Historical bird and terrestrial mammal extinction rates and causes

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation.     

Late Quaternary reptile extinctions: size matters,insularity dominates

Aim A major Late Quaternary vertebrate extinction event affected mostly large‐bodied ‘megafauna’. This is well documented in both mammals and birds, but evidence of a similar trend in reptiles is scant. We assess the relationship between body size and Late Quaternary extinction in reptiles at the global level. Location Global. Methods We compile a body size database for all 82 reptile species that are known to have gone extinct during the last 50,000 years and compare them with the sizes of 10,090 extant reptile species (97% of known extant diversity). We assess the body size distributions in the major reptile groups: crocodiles, lizards, snakes and turtles, while testing and correcting for a size bias in the fossil record. We examine geographical biases in extinction by contrasting mainland and insular reptile assemblages, and testing for biases within regions and then globally by using geographically weighted models. Results Extinct reptiles were larger than extant ones, but there was considerable variation in extinction size biases among groups. Extinct lizards and turtles were large, extinct crocodiles were small and there was no trend in snakes. Lizard lineages vary in the way their extinction is related to size. Extinctions were particularly prevalent on islands, with 73 of the 82 extinct species being island endemics. Four others occurred in Australia. The fossil record is biased towards large‐bodied reptiles, but extinct lizards were larger than extant ones even after we account for this. Main conclusions Body size played a complex role in the extinction of Late Quaternary reptiles. Larger lizard and turtle species were clearly more affected by extinction mechanisms such as over exploitation and invasive species, resulting in a prevalence of large‐bodied species among extinct taxa. Insularity was by far the strongest correlate of recent reptile extinctions, suggesting that size‐biased extinction mechanisms are amplified in insular environments.     

The form of the curves: a direct evaluation of MacArthur & Wilson's classic theory

1. We calculate the yearly numbers of bird species immigrating to – and becoming extinct on – 13 small islands of the British Isles, using a long and relatively complete data record.
2. We estimate the size of the colonist pool for each island using four methods.
3. We assume that immigrations and extinctions are distributed binomially, and use a maximum likelihood method to fit concave immigration and extinction functions to the data, utilizing all four species pool estimates.
4. Extinction rates increase significantly and consistently with increasing numbers of breeding species on each island. For nine of the 13 islands the extinction functions are significantly concave.
5. Immigration rates decrease consistently with increasing numbers of breeding species on each island. Seven islands have significantly concave immigration functions.
6. Immigration rates and extinction rates decline consistently, but not significantly, with island distance and island size, respectively. The number of breeding species does not always reflect the number of species likely to have reached an island. Moreover, some species may choose not to breed when their chance of extinction is high. These factors, plus the modest range of island areas and distances in our database, reduce our chances of finding the theoretically predicted effects of area and distance on extinction and immigration rates.     

Bermuda as an Evolutionary Life Raft for an Ancient Lineage of Endangered Lizards

Oceanic islands are well known for harboring diverse species assemblages and are frequently the basis of research on adaptive radiation and neoendemism. However, a commonly overlooked role of some islands is their function in preserving ancient lineages that have become extinct everywhere else (paleoendemism). The island archipelago of Bermuda is home to a single species of extant terrestrial vertebrate, the endemic skink Plestiodon (formerly Eumeces) longirostris. The presence of this species is surprising because Bermuda is an isolated, relatively young oceanic island approximately 1000 km from the eastern United States. Here, we apply Bayesian phylogenetic analyses using a relaxed molecular clock to demonstrate that the island of Bermuda, although no older than two million years, is home to the only extant representative of one of the earliest mainland North American Plestiodon lineages, which diverged from its closest living relatives 11.5 to 19.8 million years ago. This implies that, within a short geological time frame, mainland North American ancestors of P. longirostris colonized the recently emergent Bermuda and the entire lineage subsequently vanished from the mainland. Thus, our analyses reveal that Bermuda is an example of a “life raft” preserving millions of years of unique evolutionary history, now at the brink of extinction. Threats such as habitat destruction, littering, and non-native species have severely reduced the population size of this highly endangered lizard.     

