Cities as global biodiversity hotspots Madhusudan KattiCalifornia State University, Fresno

Nilon C., Aronson, M, La Sorte F.A., Goddard M.A., Lepczyk C.A., Warren P.S., Williams N.S., Cilliers S., Clarkson B, Dobbs C., Hedblom M., Louwe Kooijimans J., MacGregor-Fors I., Mörtberg U., Siebert S., Werner P.

City lights spreading across an urban world

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

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?

Bird data from 54 citiesPlants data from 110 cities

BirdsPlantsBoth

City checklist data

NearcticPalearctic

NeotropicsAfrotropics Indo Malaya

Australasia

Plants: surveys of natural and spontaneous vegetation since 1975Birds: standardized surveys since 1990, and naturalist checklists

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

Results• At least 20% of the world’s bird species and

5% of the world’s plant species occur in cities

Plants Birds

City Species Richness

Median = 112 (108 native; 4 exotic)Median = 766 (553 native; 213 Exotic )

Nearctic Palearctic Neotropics Afrotropics Indo Malaya Australasia

Methods: examined the representation of urban biotas within the world’s biota

Birds:BirdLife International and NatureServe range 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 modelCylindrical equal-area projection and a cell area of 12,100 km2 (1° resolution at equator)

Observed vs. Predicted richness: Plants

Native + nonnativeMedian = 84%

NativeMedian = 60%

Nearctic

Palearctic

Afrotropics

Indo Malaya

Australasia

Median = 63%

Observed vs. Predicted richness: Birds

Nearctic

Palearctic

Neotropics

Afrotropics

Indo Malaya

Australasia

Similarity in urban bird community composition is

reflective of realm

1.0 0.8 0.6 0.4 0.2 0.0

Dissimilarity (sim)

CayenneLa PazPorto AlegreWashington, DCBaltimoreOttaw aQuerétaroMoreliaMexico CityVancouverFresnoSeattleTucsonBrisbaneHamiltonMelbourneJerusalemNairobiPotchefstroomPretoriaFlorenceRomeMoscowBristolSt. PetersburgBredaAlkmaarHamburgBratislavaNieuw egeinWarsawEindhovenLublinLeipzigBerlinÖrebroViennaBonnBrusselsPragueSheff ieldSofiaZurichLucerneMainzMontpellierLisbonLuganoValenciaDunedinKolkataHong KongSendaiSingapore

Nearctic

Palearctic

Neotropics

Afrotropics

Indo Malaya

Australasia

Same for plants

1.0 0.8 0.6 0.4 0.2 0.0

Dissimilarity (sim)

San FranciscoLos AngelesSan DiegoCheonjuAmesMinneapolisDetroitBostonConcordPhiladelphiaNew YorkWorcesterChicagoSaint LouisIndianapolisWashington, DCExeterBrusselsGdańskWarsawOpoleSzczecinŁódźWrocławGlasgowTurnhoutDublinEdinburghLeedsKingston upon HullSheffieldLondonBrightonLeicesterPlymouthBraunschweigDresdenPragueAscherslebenHalberstadtQuedlinburgDessauHalle (Saale)Köthen (Anhalt)BirminghamSchmalkaldenGeraNordhausenPlzeňZurichDuisburgChemnitzKamenLeipzigMarlMannheimBrühlWiesbadenHamburgBremerhavenBremenOldenburgBielefeldMunsterKrefeldDinslakenDüsseldorfLeverkusenBonnNeussHildenGrevenbroichKölnMönchengladbachKelsterbachFrankfurtHanauBochumEssenWittenHagenSolingenWuppertalBottropGelsenkirchenHannoverDortmundHerneBrnoCottbusBerlinHennigsdorfMarkkleebergStuttgart, SüdostViennaMesolongiPatrasAlexandroupoliThessalonikiIstanbulRomeAucklandHamiltonAdelaideMelbourneGanyesaPotchefstroomSingaporeBujumburaHong Kong

Australasia

Palearctic

Nearctic

AfrotropicsIndo Malaya

Plants that occur in >90% of 110 cities

Senecio vulgaris 90%

Poa annua 96%Capsella bursa-pastoris 95%

Galium aparine 94%

Stellaria media 94%

Cirsium vulgare 93% Plantago lanceolata 93%

Sisymbrium officinale 92% Hypericum

perforatum 91%

Convolvulus arvensis 90%

Phragmites australis 90%

Birds that occur in >80% of 54 cities

Columba livia (Rock Dove) 94%

Passer domesticus (House sparrow) 88%

Sturnus vulgaris (European Starling) 81%

Hirundo rustica (Barn Swallow) 80%

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)

• 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

  Bird richness Plant richness Prop. non-native plantsModel AICc Δi AICc wi AICc Δi AICc wi AICc Δi AICc wi

Anthropogenic

City age 86.9 2.5 0.16 109.6 3.5 0.12 -140.9 4.9 0.05

Landcover 88.5 4.2 0.07 113.4 7.3 0.02 -145.1 0.7 0.39

Non-anthropogenic

Geography 88.9 4.6 0.06 106.1 0.0 0.69 8.9 154.7 0.00

Climate 87.0 2.7 0.15 121.6 15.5 0.00 -131.9 13.9 0.00

Elevation 84.3 0.0 0.55 124.1 18.0 0.00 -139 6.7 0.02

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

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

• 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.

Acknowledgements

The NCEAS Urban Biota Working Group