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The Cenozoic landscape evolution in southwestern North America is ascribed to crustal isostasy, dynamic topography, or lithosphere tectonics, but their relative contributions remain controversial. Here we reconstruct landscape history since the late Eocene by investigating the interplay between mantle convection, lithosphere dynamics, climate, and surface processes using fully coupled four-dimensional numerical models. Our quantified depth-dependent strain rate and stress history within the lithosphere, under the influence of gravitational collapse and sub-lithospheric mantle flow, show that high gravitational potential energy of a mountain chain relative to a lower Colorado Plateau can explain extension directions and stress magnitudes in the belt of metamorphic core complexes during topographic collapse. Profound lithospheric weakening through heating and partial melting, following slab rollback, promoted this extensional collapse. Landscape evolution guided northeast drainage onto the Colorado Plateau during the late Eocene-late Oligocene, south-southwest drainage reversal during the late Oligocene-middle Miocene, and southwest drainage following the late Miocene. Cenozoic landscape evolution of southwestern North America remains debated. Here, the authors reconstruct landscape using 4-D numerical models, which can explain extensional collapse and superficial geological record for the Basin and Range Province [ABSTRACT FROM AUTHOR]

The mammalian family Bovidae has been widely studied in ecomorphological research, with important applications to paleoecological and paleohabitat reconstructions. Most studies of bovid craniomandibular features in relation to diet have used linear measurements. In this study, we conduct landmark-based geometric-morphometric analyses to evaluate whether different dietary groups can be distinguished by mandibular morphology. Our analysis includes data for 100 species of extant bovids, covering all bovid tribes and 2 dietary classifications. For the first classification with 3 feeding categories, we found that browsers (including frugivores), mixed feeders, and grazers are moderately well separated using mandibular shape. A finer dietary classification (frugivore, browser, browser–grazer intermediate, generalist, variable grazer, and obligate grazer) proved to be more useful for differentiating dietary extremes (frugivores and obligate grazers) but performed equally or less well for other groups. Notably, frugivorous bovids, which belong in tribe Cephalophini, have a distinct mandibular shape that is readily distinguished from all other dietary groups, yielding a 100% correct classification rate from jackknife cross-validation. The main differences in mandibular shape found among dietary groups are related to the functional needs of species during forage prehension and mastication. Compared with browsers, both frugivores and grazers have mandibles that are adapted for higher biomechanical demand of chewing. Additionally, frugivore mandibles are adapted for selective cropping. Our results call for more work on the feeding ecology and functional morphology of frugivores and offer an approach for reconstructing the diet of extinct bovids. [ABSTRACT FROM AUTHOR]

Modern death assemblages provide insights about the early stages of fossilization and useful ecological information about the species inhabiting the ecosystem. We present the results of taphonomic monitoring of modern vertebrate carcasses and bones from Doñana National Park, a Mediterranean coastal ecosystem in Andalusia, Spain. Ten different habitats were surveyed. Half of them occur in active depositional environments (marshland, lake margin, river margin, beach and dunes). Most of the skeletal remains belong to land mammals larger than 5 kg in body weight (mainly wild and feral ungulates). Overall, the Doñana bone assemblage shows good preservation with little damage to the bones, partly as a consequence of the low predator pressure on large vertebrates. Assemblages from active depositional habitats differ significantly from other habitats in terms of the higher incidence of breakage and chewing marks on bones in the latter, which result from scavenging, mainly by wild boar and red fox. The lake-margin and river-margin death assemblages have high concentrations of well preserved bones that are undergoing burial and offer the greatest potential to produce fossil assemblages. The spatial distribution of species in the Doñana death assemblage generally reflects the preferred habitats of the species in life. Meadows seem to be a preferred winter habitat for male deer, given the high number of shed antlers recorded there. This study is further proof that taphonomy can provide powerful insights to better understand the ecology of modern species and to infer past and future scenarios for the fossil record. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The alternating mountain ranges and desert basins of the Great Basin in the western United States support higher species diversity of mammals than any other region of comparable area in temperate North America. Topographically complex regions have strong environmental gradients and heterogeneous habitats that result in fragmented geographic ranges over long periods and may promote speciation. In order to evaluate the influence of topography and climate on mammal diversification, we traced the history of mammal diversity during the formation of basin-and-range topography. We compiled species-occurrence data from the NeoMap database of fossil mammals and calculated standing diversity, origination rate, extinction rate, diversification rate (originations − extinctions), and turnover rate (originations + extinctions) for million-year intervals. We evaluated changes in faunal composition (species in mammalian orders and species in rodent families) over time and assessed whether significant changes in diversity and faunal composition tracked major changes in landscape history. Neogene geologic evolution generated by tectonic activity and changing climate created the topographic complexity and habitat heterogeneity of the Great Basin. Over the last 30 million years, extensional tectonic processes caused an older high plateau to collapse and stretch from east to west, resulting in longitudinal expansion by ~235 km to form the Great Basin. Average elevation decreased by 1-3 km. Global warming and associated increases in regional precipitation from 17 to 14 million years ago (mya; the Miocene Climatic Optimum [MCO]) interrupted the long-term trend of Cenozoic cooling and aridification. From 30 to 2 mya, Great Basin mammal diversity peaked during the MCO, then declined over the later Miocene and Pliocene. The major changes in diversity over time were robust to sampling effects. Faunal composition changed episodically, with increasing proportions of rodents, lagomorphs, and carnivores and decreasing proportions of ungulates and proboscideans. The highest diversification rate occurred during the MCO with smaller but significant diversification rates later in the Neogene. The highest turnover rates occurred during and immediately following the MCO. Comparison of rodent faunas of the Great Basin and the Great Plains showed substantial differences in the timing and magnitude of diversification and changes in taxonomic composition. These patterns support the hypothesis that climate change over complex topography stimulated diversification in the Great Basin. [ABSTRACT FROM AUTHOR]

