Conservation issues for Darwin's finches in the Galapagos Islands: invasive species and loss of genetic diversity.

Author: Jody O'Connor

O'Connor, Jody, 2012 Conservation issues for Darwin's finches in the Galapagos Islands: invasive species and loss of genetic diversity., Flinders University, School of Biological Sciences

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This study examines the impacts of a novel host-parasite system for population dynamics in Darwin's finches on Floreana Island, Galapagos Archipelago. I focus in particular on the interaction between Darwin's finches and parasitic larvae of an introduced fly, Philornis downsi, which causes high nestling mortality. This is the first project to systematically study Darwin's finches on Floreana Island since the pioneering work of David Lack in the 1930s, and Robert Bowman in the 1960s. I provide the first descriptive study of the breeding biology of the locally endemic medium tree finch, Camarhynchus pauper, which - at the start of the study - was listed as "data deficient" on the IUCN RedList. I begin with a study of the population status and population trends of finches on Floreana Island. The only population of Darwin's medium tree finches (C. pauper) had declined by 61% between 2004 and 2008 to ~1660 individuals. I also document evidence for lack of recruitment into the breeding population, given my finding that medium tree finches had an age-biased population, with few one year old or 5+ year old males. The survey reports on the lack of suitable habitat for highland birds. I devote several chapters to the study of the impacts of P. downsi on host mortality, and the potential for Darwin's finches to adapt to the negative impacts of this invasive parasite. P. downsi is unanimously considered the biggest threat to the survival of Galapagos landbirds, including Darwin's finches. The parasite caused 38-92% of nestling mortality across all five host species studied in this thesis. The impacts of this parasite are greatest for Darwin's tree finches (Camarhynchus spp) because parasite intensity is highest in their highland forest habitat. In particular, P. downsi is identified as the primary cause of nestling mortality in Darwin's medium tree finch. As a result of this research, the medium tree finch status was reassessed from "vulnerable" to "critically endangered" on the IUCN RedList. Video surveillance of finch behaviour showed that parent and nestling finches now have a range of anti-parasite behaviours that can partially mitigate the impacts of the parasite, including preening and removal of larvae. Experimental studies using parasitised and parasite-free nests showed that finch parents increased food provisioning to parasitised nestlings, but did not compensate for the negative impacts of parasitism (P. downsi caused 92% of nestling mortality in 2010). Collectively, these findings indicate that P. downsi parasitism is a major conservation concern for the finches on Floreana Island. I also examine population genetic structure and gene flow between the three sympatric tree finch species on Floreana Island, and find evidence for the loss of genetic diversity in the sympatric tree finches. High levels of hybridisation were detected within the tree finch group, suggesting that the mechanism for loss of genetic diversity is via introgression with closely-related taxa, that is - "speciation in reverse". This thesis represents a novel and multi-faceted approach to understanding the complex interactions of human impacts, introduced species, and endemic species decline in island birds. The results of this research will have immediate impacts on the development of P. downsi control programs, and highlight the need for focussed recovery plans for the medium tree finch.

Keywords: bird,ecology,fly,Galapagos,genetics,hybridisation,island,invasive species,microsatellite marker,parasite,predation
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2012
School: School of Biological Sciences
Supervisor: Sonia Kleindorfer