Naïve birds and noble savages - a review of man-caused prehistoric extinctions of island birds

Many bird species were extirpated or became extinct when prehistoric man reached oceanic islands We list > 200 species of extinct island birds only recorded as sub-fossils and which probably vanished due to prehistoric man In addition we list c 160 cases where an extant species has been found as subfossil on islands where it no longer occurs Several species today considered endemic to single islands of island groups had a much wider distribution in the past Biogeographic analyses of insular avifaunas are almost meaningless it the extensive prehistoric extinctions are not taken into account
Most extinct species belong to Anatidae Rallidae and Drcpanididae while local extirpations are numerous among doves and seabirds Smaller birds are rare mainly due to sampling bias and taphonomic factors The bird populations were depleted mainly by overhunting predation by introduced vertebrates and alteration of the original vegetation
Prehistoric humans on islands although dependent on limited animal resources regularly failed to exploit these in a sustainable way Several cases where human populations disappeared from islands in the Pacific may have been due to over-exploitation of native animals
Prehistoric man reached most tropical and temperate islands and most of the few remaining island faunas have been severely depleted in historic times The prehistoric extinctions emphasize the extreme vulnerability and value of the very few pristine island faunas that still remain     

On the extinction of the Dune Shearwater (Puffinus holeae) from the Canary Islands

Insular ecosystems have been subjected to severe hardship during the last millennia. Large numbers of insular bird species have undergone local disappearances and full extinctions, and a high number of insular birds are currently categorised as endangered species. In most of these cases, extinction—or endangerment—is in direct relation to the arrival of ‘aboriginal’ and/or imperialist waves of human settlement. Insular bird extinction events have been documented to have occurred at times corresponding to aboriginal settlement at many archipelagos and isolated islands, such as the Hawaiian Islands, New Zealand, the West Indies or the tropical Pacific Islands. However, no bird extinctions could be attributed to the first settlers of the Canary Islands—until now. The first accelerator mass spectrometer radiocarbon (¹⁴C) dating of collagen from a bone of the Dune Shearwater Puffinus holeae (3395 ± 30 year BP), an extinct bird from the Canary Islands, indicates a late Holocene extinction event. This relatively recent date, together with some features of this bird (large body size, breeding areas situated at very accessible places) and the absence of its bones from the entire archaeological record suggests that the extinction occurred close to the time that the first human settlement occurred on the islands.     

The fossil birds of Henderson Island, Pitcairn Group: natural turnover and human impact, a synopsis

Recent studies of island biotas have suggested that the impact of man on indigenous flora and fauna is much greater than previously suspected. This impact resulted in the introduction of many new species and the extinction of many unique life-forms. Henderson Island, in the Pitcairn Group, has been found to be an excellent laboratory for the study of natural faunal turnover and the impact of people on the natural environment. This was principally due to the island's remote location and its limestone structure, which resulted in the excellent preservation of fossil remains. During the Sir Peter Scott Commemorative Expedition to the Pitcairn Islands, extensive excavations were undertaken resulting in the collection of 42213 bird bones. It was possible to identify 31%. Of the 31 taxa identified, four seabirds appear to be vagrants, a surprisingly high number illustrating that the uncritical evaluation of fossil bird lists from other islands risks over-estimating the number of indigenous species. As a result of the arrival of Polynesian people during the first half of this millennium, half of Henderson's endemic landbirds became extinct, as did most of the small ground-nesting seabirds. The lower sea level during cold stages creates many temporary limestone 'high' islands. This results in many 'former-atolls' developing geological and ecological similarity to Henderson. Hence lower sea-level greatly facilitates the movement of flora and fauna between currently isolated oceanic 'high' islands.     

