Urbanization contributes to the loss of the world's biodiversity and the homogenization of its biota. However, comparative studies of urban biodiversity leading to robust generalities of the status and drivers of biodiversity in cities at the global scale are lacking. Here, we compiled the largest global dataset to date of two diverse taxa in cities: birds (54 cities) and plants (110 cities). We found that the majority of urban bird and plant species are native in the world's cities. Few plants and birds are cosmopolitan, the most common being Columba livia and Poa annua. The density of bird and plant species (the number of species per km 2 ) has declined substantially:& 2014 The Author(s) Published by the Royal Society. All rights reserved.on May 10, 2018 http://rspb.royalsocietypublishing.org/ Downloaded from only 8% of native bird and 25% of native plant species are currently present compared with estimates of non-urban density of species. The current density of species in cities and the loss in density of species was best explained by anthropogenic features (landcover, city age) rather than by non-anthropogenic factors (geography, climate, topography). As urbanization continues to expand, efforts directed towards the conservation of intact vegetation within urban landscapes could support higher concentrations of both bird and plant species. Despite declines in the density of species, cities still retain endemic native species, thus providing opportunities for regional and global biodiversity conservation, restoration and education.

Summary 0We studied the demographic viability of populations of a long!lived iteroparous prairie perennial\ Silene re`ia\ in relation to management regimes\ population sizes\ geographical region "Ohio and Indiana vs[ Missouri and Arkansas#\ degree of isolation and amount of genetic variation[ Demographic data were collected from 05 popu! lations for up to 6 years[ 1 This species has high survivorship\ slow growth\ frequent~owering and episodic seedling recruitment[ Matrix projection methods were used to summarize population performance with and without recruitment[ Median _nite rates of increase by popu! lation varied from 9[46 to 0[71 and from 9[33 to 9[88\ respectively[ 2 Populations with the highest rates of increase had been burned[ Six of eight popu! lations\ for which stochastic modelling predicted persistence for 0999 years\ included _re in their management[ None of the _ve populations with predicted 099!year extinction probabilities of 099) was managed for conservation or burned[ An inter! mediate group of three populations with at least 09) probability of extinction between 099 and 0999 years was not managed\ but was none the less kept open by mowing and herbicide application[ 3 Analysis of composite elasticities showed that growth and fecundity terms were higher for growing "vs[ declining# populations and that growth elasticity was higher in burned than unburned populations[ Lack of burning shifts the elasticity spectrum from that typical of open habitat herbs "higher growth and fecundity elasticities# to values usually found for closed habitat herbs "higher survival elasticities#[ 4 In multivariate analyses predicting _nite rates of increase "with and without recruit! ment#\ _re management and region were the strongest predictors\ followed by genetic variation\ population size\ isolation and interactions of population size and _re\ and region and _re[ Populations with the highest rates of increase were burned\ eastern\ more genetically diverse\ larger and less isolated[ Discrimination of populations with di}erent extinction risks "three classes# was related mainly to _re\ genetic variation and region[ 5 Most of these conclusions support conservation biology predictions that population viability will be highest in larger\ less!isolated\ more genetically diverse populations[ However\ management and geographic trends have overriding roles a}ecting demo! graphic viability[ Habitat fragmentation and genetic depletion have the potential to threaten residual prairie populations of S[ re`ia\ but lack of _re management appears to be the primary short!term threat[ Keywords] elasticity\ extinction probability\ habitat management\ population growth rate\ population viability assessment Journal of Ecology "0887# 75\ 52Ð67

Aim Cities represent an ideal study system for assessing how intensive land-use change and biotic interchange have altered beta diversity at broad geographic extents. Here we test the hypothesis that floras in cities located in disparate regions of the globe are being homogenized by species classified as invasive (naturalized species that have spread over a large area) or as a European archaeophyte (species introduced into Europe before ad 1500 from the Mediterranean Basin). We also test the prediction that the global influences of European activities (colonization, agriculture, commerce) have supported this outcome.Location One hundred and ten cities world-wide. MethodsWe examined the richness and composition of urban floras among European (n = 85) and non-European cities (n = 25) for species classified as native or non-native, or further classified as European archaeophyte or invasive. We modelled how geographic, climatic and anthropogenic factors were related to compositional similarity between European and non-European cities. ResultsWe found that most plants in the cities we examined, particularly nonEuropean cities, were native and unique to each city. Non-native species were similarly unique, but occurred in much lower proportions relative to natives. Although European archaeophytes and invasive species also occurred in lower proportions, they had similar compositions among cities. European archaeophytes were most prevalent in European cities, but were most similar among nonEuropean cities. Contrasting European and non-European cities, geography and climate were most relevant for native and invasive species, whereas climate and agriculture were most relevant for European archaeophytes.Main conclusions Cities in disparate regions of the globe retain regionally distinct native and non-native plant assemblages, while invasive species, and especially European archaeophytes, were associated with lower beta diversity among cities. These findings suggest that intensive land-use change and biotic interchange, shaped through European influences, have had a world-wide effect on the beta diversity of urban plant assemblages.

Seed size is normally distributed for many annual species, while mature plant size is frequently positively skewed. A study was conducted to determine the influence of seed size and the role of genetic differences in determining relative seedling size for Ludwigia leptocarpa. Seed size had a significant effect on percentage germination and time of seed germination but no effect on dry weight or leaf area of seedlings. Seed size and spacing had a significant effect on seedling dry weight for plants grown under competition, while relative day of emergence had no effect. Familial (genetic) differences were found in average seed weight between maternal plants, but not in average number of days to germination, average weight of seeds which germinated, or shoot dry weight. It is concluded that neither seed size alone nor genetic differences between plants are directly responsible for the development of size hierarchies in Ludwigia leptocarpa populations. Large seed size does convey an advantage in growth when plants from seeds of differing initial size interact.