abstracts
John Alroy, Smithsonian Institution
Reorganization of Late Quaternary Mammal
Faunas and Causes of Mass Extinction
Research on end-Pleistocene mass extinction of large-bodied North American mammals has focused on relatively short time scales like that of the extinction episode itself, and on relatively minor ecological phenomena like the geographic distributions of individual species. Here, I discuss two general lines of research intended to correct these problems. The first involves my database of Cenozoic North American mammalian paleofaunas, which provides a backdrop for understanding Pleistocene extinction rates. The second project involves the FAUNMAP database, graciously made available on-line by the FAUNMAP Working Group.
The results of these analyses have interesting
ecological implications. The biogeographic coherence of mammalian faunas challenges climate-
or vegetation-driven mechanisms for mass extinction. If small
mammal communities survived unscathed, how could environmental
change have suddenly and almost totally destroyed the continentís
large mammal communities? Together with the intense, rapid, and
selective nature of the extinction in comparison to any other
event in the Cenozoic, the results add to the already weighty
evidence against non-anthropogenic models for mass extinction.
David A. Burney, Fordham University
Rates, Patterns, and Processes of Landscape
Transformation and Extinction: Madagascar as an Experiment in
Human Ecology
Bridging the gap between methodological limits and theoretical expectations is most likely to be possible in the most isolated natural systems, such as those found on remote islands. With their severe biogeographical constraints and generally shallow human time-depth, it is sometimes possible to address questions of global relevance regarding background-level versus human-era disturbance, biotic invasion, and extinction. A series of examples from recent research in Madagascar demonstrates how explicit tests may be applied to hypotheses of landscape transformation and extinction causation that have been proposed for the Late Quaternary.
A preliminary comparison between the empirical
evidence and the predictions of five hypotheses suggests that
all available evidence is consistent with the notions that 1)
each major ecological region of Madagascar shows a different composite
history in terms of landscape transformation and perhaps extinction
chronologies; and 2) each region studied contains some variation
on the same mix of human ecological depredations (overkill, change
of fire regime, exotic species introduction, deforestation, accelerated
erosion). These factors, as well as the "natural"
background-level climatic variations of the Late Holocene, have
good potential for synergistic interactions.
Niles Eldredge, AMNH
Cretaceous Meteor Showers, the Human Ecological "Niche," and the Sixth Extinction
The geological time scale is a telegraphic precis of biotic turnovers during the Phanerozoic and thus constitutes, in summary form, the empirical basis of the reality of mass extinctions and subsequent evolutionary rebounds. Mass extinctions are real and have been caused, in the main, by 1) global climate change; 2) a combination of climate change and other physical events, such as anoxic turnovers; and 3) at least in one instance, extraterrestrial bolide impact and/or massive volcanism. It is equally well established that the earth is currently undergoing yet another mass extinction event -- sometimes called the "Sixth Extinction." And it is clear that the major agent for this current event is Homo sapiens -- primarily through direct habitat destruction and degradation, overutilization of "natural resources," and direct and inadvertent introduction of exotic species.
What is the "ecosystem" in which Homo sapiens has established an interactive presence? It is the global system, sometimes called "Gaia." If this general line of thought is correct, we can no longer think and act as if we were outside of nature -- an attitude that understandably arose with our altered ecological position starting 10,000 years ago. We must realize that we are still very much a part of the global system -- and that our future is completely locked in with the state of the rest of the living world.
Tim F. Flannery, Australian Museum
Emerging Patterns in Australasian Quaternary
Extinctions
The body of data examined here is divided into three geographic/temporal units: Australian Pleistocene; New Guinean Pleistocene; and the Holocene of Australia, New Guinea, the Moluccas, and the Melanesian island arcs. Three major phases of extinction are identified: Pleistocene, Mid-Late Holocene, and historic. Each of these is temporally associated with the arrival of a new wave of humans or their commensal animal companions.
