Thermal flexibility and a generalist life history promote urban affinity in butterflies

Abstract

Urban expansion poses a serious threat to biodiversity. Given that the expected area of urban land cover is predicted to increase by 2–3 million km2 by 2050, urban environments are one of the most widespread human‐dominated land‐uses affecting biodiversity. Responses to urbanization differ greatly among species. Some species are unable to tolerate urban environments (i.e., urban avoiders), others are able to adapt and use areas with moderate levels of urbanization (i.e., urban adapters), and yet others are able to colonize and even thrive in urban environments (i.e., urban exploiters). Quantifying species‐specific responses to urbanization remains an important goal, but our current understanding of urban tolerance is heavily biased toward traditionally well‐studied taxa (e.g., mammals and birds). We integrated a continuous measure of urbanization—night‐time lights—with over 900,000 species' observations from the Global Biodiversity Information Facility to derive a comprehensive analysis of species‐specific (N = 158 species) responses of butterflies to urbanization across Europe. The majority of butterfly species included in our analysis avoided urban areas, regardless of whether species' urban affinities were quantified as a mean score of urban affinity across all occurrences (79%) or as a species' response curve to the whole urbanization gradient (55%). We then used species‐specific responses to urbanization to assess which life history strategies promote urban affinity in butterflies. These trait‐based analyses found strong evidence that the average number of flight months, likely associated with thermal niche breath, and number of adult food types were positively associated with urban affinity, while hostplant specialism was negatively associated with urban affinity. Overall, our results demonstrate that specialist butterflies, both in terms of thermal and diet preferences, are most at risk from increasing urbanization, and should thus be considered in urban planning and prioritized for conservation.

Temporal trends in the spatial bias of species occurrence records

“…However, in further analyses, we varied the species' habitat preference by also assuming a species was an urban exploiter and urban generalist (see Table 1 – ‘Species habitat preference'). A negative assumption was selected for the main analysis since there are generally more urban avoiders than exploiters within a given taxon group (Callaghan et al 2021a, b). Occupancy states for each site were drawn from a Bernoulli distribution of the occupancy probability to determine species presence or absence.…”

Urban affinity and its associated traits: A global analysis of bats

“…Such discrete classification methods were predominant in previous studies (Kark et al, 2007; McDonnell & Hahs, 2015; McKinney, 2002; Møller, 2009), and most studies focused on plants (Hill et al, 2002; Knapp et al, 2009; Thompson & McCarthy, 2008) and birds (Callaghan, Benedetti, et al, 2020; Ferenc et al, 2018; Sayol et al, 2020; Sol et al, 2014). The application of novel methods also enables investigations on previously less well‐studied taxa in the context of urban affinity, for example, amphibians (Liu et al, 2021) and insects (Callaghan, Bowler, et al, 2021).…”

“…The terminology used to describe urban wildlife is not always consistent in the literature (e.g. Callaghan, Bowler, et al, 2021; Ferenc et al, 2018), with terms such as ‘urban tolerance’ and ‘urban affinity’ sometimes used synonymously. Clearly defining the terminology is therefore important (e.g.…”

“…Clearly defining the terminology is therefore important (e.g. Callaghan, Bowler, et al, 2021). Thus, we define and hereafter use the term ‘urban affinity’ in the sense of a continuous spectrum from a weak to a strong tendency to live in urban areas, and regard other terms, such as ‘urban avoiders’, ‘urban tolerators’ or ‘urban exploiters’ as groupings of species representing different positions along this urban affinity spectrum.…”

Long-term trends in the occupancy of ants revealed through use of multi-sourced datasets

“…Dietary specialists may be more sensitive to disturbance, such as urbanization [53]. Most Danish ants are generalist omnivores, but the diets of four recently declining species (L. fuliginosus, M. schencki, F. polyctena and F. sanguinea) tend to be especially protein-rich [48].…”