Urban food subsidies reduce natural food limitations and reproductive costs for a wetland bird

Abstract

there is a strong conservation need to understand traits of species that adapt to urban environments, but results have been equivocal. Wetland birds exhibit a strong phylogenetic signal towards urban tolerance; however, they have largely been ignored in urban studies. in their historic ranges, wetland birds inhabit dynamic systems, traveling long distances to locate food. this ability to exploit dynamic resources may translate to success in urban environments, areas characterized by novel food opportunities. We used the Wood Stork (Mycteria americana), a species of conservation concern, to determine if the ability to exploit resources in natural environments translated to exploitation of urban resources. During optimal natural foraging conditions, storks nesting in both urban and natural wetlands had narrow diet breadths and high productivity. However, during suboptimal conditions, urban stork diet expanded to include anthropogenic items, leading to increased productivity. our study provides a mechanistic understanding of how a wetland species persists, and even thrives, in urban environments. We demonstrated that species inhabiting dynamic systems can exploit urban areas resulting in increased reproductive performance during suboptimal conditions. together, urban environments may support biodiversity in a variety of ways, but species-specific mechanistic understanding will help highlight how to best mitigate potential threats of urbanization. Urbanization is one of the most extreme forms of anthropogenic change impacting species globally 1,2. Urbanization fragments and destroys natural habitats 2-6 , leading to increased pollution 7-9 , alteration of resources 5,10,11 and species interactions 5,12,13 ; all of which contribute to global biotic homogenization and biodiversity loss 2,14. Nevertheless, recent studies show a more nuanced effect of urbanization, with urban areas increasingly being recognized as potential, vital components for biodiversity 15,16 , and in some cases, acting as refugia for species of conservation concern 17. The ability of some species to persist or even thrive in urban environments is largely associated with the ability to exploit resources and avoid risk in urban areas 18. Consequently, as urbanization engulfs more of a landscape, it acts as a filter through which only some species can pass, resulting in more depauperate communities than surrounding areas 6. This ability to exploit resources is a key driver of the demographic response of avian species to urbanization; however, this response has been variable 5,11,19. For example, in urban environments supplemental anthropogenic food can increase reproductive success whereas scarcity of natural food can reduce it 5,11,19. Foraging theory predicts that as preferred resources become scarce 20 , lower value prey items should be added to the diet as individuals become more opportunistic and less selective 21. When adults are feeding nestlings, one strategy to deal with unpredictable environmental conditions is to include different prey type...

Closely related gull species show contrasting foraging strategies in an urban environment

“…The implications of feeding primarily on urban vs. natural prey resources on population dynamics of urban adapters are unclear. Though there is no strong consensus, some studies have found that individuals feeding on urban food items have higher reproductive success and greater body condition 52 , 53 , most likely due to the higher caloric density and abundance of urban food. However, other studies have found that reproductive success is lower for urban foragers, potentially due to overall low nutrient concentrations in urban food 54 , 55 .…”

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

“…While the evidence is clear that urbanization can significantly alter biological communities (Fenoglio et al, 2020), in many cases leading to biotic homogenization (McKinney, 2006), there is a large range of responses among species (Gippet et al, 2017; Lintott et al, 2016; Threlfall et al, 2012). Some species have adapted to (Homola et al, 2019), and are even thriving in, urban environments (Evans & Gawlik, 2020), while others have been extirpated by urbanization processes (Warren et al, 2019). In general, species can be placed along a continuum according to their response to urban environments.…”

Including random effects in statistical models in ecology: fewer than five levels?

“…Often researchers (sometimes nudged by peer-reviewers) cite this guideline of needing 5 levels before random effects inclusion as a reason why they were unable to use a mixed-effects model (Bain, Johnson & Jones, 2019;Bussmann & Burkhardt-Holm, 2020;Evans & Gawlik, 2020; . CC-BY 4.0 International license available under a was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.…”