The first phase of extinction affected large terrestrial reptiles and mammals as well as flightless birds in Australia, and mammals in New Guinea. These extinctions occurred more than 35,000 years ago. The second phase, which began less than 4,000 years ago, affected large terrestrial carnivores and some terrestrial herbivores in Australia, New Guinea, and the Melanesian islands, but not in Tasmania. It coincided with the introduction of Canis familiaris into the region; and in the Melanesian island arcs, with the introduction of exotic murids. Recent extinctions have been a mixture of a continuation of Holocene extinction trends and an "aftershock" event ultimately resulting from Pleistocene extinction, possibly accentuated by introduction of the fox.
presentation | interview | bio
Russell W. Graham, Denver Museum of Natural History
Thomas W. Stafford, Jr., University of Colorado
Holmes A. Semken, Jr., University of Iowa
Pleistocene Extinctions: Chronology, Non-analog
Communities, and Environmental Change
A host of models has been proposed under the broad umbrella of environmental change to explain the terminal Pleistocene extinction event. Most of these models have focused on a few taxa, and they are frequently not applicable to the wide range of mammals that became extinct. More generalized models have invoked the interactions of mammals with changing vegetational communities. However, even these models have been criticized because they presumably did not completely satisfy certain criteria. Specifically, environmental models can be refuted if they do not conform to the following: 1) The extinction event occurred circa 11,000 years ago; 2) large mammals (>100 kg) were preferentially affected by the event; and 3) extinctions did not occur in earlier glacial/interglacial fluctuations.
A new model involving the reduction in
geographic ranges with a threshold effect at the terminal Pleistocene
does meet these criteria and
is broadly applicable. Data on the distribution of mammal species
document a continuous trend for mammal range reductions throughout
the l
Late Quaternary. These changes were underway well before modern
Homo sapiens evolved and significantly in advance of human entry
into the New World. In essence, the terminal Pleistocene extinction
can be explained by climate-driven habitat reduction.
presentation | interview | bio
Gary Haynes and B. Sunday Eiselt, University
of Nevada
The Power of Pleistocene Hunter-gatherers:
A Forward and Backward Search for the Evidence about Mammoth Extinction
In this paper, we will explore the possibility that human foragers were ultimately responsible for the extinction of mammoths. For years, debate about the cause of Late Pleistocene extinctions has not been able to provide proof that either climate change or hunting by humans was the driving force behind the disappearance of so many mammalian species. One of us (GH) has examined the ways in which climatic events and trends that kill large mammals may leave unambiguous traces in preserved bone assemblages. Emerging from his actualistic and behavioral studies of free-ranging African elephants has been inferential support for the argument that climate change caused the extinctions.
We will compare the density and distribution
of elephant-bone and mammoth-bone sites throughout the world.
Study of mammoth-bone collections and modern elephant-bone assemblages
provides evidence that certain overlooked characteristics of sites
are found only when humans killed animals, and other characteristics
are found only when non-cultural mortality processes killed them.
We will compare the fossil sites of the Late Pleistocene to the
numerous modern sites studied in Africa and propose some explanations
for the similarities and differences. We will then develop our
argument that Clovis foragers were the main agent in mammoth extinction.
Richard N. Holdaway, Palaecol Research
Differential Vulnerability in the New Zealand
Vertebrate Fauna
Late Holocene vertebrate extinctions in New Zealand included small and large taxa. Extensive surveys of Quaternary sites in the South Island have shown that vertebrate faunas changed in distribution and composition from Otiran glacial to the Holocene, but that there was no extinction event at the Pleistocene-Holocene boundary. The New Zealand event occurred within the last 2,000 years. Introductions of alien predators as well as periods of habitat destruction, but not climate change, can be matched to some extinctions. The record of differential vulnerability is a key to the factors precipitating extinction.
The lack of extinctions at the end of the
Otiran glaciation (14,000-10,000 years BP) indicates that major
environmental change does not necessarily result in an extinction
event so long as it is gradual and involves movement rather than
extinction of vegetation types. Introduced predators do, however,
effect extinctions. Small ecological factors can predispose taxa
to extinction. The vulnerability to predators differs with the
prey and with predators for the same prey species. An extinction
"event" is the sum of individual extinctions: barring
global catastrophe, each species extinction is an individual event.
The identification of introduced mammalian predators as the major
cause of vertebrate extinctions in New Zealand has proven useful
for conservation scientists working on endangered birds, lizards,
and frogs, and may have wider applications for study of previous
events.
