Effects Of An Introduced Species On Marine Intertidal Trophic Interactions And Ecosystem Structure In The Aleutian Islands, AlaskaEPA Grant Number: F5E20929
Title: Effects Of An Introduced Species On Marine Intertidal Trophic Interactions And Ecosystem Structure In The Aleutian Islands, Alaska
Investigators: Kurle, Carolyn M.
Institution: University of California - Santa Cruz
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2001 through August 1, 2008
Project Amount: $107,192
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
As habitats continue to become contaminated by non-indigenous species, it becomes more vital than ever for ecologists to understand the extent to which invasive species can be destructive. Rats are one of the world’s most ubiquitous invasive species and the damage they cause to terrestrial communities is well known. My research will examine how introduced rats impact the biodiversity and population structure of marine intertidal communities on Alaska’s Aleutian Islands.
Initially the hypothesis was that introduced rats (Rattus norvegicus) forage in the intertidal thereby causing declines in marine invertebrate numbers on islands with rats. However, preliminary analysis of field data demonstrates exactly the opposite pattern. This lead to the current hypothesis that predation by introduced rats causes significant reductions in numbers of two significant predators of intertidal invertebrates, Glaucous-winged gulls (Larus glaucescens) and Black Oystercatchers (Haematopus bachmani). This releases intertidal invertebrates from heavy predation pressure resulting in increased populations of intertidal herbivores and a consequent reduction in the amount of fleshy algae. The result is a dramatically altered ecosystem structure.
Intertidal areas were surveyed on 17 islands with and 17 islands without rats over 3 summers (2002-2004) throughout the entire Aleutian archipelago. Intertidal habitats on each island were digitally photographed and invertebrate numbers and percent cover of algae were estimated. In 2003 and 2004, stomachs from 28 rats on 5 islands were collected to analyze their contents and estimate most recent diet. Four tissues were also collected from the same rats along with samples of all possible terrestrial and marine prey for stable nitrogen and carbon isotope analyses. This technique allows for biochemical analysis of prey and predator tissues to estimate components of an animal’s diet over a wide time scale. Combining stable carbon and nitrogen isotope signatures of both the rats and their possible prey using mixing models, will allow determination of how rats are feeding largely on marine birds and investigate how their diets change over time. Finally, studies determining the verification of mixing models and the use of stable isotopes to elucidate diet in wild mammals are lacking. To address this problem, captive feeding trials will be run with laboratory Norway rats to determine isotopic enrichment between rats and their prey to best estimate wild rat diet and establish proper parameters for the mixing models.
Preliminary analysis of the intertidal survey data supports my hypothesis that islands with rats have greater numbers of marine intertidal invertebrates and less fleshy algal cover while islands without rats demonstrate the opposite pattern. In addition, there appear to be fewer marine birds on islands with rats, further supporting my hypothesis of a trophic disruption caused by the presence of rats. A comprehensive analysis of all of my data along with the isotope and captive work remains to be completed.
Dissertation work contributes to the understanding of how invasive species can affect entire communities through trophic disruption. In addition, my research has a direct conservation application in that the Aleutian Islands are part of the Alaska Maritime National Wildlife Refuge and my work will contribute to the ongoing effort by the United States Fish and Wildlife Service to eradicate rats from these islands and restore their native biodiversity.