Invasion Ecology Readings text chapter 9 Part 1

Invasion Ecology Readings: text chapter 9 Part 1: predicting invasion success

What is an alien species? • Species introduced to regions outside of their historic (post-glacial) native range; • Species are being transported to new locations at up to 10, 000 times greater rate than by natural dispersal • Aliens are also called: • exotic species, non-indigenous species, nonnative species, introduced species, colonizing species. There is a general agreement now to ‘alien invasive species’, meaning non-native species introduced to new areas where they cause problems

A new debate focuses on whether we should introduce endangered species from one location to another if the habitat in the home range is the reason why the species is endangered (e. g. butterflies). The process is called assisted migration. Much of the issue has focused on helping species affected by climate change (e. g. plants).

Cumulative number of invasions NIS in the Great Lakes Hemimysis anomala (2006) bloody red shrimp Year No new alien since 2006 associated with ships, even though ships account for 55 -70% of invaders since 1959. Ricciardi (2006) CJFAS

Pattern is very similar to other aquatic ecosystems Fig. 9. 1: San Francisco Bay Mediterranean Sea (non (cumulative number) -cumulative number) 100 80 60 40 20 <1900 Shipping far less important in other water bodies globally 1940 1980 >2000 canals ships canals and ships aquaculture Galil (2011) in Encyclopedia of Biological Invasions

Studies on invaders have increased dramatically since the 1980 s for most species Studies on Water hyacinth (Eichhornia crassipes) Zebra mussel (Dreissena polymorpha) Studies Year Mac. Isaac et al. (2011) in Fifty Years of Invasion Ecology

Scientific publications pertaining to Invaders The invasion literature has exploded since 1990 Blue bars = 7 synonyms for alien species Red line = Citations of Charles Elton’s book Ricciardi & Mac. Isaac (2008) Nature

Charles Elton’s (1958) Invasion Concepts 1. species-poor habitats are more vulnerable to invasion than species-rich habitats due to lack of biotic resistance (e. g. competition, predation, parasitism); 2. islands sustain higher invasion rates and greater impacts than do continents • • based on idea that islands are biologically impoverished, and thus less stable and more vulnerable to invasions same idea became dominant in ecology (i. e. diversity begets stability) in 1960 s-1970 s 3. habitats disturbed by man are more vulnerable than less disturbed ones; cover of Elton’s book, reprinted in 2000.

Historical View What influences invasion success? 1) Species Characteristics • • • • high fecundity small body size vegetative or asexual reproduction high genetic diversity high phenotypic plasticity broad native range abundant in native range physiological tolerance habitat generalist human commensal loss of natural enemies invasional meltdown polyphagy Evidence in support of these ideas is not always supportive, and sometimes contradictory

Historical View 2) Generalizations Regarding Habitat Invasibility • • climatically matched disturbed low diversity absence of predators presence of vacant niches low connectance of food web nutrient rich (plants)

Alien Plants that Spread or Do not Spread Rejmanek and Richardson (1996) Ecology

Analysis of spreading ability in introduced plants • Analysis of 114 introduced plants in North America • looked at 11 attributes • spreading associated with invades elsewhere, vegetative reproduction, length of time fruit on plant and perfect flowers • non-spreaders were associated with evergreens, hybrids, native to the continent or to temperate Asia, need for cold exposure to germinate Rejmanek and Richardson (1996) Ecology

Invasive vs. Non-invasive fishes in the Great Lakes • used a stage based appoach to predict success • sought to explain success at each stage Kolar & Lodge (2002) Science • Successful invaders tended to have faster growth and could tolerate wider variation in temperature and salinity • Spreaders had slower growth but tolerate wide temperatures

Fire Ants • Introduced to Mobile, Alabama last century from South America and have spread across southern USA since • Spread in USA seems to correlate with super colony function (normally colonies aggress one another) • Spread to Caribbean, Australia, New Zealand, Taiwan and China, including Hong Kong and Macau from USA

Genetic assignment of thousands of individuals reveals that all but one introduced population globally came from the USA rather than the original source in South America (grey). This shows a pattern of ‘stepping stone’ invasions, where South America served as the original source, though the USA became the source for global spread once it invaded there This pattern of spread is consistent with a ‘propagule pressure’ hypothesis since there is much more trade from the USA globally than from Argentina More on propagule pressure later Asunce et al. (2011), Science

• study used 66 nuclear microsatellite markers • examined 2144 colonies of ants from 75 different locations globally • used genetics to reconstruct the pathways of invasion Asunce et al. (2011), Science

Exotic Plants invade hot spots of native plant diversity • at small scale (1 m 2), invader diversity was inversely related to native diversity in 4 prairies • at the 1000 m 2 scale, the opposite was true. Invader richness was positively correlated to native richness, soil nutrients (N, C) and foliar cover Stohlgren et al. (1999) Ecological Monographs

California plant communities (Levine, 2000, Science) • richer communities are more invaded even though at small scales seed germination success of invaders is low • suggests local phenomena (competition) is overwhelmed by ecological variation and propagule pressure at larger scales resulting in a positive relationship between NIS and native species diversity

