The Forgotten Megafauna

PERSPECTIVES
ECOLOGY
The Forgotten Megafauna
An expanded megafauna concept elucidates
how extinctions of the largest vertebrates in
any ecosystem have similar effects.
Dennis M. Hansen1 and Mauro Galetti1,2
arge terrestrial vertebrates—
Gomphothere
Giant ground sloth
called megafauna—play key
Elephant bird
Giant tortoise
roles in ecosystem dynamics by feeding on plants and by
maintaining habitat heterogeneity (1). A global wave of
megafauna extinctions occurred 50,000 to 10,000 years
ago, when many large continental mammals were lost (2–5).
Classical definitions of megafauna are based on such contiICA
M ER
TH A
U
nental mammals and are variO
S
ously given as animals larger
than 44 kg (6) or above 1000 kg
(7). Here, we argue that the megafauna concept should be extended beyond an
AR
MADAGASC
absolute animal size to be context-dependent.
In any given ecosystem, the largest vertebrates
IUS
MAURIT
have ecosystem impacts that are similar on a
relative scale to those of the largest vertebrates Scaling the megafauna. The magnitude of loss of frugivorous megafauna is currently most dramatic on
in another ecosystem: One ecosystem’s meso- islands, as illustrated by the smaller drawn sizes of the giant ground sloth and the gomphothere from South
fauna is another ecosystem’s megafauna.
America, compared with the elephant bird in Madagascar and the giant tortoise of Mauritius. However, many
An ecosystem function that clearly illus- continental regions are poised to catch up.
trates this argument is animal-mediated seed
dispersal. Here, the link between animal body
To illustrate our point, we have examined in relative terms, led to a greater megafaunal
mass and ecosystem function is straight- tropical and subtropical faunas from three downsizing than the extinction of even the
forward: The larger the fruit-eating animal kinds of ecosystems: continental, continen- largest gomphotheres in South America
(frugivore), the larger the fruits it can tal islands, and oceanic islands. For each (see the figure).
consume. Thus, extinction-mediated “ecolog- fauna, we compared the body masses of the
Moreover, in the relatively species-poor
ical shrinkage”—the loss of species inter- largest extant frugivorous vertebrate— and simple island ecosystems, cascading
actions—in community-level seed dispersal mammal, bird, or reptile—to the largest that effects of megafaunal loss may manifest
roughly scales with frugivore body mass.
has gone extinct since the late Pleistocene. themselves faster and with more devastating
Scientists have argued that in continental On continents, the body masses of extant results than in more complex continental
Central and South America, the extinction of frugivores are an order of magnitude lower ecosystems. For example, lost megafaunal
the classic mammalian megafauna—such as than those of extinct frugivores; in contrast, seed-dispersal interactions on islands will not
giant ground sloths and gomphotheres— in some continental and oceanic islands, be compensated for by surviving frugivores,
caused disruption of seed dispersal for large body masses of extant animals are two or because they are too small. In continental
fruits (4, 5). However, on islands, the extinc- even three orders of magnitude lower than ecosystems, there is a higher functional
tion of large birds and reptiles in the past two those of their extinct predecessors (see the redundancy, with medium- and even smallor three millennia has led to similar disrup- supporting online material).
sized species capable of filling at least part of
tions (8, 9). In both locations the demoFor instance, the largest frugivores in the megafaunal niche (12).
graphic and genetic consequences of large- South America were gomphoteres (7580
Anthropogenic impacts are set to cause
vertebrate extinctions for plants are likely kg), whereas the largest living frugivores are further extinctions among large vertebrates,
similar—for example, disruption of long- the tapirs (300 kg). On the continental island with dramatic consequences for ecosystem
distance gene flow or changes in species of Madagascar, the role of largest frugivore dynamics (11). If all currently threatened vercomposition (10, 11). Yet, by the classic def- has passed from the elephant bird (450 kg) to tebrate frugivores were to go extinct, the relainitions, large insular vertebrates would not the radiated tortoise (10 kg). On Mauritius, tive ecological shrinkage in many continental
be considered megafauna.
