Abstract
Urban development and species invasion are two major global threats to biodiversity. These threats often co‐occur, as developed areas are more prone to species invasion. However, few empirical studies have tested if both factors affect biodiversity in similar ways. Here we study the individual and combined effects of urban development and plant invasion on the composition of arthropod communities. We assessed 36 paired invaded and non‐invaded sample plots, invaded by the plant Antigonon leptopus, with half of these pairs located in natural and the other half in developed land‐use types on the Caribbean island of St. Eustatius. We used several taxonomic and functional variables to describe community composition and diversity. Our results show that both urban development and A. leptopus invasion affected community composition, albeit in different ways. Development significantly increased species richness and exponential Shannon diversity, while invasion had no effect on these variables. However, invasion significantly increased arthropod abundance and caused biotic homogenization. Specifically, uninvaded arthropod communities were distinctly different in species composition between developed and natural sites, while they became undistinguishable after A. leptopus invasion. Moreover, functional variables were significantly affected by species invasion, but not by urban development. Invaded communities had higher community‐weighted mean body size and the feeding guild composition of invaded arthropod communities was characterized by the exceptional numbers of nectarivores, herbivores, and detritivores. With the exception of species richness and exponential Shannon diversity, invasion influenced four out of six response variables to a greater degree than urban development did. Hence, we can conclude that species invasion is not just a passenger of urban development but also a driver of change.
Highlights
Global change is reassembling biotic communities at exceptional rates (Capinha, Essl, Seebens, Moser, & Pereira, 2015; Ceballos, Ehrlich, & Dirzo, 2017), and two of the major causes of biotic change are urban development of natural habitats and the spread of invasive species (Clavero & Garciaberthou, 2005; Galiana, Lurgi, Montoya, & López, 2014)
Our results show that both urban development and A. leptopus invasion fundamentally change arthropod communities, but urban development affected the taxonomic composition through changes in species richness and diversity, whereas plant invasion changed the functional composition of arthropod communities
We detected taxonomic and functional homogenization of arthropod communities following A. leptopus invasion, resulting in distinct communities in A. leptopus-invaded areas that are likely unique in structure and function compared to other arthropod communities on the island
Summary
Global change is reassembling biotic communities at exceptional rates (Capinha, Essl, Seebens, Moser, & Pereira, 2015; Ceballos, Ehrlich, & Dirzo, 2017), and two of the major causes of biotic change are urban development of natural habitats and the spread of invasive species (Clavero & Garciaberthou, 2005; Galiana, Lurgi, Montoya, & López, 2014) These two disturbances often co-occur (Catford et al, 2012; Macdougall et al, 2014), as the development of an area makes it more prone to species invasion (Jesse, Behm, Helmus, & Ellers, 2018; McKinney, 2006). Urban areas select for smaller species, but for large, mobile taxa, community-level body size increases along urbanization gradients, which could greatly impact ecosystem processes, such as primary productivity, carbon cycling, and decomposition (Merckx et al, 2018) Another major anthropogenic impact that can change species diversity and community composition is the establishment and invasive spread of exotic species (Hooper et al, 2005; Vilà et al, 2011). Our work will elucidate whether urban development or plant invasion is more important in shaping arthropod communities in human-impacted environments, and whether these stressors mitigate or exacerbate each other's effects
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