Biogeography of body size in Pacific island birds

Many insular vertebrates have undergone rapid and dramatic changes in body size compared to their mainland counterparts. Here we explore the relationship between two well known patterns of island body size – the tendency for large‐bodied species to dwarf and small‐bodied species to get larger on islands, known as the “island rule”, and the scaling of maximum and minimum body size of island assemblages with island area. Drawing on both fossil and modern data, we examined the relationship between body size and island area in Pacific island birds, both within clades and at the island assemblage level. We found that the size of the smallest bird on each island decreased with island area while the maximum body size increased with island area. Similarly, within clades the body size of small‐bodied groups decreased and large‐bodied groups increased from small to large islands, consistent with the island rule. However, the magnitude of size change within clades was not sufficient to explain the overall scaling of maximum size with island area. Instead, the pattern was driven primarily by the evolution of very large, flightless birds on large islands. Human‐mediated extinctions on islands over the past few millennia severely impacted large, flightless birds, to the effect that this macroecological pattern has been virtually erased. After controlling for effects of biogeographic region and island area, we found island productivity to be the best predictor of maximum size in flightless birds. This result, and the striking similarities in maximum body size between flightless birds and island mammals, suggests a common energetic mechanism linking body size and landmass area in both the island rule and the scaling of island body size extremes.     

Extinction and endemism in the New Zealand avifauna

Aim Species belonging to higher taxa endemic to islands are more likely to go extinct following human arrival. This selectivity may occur because more highly endemic island species possess features that make them uniquely vulnerable to impacts associated with human arrival, specifically: (1) restricted distribution (2) reduced predator escape response, including loss of flight, and (3) life history traits, such as large body mass, associated with greater susceptibility to hunting or habitat loss. This study aims to identify which of these features can explain the selective extinction of more highly endemic bird species in New Zealand. Location North and South Island, New Zealand. Methods Bird species breeding in New Zealand prior to human arrival were classified according to whether they became extinct or not during two periods of human settlement, prehistoric (post‐Maori but pre‐European arrival) and historic (post‐European arrival). We modelled the relationships between extinction probability, level of endemism and life history traits in both periods. Results The prehistoric extinction–endemism relationship can be explained entirely by the selective extinction of large‐bodied species, whereas the historic extinction–endemism relationship appears due to increased susceptibility to introduced predators resulting from the loss of predator escape responses, including loss of flight. Conclusions These features may explain extinction–endemism relationships more generally, given that human hunting and predator introductions are major impacts associated with human arrival on islands.     

The present, past and future of human-caused extinctions

This paper re-evaluates whether we are really at the start of a mass extinction caused by humans. I consider the present, past and future of human-caused extinctions. As regards the present, estimates of extinction rates based on Red Data Books underestimate real values by a large factor, because the books evaluate only those species that have attracted specific attention and searches. Especially in tropical areas with few resident biologists, many poorly known species go extinct without having been the object of specific attention, and others disappear even before being described. A 'green list' of species known to be secure is needed to complement 'red books' of species known to be extinct. As regards the past, it is now clear that the first arrival of humans at any oceanic island with no previous human inhabitants has always precipitated a mass extinction in the island biota. Well-known victims include New Zealand's moas, Madagascar's giant lemurs, and scores of bird species on Hawaii and other tropical Pacific islands. Late-Pleistocene or Holocene extinctions of large mammals after the first arrival of humans in North America, South America and Australia may also have been caused by humans. Hence human-caused mass extinction is not a hypothesis for the future but an event that has been underway for thousands of years. As regards the future, consideration of the main mechanisms of human-caused extinctions (overhunting, effects of introduced species, habitat destruction, and secondary ripple effects) indicates that the rate of extinction is accelerating.(ABSTRACT TRUNCATED AT 250 WORDS)     

Drivers of extinction: the case of Azorean beetles

Oceanic islands host a disproportionately high fraction of endangered or recently extinct endemic species. We report on species extinctions among endemic Azorean beetles following 97% habitat loss since AD 1440. We infer extinctions from historical and contemporary records and examine the influence of three predictors: geographical range, habitat specialization and body size. Of 55 endemic beetle species investigated (out of 63), seven can be considered extinct. Single-island endemics (SIEs) were more prone to extinction than multi-island endemics. Within SIEs restricted to native habitat, larger species were more extinction-prone. We thus show a hierarchical path to extinction in Azorean beetles: species with small geographical range face extinction first, with the larger bodied ones being the most threatened. Our study provides a clear warning of the impact of habitat loss on island endemic biotas.     