giant tortoises weighing up to 100 kg were ecosystems would equal that of islands. For
the largest native frugivores; today, the title instance, if all threatened frugivores in South
goes to a fruitbat weighing only 0.54 kg. America were to go extinct, the largest
1Department of Biology, 371 Serra Mall, Stanford UniThus, the loss of the island giants—tortoises, remaining frugivore would be the howler
2
versity, Stanford, CA 94305, USA. UNESP-São Paulo State
lizards, and flightless birds such as the dodo monkey, weighing 9 kg—a factor of 700 less
University, Department of Ecology, Rio Claro, São Paulo,
that were once found on many islands—has, than the giant ground sloth. Even some islands
Brazil 13506-900. E-mail: [email protected]
42
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CREDIT: MEGAFAUNA ARTWORK BY CARL BUELL
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PERSPECTIVES
References and Notes
1. R. Dirzo, A. Miranda, in Plant-Animal Interactions:
Evolutionary Ecology in Tropical and Temperate Regions,
P. W. Price, T. M. Lewinshon, G. W. Fernandes, W. W.
Benson, Eds. (Wiley, New York, 1991), pp. 273–287.
2. P. L. Koch, A. D. Barnosky, Ann. Rev. Ecol. Evol. Syst. 37,
215 (2006).
3. A. D. Barnosky et al., Science 306, 70 (2004).
4. D. H. Janzen, P. S. Martin, Science 215, 19 (1982).
5. P. R. Guimaraes Jr., et al., PLoS ONE 3, e1745 (2008).
6. P. S. Martin, R. G. Klein, Quaternary Extinctions: A
Prehistoric Revolution (Univ. of Arizona Press, Tucson,
1995).
7. R. N. Owen-Smith, Megaherbivores: The Influence of Very
Large Body Size on Ecology (Cambridge Univ. Press, New
York, 1988).
8. H. J. Meehan et al., J. Biogeogr. 29, 695 (2002).
9. D. M. Hansen et al., PLoS ONE 3, e2111 (2008).
COMPUTER SCIENCE
10. R. G. Colevatti et al., Mol. Ecol. 12, 105 (2003).
11. S. J. Wright et al., Biotropica 39, 289 (2007).
12. W. Hallwachs, in Frugivores and Seed Dispersal, A. Estrada,
T. H. Fleming, Eds. (Kluwer, Boston, 1986), pp. 285–304.
13. A. R. Wallace, The Geographical Distribution of Animals
(Harper, New York, 1876).
14. Supported by the Velux Foundation (D.M.H.), Fundação
de Amparo à Pesquisa do Estado de São Paulo (M.G.),
and Conselho Nacional de Desenvolvimento Científico e
Tecnológico (M.G.).
Supporting Online Material
www.sciencemag.org/cgi/content/full/324/5923/42/DC1
Fig. S1
Table S1
References
10.1126/science.1172393
Downloaded from www.sciencemag.org on May 10, 2009
stand to suffer further losses; in Mauritius, the
largest nonthreatened native frugivore is the
gray white-eye, a bird weighing a mere 0.009
kg (see the supporting online material).
An extended megafauna concept has the
potential to promote synergy between otherwise disparate research and conservation foci,
and to facilitate broader syntheses of ecosystem-level effects of extinctions of the
largest vertebrates and the resulting ecological
shrinkage. It is high time to more fully understand and ameliorate the recent and ongoing
losses of all “the hugest, and fiercest, and
strangest forms” (13).
Computers with intelligence can design and
run experiments, but learning from the results
to generate subsequent experiments requires
even more intelligence.
Automating Science
David Waltz1 and Bruce G. Buchanan2
he idea of automating asmotion; today, computer-controlled
pects of scientific activity
data collection is commonplace
dates back to the roots of
and necessary for both expericomputer science, if not to Francis
mental and observational science.
