Sept.16- Hypotheses continued (Variable resource, competition, novel weapons) 18- Hypotheses finish! (disturbance, biodiversity, anthropogenic) 23- Nevada Cooperative Extension outreach programs (Earl Creech) 25- State weed & invasive plants management (Scott Marsh) 30- Federal invasive plants research (Mark Weltz) Oct.2- Review 7- Exam 1 (Dr. Nowak is back) Notes: Hopefully we can get the last 6 hypotheses done before the guest lectures. If we can, on Oct 2 I’ll bring in old exams and we can review. *** Information presented by the guest lecturers will be on the exam! ***

3)What makes a species invasive? Biodiversity hypothesis Basic concepts: High biodiversity → high community stability Stable communities not invaded Biodiversity hypothesis does not require vacant niche But uses niche concepts that: Different species have different niches As ↑ number species, ↑ filling of niche space Thus highly diverse communities more difficult to invade

3)What makes a species invasive? Biodiversity hypothesis Theoretical basis: Tilman Ecology. ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability

3)What makes a species invasive? Biodiversity hypothesis Theoretical basis: Tilman Ecology. ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N*

3)What makes a species invasive? Biodiversity hypothesis Theoretical basis: Tilman Ecology. ↑ number species ↑ filling of niche space ↑ number species ↓ average resources availability Each species has some minimum average resource need = R* Corresponds with some minimum species diversity = N* Above N*, that species cannot invade because average community resource level is less then minimum for that species (R*) At or below N*, can invade

3)What makes a species invasive? Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature Had 147 plots originally seeded with up to 24 natives (1,2,4,6,8,12,24) Observed 13 aliens invaded naturally through time As ↑ native diversity: ↓ invader cover ↓ invader number ↓ invader max size NS median size

3)What makes a species invasive? Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature Had 147 plots originally seeded with up to 24 natives (1,2,4,6,8,12,24) Observed 13 aliens invaded naturally through time As ↑ native diversity: ↓ invader cover ↓ invader number ↓ invader max size NS median size Conclusion: Fewer invaders and reduced invader performance with increasing native diversity.

3)What makes a species invasive? Biodiversity hypothesis Experimental evidence: From Kennedy et al. (2002) Nature Invaders do more poorly with ↑ native diversity Why? With high native diversity provides Increasing density Increasing species richness and crowded neighborhoods

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Levine (2000) Examined riparian communities along South Fork Eel River, CA Dominated by native tussock sedge Carex nudata Each tussock is discrete island (neighborhood) colonized by up to 20 perennial plants & mosses Research question: The biodiversity hypothesis seems to work well in controlled experiments, but what about out in the world?

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Levine (2000) Surveyed similarly sized tussocks 3 invaders (Agrostis, Plantago, Cirsium) All invaders had ↑ occurrence with ↑ diversity, contrary to biodiversity hypothesis Why? To support high diversity, must have lots of resources Thus, diverse sites are “best” sites Best sites most likely to be invaded

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” (dashed lines) and “non-reserves” (solid lines)

3)What makes a species invasive? Biodiversity hypothesis Contrary evidence: From Lonsdale (1999) Ecology 80: Global survey – compiled data from 184 sites around the world Separated into “Island” vs. “Mainland” Within each group, broke down further into nature “reserves” (dashed lines) and “non-reserves” (solid lines) As expected, number invaders: Islands > Mainlands Non-reserves > Reserves But, for all sites, more invaders with greater diversity

3)What makes a species invasive? Biodiversity hypothesis Resolving the conflict: Shea and Chesson 2002 Within ecosystems, more species = less invasable Among ecosystems, more diverse systems (more resources) = more vulnerable Within ‘clusters’ extrinsic factors (e.g. climate) are similar Factors differ across ‘clusters’.

3)What makes a species invasive? Biodiversity hypothesis Resolving the conflict: Shea and Chesson 2002 Why is the comparison of biodiversity between two very different ecosystems valid? Different ecosystems (deserts  rainforests) will have different natural ranges of biodiversity. Account for that range and then look at the biodiversity hypothesis!

3)What makes a species invasive? Biodiversity hypothesis Increasing biodiversity increases ecosystem stability which increases resistance to invasion (due to filled niche space= decreased resource availability). Summary: Logical arguments to support the hypothesis But logical arguments contrary to hypothesis Data that support the hypothesis But other data contrary to hypothesis Thus, biodiversity alone does not account for invasibility Diversity patterns at different scales may explain paradox in part

3)What makes a species invasive? Disturbance and land use hypothesis Basic concepts: Many invasive species have a “ruderal” life history strategy. “Ruderal” = small, very-short lived plants that grow and mature rapidly and that have a large reproductive effort, especially in response to stress These species are usually associated with disturbed habitats

