Geology Reference
In-Depth Information
As these species face extinction, biotic communities lose complexity and diversity and
unravel further.
In a rapidly changing world each species is out for itself, and as a result many biotic
communities begin to fall apart. In Britain, smooth newts (
Triturus vulgaris
) all over the
country feel the urge to dive into their breeding ponds earlier and earlier as temperat-
ures climb, just as soon as there is the slightest sign of spring. This is unfortunate for
the common frog (
Rana temporaria
), which does not respond to the warming climate in
a similar way. By the time the frogs arrive to breed, the ponds are full of plump, well-
developed newt tadpoles who love nothing better than to dine on the defenceless frog
embryos and newly hatched frog tadpoles. So the common frog, already decreasing be-
cause of pollution and habitat destruction, is inched closer to oblivion by a secondary
effect of climate change. The impacts of its loss on the wider ecology are as yet un-
known— perhaps British gardeners will notice more slugs eating their lettuces.
A similar unravelling of biotic communities is going on all around the planet. It is
early spring in the Hoge Velue, the Netherlands' largest nature reserve, and great tits are
hunting for their staple food at this time of year—the caterpillars of the winter moth, that
in turn feed on newly emerged leaves of the oak tree. For millennia the great tits (
Paris
major
) all over temperate northern Europe have timed their breeding to coincide with
the extraordinary abundance of winter moths (
Operophtera brumata
) in early spring,
but for the last 23 years the great tits in the woodlands of Hoge Velue haven't been able
to find enough winter moth caterpillars with which to feed their chicks. The culprit is
climate change. Winter moth females lay their eggs high up in the canopies of oak trees,
and the caterpillars must emerge when oak leaves are good to eat just as they are unfurl-
ing from their buds. If the caterpillars emerge too soon, there will be no leaves and they
will die of starvation; and if they emerge too late, the caterpillars face the prospect of
eating oak leaves full of indigestible tannins. Winter moth caterpillars use ambient tem-
perature to time their emergence, and over countless generations this method has paid
off—but no longer. With increasing spring temperatures, the caterpillars are hatching up
to three weeks before oak bud-burst. They survive only a few days, but the great tits
at Hog Velue have not learnt to bring forward the timing of their own breeding to take
advantage of this brief glut, so they too are facing severe food shortages at a critical
time of year. These sorts of 'phenological decouplings' are happening all over the planet
as a consequence of climate change. We know little about what the impacts on biotic
communities will be, and even less about how these impacts will affect the feedbacks
between the biological realm and climate.
Hurricanes and Global Dimming