Bacon. Some of the earliest proAutomating many activities begrams automated the processes of
yond data collection offers even
creating ballistic tables, cracking
more benefits.
cyphers, collecting laboratory
In the near term, a useful metadata, etc., by carrying out a set of
phor is to consider computers as
instructions from start to finish.
intelligent assistants. Some assisStarting with DENDRAL in the
tants gather data and attend to
1960s (1), artificial intelligence
such tasks as noise filtering, data
programs such as Prospector (2),
smoothing, outlier rejection, and
Bacon (3), and Fahrenheit (4)
data storage. Other assistants are
automated some of the planning,
specialists at statistical analysis,
Semiautomated. Scientists at Stanford’s Instrumentation Research Laboratory
analysis, and discovery portions (circa 1970) linked a gas chromatograph and high-resolution mass spectrome- still others at bench work. This
of the scientific enterprise. How- ter to computers to automate studies of biological fluids, meteorites, and other metaphor has driven many reever, most of these programs were materials. Stanford’s DENDRAL Project experimented with automated interpreta- search projects over the past sevstill designed to run a calculation tion of the data and experiment planning to specify nuclear magnetic resonance eral decades and has led to many
to completion, produce an answer, or infrared data that would resolve ambiguities in the mass spectral data.
of the most successful applicaand then stop. They did not fully
tions of computers.
“close the loop” in the sense of examining the systems, derived from visual observation of
An early articulation of this metaphor
results of their actions, deciding what to try such systems. As these reports show, it is pos- is Joshua Lederberg’s effort at Stanford
next, potentially cycling forever.
sible for one computer program to step University School of Medicine to develop an
Two reports on pages 85 and 81 of this through the activities needed to conduct a con- automated biomedical laboratory to examine
issue push the boundaries of automatic scien- tinuously looping procedure that starts with a the soil of Mars for traces of life, as part of
tific experimentation and discovery. King question, carries out experiments to answer the 1975 Viking mission deployed by the
et al. (5) describe a robotic system for running the question, evaluates the results, and refor- U.S. National Aeronautics and Space Adbiological experiments, evaluating their mulates new questions.
ministration. The robot assistant Lederberg
results, and deciding what experiments to try
The main goals of automation in science designed, with engineer Elliott Levinthal,
next. Schmidt and Lipson (6) describe their have been to increase productivity by increas- consisted of a conveyor belt that scooped up
work on discovering compact equations that ing efficiency (e.g., with rapid throughput), to samples of Martian soil and deposited them
characterize complex nonlinear dynamical improve quality (e.g., by reducing error), and within a computer-controlled mass spectromto cope with scale, allowing scientific treat- eter. Each soil sample was bombarded with
1Center for Computational Learning Systems, Columbia
ment of topics that were previously impossi- electrons, producing a fragmentation pattern
University, New York, NY 10115, USA. 2Computer Science
ble to address. Tycho Brahe spent a lifetime that sorted the charged particles (ions) accordDepartment, University of Pittsburgh, Pittsburgh, PA
recording observations that allowed Johannes ing to their mass. This pattern was transmitted
15260, USA. E-mail: [email protected]; waltz@
ccls.columbia.edu
Kepler to formulate Kepler’s laws of planetary to Earth, where scientists could analyze it for
CREDIT: ROBERT K. LINDSAY
T
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www.sciencemag.org/cgi/content/full/324/5923/42/DC1
Supporting Online Material for
The Forgotten Megafauna
Dennis M. Hansen* and Mauro Galetti
*To whom correspondence should be addressed. E-mail: [email protected]
Published 3 April 2009, Science 324, 42 (2009)
DOI: 10.1126/science.1172393
This PDF file includes:
Fig. S1
Table S1
References
Supplementary online material
Figure S1. Current and projected ecological shrinkage in seed dispersal interactions on
continents, continental islands, and oceanic islands, illustrated by declines in frugivore
body mass. Arrows span declines from the largest recently extinct frugivore to the largest
extant frugivore (red arrows), as well as maximum projected future decline if all
currently threatened frugivores went extinct (IUCN status of VU, EN or CR; yellow
arrows). Regions: Africa [AF], South America [SA], Australia [AU], Southeast Asia [AS];
Cuba [CU], Madagascar [MA], New Caledonia [NC]; Tonga [TO], Mauritius [MR], Fiji
[FI].
Table S1. Largest extinct and extant frugivores in selected continents, continental islands and oceanic islands.
