Cuban science democratic and not tied to profit

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

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

Age Interpolation - Reply

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62790/1/323471b0.pd

Data from: Small-mammal isotope ecology tracks climate and vegetation gradients across western North America

Stable carbon, nitrogen, hydrogen and oxygen isotopes have been used to infer aspects of species ecology and environment in both modern ecosystems and the fossil record. Compared to large mammals, stable isotopic studies of small-mammal ecology are limited; however, high species and ecological diversity within small mammals presents several advantages for quantifying resource use and organism–environment interactions using stable isotopes over various spatial and temporal scales. We analyzed the isotopic composition of hair from two heteromyid rodent species, Dipodomys ordii and Perognathus parvus, from localities across western North America in order to characterize dietary variation in relation to vegetation and climatic gradients. Significant correlations between the carbon isotopic composition (δ13C) of these species and several climatic variables imply that seasonal temperature and precipitation control the composition and distribution of dietary resources (grass seeds). Our results also suggest a moisture influence on the nitrogen isotopic composition (δ15N) of heteromyid diets. Population- and species-level variation in δ13C and δ15N values record fine-scale habitat heterogeneity and significant differences in resource use between species. Using classification and regression-tree techniques, we modeled the geographic variation in heteromyid δ13Cdiet values based on 10 climatic variables and generated an isotope landscape model (‘isoscape’). The isoscape predictions for δ13Cdiet differ from expectations based on observed C4 distributions and instead indicate that D. ordii and P. parvus record seasonally abundant grass resources, with additional model deviations potentially attributed to geographic variation in dietary selection. The oxygen and hydrogen isotopic composition of D. ordii is enriched relative to local meteoric water and suggests that individuals rely on highly evaporated water sources, such as seed moisture. Based on the climatic influences on vegetation and diet documented in this study, the isotopic composition of small mammals has high potential for recording ecological responses to environmental changes over short and long time scales

Small-mammal isotopes, SM Appendices 1 and 2

Supplemental Material, including locality, specimen and isotopic data as well as results from conditional forest analysis described in the paper

Faunal and environmental change in the late Miocene Siwaliks of northern Pakistan

The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossiliferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and temporally resolved study of the sediments and faunas than is typical in terrestrial deposits. Consequently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven taxonomic treatment across groups. We attempt to control for them primarily by using a relative-abundance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years. Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age estimates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small species include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg. The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan system. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol sequences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation. The oxygen isotopic record also indicates significant change in the patterns of precipitation beginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma. Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7–5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3–7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Between 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vegetation. We presume exceptions to this pattern were animals of the mixed C3/C4 communities or the wetter parts of the floodplain that did not persist into the latest Miocene. The pace of extinction accelerates once there is C4 vegetation on the floodplain. The 10.3 Ma event primarily comprises disappearance of taxa that were both common and of long duration. The event does not correlate to any obvious local environmental or climatic event, and the pattern of species disappearance and appearance suggests that biotic interactions may have been more important than environmental change. The 7.8 Ma event is characterized solely by appearances, and that at 7.3 Ma by a combination of appearances and disappearances. These two latest Miocene events include more taxa that were shorter ranging and less common, a difference of mode that developed between approximately 9.0 and 8.5 Ma when many short-ranging and rare species began to make appearances. Both events also show a close temporal correlation to changes in floodplain deposition and vegetation. The 7.8 Ma event follows the widespread appearance of C4 vegetation and is coincident with the shift from equid-dominated to more evenly balanced large-mammal assemblages. The 7.3 to 7.0 Ma event starts with the first occurrence of C4-dominated floras and ends with the last occurrence of C3-dominated vegetation. Absence of a consistent relationship between depositional facies and the composition of faunal assemblages leads us to reject fluvial system dynamics as a major cause of faunal change. The close correlation of latest Miocene species turnover and ecological change to expansion of C4 plants on the floodplain, in association with oxygen isotopic and sedimentological evidence for increasingly drier and more seasonal climates, causes us to favor explanations based on climatic change for both latest Miocene pulses. The Siwalik record supports neither “coordinated stasis” nor “turnover pulse” evolutionary models. The brief, irregularly spaced pulses of high turnover are characteristic of both the stasis and pulse models, but the high level of background turnover that eliminates 65–70% of the initial species shows there is no stasis in the Siwalik record. In addition, the steadily declining species richness and abrupt, uncoordinated changes in diversity do not fit either model