This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Tropical ecosystems are famous for their teeming, exuberant diversity. In fact, the dramatic increase in biodiversity from the poles to the tropics—known as the latitudinal diversity gradient—is pervasive across branches of the tree of life, and fossil evidence suggests it has existed for millennia.
It might seem that if anything could be immune to human disruption, it would be the latitudinal diversity gradient. But human impacts on nature are also global, pervasive and dramatic. One of the most dramatic is urbanization.
Urbanization replaces natural ecosystems with environments dominated by pavement and buildings. Wetlands are drained, deserts are irrigated and grass lawns are planted. Urbanized landscapes are much more similar to each other than the ecosystems they replace, so much so that urbanized areas have been called the fastest-growing biome on the planet.
Unlike any natural biome, urbanized landscapes now exist from the Arctic to the equator. Ecologists have known for decades that urbanization generally lowers local diversity. We wanted to know if urbanization was altering global diversity patterns as well.
By analyzing data from more than 10,000 bird species worldwide, we found that the latitudinal diversity gradient is three times weaker in cities than in natural areas—an enormous reduction in one of the world's most important ecological patterns. Cities had a third fewer bird species than natural areas overall, confirming that around the world, urbanization lowers bird diversity. But tropical cities lost three times more bird diversity than high-latitude cities.
For example, imagine if we compare a 1-by-1-kilometer (0.6-by-0.6-mile) square in a city to one the same size in a natural area at the same latitude. On average, the city square would have 42% fewer bird species if it was close to the equator (think Singapore or Quito), but only 12% fewer if it was at 65 degrees latitude (think Reykjavík or Fairbanks). One of the reasons tropical cities lost more species lies in the traits of tropical birds.
Extract — continue reading at the source.
