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Lecture 8

BIOC63Fall2013 Lecture 8 Notes.docx

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Biological Sciences
Karen Williams

BIOC63Fall2013 Lecture 8 Notes: Threats to Biodiversity Reasons for ecological success of invaders o Enemy release hypothesis o When plants are introduced the herbivores and pathogens that affect them do not travel with them o By not having pathogens, the plant can do better and outcompete the other plant species there o EICA o Specialist herbivores, fungi and viruses  Selective pressure for mechanical and chemical plant defense  Natural native populations are a mix of well-defended and not-well-defended individuals = high mean population defense level o During the lag pahse, the composition of the population will be genetically the same o But because there are no pests, the individuals that do not ‘waste’ energy on defense mechanisms can use that energy to reproduce and grow o Introduced pop = native range pop o Less well defended individuals increases and becomes more prominent then the well defended counterpart o So the population in the introduced range becomes less well defended on average than the population in the native range o Species undergoes evolutionary adaptation to new conditions, and then levels off ER vs. EICA ER versus EICA No introductionthogen Introduced range Native range Plant introduction ER No evolution, no change EICA Evolutionary adaptation o to new conditions Invasive species as ecosystem engineers o Ecosystem engineer o Any organism creating, destroying, or modifying habitas o affect a whole range of species = whole ecosystem o example: beaver and beaver damsn can turn dry land into a wet land and therefore can affect all the species in that area (whole ecosystem) o Cheatgrass in California  introduced in N. America from Europe in 1861  spread from coast to coast by 1928  60 years  large scale extirpation of native species  prefers mediterannan habitats  decrease biodiversity  forms cheat grass monocultures  cheatgrass also changes biochemical characteristics within the ecosystem   bioavailable is 2x higher than after the invasion of cheatgrass  speeds up fire cycle  10-500x more likely to have fire  having a fire increases the chances of the area being populated mostly by cheatgrass (positive feedback loop) 1 o Garlic mustard  #1 terrestrial invasive species in Canada  others include common buckthorn, glossy buckthorn, and leafy spurge  introduced in 1860 from Europe  often dominant understory herb in forests and flood plains  dramatically decreases diversity  the more garlic mustard individuals, the lower the measure of diversity in the plots  in invaded plots more than 95% are made up by garlic mustard  no forbs, no grasses  if you remove the garlic mustard, about 20% then becomes garlic mustard, so ecosystem bevomes more diverse   if garlic mustard is present in the ecosystem for a long time, the understory becomes a monoculture and none of the plants you would usually see are present  garlic mustard supresses beneficial soil fungi that participate in plant symbiosis  plants grow better in plots lacking garlic mustard  in garlic mustard plots the length of the hyphae is about half than in control plots o o garlic mustard decreases establishment of native trees through decrease of symbiotic fungal partners  affects forest regeneration because lack of fungi causes slow growth of trees o there is almost no colonization of fungi where garlic mustard is present o so regeneration of trees is stumped by garlic mustard   it will get worse before it gets better  climatically possible potential distribution is a lot greater than current distribution 2 Zebra mussels o zebra mussel in the great lakes o every port in the world is somehow connected whether directly or indirectly – aquatic species are carried on ships in ballast water (wat
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