Cities as global biodiversity hotspots

1. Cities as global biodiversity hotspots Madhusudan Katti California State University, Fresno NilonC., Aronson, M, La SorteF.A., Goddard M.A., LepczykC.A., Warren P.S., Williams N.S., CilliersS., Clarkson B, Dobbs C., HedblomM., LouweKooijimansJ., MacGregor-ForsI., MörtbergU., Siebert S., Werner P.

2. City lights spreading across an urban world

3. Global Biotic Homogenisation • Cities are novel ecosystems offering unique challenges for biodiversity, such as • fragmented and disturbed environments with high spatial heterogeneity • invasions of a similar suite of non-native species due to human mediated biotic interchange • extinctions of indigenous species due to habitat destruction which may lead to a homogenised biota across the world’s cities

4. Questions • How much of the world’s plant and bird diversity occurs in cities? • What is the structure and composition of urban diversity for plants and birds worldwide? • What are the drivers of urban biodiversity patterns?

5. City checklist data Bird data from 54 cities Plants data from 110 cities Nearctic Palearctic Indo Malaya Afrotropics Neotropics Australasia Plants: surveys of natural and spontaneous vegetation since 1975 Birds: standardized surveys since 1990, and naturalist checklists

6. Summary of Methods • Species richness patterns within cities were examined by biogeographic realm using Student’s t-tests • Examined the representation of urban biotas within the world’s biota • Compositional similarity among cities examined using hierarchical cluster analysis with the βsim dissimilarity index • Developed models predicting Urban Species Diversity

7. Results • At least 20% of the world’s bird species and 5% of the world’s plant species occur in cities

8. City Species Richness Plants Birds Median = 766 (553 native; 213 Exotic ) Median = 112 (108 native; 4 exotic) Nearctic Palearctic Neotropics Afrotropics Indo Malaya Australasia

9. Methods: examined the representation of urban biotas within the world’s biota Birds: BirdLifeInternational and NatureServerange maps Cylindrical equal-area projection and a cell area of 3,091 km2 (0.5° resolution at equator) Plants: Kreft& Jetz, 2007, PNAS Co-Kriging model Cylindrical equal-area projection and a cell area of 12,100 km2 (1° resolution at equator)

10. Observed vs. Predicted richness: Plants Nearctic Native Median = 60% Palearctic Native + nonnative Median = 84% Afrotropics Indo Malaya Australasia

11. Observed vs. Predicted richness: Birds Nearctic Median = 63% Palearctic Neotropics Afrotropics Indo Malaya Australasia

12. Similarity in urban bird community composition is reflective of realm Indo Malaya Palearctic Afrotropics Australasia Nearctic Neotropics

13. Indo Malaya Afrotropics Same for plants Australasia Palearctic Nearctic

14. Plants that occur in >90% of 110 cities Galiumaparine94% Seneciovulgaris90% Capsella bursa-pastoris 95% Poaannua 96% Stellaria media 94% Plantagolanceolata93% Sisymbriumofficinale92% Convolvulus arvensis90% Cirsiumvulgare93% Hypericumperforatum91% Phragmitesaustralis90%

15. Birds that occur in >80% of 54 cities Passer domesticus (House sparrow) 88% Columba livia (Rock Dove) 94% Sturnusvulgaris (European Starling) 81% Hirundorustica(Barn Swallow) 80%

16. Predictors of Urban Species Diversity • Considered 12 statistically independent predictors of observed bird and plant richness and the proportion of non-native plants • Urban extent , % remnant vegetation, city establishment date, realm, latitude, temperature, temperature seasonality, rainfall, rainfall seasonality, elevation, elevation variability • Contrasted drivers using 9 nested linear-models that controlled for city size and an information-theoretic approach (AICs)

17. Birds • Richness higher for younger cities at lower elevations with more uniform topography and higher temperatures • Plants • Richness higher for younger cities at lower latitudes • Non-native plants • Proportions greater for older cities that were less urbanized and contained more intact vegetation

18. Conclusions • Cities contain a considerable proportion of global plant and bird diversity • Urbanization results in declines in alpha diversity • Evident for native birds and plants based on species richness (loss ~40%) • Plants compensate through introduced species • Cities are richer in species and more unique than generally expected. • Although some non-native species are shared, urban biotas are not globally homogenized and continue to reflect biogeographical context and unique settlement histories

19. Conclusions • Plant and Bird richness determined by a combination of anthropogenic and non-anthropogenic factors • Younger cities have more species • The proportion of nonnative plants determined by anthropogenic factors • Older cities with more intact vegetation have more nonnative species • Need for better compilation and monitoring of urban biota in areas of high regional biodiversity, such as tropical cities

20. Acknowledgements • This work was supported by the National Center for Ecological Analysis and Synthesis and the Cornell Lab of Ornithology. • We thank all who contributed data to the NCEAS working group including L. Celesti-Grapow, R. Corlett,R. Duncan, A.K. Hahs, M. Hermy, S. Hose, E. Landolt, A. Mrkvicka, A. Naik, J. Njoroge, H. Nouman, R. Perry, R. Pineda López, G.L. Rapson, H. A. Rodríguez-Correa, M. Schwartz, S. Sen, K. Thompson, and K. Watson. The NCEAS Urban Biota Working Group