Extinction patterns in the avifauna of the Hawaiian islands

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.     

Global late Quaternary megafauna extinctions linked to humans,not climate change

The late Quaternary megafauna extinction was a severe global-scale event. Two factors, climate change and modern humans, have received broad support as the primary drivers, but their absolute and relative importance remains controversial. To date, focus has been on the extinction chronology of individual or small groups of species, specific geographical regions or macroscale studies at very coarse geographical and taxonomic resolution, limiting the possibility of adequately testing the proposed hypotheses. We present, to our knowledge, the first global analysis of this extinction based on comprehensive country-level data on the geographical distribution of all large mammal species (more than or equal to 10 kg) that have gone globally or continentally extinct between the beginning of the Last Interglacial at 132 000 years BP and the late Holocene 1000 years BP, testing the relative roles played by glacial–interglacial climate change and humans. We show that the severity of extinction is strongly tied to hominin palaeobiogeography, with at most a weak, Eurasia-specific link to climate change. This first species-level macroscale analysis at relatively high geographical resolution provides strong support for modern humans as the primary driver of the worldwide megafauna losses during the late Quaternary.     

Extinctions of herbivorous mammals in the late Pleistocene of Australia in relation to their feeding ecology: No evidence for environmental change as cause of extinction

Abstract There has been debate over the cause of the extinction of ‘megafauna’ species during the late Pleistocene of Australia. One view is that environmental change, either natural or human‐induced, was the main factor in the extinctions. Some support for this comes from the observation that, among herbivores, most of the species that went extinct were apparently browsers rather than grazers. Browsers would presumably have been more dependent on shrubland and woodland habitats than grazers, and it has been argued that such habitats might have contracted in response to aridity or changed fire regimes in the late Pleistocene. Here, we test this idea by comparing extinction rates of browsers and grazers in the late Pleistocene, controlling for body mass in both groups. We show that in both browsers and grazers the probability of extinction was very strongly related to body mass, and the body mass at which extinction became likely was similar in the two groups. It is true that more browsers than grazers went extinct, but this is largely because most very large herbivores in the late Pleistocene were browsers, not because large browsers were more likely to go extinct than similarly sized grazers. This result provides evidence against some forms of environmental change as a cause of the extinctions.     

Optimal hunting and Pleistocene extinction

A basic assumption of the Pleistocene extinction, or overkill hypothesis, is that rates of human predation on numerous genera of megafauna exceeded prey replacement rates. Previous assessments of this hypothesis have often stressed the technological or organizational capabilities of Paleolithic hunters to harvest prey in sufficient numbers to threaten extinction. Optimal foraging models and ethnographic observations of modern hunters-gatherers provide a logical basis for assessing the feasibility of alternative reconstructions of Paleolithic hunting strategies as well as their compatibility with the concept of critically high rates of predation sufficient to cause extinction.An earlier version of this paper was delivered under the title Optimal Foraging and Pleistocene Extinction as part of a symposium entitled, Environments and Extinctions: Man in the Late Glacial North America (J. I. Mead and D. J. Meltzer, Organizers) held at the 47th Annual Meeting of the Society for American Archaeology, Minneapolis, Minnesota, April 14–17 1982.     

Geographically contrasting biodiversity reductions in a widespread New Zealand seabird

Unravelling prehistoric anthropogenic impacts on biodiversity represents a key challenge for biologists and archaeologists. New Zealand's endemic Stewart Island Shag (Leucocarbo chalconotus) comprises two distinct phylogeographic lineages, currently restricted to the country's south and southeast. However, fossil and archaeological remains suggest a far more widespread distribution at the time of Polynesian settlement ca. 1280 AD, encompassing much of coastal South Island. We used modern and ancient DNA, radiocarbon dating, and Bayesian modelling, to assess the impacts of human arrival on this taxon. Our analyses show that the southeast South Island (Otago) lineage was formerly widespread across coastal South Island, but experienced dramatic population extinctions, range retraction and lineage loss soon after human arrival. By comparison, the southernmost (Foveaux Strait) lineage has experienced a relatively stable demographic and biogeographic history since human arrival, retaining much of its mitochondrial diversity. Archaeological data suggest that these contrasting demographic histories (retraction vs. stability) reflect differential human impacts in mainland South Island vs. Foveaux Strait, highlighting the importance of testing for temporal and spatial variation in human‐driven faunal declines.     

Correlates of rediscovery and the detectability of extinction in mammals

Extinction is difficult to detect, even in well-known taxa such as mammals. Species with long gaps in their sighting records, which might be considered possibly extinct, are often rediscovered. We used data on rediscovery rates of missing mammals to test whether extinction from different causes is equally detectable and to find which traits affect the probability of rediscovery. We find that species affected by habitat loss were much more likely to be misclassified as extinct or to remain missing than those affected by introduced predators and diseases, or overkill, unless they had very restricted distributions. We conclude that extinctions owing to habitat loss are most difficult to detect; hence, impacts of habitat loss on extinction have probably been overestimated, especially relative to introduced species. It is most likely that the highest rates of rediscovery will come from searching for species that have gone missing during the 20th century and have relatively large ranges threatened by habitat loss, rather than from additional effort focused on charismatic missing species.     

