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AIM: Because of the negative impact that ongoing biodiversity loss may have on ecosystem properties that are critical for humans, understanding the relationship between extinction and functional diversity over time is of critical importance for conservation. However, empirical evidence concerning the sensitivity of vertebrate community function to species loss is very limited. Here we assess documented prehistoric and historic extinctions of birds on Pacific islands in an effort to quantify the consequences of extinctions for functional structure and diversity in natural communities over broad spatial scales. LOCATION: Forty‐four islands from across the Pacific. METHODS: We estimated functional aspects of island bird communities before and after Holocene extinctions based on body size, foraging niche, diet and activity period. We used four separate metrics to measure ecological function: functional diversity (FD), functional richness (FRic), functional evenness and functional divergence. We employed null models to separate the effects of observed extinctions from changes expected due to declining species richness. RESULTS: We find that Holocene bird extinctions led to substantial changes in community‐level functional diversity. Observed declines in FD and FRic were predictable from the pre‐extinction composition of communities, and did not differ from null model expectations. Across all islands, we observed non‐random changes in functional trait composition, with shifts away from ground‐level foraging, granivory and herbivory after extinctions. Extinctions have resulted in the loss of up to 80% of original functional diversity on some islands and caused a sharp decrease in the variety of ecological functions provided by birds. MAIN CONCLUSIONS: Our findings illustrate the significant losses of functional diversity that are already taking place on many islands and demonstrate its close connection with the loss of species. Accounting for the functional roles of species allows a more integrative understanding of ecological function and helps to bridge species and ecosystem perspectives in conservation science.

The largest extinction event in the Holocene occurred on Pacific islands, where Late Quaternary fossils reveal the loss of thousands of bird populations following human colonization of the region. However, gaps in the fossil record mean that considerable uncertainty surrounds the magnitude and pattern of these extinctions. We use a Bayesian mark-recapture approach to model gaps in the fossil record and to quantify losses of nonpasserine landbirds on 41 Pacific islands. Two-thirds of the populations on these islands went extinct in the period between first human arrival and European contact, with extinction rates linked to island and species characteristics that increased susceptibility to hunting and habitat destruction. We calculate that human colonization of remote Pacific islands caused the global extinction of close to 1,000 species of nonpasserine landbird alone; nonpasserine seabird and passerine extinctions will add to this total.

The world's oceans are undergoing profound changes as a result of human activities. However, the consequences of escalating human impacts on marine mammal biodiversity remain poorly understood. The International Union for the Conservation of Nature (IUCN) identifies 25% of marine mammals as at risk of extinction, but the conservation status of nearly 40% of marine mammals remains unknown due to insufficient data. Predictive models of extinction risk are crucial to informing present and future conservation needs, yet such models have not been developed for marine mammals. In this paper, we: (i) used powerful machine-learning and spatial-modeling approaches to understand the intrinsic and extrinsic drivers of marine mammal extinction risk; (ii) used this information to predict risk across all marine mammals, including IUCN \"Data Deficient\" species; and (iii) conducted a spatially explicit assessment of these results to understand how risk is distributed across the world's oceans. Rate of offspring production was the most important predictor of risk. Additional predictors included taxonomic group, small geographic range area, and small social group size. Although the interaction of both intrinsic and extrinsic variables was important in predicting risk, overall, intrinsic traits were more important than extrinsic variables. In addition to the 32 species already on the IUCN Red List, our model identified 15 more species, suggesting that 37% of all marine mammals are at risk of extinction. Most at-risk species occur in coastal areas and in productive regions of the high seas. We identify 13 global hotspots of risk and show how they overlap with human impacts and Marine Protected Areas.

As human population and resource demands continue to grow, biodiversity conservation has never been more critical. About one-quarter of all mammals are in danger of extinction, and more than half of all mammal populations are in decline. A major priority for conservation science is to understand the ecological traits that predict extinction risk and the interactions among those predictors that make certain species more vulnerable than others. Here, using a new database of nearly 4,500 mammal species, we use decision-tree models to quantify the multiple interacting factors associated with extinction risk. We show that the correlates of extinction risk vary widely across mammals and that there are unique pathways to extinction for species with different lifestyles and combinations of traits. We find that risk is relative and that all kinds of mammals, across all body sizes, can be at risk depending on their specific ecologies. Our results increase the understanding of extinction processes, generate simple rules of thumb that identify species at greatest risk, and highlight the potential of decision-tree analyses to inform conservation efforts.

Understanding the ecological mechanisms that lead to extinction is a central goal of conservation. Can understanding ancient avian extinctions help to predict extinction risk in modern birds? I used classification trees trained on both paleoecological and historical data from islands across the Pacific to determine the ecological traits associated with extinction risk. Intrinsic traits, including endemism, large body size, and certain feeding guilds, were tightly linked with avian extinction over the past 3500 years. Species ecology and phylogeny were better predictors of extinction risk through time than extrinsic or abiotic factors. Although human impacts on birds and their habitats have changed over time, modern endangered birds share many of the same ecological characteristics as victims of previous extinction waves. My use of detailed predictions of extinction risk to identify species potentially in need of conservation attention demonstrates the utility of paleoecological knowledge for modern conservation biology.

