Working together helps spiders capture larger prey

August 7th, 2008 - 3:13 pm ICT by ANI  

Washington, August 7 (ANI): Spiders” ability to work together and capture larger prey has enabled them to reach enormous colony sizes, say Canadian zoologists.
Researchers at the University of British Columbia say that their findings may help explain why social spiders thrive in tropical areas but dwindle with increasing latitude and elevation.
The size of organisms tends to be constrained by a scaling principle scientists call surface to volume ratio, says Associate Professor Leticia Aviles, lead author of the study published in the Proceedings of the National Academy of Science.
As the organism grows, this surface to volume ratio declines. In a way, this is how nature keeps the sizes of various species in check, adds Aviles.
She feels that the same principle may be applicable to social groups.
The researcher highlights the fact that the surface area of the three-dimensional webs social spiders use to capture prey does not grow as fast as the number of spiders contained in the nests, and thus the number of incoming prey per spider declines with colony size.
However, Anelosimus eximius, a species of social spider notable for its enormous colony size, have developed the ability to cooperate and capture increasingly large insects as their colonies grow.
The average size of the prey captured by the colony increased 20-fold as colony size increased from less than 100 to 10,000 spiders, says Aviles, who studied the spiders in the wild in Amazonian Ecuador with undergraduate student Eric Yip and graduate student Kimberly Powers.
So even though the number of prey falls sharply as the colony grows, the biomass that individual spiders acquire actually increases, she adds.
Her team also discovered that large prey, while making up only eight per cent of the colonys diet, contribute to more than 75 per cent of its nutritional needs.
But that only works to a certain point, Aviles says.
She says that the biomass of prey consumed by the colony peaks when the colony reaches between 500 and 1,000 individuals.
As for the scarcity of social Anelosimus species in higher elevations and latitudes, she says: There simply arent enough large insects in those areas to sustain this type of foraging behaviour. (ANI)

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