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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62931/1/437192a.pd

Ecological biogeography of North American mammals: species density and ecological structure in relation to environmental gradients

Aim To evaluate the relationship of climate and physiography to species density and ecological diversity of North American mammals. Location North America, including Mexico and Central America. Methods Species density, size structure and trophic structure of mammalian faunas and nine environmental variables were documented for quadrats covering the entire continent. Spatial autocorrelation of species density and the environmental variables illustrated differences in their spatial structure at the continental scale. We used principal component analysis to reduce the dimensionality of the climatic variables, linear multiple regression to determine which environmental variables best predict species density for the continent and several regions of the continent, and canonical ordination to evaluate how well the environmental variables predict ecological structure of mammalian faunas over North America. Results In the best regression model, five environmental variables, representing seasonal extremes of temperature, annual energy and moisture, and elevation, predicted 88 of the variation in species density for the whole continent. Among different regions of North America, the environmental variables that predicted species density vary. Changes in the size and trophic structure of mammalian faunas accompany changes in species density. Redundancy analysis demonstrated that environmental variables representing winter temperature, frostfree period, potential and actual evapotranspiration, and elevation account for 77 of the variation in ecological structure. Main conclusions The latitudinal gradient in mammalian species density is strong, but most of it is explained by variation in the environmental variables. Each ecological category peaks in species richness under particular environmental conditions. The changes of greatest magnitude involve the smallest size categories (< 10 g, 11 100 g), aerial insectivores and frugivores. Species in these categories, mostly bats, increase along a gradient of decreasing winter temperature and increasing annual moisture and frostfree period, trends correlated with latitude. At the opposite end of this gradient, species in the largest size category (101 1000 kg) increase in frequency. Species in size categories 3 (101 1000 g), 5 (11 100 kg) and 6 (101 1000 kg), herbivores, and granivores increase along a longitudinal gradient of increasing annual potential evapotranspiration and elevation. Much of the spatial pattern is consistent with ecological sorting of species ranges along environmental gradients, but differential rates of speciation and extinction also may have shaped the ecological diversity of extant North American mammals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75250/1/j.1365-2699.2000.00498.x.pd

Miocene hominoids from Pakistan

Remains of hominoid primates collected by Yale Peabody Museum - Geological Survey of Pakistan expeditions to the Siwalik Group rocks of the Potwar Plateau, Pakistan, are described. They consist of facial, gnathic, dental, and postcranial remains of Ramapithecus, Sivapithecus, and Gigantopithecus. They are discussed anatomically and without precise taxonomic attributions. The hominoids come from 24 localities, the majority being around eight million years old. The depositional environments of 21 hominoid localities are documented in the form of microstratigraphic sections. These sections depict depositional and postdepositional features that are necessary for interpreting the facies of fossiliferous horizons. Within the predominantly fluvial Siwalik Group sediments, a three-fold division of facies is convenient for distinguishing certain taphonomic influences on hominoid and other vertebrate fossils. These facies are 1) channel, 2) channel margin, and 3) floodplain. A locality consists of one or more fossiliferous horizons, and thus one or more facies may be represented. Interpretations of the facies represented at each locality accompany the microstratigraphic sections

Diet segregation in American bison (Bison bison) of Yellowstone National Park (Wyoming, USA)

Abstract Background Body size is a major factor in the nutritional ecology of ruminant mammals. Females, due to their smaller size and smaller rumen, have more rapid food-passage times than males and thereby require higher quality forage. Males are more efficient at converting high-fiber forage into usable energy and thus, are more concerned with quantity. American bison are sexually dimorphic and sexually segregate for the majority of their adult lives, and in Yellowstone National Park, they occur in two distinct subpopulations within the Northern and Central ranges. We used fecal nitrogen and stable isotopes of carbon and nitrogen from American bison to investigate sex-specific differences in diet composition, diet quality, and dietary breadth between the mating season and a time period spanning multiple years, and compared diet indicators for these different time periods between the Northern and Central ranges. Results During mating season, diet composition of male and female American bison differed significantly; females had higher quality diets, and males had greater dietary breadth. Over the multi-year period, females had higher quality diets and males, greater dietary breadth. Diet segregation for bison in the Central Range was more pronounced during the mating season than for the multi-year period and females had higher quality diets than males. Finally, diet segregation in the Northern Range was more pronounced during the multi-year period than during the mating season, and males had greater dietary breadth. Conclusions Female bison in Yellowstone National Park have higher quality diets than males, whereas males ingest a greater diversity of plants or plants parts, and bison from different ranges exhibited more pronounced diet segregation during different times. Collectively, our results suggest that diet segregation in bison of Yellowstone National Park is associated with sex-specific differences in nutritional demands. Altogether, our results highlight the importance of accounting for spatial and temporal heterogeneity when conducting dietary studies on wild ungulates.https://deepblue.lib.umich.edu/bitstream/2027.42/137700/1/12898_2017_Article_137.pd