Global Patterns and Drivers of Avian Extinctions at the Species and Subspecies Level

Birds have long fascinated scientists and travellers, so their distribution and abundance through time have been better documented than those of other organisms. Many bird species are known to have gone extinct, but information on subspecies extinctions has never been synthesised comprehensively. We reviewed the timing, spatial patterns, trends and causes of avian extinctions on a global scale, identifying 279 ultrataxa (141 monotypic species and 138 subspecies of polytypic species) that have gone extinct since 1500. Species extinctions peaked in the early 20^th century, then fell until the mid 20^th century, and have subsequently accelerated. However, extinctions of ultrataxa peaked in the second half of the 20^th century. This trend reflects a consistent decline in the rate of extinctions on islands since the beginning of the 20^th century, but an acceleration in the extinction rate on continents. Most losses (78.7% of species and 63.0% of subspecies) occurred on oceanic islands. Geographic foci of extinctions include the Hawaiian Islands (36 taxa), mainland Australia and islands (29 taxa), the Mascarene Islands (27 taxa), New Zealand (22 taxa) and French Polynesia (19 taxa). The major proximate drivers of extinction for both species and subspecies are invasive alien species (58.2% and 50.7% of species and subspecies, respectively), hunting (52.4% and 18.8%) and agriculture, including non-timber crops and livestock farming (14.9% and 31.9%). In general, the distribution and drivers of subspecific extinctions are similar to those for species extinctions. However, our finding that, when subspecies are considered, the extinction rate has accelerated in recent decades is both novel and alarming.     

Changing perspectives on the biogeography of the tropical South Pacific: influences of dispersal, vicariance and extinction

Aim The biogeographical patterns and drivers of diversity on oceanic islands in the tropical South Pacific (TSP) are synthesized. We use published studies to determine present patterns of diversity on TSP islands, the likely sources of the biota on these islands and how the islands were colonized. We also investigate the effect of extinctions. Location We focus on oceanic islands in the TSP. Methods We review available literature and published molecular studies. Results Examples of typical island features (e.g. gigantism, flightlessness, gender dimorphism) are common, as are adaptive radiations. Diversity decreases with increasing isolation from mainland sources and with decreasing size and age of archipelagos, corresponding well with island biogeographical expectations. Molecular studies support New Guinea/Malesia, New Caledonia and Australia as major source areas for the Pacific biota. Numerous studies support dispersal‐based scenarios, either over several 100 km (long‐distance dispersal) or over shorter distances by island‐hopping (stepping stones) and transport by human means (hitch‐hiking). Only one vicariance explanation, the eastward drift of continental fragments (shuttles) that may have contributed biota to Fiji from New Caledonia, is supported by some geological evidence, although there is no evidence for the transport of taxa on shuttle fragments. Another vicariance explanation, the existence of a major continental landmass in the Pacific within the last 100 Myr (Atlantis theory), receives little support and appears unlikely. Extinction of lineages in source areas and persistence in the TSP has probably occurred many times and has resulted in misinterpretation of biogeographical data. Main conclusions Malesia has long been considered the major source region for the biota of oceanic islands in the TSP because of shared taxa and high species diversity. However, recent molecular studies have produced compelling support for New Caledonia and Australia as alternative important source areas. They also show dispersal events, and not vicariance, to have been the major contributors to the current biota of the TSP. Past extinction events can obscure interpretations of diversity patterns.     

