Urbanization and the more-individuals hypothesis
Article first published online: 27 OCT 2009
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
Journal of Animal Ecology
Volume 79, Issue 2, pages 366–371, March 2010
How to Cite
Chiari, C., Dinetti, M., Licciardello, C., Licitra, G. and Pautasso, M. (2010), Urbanization and the more-individuals hypothesis. Journal of Animal Ecology, 79: 366–371. doi: 10.1111/j.1365-2656.2009.01631.x
- Issue published online: 5 FEB 2010
- Article first published online: 27 OCT 2009
- Received 28 July 2009; accepted 2 October 2009 Handling Editor: Murray Humphries
- animal diversity;
- conservation biology;
- species–people coexistence;
- urban ecosystems
1. Urbanization is a landscape process affecting biodiversity world-wide. Despite many urban–rural studies of bird assemblages, it is still unclear whether more species-rich communities have more individuals, regardless of the level of urbanization. The more-individuals hypothesis assumes that species-rich communities have larger populations, thus reducing the chance of local extinctions.
2. Using newly collated avian distribution data for 1 km2 grid cells across Florence, Italy, we show a significantly positive relationship between species richness and assemblage abundance for the whole urban area. This richness–abundance relationship persists for the 1 km2 grid cells with less than 50% of urbanized territory, as well as for the remaining grid cells, with no significant difference in the slope of the relationship. These results support the more-individuals hypothesis as an explanation of patterns in species richness, also in human modified and fragmented habitats.
3. However, the intercept of the species richness–abundance relationship is significantly lower for highly urbanized grid cells. Our study confirms that urban communities have lower species richness but counters the common notion that assemblages in densely urbanized ecosystems have more individuals. In Florence, highly inhabited areas show fewer species and lower assemblage abundance.
4. Urbanized ecosystems are an ongoing large-scale natural experiment which can be used to test ecological theories empirically.