Helen F. James, Smithsonian Institution
Douglas Siegel-Causey, National Science
Foundation
Prehistoric Extinctions in Hawaii: The
Search for Causes
The Hawaiian Islands, first colonized by Polynesians only about 1,400-1,600 years ago, experienced extinction of two-thirds of its native vertebrate species after human arrival. The primary causes of extinction and the history of ecological collapse are poorly understood, but the extinctions are very recent in geologic terms and the relevant paleontological, paleoecological, and archaeological records are fairly complete.
This evidence is reviewed in relation to a number of factors commonly thought to have played a role in Quaternary extinctions: 1) Climatic forcing; 2) a blitzkrieg of overharvesting soon after initial human contact with the native fauna; 3) gradual overharvesting by humans; 4) predation by animals that arrived with prehistoric humans; 5) resource competition from animals that arrived with prehistoric humans; 6) cascading extinctions after the disappearance of key species; 7) introduced infectious diseases; and 8) destruction and degradation of habitat.
Archaeologists' reconstructions
of population growth, settlement patterns, and land use suggest
that the aboriginal human population eventually reached and may
have exceeded the carrying capacity of the islands, thus raising
the possibility that this human population expansion, rather than
mere human presence, was the key to ecological collapse.
Ross D.E. MacPhee, AMNH
Preston A. Marx, Aaron Diamond AIDS Research
Center
Lightning Strikes Twice: Blitzkrieg, Hyperdisease,
and Global Explanations of the Late Quaternary Catastrophic Extinctions
There is a recurring pattern to large-scale mammalian extinctions that have occurred within the last 40,000-60,000 years. With certain exceptions, 1) losses have occurred in temporally and geographically discrete clusters; 2) geographical areas that suffered a major extinction within this period did not experience large-scale losses thereafter; and 3) extinctions have closely tracked the human diaspora, in both time and space. On present evidence, this dreadful syncopation -- humans arrive, animals disappear -- seems to have occurred to a greater or lesser degree on every land mass except the continents of earliest human evolution, Africa and Eurasia. But after the period of first contact and initial substantial loss, the pattern changes markedly: the rate of loss drops precipitously and stays depressed until the present era (i.e., the last 500 years).
We propose that the dominant features of
at least some first-contact extinctions can be explained by inferring
that the principal agency of loss was not overhunting or environmental
degradation, but hypervirulent, hyperlethal diseases ("hyperdiseases")
introduced into immunologically naive populations by colonizing
humans and/or their commensals and synanthropics. This hypothesis
potentially 1) explains differential losses in K-selected versus
r-selected taxa; 2) requires no ad hoc explanations for the absence
of mass kill sites in affected areas; and 3) accounts for pattern
change in the character of anthropogenic extinction after first-contact
losses.
Paul S. Martin, University of Arizona
Prehistoric Overkill: Four Decades of Discovery
and Debate
The discovery of prehistoric overkill has triggered a major breakthrough in natural and cultural history. In the last 40,000 years our species, Homo sapiens, spread out of our Afro-Asian homeland into other parts of the globe. In the process, desirable and vulnerable prey declined or vanished. The fossil record on some islands suggests "hit and run" wipe-outs or "commando raids" in which the more vulnerable and desirable species, including rookeries of nesting pelagic seabirds, were obliterated hundreds of years before settlement and horticulture. While not a mass extinction by geological standards, since marine phyla were immune, the continental losses involved "flagship species," large land mammals whose absence profoundly biases our understanding of biogeography, global change, conservation, and range management.
Beyond the debate on prehistoric extinctions
is an even more significant matter, that is their meaning. Radical
new ideas of land use are at stake. The last ice age of some 1.7
million years is no longer regarded as too remote to be worth
considering in "negotiations with nature." Paleontological
and archaeological data are critical in managerial choices for
national parks; these data bear on the potential replacement of
livestock on the western range and on the restoration of "wildness."
An extinct megafauna ranged the continent when it last displayed
its wildness, its evolutionary potential. The biotic potential
of the land must be considered.
Norman Owen-Smith, University of Witwatersrand
The Interaction of Humans, Megaherbivores,
and Habitats in the Late Pleistocene Extinction Event
The extinction event at the end of the Pleistocene differed from preceding extinction episodes in two peculiar features: 1) Extinction likelihood rose sharply with increasing body size; and 2) certain continents, specifically Africa and tropical Asia, escaped the extinctions. It resulted in the demise of all megaherbivores throughout the Americas, northern Eurasia, and Australia. It was associated in time not only with a period of climate shift, but also with a large-scale expansion in the geographic range occupied by humans.
