Increasing species richness but decreasing phylogenetic richness and divergence over a 320‐year period of urbanization

Abstract

Summary Urbanization is increasing faster than ever, contributing to a global extinction crisis. Recently, scientists have debated whether species richness on local and regional scales is mostly declining, but long‐term changes in phylogenetic richness and divergence were largely disregarded. Space‐for‐time approaches revealed that plant phylogenetic divergence is lower in urban than in non‐urban areas. However, such approaches cannot fully disentangle the relative importance of the biotic processes that drive temporal changes in diversity. Using a unique European urban flora covering 320 years in seven time steps, combined with a comprehensive plant phylogeny, we examined (i) how species richness changed with urbanization over time; (ii) whether trends in phylogenetic richness and divergence parallel trends in species richness; and (iii) whether species extirpation or immigration is driving these changes. We found that over time urban species richness increased, but phylogenetic richness and divergence decreased. Extirpations of phylogenetically distinct native species and immigrations of phylogenetically common native and non‐native species caused a non‐random loss of phylogenetic diversity. Our analyses suggest that if future extirpations and immigrations continue to follow the patterns observed over history, this loss will continue. Synthesis and applications. Measures to protect phylogenetic diversity should combine the protection of threatened habitats and their species with the maintenance of habitats that mitigate heat and safeguard evolutionary history. Urban planners should consider a phylogenetically diverse set of species when designing green spaces.

Testing the effects of four urbanization filters on forest plant taxonomic, functional, and phylogenetic diversity

“…In a similar case, Knapp et al. () found that colonization by ornamental species that are phylogenetically similar to natives did not counteract the loss of phylogenetic diversity caused by local extinction of native species with urbanization in Halle, Germany. Human preferences are more likely to increase phylogenetic diversity in regions where ornamental species are more phylogenetically distinct from native species (Knapp et al.…”

“…Human preferences are more likely to increase phylogenetic diversity in regions where ornamental species are more phylogenetically distinct from native species (Knapp et al. ). Studies focusing on the scale of an entire city (i.e., gamma diversity) rather than individual sites within an urban landscape (i.e., alpha diversity) would also be more likely to find positive effects of ornamental species introductions on biodiversity.…”

“…While most studies have measured biodiversity as simple species richness (reviewed by McDonnell and Hahs 2008, McKinney ), a few have also examined changes in functional or phylogenetic diversity, measures that describe the distribution of functional traits or the phylogenetic relationships between co‐occurring species (e.g., Knapp et al. , , Nock et al. ).…”

Species richness and phylogenetic structure in plant communities: 20 years of succession

“…These studies as well as studies on urbanization (e.g. Knapp et al, 2017) suggest that metrics of phylodiversity decrease with increasing land-use intensity. Few studies, however, assessed the effects of different types of land use on phylodiversity (e.g.…”

“…However, by restricting the measurement of biodiversity to species richness, one ignores almost 90 % of the "overall diversity" (Lyashevska and Farnsworth, 2012). Measures of phylodiversity represent the amount of evolutionary history contained within species assemblages (Laity et al, 2015). Phylodiversity was identified as an important driver of ecosystem stability (Cadotte et al, 2012) and has been suggested as criterion of choice for the designation of protected areas (Vane-Wright et al, 1991; but see Winter et al, 2013).…”