Invasion Biology Notes for Lectures 1-3 PDF

Invasion Biology Notes for lectures 1-3 Lecture 1: Introduction of Invasion Biology Invasive species fit two general criteria: 1). Must be exotic, rather than native. 2). Must cause significant economic or ecological damage. Only about 10% of exotics are invasive. What causes inva...

Invasion Biology Notes for lectures 1-3 Lecture 1: Introduction of Invasion Biology Invasive species fit two general criteria: 1). Must be exotic, rather than native. 2). Must cause significant economic or ecological damage. Only about 10% of exotics are invasive. What causes invasion? Many different factors; often case by case. Common ones are: 1). Human facilitation 2). Lack of natural enemies 3). Interactions with other invaders Here on Purpose Exotics intentionally introduced to new habitat. Negative consequences not foreseen or disregarded at time of release. Biological control The enemy of my enemy is my friend. Use of natural enemies to achieve top down regulation of pests or weeds. From hero to villain In early days of biological control, many exotic agents released without careful screening. Negative impacts not foreseen Accidental releases can result from: 1. Inadequate screening of imports 2. Stowaways during transport of goods 3. Gross negligence( ex: bait bucket introductions) Indirect influences Human activity could facilitate range expansion of exotics via: 1). Climate change 2). Natural enemy reductions (ex: overfishing) 3). Habitat modification The importance of ecological theory 1. There are general ecological mechanisms that impact biological invasions in a testable way. 2. Examination of these can yield predictions about invasion process. 3. A predictive basis to invasion biology may permit more proactive strategies- as opposed to reactive strategies. The importance of case studies 1. Case studies provide empirical data for testing theoretical principles. 2. Exceptions to well established theoretical rules can lead to paradigm shifts. 3. Those who forget history are doomed to repeat it( the retroactive approach). An example of invasive species is: Cane toad in Australia ** learn about this Cane toad and when, and how. Lecture 2: Corridors of Invasion The spongy moth - Lymantria dispar - Introduced by Etenne Leopold Trouvelot - Has spread rapidly since introduction, resulting in > (greater than) 80 million deforested acres since 1970. Two key concepts 1. Vectors: mechanism of organism transport from native habitat (source) to novel habitat. 2. Pathways: Route between source and novel habitat. Triangular trade route Extra- range dispersal( ERD) Movements by individuals beyond current range of species, & into novel range. Does not need to be human-mediated. What are some natural mechanisms of ERD?- wind dispersal( for seeds), water currents( for aquatic organisms), animal migration( for land animals). Why should we distinguish between natural vs. human-mediated EDR? We should distinguish between natural and human mediated EDR because human activities can significantly alter the dispersal patterns and rates of species, often introducing them to new areas in much larger numbers and with greater genetic diversity compared to natural dispersal, leading to increased potential for invasive species establishment and ecological disruption. Rates of ERD Human- mediated ERD deposits species at faster rate Ex: Species dispersal to islands Theory of island biogeography Robert MacArthur & E.O Wilson Species richness in isolated habitats results from two processes: 1) Immigration(adds) 2) Extinction(subtracts) Natural immigration rate needed to produce native flora of Hawai’i 1094 species): One new colonization/100,000 years, resulting in 280 colonizations and subsequent radiations. 1 new introductions/50 years after Polynesians came to Hawai’i. 1 new introduction/22 years after Europeans came to Hawai’i. Due to change in dispersal vectors( wind/ocean currents à limited boat travel à boats/planes making multiple trips). Human-Mediated effects Cultivation requires human mediation( other 5 can be either human- mediated or natural). More likely to yield multiple introductions. More likely to introduce from multiple source populations. Transport Vectors 2 main categories: 1). Intentional: Movement of organism to new area for express purpose( e.g. Crops, pets, biocontrol) Unintentional: Movement of organism to new area an unintended by product of travel or other intentional introduction. Intentional Vectors: Food Most plant & animal related foodstuffs are derived from intentionally introduced exotic taxa. In North America, many crops still require cultivation but some escaped cultivation and grow in natural areas now. St. John’s Wort - Medicinal plant - Introduced to New and Mid-Atlantic in early 1800s - Now major weed in many western states. Kudzu - Introduced to Philadelphia in 1876 as forage crop and Ornamental - Planted in southern USA intentionally, but has spread extensively since( recognized as weed in 1970). Intention vectors: non-food Biofuel crops (bred for low maintenance & high productivity)  Movement of fish ( e.g. rainbow trout from Western USA to nearly everywhere) & bait to catch them(accidental introduction) Environmental environmental enhancement (broad category including ornamental plants & exotic pets) 1) 60% of established non-native plants in USA due to intentional introduction for ornamental/horticultural purposes. 