بعض الطيور
و
الفراشات
مهددة بالإنقراض
(Eng/Arb)
كشف تقرير حديث متعلق بأوضاع الطيور والفراشات في بريطانيا تراجع عدد هذه
الأنواع بنسبة تتراوح بين 54 إلى 71 بالمائة، وهو ما يشير إلى أن العالم سيواجه
انقراضا رئيسيا لهذه الأنواع الحية.
وقال الباحثون إن البحث دعم نظرية أن سادس أكبر عملية انقراض لأنواع حية على
الكرة الأرضية في طريقها للتحقق، وسببها هذه المرة البشر.
وكان تم تنفيذ عدد من المسوح لعدد هذه الأصناف عبر تمشيط كل ياردة مربعة في
بريطانيا وسكوتلندا وويلز وخلال 40 عاما، حيث قام قرابة 20 ألف متطوع بإحصاء كل
طير وفراشة ونبتة برية وجدوها، بحسب وكالة الأسوشيتد برس.
وقد أظهرت النتائج أن عدد هذه الأصناف في تدهور كبير على مجمل أراضي بريطانيا
وسكوتلاندا وويلز، فيما انقرضت فعلا بعض الأنواع.
وقال سكوت ميللر وهو خبير علم أحياء في متحف سميثسونيان الوطني للتاريخ الطبيعي،
إن نتائج الدراسة مثيرة للاهتمام وقوية جدا لأنها شاملة.
وقال ان نظام المراقبة للطيور والنباتات والحياة البرية الذي تملكه بريطانيا لا
يضاهى.
وقال ميللر إن المثير للاهتمام بالدراسة البريطانية هو أنها تعطي مسحا شاملا عن
الحشرات خاصة الفراشات وتشير بوضوح إلى أن عددها في تدهور.
وأظهر مسح لـ 58 نوعا من الفراشات أن بعضها واجه تراجعا في تعدادها، قُدر بنسبة
71 بالمائة، منذ آخر دراستين مشابهتين نفذتا في عامي 1970 و 1982.
وكانت حركة 201 نوعا من الطيور رصدت بين الأعوام 1968 و 1971 ومجددا بين
الأعوام 1988 إلى 1991، ليكشف تحليل أن عدد الطيور تراجع أيضا بنسبة 54 بالمائة.
وكشف مسحان آخران أن 1254 نوع بري من النبات تراجع ظهوره بنسبة 28 بالمائة خلال
الأربعين عاما السابقة.
*****
The world
may be
Undergoing Another
Major Extinction
Of Birds and Butterflies
( عربي / إنكليزي )
A detailed survey of birds and
butterflies in Britain shows a population decline of 54 percent to 71
percent, a finding that suggests the world may be undergoing another major
extinction.
Researchers said the study helps support the theory that the sixth big
extinction in Earth's history is under way, and this one is caused by
humans.
In a series of population surveys that combed virtually every square yard of
England, Scotland and Wales over 40 years, more than 20,000 volunteers
counted each bird, butterfly and native plant they could find. An analysis
of the findings appears this week in the journal Science.
The results showed that populations of the surveyed species are in sharp
decline throughout England, Wales and Scotland, with some species gone
altogether.
A survey of 58 butterfly species found that some species had experienced a
71 percent population swoon since similar surveys were taken in 1970 through
1982. Some 201 bird species were tracked between 1968 and 1971, and then
again from 1988 to 1991. An analysis showed that that avian population had
declined by about 54 percent.
Two surveys of 1,254 native plant species showed a decrease of about 28
percent over the past 40 years.
"Population extinctions were recorded in all the main ecosystems of
Britain," the authors report in Science. They suggested that the finding
strengthens the hypothesis shared by many scientists that "the biological
world is approaching the sixth major extinction event in its history."
Scott Miller, a biologist with the Smithsonian's National Museum of Natural
History, said the British study was impressive and powerful because it was
so thorough.
"The United Kingdom has a monitoring system [for birds, plants and wildlife]
that is unmatched," Miller said. "They may not be representative of the
world as a whole, but they have the best data."
He said the data supports the idea that the rise of humans over the tens of
thousands of years along with climate changes are bringing on an extinction
of many species and reshaping the natural world in ways that aren't
thoroughly understood.
Scientists have identified five extinction events in Earth's history, with
some so severe that more than 90 percent of all life forms were killed off.
The last and most famous extinction was the Cretaceous-Tertiary event some
63 million years ago that killed off the dinosaurs and allowed the rise of
mammals. It is thought to have been caused by an asteroid hitting Earth.
The causes of the other extinctions are not well understood. The largest
ended the Permian Period some 250 million years ago. All but about 4 percent
of all species disappeared then. There were three other lesser-known events
in the Ordovician (435 million years ago), the Devonian (357 million years
ago) and the Triassic (198 million years ago) periods.
"We are in the middle of a sixth extinction event that began about 50,000
years ago" with the expanding role in the world of human beings, said Paul
S. Martin, a zoologist and geochemist at the University of Arizona in
Tucson. "It's happening, but it's slower and it is not clear it will be as
severe as some of the others."
Stuart Pimm, an ecologist at Duke University, said in Science that the
British study results "show that we have likely underestimated the magnitude
of the pending extinctions."
Miller and Martin both point to the hundreds of species, mostly large
animals and birds, that already are gone, some wiped out directly through
human action.
Martin said the fossil records show that the disappearance of many animals
in Australia, Madagascar and North America started about the time that
humans arrived at those sites. Gone from the natural North American
environment, for instance, are mammoths, camels, giant sloths and
saber-toothed tigers.
"For tens of millions of years there were much larger animals on this
continent," said Martin. "We have to settle now for deer, antelope and
bison. But there was much more" before humans came.
Miller said the most significant thing about the British study is that it
makes a detailed survey of insects, specifically the butterfly, and finds
that they are in decline.
"They have good evidence of an insect population decline that is at a much
higher rate than assumed in the literature," said Miller. "The butterfly may
be a good indicator for what is happening to the other insects. We don't
even know which factors in our changing environment is affecting the insects
more."
The study, conducted by a group of British scientists led by J.A. Thomas of
the Natural Environment Research Council, analyzed data collected by an army
of volunteers whom Pimm described in Science as "amateurs of a very high
level
