Urbanization alters interactions between Darwin's finches and Tribulus cistoides on the Galápagos Islands - PubMed (original) (raw)

. 2021 Oct 26;11(22):15754-15765.

doi: 10.1002/ece3.8236. eCollection 2021 Nov.

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

L Ruth Rivkin et al. Ecol Evol. 2021.

Abstract

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 Galápagos 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.

Keywords: Jamaican feverplant; anthropocene; herbivory; pinzon; plant defense; plant‐herbivore; puncture vine; seed predation; urban ecology; urban evolution.

© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

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Conflict of interest statement

None declared.

Figures

FIGURE 1

FIGURE 1

(a) Map of the Galápagos Islands, with the three islands sampled and their principal towns. Maps were taken from Google Satellite dating from 2018. (b) Change in population size in each town from 1990–2010 (INEC 2010), ordered from largest (Santa Cruz) to smallest (Floreana); note, the human population has continued to grow rapidly but censuses on all three islands are carried out only every 10 years. (c) A female medium ground finch (Geospiza fortis) holding a Tribulus cistoides mericarp in its beak. (d) Dorsal and lateral images of a T. cistoides mericarp, with each of the six morphological traits measured. Images in C and D taken by M.T.J.J

FIGURE 2

FIGURE 2

Seed and fruit removal by finches in natural and experimental populations of Tribulus cistoides. (a) The number of seeds eaten per mericarp declined with cumulative mericarp size (PC1) in natural habitats of T. cistoides, with small mericarps being eaten more in town habitats than in natural habitats. (b) Mericarp removal (1 = mericarp removed; 0 = mericarp remained) from experimental populations increased with mericarp defense (PC2) in town habitats but declined in natural habitats. Shading around the lines represents the 95% confidence errors of the model

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