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Urban Spiders Tend To Be Larger, More Fertile Than Their Rural Counterparts

August 21, 2014
Image Caption: This is a photo of an orb-weaving spider. Credit: Elizabeth Lowe

redOrbit Staff & Wire Reports – Your Universe Online

Living in the city can have its benefits – especially if you’re an arachnid, according to new research reporting that some types of spiders grow larger and have increased reproductive capabilities in urban areas.

Writing in the latest edition of the journal PLOS ONE, scientists from the University of Sydney School of Biological Sciences explain that golden orb-weaving spiders tended to have smaller bodies when they lived in areas with more vegetation cover and larger ones in regions associated with urban development (as characterized by the presence of hard surfaces).

Furthermore, they discovered that the reproductive ability of the spiders (as measured by increased ovary weight) may have increased in higher socioeconomic areas, including locations with hard surfaces or leaf litter. They believe that the increased size and reproductive capacity of orb-weaving spiders in urban areas provides new support to the notion that some types of creatures could benefit from habitat changes associated with urbanization.

In a statement, lead author and Ph. D. student Elizabeth Lowe explained that she and her colleagues collected golden orb-weaving spiders (Nephila plumipes) from throughout the greater Sydney area. They also rated the degree of urbanization of 20 different locations, then analyzed the changes in the body size, ovary weight and fat reserves of the arachnids.

“The researchers think this is in part because spiders tend to do better in warmer environments, and cities are ‘urban heat islands’” due to the heat-absorbing abilities of concrete and buildings, explained Amina Khan of the Los Angeles Times. “It’s also possible that tasty insect meals tend to cluster near city lights, making them easier to catch, or that there tends to be a higher density in the boundaries between the fragmented patches of urban and wild lands.”

Lowe confirmed to BBC Nature reporter Zoe Gough that she and her colleagues believe that both temperature and the availability of prey could explain the differences between rural and urban spiders. Higher temperatures have previously been linked to increased growth and size in invertebrates, suggesting that the spiders would benefit from the heat island effect, but other factors may also be involved.

Specifically, Jennifer Viegas of Discovery News suggested that streetlights might have an impact on the spiders. Lowe told Viegas that artificial night lighting leads to an increase in the abundance of insects, which increases the amount of prey available to the arachnids and causes them to become larger, heavier and more fertile.

“Another important difference between these city and country spiders is that country spiders seem to suffer from more parasites,” Viegas said. “The heat, hard surfaces and more discourage the growth of the tiny parasites that prey on spiders. City spiders therefore don’t have to deal with this problem as much as their country cousins do.”

“The fact that some spiders benefit from urbanization is a good thing,” Lowe told BBC News. “In order to maintain biodiversity in cities, we need to be able to support diverse populations of spiders and other invertebrates. By gaining a better understanding of the impacts of urbanization on wildlife in cities, we can work towards creating healthy, functioning ecosystems in urban areas.”


Source: redOrbit Staff & Wire Reports - Your Universe Online



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