3)What makes a species invasive? Disturbance and land use hypothesis Basic concepts: Many invasive species have a “ruderal” life history strategy. “Ruderal” = small, very-short lived plants that grow and mature rapidly and that have a large reproductive effort, especially in response to stress These species are usually associated with disturbed habitats Every system has a natural disturbance regime (fire return, flooding interval, etc) So changes in land use can alter the natural disturbance regime (more or less frequent, bigger or smaller events…)

Basic concepts: Invasive species are ruderals Ruderals associated with disturbed habitats Land use changes affect disturbance Examples from Hobbs in Mooney & Hobbs (2000) Change can be abrupt or gradual Change can be permanent 3)What makes a species invasive? Disturbance and land use hypothesis

Basic concepts: Invasive species are ruderals Ruderals associated with disturbed habitats Land use changes affect disturbance Examples from Hobbs in Mooney & Hobbs (2000) Change can be abrupt or gradual Change can be permanent or transitory --Sites can recover to the original state or an alternate state 3)What makes a species invasive? Disturbance and land use hypothesis

Basic concepts: Invasive species are ruderals Ruderals associated with disturbed habitats Land use changes affect disturbance Examples from Hobbs in Mooney & Hobbs (2000) Change can be abrupt or gradual Change can be permanent or transitory Transition to original or new state Transition can be natural or deliberate, with deliberately different end states 3)What makes a species invasive? Disturbance and land use hypothesis

Basic concepts: Invasive species are ruderals Ruderals associated with disturbed habitats Land use changes affect disturbance How can disturbance and land use changes enhance invasions? 3)What makes a species invasive? Disturbance and land use hypothesis

Basic concepts: Invasive species are ruderals Ruderals associated with disturbed habitats Land use changes affect disturbance Disturbance and land use changes enhance invasions by: --Changing the amount or flow of resources hence inducing a change in resource availability --Increases the probability of success for ruderals --Because of the changes in vegetation states there is opportunities for other species to exist 3)What makes a species invasive? Disturbance and land use hypothesis

Evidence: D’Antonio & Vitousek (1992) Without invasive species, typically when woodland are disturbed, they eventually return back to woodlands 3)What makes a species invasive? Disturbance and land use hypothesis Disturbance Recovery

Evidence: D’Antonio & Vitousek (1992) Without invasive species, typically when woodland are disturbed, they eventually return back to woodlands With ruderal alien grass invasion: a novel disturbance = fire Once have a fire, initiate a series of feedback effects that virtually preclude the re-establishment of woody plants 3)What makes a species invasive? Disturbance and land use hypothesis

Evidence:From Kalin Arroyo et al. in Mooney & Hobbs (2000) Determined number of alien plants in 12 political regions of Chile Total of 430 alien weeds and 260 alien non-weeds Developed a land use index using data about agriculture use, urban areas and road density. 3)What makes a species invasive? Disturbance and land use hypothesis disturbance

Changes in land use cause changes in the extent and frequency of disturbance to an ecosystem which are then opened up for ruderal plant establishment. Summary: Consistent with ecological theories Evidence from woodland / grasslands Empirical correlations But Is disturbance / land use the factor, or is it something associated with these? Species traits Resource availability Changes in competitive balance Temporary “vacant” niche What about plants that establish without disturbance? 3)What makes a species invasive? Disturbance and land use hypothesis

3)What makes a species invasive? Anthropogenic hypothesis “Human activity moves species from plant to place both accidentally and deliberately and it does so at rates that are without precedent in the last tens of millions of years. As a result, taxa that evolved in isolation from each other are being forced into contact in an instant of evolutionary time” -D’Antonio and Vitousek 1992

Basic concepts: Human activities are the cause of invasive species Humans help invasives overcome barriers; e.g. Richardson et al. (2000) Humans overcome geographic barriers Humans overcome environmental & reproductive barriers Humans help disperse invasives in new range Home range Introduced area Disturbed area Natural area Geographic ReproduceEnvironment Disperse 3)What makes a species invasive? Anthropogenic hypothesis

Basic concepts: Human activities are the cause of invasive species Humans help invasives overcome barriers Thus, humans and invasive species are interdependent Home range Introduced area Disturbed area Natural area Geographic ReproduceEnvironment Disperse 3)What makes a species invasive? Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000) Humans and invasive species are interdependent Direct effects by introducing invading species 3)What makes a species invasive? Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000) Humans and invasive species are interdependent Direct effects by introducing invading species Direct effects by altering ecosystem properties 3)What makes a species invasive? Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000) Humans and invasive species are interdependent Direct effects by introducing invading species Direct effects by altering ecosystem properties Cascading, indirect effects 3)What makes a species invasive? Anthropogenic hypothesis

