Of all species
that have existed on Earth, 99.9 percent are now extinct. Many of them perished
in five cataclysmic events.
According to a recent poll, seven out of ten biologists think we are
currently in the throes of a sixth mass extinction. Some say it could
wipe out as many as 90 percent of all species living today. Yet other scientists
dispute such dire projections.
As our panelists debate the issue, they also consider how one species
-- Homo sapiens -- may be triggering a modern mass extinction.
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Ariel
E. Lugo is director of the USDA Forest Service
International Institute of Tropical Forestry in
Río Piedras, Puerto Rico. An ecologist, his
research has focused on tropical ecosystems, particularly
rain and dry forests and forested wetlands.
Predictions about the level of species extinctions
on Earth have all overestimated the process.
There are many reasons why scientists are failing
with these predictions. For example, we don't
know how many species there are in the world,
we don't have a sound method for estimating
extinction rates, and we don't understand
how species respond to human and natural disturbances.
Subjectivity dominates the dialogue when facts
are hard to come by.
I believe that we
are not in the throes of mass extinction. Our
approach to the problem is not balanced.
Rates of species extinction are overestimated
because natural resilience is underestimated.
We list the reasons why natural ecosystems
are fragile, but we don't list the reasons
why they are resilient.
Attention is given to the factors that might
play against species survival, while little attention
is given to the mechanisms that allow species
survival in a human-dominated world.
Attention is given to deforestation, but
not as much to forest recovery.
The negative effects of alien species (those
that are relatively new to a habitat) are highlighted,
but their positive roles are ignored.
Data that show increasing number of species
per area after disturbances are ignored, because
we tend to value species by their rarity or
date of arrival to a particular location.
We focus on destructive human activities
but ignore the positive contributions that humans
make through ecosystem management.
The
quality of the debate will improve when we adopt
a holistic approach to evaluating the turnover of
species on Earth, incorporate all relevant factors
into the equation of extinction and survival, and
shed our biases against those species that somehow
are held in low regard.
Ariel
E. Lugo is director of the USDA Forest Service
International Institute of Tropical Forestry in
Río Piedras, Puerto Rico. An ecologist, his
research has focused on tropical ecosystems, particularly
rain and dry forests and forested wetlands.
