Global
Environmental Change and Biodiversity
1-4 May, 2005,
Dourdan, France
Background:
Population
declines and extinctions of plant and animal species due to human activities
have been primarily caused by habitat destruction and degradation,
overexploitation, and invasive species. Most
conservation strategies have been designed to limit the negative effects of
these human impacts on biodiversity. In the future, global environmental change - increasing
temperature, changes in precipitation patterns, increasing atmospheric CO2
concentration, N deposition, etc. - is likely to become a major factor
influencing species abundance, distribution, and behavior (Peters &
Lovejoy 1992, Chapin et al. 2001, Hannah & Lovejoy 2003).
It is essential that we develop a sound scientific understanding of how
global environmental change will modify biodiversity so that decision makers can
be appropriately alerted to the possible effects of global change on
biodiversity, conservation strategies can be adapted to account for
environmental change, and assessments can be made of the potential effects of
changes in biodiversity on ecosystem services.
A
wide variety of observations, models, and experiments suggest that global
environmental change has modified and will continue to modify biodiversity in
important ways. For example, shifts in species ranges, population declines, and
changes in timing of activities of plants and animals have already occurred in
the past century and are often correlated with increased temperature or changes
in precipitation patterns (e.g., Pounds et al. 1999, Parmesan & Yohe
2003, Root et al. 2003).
Bioclimatic models - which are based on climate projections and climatic
constraints on species estimated from current spatial distributions - suggest
that projected changes in temperature and precipitation will lead to a
continuation of these range shifts in the future with negative effects on
biodiversity at regional and global scales (e.g., Bakkenes et al. 2002,
Midgley et al. 2002, Thomas et al. 2004) and on the health of humans and
agriculturally important plants and animals (e.g., Sutherst 2001, 2004).
Dynamic Global Vegetation Models (DGVMS) - which simulate the response of
vegetation to atmospheric and climatic change at global scales - suggest that
distributions of major species groups and biomes are also likely to shift
towards the poles and higher altitudes (e.g., Cramer et al.
2001, Bachelet et al. 2003, Bonan et al. 2003, Bond et al. 2003, Gerber
et al. 2004). Experiments with
elevated CO2, elevated temperature, and N additions suggest that all
these factors will affect plant community structure and, in some cases, lead to
substantial reductions in biodiversity (e.g., Leadley et al. 1999, Shaver et al.
2000, Roem et al. 2002, Körner 2003, Zavaleta et al. 2003).
All
of these approaches - observations, experiments, and models - have strengths,
but also have weaknesses that limit our ability to determine the reliability of
predictions of the effects of global environmental change on biodiversity in the
future. For example:
•
Observations provide evidence that global warming has already modified diversity
at regional scales in situ and, as such, are exceptionally useful for
persuading scientists and the public that even relatively small changes in
climate can influence species distributions.
However, historical changes in climate are potentially confounded with a
number of other factors including land use change, making it difficult to
demonstrate a causal link between observed shifts in species distributions and
climate.
•
Current species distributions provide an extraordinary database for estimating
long-term climatic limits on species range and, thus, a relatively simple and
powerful means of extrapolating into the future. However, bioclimatic models
have not yet included rising atmospheric CO2 concentrations or N
deposition as driving factors in future species distributions, even those these
have already driven shifts in plant community structure and may become much more
important in the future (Sala et al. 2000, Chapin et al. 2001). In addition, the
positive and negative interactions between species that may maintain coherent
community structure are not accounted for in these models.
•
Dynamic Global Vegetation Models provide more mechanistic representations of
climatic constraints on plant distributions than bioclimatic models and some
account explicitly for inter-specific interactions.
However, these models assume that plants can be grouped into large
classes that have similar responses to environmental change (plant functional
types), even though experiments suggest that plant functional types can be
difficult to identify in situ (e.g., Poorter & Navas 2003, Morgan et
al. 2004).
•
Experiments provide a means of rigorously separating cause and effect for
individual factors involved in environmental change, but the small spatial and
temporal scale of these experiments may make it difficult to extrapolate from
experiments to real systems. In
addition, relatively few experiments to date have examined the interactions
between several environmental factors and their impact on biodiversity.
Objectives:
This
meeting brought together researchers 1) doing experimental work at the patch
scale with elevated CO2, warming, and N deposition, 2) modeling
species response to climate change at regional scales using bioclimatic
envelopes, 3) modeling in shifts in plant species groups at global scales (DGVM
models), and 4) analyzing observational data and developing biodiversity
observation networks. The goal was to develop a research agenda that contributes
to exchanges of ideas between fields of research, tests of hypotheses underlying
models, and reflections on the use of observational and experimental studies.
Our belief is that we can improve our confidence in the ability to predict the
effects of global environmental change on biodiversity by combining and
comparing a variety approaches.
Several
previous international meetings have addressed issues related to climate change
effects on biodiversity. For
example, researchers studying the observed impacts of climate change on wildlife
have already met several times, including a recent meeting at the Tyndall Centre,
UK in April 2003 (Green et al. 2003). The
objectives of our meeting differed in that we focused on the developing ties
across groups of scientists having widely varying approaches to studying the
effects of global change on biodiversity. Because
of the complexity of this task we limited the scope of this meeting
to terrestrial ecosystems.