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ECOLOGY
Moving farther and faster
The distributions of terrestrial organisms are shifting in response to climate change. Research shows that these
changes are happening at a much faster rate than previously estimated.
Joshua J. Tewksbury, Kimberly S. Sheldon and Ailene K. Ettinger
F
orecasting the ecological effects of
climate change is a tricky business,
as species tend to move when
conditions around them change. The
movement of species affects everything
from endangered-species management and
reserve planning 1 to the spread of invasive
species, agricultural pests and disease
vectors2 (Fig. 1). Eight years ago, an analysis
of published data on the distribution of
terrestrial species demonstrated that many
species were moving in response to climate
change3, and estimated the average range
shift per decade to be 6.1 km poleward
and 6.1 m upwards in elevation. We
have now received a startling update. By
compiling data from many studies finished
in the past eight years, I-Ching Chen
and colleagues4 show the median rate
of movement towards the poles is now
16.9 km per decade, almost three times
as fast as previously estimated, and the
median movement upwards in elevation is
11.0 m per decade, almost twice as fast as
previously estimated4.
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Tracking changes in species’ range limits
requires taking detailed measurements at
multiple points in time. Almost a decade
ago, Camille Parmesan and Gary Yohe3 set
out to document a “coherent fingerprint
of climate change” in biological systems,
yet at that time few ecologists were
measuring and re-measuring range
boundaries. Parmesan and Yohe thus
had only three datasets they could use
to examine the rate at which species
were moving — one focused on British
birds, another on Swedish butterflies and
a third documented the shifts in alpine
plants in Switzerland. After their paper
was published, however, dusty natural
history monographs of species’ presence
and absence data suddenly became the
justification for whole new expeditions
to re-measure range boundaries, and the
inherent value of systematic observation
of the natural world became much clearer
to many younger ecologists. Eight years
after the work by Parmesan and Yohe3,
the results of this work have now been
summarized and published in Science 4.
This time, instead of just three studies with
quantitative estimates of movement, Chen
and colleagues4 had 53 different studies —
23 estimating shifts in latitude and 31
estimating shifts in elevation.
Yet the reason for the big change in
the estimated rate of movement is not the
number of studies, or even the location
(a north-temperate bias still persists
owing to the lack of investment in the
natural history of the tropics). Instead, the
discrepancy stems from the different time
spans investigated in the two analyses,
and the fact that the rate of warming is
increasing 5. Two of the studies analysed
by Parmesan and Yohe compared range
boundaries at the beginning of the
twentieth century with those at the end,
whereas all but two of the 53 estimates
used by Chen and colleagues compare
range boundaries during the last half
of the twentieth century. This makes a
startling difference, because climate change
during the twentieth century has not
NATURE CLIMATE CHANGE | VOL 1 | NOVEMBER 2011 | www.nature.com/natureclimatechange
© 2011 Macmillan Publishers Limited. All rights reserved
been uniform; the rate of change in global
surface temperature from 1970 to present
is four times that observed from 1900 to
1970 (ref. 5). Range shifts are estimated
per decade, so previous estimates probably
included large periods of time during
which there was little pressure on species
to move. As the pace of climate change
increases, so too does the rate at which
species relocate.Because the rate of climate
change is expected to increase further
in the future5, we may expect upward
revisions in the rates observed by Chen
and colleagues.
They were also able to make a
critical link that had evaded previous
researchers — they showed that the
response rate was positively correlated
with the amount of warming experienced:
the greater the mean temperature change
in a location, the farther the average shift
in the range of the species measured
in that location. This link suggests
causality, but aspects of the relationship
also point to the complexity of the
response to warming.
Observed shifts in elevation suggest
that species are generally not moving fast
enough to track climate up mountains, but
this was not seen for latitudinal shifts; here,
the median response was about as fast as
expected based on the minimum distance
needed to keep up with the changing
location of annual mean temperatures.
In other words, species are moving
northwards at about the same pace as mean
temperatures are moving. However, species
are not ‘keeping up’ with elevational shifts
in mean temperatures. This difference
is probably caused by two issues, one
biological and the other methodological.
