Ecostratigraphic criteria for evaluating the magnitude, character and duration of bioevents

To determine the distribution and causes of extinction threat across functional groups of terrestrial vertebrates, we assembled an ecological trait data set for 18,016 species of terrestrial vertebrates and utilized phylogenetic comparative methods to test which categories of habitat association, mode of locomotion, and feeding mode best predicted extinction risk.We also examined the individual categories of the International Union for Conservation of Nature Red List extinction drivers (e.g., agriculture and logging) threatening each species and determined the greatest threats for each of the four terrestrial vertebrate groups.We then quantified the sum of extinction drivers threatening each species to provide a multistressor perspective on threat.Cave dwelling amphibians (p < 0.01), arboreal quadrupedal mammals (all of which are primates) (p < 0.01), aerial and scavenging birds (p < 0.01), and pedal (i.e., walking) squamates (p < 0.01) were all disproportionately threatened with extinction in comparison with the other assessed ecological traits.Across all threatened vertebrate species in the study, the most common risk factors were agriculture, threatening 4491 species, followed by logging, threatening 3187 species, and then invasive species and disease, threatening 2053 species.Species at higher risk of extinction were simultaneously at risk from a greater number of threat types.If left unabated, the disproportionate loss of species with certain functional traits and increasing anthropogenic pressures are likely to disrupt ecosystem functions globally.A shift in focus from species-to trait-centric conservation practices will allow for protection of at-risk functional diversity from regional to global scales.

Procedures introduced here make it possible, first, to show that background (piecemeal) extinction is recorded throughout geologic stages and substages (not all extinction has occurred suddenly at the ends of such intervals); second, to separate out background extinction from mass extinction for a major crisis in earth history; and third, to correct for clustering of extinctions when using the rarefaction method to estimate the percentage of species lost in a mass extinction. Also presented here is a method for estimating the magnitude of the Signor-Lipps effect, which is the incorrect assignment of extinctions that occurred during a crisis to an interval preceding the crisis because of the incompleteness of the fossil record. Estimates for the magnitudes of mass extinctions presented here are in most cases lower than those previously published. They indicate that only ∼81% of marine species died out in the great terminal Permian crisis, whereas levels of 90-96% have frequently been quoted in the literature. Calculations of the latter numbers were incorrectly based on combined data for the Middle and Late Permian mass extinctions. About 90 orders and more than 220 families of marine animals survived the terminal Permian crisis, and they embodied an enormous amount of morphological, physiological, and ecological diversity. Life did not nearly disappear at the end of the Permian, as has often been claimed.

A computer model of background and mass extinctions in a taxonomic hierarchy has been used to study the effects of different extinction patterns in a search for clues as to the causes of actual extinction events. Model taxa at four levels were built up from speciation events in adaptive space according to rules of origination which seem plausible biologically. The frequency distribution of species among the three higher taxonomic levels in the model is similar to that in living marine taxa which have good fossil records. Three mass extinction patterns were imposed on the model after species diversity had attained equilibrium (i.e., when speciation = background extinction): random; bloc (contiguous niches were cleared); and clade (all members of selected higher taxa were removed). Effects on the taxonomic profile varied with pattern. Four of the five historical mass extinctions resemble the effects of the random pattern. End-Permian families were harder hit than those in the random model, but this may be a result of an extremely high species extinction level. It is concluded that the effect of extinctions on the taxonomic hierarchy provides a tool to help in understanding extinction causes.

