Ann. N.Y. Acad. Sci. ISSN 0077-8923 ANNALS OF THE NEW YORK ACADEMY OF SCIENCES Issue: The Year in Ecology and Conservation Biology Urban biodiversity: patterns and mechanisms Stanley H. Faeth, 1 Christofer Bang, 2 and Susanna Saari 1 1 Department of Biology, University of North Carolina Greensboro, Greensboro, North Carolina. 2 School of Life Sciences, Arizona State University, Tempe, Arizona Address for correspondence: Stanley H. Faeth, Department of Biology, University of North Carolina Greensboro, Greensboro, NC 27402-6170. shfaeth@uncg.edu The patterns of biodiversity changes in cities are now fairly well established, although diversity changes in temperate cities are much better studied than cities in other climate zones. Generally, plant species richness often increases in cities due to importation of exotic species, whereas animal species richness declines. Abundances of some groups, especially birds and arthropods, often increase in urban areas despite declines in species richness. Although several models have been proposed for biodiversity change, the processes underlying the patterns of biodiversity in cities are poorly understood. We argue that humans directly control plants but relatively few animals and microbes— the remaining biological community is determined by this plant “template” upon which natural ecological and evolutionary processes act. As a result, conserving or reconstructing natural habitats defined by vegetation within urban areas is no guarantee that other components of the biological community will follow suit. Understanding the human-controlled and natural processes that alter biodiversity is essential for conserving urban biodiversity. This urban biodiversity will comprise a growing fraction of the world’s repository of biodiversity in the future. Keywords: urbanization; biodiversity; species interactions Introduction As the world’s population increasingly inhabits cities, urbanized areas have become the most rapidly expanding habitat type worldwide. 1 Cities currently represent about 3% of the world’s land usage, but their effects on climate, resources, pollution, and biodiversity extend far beyond their municipal bor- ders. 1 Within cities, biological communities are usu- ally radically altered in terms of species composition, abundances, richness (number of species and a com- ponent of diversity), and evenness (how individuals are distributed among species and another compo- nent of diversity). 2,3 We first explore how patterns of biodiversity of various groups of animals vary across cities that vary in general climate. We then examine the causes for these patterns. Patterns of animal biodiversity in cities To understand the patterns of biodiversity changes in cities, we reviewed studies on urbanization (the ecological forcing functions created by the growth of cities and associated human activities 4 ) effects on abundance, diversity, and species richness of terres- trial animals. We asked if there is a general pattern of the effects of urbanization on diversity and abun- dances and if urbanization effects vary with different climatic zone and among animal taxa (birds, arthro- pods, reptiles, mammals, nematodes, and amphib- ians). Web of Science was used to identify 1,509 articles with abstracts containing the words urban, ecology , and biodiversity . Each paper was examined to see if they contained information about changes in diversity, abundance, and species richness related to urbanization. Analysis was limited to only ter- restrial animals because there are few studies of the effects of urbanization on microbial diversity (how- ever, see Refs. 5 and 6), and effects on aquatic animal diversity have been reviewed elsewhere. 7 We found 92 articles that reported diversity measures, species richness, and abundance (number of individuals) data of terrestrial animals along some gradient of urbanization. These studies span a wide geographic spectrum and include urban environments of all doi: 10.1111/j.1749-6632.2010.05925.x Ann. N.Y. Acad. Sci. 1223 (2011) 69–81 c  2011 New York Academy of Sciences. 69