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Organismic & Evolutionary Biology
Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
Galapagos Islands, Geospiza fortis, urbanization, movement, abundance, diversity
Many insights into ecological and evolutionary processes have come from studies of island systems. Diversity, abundance, and movement of species are restricted on smaller islands, but these dynamics can become increasingly complex as island size increases.
In recent decades urbanization and the human population on the Galápagos islands has increased rapidly, affecting wildlife in unknown ways. During 2005 and 2006, we sampled birds along a 4-km transect extending northeast of the city of Puerto Ayora, Santa Cruz Island. This allowed us to collect data on the potential impacts of rapidly growing urban center on passerine bird diversity and abundance. We also documented movement patterns of the medium ground finch (Geospiza fortis), the most abundant species on the transect, with a mark/recapture protocol. Although Darwin's finches have been an influencial model for the last 150 years, little is known about their movements on larger islands.
Avian species diversity did not vary significantly along a transect from a periurban area into more remote habitat. Avian abundance, however, was inversely correlated with distance from the urban center. This latter finding is consistent with a well-documented trend in urban ecology, in which periurban areas show higher abundance as compared to adjacent, less developed regions. We also found recapture/re-sight rates for G. fortis within years were 7% and 11% in 2005 and 2006, respectively. The mean distance traveled by individual birds between recaptures or re-sightings was 430.4 m. The majority of movements were less than 500 m from the location of previous sighting. There was no relationship between the distance moved and the time between captures or re-sightings; birds were equally likely to move large distances over short intervals (days) as over longer intervals (years). There was no significant difference in movement distances between males and females. These data document the movement of G. fortis on a larger island. Further studies of gene flow among populations may provide further insight into the genetic and evolutionary consequences of movement patterns documented here.