As the field of urban ecology and evolution advances, one major issue consistently jumps out at me: the lack of information on basic ecology and natural history of many species in urban environments. Such information provides a background for hypothesis driven research, a context for interpreting results, and a comparative baseline. Evolutionary studies, particularly those framed in the context of anthropogenic global change, rely on this information to understand the scope and extent of adaptation. Studies of natural history, the biology of organisms and how they interact with their environment, are increasingly taking the backseat to modern molecular and computational methods. Yet natural history studies are integral to many biological questions, a perspective that has been echoed over time (Schmidt 1946; Greene 1986; Tewksbury et al. 2014).
A foundation for hypothesis-driven research
When a wealth of natural history information exists for a study organism, researchers can develop theoretically sound hypotheses about urban adaptation. For example, my own research on Anolis lizards is founded on decades of research that established relationships between ecology, morphology, behavior, genetics, and fitness. In the urban context, this enables novel questions to be formulated that build on this foundation. For example, in natural forest habitats there is a clear link between limb morphology, habitat use, performance, and fitness. This background enabled me to hypothesize that there would be morphological shifts associated with urban habitat use in the lizard Anolis cristatellus (Winchell et al. 2016). The morphological shifts we documented were in the directions predicted based on the relationships between the traits, habitat use, and fitness in forest habitats. Without such a background, identifying traits that are likely targets of selection and predicting directionality of changes based on differences in habitat would be significantly more difficult. Moreover, hypotheses may be based on inaccurate assumptions making interpretation of results more difficult.
A context for interpretation
Natural history information can also help with interpreting unexpected results. Researchers have studied cyanogenesis, an antiherbivory trait, in white clover (Trifolium repens) for over a century. Latitudinal and elevational trends in the distribution of cyanogenic plants are likely because of competing selective pressures on herbivore defense and cold tolerance. Consequently, Thompson et al. (2016) hypothesized that frequency of cyanogenic plants would increase in city centers where ambient temperatures are often warmer than nearby non-urban areas. Although they actually found the opposite, because Thompson and colleagues also collected ecological data on ground temperature and snow depth they were able to reconcile this unexpected result. Despite warmer air temperatures, ground temperatures in cities were significantly lower resulting in freezing soil temperatures that would cause cell lysis, hydrogen cyanide release, and ultimately self-toxicity. Anomalous results such as these may make more sense when placed in the appropriate context. We can’t simply investigate traits, we must also understand how those traits interact with the environment.
A baseline for comparison
In contrast, when gaps exist in our knowledge of how organisms function and interact with their environment, our ability to investigate more advanced questions, parameterize complex models, and interpret results is hindered. Even in well-studied organisms, conclusions can be limited when relevant natural history information is not collected. For example, a recent transcriptomic study of white-footed mice in New York City found signatures of natural selection in several genes (Harris et al. 2015). This study is one of the first to present data demonstrating divergent signatures of selection at the genetic level in urban organisms and represents an important contribution to the field. Yet the meaning of this divergence is interpreted without the context of phenotypic and ecological study. Natural history data such as diet, habitat use, and activity patterns would have provided a context for these findings.
The problem is even more significant in less-studied species, where the scope of research questions that might be addressed in urban environments is severely limited by a lack of basic information such as phenology, morphology, pathogens, pollinator interactions, growing conditions, herbivores/predators, and competitors. Nevertheless, purely molecular studies provide a great jumping off point for future studies to interpret genetic differences and help to identify new areas of investigation for urban organisms. To advance urban evolutionary studies for such groups, it is necessary to first conduct the less attractive (from some perspectives) and lower payoff studies of natural history before delving into more complex questions and molecular studies.
Looking forward
So what should be done? Well for starters, let’s collectively acknowledge the importance of these types of studies and not discount them as simple or unimportant. Natural history studies form the foundation of future research and are worthy of our time and respect. Second, we should all make an effort to incorporate more natural history into our research. Spend some time getting to know your study species in the wild and, equally importantly, publish your results so that others can build on your knowledge. I’ve put out a few ideas above, but my short list of things I have found important to understand in urban animals for my own research includes:
- injury causes and rates
- predation dynamics
- discriminatory habitat use
- diet
- activity patterns (daily and seasonally)
- population size, density, and distribution
Do you have some suggestions on what would be interesting to know about urban animals? Let us know in the comments or on Twitter!
- New Lit Alert: Urban environment determines population genetics in the green toad, Bufotes viridis - September 11, 2023
- Contribute to the New York Canid Project! - July 21, 2023
- Parallel Urban Adaptation from Phenotype to Genotype in Anolis Lizards - January 19, 2023
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