If you are reading this blog, you probably know well that cities create unique environments that can drive rapid evolution of species. However, cities are also hotspots for the entry and establishment of invasive species, harboring high numbers of non-native species. So, is it possible that urban evolution of non-native species is enhancing their ability to invade new regions? In our recent paper, we synthesized current literature and found evidence shows urban evolution is likely altering traits in non-native species (Fig. 1) which increases their invasion risk. Here are some of the key takeaways from our paper!
Urban evolution may facilitate the establishment of invaders in multiple ways. First, since urban ecosystems around the world have relatively similar environmental conditions (Grimm et al., 2008), if a species evolves to succeed in cities in one region, this population may become a source for invasive populations in cities in other regions. Once introduced to a new non-native range and established in a new city, the growing population will be increasingly likely to escape and spread into the surrounding natural areas (Fig. 2). In this way, cities could act as “gateways” among regions and continents for urbanized invaders. Importantly, this process could also create gateways across environmental gradients that would otherwise function as environmental filters preventing establishment. For example, the urban heat island effect in conjunction with urban evolution might facilitate the establishment of tropical invaders in more temperate regions, allowing them to bypass the environmental filter of colder climates (Fig. 3a).
Second, urban evolution will likely increase invader spread and impact if it selects for traits that increase invader dispersal ability, propagule pressure, aggressiveness, or ability to compete with native species. One clear example of this, that we highlight in our paper, comes from the cabbage white butterfly (Fig. 1). Urban populations of the cabbage white butterfly, a widely invasive agricultural pest, have evolved larger wings to aid in dispersal among fragmented urban habitats (Ducatez et al. 2013; Schoville et al. 2013). Thus, the urban evolved butterflies pose a greater invasion threat than their non-urbanized counterparts, as they have an enhanced ability to disperse across new landscapes.
Urban evolution can also alter traits that increase an invader’s impacts on native species. For example, some anole lizard species, invasive in the USA, show evidence of morphological changes in urban environments. The specific morphological changes (gaining more lamellae on their toe pads) enhances their ability to run more effectively on smooth surfaces (Winchell et al., 2016). These traits are known to be important for anole species competing for habitat space and partitioning resources (Stuart et al., 2014). Thus, urban evolved invasive anoles may have a greater impact on native anole species, having gained enhanced competitive ability via urban selection.
But how will these processes play out in the wake of global change? Well, cities are thought to mimic conditions expected to increase with global change, for example, cities are often warmer, and have higher levels of pollution and CO2 than the surrounding natural environment—both changes associated with global climate change. Thus, urbanized invaders are likely gaining a head start to, and may be pre-adapted to, global climate change conditions compared to native species, which are often extirpated from urban habitats as they retreat to remaining natural habitat fragments. Thus, many urban populations of invaders once restricted to urban areas are likely poised to spread outwards into surrounding natural environments as anthropogenic global changes progress (Fig. 3) (Géron et al., 2021).
While, in our paper, we discuss many specific examples from current literature illustrating different mechanisms by which urban evolution can enhance and accelerate the global spread of invasive species, much more research is needed. We propose some specific directions for future research, but broadly researchers should seek to understand the eco-evolutionary dynamics at play impacting invasive species spread in and through urban environments. Understanding these mechanism and processes may lead to novel ways of managing invasive species spread, as well as a better ability to predict invasion into new regions.
To read more, find the full paper here: https://doi.org/10.1002/fee.2295
Featured Image: ©Murielle Desrois via iNaturalist CC0
Citations:
Géron, C., Lembrechts, J. J., Borgelt, J., Lenoir, J., Hamdi, R., Mahy, G., Nijs, I., & Monty, A. (2021). Urban alien plants in temperate oceanic regions of Europe originate from warmer native ranges. Biological Invasions, 1–15. https://doi.org/10.1007/s10530-021-02469-9
Grimm, N. B., Faeth, S. H., Golubiewski, N. E., Redman, C. L., Wu, J., Bai, X., & Briggs, J. M. (2008). Global Change and the Ecology of Cities. Science, 319(5864), 756–760. https://doi.org/10.1126/SCIENCE.1150195
Stuart, Y. E., Campbell, T. S., Hohenlohe, P. A., Reynolds, R. G., Revell, L. J., & Losos, J. B. (2014). Rapid evolution of a native species following invasion by a congener. Science, 346(6208), 463–466.
Winchell, K. M., Reynolds, R. G., Prado-Irwin, S. R., Puente-Rolón, A. R., & Revell, L. J. (2016). Phenotypic shifts in urban areas in the tropical lizard Anolis cristatellus. Evolution, 70(5), 1009–1022. https://doi.org/10.1111/evo.12925
My current research focuses on the impacts of urbanizaiton and invasive species on native species' behavior, distribution and evolution. I am fascinated by the interconnectedness of species in ecological communities and the complex, indirect, and cryptic impacts of different anthropogenic changes on these communities.