Urbanization Erodes Plant–Hummingbird Networks Mainly Through Interaction Rewiring Rather than Species Turnover Along a Tropical Urban–Rural Gradient

Urbanization is a pervasive driver of ecological change, yet its consequences for mutualistic interaction networks remain poorly resolved in lowland tropical regions. We described and compared the structure of plant–hummingbird interaction networks across a continuous urban–peri-urban–rural gradient in Huejutla de Reyes, a humid tropical city in northern Hidalgo, Mexico, for which no plant–hummingbird interactions had previously been documented. From twice-monthly transect surveys conducted over a full annual cycle (March 2023–April 2024), we recorded 335 interactions between four hummingbird species and 29 flowering plant species, and built quantitative bipartite networks for the whole landscape and for each of three urbanization zones. Network specialization (H2′) decreased from the rural (0.35) through the peri-urban (0.26) to the urban zone (0.21), whereas connectance was highest in the urban zone (0.52), intermediate in the rural zone (0.46), and lowest in the peri-urban zone (0.41). Tested against null models, specialization departed significantly from chance expectation in the rural and peri-urban networks and at the landscape scale; nestedness did so in the peri-urban network, and marginally in the rural network; and modularity reached significance only in the rural network and at the landscape scale. The urban network showed no such departure in any of the five indices, indicating that the urban network exhibited weaker departures from random expectations. The dissimilarity of interactions between zonal networks was driven mainly by rewiring among shared species rather than by species turnover, the latter gaining weight only between the urban and rural extremes. Community composition of visits differed significantly among zones (PERMANOVA, R2 = 0.18, p = 0.001), with zone explaining 18% of the variation in visitation composition and no significant differences in multivariate dispersion. Visitation to native versus exotic plants did not differ significantly (χ2 = 5.95, df = 2, p = 0.051). The Buff-bellied Hummingbird (Amazilia yucatanensis) acted as a central, generalist node across the gradient, and the native firebush together with the exotic paperflower emerged as dominant floral resources sustaining network cohesion. Our results suggests that urbanization is associated with a shift toward more generalized plant–hummingbird networks, driven mainly by rewiring among persistent species rather than by species turnover, and underline the value of native keystone flora for pollinator-friendly urban green space.