Mechanisms leading to extinction may entail habitat deterioration, competitive replacement, unsustainable levels of predation, or disease outbreaks. Whatever the process, populations must become non-viable throughout the geographic range of the species. The crucial feature distinguishing the change to interglacial conditions at the end of the Pleistocene was the almost worldwide presence of humans. Human elimination of megaherbivores, and hence of their consumptive and engineering effects on habitats, adversely transformed habitats that were beneficial for the coexistence of many other large herbivores, creating fragmented localized islands with deteriorating vegetation conditions. A sequence of local extinctions led inevitably to global demise of these herbivore species, perhaps assisted by human predation.
Stuart L. Pimm, University of Tennessee
Plenary Address
Extinctions, Geographic Ranges, and Patterns of Loss
Over the last few centuries the loss of species in well-known groups of plants, invertebrates, and vertebrates exceeds by one-hundred fold the rate expected from the fossil record. In all instances, these extinctions are dominated by special cases: birds on Pacific islands, fish in African lakes, mollusks in North American rivers, mammals in Australia, and so on. The feature that unites these widely divergent systems and groups is that all contain large numbers of geographically restricted species. A second observation is that existing technologies -- indeed, in the Pacific, only Stone Age -- technologies are capable of causing double-digit percentages of species extinctions.
The lessons for the future are that our technologies are more than adequate to continue to eliminate large number of species. Moreover, many areas remain where habitat destruction, on a scale no larger than the forest losses in 19th-century eastern North America, could rapidly eliminate 20 percent or more of the world's species.
plenary address | interview |bio
Melanie L.J. Stiassny and Ian J. Harrison,
AMNH
Vanishing from Freshwater: Species Decline
and the Machinery of Extinction
Throughout most of human history, freshwater resources have been more than adequate to serve human needs while maintaining the integrity and biological diversity of the earth's ecosystems. But today's stark reality is that massive habitat modification and the widespread introduction of exotic species are straining sustainability to its limit as global freshwater resources are consumed and degraded, and aquatic biodiversity is decimated. Globally, the true degree of aquatic impoverishment is largely unknown, yet there can be no doubt that the losses are already great. In the United States, the Nationwide Rivers Inventory estimates that of the 5.2 million km of streams in the nation, most have been so dramatically altered that only 2 percent have sufficient high quality to be worthy of federal protection status. In the former Soviet Union, long-term diversion of the Aral Sea for cotton irrigation has resulted in a volume decrease of 65 percent, salinity has more than tripled, and the endemic biota is decimated.
Widespread extinction is a pervasive theme
in freshwater systems throughout the world; and while best documented
in lake ecosystems, the losses in rivers and other wetlands are
also profound. The reasons for the particular vulnerability of
freshwater habitats will be explored and the frightful roster
of extinction among selected fish faunas will be described.
A.J. Stuart, Norfolk Museum Services/Castle
Museum
The Role of Humans in Late Pleistocene
Megafaunal Extinction, with Particular Reference to Northern Eurasia
and North America
This paper focuses on the accelerated extinctions that occurred within the Late Pleistocene, with some reference to earlier and later events. Although a global phenomenon, Late Pleistocene extinctions of terrestrial megafauna were very variable in their severity between different zoogeographical regions. Patterns and timing were also different. Losses were highest in North America, South America, and Australia, moderate in Europe, and lowest in sub-Saharan Africa, where all four Late Pleistocene mammals of 1,000 kg or over (elephant, white rhino, black rhino, hippopotamus) survive today.
Any extinction hypothesis must be able
to explain why extinctions were severe and sudden in North America,
but moderate and staggered in northern Eurasia. Since Late Glacial
environmental changes in North America were broadly similar to
those in northern Eurasia, why should the extinction patterns
have been so different? Moreover, very similar environmental changes
occurred several times previously but did not cause major megafaunal
extinctions. The one new factor in the Late Glacial not present
at the end of previous cold stages was the presence of modern Homo sapiens. However, the arrival of advanced humans
took place tens of thousands of years before many of the megafaunal
extinctions. Hunting pressure on megafauna that were severely
reduced in population size and geographical area by climatic changes may
prove to be the key to Late Pleistocene extinctions on a global
scale.
