WHEN the climate hots up, insects declare war. The fossil record shows that
insects species became more diverse and stepped up their attacks on plants as
the world became warmer tens of millions of years ago.
The number of different species gradually increases from the Earth鈥檚 poles to
the equator. Tropical rainforests teem with life, while temperate zones, on the
other hand, have relatively few species. 鈥淭here鈥檚 a lot of debate about why the
tropics are so diverse,鈥� says Phyllis Coley, a biologist at the University of
Utah. 鈥淧erhaps the climate is more stable and winters don鈥檛 kill off
蝉辫别肠颈别蝉.鈥�
It鈥檚 difficult to answer this question by comparing tropical zones to
temperate regions, because the histories of these areas might be as important as
their climate. To get round this problem, Peter Wilf and Conrad Labandeira of
the National Museum of Natural History in Washington DC looked at fossils from
Wyoming to compare species diversity in the same place as the temperature
changed. The researchers examined fossils from the Palaeocene epoch, which ended
about 58 million years ago, and compared them with fossils from the Eocene epoch
that followed. Over this period, the planet warmed up by about 7 掳C.
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The fossils showed that the diversity of insects and the types of damage they
caused increased as the temperature went up (Science, vol 284, p 2153).
鈥淭he average number of ways a plant species was eaten went up, and the
probability that a leaf from a particular species is eaten was higher,鈥� says
Wilf.
The study shows that heat directly influences species diversity. 鈥淭hey鈥檙e
looking at it in one spot, which gets rid of some of the confounding issues,鈥�
comments Coley. 鈥淭his is the first stuff to do that and do it well.鈥