction were significantly more variable morphologically than victims. Greater morphological variation may promote survivorship by directly enhancing species adaptations to changing conditions or by permitting the occupation of a larger geographic range. Alternatively, high morphological variation and survivorship may both be mediated by a third variable, such as large geographic range.