Amphibian Decline or Extinction? Current Declines Dwarf Background Extinction Rate

A key measure of humanity's global impact is by how much it has increased species extinction rates. Familiar statements are that these are 100-1000 times pre-human or background extinction levels. Estimating recent rates is straightforward, but establishing a background rate for comparison is not. Previous researchers chose an approximate benchmark of 1 extinction per million species per year (E/MSY). We explored disparate lines of evidence that suggest a substantially lower estimate. Fossil data yield direct estimates of extinction rates, but they are temporally coarse, mostly limited to marine hard-bodied taxa, and generally involve genera not species. Based on these data, typical background loss is 0.01 genera per million genera per year. Molecular phylogenies are available for more taxa and ecosystems, but it is debated whether they can be used to estimate separately speciation and extinction rates. We selected data to address known concerns and used them to determine median extinction estimates from statistical distributions of probable values for terrestrial plants and animals. We then created simulations to explore effects of violating model assumptions. Finally, we compiled estimates of diversification-the difference between speciation and extinction rates for different taxa. Median estimates of extinction rates ranged from 0.023 to 0.135 E/MSY. Simulation results suggested over- and under-estimation of extinction from individual phylogenies partially canceled each other out when large sets of phylogenies were analyzed. There was no evidence for recent and widespread pre-human overall declines in diversity. This implies that average extinction rates are less than average diversification rates. Median diversification rates were 0.05-0.2 new species per million species per year. On the basis of these results, we concluded that typical rates of background extinction may be closer to 0.1 E/MSY. Thus, current extinction rates are 1,000 times higher than natural background rates of extinction and future rates are likely to be 10,000 times higher.

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.

In order to have the capability for recognizing as many of the extinction and adaptive radiations in the fossil record as possible we should take advantage of the ecostratigraphic approach in our work. This means that we will carefully collect, stratum by stratum, data about the stratigraphic ranges of the individual taxa within individual community groups, biofacies narrowly construed, as opposed to the all too customary habit of lumping taxa from varied community groups together indiscriminately. Following this procedure enables one to far more easily recognize as well, those brief intervals when portions of the ecosystem were restructured, which is important owing to the fact that such restructuring commonly coincides with extinction and adaptive radiation events. It must be recognized that major changes in supra-specific abundance are fully as useful in pin pointing extinction and adaptive radiation events as are mere taxonomic compilations. The ecostratigraphic approach also emphasizes the fact that so-called "known" stratigraphic ranges are commonly far less than "true" ranges except for the small number of abundant genera and their species. Awareness of this last relationship makes it clear that there is no such thing as a "Background Extinction Rate" within any one community group, i.e., biofacies, because the species to species name changes within the genera of each community group are merely evidence of phyletic evolution, not the termination of a lineage. Emphasis is placed on the importance of separating out the major ecosystem components, such as the level bottom from the reef complex when trying to recognize event horizons, i.e., compilations that lump taxa from such ecosystem components together tend to blur the actual nature of the units being mixed together, giving rise to an artifactual background extinction (and adaptive radiation) rate. We now need to far more carefully sample beds above and below suspected event horizons, community group by community group, in order to discover whether or not the taxa involved in radiations and extinctions undergo a sigmoidal change in abundance or not. All of this requires that we carefully evaluate our data against a sound knowledge of classical biostratigraphy, based on the evolutionarily useful data developed during the past century and more.

This study examines estimates of extinction rates for the current purported biotic crisis and from the fossil record. Studies that compare current and geological extinctions sometimes use metrics that confound different sources of error and reflect different features of extinction processes. The per taxon extinction rate is a standard measure in paleontology that avoids some of the pitfalls of alternative approaches. Extinction rates reported in the conservation literature are rarely accompanied by measures of uncertainty, despite many elements of the calculations being subject to considerable error. We quantify some of the most important sources of uncertainty and carry them through the arithmetic of extinction rate calculations using fuzzy numbers. The results emphasize that estimates of current and future rates rely heavily on assumptions about the tempo of extinction and on extrapolations among taxa. Available data are unlikely to be useful in measuring magnitudes or trends in current extinction rates.

This study examines estimates of extinction rates for the current purported biotic crisis and from the fossil record. Studies that compare current and geological extinctions sometimes use metrics that confound different sources of error and reflect different features of extinction processes. The per taxon extinction rate is a standard measure in paleontology that avoids some of the pitfalls of alternative approaches. Extinction rates reported in the conservation literature are rarely accompanied by measures of uncertainty, despite many elements of the calculations being subject to considerable error. We quantify some of the most important sources of uncertainty and carry them through the arithmetic of extinction rate calculations using fuzzy numbers. The results emphasize that estimates of current and future rates rely heavily on assumptions about the tempo of extinction and on extrapolations among taxa. Available data are unlikely to be useful in measuring magnitudes or trends in current extinction rates.

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.

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.