The fossil record of non-marine tetrapods (amphibians, reptiles, birds and mammals) has been described by numerous authors1–3, and major ecological replacements, mass extinctions and adaptive radiations have been identified. However, most of these features of the large-scale evolution of tetrapods have been noted without numerical data of the kind assembled for marine invertebrates4–10, marine vertebrates7–10 and vascular land plants11. Much has been learnt from the record of marine invertebrates, particularly about the overall patterns of diversification with time, the performance of different major taxonomic groups at different times, and the magnitude and timing of mass extinctions. The present study tests some of the general conclusions on the basis of a new compilation of data on the fossil record of terrestrial tetrapods. I show that family diversity rose with time, and in particular from the Cretaceous to the present day. There were several mass extinction events, but none of these was associated with a statistically high extinction rate. The extinction events, including the famous terminal Cretaceous extinction, were the result of a slightly elevated extinction rate combined with a depressed origination rate, and the present evidence does not support the view that mass extinctions are statistically distinguishable from background extinctions. Further, the record of non-marine tetrapods shows an increasing total extinction rate and an only marginally decreasing probability of extinction (per-taxon rate) from the late Devonian to the present, the opposite of the findings from the record of marine animals.

We are living through the first mass extinction since the end of the Cretaceous period 65 million years ago. During most of the past 600 million years, only one species of plant or animal had gone extinct each year, on average, corresponding to an average species life span of five to ten million years (May et al. 1995). During the past four centuries, however, known extinctions occurred at a rate of two to three per year, and nearly five species per year are known to have gone extinct in the past century (Smith et al. 1993). Even this fivefold increase in background extinction rates, however, vastly understates the magnitude of the current extinction event because it is derived only from extinction of species known to science. Restricting our attention to birds and mammals allows us to better judge the extent to which current and past extinction rates differ. In the past century, roughly 100 of the 14,000 known species of birds and mammals became extinct. If extinction were to continue at this rate, it would correspond to an average species life span of less than 10,000 years (May et al. 1995)-far longer than all of recorded history, but three orders of magnitude shorter than average species life spans of mammals in the fossil record (Martin 1993). Moreover, three completely different methods for projecting future extinction rates suggest that the average life span of a bird or mammal species may soon be reduced to only 200-400 years (May et al. 1995). Faced with the immensity of this crisis, biologists of many stripes, geneticists and evolutionary biologists included, have tried to identify ways in which their specialty can contribute to slowing its advance. This book shows, by force of example, some of the ways that genetics can contribute to conservation. It also suggests, largely through what the editors have wisely not included, some of the ways that genetics has little to contribute.

How quickly does biodiversity rebound after extinctions? Palaeobiologists have examined the temporal, taxonomic and geographic patterns of recovery following individual mass extinctions in detail, but have not analysed recoveries from extinctions throughout the fossil record as a whole. Here, we measure how fast biodiversity rebounds after extinctions in general, rather than after individual mass extinctions, by calculating the cross-correlation between extinction and origination rates across the entire Phanerozoic marine fossil record. Our results show that extinction rates are not significantly correlated with contemporaneous origination rates, but instead are correlated with origination rates roughly 10 million years later. This lagged correlation persists when we remove the 'Big Five' major mass extinctions, indicating that recovery times following mass extinctions and background extinctions are similar. Our results suggest that there are intrinsic limits to how quickly global biodiversity can recover after extinction events, regardless of their magnitude. They also imply that today's anthropogenic extinctions will diminish biodiversity for millions of years to come.

Based on fossil mammals from North America, extinction rates since the last mass extinction, but before human influences, are estimated at 0.4 species/species/million years, which implies a species typically persisted for about 2.5 million years. The background extinction rate has been punctuated by mass extinctions, which are defined as more than 75% of species in the fossil record going extinct over a relatively short period of time, the last of which was 66 million years ago. Over the past 50,000 years humans have caused extinctions of at least 30% of large mammals, and at least 30% of Pacific island bird species. Over the past 500 years, between 1% and 5% of all remaining vertebrates on continents have been lost, which is 50 to 250 times faster than the estimated background rate of fossil mammals and implies that we will reach mass extinction levels within a few thousand years. This time will be shorter if current extinction rates are underestimated, or rates increase in the future.

