JDB Sample Discussion Notes
Pimentel et al. 2001
Economic and Environmental threats of alien
plant, animal, and microbe invasions
Tested / General Goal / Themes of Paper:
Summarize the number of introduced
species in six countries (US, UK, Brazil, South Africa, India, and Brazil),
and estimate the economic impacts of these species on the native biota,
the overall ecological health, and that of the humans in different areas.
Primarily was an extension of
Pimentel et al. 2000 that summarized these factors for the US.
Main contribution of the rather
tediously written paper are tables 1, 2, and 3 which summarize the relative
number of native vs. introduced species (1), economic losses by each major
general taxonomic category of invasives (2), the environmental losses to
each government, measured in dollars (3).
Goes through the major ecological
categories that are damaged by invasives:
Crop, pasture, and forest losses
Environmental damages and control
Livestock pests and losses
Discusses the control implications
and concludes that
Most of the control costs are
associated with agricultural production
Usually these efforts are not
very successful and only succeed in reducing pest populations (sole exception
was the complete eradication of the Med fly (Ceratitis capitata)in
There has been a 10-fold increase
in the number of invading species (annually? Not clear in paper)
Conclusions of paper
120,000 non-indigenous spp have
invaded these 6 countries (relatively few are pests (tens rule)
Reasons why introduced spp succeed
is competitive and predation release, development of new associations (hosts),
newly effective predators, abundance of disturbed habitats (for edge species),
introduction of highly adaptable and successful alien species.
Impossible to assess the costs
of species that are driven to extinction
Per capita losses in the 6 countries
is estimated at US$240
98% of the world’s food supply
comes from introduced species
Only control method suggested
is that we increase governmental restrictions on movement of species –
hedged and didn’t call for restrictions on movement of people.
Estimates of rats and cats were
wildly high and seemingly without too many bases –
perhaps they were discussed elsewhere in other publications? These estimates
accounted for almost 80% of the total costs due to introduced species.
Point out that most of the cells
in the matrix in table 1 were empty because of lacking data – could lead
to a huge underestimation of the costs
How accurate are the estimates? What
problems would you find with the assumptions behind them? Are most of them
too liberal or too conservative?
Would native weeds (which are
at least 25% of the weeds, if not more) have moved in to fill the gap left
if the introduced weeds were removed? Perhaps
much of the problem, with weeds anyway, is that of habitat modification
and fragmentation? This would have mitigated the supposed losses from the
Perhaps many of these influences
were acting simultaneously on endangered species – this would reduce the
total cost losses from introduced species
Costs related to the depletion
of birds (by cats) and a decrease in the money spent by hunters or dollars
per hunter decreasing linearly may be erroneous. Hunters would still go
out and hunt, irrespective of the number of ducks or hunting birds and
birders would still go out even if a huge percentage of the birds were
gone – down to a threshold, of course, below which the costs would really
go down. As a consequence the
amount that a hunter or birder or specialists would spend per bird would
escalate with a decrease in the total number of birds remaining. This is
not a linear relationship.
Are government restrictions
and regulations really enough to reduce the flow of introduced species?
How would the authors feel about
huge expenses related to control of introduced species?
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