2) 56-65% of woody & herbaceous non-native plants in Australia introduced for horticultural reasons. The live wildlife trade vector Data from 2000 to 2006 for USA 500,000 shipments recorded 1.5 Billion live animals imported 30% of shipments labeled vaguely( e.g., “marine fish”, “live invertebrates”)  The biocontrol vector Early days of classical biological control: many introduced agents were vertebrates w/ generalized diets ( e.g. , Cane toad, small Indian mongoose, western mosquitofish) Modern efforts tend to focus on more specialized insect natural enemies (e.g., parasitic wasps, entomopathogens), w/ emphasis on safety testing in quarantine. The best of intentions 1. Transport of exotic organisms for research & conservation purposes can be important intentional vector. 2. Includes maintenance of research colonies or programs @ zoos or arboreta. The arboretum conundrum Arboreta & zoos provide important service in outreach education regarding natural world (especially in urban areas) Can provide barrier to invasion, but is the risk (e.g., seed contaminated soil, disposal of clippings) worth it? Unintentional vectors Hitchhiking on other non-native species (e.g., pest insects infesting transported fruit) Transport within materials/structures (e.g., cargo holds, packing materials) Clear relationships between trade & non-native species load for given nation. Ship ballast: could be solid ( stones, gravel, soil) or water The nursery vector Sample of 7 plant nurseries in Sheffield, UK 51% of examined plant pots had 1-2 unintended plants Nursery plants can also vector exotic insect herbivores(e.g., whiteflies) & fungi Back to pathways Strength of transport pathway determined by: 1). # of species transported 2). State of organisms on arrival The scary of nature of air trade Data from about 44,000 flight pathways over 1 year Climate similarity is greatest between global airports from June-August June-August matches peak air traffic time, limiting environmental mismatches.  Prediction is never easy Floerl et al. (2009) found that “ hub & spoke” model has limitations: 1). Hubs are 75% more likely to be invaded, but faster spread to spokes doesn’t always follow ( YAY!) 2). Rate of invasive species spread from hubs less variable than from spokes( BOO!) Lecture 3: Rates of Invasion nutria (or coypu) introduced to Louisiana from Argentina in 1930s much larger than muskrat, desired for fur trade fur demand declined, so supply of nutria outstripped demand high reproductive rate + negative impact on wetland plants = BIG problem! Muskrat spread in Eurasia. It’s invasive species there. Classic trend: The ‘tens rule’ Williamson & Fitter (1996) Four stages of range expansion Probability of passing to next stage is 1 in 10 Imported à Introduced à Established à Pest  How general is the tens rule? Depends on taxon (e.g., holds well for plants, too low for vertebrates) Depends on geography( e.g., islands have higher successful introduction rates)  At given location, # of exotic species recorded tends to increase over time. = The big, ole but Apparent that transportation vectors have changed over time Taxonomic & region of orgin component to this (idosyncratic) Results in accelerating trend not always being observed Why? Pearl Harbor= naval port(not just a crappy movie) 1st dredging of harbor in 1911, followed by extensive use in WWI Headquarters for Allied pacific naval operations in WWII (1941-1945)  Key question Should introduction rates always continue to increase after transport pathway is opened? How to tackle this question? Issue: not every ship container contains new species suite; instead, ships bring samples from donor regions already sampled by other ships. Consequence: Process is analogous to species accumulation curves. Species accumulation curves When examining area for biodiversity, ecologists sample several plots. Newly-sampled plots have species already found, as well as possible new species. As number of plots sampled increases, rate of species discovery decelerates ( due to repeats). America  Critical assumptions of approach 1) Trade volume doesn’t increase in way that increases number of individuals deposited. 2) No change in types of trade goods 3) Inspections & regulations doesn’t change. Delays Changes in vector strength don’t always immediately result in increased introductions of exotic species. Prediction: If delays are common, should see lags in relationship between GDP (surrogate for trade) & number of established exotic species.  Invasion debt Previous booms in trade may yield future increases in invasive species. Hidden cost to massive boom in trade occurring now? Invasiveness: characteristic of organisms Invasibility: Characteristic of habitat/location. On “Invasibility” Concept that different habitats are more susceptible to invasion by exotic species. Issue: other mechanisms besides geography could explain these relationships. Father of invasion biology Major geographic trends Higher number of invasive species on islands, compared to mainland. Reversed latitundial trend from baseline “old” vs. “New” world California Vs. Mediterranean Basin Similar climate ( control for abiotic factors) MB: no more than 400 exotic spp/20,000 total (around 2%)  CA: >(greater than) 1000 exotic spp/5200 total (around 20%) Are these valid comparisons? invasibility patterns commonly assume that # of exotics transported to compared regions is equal likely not true, given taxa & areas of origin of vectors can change over time Modeling transport patterns E = I x S; where: E = # of exotic spp I = # of exotic spp introduced S = survival rate or rate of establishment A key insight invasibility only focuses on effect of S on E to understand the # of exotic spp in any two locations, you need to understand both the establishment rate & # of introductions  to test for invasibility, must control for I The effect of I Lonsdale (1999): I can explain up to 56% of variation in E through comparisons across wide range of E Blackburn & Duncan (2001): 389 bird spp & 1466 introduction events; after controlling for # of introductions & life history strategies of birds, found no evidence of island/mainland status effect.