The white monotonous chalk from the Upper Cretaceouslowermost Tertiary ofNorthwest Europe spans at least 24 million years and contains a rich, well-preserved fauna of minute brachiopods. Based on taxonomical range charts and timespecific diversities, this fauna is studied in terms of mean species longevity, rate of species origination, and rate of extinction. The brachiopodfauna initially appears to have colonized the chalk sea in mid-Coniacian times. From there on a slow buildup of species diversity reflects a gradual niche diversification of the chalk. Adjustment and evolutionary stability reaches a climax in Late Maastrichtian time. During the Coniacian-Maastrichtian interval, mean rate of extinction is low (0.07 My-1) and mean rate of origination equally low (0.09 My-1). A sudden mass extinction at the Maastrichtian-Danian boundary, however, eliminated more than 70% of the species. The most specialized species, in particular the secondarily free-lying species, apparently became extinct at the boundary. Only six species are known to cross the Maastrichtian-Danian boundary. These are all relatively featureless, non-specialized forms and, together with possible survivors in basin margin areas, gave rise to a rapidly formed, highly diverse Early Danian fauna through adaptive radiation. The Early Danian fauna differs in taxonomic composition from the Maastrichtian fauna both on species as well as on higher taxonomic levels. A dichotomous classification of extinction seems real for the brachiopods from the chalk as their mass extinction at the Maastrichtian-Danian boundaty both quantitatively and qualitatively differ from their Late Cretaceous background extinction.

Direct comparison of ancient extinctions to the present-day situation is difficult, because quantitative palaeontological data come primarily from marine invertebrates, fossilized species are usually drawn from the more abundant and widespread taxa, and time resolution is rarely better than 103— 104 years. A growing array of techniques permits quantitative error estimates on some of these potential biases, and allows calculation of species extinction intensities from genus-level data, which are more robust. Extensive as today’s species losses probably are, they have yet to equal any of the Big Five mass extinctions. Background extinction patterns are potential sources of insight regarding present-day biotic losses; over 90% of past species extinction has occurred at times other than the Big Five mass extinctions. Mean durations of fossil species vary by more than an order of magnitude even within clades, rendering uninformative any global average for background extinction. Taxon-specific variation is evidently related to intrinsic biotic factors such as geographic range and population size. Approaches to extinction analysis and prediction based on morphological variety or biodisparity should be explored as an adjunct or alternative to taxon inventories or phylogenetic metrics. Rebounds from mass extinctions are geologically rapid but ecologically slow; biodiversity communities typically requires 5-10 million years.

Four Commentaries on the Pope’s Message on Climate Change and Income Inequality. IV. Pope Francis’ Encyclical Letter Laudato Si’, Global Environmental Risks, and the Future of Humanity.

Mass extinctions are important to macroevolution not only because they involve a sharp increase in extinction intensity over “background” levels, but also because they bring a change in extinction selectivity, and these quantitative and qualitative shifts set the stage for evolutionary recoveries. The set of extinction intensities for all stratigraphic stages appears to fall into a single right-skewed distribution, but this apparent continuity may derive from failure to factor out the well-known secular trend in background extinction: high early Paleozoic rates fill in the gap between later background extinction and the major mass extinctions. In any case, the failure of many organism-, species-, and clade-level traits to predict survivorship during mass extinctions is a more important challenge to the extrapolationist premise that all macroevolutionary processes are simply smooth extensions of microevolution. Although a variety of factors have been found to correlate with taxon survivorship for particular extinction events, the most pervasive effect involves geographic range at the clade level, an emergent property independent of the range sizes of constituent species. Such differential extinction would impose “nonconstructive selectivity,” in which survivorship is unrelated to many organismic traits but is not strictly random. It also implies that correlations among taxon attributes may obscure causation, and even the focal level of selection, in the survival of a trait or clade, for example when widespread taxa within a major group tend to have particular body sizes, trophic habits, or metabolic rates. Survivorship patterns will also be sensitive to the inexact correlations of taxonomic, morphological, and functional diversity, to phylogenetically nonrandom extinction, and to the topology of evolutionary trees. Evolutionary recoveries may be as important as the extinction events themselves in shaping the long-term trajectories of individual clades and permitting once-marginal groups to diversify, but we know little about sorting processes during recovery intervals. However, both empirical extrapolationism (where outcomes can be predicted from observation of pre- or post-extinction patterns) and theoretical extrapolationism (where mechanisms reside exclusively at the level of organisms within populations) evidently fail during mass extinctions and their evolutionary aftermath. This does not mean that conventional natural selection was inoperative during mass extinctions, but that many features that promoted survivorship during background times were superseded as predictive factors by higher-level attributes. Many intriguing issues remain, including the generality of survivorship rules across extinction events; the potential for gradational changes in selectivity patterns with extinction intensity or the volatility of target clades; the heritability of clade-level traits; the macroevolutionary consequences of the inexact correlations between taxonomic, morphological, and functional diversity; the factors governing the dynamics and outcome of recoveries; and the spatial fabric of extinctions and recoveries. The detection of general survivorship rules—including the disappearance of many patterns evident during background times—demonstrates that studies of mass extinctions and recovery can contribute substantially to evolutionary theory.

