Indirect effects of invasive species removal devastate World Heritage Islands Bergstrom et al., 2009, Journal of Applied Ecology “Biological invasions can lead to large-scale alterations in ecosystem functioning.” Control and eradication important and recommended. Idea: Recover of indigenous species through eradication Unintended consequences through removal of an alien transformer. Little Barrier Island http://pawpeds.com/pawacademy/general/siberianexile/Sib1/SiberianExile6.jpg Removal cats less breeding success of cooks petrel. Better after eradication of rats. X Little Barrier Island http://pawpeds.com/pawacademy/general/siberianexile/Sib1/SiberianExile6.jpg Macquarie island 34 km long, cool maritime climate. Tundra like vegetation. (Tussock grass, mega-herbs and bryophytes) Rabbits 1878, Cats 60 years before. Hyper-predation loss of two flightless bird species. Management: Virus vectored by flea: Rabbits populations decreased from 130 000 to 20 000. 2006 stop of virus spreading. http://www.ncbi.nlm.nih.gov/ICTVdb/Images/Murphy/Smallpoxns.jpg http://www.biolib.cz/IMG/GAL/24877.jpg X Hypothesis: Increased population due to eradication of top-level predator. X Cat predation and rabbit population estimates. Estimates of consumption by cats of rabbits, rats and mice were calculated. Based on cat daily food intake and proportion of food items in guts. Rabbit populations: mean rabbit densities from 8 rabbit count areas. Rabbit Population Change Hypothesis: Population size increasing due to eradication of Top predator. But also virus and climate variation might have influence. Model: Rabbit abundance: dependent variable presence / absence of virus + (season mean temperature and precipitation): independent variable Vegetation Change In 2001 45 plots 5x5m, 2007 18 revisited. Individual plant species cover as a percentage. Use of remote sensing imagery Satellite imagery: Change Vector Analysis (CVA): Change measure Difference in pixel intensity. (100% from total absorption to total reflection) Threshold for no change: 17% Normalized Difference Vegetation Index (NDVI): loss or gain of chlorophyll. Results: Rabbit Population Bergstrom et al. 2009 Results: Rabbit Population ? virus present cats present Bergstrom et al. 2009 Results: Vegetation 15 of 18 sampled plots changed significantly loss of species cover, gain of new (smaller) taxa Bergstrom et al. 2009, supporting information Results: Vegetation Substantial island-wide vegetation change (36 % of island area) NDVI Change Bergstrom et al. 2009, supporting information CVA Magnitude Results • Rabbit numbers returned to pre control levels • increased herbivory caused significant damage (local and on landscape scale) • Efforts to control rabbit population reversed in only 6 years ➡ strong top-down control of rabbits by a small cat population (ca. 160 adult cats) Discussion • Further effects of cat extinction – more rodents, further impacts on multiple trophic levels – rabbit abundance also influences other species (e.g. destroying petrel burrows, making them more vulnerable to attack by skuas) – changes to soil structure & nutrient cycling Implications for Management • Appreciation of complex interactions • more thorough assessment of ecological risks – general biology of the target species – interspecific interactions – trophic interactions • better modeling of expected results References D.M. Bergstrom, A. Lucieer, K. Kiefer, J. Wasley, L. Belbin, T.K. Pedersen, & S.L. Chown. 2009. Indirect effects of invasive species removal devastate World Heritage Island. Journal of Applied Ecology 46: 73–81. Supporting Information to the article, retrieved from http://www3.interscience.wiley.com/journal/121638291/suppinfo on 18.03.2008 Questions ?