Body size downgrading of mammals over the late Quaternary Smith, Felisa A; Elliott Smith, Rosemary E; Lyons, S Kathleen ...
Science (American Association for the Advancement of Science),
2018-Apr-20, 2018-04-20, 20180420, Letnik:
360, Številka:
6386
Journal Article
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Since the late Pleistocene, large-bodied mammals have been extirpated from much of Earth. Although all habitable continents once harbored giant mammals, the few remaining species are largely confined ...to Africa. This decline is coincident with the global expansion of hominins over the late Quaternary. Here, we quantify mammalian extinction selectivity, continental body size distributions, and taxonomic diversity over five time periods spanning the past 125,000 years and stretching approximately 200 years into the future. We demonstrate that size-selective extinction was already under way in the oldest interval and occurred on all continents, within all trophic modes, and across all time intervals. Moreover, the degree of selectivity was unprecedented in 65 million years of mammalian evolution. The distinctive selectivity signature implicates hominin activity as a primary driver of taxonomic losses and ecosystem homogenization. Because megafauna have a disproportionate influence on ecosystem structure and function, past and present body size downgrading is reshaping Earth's biosphere.
The road to a larger brain Smith, Felisa A
Science (American Association for the Advancement of Science),
04/2022, Letnik:
376, Številka:
6588
Journal Article
Recenzirano
Ecological opportunities in the early Cenozoic favored larger, not smarter, mammals.
Large herbivores and carnivores (the megafauna) have been in a state of decline and extinction since the Late Pleistocene, both on land and more recently in the oceans. Much has been written on the ...timing and causes of these declines, but only recently has scientific attention focused on the consequences of these declines for ecosystem function. Here, we review progress in our understanding of how megafauna affect ecosystem physical and trophic structure, species composition, biogeochemistry, and climate, drawing on special features of PNAS and Ecography that have been published as a result of an international workshop on this topic held in Oxford in 2014. Insights emerging from this work have consequences for our understanding of changes in biosphere function since the Late Pleistocene and of the functioning of contemporary ecosystems, as well as offering a rationale and framework for scientifically informed restoration of megafaunal function where possible and appropriate.
Despite dominating biodiversity in the Mesozoic, dinosaurs were not speciose. Oviparity constrained even gigantic dinosaurs to less than 15 kg at birth; growth through multiple morphologies led to ...the consumption of different resources at each stage. Such disparity between neonates and adults could have influenced the structure and diversity of dinosaur communities. Here, we quantified this effect for 43 communities across 136 million years and seven continents. We found that megatheropods (more than 1000 kg) such as tyrannosaurs had specific effects on dinosaur community structure. Although herbivores spanned the body size range, communities with megatheropods lacked carnivores weighing 100 to 1000 kg. We demonstrate that juvenile megatheropods likely filled the mesocarnivore niche, resulting in reduced overall taxonomic diversity. The consistency of this pattern suggests that ontogenetic niche shift was an important factor in generating dinosaur community structure and diversity.
Trophic rewilding as a climate change mitigation strategy? Cromsigt, Joris P. G. M.; te Beest, Mariska; Kerley, Graham I. H. ...
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
10/2018, Letnik:
373, Številka:
1761
Journal Article
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The loss of megafauna at the terminal Pleistocene has been linked to a wide range of Earth-system-level changes, such as altered greenhouse gas budgets, fire regimes and biome-level vegetation ...changes. Given these influences and feedbacks, might part of the solution for mitigating anthropogenic climate change lie in the restoration of extant megafauna to ecosystems? Here, we explore the potential role of trophic rewilding on Earth's climate system. We first provide a novel synthesis of the various ways that megafauna interact with the major drivers of anthropogenic climate change, including greenhouse gas storage and emission, aerosols and albedo. We then explore the role of rewilding as a mitigation tool at two scales: (i) current and near-future opportunities for national or regional climate change mitigation portfolios, and (ii) more radical opportunities at the global scale. Finally, we identify major knowledge gaps that complicate the complete characterization of rewilding as a climate change mitigation strategy. Our perspective is urgent since we are losing the Earth's last remaining megafauna, and with it a potential option to address climate change.
