Common species have lower taxonomic diversity Evidence from the urban floras of Brussels and Rome

Abstract

The species pool hypothesis claims that the large‐scale regional species pool is the chief parameter in determining small‐scale species richness through filtering of species that can persist within a community on the basis of their tolerance of the abiotic environment. Accordingly, different environmental conditions give rise to different species assemblages. From a taxonomic perspective, under the assumption of trait conservatism, co‐occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. The next step consists in understanding how commonness and rarity of individual species produce the observed taxonomic diversity. In this paper, the importance of environmental filtering in regulating the taxonomic structure of rare and common plant species in the urban floras of Brussels (Belgium) and Rome (Italy) is tested. First, we computed the taxonomic diversity of the rare and common species of Brussels and Rome based on the branching topology of the Linnaean taxonomic trees. Next, using a randomization procedure, we determined whether the taxonomic diversity of the rare species was significantly higher than the diversity of the common species. Results show that, for both urban floras, common species that shape the community matrix and experience similar environmental conditions have a taxonomic diversity that is significantly lower than that of the rare species that represent a relatively incidental set of species of more ‘disperse’ origin. Finally, from a conservation/management perspective our results imply that, given their high taxonomic heterogeneity, the protection of rare species is a central issue for preserving high levels of diversity in urban areas.

Patterns of land snail diversity over a gradient of habitat degradation: a comparison of three Czech cities

“…Vertigo angustior, V. antivertigo, Pseudotrichia rubiginosa, ''Appendix''). Such rare species, collectively, may comprise greater taxonomic diversity than common species (Ricotta et al 2008), and their protection maintains high diversity in urban environments. There were also several lowdisturbance sites close to the city centre (Fig.…”

Effects of visitor pressure on understory vegetation in Warsaw forested parks (Poland)

“…The number of new non-forest species in PR forest stands subjected to visitor pressure was sufficiently high to affect plant floristic diversity and was higher than the numbers found in RO and RR forest stands. For forest species that are sporadically present in urban environments (sometimes called “the losers”), this phenomenon is unfavourable and contributes to homogenisation (McKinney and Lockwood 1999; Ricotta et al 2008). …”

Phylogenetic and functional characteristics of household yard floras and their changes along an urbanization gradient

“…Accordingly, the phylogenetic distinctness of the total spontaneous flora in our study yards was reduced by the high number of cosmopolitan and exotic species. Cosmopolitan species tend to have a higher affinity to urban areas (Knapp et al 2009) and a lower taxonomic diversity than rare species (Ricotta et al 2008). Communities with high proportions of exotics tend to have a lower phylogenetic diversity than those dominated by native species (Ricotta et al 2009, Cadotte et al 2010.…”

“…Accordingly, the lack of specific niches in urban areas restricts the occurrence and phylogenetic diversity of these species. Moreover, rare species are taxonomically more diverse than common species in urban floras (Ricotta et al 2008), and at the same time, common plant species have a higher affinity to urban areas than rare plant species (Knapp et al 2009). Thus, the high proportion of common and closely related species in cities decreases total urban lineage diversity.…”