In order to assay the magnitude of potential extinctions resulting from the current deforestation of tropical rain forests, I compared the changes in mammalian faunas in Amazonia, Central and Western Africa, SoutheastAsia, and Madagascar to background extinction rates and mass extinctions at other times in the Cenozoic. Within 165 years human-mediated extinctions will have befallen 45% of the genera and 54% of the families within tropical forests. These taxa are mainly members of endemic and relict faunas. This contemporary event is comparable to other Cenozoic extinctions, with extinction rates much greater than the background extinction rates affecting earlier Cenozoic mammals. These comparisons are based on the following assumptions: within-habitat extinction rates are comparable to mean extinction rates from multiple-habitat ecosystems; and all threatened genera go extinct and are preserved. However, constraints on my assumptions will reduce the perceived magnitude when viewed historically. The distinctness of this extinction is questioned with reference to the Pleistocene events.

Extinction and viruses

The fossil record of insect extinction at the family level is characterized by two basic modes: background extinction, which represents an ambient level of taxa extirpation, and mass extinctions, which are occasional severe events in which taxa are eliminated significantly above background levels. The most significant mass extinction, at the end-Permian (Permian–Triassic; P-T), divides the history of insects into two major evolutionary faunas: an earlier Paleozoic Evolutionary Fauna of apterygotes, paleopterans, and basal clades of orthopteroids and hemipteroids; and a subsequent Modern Evolutionary Fauna of more derived clades of orthopteroids and hemipteroids and especially holometabolous insects. In addition to the P-T event, four other extinctions are documented by multiple types of data: Late Pennsylvanian, Late Jurassic, later Early Cretaceous; and the end-Cretaceous (Cretaceous–Paleocene; K-P). There also is an analogous record of insect origination that is characterized by major, above-background events. Four methods are used to detect insect extinction in the fossil record. The taxic approach is widely used, whereby the temporal durations of fossil taxa are tallied for each geologic unit of interest and analyzed in a manner analogous to demography used in ecology. By contrast, the phylogenetic approach uses clades as the basic units of interest. A recent approach uses proxy data such as quantification of plant–insect associations across major boundaries in lieu of an insect body–fossil record. Last, the clustering of times of origin from modern coevolved plant–insect associations provides data for likely interruptions from major paleoenvironmental perturbations. Pluralism, emphasizing multiple approaches to determine the ecological dynamics of insects during an extinction, is the best strategy to evaluate insect demise or survival in the fossil record.

Amphibian declines and extinctions are critical concerns of biologists around the world. The estimated current rate of amphibian extinction is known, but how it compares to the background amphibian extinction rate from the fossil record has not been well studied. I compared current amphibian extinction rates with their reported background extinction rates using standard and fuzzy arithmetic. These calculations suggest that the current extinction rate of amphibians could be 211 times the background amphibian extinction rate. If current estimates of amphibian species in imminent danger of extinction are included in these calculations, then the current amphibian extinction rate may range from 25,039–45,474 times the background extinction rate for amphibians. It is difficult to explain this unprecedented and accelerating rate of extinction as a natural phenomenon.