Terrestrial vertebrates show striking changes in species richness across topographic gradients. For mammals, nearly twice as many species per unit area occur in topographically complex regions as in adjacent lowlands. The geological context of this pervasive biogeographic pattern suggests that tectonic processes have a first-order impact on regional diversity. I evaluate ecological, evolutionary, and historical influences of tectonics and topography on the regional diversity of terrestrial mammals, focusing on the hypothesis that diversification rates are higher in active versus passive tectonic settings. Ten predictions follow from this hypothesis. 1) The timing of peaks in speciation should be congruent with the timescale for tectonic episodes. 2) The rates of speciation and genetic differentiation of populations should be greater for species inhabiting topographically complex regions than spatially continuous landscapes. 3) If topographic complexity per se promotes diversification, then a cluster of young divergences should occur for montane species compared to lowland relatives. 4) Endemism in tectonically active regions should reflect origination within the region rather than range reduction from larger areas. 5) Extinction rates should differ for lineages in tectonically active regions compared to adjacent lowlands. 6) The relationship between local and regional species richness should differ between topographic settings because of higher beta diversity in topographically complex regions. 7) Species originating in topographically complex regions should colonize adjacent lowlands more often than the reverse pattern. 8) North-south mountain ranges should have higher regional species richness than east-west mountain ranges. 9) Areas with multiple mountain ranges should have higher regional species richness than comparable areas with single mountain ranges. 10) Global climate changes should affect diversification in tectonically active regions. Research addressing these topics places elevational diversity gradients into a geohistorical context and integrates data from modern biotas and the fossil record. [ABSTRACT FROM AUTHOR]

Aim Spatial turnover of species, or beta diversity, varies in relation to geographical distance and environmental conditions, as well as spatial scale. We evaluated the explanatory power of distance, climate and topography on beta diversity of mammalian faunas of North America in relation to latitude. Location North America north of Mexico. Methods The study area was divided into 313 equal-area quadrats (241 × 241 km). Faunal data for all continental mammals were compiled for these quadrats, which were divided among five latitudinal zones. These zones were comparable in terms of latitudinal and longitudinal span, climatic gradients and elevational gradients. We used the natural logarithm of the Jaccard index (ln J) to measure species turnover between pairs of quadrats within each latitudinal zone. The slope of ln J in relation to distance was compared among latitudinal zones. We used partial regression to partition the variance in ln J into the components uniquely explained by distance and by environmental differences, as well as jointly by distance and environmental differences. Results Mammalian faunas of North America differ more from each other at lower latitudes than at higher latitudes. Regression models of ln J in relation to distance, climatic difference and topographic difference for each zone demonstrated that these variables have high explanatory power that diminishes with latitude. Beta diversity is higher for zones with higher mean annual temperature, lower seasonality of temperature and greater topographic complexity. For each latitudinal zone, distance and environmental differences explain a greater proportion of the variance in ln J than distance, climate or topography does separately. Main conclusions The latitudinal gradient in beta diversity of North American mammals corresponds to a macroclimatic gradient of decreasing mean annual temperature and increasing seasonality of temperature from south to north. Most of the variance in spatial turnover is explained by distance and environmental differences jointly rather than distance, climate or topography separately. The high predictive power of geographical distance, climatic conditions and topography on spatial turnover could result from the direct effects of physical limiting factors or from ecological and evolutionary processes that are also influenced by the geographical template. [ABSTRACT FROM AUTHOR]