Ecological and socio-economic factors affecting extinction risk in parrots

Parrots (Psittaciformes) are among the most threatened bird orders with 28 % (111 of 398) of extant species classified as threatened under IUCN criteria. We confirmed that parrots have a lower Red List Index (higher aggregate extinction risk) than other comparable bird groups, and modeled the factors associated with extinction risk. Our analyses included intrinsic biological, life history and ecological attributes, external anthropogenic threats, and socio-economic variables associated with the countries where the parrot species occur, while we controlled for phylogenetic dependence among species. We found that the likelihood of parrot species being classified as threatened was less for species with larger historical distribution size, but was greater for species with high forest dependency, large body size, long generation time, and greater proportion of the human population living in urban areas in the countries encompassing the parrots’ home ranges. The severity of extinction risk (from vulnerable to critically endangered) was positively related to the per capita gross domestic product (GDP) of the countries of occurrence, endemism to a single country, and lower for species used as pets. A disproportionate number of 16 extinct parrot species were endemic to islands and single countries, and were large bodied, habitat specialists. Agriculture, hunting, trapping, and logging are the most frequent threats to parrots worldwide, with variation in importance among regions. We use multiple methods to rank countries with disproportionately high numbers of threatened parrot species. Our results promote understanding of global and regional factors associated with endangerment in this highly threatened taxonomic group, and will enhance the prioritization of conservation actions.     

海洋岛屿生物多样性保育研究进展

海洋岛屿生态系统因具有明显的海域地理隔离而区别于陆地生态系统,被誉为生物地理与进化生态学研究的"天然实验室".陆地或其它邻近岛屿的种源物种迁移到新的岛屿后,经历地理隔离、特征置换或适应辐射等一系列的岛屿进化过程,形成与种源物种具有显著遗传差异的岛屿特有种.岛屿在小面积范围内分化形成大量的特有种,是岛屿生物多样性最为重要的特点之一.但是,岛屿种群由于分布范围局限、生境脆弱且种群规模较小,岛屿种群较陆地种群具有更高的灭绝风险.本文通过对海洋岛屿物种的起源与演化、遗传结构以及岛屿物种的濒危与保护3个热点问题的讨论,阐述岛屿生物多样性的形成机制、濒危肇因以及岛屿生物多样性保育的重要性.     

Unravelling the peculiarities of island life: vicariance, dispersal and the diversification of the extinct and extant giant Galápagos tortoises

In isolated oceanic islands, colonization patterns are often interpreted as resulting from dispersal rather than vicariant events. Such inferences may not be appropriate when island associations change over time and new islands do not form in a simple linear trend. Further complexity in the phylogeography of ocean islands arises when dealing with endangered taxa as extinctions, uncertainty on the number of evolutionary ‘units’, and human activities can obscure the progression of colonization events. Here, we address these issues through a reconstruction of the evolutionary history of giant Galápagos tortoises, integrating DNA data from extinct and extant species with information on recent human activities and newly available geological data. Our results show that only three of the five extinct or nearly extinct species should be considered independent evolutionary units. Dispersal from mainland South America started at approximately 3.2 Ma after the emergence of the two oldest islands of San Cristobal and Española. Dispersal from older to younger islands began approximately 1.74 Ma and was followed by multiple colonizations from different sources within the archipelago. Vicariant events, spurred by island formation, coalescence, and separation, contributed to lineage diversifications on Pinzón and Floreana dating from 1.26 and 0.85 Ma. This work provides an example of how to reconstruct the history of endangered taxa in spite of extinctions and human‐mediated dispersal events and highlights the need to take into account both vicariance and dispersal when dealing with organisms from islands whose associations are not simply explained by a linear emergence model.     

