The effects of overdispersion and zero inflation (e.g., poor model fits) can result in misinterpretation in studies using count data. These effects have not been evaluated in paleoecological studies ...of predation and are further complicated by preservational bias and time averaging. We develop a hierarchical Bayesian framework to account for uncertainty from overdispersion and zero inflation in estimates of specimen and predation trace counts. We demonstrate its application using published data on drilling predators and their prey in time-averaged death assemblages from the Great Barrier Reef, Australia. Our results indicate that estimates of predation frequencies are underestimated when zero inflation is not considered, and this effect is likely compounded by removal of individuals and predation traces via preservational bias. Time averaging likely reduces zero inflation via accumulation of rare taxa and events; however, it increases the uncertainty in comparisons between assemblages by introducing variability in sampling effort. That is, there is an analytical cost with time-averaged count data, manifesting as broader confidence regions. Ecological inferences in paleoecology can be strengthened by accounting for the uncertainty inherent to paleoecological count data and the sampling processes by which they are generated.
Geographically separate biotas often show differences in species composition, diversity, and adaptations. Such differences, which often reflect historical differences in regimes of productivity and ...selection, have received little attention from ecologists. Here we concentrate on diversity and maximum body size in 18 guilds of shallow-water marine shell-bearing mollusks and barnacles from the European and North American sides of the temperate North Atlantic. These guilds represent suspension-feeders (epifaunal, shallow infaunal, and deep infaunal), chemosymbiotic bivalves, predators, and grazers. Geographic patterns among Recent guilds were compared to those during Pliocene and early Miocene time in order to determine how diversity and maximum size changed over the last 17 million years in the face of high levels of extinction and species invasion. Recent European guilds are generally more diverse than their American counterparts, a finding consistent with previous biota-wide analyses. Diversity within Pliocene guilds was often higher on the American side, but this stems in part from the large subtropical component in preserved temperate Pliocene guilds in Virginia but not in Europe. The largest species in hard-bottom guilds in Europe reach greater sizes than those in comparable American guilds, but for sand-bottom guilds, American species almost always attain greater sizes than their European counterparts. These size differences have changed little since early Miocene time despite high levels of Pliocene and Pleistocene extinction in invasion, particularly on the American side. Large-bodied species are overrepresented among both extinct and invading lineages, meaning that lineage replacement has been the rule for the largest species in guilds on both sides of the Atlantic. Together with previous studies, these results may imply that sand-bottom environments in North America have been more productive and have experienced more far-reaching escalation between shell-bearing species and their predators than their European counterparts since early Miocene time. The Pliocene to Recent record of hard-bottom guilds implies that productivity and/or escalation in these systems may have been higher on the European side than in eastern North America. Shallow-water guilds on opposite sides of the Atlantic have retained differences despite great upheavals caused by extinctions and invasions during the last 3 million years.
Conservation paleobiology aims to provide a longer-term perspective on environmental problems to inform decisions about natural resource conservation. As such, conservation paleobiology research ...falls short when geohistorical data and insights do not inform conservation practice, contributing to the well-known idea that a “gap” exists between the production and use of science in the environmental realm. Our study quantified the extent of this research-implementation (or knowing-doing) gap through a systematic literature review and survey questionnaire. We determined whether empirical studies in conservation paleobiology with a link to conservation, management, or restoration documented the use of geohistorical data to implement some form of action or if there was a specific mention of how the geohistorical data could be used in theory. Results indicate that “applied” conservation paleobiology has a poor record of translating research into action. Tangible conservation impacts were evident in only 10.8% of studies. Over half of these studies included coauthors affiliated with a conservation organization. Among the studies coded as having a theoretical application, 25.2% specified how the geohistorical data could be implemented to enhance conservation, management, or restoration actions. All studies documenting action used geohistorical data from the geologically recent past where the species and habitats are familiar to those found today. Drawing insights from the bright spots we identified, we offer some practical suggestions to narrow the gap between knowing and doing in conservation paleobiology.
Extinction may alter competitive interactions among surviving species, affecting their subsequent recovery and evolution, but these processes remain poorly understood. Analysis of predation traces ...produced by shell-drilling muricid snails on bivalve prey reveals that species interactions were substantially different before and after a Plio-Pleistocene mass extinction in the western Atlantic. Muricids edge- and wall-drilled their prey in the Pliocene, but Pleistocene and Recent snails attacked prey only through the shell wall. Experiments with living animals suggest that intense competition induces muricid snails to attack shell edges. Pliocene predators, therefore, probably competed for resources more intensely than their post-extinction counterparts.
River systems worldwide have been modified for human use and the downstream ecological consequences are often poorly understood. In the Colorado River estuary, where upstream water diversions have ...limited freshwater input during the last century, mollusc remains from the last several hundred years suggest widespread ecological change. The once abundant clam Mulinia modesta has undergone population declines of approximately 94% and populations of predators relying on this species as a food source have probably declined, switched to alternative prey species or both. We distinguish between the first two hypotheses using a null model of predation preference to test whether M. modesta was preyed upon selectively by the naticid snail, Neverita reclusiana, along the estuary's past salinity gradient. To evaluate the third hypothesis, we estimate available prey biomass today and in the past, assuming prey were a limiting resource. Data on the frequency of drill holes—identifiable traces of naticid predation on prey shells—showed several species, including M. modesta, were preferred prey. Neverita reclusiana was probably able to switch prey. Available prey biomass also declined, suggesting the N. reclusiana population probably also declined. These results indicate a substantial change to the structure of the benthic food web. Given the global scale of water management, such changes have probably also occurred in many of the world's estuaries.
