6048 words (excluding figures and references), 2 figures
Although cities are dramatically different in many dimensions from the
non-urban environments they replace, including structure, species
composition, and climate, they host a diverse suite of organisms that
interact with each other and the abiotic and biotic environment (Szulkin
et al. 2020a). Cities are typically characterized by built-up surfaces,
warmer temperatures than the surrounding non-urban environment, and
dense human populations, although there are also green spaces, such as
parks and gardens, and landscape features such as rivers and lakes
(Venter et al. 2016, Szulkin et al. 2020b). Some species are filtered
out of the urban ecosystem whereas others are able to persist (McKinney
2002, McDonnell and Hahs 2015), leading to a range of interacting
ecological and evolutionary responses (Alberti 2015, Alberti et al.
2020). In urban ecosystems, the interaction of human society (e.g.,
cultural, social, economic, political, and technological) with nature
generates complex socio-eco-evolutionary dynamics across heterogeneous
and novel landscapes (Pincetl 2015, Alberti 2015, McPhearson et al.
2016, Rivkin et al. 2019, Des Roches et al. 2021, Schell et al. 2020).
We are only beginning to understand how increased frequency of direct
and indirect human influences impact eco-evolutionary dynamics as well
as the ability of researchers to study them (Miles et al. 2021).
Accumulating evidence to evaluate adaptation — the evolutionary
response to natural selection — is challenging in any environment.
Difficulties in identifying adaptive evolution stem from the complexity
of the processes facilitating or impeding responses: mutation, gene
flow, genetic drift, and natural selection (Kawecki and Ebert 2004).
These processes are dependent on life history, habitat use, and movement
throughout the landscape, with variable influence and interaction across
spatial and temporal scales (Levin 1992, Olson-Manning et al. 2012,
Hoban et al. 2016). Challenges to adaptation research in general have
been extensively treated elsewhere (e.g., Endler 1986, Kawecki & Ebert
2004, Blanquart et al. 2013). In addition, a number of reviews of urban
evolutionary ecology have provided excellent syntheses on
eco-evolutionary processes, including adaptation, in urban ecosystems
(Donihue and Lambert 2015, McDonnell and Hahs 2015, Alberti 2015,
Johnson & Munshi-South 2017, Miles et al. 2019, Rivkin et al. 2019,
Szulkin et al. 2020a, Des Roches et al. 2021, Lambert et al. 2021,
Diamond and Martin 2021, Diamond et al. 2022). However, what is missing
from this discourse is an overall reflection on how conducting
adaptation research is challenged by human interactions and influence in
urban ecosystems.
The aim of this perspective is to highlight challenges in urban
adaptation research, and outline strategies to move forward, including
the discussion of opportunities harbored by this fascinating field of
research. Our unique perspective brings these ideas together in a
framework that provides both conceptual and practical advice with the
goal of providing guidance to researchers, especially those in early
career positions, regarding the pitfalls that can hinder success in
urban adaptation research. In not considering these challenges, urban
researchers may unintentionally propagate misconceptions – inaccurate
conclusions as a result of faulty information – regarding adaptation.
These misconceptions can include the commonality, nature, and strength
of adaptive responses, and can influence expectations based on non-urban
ecosystems or advocate methods that may not be applicable across diverse
habitats and taxa.
We explore four challenges commonly encountered when conducting
adaptation research and which can be further compounded by the human
element in urban environments: (1) methodological approaches, (2)
trait-environment relationships and natural history, (3) agents and
targets of natural selection, and (4) habitat heterogeneity. For each
challenge, we employ a four-point framework to bring together ideas from
the fields of urban ecology and evolutionary biology, adaptation
research more generally, and urban adaptation research specifically. We
first note how each challenge applies to adaptation research in any
ecosystem, then explore how the human element in urban areas can play a
specific role in adaptation. We follow this comparative framework with
misconceptions that can arise and potential ways to move forward in
addressing the challenges of urban adaptation research using examples
from the urban evolutionary ecology literature. We conclude with
emphasizing the opportunities and applications of conducting research on
urban adaptation. We recognize that many of these ideas have been
addressed throughout the literature and that they may not all be
novel to every urban environment. However, our four-point
framework brings together both conceptual and practical discussion of
these ideas to move the field of urban evolutionary ecology forward
productively and inclusively. In this respect, in the coming decades
with predicted novel research directions in urban evolutionary ecology
incorporating technology, sustainability, climate change, and
socio-political considerations (Verrelli et al. 2022), we see our
perspective as providing a valuable review to those entering this
burgeoning field from many different disciplines.