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.