Here we report on a large brachyuran crab species from the Late Cretaceous of Mexico that has claws indicative of highly specialized shell-breaking behaviour. This crab possessed dimorphic claws (the ...right larger than the left), armed with several broad teeth, including a curved tooth structure found at the base of the movable finger of the right claw. The curved tooth is similar to the one observed on claws of many living durophagous crabs that use it as a weapon to peel, crush or chip the edges of hard-shelled prey, particularly molluscs. These morphological traits suggest that specialized shell-breaking crab predators had evolved during the Cretaceous, which contradicts previous findings supporting an Early Cenozoic origin for specialized shell crushers within the brachyuran clade.
AIM: Throughout the Colorado River basin, numerous dams have captured and diverted the entirety of the basin's c. 1.85 × 10¹⁰ m³ year⁻¹ of water, altering the downstream delta ecosystem. In the ...absence of pre‐dam studies, geohistorical data can play a critical role in reconstructing ecological aspects of the past ecosystem. Here, we use geohistorical data to test the hypothesis that a shell‐drilling naticid gastropod predator, Notocochlis chemnitzii, has recently undergone a human‐induced range expansion to the Colorado River delta (CRD). Based on uncertainty in the literature surrounding the membership of N. chemnitzii in the CRD benthic community before the dams were built, we predicted that, for pre‐dam samples, N. chemnitzii would be absent and there would be less variance in predator size selectivity and drillhole stereotypy. LOCATION: Colorado River delta, Mexico. METHODS: At two localities we sampled naticid shells and collected bivalve prey from the tidal flat and pre‐dam era cheniers – dune‐like structures composed primarily of molluscan remains. Naticids were sorted and counted by species. Variation in the stereotypic placement of drillholes in the pre‐ and post‐dam construction eras was assessed by grouping drillholes into a nine‐sector grid superimposed on the prey's shell. Predator size was regressed on bivalve prey size to assess variation in predator size selectivity pre‐ and post‐damming of the Colorado River. RESULTS: As predicted, we found no N. chemnitzii in cheniers of pre‐dam age, whereas another naticid species, Neverita reclusiana, was common. Notocochlis chemnitzii and N. reclusiana were found in the actively forming chenier and on the tidal flat. As expected with the addition of another naticid species, the preferred site of drilling and size selectivity of prey by predators changed significantly between cheniers from the pre‐ and post‐dam construction eras due to variation in prey‐handling behaviour by different naticid species. MAIN CONCLUSIONS: Geohistorical evidence, from body and trace fossils, suggests that N. chemnitzii has recently expanded its geographical range to the CRD, whereas N. reclusiana has long dwelled in the delta. Geohistorical baseline data are an underutilized source of information that can provide unique ecological perspectives for restoration efforts in estuaries of dammed rivers world‐wide.
Abstract
In the current era of Big Data, existing synthesis tools such as formal meta-analyses are critical means to handle the deluge of information. However, there is a need for complementary tools ...that help to (a) organize evidence, (b) organize theory, and (c) closely connect evidence to theory. We present the hierarchy-of-hypotheses (HoH) approach to address these issues. In an HoH, hypotheses are conceptually and visually structured in a hierarchically nested way where the lower branches can be directly connected to empirical results. Used for organizing evidence, this tool allows researchers to conceptually connect empirical results derived through diverse approaches and to reveal under which circumstances hypotheses are applicable. Used for organizing theory, it allows researchers to uncover mechanistic components of hypotheses and previously neglected conceptual connections. In the present article, we offer guidance on how to build an HoH, provide examples from population and evolutionary biology and propose terminological clarifications.
Water management that alters riverine ecosystem processes has strongly influenced deltas and the people who depend on them, but a full accounting of the trade-offs is still emerging. Using ...palaeoecological data, we document a surprising biogeochemical consequence of water management in the Colorado River basin. Complete allocation and consumptive use of the river's flow has altered the downstream estuarine ecosystem, including the abundance and composition of the mollusc community, an important component in estuarine carbon cycling. In particular, population declines in the endemic Colorado delta clam, Mulinia coloradoensis, from 50--125 individuals m−2 in the pre-dam era to three individuals m−2 today, have likely resulted in a reduction, on the order of 5900–15 000 t C yr−1 (4.1–10.6 mol C m−2 yr−1), in the net carbon emissions associated with molluscs. Although this reduction is large within the estuarine system, it is small in comparison with annual global carbon emissions. Nonetheless, this finding highlights the need for further research into the effects of dams, diversions and reservoirs on the biogeochemistry of deltas and estuaries worldwide, underscoring a present need for integrated water and carbon planning.
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