Non‐random patterns of invasion and extinction reduce phylogenetic diversity in island bird assemblages

Anthropogenically driven changes in bird communities on oceanic islands exemplify the biotic upheaval experienced by island floras and faunas. While the influence of invasions and extinctions on species richness and beta‐diversity of island bird assemblages has been explored, little is known about the impact of these invasions and extinctions on phylogenetic diversity. Here we quantify phylogenetic diversity of island bird assemblages resulting from extinctions alone, invasions alone, and the combination of extinctions and invasions in the historic time period (1500 CE to the current), and compare it to the expected phylogenetic diversity that would result if these processes involved randomly selected island bird species. We assessed phylogenetic diversity and structure at the scale of the island (n = 152), the archipelago containing the islands (n = 22), and the four oceans containing the archipelagos using three measures. We found that extinction, invasion, and the combination of invasion and extinction generally resulted in lower phylogenetic diversity than expected, regardless of the spatial scale examined. We conclude that extinction and invasion of birds on islands are non‐random with respect to phylogeny and that these processes generally leave bird assemblages with lower phylogenetic diversity than we would expect under random invasion or extinction.     

Species richness, extinction and immigration rates of vascular plants on islands in the Stockholm archipelago, Sweden, during a century of ceasing management

Survey of eighteen islands in the Stockholm archipelago from 1884–1908 was re-examined during 1996–1998 to investigate how island size, degree of isolation and human impact affect the species number, extinction and immigration rates of terrestrial vascular plants. Cattle grazing and haymaking was widely and commonly in practice on the islands, but became less intensive since the 1920s and ceased during the 1960s. In the first survey species number was positively correlated with area and negatively correlated with distance to mainland. This pattern was similar in the later survey. However, the number of surrounding islands was positively correlated with island specific species number. During the period from the first to the second survey twenty species disappeared and ninety-three appeared as new. The increased abundance of trees, bushes and shade tolerant herbs suggest that this increase in species number is the effect of an ongoing succession in the landscape. The absolute extinction rate was negatively correlated with island size and distance to mainland, while the immigration rate was positively correlated to island size. The extinction rate was negatively correlated with the distance to mainland probably due to an earlier more intense cultural exploitation closer to the mainland. Our measure of human impact, the presence of houses on islands, was not related to terrestrial plant species number or extinction rate. However, there was a trend for the immigration rate to be higher on islands with houses in 1942 than those without, indicating the importance of human activities for dispersal and/or recruitment.     

Avian translocations restore dual interaction networks in an island ecosystem

Many island bird species have been driven to extinction by introduced predators. Although poorly understood, these extinctions could have a 2-fold impact on bird–plant mutualisms, because island bird species can serve as both pollinators and seed dispersers. We investigated how avian translocations into a mammal-free reserve in New Zealand affected the structure of bird–flower and bird–fruit interactions. We observed bird–fruit and bird–flower interactions over a 9-year period to establish (1) the extent to which native birds are both nectivorous and frugivorous (i.e. “dual mutualists”) and (2) how avian translocations and conservation reestablished nectivory and frugivory networks. Results showed that all but one native bird species were dual mutualists. Pairwise species interaction frequencies were positively correlated between networks. However, overall levels of nectivory by each bird species were unrelated to levels of frugivory. Interaction specialization and species strength also did not differ between networks. The reintroduction of threatened and endangered bird species appeared to have restored both interaction networks, and the sequence of species recovery accelerated restorative changes. Overall results indicate that not only does the extinction of dual mutualists have a 2-fold, negative effect on mutualistic interactions with plants, they can also accelerate the recovery of ecosystem services following restoration efforts.     

Island incidence and mainland population density: mammals from Mediterranean islands

Abstract. The reasons why some species are resistant to extinction or are better invaders of islands than others remain unexplained. In this study, we test the hypothesis that mammals living on the mainland at higher density than predicted by the density/body mass relationship have a much greater chance to colonize a small island successfully, and/or that they are less likely to become extinct when living on small islands. For this, we used data compiled on mammals from a number of Mediterranean islands. We show a nested pattern for mammals on western Mediterranean islands, which suggests that the distribution of mammals on these islands is not the result of a random process. Using two comparative methods, we show that mammal density on the mainland, corrected for body mass, is negatively correlated with island size. Mammals with a high density compared to the density/mass relationship are the best invaders and/or probably have less chance of going extinct on small islands when population size is small.