Spatial and temporal variation in population dynamics of Andean frogs: Effects of forest disturbance and evidence for declines

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.

Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.

The data deluge is changing the operating environment of many sensing systems from data-poor to data-rich-so data-rich that we are in jeopardy of being overwhelmed. Managing and exploiting the data deluge require a reinvention of sensor system design and signal processing theory. The potential pay-offs are huge, as the resulting sensor systems will enable radically new information technologies and powerful new tools for scientific discovery.

Biodiversity is the very basis of human survival and economic well-being, and encompasses all life forms, ecosystems and ecological processes. The current estimates of the total number of species on earth vary from 5 to more than 100 million, with a more conservative figure of 13.6 million species. Of these, only 1.78 million species have yet been described and awarded scientific names. Thus, our knowledge of diversity is remarkably incomplete. Biodiversity at any point in time is the balance between the rates of speciation and extinction. Biodiversity is not uniformly distributed on the earth and shows prominent latitudinal and altitudinal gradients. At least five major mass extinctions have occurred in the past at geologic-time boundaries. Studies indicate that we have entered into the sixth phase of mass extinctions. In all ecosystem types, terrestrial, freshwater and marine, species populations are declining. The current rates of species extinction are 100–1000 times higher than the background rate of 10−7 species/species year inferred from fossil record. It is now in the order of 1,000 species per decade per million species. Today we seem to be losing two to five species per hour from tropical forests alone. This amounts to a loss of 16 m populations/year or 1,800 populations/h. Major drivers for changes of biodiversity in future, in decreasing rank of their impact are land use change, climate change, N deposition, biotic exchange and atmospheric loading of CO2. Accuracy of estimates of the total number of resident species and current rates of extinction remains undetermined, and the impact of species deletions on ecosystem function and stability is still a subject of debate among ecologists. There are two basic, often complementary strategies for biodiversity conservation. The in situ strategy emphasizes the protection of ecosystems for the conservation of overall diversity of genes, populations, species, communities and the ecological processes which are crucial for ecosystem services. Establishment of networks of protected areas are effective in this regard as these have the possibility to conserve primary forests and red-listed ecosystems. The concept of biodiversity banking could induce public participation. Establishment of the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services, an independent, international science panel (like IPCC) would help coordinate and highlight research on pressing topics, conduct periodic assessments on regional as well as global scales and provide predictions.

Graptoloid evolutionary dynamics show a marked contrast from the Ordovician to the Silurian. Subdued extinction and origination rates during the Ordovician give way, during the late Katian, to rates that were highly volatile and of higher mean value through the Silurian, reflecting the significantly shorter lifespan of Silurian species. These patterns are revealed in high-resolution rate curves derived from the CONOP (constrained optimization) scaled and calibrated global composite sequence of 2094 graptoloid species. The end-Ordovician mass depletion was driven primarily by an elevated extinction rate which lasted forc. 1.2 Ma with two main spikes during the Hirnantian. The early Silurian recovery, although initiated by a peak in origination rate, was maintained by a complex interplay of origination and extinction rates, with both rates rising and falling sharply. The global δ13C curve echoes the graptoloid evolutionary rates pattern; the prominent and well-known positive isotope excursions during the Late Ordovician and Silurian lie on or close to times of sharp decline in graptoloid species richness, commonly associated with extinction rate spikes. The graptoloid and isotope data point to a relatively steady marine environment in the Ordovician with mainly background extinction rates, changing during the Katian to a more volatile climatic regime that prevailed through the Silurian, with several sharp extinction episodes triggered by environmental crises. The correlation of graptoloid species diversity with isotopic ratios was positive in the Ordovician and negative in the Silurian, suggesting different causal linkages. Throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate.

There are a number of clearly defined processes leading to destruction of habitat and loss of biodiversity, but the ultimate cause of all these is the increasing human population. Most endangered species are threatened by numerous factors, but habitat loss worldwide is generally viewed as the single largest cause of biodiversity loss. When humans convert uninhabited areas for agriculture, forestry, urban development, or water projects like construction of dams, hydropower, and irrigation channels, they reduce or eliminate its usefulness as a habitat for the other species that live there. Biodiversity is the natural variety of living creatures we see around us. It is the variety of all forms of life on this terrestrial ecosystem. High rates of extinction are quickly reducing biodiversity especially in areas with high human population density and growth in the world. The direct and indirect effects of human interference on biodiversity are very challenging. Quantifying loss of genetic diversity is difficult, but it is clear that the extinction of species and declines in their population lead to a loss of genetic diversity. Unfortunately, the majority of the human population growth is seen within the greatest biodiversity hotspots. Scientific studies demonstrates that 87.9 percent of variation in endangered species can be explained by the single factor of human population density. In history many natural extinctions of species were witnessed, but the current rates of extinction are estimated to be roughly 100- times higher than the typical rates in the fossil record, and this increase of extinction will be 1000- 10,000 times higher in the future.

Extinction in the Anthropocene.