Supplementary figures and data S1: Isolating sedimentary rock units in ArcMap: data were derived ... more Supplementary figures and data S1: Isolating sedimentary rock units in ArcMap: data were derived from USGS state-by-state geological maps (https://mrdata.usgs.gov/geology/state/). Sedimentary rock polygons were isolated for a given geological stage in ArcMap and assigned to stage-level time bins based on the formal lithostratigraphic name of their encompassing geological group, formation, or member using data from the National Geological Map Database (https://ngmdb.usgs.gov/Geolex/search) and extensive review of the literature (see 'Stratigraphic References' section at end of Supplementary Material document). We kept the polygon as a 'sedimentary unit' if the rock type matched any of the following: '
GSA Annual Meeting in Seattle, Washington, USA - 2017, 2017
Drill-holes found in the fossil record are an important tool to study ecological patterns of the ... more Drill-holes found in the fossil record are an important tool to study ecological patterns of the past. It is therefore important to gain a better understanding of the role of extant drilling snails in modern ecosystems. Although traditionally considered a predator, trophic position of 3.0, specimens of the muricid Urosalpinx cinerea from Long Island Sound revealed trophic positions between 2.3 and 2.5, suggestive of an omnivorous diet. This study addresses the generality of this result by examining a U. cinerea population from Wilmington, North Carolina. Preliminary whole body, soft tissue stable isotope analysis of nitrogen and carbon was conducted on five U. cinerea specimens. Isotopic baseline for the study area was calculated using proxy taxa, including Geukensia demissa for the pelagic baseline and Littoraria irrorata for the littoral baseline. Trophic position for these U. cinerea specimens ranged from 2.4 to 2.9. Working hypotheses to explain a trophic position lower than 3.0 in U. cinerea include: trophic omnivory driven by plant consumption, or a lower-than-average nitrogen discrimination factor. Although no studies on the nitrogen fractionation factors of muricids currently exist, the naticid Neverita duplicata from Long Island Sound has recently been demonstrated to have a normal nitrogen fractionation factor and omnivorous isotopic signatures. The difference between the trophic ranges of the two locations may indicate that U. cinerea have a more predatory diet in North Carolina than in Long Island Sound. However, further work is needed to confirm that these values reflect dietary differences, not a below average nitrogen fractionation factor.
Geographic ranges are a fundamental unit of biogeography and macroecology. Increasingly, paleonto... more Geographic ranges are a fundamental unit of biogeography and macroecology. Increasingly, paleontologists and ecologists alike are reconstructing geographic ranges of species from fossils, in order to understand the long-term processes governing biogeographic and macroevolutionary patterns. As these reconstructions have become increasingly common, uncertainty has arisen over the equivalency of paleo-ranges and modern ranges. Here, we argue geographic ranges are time-averaged at all temporal scales, and reflect the biotic and abiotic processes operating across an equivalent range of time and space scales. This conceptual framework integrates the study of geographic ranges reconstructed using modern and ancient data, and highlights the potential for ranges to illuminate processes responsible for diversity patterns over intervals spanning days to tens of millions of years of Earth history.
Geographic range size and abundance are important determinants of extinction risk in fossil and e... more Geographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily "quiescent" times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian-Permian), a time of "sluggish" evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinction in this time and place may reflect the relative preponderance of larger-ranged taxa combined with the physiographic conditions of the region that allowed for easy habitat tracking that dampened both extinction and speciation. These conditions led to a prolonged period (19-25 Myr) during which standard macroevolutionary rules did not apply.
Proceedings of the Royal Society B: Biological Sciences
Extinction events in the geological past are similar to the present-day biodiversity crisis in th... more Extinction events in the geological past are similar to the present-day biodiversity crisis in that they have a pronounced biogeography, producing dramatic changes in the spatial distributions of species. Reconstructing palaeobiogeographic patterns from fossils therefore allows us to examine the long-term processes governing the formation of regional biotas, and potentially helps build spatially explicit models for future biodiversity loss. However, the extent to which biogeographic patterns can be preserved in the fossil record is not well understood. Here, we perform a suite of simulations based on the present-day distribution of North American mammals, aimed at quantifying the preservation potential of beta diversity and spatial richness patterns over extinction events of varying intensities, and after applying a stepped series of taphonomic filters. We show that taphonomic biases related to body size are the biggest barrier to reconstructing biogeographic patterns over extinctio...
