The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Historical biogeography has been characterized by a large diversity of methods and unresolved debates about which processes, such as dispersal or vicariance, are most important for explaining distributions. A new R package, BioGeoBEARS, implements many models in a common likelihood framework, so that standard statistical model selection procedures can be applied to let the data choose the best model. Available models include a likelihood version of DIVA (“DIVALIKE”), LAGRANGE’s DEC model, and BAYAREA, as well as “+J” versions of these models which include founder-event speciation, an important process left out of most inference methods. I use BioGeoBEARS on a large sample of island and non-island clades (including two fossil clades) to show that founder-event speciation is a crucial process in almost every clade, and that most published datasets reject the non-J models currently in widespread use. BioGeoBEARS is open-source and freely available for installation at the Comprehensive R Archive Network at http://CRAN.R-project.org/package=BioGeoBEARS. A step-by-step tutorial is available at http://phylo.wikidot.com/biogeobears.

/pdf/probabilistic-historical-biogeography-new-models-for-founder-33j2vpcyd4.pdf

Probabilistic historical biogeography: new models for founder-event speciation, imperfect detection, and fossils allow improved accuracy and model-testing

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-1800s, 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.



Integracion de Paleobiologia, Arqueologia e Historia para Informar a la Biologia de la Conservacion

Resumen

La busqueda de metodos nuevos para establecer lineas de base ecologicas (condiciones de referencia) esta limitada por el hecho de que la mayoria de los estudios ecologicos abarcan las ultimas decadas, cuando mucho, e investigan ecosistemas que han sido alterados sustancialmente por actividades humanas, por decadas, siglos o, posiblemente, mas. La paleobiologia, arqueologia e historia proporcionan contexto ecologico historico a la biologia de la conservacion, la remediacion y restauracion. Argumentamos que la integracion explicita de la ecologia historica con la conservacion puede ayudar a unificar disciplinas relacionadas de paleobiologia de la conservacion, arqueobiologia de la conservacion e historia ambiental. Diferencias en la resolucion espacial y temporal y la extension (escala) de datos prehistoricos, historicos y modernos aun son obstaculos para la integracion de la ecologia historica y la biologia de la conservacion, pero las extensiones temporales prolongadas de datos ecologicos historicos pueden ayudar a establecer lineas de base mas completas para la restauracion, documentar un rango historico de variabilidad ecologica y ayudar a la determinacion de condiciones futuras deseadas. Utilizamos la pesqueria del ostion oriental (Crassostrea virginica) de la Bahia de Chesapeake (E.U.A.) para demostrar la utilidad de los datos ecologicos historicos para dilucidar la conservacion del ostion y la necesidad de un metodo de conservacion que trascienda limites disciplinares. Los estudios ecologicos historicos de Chesapeake han documentado declinaciones dramaticas (tanto como 99%) en la abundancia de ostiones de inicios a mediados de los 1800, cambios en el tamano de ostiones en respuesta a diferentes niveles de nutrientes del siglo dieciseis al diecinueve y reducciones sustanciales en las tasas de acrecion de ostiones (de 10 mm/ano a 0 mm/ano) desde el Holoceno Tardio a tiempos modernos. Una mejor integracion de diferentes conjuntos de datos ecologicos historicos y una mayor colaboracion entre paleobiologos, geologos, arqueologos, historiadores ambientales y ecologos para definir disenos de investigacion estandarizados y metodologias ayudaran a unificar perspectivas de la biologia de la conservacion prehistoricas, historicas y modernas.

/pdf/integrating-paleobiology-archeology-and-history-to-inform-1ck5ga8lg5.pdf

Integrating paleobiology, archeology, and history to inform biological conservation.

About 3 million years ago (Ma), the Isthmus of Panama joined the Americas, forming a land bridge over which inhabitants of each America invaded the other—the Great American Biotic Interchange. These invasions transformed land ecosystems in South and Middle America. Humans invading from Asia over 12000 years ago killed most mammals over 44 kg, again transforming tropical American ecosystems. As a sea barrier, the isthmus induced divergent environmental change off its two coasts—creating contrasting ecosystems through differential extinction and diversification. Approximately 65 Ma invading marsupials and ungulates of North American ancestry, and xenarthrans of uncertain provenance replaced nearly all South America’s non-volant mammals. There is no geological evidence for a land bridge at that time. Together with rodents and primates crossing from Africa 42 to 30 Ma, South America’s mammals evolved in isolation until the interchange’s first heralds less than 10 Ma. Its carnivores were ineffective marsupials. Meanwhile, North America was invaded by more competitive Eurasian mammals. The Americas had comparable expanses of tropical forest 55 Ma; later, climate change confined North American tropical forest to a far smaller area. When the isthmus formed, North American carnivores replaced their marsupial counterparts. Although invaders crossed in both directions, North American mammals spread widely, diversified greatly, and steadily replaced South American open-country counterparts, unused to effective predators. Invading South American mammals were less successful. South America’s birds, bats, and smaller rainforest mammals, equally isolated, mostly survived invasion. Its vegetation, enriched by many overseas invaders, remained intact. This vegetation resists herbivory effectively. When climate permitted, South America’s rainforest, with its bats, birds and mammals, spread to Mexico. Present-day tropical American vegetation is largely zoned by trade-offs between exploiting well-watered settings versus surviving droughts, exploiting fertile versus coping with poor soil, and exploiting lowland warmth versus coping with cooler altitudes. At the start of the Miocene, a common marine biota extended from Trinidad to Ecuador and western Mexico, which evolved in isolation from the Indo-Pacific until the Pleistocene. The seaway between the Americas began shoaling over 12 Ma. About 10 Ma the land bridge was briefly near-complete, allowing some interchange of land mammals between the continents. By 7 Ma, the rising sill had split deeper-water populations. Sea temperature, salinity and sedimentary carbon content had begun to increase in the Southern Caribbean, but not the Pacific. By 4 Ma, the seaway’s narrowing began to extinguish Caribbean upwellings. By 2 Ma, upwellings remained only along Venezuela; Caribbean plankton, suspension-feeding molluscs and their predators had declined sharply, largely replaced by bottom-dwelling corals and calcareous algae and magnificent coral reefs. Closing the seaway extinguished the Eastern Pacific’s reef corals (successors recolonized from the Indo-Pacific 6000 years ago), whereas many molluscs of productive waters that once thrived in the Caribbean now survive only in the Eastern Pacific. The present-day productive Eastern Pacific, with few, small coral reefs and a plankton-based ecosystem contrasts with the Caribbean, whose clear water favours expansive coral reefs and bottom-dwelling primary producers. These ecosystems reflect the trade-off between fast growth and effective defence with attendant longevity. Overfishing with new technologies during the last few centuries, however, has caused population crashes of ever-smaller marine animals, devastating Caribbean ecosystems.