The extinction of dinosaurs at the Cretaceous/Paleogene (K/Pg) boundary was the seminal event that opened the door for the subsequent diversification of terrestrial mammals. Our compilation of maximum body size at the ordinal level by sub-epoch shows a near-exponential increase after the K/Pg. On each continent, the maximum size of mammals leveled off after 40 million years ago and thereafter remained approximately constant. There was remarkable congruence in the rate, trajectory, and upper limit across continents, orders, and trophic guilds, despite differences in geological and climatic history, turnover of lineages, and ecological variation. Our analysis suggests that although the primary driver for the evolution of giant mammals was diversification to fill ecological niches, environmental temperature and land area may have ultimately constrained the maximum size achieved.

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era ([almost equal to]1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6-0.45 Gya). Each size step required a major innovation in organismal complexity--first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.

How fast can a mammal evolve from the size of a mouse to the size of an elephant? Achieving such a large transformation calls for major biological reorganization. Thus, the speed at which this occurs has important implications for extensive faunal changes, including adaptive radiations and recovery from mass extinctions. To quantify the pace of large-scale evolution we developed a metric, clade maximum rate, which represents the maximum evolutionary rate of a trait within a clade. We applied this metric to body mass evolution in mammals over the last 70 million years, during which multiple large evolutionary transitions occurred in oceans and on continents and islands. Our computations suggest that it took a minimum of 1.6, 5.1, and 10 million generations for terrestrial mammal mass to increase 100-, and 1,000-, and 5,000-fold, respectively. Values for whales were down to half the length (i.e., 1.1, 3, and 5 million generations), perhaps due to the reduced mechanical constraints of living in an aquatic environment. When differences in generation time are considered, we find an exponential increase in maximum mammal body mass during the 35 million years following the Cretaceous–Paleogene (K–Pg) extinction event. Our results also indicate a basic asymmetry in macroevolution: very large decreases (such as extreme insular dwarfism) can happen at more than 10 times the rate of increases. Our findings allow more rigorous comparisons of microevolutionary and macroevolutionary patterns and processes.

The high concentration of molecular oxygen in Earth's atmosphere is arguably the most conspicuous and geologically important signature of life. Earth's early atmosphere lacked oxygen; accumulation began after the evolution of oxygenic photosynthesis in cyanobacteria around 3.0-2.5 billion years ago (Gya). Concentrations of oxygen have since varied, first reaching near-modern values ~600 million years ago (Mya). These fluctuations have been hypothesized to constrain many biological patterns, among them the evolution of body size. Here, we review the state of knowledge relating oxygen availability to body size. Laboratory studies increasingly illuminate the mechanisms by which organisms can adapt physiologically to the variation in oxygen availability, but the extent to which these findings can be extrapolated to evolutionary timescales remains poorly understood. Experiments confirm that animal size is limited by experimental hypoxia, but show that plant vegetative growth is enhanced due to reduced photorespiration at lower O₂:CO₂. Field studies of size distributions across extant higher taxa and individual species in the modern provide qualitative support for a correlation between animal and protist size and oxygen availability, but few allow prediction of maximum or mean size from oxygen concentrations in unstudied regions. There is qualitative support for a link between oxygen availability and body size from the fossil record of protists and animals, but there have been few quantitative analyses confirming or refuting this impression. As oxygen transport limits the thickness or volume-to-surface area ratio--rather than mass or volume--predictions of maximum possible size cannot be constructed simply from metabolic rate and oxygen availability. Thus, it remains difficult to confirm that the largest representatives of fossil or living taxa are limited by oxygen transport rather than other factors. Despite the challenges of integrating findings from experiments on model organisms, comparative observations across living species, and fossil specimens spanning millions to billions of years, numerous tractable avenues of research could greatly improve quantitative constraints on the role of oxygen in the macroevolutionary history of organismal size.

Through the continuing accumulation of fossil evidence, it is clear that the avifauna of the Hawaiian Islands underwent a large-scale extinction event around the time of Polynesian arrival. A second wave of extinctions since European colonization has further altered this unique avifauna. Here I present the first systematic analysis of the factors characterizing the species that went extinct in each time period and those that survived in order to provide a clearer picture of the possible causal mechanisms. These analyses were based on mean body size, dietary and ecological information and phylogenetic lineage of all known indigenous, non-migratory land and freshwater bird species of the five largest Hawaiian Islands. Extinct species were divided into 'prehistoric' and 'historic' extinction categories based on the timing of their last occurrence. A model of fossil preservation bias was also incorporated. I used regression trees to predict probability of prehistoric and historic extinction based on ecological variables. Prehistoric extinctions showed a strong bias toward larger body sizes and flightless, ground-nesting species, even after accounting for preservation bias. Many small, specialized species, mostly granivores and frugivores, also disappeared, implicating a wide suite of human impacts including destruction of dry forest habitat. In contrast, the highest extinction rates in the historic period were in medium-sized nectarivorous and insectivorous species. These differences result from different causal mechanisms underlying the two waves of extinction.