Body mass in kg. IUCN status, from least concern to critically endangered: LC = Least Concern, NT = Near
Threatened, VU = Vulnerable, EN = Endangered, CR = Critically Endangered.
Region
Largest extinct
Largest extant
Body
mass
Largest extant non-threatened
Body IUCN
mass status (1)
Body
mass
IUCN
status (1)
Africa
Pleistocene elephant
Elephas iolensis (2)
6500
African bush elephant
Loxodonta africana (2)
3940
NT
African bush elephant
Loxodonta africana (2)
3940
NT
South
America
Gomphothere
Stegomastodon superbus (2)
7580
Baird’s tapir
Tapirus bairdii (2)
300
EN
Red howler monkey
Alouatta seniculus (2)
9
LC
Australia
Diprotodon
Diprotodon australis (3)
2700
Southern cassowary
85
Casuarius casuarius (8)
VU
Emu
Dromaius novaehollandiae (8)
60
LC
SE Asia
Stegodon
Stegodon sp. (2)
10000
Asian elephant
Elephas maximus (2)
3000
VU
Tibetan macaque
Macaca thibetana (2)
45
NT
Cuba
Cuban ground sloth
Megalocnus rodens (4)
200
Cuban rock iguana
Cyclura nubila (9)
4.1
VU
Prehensile-tailed hutia
Mysateles prehensilis (11)
1.9
NT
Madagascar Elephant bird
Aepyornis maximus (5)
450
Radiated tortoise
10
Astrochelys radiata (10)
VU
Brown lemur
Eulemur fulvus (2)
5.8
LC
New
Caledonia
Giant horned tortoise
Meiolania sp. (6)
500
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Tonga
Giant iguana
Brachylophus gibbonsi (7)
3.3
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Mauritius
Mauritian saddle-backed giant
tortoise
Cylindraspis triserrata (6)
100
Greater Mascarene
flying fox
Pteropus niger (2)
0.54
EN
Mauritius grey white-eye
Zosterops mauritianus (8)
0.009
LC
Fiji
Giant horned tortoise
Meiolania sp. (6)
300
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Pacific flying fox
Pteropus tonganus (2)
0.6
LC
Acknowledgements:
Thanks to the following for providing information relating to Table S1: Richard Corlett,
Anthony Cheke, Trevor Worthy, Christopher Johnson, Pedro Jordano.
References:
1.
IUCN Redlist online: http://www.iucnredlist.org (accessed February 01,
2009).
2.
Smith, F. A. et al. Ecological Archives E084-094, (2003) and personal
communications (see above).
3.
C. Johnson, Australia’s Mammal Extinctions: A 50,000 year history.
Cambridge University Press (2006)
4.
D. W. Steadman et al., Proc. Natl. Acad. Sci. U.S.A. 102, 11763 (2005).
5.
D. Amadon, Condor 49, 159 (1947).
6.
No published body mass estimates exist for these species; we estimated the
body masses based on known carapace length/body mass relations for the
giant Aldabran tortoise, Aldabrachelys gigantea, from M. J. Coe, D. Bourn, I.
R. Swingland, Phil. Trans. R. Soc. Lond. B. 286, 163 (1979).
7.
No published body mass estimate exists for this species; we estimated the
body mass using the SVL reported in G. K. Pregill, D. W. Steadman, J.
Herpetol. 38, 15 (2004), and the relationship between SVL and body mass for
Iguana iguana reported in R. W. Van Devender, in Iguanas of the World, G.
M. Burghardt, A. S. Rand, Eds. (Noyes Publications, Park Ridge, 1982), pp.
162–183.
8.
J. B. Dunning, Ed., CRC Handbook of Avian Body Mass, 2nd edition (CRC
Press, Cleveland, 2007).
9.
K. Beovides–Casas, C. A. Mancina, Animal Conservation and Biodiversity 29,
1 (2006).
10.
M. Pedrono, The Tortoises and Turtles of Madagascar (Natural History
Publications, Borneo, 2008).
11.
M. Hutchins, D. Kleiman, V. Geist, M. McDade, Eds. Grzimek's Animal Life
Encyclopedia, Second Edition (Thomson-Gale, Farmington Hills, 2003).