Spiders 'do better' in cities, study shows

Orb-weaving spider Golden orb-weaving spiders are abundant in both urban and rural areas of Sydney

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Orb-weaving spiders living in urban areas of Australia grow larger and are better able to reproduce than rural dwellers, a new study has shown.

Female spiders had larger bodies and bigger ovaries in areas of urban development compared with those in places with more vegetation.

Urbanisation can dramatically alter natural landscapes and local climate.

Researchers said their results support the idea that some species may benefit from such habitat changes.

The findings are reported in the journal Plos One.

Researchers led by Elizabeth Lowe from the University of Sydney, Australia, wanted to find out how wildlife is affected by the expansion of cities.

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The transformation of natural areas can decrease biodiversity but some species are able to benefit from urban development.

Most research on the impact of urbanisation has been conducted in birds, and few studies have looked at anatomical changes.

Golden orb-weaving spiders, Nephila plumipes, are commonly found in both urban and natural landscapes in Australia.

They build semi-permanent webs which they remain in for their entire adult life.

The research team collected 222 mature female spiders from urban parks and small and large areas of native vegetation (bush) in Sydney. They quantified the degree of urbanisation at the sites and recorded the body size, fat reserves, and ovary weight of spiders living there.

They found that the spiders had smaller bodies in areas with more vegetation cover and larger bodies in urbanised areas, characterised by higher levels of housing and population density, along with hard surfaces such as a roads and buildings.

The spiders' reproductive ability, measured by ovary weight, also increased in urban areas.

According to the authors, the results are further evidence that urbanisation is affecting wildlife living in cities.

Orb-weaving spider The authors say temperature and the availability of prey could explain the changes in spider size

Miss Lowe said both temperature and the availability of prey could explain the differences between the spiders in urban and non-urban areas.

"Hard surfaces and lack of vegetation lead to the well-known 'urban heat island' effect, with more heat retained than in areas with continuous vegetation," she said.

"Higher temperature is associated with increased growth and size in invertebrates.

"Urban lighting may also be a contributing factor, as it attracts insects and means more food for spiders in those environments. This increase in prey would result in bigger, heavier, more fecund spiders."

Miss Lowe said more research is needed to determine which one is responsible for the changes in size.

"The fact that some spiders benefit from urbanisation is a good thing," she added.

"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 urbanisation on wildlife in cities, we can work towards creating healthy, functioning ecosystems in urban areas."

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