Biodiversidad - o la diversidad biológica - es un término
ahora tan familiar que los políticos utilizan para convencernos de que realmente
se preocupan por el mundo natural. Muchos periódicos y revistas incluso la
totalidad, están dedicadas a explicar cómo las especies coexisten, por qué
algunas localidades son más diversas que otras, y para el seguimiento de la
velocidad a la que se está perdiendo la biodiversidad. Podría parecer que hay
poco que añadir al debate. Sin embargo, aunque ha habido notables progresos en
la comprensión de cómo se estructuran las comunidades ecológicas, y la mejor
manera de protegerlos, todavía hay muchas cuestiones sin resolver. Éstos son
sólo tres de ellos.
Open
questions: some unresolved issues in biodiversity
Anne E Magurran
Author
Affiliations
Centre for
Biological Diversity, School of Biology, University of St Andrews, St Andrews,
Fife, KY16 8LB, Scotland, UK
BMC Biology
2013, 11:118
doi:10.1186/1741-7007-11-118
The
electronic version of this article is the complete one and can be found online
at: http://www.biomedcentral.com/1741-7007/11/118
Comment
Biodiversity
- or biological diversity - is a term now so familiar that politicians use it
to persuade us that they really care about the natural world. Many papers, and
indeed entire journals, are devoted to explaining how species coexist, why some
localities are more diverse than others, and to tracking the rate at which
biodiversity is being lost. It might seem that there is little to add to the
debate. Yet, while there has been remarkable progress in understanding how
ecological communities are structured, and how best to protect them, there are
still many unresolved issues. Here are just three of them.
Relative abundance of species
It must
always have been obvious to observers that species vary in their abundances.
Darwin remarked on the ‘beautiful diversity and proportion of kinds’ in his
Origin of Species. We know that all ecological communities are characterized by
a few common and typically many rare species. Although this pattern is
ubiquitous, ecologists still struggle to provide a convincing explanation why
species abundances are as uneven as they are. Dozens of models have been
proposed (the first in 1932). Some of these take account of biological
interactions such as competition, while others reflect the statistical behavior
of large numbers. Since models can be based on conflicting assumptions yet
generate patterns seen in the real world, a good ‘fit’ to empirical data does not
in itself vindicate the theory underpinning the model. There is still a need
for a much better understanding of the processes that influence the relative
abundance of species, and that determine which species are abundant and which
ones are rare. This will likely take account of species traits, and the
positioning of a species in its range (populations tend to be larger when taxa
are close to the center of their range). But the spatial and temporal context
of a community is also important as species turnover in space and time plays a
crucial role in maintaining the diversity of an assemblage. Understanding the
processes that shape diversity over both macroecological and local assemblage
scales will play an essential part in this [1].
Anthropogenic change and biodiversity
Many
diversity measures have been developed with the goal of finding a metric that
can quantify the effects of impacts such as pollution on natural communities.
This quest has been only partially successful. One reason is that community responses
to different types of disturbance can be complex [2]. Moreover, even the best
known predictive framework, the Intermediate Disturbance Hypothesis, has been
subject to growing criticism [3]. A further problem is that a diversity metric
reported in isolation is uninformative. It is only when there are good comptive
data on species identities and abundances in an undisturbed community that
meaningful conclusions can be drawn.
Biodiversity
offsetting
Biodiversity
offsetting is increasingly hailed as a way of balancing the demands of
development and conservation. It provides compensation for damaged sites. For
example, if habitat such as woodland is destroyed to make way for housing or
industry, offsetting means that equivalent habitat must be created or restored
to protect the same level of biodiversity. In principle this sounds
encouraging, but there are considerable challenges even when developers are
keen to abide by the spirit as well as the letter of local guidelines. For
example, some ancient habitats are irreplaceable, and it may be difficult or
impossible to recreate ecological communities that have been established over
decades and form part of important ecological networks. The Lawton report [4]
discusses many of the concerns that biodiversity offsetting raises, and makes
recommendations for dealing with them. In short, given the knowledge gaps that
exist in relation to the processes that shape biodiversity, and how natural
systems respond to impacts, biodiversity offsetting is not an easy solution,
and substantial uncertainties remain.
References
McGill BJ:
Linking biodiversity patterns by autocorrelated random sampling.
Am J Bot
2011, 98:481-502. PubMed Abstract | Publisher Full Text OpenURL
Dornelas M:
Disturbance and change in biodiversity.
Phil Trans
R Soc B Biol Sci 2010, 365:3719-3727. Publisher Full Text OpenURL
Fox JW: The
intermediate disturbance hypothesis should be abandoned.
Trends Ecol
Evol 2013, 28:86-92. PubMed Abstract | Publisher Full Text OpenURL
Lawton JH,
Brotherton PNM, Brown VK, Elphick C, Fitter AH, Forshaw J, Haddow RW, Hilborne
S, Leafe RN, Mace GM, et al.:
Making
Space for Nature: a Review of England’s Wildlife Sites and Ecological Network.
http://archive.defra.gov.uk/environment/biodiversity/documents/201009space-for-nature.pdf
webcite
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