Weeds, Exotics or Invasives?

Transcription

1 Invasive Species Geography 444 Adopted from Dr. Deborah Kennard Weeds, Exotics or Invasives? What is a weed? Invasive species? 1

2 Weeds, Exotics or Invasives? Exotic or non-native: Non-native invasive pest plant Where do our non-native invasives plants come from? From a different? From a similar? 2

3 What are biotic provinces? Areas on the earth that have evolutionarily related organisms because of geographic isolation Animals are more related to other animals in their biotic province than to animals that fill the same niche in a different province Large mammal herbivores: Bison and pronghorn antelope in North America giraffes and antelopes in Africa large rodents like capybara in S. America kangaroo in Australia In each major biome, certain animal or plant families dominate. Si il f t l Similar features evolve because of similar environments Thorns on some plants are modified leaves, on other plants thorns are modified branches Stem succulence in cacti (Americas) and euphorbias (Africa) Convergent evolution ecological equivalents 3

4 Species introductions bring species that have not evolved and adapted in the presence of the native species. Why is this significant? Competitive exclusion principle : Two species that have exactly the same requirements (niches) cannot coexist in the same habitat. Native species have adapted to this through niche partitioning. 4

5 Do all species introductions lead to invasive species? A group of similar ecosystems Desert, tropical rain forest, grassland Biomes Determined by physical factors precipitation temperature sunlight & seasons 5

6 Similar environments lead to the evolution of organisms similar in form and function (but not necessarily genetic heritage) Similar biomes generally share same physiognomy (shape of vegetation) or vegetation characteristics Convergent evolution Moving Species Around Local moves are less harmful than global moves. Less likely to be harmful if you move a species within its biotic province Moving a species es into the same biome in a different biotic province is likely to be harmful. 6

7 What makes a species more likely to be invasive? perennial germination in wide range of physical conditions grows quickly flowers early self-compatible produces many seeds which disperse widely reproduces vegetatively good competitor Few species will have ALL of these characteristics Having these characteristics does not mean a species is a successful invader What makes a place more likely to be invaded? If it has high native species richness Islands have more than mainlands Temperate agricultural areas and urban areas Nature reserves had less than non-reserves The larger the area, the more invasives 7

8 Effects Economic cost $97 billion/year cost to the U.S. economy crop losses, reduced grazing potential, weed control costs Leafy spurge (Euphorbia esula) introduced in Minnesota with oats shipment currently ~ 2.5 million acres infested in Canada & U.S. invades rangelands forage yield reductions of % Effects Decreases Diversity decreases species richness by out-competing natives Miconia (Miconia calvescens) spread in Tahiti from Papeari Botanical Gardens, 1937, now invaded 70% Tahitian forests, with 25% dense monospecific stands plant species threatened (35-45 endemics) 8

9 Invasive species and diversity Brown tree snake Extinctions and loss of species diversity from Guam Safety and health of Pacific Island residents and tourists Economic damages from the Brown Treesnake Impacts on military from the Brown Treesnake Effects Ecosystem function may change primary production, nutrient cycling, water consumption Myrica Faya Invasive in Hawaii N fixing tree alters N dynamics N inputs mostly from Myrica in some communities since volcanic soils are N-poor Hawaii the exotic invasive capital of the world species more susceptible to invasives: 1200 species, 90% endemic humans have added ~4600 species 9

10 Effects Altered fire regimes Can either promote fire or suppress fire Cheatgrass (Bromus tectorum) Provides fine flashy fuels in arid ecosystem it invades Fires ignite and carry well Comes back VERY well after fire Increases the frequency of fires Saltcedar (Tamarix spp.) From Eurasia sold in 1850 s for erosion control on stream banks 1 million acres in U.S. southwest outcompetes native riparian cottonwood-willow forests decreases diversity of birds, small mammals, invertebrates Changes the functioning of riparian zones 10

11 Invasives in California 11