Unexpected spatial aggregation between two species of hummingbirds and their inconsistent spatial interactions with native and exotic plants in an urban ecological reserve

Abstract

Hummingbirds play an important role as pollinators and are one of the primary examples of animal–plant coevolution. However, factors such as land-use change, urbanization, exotic species introductions and the disappearance of native plants can negatively affect the persistence of hummingbird populations. Thus, understanding the ecological factors that may favour their presence is essential for their effective conservation in urban areas. We conducted repeated surveys in a native scrubland reserve within Mexico City from 2015 to 2018, and used conditional two-species occupancy models to estimate a species interaction factor, and to analyse the effect of five native plants (Agave salmiana, Echeveria gibbiflora, Opuntia lasiacantha, O. tomentosa and Wigandia urens) and one exotic plant (Leonotis nepetifolia) on the occupancy probability of two hummingbirds: the Broad-billed Hummingbird (Cynanthus latirostris) and the Berylline Hummingbird (Saucerottia beryllina). Considering that both of the hummingbird species could be competing for similar resources, we also tested the effect of the presence of the Berylline Hummingbird on the occupancy of the Broad-billed Hummingbird, assuming its dominance based on larger body-size. We found evidence of positive spatial interactions between plants and hummingbirds, but we did not find these to be consistent throughout the 3 years of monitoring, which could indicate a modification of the original hummingbird–plant interaction networks resulting from urban disturbance. In addition, there were no negative spatial interactions between the two hummingbirds. Instead, we detected an aggregation of both species during two separate seasons, probably owing to one species using the other as a cue for profitable sites. Even though the populations of these two hummingbird species can thrive in an urban ecosystem, changes in spatial interactions might reflect alterations on the structure and functioning of a community. Therefore, we consider it crucial to continue studying their population dynamics and their implications for the conservation of urban hummingbirds.