Basic concepts: From Hobbs in Mooney & Hobbs (2000) Humans and invasive species are interdependent Direct effects by introducing invading species Direct effects by altering ecosystem properties Cascading, indirect effects, which sets up an invasive cycle 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: Humans as vector for introduction? Any examples of introduced plants that are now a problem? 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Mack et al. (2000) Humans as vector for introduction Lantana camara (lantana; shrub verbena) shrub native to tropical New World Prized for showy flowers and fragrant leaves 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Mack et al. (2000) Humans as vector for introduction Lantana camara native to tropical New World Introduced as a horticultural species repeatedly throughout the world, especially tropics and sub-tropics 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Lonsdale (1999) Ecology 80: Humans as vector for introduction Asked: Do the number of invasive species increase with number of visitors to natural areas? 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Lonsdale (1999) Humans as vector for introduction Do invasives ↑ with visitation? First, control for larger parks have more natives which draws more visitors (a) 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Lonsdale (1999) Humans as vector for introduction Do invasives ↑ with visitation? First, more natives → more visitors Then look at visitors corrected for number of natives (= “visitor residuals”) vs. number of exotics (b) 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: From Lonsdale (1999) Humans as vector for introduction Do invasives ↑ with visitation? First, more natives → more visitors Number of exotics significantly (P<0.001; adj. r 2 =0.68) with visitors 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: Humans as vector for introduction Human alterations of ecosystem properties Example : Riparian areas in western US Originally “cottonwood gallery forest” Settlement brought ranching and irrigated agriculture (sedimentation, clearing, disturbance) Dam construction (early 1900’s): prevented spring flood; fires 3)What makes a species invasive? Anthropogenic hypothesis

Evidence: Humans as vector for introduction Human alterations of ecosystem properties Example : Riparian areas in western US Saltcedars & Russian olive introductions (mid-late 1800’s) for windbreaks, erosion control & stream bank stabilization, ornamentals Originally encouraged and subsidized by governments More drought tolerant; less exacting on seed dispersal & establishment requirements Now dominant species on much of the riparian areas of western US 3)What makes a species invasive? Anthropogenic hypothesis

Humans have broken down barriers that once kept plants in their native area. Summary: Abundant evidence that Humans are major vector for introduction Humans greatly alter ecosystem properties But: Invasive species problems are no longer just a natural, ecological problem 3)What makes a species invasive? Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis 2.Allelopathy hypothesis 3.Environmental change hypothesis 4.Variable resource availability hypothesis 5.Competition hypothesis 6.Microevolutionary change hypothesis 7.Escape from biotic constraints hypothesis 8.Biodiversity hypothesis 9.Disturbance and land use hypothesis 10.Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis No support 2.Allelopathy hypothesis 3.Environmental change hypothesis 4.Variable resource availability hypothesis 5.Competition hypothesis 6.Microevolutionary change hypothesis 7.Escape from biotic constraints hypothesis 8.Biodiversity hypothesis Conflicting support 9.Disturbance and land use hypothesis 10.Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis No support 2.Allelopathy hypothesis 3.Environmental change hypothesis 4.Variable resource availability hypothesis Very limited support 5.Competition hypothesis 6.Microevolutionary change hypothesis 7.Escape from biotic constraints hypothesis 8.Biodiversity hypothesis Conflicting support 9.Disturbance and land use hypothesis Special case of #10 10.Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis No support 2.Allelopathy hypothesis Specific cases, but how many? 3.Environmental change hypothesis 4.Variable resource availability hypothesis Very limited support 5.Competition hypothesis 6.Microevolutionary change hypothesis Specific cases ; how many? 7.Escape from biotic constraints hypothesis 8.Biodiversity hypothesis Conflicting support 9.Disturbance and land use hypothesis Special case of #10 10.Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis No support 2.Allelopathy hypothesis Specific cases, but how many? 3.Environmental change hypothesis Broad support, but exceptions 4.Variable resource availability hypothesis Very limited support 5.Competition hypothesis Broad support, but exceptions 6.Microevolutionary change hypothesis Specific cases ; how many? 7.Escape from biotic constraints Broad support;exceptions 8.Biodiversity hypothesis Conflicting support 9.Disturbance and land use hypothesis Special case of #10 10.Anthropogenic hypothesis

3)What makes a species invasive? 10 hypotheses: 1.Vacant niche hypothesis No support 2.Allelopathy hypothesis Specific cases, but how many? 3.Environmental change hypothesis Broad support, but exceptions 4.Variable resource availability hypothesis Very limited support 5.Competition hypothesis Broad support, but exceptions 6.Microevolutionary change hypothesis Specific cases ; how many? 7.Escape from biotic constraints Broad support;exceptions 8.Biodiversity hypothesis Conflicting support 9.Disturbance and land use hypothesis Special case of #10 10.Anthropogenic hypothesis Broad support, few exceptions

The literature on invasion ecology contains a growing number of theories and generalization, with much duplication, redundancy and reinventing of the wheel. There is a need to distill the fundamental issues from the different theories, while realizing that invasions are context specific. Richardson and Pysek from Fifty years of invasion ecology –the legacy of Charles Elton, 2008