Closing Remarks
Here, we have addressed some of the challenges researchers face when embarking on adaptation research in urban environments related to four themes: methodological approaches, trait-environment relationships and natural history, agents and targets of natural selection, and habitat heterogeneity (Figure 2). Although these challenges are not unique to urban environments, there are unique aspects that stem from the human element in these ecosystems. Our four-point framework emphasizes how general challenges to adaptation research are relevant to urban adaptation research and considers how each may differ in urban environments. When researchers study urban evolutionary processes without considering these challenges, erroneous conclusions can arise regarding the nature and strength of selection, as well as the generalizability of findings across taxa and cities. Our four-point framework provides a conceptual discussion of these potential misconceptions. Although these pitfalls may slow progress in urban adaptation research, in the last point of our framework we offer practical steps to move past these misconceptions with multiple recent examples of how researchers are moving this burgeoning field forward productively and inclusively. Developing an understanding and appreciation of the human element and how it challenges adaptation research has broad applications to the diverse socio-cultural aspects of urban ecosystems, including the evolution of urban organisms. As federal and other agencies align their funding roadmaps with urban research, we believe outlining these challenges from biological, methodological, theoretical, and socio-cultural perspectives is critical to the success of the field.
Although we have focused on the challenges to conducting urban adaptation research, we also recognize that urban areas are rapidly evolving environments that are globally distributed, and thus are powerful opportunities for contemporary adaptation research (Donihue and Lambert 2015, Szulkin et al. 2020a, Diamond and Martin 2021). This is not to say that urban ecosystems are qualitatively “good”, nor are they more appropriate than non-urban systems for adaptation research. In fact, how humans interact with and influence nature cannot be extricated from wildlife conservation practices (McKinney 2006, Bergey et al. 2020, Egerer et al. 2021). Even so, cities provide the opportunity to study ecological interactions and evolutionary outcomes that may uniquely result from the dynamic interactions that include humans. In addition, adaptation research can utilize aspects of urban ecosystems to carry out research that would otherwise be challenging or not possible in non-urban systems. For example, habitat fragmentation and the frequent and ongoing management actions in cities can be leveraged to test hypotheses about connectivity without needing to actively modify the habitat. Indirect consequences of human activities also offer natural “laboratories” for addressing some of the most pressing issues of the Anthropocene. For example, cities can be viewed as experimental arenas to study adaptation to climate change because of the urban heat island effect (Oke 1973), which in some ways is a spatial analogy of climate change (a temporal trend, Verheyen et al. 2019), and allows for a broader perspective on adaptation to warming than would be possible with laboratory experiments (Lahr et al. 2018). Similarly, cities increase scope for the study of adaptation to anthropogenic materials such as plastic or other solid waste found in the environment, for example when these are used as replacement material in biological structures. This can be best illustrated in nest building, viewed as an extended phenotype, when natural nest-building elements such as fur and feathers are replaced by anthropogenic solid waste pollutants such as plastic or paper (Jagiello et al. 2022).
Finally, the generation and application of ecological and evolutionary information in urban areas may be facilitated because these ecosystems are intimately integrated with human societies. For some types of data such as historical land use and aerial imagery, researchers may find more resources for urban areas than non-urban areas, although there may be geographic biases in the quality and temporal extent of these resources. Urban environments also provide an opportunity to learn about the ecosystems where we live and within which we have a vested interest. Community applications follow naturally from urban research via: regular interactions with the public while conducting fieldwork; museum exhibitions highlighting urban ecosystems (e.g., Carnegie Museum of Natural History’s 2017 “We are Nature” exhibit); community science initiatives that involve urban communities in research activities (e.g., iNaturalist, BioBlitzes, SquirrelMapper: Cosentino and Gibbs 2022); and inter-disciplinary projects in urban spaces involving policy makers, artists, educators, and researchers (Sexton et al. 2015, Vega et al. 2021, Wallis et al. 2021). By conducting research on how the organisms around us are adapting to human modifications of the environment, we celebrate the diversity of where we live and engage communities to discover and celebrate this diversity. Ultimately, these initiatives expose those who live within cities to the excitement of evolutionary ecology and foster a sense of environmental stewardship.