An Urban Fairy-Tale: Saving Butterflies from Urbanization

Cities are expanding and the world has become increasingly urbanised in recent decades. Urbanization is a main driver of global biodiversity loss and insect declines due to loss and fragmentation of habitats and reduction of the quality of remaining habitat patches (1–3). Butterflies are often the focus of urban biodiversity studies and used as indicator species to represent response of other less well-monitored insects to environmental changes, because they respond sensitively and rapidly to changes in climate and habitat due to their high mobility and short generation time (2–5). Negative effects of urbanization on butterflies are well established. However, how these negative effects develop and what factors can influence them are still not fully understood (5,6). Here I review several recent articles/studies regarding butterflies’ response to increasingly urban environments. In a more positive outlook on butterflies living in cities, this research shows hat some species are able to persist or thrive in urban environments. This ability depends on several factors, which creates potential to modify urban environments to increase butterflies’ suitable habitat in cities.

Influence of urbanization on butterflies

Research on the influence of urbanisation on butterflies generally shows a negative impact on both species richness and abundance (3). An example of this is a study in Beijing where decreasing butterfly species richness and abundance was demonstrated along a rural-urban gradient in parks (4). Similarly, in Austria it was shown that abundance and species richness were lower in urban landscapes compared to nature reserves. They also reported a loss of butterfly biodiversity and changes in community composition as a result of urbanization (7). A study by Rivest and Kharouba (2024) described that changes in community composition were due to the homogenization of butterfly communities along an urban gradient. Here, total abundance did not change with increasing urbanization, but richness did decrease due to losses of native species and increases in the individual numbers of a few, highly abundant, non-native butterfly species. Thus, urbanization leads to increasing similarity of butterfly communities (2). Another study also showed that urbanization can support a higher abundance of non-native species. It confirmed that the invasion of P. mannii across Central Europe was promoted by urbanization and that this species currently is found exclusively in urban environments (1). However, even though urban environments are often considered hot spots for the establishment of non-native species, some native species also seem capable of thriving in urban areas (1,2).

Factors that influence urban habitability

Although it remains unclear why certain butterfly species can persist, and even thrive, in urban areas, multiple recent studies elucidate several factors that likely mediate their responses to urbanization (2). Their response is probably in part influenced by their functional attributes. For example, butterflies that display traits associated with longer dispersal ability or more generalist larval diet breath are more common in urban areas (2,3). However, local environmental and landscape conditions are also highly influential in butterflies’ survival in cities. Factors such as temperature and habitat type or land use composition play a role. For example, areas where temperatures are warmer, or where there are larger greenspaces, butterfly counts are higher (4,5,8). Additionally, butterfly abundance is increased when there is more connectivity between greenspace patches in cities (5,6).

Potential for urban initiatives to help butterflies

Initiatives building on the habitat and landscape factors mentioned above  can be applied in urban areas to help butterflies survive. Some of these have already proven to positively influence butterfly communities. One example is through butterfly-friendly gardening, where the public is provided with information on the best plant choices to make their gardens more attractive to butterflies. Over the past years, this has been widely endorsed as a meaningful way for the public to help reverse butterfly declines. However, until recently this method actually lacked scientific evidence underpinning many of the recommended plant choices. A recent study by Hordley and Fox (2024) confirm that many of these practices, such as planting long grasses and flowering ivy, increase both butterfly abundance and species richness (9). Another initiative regarding habitat management for butterflies targets urban road verges. It was shown that despite their small sizes and harsh environmental conditions, they can provide habitat for butterflies when converted from standard lawn to containing predominantly native understory plants that are selected for their abilities to tolerate harsh growing conditions (10).

Modeling habitat associations can be a valuable tool to ensure the survival of butterflies during urban development (5). If urban planning combines the findings from these studies, the factors influencing urban habitability for butterflies, and habitat modeling, there is the potential for even more successful urban initiatives to be developed.

 

References

1. Ruffener SC, Matthey-de-l’Endroit N, Berner D. Invasion of Pieris mannii butterflies across Central Europe facilitated by urbanization. Urban Ecosyst. 2024;
2. Rivest SA, Kharouba HM. Taxonomic and functional homogenization of butterfly communities along an urban gradient. Insect Conserv Divers. 2024;17(2).
3. Dennis EB, Morgan BJT, Roy DB, Brereton TM. Urban indicators for UK butterflies. Ecol Indic. 2017;76.
4. Sing KW, Luo J, Wang W, Jaturas N, Soga M, Yang X, et al. Ring roads and urban biodiversity: distribution of butterflies in urban parks in Beijing city and correlations with other indicator species. Sci Rep. 2019;9(1).
5. Cooper JEJ, Plummer KE, Middlebrook I, Siriwardena GM. Using butterfly survey data to model habitat associations in urban developments. J Appl Ecol. 2024;61(4).
6. Ancillotto L, Mosconi F, Labadessa R. A matter of connection: the importance of habitat networks for endangered butterflies in anthropogenic landscapes. Urban Ecosyst [Internet]. 2024; Available from: https://doi.org/10.1007/s11252-024-01542-0
7. Christian Habel J, Ulrich W, Gros P, Teucher M. Butterfly loss in urban landscapes and nature reserves. J Nat Conserv. 2024;78.
8. Ombugadu A, Hassan ZA, Ibrahim JI, Atabo LO, Ayim JO, Attah SA, et al. Butterfly community composition within a tropical urban landscape is influenced by habitat type and temperature. Insect Conserv Divers. 2024;17(2).
9. Hordley LA, Fox R. Wildlife-friendly garden practices increase butterfly abundance and species richness in urban and arable landscapes. Sci Total Environ. 2024;929.
10. Brown J, Threlfall CG, Harrison L, Baumann J, Williams NSG. Rapid responses of bees and butterflies but not birds to targeted urban road verge habitat enhancements. J Appl Ecol [Internet]. 2024 Jun 1;61(6):1312–22. Available from: https://doi.org/10.1111/1365-2664.14648