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2-Plants: Scientific model shows decrease of bird biodiversity in HT crops

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TITLE:  A) Prediction of biodiversity response to genetically
           modified herbicide-tolerant crops
        B) Farmers and GM crops should both impact farmland birds,
           Science study predicts
SOURCE: A) Science, Vol. 289, p. 1554-1556, by Watkinson et al.
        B) American Association for the Advancement of Science
DATE:   A) September 2000
        B) August 31, 2000

-------------------- archive: --------------------

Prediction of biodiversity response to genetically modified herbicide-
tolerant crops

A. R. Watkinson, 1 * R. P. Freckleton, 1   R. A. Robinson, 2 W. J. 
Sutherland 1

We simulated the effects of the introduction of genetically modified 
herbicide tolerant (GMHT) crops on weed populations and the 
consequences for seed eating birds. We predict that weed populations 
might be reduced to low levels or practically eradicated, depending 
on the exact resources. The regional impacts of GMHT crops are shown 
to depend on whether the adoption of GMHT crops by farmers covaries 
with current weed levels.

1 Schools of Environmental and Biological Sciences, University of 
East Anglia, Norwich NR4 7TJ, UK.
2 British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 
2PU, UK.
*To whom correspondence should be addressed. E- mail:

There is a growing research interest in the potential effects of the 
release of genetically modified (GM) crops (1) on biodiversity. This 
is prompted by concerns relating to the direct impact of GM crops on 
target organ-isms and the indirect effects on the wider environment. 
The environmental debate has to be set within a biodiversity 
landscape that is already affected by the intensification of 
agriculture (2). Although, in some senses, the introduction of GM 
crops may be no different than the introduction of any other 
technology that leads to the further intensification of agriculture, 
this new technology might offer a uniquely rapid increase in 
intensification. We modeled the effects of the introduction of a 
herbicide-resistant sugar beet (a spring-sown crop grown throughout 
Europe and North America) on the population dynamics of an annual 
weed, Chenopodium al-bum.

This weed occurs worldwide, and its seeds are an important source of 
food for farmland birds (3, 4). We asked two questions: How do weed 
populations respond to changing the efficiency and mode of weed 
control, and what impact will the introduction of GMHT crops have on 
biodiversity and, specifically, a seed-eating bird, the skylark 
(Alauda arvensis)? We based our analysis on a model of the population 
dynamics of C. album in the sugar beet that predicts the change in 
plant and seed bank numbers from one sugar beet crop to the next (5) 
(Table 1). We modeled a five-course rotation where sugar beet is 
grown every fifth year, with winter cereals grown in the other 4 
years. C. album can establish only every fifth year, when sugar beet 
is grown. Between sugar beet crops, populations of C. album persist 
in the form of a dormant seed pool. Seeds germinate in the spring, 
and survival from germination to flowering in the autumn is 
determined by herbicidal and mechanical control. In conventional 
systems, this control is modeled through a parameter q, defined as 
the proportion of plants that survive control (all plants survive 
control when q 5 1, and none survive when q 5 0). Seed production is 
a function of competition for resources during growth between 
individual weed plants (density dependence) and the crop.


Our ability to predict the impact of GM technology on biodiversity 
therefore depends critically not only on an under-standing of how the 
ecological system will respond to technological change at a local 
scale, but also on how the farming community will respond. Although 
the model that we have developed is very simple, we think that it is 
generic for weeds, seed-eating birds, and, indeed, for any 
technological innovation.


Farmers and GM crops should both impact farmland birds, Science study 

The use of genetically modified herbicide-tolerant (GMHT) crops may 
severely reduce bird populations on a small percentage of farms, 
while having little effect on most others, predicts a new study in 
the 1 September issue of the international journal, Science. Overall, 
the consequences should depend upon which farmers adopt the new crop 
types, the study's authors conclude. The possible effects of GMHT 
crops on wildlife in the countryside has been the subject of ongoing 
debate, and the British Government has introduced a moratorium on the 
use of these crops until the issue is resolved.

Lead Science author Andrew Watkinson, from the University of East 
Anglia, in Norwich, England, and his colleagues have created a model 
that simulates the growth of weed populations within crops. Using the 
model, the team investigated the consequences of the changed 
herbicide use likely to be associated with GMHT crops. The results 
showed that weed seed populations can be expected to decline by at 
least 90% in some cases. An important part of the study links the 
decline in weed numbers to bird numbers, predicting that such a 
decline in seed abundance should seriously reduce the numbers of 
skylarks using these fields.

The controversial field trials currently underway in the United 
Kingdom are intended to investigate the consequences of GMHT crops 
for biodiversity. "The field trials will be very valuable, but will 
not tell us what will happen to bird populations. They are carried 
out on too small a scale. One considerable advantage of the 
methodology we have adopted is that it enables us to make predictions 
now rather than having to wait for the results of a three year 
trial," Watkinson said. Several decades of intensified agriculture in 
Europe have had a particularly serious effect on birds, whose 
populations in the United Kingdom have declined by up to 90 percent 
in the last 25 years, according to Watkinson.

"It seems likely that the widespread introduction of herbicide-
tolerant crops will result in further declines for many farmland 
birds unless other mitigating measures are taken," Watkinson said. 
The model developed by Watkinson's team examines the management of 
herbicide-resistant sugar beet and its effects on a major annual weed 
of that crop (Chenopodium album, more commonly known as Lamb's 
Quarters in North America and Fat Hen in Britain) and the seed-eating 
skylark Alauda arvensis.

"These results probably apply widely to other crops, weeds, and seed 
eating birds," noted Watkinson. The study showed that a key issue in 
predicting the impacts on bird numbers was the pattern of farmers' 
uptake of the new GM technology. Most fields have very low seed 
densities. It's the smaller proportion of fields with high seed 
densities that is particularly important for bird populations.

The researchers predict that the severity of the bird declines will 
depend upon which farmers are most likely to adopt the GMHT crops. If 
their use is restricted to intensive farms with low seed densities 
then the effect will be minor. However, if the herbicide-hardy crops 
are adopted by a wide range of farmers -- especially farmers with 
very weedy fields -- then the bird declines are likely to be more 
severe, according to the study. In their Science paper, Watkinson and 
his colleagues emphasize that their findings don't just apply to the 
effects of genetic engineering. The same approach could be used to 
predict the consequences of other changes in farming practice, they 

A commentary by Les Firbank, of the Centre for Ecology and Hydrology, 
in Cumbria, England, and Frank Forcella at the USDA Agricultural 
Research Station, in Morris, Minnesota, and the University of 
Minnesota, in St. Paul, Minnesota, accompanies the Science paper. 
Firbank and Forcella write that the model provides a "welcome 
conceptual framework," but that further work will be necessary to 
resolve some of the model's simplifications. According to the 
commentary, some data from the United States, where GMHT crops are 
currently growing, suggest that weed control with GMHT crops may not 
be as effective as some of the model results indicate. Such 
differences emphasize the need for field trials to complement 
theoretical studies like this one, Firbank and Forcella point out.

The other members of Watkinson's team are Robert Freckleton, and 
William Sutherland, of the University of East Anglia, in Norwich, 
England, and Robert Robinson, of the British Trust for Ornithology, 
in Norfolk, England. Their study was funded by the University of East 
Anglia and the Natural Environment Research Council.


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