This article is part of the theme issue ‘Trophic rewilding: consequences for ecosystems under global change’.
Classic paleontology has focused on the study of fossils and the reconstruction of lineages of extinct species. But as diverse fossils of animals and plants were unearthed and catalogued, it became ...possible to reconstruct more elaborate ecosystems, tying together plants, animals, and geology. By the second half of the twentieth century, this effort gave birth to the field of paleoecology: the study of the interactions between organisms and their environments across geologic timescales.
In Mammalian Paleoecology, Felisa Smith broadly considers extinct mammals in an ecological context. Arguing that the past has much to teach us, and that mammals, which display an impressive array of diverse life history and ecological characteristics, are the ideal organism through which to view the fossil record, Smith
• reviews the history, major fossil-hunting figures, and fundamental principles of paleoecology, including stratigraphy, dating, and taphonomy
• discusses the importance of mammal body size, how to estimate size, and what size and shape reveal about long-dead organisms
• explains the structure, function, and utility of different types of mammal teeth
• highlights other important methods and proxies used in modern paleoecology, including stable isotopes, ancient DNA, owl pellets, Sporormiella fungal spores, and paleomidden analyses
• assesses nontraditional fossils
• presents readers with several case studies that describe how the fossil record can help inform the scientific discussion on anthropogenic climate change
Mammalian Paleoecology is an approachable overview of how we obtain information from long-dead animals and what this information can tell us about the environments of the distant past. It will profoundly affect the way paleontologists and climatologists view the lives of ancient mammals.
Species richness of marine mammals and birds is highest in cold, temperate seas-a conspicuous exception to the general latitudinal gradient of decreasing diversity from the tropics to the poles. We ...compiled a comprehensive dataset for 998 species of sharks, fish, reptiles, mammals, and birds to identify and quantify inverse latitudinal gradients in diversity, and derived a theory to explain these patterns. We found that richness, phylogenetic diversity, and abundance of marine predators diverge systematically with thermoregulatory strategy and water temperature, reflecting metabolic differences between endotherms and ectotherms that drive trophic and competitive interactions. Spatial patterns of foraging support theoretical predictions, with total prey consumption by mammals increasing by a factor of 80 from the equator to the poles after controlling for productivity.
Evidence for mesothermy in dinosaurs Grady, John M.; Enquist, Brian J.; Dettweiler-Robinson, Eva ...
Science (American Association for the Advancement of Science),
06/2014, Letnik:
344, Številka:
6189
Journal Article
Recenzirano
Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy comes from the rapid growth rates ...derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades. Using a metabolic scaling approach, we find that growth and metabolic rates follow theoretical predictions across clades, although some groups deviate. Moreover, when the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms. Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic.
Of the primary responses to contemporary climate change – "move, adapt, acclimate, or die" – that are available to organisms, "acclimate" may be effectively achieved through behavioral modification. ...Behavioral flexibility allows animals to rapidly cope with changing environmental conditions, and behavior represents an important component of a species' adaptive capacity in the face of climate change. However, there is currently a lack of knowledge about the limits or constraints on behavioral responses to changing conditions. Here, we characterize the contexts in which organisms respond to climate variability through behavior. First, we quantify patterns in behavioral responses across taxa with respect to timescales, climatic stimuli, life-history traits, and ecology. Next, we identify existing knowledge gaps, research biases, and other challenges. Finally, we discuss how conservation practitioners and resource managers can incorporate an improved understanding of behavioral flexibility into natural resource management and policy decisions.
Dinosaur physiology. Evidence for mesothermy in dinosaurs Grady, John M; Enquist, Brian J; Dettweiler-Robinson, Eva ...
Science (American Association for the Advancement of Science),
2014-Jun-13, 20140613, Letnik:
344, Številka:
6189
Journal Article
Recenzirano
Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy comes from the rapid growth rates ...derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades. Using a metabolic scaling approach, we find that growth and metabolic rates follow theoretical predictions across clades, although some groups deviate. Moreover, when the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms and ectotherms and closest to those of extant mesotherms. Our results suggest that the modern dichotomy of endothermic versus ectothermic is overly simplistic.
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