Montgomery, G. A. | Search bioRxiv

bioRxiv2023

Using Unstructured Crowd-sourced Data to Evaluate Urban Tolerance of Terrestrial Native Species within a California Mega-City

In response to biodiversity loss and biotic community homogenization in urbanized landscapes, City managers around the world are increasingly working to conserve and increase urban biodiversity. Accordingly, around the world, previously extirpated species are (re)colonizing and otherwise infiltrating urban landscapes, while once abundant species are in various states of decline. Tracking the occurrence of traditionally urban intolerant species and loss of traditionally urban tolerant species should be a management goal of urban areas, but we generally lack tools to study this phenomenon. To address this, we first used species occurrences from iNaturalist, a large collaborative dataset of species observations, to measure an urban association index (UAI) for 967 native animal species that occur in the city of Los Angeles. On average, the occurrence of native species was negatively associated with our composite measure of urban intensity, with the exception of snails and slugs, which instead occur more frequently in areas of increased urban intensity. Next, we assessed 8,348 0.25 x 0.25 mile grids across the City of Los Angeles to determine the average grid-level UAI scores (i.e., a summary of the UAIs present in a grid cell, which we term Community Urban Tolerance Index or CUTI). We found that areas of higher urban intensity host more urban tolerant species, but also that taxonomic groups differ in their aggregate tolerance of urban areas, and that spatial patterns of tolerance vary between groups (e.g., mammals are not the same as birds). The framework established here was designed to be iteratively reevaluated by city managers of Los Angeles in order to track the progress of initiatives to preserve and encourage urban biodiversity, but can be rescaled to sample different regions within the city or different cities altogether to provide a valuable tool for city managers globally.

ecology↗

bioRxiv2022

What is an urban bird? Trait-based predictions of urban tolerance for the world's birds are modulated by latitude and human population density

As human density increases, biodiversity must increasingly co-exist with urbanization or face local extinction. Tolerance of urban areas has been linked to numerous functional traits, yet few globally-consistent patterns have emerged to explain variation in urban tolerance, which stymies attempts at a generalizable predictive framework. Here, we calculate an Urban Association Index (UAI) for 3768 bird species in 137 cities across all permanently inhabited continents. We then assess how UAI varies as a function of ten species-specific traits and further test whether the strength of trait relationships vary as a function of three city-specific variables. Of the ten species traits, nine were significantly associated with urban tolerance. Urban-associated species tend to be smaller, less territorial, have greater dispersal ability, broader dietary and habitat niches, larger clutch sizes, greater longevity, and have lower elevational limits. Only bill shape showed no global association with urban tolerance. Additionally, the strength of several trait relationships varied across cities as a function of latitude and/or human population density. For example, the effects of body mass and diet breadth are more pronounced at higher latitudes, while the effects of territoriality and longevity were reduced in cities with higher population density. Thus, the importance of trait filters in birds varies predictably across cities, indicating biogeographic variation in selection for urban tolerance that could explain prior challenges in the search for global patterns. A globally-informed framework that predicts urban tolerance will be integral to conservation as increasing proportions of the worlds biodiversity are impacted by urbanization.

ecology↗