1. Impacts of Invasions Measuring impact is complex –What should be measured and how? −For individual plant, individual species, or multiple species? −Over what time frame? −Lack of comprehensive data

2. Ecological Impacts Invasive species affect different community & ecosystem processes 1.Disturbance regimes Fire 2.Resource dynamics Nutrients: N and C cycling Water: amount, timing, location

5. Ecological Impacts Ecosystem engineers: species able to physically alter habitats (Crooks 2002) Alter ecosystem physical processes (sedimentation, water availability, N cycling) Change habitat structure (more or less complexity) Effects cascade through community Jager et al (2009) J of Ecology 97:1252-1263

6. Ecological Impacts Impacts on community structure 1. Productivity

7. Ecological Impacts Impacts on community structure 2. Community dynamics

8. Ecological Impacts Changes in productivity and community dynamics often observed as: 1. Direct competition 2. Large scale species displacement

9. Ecological Impacts: Competition Question: How is invasion by exotic grasses impacting native recruitment in dry forests of Hawaii? Methods: Experimental field studies removing invasive grasses Denslow et al. (2006) Oecologia 148: 118-128 Dodonea viscosa A’ali’i Pipturus albidus Mamaki Sophora chrysophylla Mamane Acacia koa Koa

10. Denslow et al. (2006) Oecologia 148: 118-128

11. Question: How has invasion by Cape ivy affected 3 coastal habitats in SF Bay Area? Methods: Comparative and experimental field studies Alvarez & Cushman (2002) Ecological Applications 12:1434-1444 Ecological Impacts: Replacement Delairea odorata - Cape Ivy

12. Alvarez & Cushman (2002) Ecological Applications 12:1434-1444

16. Ecological Impacts: Mutualisms Question: How does invasion by Alliaria petiolata alter plant composition of NA forests? Methods: Examined mycorrhizal colonization of tree roots from soil cultured with Alliaria Stinson et al. (2006) PLoS Biology 4: 140

19. Ecological Impacts Species impacts can be by: Indirect effects on community structure or function Direct species replacement

21. Ecological Impacts Threatened & endangered species ~ 614 animals and 749 plants are federally listed in US ~ a quarter of species are believed to be threatened by direct effects of invasive species ~ half of federally listed species are believed to be associated with invasives (includes plants plus other organisms) http://www.fws.gov/Endangered/wildlife.html#Species

22. Ecological Impacts: T&E Species Question: Is there a relationship between species invasion and imperiled species in CA? Methods: examined distribution of 834 exotic plants in CA & correlated it to imperiled species using multivariate analyses (CCA, SEM) Seabloom et al. (2006) Ecological Applications 16: 1338 - 1350

25. Ecological Impacts: Extinctions Question: How have 8 endangered plants been impacted by introduced species? Method: Literature and field surveys

26. galopagos

27. Ecological impacts: Extinctions How much of a role do invasive species really play? Extinctions are caused by multiple factors: 1.Habitat destruction 2.Invasive species 3.Pollution 4.Disease Most ‘documented’ extinctions involve speculation

28. Ecological impacts: Extinctions Animals more impacted than plants Mainland less impacted than islands Sax & Gains (2008) PNAS 105: 11490-11497

30. Sax et al. (2002) American Naturalist 160: 766-783

31. Ecological Impacts Do invasions always negatively impact ecosystem properties and community structure?

32. Positive impacts All of the factors that have a negative impact on native plants can also be positive under certain conditions –Competitive release –Facilitation by acting as nurse plants –Trophic subsidy –Pollination –Predatory release

33. Summary Ecological impacts typically involve: (1) nutrients/water flow (2) primary production impacts (3) alterations of disturbance regimes (4) changes in community dynamics Ecological Impacts

34. Summary Ecological impacts typically involve: (1) nutrients/water flow (2) primary production impacts (3) alterations of disturbance regimes (4) changes in community dynamics Ecological Impacts Ecosystem functions (C sequestration, N cycling, water, fire frequency/intensity)

35. Summary Ecological impacts typically involve: (1) nutrients/water flow (2) primary production impacts (3) alterations of disturbance regimes (4) changes in community dynamics Ecological Impacts Ecosystem functions (C sequestration, N cycling, water, fire frequency/intensity) Effects observed as: Species replacements (direct/individual or large scale)

36. Summary Ecological impacts typically involve: (1) nutrients/water flow (2) primary production impacts (3) alterations of disturbance regimes (4) changes in community dynamics Ecological Impacts Ecosystem functions (C sequestration, N cycling, water, fire frequency/intensity) Effects observed as: Species replacements (direct/individual or large scale) Loss of native species (threatened or endangered species) Often in conjunction with human-caused habitat change Especially on islands Especially rare/specialized species More evidence for population reduction than for extinction (e.g. Harrison et al 2006)