Abstract The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for t... more Abstract The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hypotheses surrounding the environmental and ecological effects on marine fauna. To conduct these studies in a rigorous manner, a reliable taxonomy must be established for the organisms within this physiographic province. In this study, we focus on the bivalve genus Astarte, which is commonly found in this region, and has many formally recognized species. We test between two competing hypotheses for the unusually high species richness of this genus: 1) taxonomy – the presence of discrete morphotypes represent valid species within this genus; and, 2) ecology – the many recognized ‘species’ in this genus in fact represent ecophenotypic variants of a smaller number of species, and thus richness is inflated. We test between these two hypotheses using a geometric morphometric analysis of landmarks placed on 646 shells, representing six different taxa from the Pliocene of the Atlantic Coastal Plain. We performed Procrustes transformation and Principle Components Analysis (PCA) on landmark data, allometric residuals, and outline harmonics to fully understand the variability of morphologies present. All PCA results show large amounts of overlap between all species. It is likely some of these species are valid taxonomic groups within the genus but should be classified as sub-species instead of separate species. These results provide strong support for our ‘ecology’ hypothesis, and suggests the genus Astarte needs revision. Future studies incorporating detailed sedimentological characteristics or ecological information (e.g., drilling frequency) will further elucidate palaeoecological and palaeoenvironmental drivers of ecophenotypic variation present in this genus. Further, the accurate identification of fossil species has important implications for our ability to reconstruct biodiversity trends in relation to the emergence of the Central American Isthmus and subsequent changes in ocean circulation.
Species belonging to the family Naticidae (commonly called moon snails) are important infaunal ga... more Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for 1 year. The median N fractionation factor derived from the experimental moon snails was 3.58‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiment. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the possible identity of plants consumed.
Drillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecologi... more Drillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecological studies because they provide direct, preservable evidence of predation. The muricidEcphorais common in many Neogene Atlantic Coastal Plain assemblages in the United States, but is frequently ignored in studies of naticid predation. We used a combination of Pliocene fossil, modern beach, and experimentally derived samples to evaluate the hypothesis thatEcphorawas an important source of drillholes in infaunal bivalve prey shared with naticids. We focused on the large, thick-shelled venerid,Mercenaria,which is commonly drilled by naticids today. Laboratory experiments, modern beach samples, and the published literature confirm that naticids preferentially drill near the umbo (significant clumping of holes), show a significant correlation between prey size and predator size (estimated by outer borehole diameter), and preferMercenaria<50 mm antero-posterior width when other prey are pr...
Recent closures of rural obstetric units and entire hospitals have exacerbated concerns about acc... more Recent closures of rural obstetric units and entire hospitals have exacerbated concerns about access to care for more than twenty-eight million women of reproductive age living in rural America. Yet the extent of recent obstetric unit closures has not yet been measured. Using national data, we found that 9 percent of rural counties experienced the loss of all hospital obstetric services in the period 2004-14. In addition, another 45 percent of rural US counties had no hospital obstetric services at all during the study period. That left more than half of all rural US counties without hospital obstetric services. Counties with fewer obstetricians and family physicians per women of reproductive age and per capita, respectively; a higher percentage of non-Hispanic black women of reproductive age; and lower median household incomes and those in states with more restrictive Medicaid income eligibility thresholds for pregnant women had higher odds of lacking hospital obstetric services. The same types of counties were also more likely to experience the loss of obstetric services, which highlights the challenge of providing adequate geographic access to obstetric care in vulnerable and underserved rural communities.
Abstract. Geographic range size and abundance are important determinants of extinction risk in fo... more Abstract. Geographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily “quiescent” times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian–Permian), a time of “sluggish” evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinctio...
Species belonging to the family Naticidae (commonly called moon snails) are important infaunal ga... more Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for 1 year. The median N fractionation factor derived from the experimental moon snails was 3.58‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiment. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the possible identity of plants consumed.