Sampling and faunal turnover in early Eocene mammals

Faunal turnovers in the fossil record are episodes of synchronous appearance and disapperance of species from a community, often resulting in net change in species richness. We studied the biostratigraphic record of faunal turnover involving early Wasatchian (early Eocene) mammals from the Clark's Fork Basin, Wyoming, U.S.A. Two faunal turnovers occur in this record -- one at the base of the Wasatchian, comprised mainly of apperances of taxonomically and ecologically distinctive species, and a later one, Biohorizon A of Schankler (1980), comprised mainly of disappearances, especially of carnivorous species. This study focuses on Biohorizon A.In the record of the Clark's Fork Basin, Biohorizon A may be an artifact of sampling. Sample size and species richness are highly correlated (r = 0.95) throughout this record. Moreover, sample size and species richness fluctuate markedly between successive stratigraphic intervals; peaks of apperances coincide with large sample sizes and peaks of disappearances with low sample sizes. The peaks and valleys in fossil productivity over time mask the real timing of apperances and disapperances of species. Changes in fossil productivity in the stratigraphic section may result from changes in exposure area, taphonomic factors, or ecological factors.Evaluation of the effects of sampling is a necessary prerequisite for investigating the chronological and ecological significance of faunal turnovers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27398/1/0000429.pd

Taphonomic bias in fish diversity from cenozoic floodplain environments

The fossil record of Cenozoic floodplain fishes increases from few species in the Paleocene and Eocene to about 5-15 species per locality in the Pliocene and Pleistocene. Modern floodplain habitats usually have more than 5-10 times this many species. The trend could be interpreted as an evolutionary increase, except that there seem to be no ecological or evolutionary reasons to expect ancient floodplains to have fewer species than modern floodplains.The alternate hypothesis is that ecological and fluvial processes destroy most fish bones before they are finally buried. Although floodplain depositional environments trap many fishes, these are subjected to extensive predation and scavenging, thereby reducing the opportunities for bones of small fishes, which make up most of the diversity, to be preserved in the fossil record. Abrasion in bedload probably destroys most small bones that are reworked. Surface collecting methods exaggerate the bias further because fish bones from fluvial rocks are fragmentary, difficult to discover, and difficult to identify. Screen washing for fossils from fine-grained sedimentary lenses should increase the known diversity from floodplain deposits.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27399/1/0000430.pd

Data from: Diversity dynamics of mammals in relation to tectonic and climatic history: comparison of three Neogene records from North America

In modern ecosystems, regions of topographic heterogeneity, when compared with nearby topographically homogeneous regions, support high species densities of mammals and other groups. This biogeographic pattern could be explained by either greater diversification rates or greater accommodation of species in topographically complex regions. In this context, we assess the hypothesis that changes in landscape history have stimulated diversification in mammals. Landscape history includes tectonic and climatic processes that influence topographic complexity at regional scales. We evaluated the influence of changes in topographic complexity and climate on origination and extinction rates of rodents, the most diverse clade of mammals. We compared the Neogene records of rodent diversity for three regions in North America. The Columbia Basin of the Pacific Northwest (Region 1) and the northern Rocky Mountains (Region 2) were tectonically active over much of the Cenozoic and are characterized by high topographic complexity today. The northern Great Plains (Region 3) have been tectonically quiescent, with low relief, throughout the Cenozoic. These three regions have distinctive geologic histories and substantial fossil records. All three regions showed significant changes in diversification and faunal composition over the Neogene. In the montane regions, originations and extinctions peaked at the onset and close, respectively, of the Miocene Climatic Optimum (17–14 Ma), with significant changes in faunal composition accompanying these episodes of diversification. In the Great Plains, rodents showed considerable turnover but infrequent diversification. Peak Neogene diversity in the Great Plains occurred during cooling after the Miocene Climatic Optimum. These histories suggest that climatic changes interacting with increasing topographic complexity intensify macroevolutionary processes. In addition, close tracking of diversity and fossil productivity with the stratigraphic record suggests either large-scale sampling biases or the mutual response of diversity and depositional processes to changes in landscape history