Note for ECOL 406R at UA
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Date Created: 02/06/15
BiologiCal Invasions Kathy Gerst Dept of Ecology and Evolutionary Biology What is an Invasive Species Plants animals amp microbes not native to a region Introduced accidentally or intentionally Outcompete native species for available resources reproduce prolifically and dominate regions and ecosystems Difficult to control wo native predators Remember not all invasive species are exotic and not all exotic species are invasive Historical Context in North America Originally viewed as welcome additions to landscape Domesticated plants and animals Ornamental plants and animalsto remind settlers of home Current state More than 6500 species of established self sustaining populations of nonnative animals plants and microbes in the US result from increased movements of people transportation of products and reduced travel time between destinations How serious of a problem Costs due to invasive spp in US is 125 140 billion year 25 of US agriculture GNP lost to foreign pests Nearly 12 of species listed as threatened or endangered underthe ESA are at risk due to competition with or predation by nonnative species Considered by biologists to be the second greatest threat to biodiversity Not all Introduced Species Are Successful The Tens Rule 10 of nonnative species become established 10 of those become ecological problems invasivesll Characteristics of Invasive Species Widespread distribution AND abundance Great dispersal ability or migratory tendencies Great reproductive capability being rselected Early maturation short generation time Small body size Edge species Affinity with humans anthrophilic Capacity for clonalasexual reproduction Characteristics of lnvaded Habitats Disturbance Low diversity Absence of predators of invading species Absence of native species morphologically or ecologically similar to invader Absence of predators or grazers in evolutionary history naive prey Accidental Introductions Seeds on livestock Disease on agricultural and forestry plants Aquatic organisms in ship ballast waters from international shipping Canals that connect formerly disconnected oceans seas and lakes Zebra Mussels fresh water mussels native to Black Sea transported to Great Lakes via ballast water from a transoceanic vessel Mussel discovered near Detroit in 1988 down to Gulf of Mexico and into Connecticut cover large areas of lakes amp rivers prevent establishment of native species clog pipes Escaped Introductions Agricultural species Ornamental species aquarium fish residential trees European birds 2 Planted for erosion control forage forestry Introduced for hunting fishing Arundo donax Giant Reed Ecoloqical Impacts of Invasive Species 1 Direct interactions with native species Competition Predation 2 Impact ecosystem function 3 Spread of disease 4 Hybridization with natives Ecological Impacts 1 Direct interactions with native species Competition and Predation Compete for light space nutrients pollinators etc Community has evolved without defense mechanisms to nonnative predators Purple Loosestrife Aggressive wetland invader Produce up to 27 million seeds per plant yearly Spreads across approximately 480000 additional hectares of wetlands each year Local fauna do NOT eat plant Did not become invasive for first 100 years in US W fastgrowing vine introduced to prevent soil erosion major pest in the southern US Grows up to 1 footday Costs 50 millionyear in lost farm amp timber production Brown Tree Snake originating in the South Pacific and Australia extirpated 10 of 13 native bird species 6 of 12 native lizard species and 11 2 of 3 bat species on the 1quot island of Guam Now found on Hawaii Domestic Cats Originated from wild cats in the middle east Hunt native birds lizards small mammals Carry infectious diseases that can be transferred to native animals domestic livestock and humans VERY significant impact on islands where native birds have not evolved to fear predators Insect Invasions Argentine Ants Fire Ants Africanized Honey bees Asian longhorned beetle Ecological Impacts Change to ecosystem function Biogeochemistry ex change in soil type Biophysical processes water uptake and transpiration Trophic structure food webs Disturbance regime ex fire 10 Grasses in the Sonoran Desert Bu1quotfel grass from Africa is the most rapidly spreading invasive plant in Arizona Promotes fire and resprout easily Decreases water filtration into the soil Fire is NOT a natural part of the saguaropalo verde plant communities Kills tortoises too Invasion facilitated by open space in desert entire structure of communities changes Ecoloqical Impacts 3 Disease invasive species may carry diseases to which native species are not adapted Avian malaria Chestnut blight Dutch Elm disease Small pox 11 Chestnut Blight Deciduous forests of eastern NA Made up to 40 of overstory trees In early 19005 fungal disease noticed Fungus originated in nursery stock from Asia where it is native Many animal species depend on chestnuts 7 spp of moths and butterflies now extinct Ecoloqical Impacts 4 Hybridization introduced species may not be genetically separated from a native species and can proceed to hybridize EX introduced trout 9 may mean the end of a genetically unique local population 12 Invasives on Islands Example Hawaii 50 of flora considered invasive Priorto human colonization over 90 of flora was endemic All reptiles and amphibians are introduced Over 100 species of birds introduced Mass extinctions of native flora and fauna are in progress due to destruction of habitat and invasion of new species Control and Manaqement Options Inspectionrestrictions on travel and trade Genetic breeding Eradication physically remove plantsanimals Herbicides chemically kill plants Exotic pests bring in biological control agent 13 Salt Cedar Tamarisk Introduced as an ornamental and for windbreaks Invades riparian areas Accumulates salts in tissues which alters soil Q j composition Uses lots of water Provides poor wildlife habitat Forms monocultures decreases biodiversity Manaqement of Salt Cedar Manual removal Costly and takes a LONG time Chemicalherbicide Restore flood regime Biological control use of natural enemies to reduce damage caused by pest population Possible more effective and less costly solution 14 Biological Control Used successfully in the US since 1889 About 420 invasive spp have been controlled successfully with biocontrol Benefitcost ratio can be very high the derived benefit of controlling a pest divided by the total cost of the biological control project Whv introduce insect herbivores Salt cedar has littleno natural enemies in new habitat This gives it a competitive advantage over native species Introduction of herbivores from native habitat will help control it and slow reproduction 15 Diorhabda elongate Beetle coevolved with salt cedar in China Salt cedar is only plant insect feeds or reproduces on Has special adaptations to be a specialist on salt cedar Salt Cedar defoliation NV 16 The Big Question What if the biocontrol agent itself becomes invasive Beetle was tested for 13 years in quarantine before release to be sure it was not going to feed on native plants The very small risk of beetle changing hosts are outweighed by benefits Tamarisk has no close relatives in NA Biocontrol Success Stories Prickly Pear Cactus and moth borer in Australia i 1926 a s l g A a I Vedalia Beetle in California saved citrus industry from scales 1890s quot Cassava mealybug in 39 Africa with a wasp from South America 1980s l I 17 Biocontrol Horror Stories Cane Toads in Australia introduced to control Cane 39 a grub Cane Toads An Unnatural History 1987 Rosy Wolfsnail in Hawaii introduced to control Giant African Snail Prefers small native spp 1520 native snails extinct Biocontrol mistakes Take home message Control agent must be a specialist on target Generalist vertebrates bad biocontrol Some of worst invaders today were originally introduced for control of other invasive species What works in one site won t work in others 18 Conclusion Invasive species are a threat to human health biodiversity and ecosystem functions Need to put an ECONOMIC value on loss of species habitats and ecosystem functions as a result of invasive species impact Most important solution is early detection and PREVENTION EDUCATION 19
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