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.