An introduced parasitic fly may lead to local extinction of Darwin's finch populations

Abstract

<p id="P5"> <div class="list"> <a class="named-anchor" id="L1"> <!-- named anchor --> </a> <ol style="list-style-type: &#xA;&#x9;&#x9;&#x9;&#x9;&#x9;decimal&#xA;&#x9;&#x9;&#x9;&#x9;"> <li id="d5198764e178"> <div class="so-custom-list-content so-ol"> <p class="first" id="P6">Introduced pathogens and other parasites are often implicated in host population level declines and extinctions. However, such claims are rarely supported by rigorous real-time data. Indeed, the threat of introduced parasites often goes unnoticed until after host populations have declined severely. The recent introduction of the parasitic nest fly, <i>Philornis downsi</i>, to the Galápagos Islands provides an opportunity to monitor the current impact of an invasive parasite on endemic land bird populations, including Darwin’s finches. </p> </div> </li> <li id="d5198764e184"> <div class="so-custom-list-content so-ol"> <p class="first" id="P7">In this paper we present a population viability model to explore the potential long-term effect of <i>P. downsi</i> on Darwin’s finch populations. The goal of our study was to determine whether <i>P. downsi</i> has the potential to drive host populations to extinction and whether management efforts are likely to be effective. </p> </div> </li> <li id="d5198764e193"> <div class="so-custom-list-content so-ol"> <p class="first" id="P8">Our model is based on data from five years of experimental field work documenting the effect of <i>P. downsi</i> on the reproductive success of medium ground finch <i>Geospiza fortis</i> populations on Santa Cruz Island. Under two of the three scenarios tested, the model predicted medium ground finches are at risk of extinction within the next century. </p> </div> </li> <li id="d5198764e202"> <div class="so-custom-list-content so-ol"> <p class="first" id="P9">However, sensitivity analyses reveal that even a modest reduction in the prevalence of the parasite could improve the stability of finch populations. We discuss the practicality of several management options aimed at achieving this goal. </p> </div> </li> <li id="d5198764e205"> <div class="so-custom-list-content so-ol"> <p class="first" id="P10"> <i>Synthesis and applications</i>. Our study demonstrates the predicted high risk of local extinction of an abundant host species, the medium ground finch <i>Geospiza fortis</i> due to an introduced parasite, <i>Philornis downsi</i>. However, our study further suggests that careful management practices aimed at reducing parasite prevalence have the potential to significantly lower the risk of host species extinction. </p> </div> </li> </ol> </div> </p>