The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hy... more The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hypotheses surrounding the environmental and ecological effects on marine fauna. To conduct these studies in a rigorous manner, a reliable taxonomy must be established for the organisms within this physiographic province. In this study, we focus on the bivalve genus Astarte, which is commonly found in this region, and has many formally recognized species. We test between two competing hypotheses for the unusually high species richness of this genus: 1) taxonomy-the presence of discrete morphotypes represent valid species within this genus; and, 2) ecology-the many recognized 'species' in this genus in fact represent ecophenotypic variants of a smaller number of species, and thus richness is inflated. We test between these two hypotheses using a geometric morphometric analysis of landmarks placed on 646 shells, representing six different taxa from the Pliocene of the Atlantic Coastal Plain. We performed Procrustes transformation and Principle Components Analysis (PCA) on landmark data, allometric residuals, and outline harmonics to fully understand the variability of morphologies present. All PCA results show large amounts of overlap between all species. It is likely some of these species are valid taxonomic groups within the genus but should be classified as sub-species instead of separate species. These results provide strong support for our 'ecology' hypothesis, and suggests the genus Astarte needs revision. Future studies incorporating detailed sedimentological characteristics or ecological information (e.g., drilling frequency) will further elucidate palaeoecological and palaeoenvironmental drivers of ecophenotypic variation present in this genus. Further, the accurate identification of fossil species has important implications for our ability to reconstruct biodiversity trends in relation to the emergence of the Central American Isthmus and subsequent changes in ocean circulation.
Journal of Experimental Marine Biology and Ecology, Dec 1, 2008
Drilling gastropod predators are of particular interest to paleontologists, because predatory dri... more Drilling gastropod predators are of particular interest to paleontologists, because predatory drill-holes in marine invertebrates serve as one of the rare sources of data for the study of ancient predator-prey interactions. Modern laboratory studies are an important part of predation research providing valuable ecological insight and constraining fossil evidence and interpretations. Previous studies have shown that mussels use clumping behavior against durophagous predation . Group living and the effects of spatial position in aggregations of Mylitus edulis. Oecologia 69, 341-347.; Lin, J., 1991. Predator-prey interactions between blue crabs and ribbed mussels living in clumps. Estuar. Coast. Shelf Sci. 32, 61-69.], but its role against drilling predation had not been explored. In this study, we explore the effect of clumping on predator success (drill-hole frequency) and prey handling (drill-hole position) using the mussel, Mytilus trossulus, as prey and the gastropod, Nucella lamellosa, as drilling predator. We assigned mussels to two groups: in one, mussels were allowed to clump together with their byssal threads, and in the other, they were kept separate. We observed a significant decrease in the drilling frequency within the group containing clumped mussels, confirming that clumping acts as a successful anti-predatory strategy against drilling predators. The use of clumping as an effective strategy against multiple types of predators may relax the trade-offs associated with aggregated lifestyles . Population dynamics of the ribbed mussel, Geukensia demissa: the costs and benefits of an aggregated distribution. Oecologia 67,[192][193][194][195][196][197][198][199][200][201][202][203][204]. The increased benefit and unchanged metabolic cost of clumped living alters estimates of individual fitness with evolutionarily significant implications (e.g., eliminating the need to invoke group or species selection to explain the adaptive benefit of an aggregated lifestyle). In spite of potential differences in prey handling and grappling due to clumping, mean drill-hole placement and variation in drill-hole placement showed no significant differences between the two groups. These observations suggest that comparison of predation intensities across clumping and nonclumping taxa must consider the anti-predatory effect of this behavior.
