Urbanization alters interactions between Darwin's finches and Tribulus cistoides on the Galapagos Islands

Emerging evidence suggests that humans shape the ecology and evolution of species interactions. Islands are particularly susceptible to anthropogenic disturbance due to the fragility of their ecosystems; however, we know little about the susceptibility of species interactions to urbanization on islands. To address this gap, we studied how the earliest stages of urban development affect interactions between Darwin's finches and its key food resource, Tribulus cistoides, in three towns on the Galapagos Islands. We measured variation in mericarp predation rates, mericarp morphology, and finch community composition using population surveys, experimental manipulations, and finch observations conducted in habitats within and outside of each town. We found that both seed and mericarp removal rates were higher in towns than natural habitats. We also found that selection on mericarp size and defense differed between habitats in the survey and experimental populations and that towns supported smaller and less diverse finch communities than natural habitats. Together, our results suggest that even moderate levels of urbanization can alter ecological interactions between Darwin's finches and T. cistoides, leading to modified natural selection on T. cistoides populations. Our study demonstrates that trophic interactions on islands may be susceptible to the anthropogenic disturbance associated with urbanization. Despite containing the highest diversity in the world, studies of urbanization are lacking from the tropics. Our study identified signatures of urbanization on species interactions in a tropical island ecosystem and suggests that changes to the ecology of species interactions has the potential to alter evolution in urban environments.

Automated summary

Recent evidence has shown that human activities have a significant impact on species interactions and ecological dynamics. Islands, being more vulnerable to anthropogenic disturbances due to their delicate ecosystems, are particularly affected by urbanization. This study conducted in the Galapagos Islands demonstrates how early stages of urban development can alter the interactions between Darwin's finches and Tribulus cistoides, leading to changes in natural selection and community composition. Urbanization was found to result in higher rates of seed and mericarp removal, as well as differences in mericarp morphology and defensive strategies between urban and natural habitats. The findings suggest that even moderate levels of urbanization can have profound effects on species interactions and evolutionary processes in island ecosystems.