First, there are fundamental differences
between latitudinal and elevational
range boundaries. Habitat and substrate
availability may strongly constrain upward
movement at high elevations. Furthermore,
mountains are topographically complex,
providing diverse microclimates at a
small scale, such that species may not
need to shift as far or as fast to find
climatically suitable habitat. Both of these
issues point to biological differences
between latitudinal and elevational range
boundaries. However, there are also
differences in the regional bias of the
studies used in the analysis that could
affect range-shift estimates. Most of the
latitudinal studies were from northtemperate regions, whereas the majority
of elevational studies were from tropical
mountains. Differences between temperate
and tropical locations extend far beyond
differences in the amount of warming they
experience. Substantial evidence suggests
© FRANK PEAIRS/COLORADO STATE UNIV./BUGWOOD.ORG
news & views
Figure 1 | The southwestern corn borer, Diatraea grandiosella, is a serious agricultural pest in the
United States and Mexico. Recent research by Chen and colleagues4 shows that in response to more
rapid warming in the past 40 years, species are shifting their latitudinal range up to three times
faster than previously reported. Movement towards higher latitudes and elevations could allow
agricultural pests such as the corn borer to expand into new areas and undermine food security.
that tropical and temperate communities
may also differ in their sensitivity to
climate change6 and their capacity to
respond by moving 7.
Chen and colleagues also found
that some groups of species had moved
farther poleward than would be needed
to track changing mean temperatures.
This result probably reflects the fact that
range boundaries are not generally set by
mean annual temperature, and are instead
the result of a complex set of biotic and
abiotic processes. Future work will probably
provide researchers with a more robust set
of expectations for shifting boundaries as
we refine our understanding of the climate
controls on species’ range limits.
The headline from this work will clearly
be that current rates of movement are
much larger than previously reported,
but the danger is that some readers will
see this as evidence that most species are
actually tracking changes in their climate.
Yet, species shift their distribution in
response to warming at different rates,
and some species in a community may not
shift at all8. This variation in movement
among members within a community
is the metric that will determine the
rate at which existing communities
unravel or disassemble9. Given the
importance of biotic interactions in setting
demographic rates and constraining
species’ movements, such shifts in
community structure may be as important
as the movement of individual species.
NATURE CLIMATE CHANGE | VOL 1 | NOVEMBER 2011 | www.nature.com/natureclimatechange
© 2011 Macmillan Publishers Limited. All rights reserved
From a conservation perspective, it may be
the species left behind that we should be
most focused on.
Nevertheless, the current work by Chen
and colleagues has broad implications.
Many species are moving much faster
than previously appreciated. This should
give us pause as we design reserves, plan
strategies for combating insect pests, and
map the spread of communicable diseases,
the majority of which spend time in mobile
animal hosts10.
❐
Joshua J. Tewksbury, Kimberly S. Sheldon and
Ailene K. Ettinger are in the Department of Biology,
University of Washington, Box 351800, Seattle,
Washington 98195, USA.
e-mail: [email protected]
References
1. Krosby, M., Tewksbury, J., Haddad, N. M. & Hoekstra, J.
Conserv. Biol. 24, 1686–1689 (2010).
2.IPCC Climate Change 2007: Impacts, Adaptation and
Vulnerability (eds Perry, M. L., Canzianai, O. F., Palutikof, J. P.,
van der Lindon, P. J. & Hanson, C. E.) (Cambridge Univ.
Press, 2007).
3. Parmesan, C. & Yohe, G. Nature 421, 37–42 (2003).
4. Chen, I. C., Hill, J. K., Ohlemuller, R., Roy, D. B. & Thomas, C. D.
Science 333, 1024–1026 (2011).
5.IPCC Climate Change 2007: The Physical Science Basis (eds.
Solomon, S. et al.) (Cambridge Univ. Press, 2007).
6. Deutsch, C. A. et al. Proc. Natl Acad. Sci. USA
105, 6668–6672 (2008).
7. Dynesius, M. & Jansson, R. Proc. Natl Acad. Sci. USA
97, 9115–9120 (2000).
8. Moritz, C. et al. Science 322, 261–264 (2008).
9. Sheldon, K. S., Yang, S. & Tewksbury, J. J. Ecol. Lett. http://dx.doi.
org/10.1111/j.1461-0248.2011.01689.x (2011).
10.World Health Organization The Control of Neglected Zoonotic
Diseases (WHO, 2011); available at http://www.who.int/zoonoses/
control_neglected_zoonoses/en/index.html.
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