BIODIVERSITY LETTER: The North American Pleistocene overkill hypothesis and the re‐wilding debate

The conservation agenda to re‐wild North America may or may not be realistic in terms of political ecology. However, it represents a real conservation recommendation to re‐wild North America with the extant megafauna most closely related to those that became extinct at the end of the Pleistocene. The recommendation is based on the presumption that society bears an ethical responsibility to re‐wild because humans caused the extinctions. However, the extent to which Pleistocene megafaunal extinctions were the result of overkill is hotly debated. As a result, the ethical imperative for North American re‐wilding should be questioned. It will not be questioned unless members of the conservation community read the extensive archaeological and geological literature concerning the North American Pleistocene extinctions. Overlooking the assumptions underlying this particular recommendation is costly to conservation science and to archaeology because it represents an over‐simplified, unwieldy and troubling fusion of the two.     

The uncertain blitzkrieg of Pleistocene megafauna

We investigated, using meta‐analysis of empirical data and population modelling, plausible scenarios for the cause of late Pleistocene global mammal extinctions. We also considered the rate at which these extinctions may have occurred, providing a test of the so‐called ‘blitzkrieg’ hypothesis, which postulates a rapid, anthropogenically driven, extinction event. The empirical foundation for this work was a comprehensive data base of estimated body masses of mammals, comprising 198 extinct and 433 surviving species > 5 kg, which we compiled through an extensive literature search. We used mechanistic population modelling to simulate the role of human hunting efficiency, meat off‐take, relative naivety of prey to invading humans, variation in reproductive fitness of prey and deterioration of habitat quality (due to either anthropogenic landscape burning or climate change), and explored the capacity of different modelling scenarios to recover the observed empirical relationship between body mass and extinction proneness. For the best‐fitting scenarios, we calculated the rate at which the extinction event would have occurred. All of the modelling was based on sampling randomly from a plausible range of parameters (and their interactions), which affect human and animal population demographics. Our analyses of the empirical data base revealed that the relationship between body mass and extinction risk relationship increases continuously from small‐ to large‐sized animals, with no clear ‘megafaunal’ threshold. A logistic ancova model incorporating body mass and geography (continent) explains 92% of the variation in the observed extinctions. Population modelling demonstrates that there were many plausible mechanistic scenarios capable of reproducing the empirical body mass–extinction risk relationship, such as specific targeting of large animals by humans, or various combinations of habitat change and opportunistic hunting. Yet, given the current imperfect knowledge base, it is equally impossible to use modelling to isolate definitively any single scenario to explain the observed extinctions. However, one universal prediction, which applied in all scenarios in which the empirical distribution was correctly predicted, was for the extinctions to be rapid following human arrival and for surviving fauna to be suppressed below their pre‐‘blitzkrieg’ densities. In sum, human colonization in the late Pleistocene almost certainly triggered a ‘blitzkrieg’ of the ‘megafauna’, but the operational details remain elusive.     

Aboriginal overkill in the intermountain west of North America

Zooarchaeological evidence has often been called on to help researchers determine prehistoric relative abundances of elk (Cervus elaphus) in the Greater Yellowstone ecosystem. Some interpret that evidence as indicating elk were abundant; others interpret it as indicating elk were rare. Wildlife biologist Charles Kay argues that prehistoric faunal remains recovered from archaeological sites support his contention that aboriginal hunters depleted elk populations throughout the Intermountain West, including the Yellowstone area. To support his contention Kay cites differences between modern and prehistoric relative abundances of artiodactyls, age and sex demographics of ungulates in the prehistoric record indicating selective predation of prime-age females, and a high degree of fragmentation of artiodactyl bones indicating humans were under nutritional stress. Kay’s data on taxonomic abundances are time and space averaged and thus mask much variation in elk abundances. When these data are not lumped they suggest that elk were at some times, in some places, as abundant as they are today. Data on the age-sex demography of artiodactyl prey are ambiguous or contradict Kay’s predictions. Bone fragmentation data are variously nonexistent or ambiguous. The zooarchaeological implications of Kay’s aboriginal overkill hypothesis have not yet undergone rigorous testing. Insightful comments of two anonymous reviewers helped improve this paper. Lyman earned his Ph.D. in anthropology from the University of Washington in 1982. His research interests include the cultural and natural history of the Pacific northwestern United States. He is presently a professor in, and chair of, the Department of Anthropology at the University of Missouri-Columbia.