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What makes a weed a weed? Traits associated with invasive behavior And Predicting invasive potential Sutherland: Predictable weedy traits? • Predictions: – – – – – – – – – Vegetative reproduction Hermaphroditic or monecious Self-compatible Wind-pollinated Tolerant of high light Tolerant of low moisture Annuals or biennials Perennial grasses or forbs Armed and Toxic Weed list sources • Synthesis of the North American Flora (3,038 spp.) – Weed def: “plants that generally grow in disturbed areas where they are unwanted and unappreciated.” • PLANTS, Invasive plants of the US (1,336 spp.) • US Fed. and State Noxious Weed Lists (385 spp.) • Daehler (1998) (311 spp.) – Spp. that are “global natural area invaders” Data Analysis • Compared frequency of traits for: – Weeds vs. Non-weeds – Native vs. Exotic weeds – Invasive vs. Non-invasive weeds Results of Analysis Weed Native Invasive Trait Prediction Non-weed Exotic Non-invasive Veg. Reproduction More K, P, N K, P NS Breeding system Mon. or hermaph NS K K, P Compatibility Self-compat P, N K K, P, N Pollination system Wind NS K NS Shade tolerance Intolerant K, P, I K NS Habitat Non-wetland K, P, N, I K, P, N, I N Lifespan Annual or Bienn K, P, N, I K K, P, N Life form Herbaceous Mixed Mixed K, P, N Morphology Armed K, P, N, I NS NS Toxicity Toxic K, P, N, I K N Weeds (compared to non-weeds) are: • More likely to be Annual or Biennial • Less likely to be Perennial • More likely wetland spp., toxic, vines, and trees • Less likely to be forbs and sub-shrubs • Annual and Biennial weeds more likely to be armed • Perennial weeds more to be shade intolerant Exotic (compared to native) weeds are: • Less likely to be wetland spp. Than native weeds. • Still more likely to be wetland spp. Than non-weeds. Invasive (compared to noninvasive) exotics weeds are: • Less likely to be forbs. • More likely to be perennial, monoecious, self-incompatible, shrubs, and trees. • Above traits are related. • Magnitude of Chi Square values suggest that life form may be more important than breeding system or compatibility. Other Conclusions • Lifespan constrains other life history traits. Separating spp by life history makes some characteristics non-significant. • Habitat is a significant predictive trait for all weed spp (native, exotic, or invasive). • Toxicity is a sig. Life history trait for weds independent of lifespan. – If alleopathic: supports competitive release hyp. – If anti-herb Defense: supports escape predation hyp. Other Conclusions • Agree with some of Baker’s predictions (1965). Disagree on Veg. Reproduction, self-incompatibility, wind pollination. • With the exception of increased probability of being a tree, invasive exotics differ very little in life history from other weeds. • There are life history traits that distinguish weeds from non-weeds. Sutherland: Predictable weedy traits? • Predictions: – – – – – – – – – Vegetative reproduction Hermaphroditic or monecious Self-compatible Wind-pollinated Tolerant of high light Tolerant of low moisture Annuals or biennials Perennial grasses or forbs Armed and Toxic Risk Assessments • Allow managers, horticulturalists, and politicians to determine what plants to permit and which to deny entry. • Not all errors are equally important. It’s worse to let in a pest species than keep out a non-pest species. Minimize spp. held for evaluation. Comparing Australian and Reichard systems • AU 3 tiered scheme vs. Reichard’s decision tree • Similar levels of success • Use 5 kinds of criteria: – – – – – History of invasiveness elsewhere Relatedness to other invaders Climatic match between home and novel ranges Noxious and undesirable traits Biological attributes of plant itself 4 Categories of traits associated with weeds • Vegetative growth and reproduction – Contrary to findings of Sutherland • Persistence, tolerance, and recovery • Sexual and Asexual propagule production and dispersal. • Easy germination and establishment. Risk Assessment take home message • Fairly accurate • Moderately tolerant of missing data • Important variables fairly constant across analyses and assessment methodology. Potential responses by Botanical gardens • The conservation aware garden. – Do impact and risk assessments • The strict conservation garden. – Do not transport organisms across natural barriers to dispersal. Questions for thought • What will it take to get horticulturalists on-board? • To what degree are traits associated with invasive species the result of their selection vs. a random sampling of potential invasives? • What step could be taken to improve the accuracy of Risk Assessments? • Why the discrepancy over vegetative preproduction?