Supplementary figures and data S1: Isolating sedimentary rock units in ArcMap: data were derived ... more Supplementary figures and data S1: Isolating sedimentary rock units in ArcMap: data were derived from USGS state-by-state geological maps (https://mrdata.usgs.gov/geology/state/). Sedimentary rock polygons were isolated for a given geological stage in ArcMap and assigned to stage-level time bins based on the formal lithostratigraphic name of their encompassing geological group, formation, or member using data from the National Geological Map Database (https://ngmdb.usgs.gov/Geolex/search) and extensive review of the literature (see 'Stratigraphic References' section at end of Supplementary Material document). We kept the polygon as a 'sedimentary unit' if the rock type matched any of the following: '
GSA Annual Meeting in Seattle, Washington, USA - 2017, 2017
Drill-holes found in the fossil record are an important tool to study ecological patterns of the ... more Drill-holes found in the fossil record are an important tool to study ecological patterns of the past. It is therefore important to gain a better understanding of the role of extant drilling snails in modern ecosystems. Although traditionally considered a predator, trophic position of 3.0, specimens of the muricid Urosalpinx cinerea from Long Island Sound revealed trophic positions between 2.3 and 2.5, suggestive of an omnivorous diet. This study addresses the generality of this result by examining a U. cinerea population from Wilmington, North Carolina. Preliminary whole body, soft tissue stable isotope analysis of nitrogen and carbon was conducted on five U. cinerea specimens. Isotopic baseline for the study area was calculated using proxy taxa, including Geukensia demissa for the pelagic baseline and Littoraria irrorata for the littoral baseline. Trophic position for these U. cinerea specimens ranged from 2.4 to 2.9. Working hypotheses to explain a trophic position lower than 3.0 in U. cinerea include: trophic omnivory driven by plant consumption, or a lower-than-average nitrogen discrimination factor. Although no studies on the nitrogen fractionation factors of muricids currently exist, the naticid Neverita duplicata from Long Island Sound has recently been demonstrated to have a normal nitrogen fractionation factor and omnivorous isotopic signatures. The difference between the trophic ranges of the two locations may indicate that U. cinerea have a more predatory diet in North Carolina than in Long Island Sound. However, further work is needed to confirm that these values reflect dietary differences, not a below average nitrogen fractionation factor.
Geographic ranges are a fundamental unit of biogeography and macroecology. Increasingly, paleonto... more Geographic ranges are a fundamental unit of biogeography and macroecology. Increasingly, paleontologists and ecologists alike are reconstructing geographic ranges of species from fossils, in order to understand the long-term processes governing biogeographic and macroevolutionary patterns. As these reconstructions have become increasingly common, uncertainty has arisen over the equivalency of paleo-ranges and modern ranges. Here, we argue geographic ranges are time-averaged at all temporal scales, and reflect the biotic and abiotic processes operating across an equivalent range of time and space scales. This conceptual framework integrates the study of geographic ranges reconstructed using modern and ancient data, and highlights the potential for ranges to illuminate processes responsible for diversity patterns over intervals spanning days to tens of millions of years of Earth history.
Geographic range size and abundance are important determinants of extinction risk in fossil and e... more Geographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily "quiescent" times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian-Permian), a time of "sluggish" evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinction in this time and place may reflect the relative preponderance of larger-ranged taxa combined with the physiographic conditions of the region that allowed for easy habitat tracking that dampened both extinction and speciation. These conditions led to a prolonged period (19-25 Myr) during which standard macroevolutionary rules did not apply.
Proceedings of the Royal Society B: Biological Sciences
Extinction events in the geological past are similar to the present-day biodiversity crisis in th... more Extinction events in the geological past are similar to the present-day biodiversity crisis in that they have a pronounced biogeography, producing dramatic changes in the spatial distributions of species. Reconstructing palaeobiogeographic patterns from fossils therefore allows us to examine the long-term processes governing the formation of regional biotas, and potentially helps build spatially explicit models for future biodiversity loss. However, the extent to which biogeographic patterns can be preserved in the fossil record is not well understood. Here, we perform a suite of simulations based on the present-day distribution of North American mammals, aimed at quantifying the preservation potential of beta diversity and spatial richness patterns over extinction events of varying intensities, and after applying a stepped series of taphonomic filters. We show that taphonomic biases related to body size are the biggest barrier to reconstructing biogeographic patterns over extinctio...
Abstract The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for t... more Abstract The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hypotheses surrounding the environmental and ecological effects on marine fauna. To conduct these studies in a rigorous manner, a reliable taxonomy must be established for the organisms within this physiographic province. In this study, we focus on the bivalve genus Astarte, which is commonly found in this region, and has many formally recognized species. We test between two competing hypotheses for the unusually high species richness of this genus: 1) taxonomy – the presence of discrete morphotypes represent valid species within this genus; and, 2) ecology – the many recognized ‘species’ in this genus in fact represent ecophenotypic variants of a smaller number of species, and thus richness is inflated. We test between these two hypotheses using a geometric morphometric analysis of landmarks placed on 646 shells, representing six different taxa from the Pliocene of the Atlantic Coastal Plain. We performed Procrustes transformation and Principle Components Analysis (PCA) on landmark data, allometric residuals, and outline harmonics to fully understand the variability of morphologies present. All PCA results show large amounts of overlap between all species. It is likely some of these species are valid taxonomic groups within the genus but should be classified as sub-species instead of separate species. These results provide strong support for our ‘ecology’ hypothesis, and suggests the genus Astarte needs revision. Future studies incorporating detailed sedimentological characteristics or ecological information (e.g., drilling frequency) will further elucidate palaeoecological and palaeoenvironmental drivers of ecophenotypic variation present in this genus. Further, the accurate identification of fossil species has important implications for our ability to reconstruct biodiversity trends in relation to the emergence of the Central American Isthmus and subsequent changes in ocean circulation.