/pdf/historical-biogeography-of-the-isthmus-of-panama-3mx1unse14.pdf

Historical biogeography of the Isthmus of Panama.

Evolution and escalation, an ecological history of life

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.

Reduced competition and altered feeding behavior among marine snails after a mass extinction.

Paleontologists increasingly appreciate the importance of studying the ecological context of fossil species and communities. Measuring abundance is a vital component not just for describing this context, but also for evaluating biases related to preservation and sampling and for estimating species richness (Jackson et al. 1999; Jackson and Johnson 2001; Kidwell 2001). Our purpose here is to identify a previously unrecognized problem that could lead to incorrect interpretation of observed patterns of abundance. Understanding ancient and living communities and ecosystems requires intimate knowledge of their members. We need to know who the members are, how many of them there are, how they interact, and how they collectively forge a workable, durable whole. Not all species contribute equally to ecosystems. Although some rare species have disproportionate effects because of their very high per capita power-large warm-blooded vertebrates come to mind as examples-many others are what Birkeland (1996) referred to as ornaments, pleasing and interesting but economically of little consequence. Abundance is one measure of a species' success. If a species is common, its characteristics-individual features as well as the attributes of populationsmust be responsible for its success. Jernvall and Fortelius (2002), in fact, applied this rationale to show that abundant and widespread species of Miocene mammals in Europe typically show a trend toward hypsodonty (the development of high-crowned cheek teeth), whereas rare ones often do not. They argued that abundance is a legitimate measure of suc

Measuring relative abundance in fossil and living assemblages

Edge drilling is a form of predation in which a predatory snail excavates a hole at a point along the margin of the closed valves of a bivalved animal. We tested the hypothesis that edge-drilling attacks by the predatory snail Chicoreus dilectus on its clam prey Chione elevata shorten the duration of the predation process relative to the alternative behaviour of drilling through the prey's shell wall away from its edges. The time required to complete an edge-drilling attack was on average about three times less than when prey were attacked through the shell wall. This improvement in predation speed was a function of the thickness of the prey's shell at the point of attack. We suggest that owing to the shorter length of time required to kill prey, the edge-drilling behaviour may be selectively advantageous in environments where enemies are abundant, especially competitors that might attempt to steal prey. Behaviours that speed up the predation process may create opportunities for more effective exploitation of available prey resources in highly competitive environments.

Influence of alternative shell‐drilling behaviours on attack duration of the predatory snail, Chicoreus dilectus

Oysters (Crassostrea virginica) were a central component of the Chesapeake Bay ecosystem in 1607 when European settlers established Jamestown, VA, the first permanent English settlement in North America. These estuarine bivalves were an important food resource during the early years of the James Fort (Jamestown) settlement while the colonists were struggling to survive in the face of inadequate supplies and a severe regional drought. Although oyster shells were discarded as trash after the oysters were eaten, the environmental and ecological data recorded in the bivalve geochemistry during shell deposition remain intact over centuries, thereby providing a unique window into conditions during the earliest Jamestown years. We compare oxygen isotope data from these 17th century oyster shells with modern shells to quantify and contrast estuarine salinity, season of oyster collection, and shell provenance during Jamestown colonization (1609-1616) and the 21st century. Data show that oysters were collected during an extended drought between fall 1611 and summer 1612. The drought shifted the 14 psu isohaline above Jamestown Island, facilitating individual oyster growth and extension of oyster habitat upriver toward the colony, thereby enhancing local oyster food resources. Data from distinct well layers suggest that the colonists also obtained oysters from reefs near Chesapeake Bay to augment oyster resources near Jamestown Island. The oyster shell season of harvest reconstructions suggest that these data come from either a 1611 well with a very short useful period or an undocumented older well abandoned by late 1611.

/pdf/reconstructing-early-17th-century-estuarine-drought-2r24jok9wj.pdf

Gregory S. Herbert

Papers

Reduced competition and altered feeding behavior among marine snails after a mass extinction.

Measuring relative abundance in fossil and living assemblages

Influence of alternative shell‐drilling behaviours on attack duration of the predatory snail, Chicoreus dilectus

Reconstructing early 17th century estuarine drought conditions from Jamestown oysters

No honor among snails: Conspecific competition leads to incomplete drill holes by a naticid gastropod