Cultivation and spread of non‐native plant species may result in either phylogenetic homogenization (increasing similarity) or differentiation (decreasing similarity) of urban floras. However, it is unknown how non‐native species influence homogenization of cultivated versus spontaneously occurring species in cities, and which traits are associated with species that promote homogenization versus differentiation. In this study, we compared homogenization effects of cultivated and spontaneous non‐native species in yard floras across and within seven widely distributed U.S. cities. Additionally, we explored which traits explained their particular contribution to homogenization. We recorded plant presence/absence in 178 private yards distributed among seven metropolitan statistical areas in the United States. We compared phylogenetic homogenization effects of non‐native species within both the cultivated and spontaneous species pools using phylogenetic dissimilarities and the homogenization index. Then, we expressed contributions of non‐native species to the homogenization of each pool as a function of two different sets of plant functional traits using phylogenetic generalized least square (PGLS) models across and within cities. Across cities, spontaneous non‐native species homogenized, and cultivated non‐native species differentiated, yard floras. Within the spontaneous pool, short, small‐seeded non‐native plants and non‐native grasses significantly homogenized yard floras. Within the cultivated pool, species contribution to homogenization was best predicted by plant height, presence of showy flowers, and growth form, with non‐native grasses significantly homogenizing cultivated yard floras. Within cities, non‐native species—whether they were cultivated or spontaneous—consistently homogenized yard floras of the three northern cities and differentiated yard floras of three of the four southern cities, suggesting that homogenization processes are context‐ and scale‐dependent. Likewise, traits explaining homogenization differed substantially among cities. The inconsistent patterns among cities in the plant traits that promoted homogenization of both cultivated and spontaneous species suggest that local environmental and anthropogenic conditions of individual cities imposed strong constraints on trait selection. Linking plant functional traits that promote homogenization with residents’ preferences for vegetation may further enhance understanding of how yard plant communities assemble at regional and local scales.
Native biodiversity decline and non-native species spread are major features of the Anthropocene. Both processes can drive biotic homogenization by reducing trait and phylogenetic differences in species assemblages between regions, thus diminishing the regional distinctiveness of biotas and likely have negative impacts on key ecosystem functions. However, a global assessment of this phenomenon is lacking. Here, using a dataset of >200,000 plant species, we demonstrate widespread and temporal decreases in species and phylogenetic turnover across grain sizes and spatial extents. The extent of homogenization within major biomes is pronounced and is overwhelmingly explained by non-native species naturalizations. Asia and North America are major sources of non-native species; however, the species they export tend to be phylogenetically close to recipient floras. Australia, the Pacific and Europe, in contrast, contribute fewer species to the global pool of non-natives, but represent a disproportionate amount of phylogenetic diversity. The timeline of most naturalisations coincides with widespread human migration within the last ~500 years, and demonstrates the profound influence humans exert on regional biotas beyond changes in species richness.
more » « less- NSF-PAR ID:
- 10383471
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Aim Angiosperm epiphytes have long been reported to have larger geographic ranges than terrestrial species, despite evidence of their outstanding diversity and endemism. This apparent contradiction calls for further investigation of epiphytes' poorly understood range size patterns. Here, we address the question of whether epiphytes have larger geographic ranges and different vulnerability to extinction than terrestrial species.
Location The Atlantic Forest of Brazil, a global centre of tropical epiphyte diversity with relatively well‐known flora, where we can estimate the geographic ranges of a large number of species with reasonable confidence.
Time period Occurrence records from the 17th century to the year 2021.
Major taxa studied Flowering plants (angiosperms).
Methods We downloaded, processed and cleaned all occurrence records for the angiosperm species native to the Atlantic Forest of Brazil available in the speciesLink network and the Global Biodiversity Information Facility. We estimated the extent of occurrence and area of occupancy of 12,679 native flowering plants, including 1251 epiphytic species. We compared the geographic ranges of epiphytes and other life forms at broad (e.g. Angiosperms, Monocots) and more restricted taxonomic scales (e.g. individual families), assuming species are independent entities and also when accounting for species phylogenetic dependence.
Results We found that epiphytes have among the smallest geographic ranges of flowering plants. We found no consistent evidence that epiphytism leads to differences in geographic ranges between close relatives. However, both epiphytes and non‐epiphytes in epiphyte‐rich lineages have small ranges and likely a high vulnerability to extinction.
Main Conclusions Our findings contrast with the long‐held hypothesis that epiphytes have larger geographic ranges than terrestrial species. Epiphytes and their close relatives share many diversification mechanisms and ecological adaptations (‘epiphyte‐like traits’), which probably explain why both sets of species have small range sizes and high vulnerability to extinction.
