Reading assignments: ecological impacts • Invasives and fire: – D’Antonio and Vitousek 1992. Biological invasions by exotic grasses, the grass-fire cycle, and global change. Annual review of Ecology and Sytematics 23:65-87. – Brooks et al. 2004. Effects of invasive alien plants on fire regimes. BioScience 54: 677-688. • Ecosystem changes: – Crooks 2002. Characterizing ecosystem-level consequences of biological invasions: the role of ecosystem engineers. Oikos 97:153-166. 3) Impacts a) Ecological ii) Ecosystem functions Ecosystem engineers: What are they? 3) Impacts a) Ecological ii) Ecosystem functions Ecosystem engineers: What are they? • Alter ecosystem physical processes (water use, N cycling) • Change habitat structure (more complexity, less complexity) • Effects cascade through community 3) Impacts a) Ecological ii) Ecosystem functions • Overview • Specific examples: General compilation From Crooks (2002) Effects on Nitrogen N loss Invasive plants Fire Altered composition Altered litter quality Altered microbial activity Altered microclimate Altered root exudation Altered microbial community N fixation Altered NPP Altered timing of uptake N cycling and pools Modified from D’Antonio and Hobbie in Sax et al. 2005 3) Impacts a) Ecological iii) Threatened & endangered species • Overview ~409 animals and 598 plants are federally listed species in US 3) Impacts a) Ecological iii) Threatened & endangered species • Overview ~409 animals and 598 plants are federally listed species in US 294 (29%) threatened by direct effects of invasive species (IUCN) 3) Impacts a) Ecological iii) Threatened & endangered species • Overview Effects can be by: Direct species replacement Indirect through effects on community structure or function 3) Impacts a) Ecological iii) Threatened & endangered species : IUCN database • Overview Effects can be by: Direct species replacement Indirect through effects on community structure or function Worldwide Extinctions: 104 records of extinctions directly due to invasives 88 animals (many birds, NZ and HI) 16 plants Endangered and vulnerable: 1317 directly due to invasives 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: King Ranch bluestem Bothriochloa ischaemum (Caucasian bluestem) brought in to southern Great Plains (NM, OK, TX) from Russia in 1929 C4 perennial bunchgrass: establishes readily from seed long growing season tolerates heavy grazing fair forage quality forms dense sod in mature pastures 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: King Ranch bluestem Bothriochloa ischaemum (Caucasian bluestem) brought in to southern Great Plains (NM, OK, TX) from Russia in 1929 C4 perennial bunchgrass: desirable forage species Seeded extensively (for example, ~2 million acres in western OK) 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: King Ranch bluestem Bothriochloa ischaemum (Caucasian bluestem) brought in to southern Great Plains (NM, OK, TX) from Russia in 1929 C4 perennial bunchgrass: desirable forage species Seeded extensively But extremely invasive: Spread along highways into native areas (cemetaries, native grasslands) Difficult to control Threatens federally listed endangered plant Ambrosia cheiranthefolia (south Texas ambrosia) 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: Hawaii 80-90 native plant species extinct 270 plant species listed as threatened or endangered 94 noxious weeds, many more alien species 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: California • Seabloom et al (2006) examined distribution of 834 exotic plants in CA. Multivariate analyses (CCA, SEM) 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: California • Seabloom et al (2006) examined distribution of 834 exotic plants in CA. Multivariate analyses (CCA, SEM) • exotic/invasive species tightly linked to distribution of imperiled species (regression, CCA) 3) Impacts a) Ecological iii) Threatened & endangered species • Overview • Specific examples: California • Seabloom et al (2006) examined distribution of 834 exotic plants in CA. Multivariate analyses (CCA, SEM) • exotic/invasive species tightly linked to distribution of imperiled species (CCA) • Human activities facilitate initial invasion but exotics spread ahead of front of human development into areas with high numbers of threatened plants (SEMs) 3) Impacts a) Ecological iii) Threatened & endangered species • Not a lot of evidence for extinctions (Gurevitch and Padilla 2004) • But: ‘Winners and Losers’ in anthropogenic biotic homogenization (McKinney and Lockwood 1999) • Invasive plants are ‘winners’ • ‘losers’ are species whose numbers/range decline • Geographically restricted natives with specific habitat requirements = high extinction rates 3) Impacts a) Ecological iii) Threatened & endangered species • Not a lot of evidence for extinctions (Gurevitch and Padilla 2004) • But: ‘Winners and Losers’ in anthropogenic biotic homogenization (McKinney and Lockwood 1999) • Invasive plants are ‘winners’ • ‘losers’ are species whose numbers/range decline • Geographically restricted natives with specific habitat requirements = high extinction rates Traits of ‘winners’ r selected Widespread Rapid dispersal High variability Generalist Human commensalism Traits of ‘losers’ K selected Rare Slow dispersal Low variability specialist Maladapted to humans 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem • Ecological impacts typically involve: (1) nutrients/water flow; (2) primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem • Ecological impacts typically involve: (1) nutrients/water flow; (2) primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics • Effects observed as: Species replacements (direct/individual or large scale, w/ or w/o interactions with other factors such as fire) 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem • Ecological impacts typically involve: (1) nutrients/water flow; (2) primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics • Effects observed as: Species replacements (direct/individual or large scale, w/ or w/o interactions with other factors such as fire) Ecosystem functions (C sequestration, N fixation, fire frequency/intensity) 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem • Ecological impacts typically involve: (1) nutrients/water flow; (2) primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics • Effects observed as: Species replacements (direct/individual or large scale, w/ or w/o interactions with other factors such as fire) Ecosystem functions (C sequestration, N fixation, fire frequency/intensity) Loss of native species (threatened or endangered species) Often in conjunction with human-caused habitat change 3) Impacts a) Ecological Summary • Only a small percentage (0.1%) of introduced plants become a problem • Ecological impacts typically involve: (1) nutrients/water flow; (2) primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics • Effects observed as: Species replacements (direct/individual or large scale, w/ or w/o interactions with other factors such as fire) Ecosystem functions (C sequestration, N fixation, fire frequency/intensity) 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)