Species belonging to the family Naticidae (commonly called moon snails) are important infaunal ga... more Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for 1 year. The median N fractionation factor derived from the experimental moon snails was 3.58‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiment. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the possible identity of plants consumed.
Drillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecologi... more Drillholes made by naticid and muricid gastropods are frequently used in evolutionary and ecological studies because they provide direct, preservable evidence of predation. The muricidEcphorais common in many Neogene Atlantic Coastal Plain assemblages in the United States, but is frequently ignored in studies of naticid predation. We used a combination of Pliocene fossil, modern beach, and experimentally derived samples to evaluate the hypothesis thatEcphorawas an important source of drillholes in infaunal bivalve prey shared with naticids. We focused on the large, thick-shelled venerid,Mercenaria,which is commonly drilled by naticids today. Laboratory experiments, modern beach samples, and the published literature confirm that naticids preferentially drill near the umbo (significant clumping of holes), show a significant correlation between prey size and predator size (estimated by outer borehole diameter), and preferMercenaria<50 mm antero-posterior width when other prey are pr...
Recent closures of rural obstetric units and entire hospitals have exacerbated concerns about acc... more Recent closures of rural obstetric units and entire hospitals have exacerbated concerns about access to care for more than twenty-eight million women of reproductive age living in rural America. Yet the extent of recent obstetric unit closures has not yet been measured. Using national data, we found that 9 percent of rural counties experienced the loss of all hospital obstetric services in the period 2004-14. In addition, another 45 percent of rural US counties had no hospital obstetric services at all during the study period. That left more than half of all rural US counties without hospital obstetric services. Counties with fewer obstetricians and family physicians per women of reproductive age and per capita, respectively; a higher percentage of non-Hispanic black women of reproductive age; and lower median household incomes and those in states with more restrictive Medicaid income eligibility thresholds for pregnant women had higher odds of lacking hospital obstetric services. The same types of counties were also more likely to experience the loss of obstetric services, which highlights the challenge of providing adequate geographic access to obstetric care in vulnerable and underserved rural communities.
Abstract. Geographic range size and abundance are important determinants of extinction risk in fo... more Abstract. Geographic range size and abundance are important determinants of extinction risk in fossil and extant taxa. However, the relationship between these variables and extinction risk has not been tested extensively during evolutionarily “quiescent” times of low extinction and speciation in the fossil record. Here we examine the influence of geographic range size and abundance on extinction risk during the late Paleozoic (Mississippian–Permian), a time of “sluggish” evolution when global rates of origination and extinction were roughly half those of other Paleozoic intervals. Analyses used spatiotemporal occurrences for 164 brachiopod species from the North American midcontinent. We found abundance to be a better predictor of extinction risk than measures of geographic range size. Moreover, species exhibited reductions in abundance before their extinction but did not display contractions in geographic range size. The weak relationship between geographic range size and extinctio...
Species belonging to the family Naticidae (commonly called moon snails) are important infaunal ga... more Species belonging to the family Naticidae (commonly called moon snails) are important infaunal gastropod predators found in soft-bottom marine communities worldwide that traditionally have been thought to prey on other mollusks, giving them the expected trophic position of a predator (trophic position = 3). Realized trophic position estimates of the naticid Neverita duplicata from Long Island Sound, however, range between 2.3 and 2.5, indicating omnivory or an anomalously low nitrogen (N) fractionation factor. To evaluate the likelihood of omnivory, this study presents whole body stable isotopic analysis of nitrogen and carbon from the soft tissues of laboratory-reared and field-collected N. duplicata. Experimental organisms were maintained on a diet of the bivalve prey Mercenaria mercenaria for 1 year. The median N fractionation factor derived from the experimental moon snails was 3.58‰ thus precluding the presence of an atypical fractionation factor (substantially lower than 3.4‰). Numerous molluscan taxa were collected from Long Island Sound in order to evaluate the trophic ecology of N. duplicata in the context of a natural food web. Evidence from the carbon (C) signatures of field-collected N. duplicata indicate a reliance on littoral food sources that is inconsistent with a diet of filter-feeding M. mercenaria, even when calculated using the species-specific C fractionation factor derived from the laboratory experiment. Field-collected N. duplicata also show considerable isotopic overlap (N and C) with grazing Littorina littorea. For these reasons, we hypothesize that N. duplicata feeds on some combination of benthic primary producers (most likely macroalgae and/or epiphytic diatoms), carrion, and bivalve/gastropod tissue and discuss the possible identity of plants consumed.
