Global Warming on the forest floor
Along with rising temperatures, global warming is very likely to
cause a shift toward more extreme weather - stronger storms with more
rainfall, and longer and more severe droughts. Those changes are likely
to have large-scale, obvious effects on farmlands, grasslands and
forests and on the creatures that inhabit them.
But many smaller, more subtle effects are likely too. Researchers at
the University of Kentucky looked at one: the impact of climate change
on the decomposition of leaf litter on the forest floor.
The main instigator in leaf decay is fungi, which get nutrients from
the organic matter. But fungi don't exist in a vacuum. They are grazed
upon by springtails, primitive insects of the Collembola order. In turn,
springtails are the prey of wandering spiders.
Fungal activity
The who-eats-whom makes for a complex web, where changes at one level
can have cascading effects. Too much or too little grazing by
springtails, for example, can reduce fungal activity and slow decay.
Environmental changes can have an impact, too, and that's what the
researchers studied. They set up forest plots and manipulated
precipitation to match anticipated future levels, both wet and dry. They
didn't see much change in leaf decomposition under higher-rainfall
conditions.
Under these circumstances, by preying on the springtails, the spiders
reduce the pressure on the fungi, thus allowing for more leaf decay.
Under wetter conditions the fungi are not so stressed and so easily
overgrazed, so spider predation on springtails has less effect.
It's not that the dryness has a direct influence on populations of
spiders, say, or springtails. Instead, Dr. Lensing said, "it affects how
the cascading occurs" within the food web. One idea is that a species
with a restricted range should have a specialized diet, in part because
there is a less diverse selection of foods available in a smaller area.
By the same reasoning, a species with a broad range should have a more
varied diet, because there are more menu choices.
Selection might come into play as well. With a species shoehorned
into a small space, there is a greater likelihood that any adaptation -
to a single food source, for example - will spread through the species.
This is less likely in a species with a broader range, where there would
always be some mixing among individuals from different environments.
A new study shows the opposite is true, at least for rainforest frogs
from the wet tropics area of northeastern Australia.
All of the frogs dined on ants, spiders, beetles and other bugs, but
the species with the smallest ranges had the most diverse diets. Those
with the largest ranges ate mostly ants. The findings were reported in
Biology Letters.
The smaller the range, the more prone a species is to extinction. A
small-range species that depends on one food source, then, risks being
wiped out if that food source dries up. But one that is a generalist
eater can better survive the vagaries of the food supply.
Silk Stockings
Web-spinning spiders have specialized organs, called spinnerets, that
produce silk. They are usually located on the underside of the abdomen.
The spider, which is about an inch and a half long, produces the silk
through tiny nozzles in the base of the feet. The finding was reported
in the journal Nature.
Like other spiders, the zebra tarantula also has thousands of tiny
hairs on its feet that help it stick to surfaces through molecular
attraction. But the researchers found that the foot silk, laid down as
tracks, helped the spider walk on vertical surfaces. In experiments on
glass, the researchers found that if the spiders slipped, the silk
arrested their fall.
Silk-making evolution
It's not known if other spider species also have this capability. But
however widespread it is, the researchers say, it raises new questions
about the evolution of silk-making. Comparison of the genes involved in
silk production from the feet and from spinnerets, the researchers say,
should provide some clues.
With their swirling atmospheres, gaseous planets occasionally produce
dark spots (Jupiter's red spot being the most famous example). Spots are
rare on Uranus, however, and no definitive images of them have ever been
obtained.
The spot, about 1,900 miles long and 1,100 miles wide, is in the
planet's northern hemisphere. The researchers say the spot may be new, a
result of gradual warming of the northern hemisphere as Uranus moves
into "spring" in its 84-year orbit around the Sun.
(New York Times)
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