Geohistorical records reveal the long-term impacts of climate change on ecosystem structure. A 5-myr record of mammalian faunas from floodplain ecosystems of South Asia shows substantial change in species richness and ecological structure in relation to vegetation change as documented by stable isotopes of C and O from paleosols. Between 8.5 and 6.0 Ma, C4 savannah replaced C3 forest and woodland. Isotopic historical trends for 27 mammalian herbivore species, in combination with ecomorphological data from teeth, show three patterns of response. Most forest frugivores and browsers maintained their dietary habits and disappeared. Other herbivores altered their dietary habits to include increasing amounts of C4 plants and persisted for >1 myr during the vegetation transition. The few lineages that persisted through the vegetation transition show isotopic enrichment of δ13C values overtime. These results are evidence for long-term climatic forcing of vegetation structure and mammalian ecological diversity at the subcontinental scale. [ABSTRACT FROM AUTHOR]

Agricultural landscapes are essential for preserving biodiversity, even though agricultural activities are the leading cause of habitat degradation worldwide. About half of the Earth's productive land area is farmed or grazed, whereas only about 6% of the total land area is protected for native species and ecosystems. The ecological services of healthy ecosystems are fundamental to agriculture, and these services depend upon a large number of species interacting with each other and with inorganic nutrient cycles. Likewise, the quality of ecosystems between reserves is critical to the persistence of species and ecological processes within reserves. Thus, conservation-oriented farming methods are critically important for both agriculture and biodiversity. Three examples illustrate agricultural practices that benefit the farmers, the local ecosystem and the landscape: (1) In Minnesota, rotational grazing, evaluated by the collaborative research of farmers and scientists, improved soil, pasture and stream quality, and boosted the confidence of the farmers in developing more sustainable grazing practices. (2) Predator-friendly ranching in Montana, in which nonlethal methods are used to protect livestock from depredation by native predators, benefited the ranchers with premium prices for wool and meat. The persistence of native predators, many of which have been on endangered species lists for years, benefited the regional ecosystem. (3) Shade-grown coffee in Latin America, in which coffee shrubs grow under an intact forest canopy, often looks and behaves ecologically like native forest and may house high levels of native biodiversity. This system benefited farmers, as long as they received a price premium for shade-grown coffee. The economic viability of these conservation-oriented practices depends upon farmers receiving price premiums for their products and by society rewarding farmers for their practices. A vision of ecological farming as the dominant form of... [ABSTRACT FROM AUTHOR]

This article presents the author's experience when she visited East Rosebud, a valley in the Beartooth Mountains of southern Montana. The author describes the strangeness of the moment when a place encountered for the first time has so many familiar qualities and details that it seems to be the discovery of a long-lost home. According to the author, Beartooths have been a place of formative experiences. Perhaps most important is the unity of knowledge and experience that she found there. This knowledge was often more academic than felt. In the Beartooths, the knowledge, the sensory immersion in wilderness, the confidence from being self-reliant for a few days, the comforts and the discomforts combined in an understanding that she was also part of the ancient, immortal play, not just a distant observer.

Investigates the relationship of climate and physiography on the density and ecological diversity of mammals in North America. Percentage of environmental variables representing the entire continent; Variance in the environmental variables of predicted species density; Implication of changes in the size and trophic structure of mammalian fauna on species density.

A letter to the editor is presented in response to the article "Front Ecol Environ," by Joern Fischer, Berry Brosi, and Gretchen C. Daily in the 2008 issue.

The exceptional fossil sites of Cerro de los Batallones (Madrid Basin, Spain) contain abundant remains of Late Miocene mammals. From these fossil assemblages, we have inferred diet, resource partitioning and habitat of three sympatric carnivorous mammals based on stable isotopes. The carnivorans include three apex predators: two sabre-toothed cats (Felidae) and a bear dog (Amphicyonidae). Herbivore and carnivore carbon isotope (δ13C) values from tooth enamel imply the presence of a woodland ecosystem dominated by C3 plants. δ13C values and mixing-model analyses suggest that the two sabre-toothed cats, one the size of a leopard and the other the size of a tiger, consumed herbivores with similar δ13C values from a more wooded portion of the ecosystem. The two sabre-toothed cats probably hunted prey of different body sizes, and the smaller species could have used tree cover to avoid encounters with the larger felid. For the bear dog, δ13C values are higher and differ significantly from those of the sabre-toothed cats, suggesting a diet that includes prey from more open woodland. Coexistence of the sabre-toothed cats and the bear dog was likely facilitated by prey capture in different portions of the habitat. This study demonstrates the utility of stable isotope analysis for investigating the behaviour and ecology of members of past carnivoran guilds. [ABSTRACT FROM AUTHOR]

Presents a letter to the editor concerning Cuban government-funded science.

Discusses problems of and prospects for agriculture. Concerns about ways to feed people living on the Earth; Development of agricultural technologies to provide food for the population; Challenges faced by agriculture.