The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hy... more The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hypotheses surrounding the environmental and ecological effects on marine fauna. To conduct these studies in a rigorous manner, a reliable taxonomy must be established for the organisms within this physiographic province. In this study, we focus on the bivalve genus Astarte, which is commonly found in this region, and has many formally recognized species. We test between two competing hypotheses for the unusually high species richness of this genus: 1) taxonomy-the presence of discrete morphotypes represent valid species within this genus; and, 2) ecology-the many recognized 'species' in this genus in fact represent ecophenotypic variants of a smaller number of species, and thus richness is inflated. We test between these two hypotheses using a geometric morphometric analysis of landmarks placed on 646 shells, representing six different taxa from the Pliocene of the Atlantic Coastal Plain. We performed Procrustes transformation and Principle Components Analysis (PCA) on landmark data, allometric residuals, and outline harmonics to fully understand the variability of morphologies present. All PCA results show large amounts of overlap between all species. It is likely some of these species are valid taxonomic groups within the genus but should be classified as sub-species instead of separate species. These results provide strong support for our 'ecology' hypothesis, and suggests the genus Astarte needs revision. Future studies incorporating detailed sedimentological characteristics or ecological information (e.g., drilling frequency) will further elucidate palaeoecological and palaeoenvironmental drivers of ecophenotypic variation present in this genus. Further, the accurate identification of fossil species has important implications for our ability to reconstruct biodiversity trends in relation to the emergence of the Central American Isthmus and subsequent changes in ocean circulation.
Journal of Experimental Marine Biology and Ecology, Dec 1, 2008
Drilling gastropod predators are of particular interest to paleontologists, because predatory dri... more Drilling gastropod predators are of particular interest to paleontologists, because predatory drill-holes in marine invertebrates serve as one of the rare sources of data for the study of ancient predator-prey interactions. Modern laboratory studies are an important part of predation research providing valuable ecological insight and constraining fossil evidence and interpretations. Previous studies have shown that mussels use clumping behavior against durophagous predation . Group living and the effects of spatial position in aggregations of Mylitus edulis. Oecologia 69, 341-347.; Lin, J., 1991. Predator-prey interactions between blue crabs and ribbed mussels living in clumps. Estuar. Coast. Shelf Sci. 32, 61-69.], but its role against drilling predation had not been explored. In this study, we explore the effect of clumping on predator success (drill-hole frequency) and prey handling (drill-hole position) using the mussel, Mytilus trossulus, as prey and the gastropod, Nucella lamellosa, as drilling predator. We assigned mussels to two groups: in one, mussels were allowed to clump together with their byssal threads, and in the other, they were kept separate. We observed a significant decrease in the drilling frequency within the group containing clumped mussels, confirming that clumping acts as a successful anti-predatory strategy against drilling predators. The use of clumping as an effective strategy against multiple types of predators may relax the trade-offs associated with aggregated lifestyles . Population dynamics of the ribbed mussel, Geukensia demissa: the costs and benefits of an aggregated distribution. Oecologia 67,[192][193][194][195][196][197][198][199][200][201][202][203][204]. The increased benefit and unchanged metabolic cost of clumped living alters estimates of individual fitness with evolutionarily significant implications (e.g., eliminating the need to invoke group or species selection to explain the adaptive benefit of an aggregated lifestyle). In spite of potential differences in prey handling and grappling due to clumping, mean drill-hole placement and variation in drill-hole placement showed no significant differences between the two groups. These observations suggest that comparison of predation intensities across clumping and nonclumping taxa must consider the anti-predatory effect of this behavior.
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Papers by Michelle Casey