Editorial: Ecological and evolutionary processes in Neotropical urban ecosystems

Editorial on the Research Topic
Ecological and evolutionary processes in Neotropical urban ecosystems

Traditionally, cities have been founded in locations with high biodiversity. There, urban growth has brought about fragmentation of the landscape and loss of original habitats, impacting directly upon biodiversity. Currently, we are just beginning to understand the processes and mechanisms involved in these phenomena. The Neotropical realm is a biogeographic region that widely coincides with Latin America because it includes South America, Central America, the Caribbean, and southern North America (Wallace, 1876), and is the most biodiverse realm on the world. Its high biodiversity involves not only species richness and endemism, but unique supra-specific groups. Nonetheless, its awesome biodiversity is threatened by human occupation trends (Myers et al., 2000), and it is estimated that many species are becoming extinct even before they are described.

In the current feature, we made efforts to convene the presentation of emerging studies carried out in Neotropical cities, focalized mainly on birds. We seek to highlight how these studies have advanced an important topic, that of urban ecology. And our focus is mainly on ecological processes involving urban birds.

Nava-Díaz et al. used taxonomic, functional and phylogenetic diversities for describing bird communities in green areas of Mexico City. They asked whether urban areas act as filters for some lineages and functional traits in relation to random expectations obtained from null models. Their results showed that although area in itself increased taxonomic diversity, the phylogenetic and functional structures were mainly affected by green space isolation, with no evidence that the most urbanized green spaces represented a filter for functional traits or clades. Caula and Sanz D'Angelo studied the effect of urbanization on the biodiversity of islands by comparing bird communities between the urban areas of Margarita Island in the Caribbean Sea, with Valencia City, located in continental Venezuela. They asked whether the spatial turnover or nestedness were more important for the conformation of urban bird communities. Nestedness is the subsampling of species in poorer sites from the richer sites, whereas species turnover is the replacement of species between sites. Their results showed that on the island the biodiversity loss caused by urbanization was most severe. However, dissimilarity in species composition along the urban gradient was driven by nestedness on the island, whereas species turnover was the main driver of species dissimilarity on the continent.

Studies focused on avian migrant species are particularly relevant in Neotropical cities because several are located in important wintering or stopover areas for regional or local bird migrants. Pacheco-Muñoz et al. conducted their study on two Nearctic-Neotropical migrants, the Yellow-rumped Warbler (Setophaga coronata) and the Nashville Warbler (Leiothlypis ruficapilla). These two overwintering migrants are commonly observed in green areas of Morelia, Mexico. The authors asked whether such areas inside the urban matrix are suitable for supporting the overwintering populations of both species, or instead they are ecological traps. Thus, they compared the body condition and population densities of those two species in urban green areas vs. non-urban sites, showing that although both species avoid densely constructed urban areas, the green areas within the urban matrix are suitable to maintain viable overwintering populations that allow warblers to replenish their fat reserves.

Villaseñor and Escobar studied the Green-backed Firecrown (Sephanoides sephaniodes), a keystone species for the maintenance and regeneration of endemic southern forests of South America. These authors studied the occurrence of that species in Santiago (Chile), during the austral winter, in relation to the socioeconomic status of different neighborhoods. Their results showed that this hummingbird was less frequent in the poorer neighborhoods, where vegetation cover was scant, than in wealthier districts where higher woody and shrub cover provided food and shelter for the birds.

Most of urban areas in the world are located along coastlines (Baird, 2009). Nevertheless, the effects of urbanization on bird communities of coastal areas have been scarcely studied. Graells et al. analyzed the variation of bird communities in several coastal and inland habitats of Valparaiso (Chile) during winter and spring. Although they found similar species richness between urbanized and natural coastal habitats, species composition changed significantly. Depending on the season, species such as the Inca Tern (Larosterna inca) and the Peruvian Pelican (Pelecanus thagus) were more abundant in urbanized coastal areas, whereas the Kelp Gull (Larus dominicanus) and Franklin's Gull (Leucophaeus pipixcan) were more abundant in natural coastal habitats. The authors emphasize the need for urban planning to conserve bird coastal assemblages.

The tropical Andes constitute a global hotspot of bird diversity (Hawkins et al., 2007). Still, studies that analyze bird community responses to urbanization in such region are scarce. Ordóñez-Delgado et al. analyzed bird diversity and foraging guilds across different land uses. They found significant decreases in bird diversity from forest to urban areas. Although the abundance of insectivorous birds declined from forest to urban sites, on the contrary the abundance of granivorous birds was higher in urban areas. Regarding foraging substrate, aerial, understory, and canopy birds decreased in abundance from forest to urban areas, whereas terrestrial birds increased in urban sites. Therefore, the authors conclude that food resources are the main factor influencing bird communities along the gradient studied, although the availability of nesting substrates could also be relevant.

In addition to foraging traits of bird species, behavioral adaptations may facilitate the bird colonization of urban areas (Blumstein, 2014). Nonetheless, studies about behavioral responses to urbanization in the Neotropics are scant too. Garitano-Zavala et al. analyzed the variation of boldness, neophobia, and problem solving in the Chiguanco Thrush (Turdus chiguanco) between urban and extra-urban habitats in La Paz (Bolivia). They found that birds in urban areas were bolder (lower flight initiation distance), less neophobic, and performed better in problem-solving tests than their rural siblings. These authors argued that the observed behavioral shifts came from preadapted traits rather than from evolutionary adaptation or epigenetic effects.

Although our initial objective was to focus on Neotropical examples of multi-taxa ecological and evolutionary processes in urban areas, the presented articles were dominated by ecological studies about birds. Therefore, studies on other taxa and focused on evolutionary processes are fundamental to advance the urban ecology topic in the Neotropical Region. In closing, we hope that these featured articles focused on urban birds will become an incentive to promote the study of biodiversity conservation from a broader perspective, and that they will contribute to understanding how cities are determining current and future Neotropical biodiversity trends.

Author contributions

ÁG-Z and LML critically reviewed articles on urban birds. All authors participated in the gestation of the idea of a Research Topic in the field of urban ecology and in the review process of submitted manuscripts. All authors contributed to the article and approved the submitted version.

Funding

LML was supported by the Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación, PICT 2018 03871. JAF acknowledge gratefully the support of ANID/IDeA I+D ID21I10028, and CIP 2020016 (Universidad Central de Chile).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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References

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