Marine ascidians (tunicates) Stachowicz et al. (2006) Marine Ecology Progress Series • Survival of invaders was inversely related to native diversity. • Space availability inversely related to native diversity. • Colonization by invaders occurs when native are not recruiting

Facilitators Common Facilitators Rare • When resources (open space) are not limiting, biotic resistance mechanisms cannot operate and NIS and native diversity are positively correlated; • as space become limiting, biotic resistance increases and relationship becomes negative • facilitators can offset the effect of biotic resistance by providing habitat for NIS to colonize Stachowicz et al. (2006) Marine Ecology Progress Series

Paradox of invasion: positive relationship between invader and native diversity at large scales, but negative relationship at small scales • Extrinsic conditions differ between point clusters, but are the same within (e. g. nutrient levels). • Within a cluster, high native diversity leaves few vacant niches, so a negative relationship exists for NIS (small spatial scales). • At larger scales or in environments that promote high native diversity, the same factors may promote high NIS diversity. Shea and Chesson (2002) Trends in Ecology and Evolution

Are Islands more Invasible? Number of NIS appears positively related to number of native species, and islands appear more invaded than mainland Lonsdale (1999) Ecology

Invader number is strongly associated with native richness (the rich get richer), habitat area, whether it is a mainland or island, and whether it is protected or not Lonsdale (1999) Ecology Visitors bring exotic plants with them to islands (open dots) than on mainlands (closed dots)

Number NIS plants increases with # of Visitors and native plant species in South Africa # NIS plant species • # invader plant species directly correlated with visitor number and native plant species diversity in S. Africa • Suggests human are bringing seeds in with them (=propagule pressure)

Assessing the role of Disturbance is not easy due to confounding by other factors Do invader plants colonize fields with cows because: 1) removal of competing native plants? 2) soil disruption/compaction? 3) manure fertilization? 4) seed introduction? 5) all of the above?

Habitat Characteristics favouring invasibility Mark Davis has suggested that it is the ratio of supply and demand of key resources that determines whether invaders can colonize

Testing for Elton’s Ideas 1) Disturbance: Meta-analysis (Lozon & Mac. Isaac 1997) YES - 299 plant species: 86% - be careful since data could be biased YES - 103 animal species: 12% 2) Native Species Diversity: plants: YES: Fox & Fox 1986; Rejmanek 1996? ; Tilman 1997 NO: Lonsdale 1999; Smith & Knapp 1999; Stohlgren et al. 1999 animals: YES: Case 1991; Stachowicz et al. 1999; Shurin 2000 NO: Hengeveld 1988; Moyle & Light 1996; Cohen & Carlton 1998 3) Islands vs. Mainlands: YES: Plants (Lonsdale 1999)

Modern View Stage-based methods to predict invasion success • a number of groups have argued that more progress would be made predicting invasions by disentangling stages of the process than by looking for species attributes or ecosystem attributes to explain the entire process • A stage based process looks at the different factors that affect transitions between one stage in the invasion process and the next

Model to Predict Invasions Species Pool A B C D E F G Human Introduction Transport (Dispersal) Filter Physiological Filter (+/-) Biotic Filter (+/-) Natural Colonization E G Founding Alien Population

Alien Invasive Species (AIS) Colonization, Spread and Management Blackburn et al. (2011), Trends in Ecology & Evolution

Predicting Asian tiger mosquito Aedes albopictus invasions using vectors and climate Native region: red Introduced: orange Intercepted: yellow Traffic to invaded areas was 2 x higher than to non-invaded areas with similar climate Climate matching of ports (top) and airports (bottom) Tatem et al. 2006, PNAS

Predicting invasions by Chinese mitten crab (Eriocheir sinensis) • native to South-East Asia • Extensive invasion history in Europe • Catadramous lifecycle, undergoing extensive migrations • Occasionally found in Great Lakes

Predicting European occurrence from where it lives in Asia • Data obtained for 457 mitten crab reports in invaded Europe and for 41 sites from its native China Mitten crab reports Model used to predict European distribution, and then it was applied to predict in North America

Herborg et al. (2007) Conservation Biology • Model developed for Europe using Asian distribution data very accurately (dark red) predicted the crab’s actual distribution (green) • Very rarely predicted occurrence in areas where the crab is not found • Very rare crab is found where it is predicted to be poor habitat

Relative risk based on ballast water proxy for propagule pressure and environmental suitability Risk group High Med Low NA Port Asian Model Mean SD Ballast Volume (tonnes x 103) Relative risk Norfolk VA 98 8 365427 4. 8 Baltimore MD 98 8 76160 1 Portland OR 67 34 65465 160. 6 Houston TX 80 12 24836 60. 9 New York NY 84 31 21019 51. 6 Seattle WA 68 37 13266 32. 6 Tampa FL 59 19 1021 2. 5 Jacksonville FL 75 19 408 1 Oakland CA 33 44 21718 5. 7 Boston MA 49 44 3792 1 Los Angeles / Long Beach CA 0 0 30458 21. 7 Miami FL 13 13 1402 1 San Diego CA 0 0 0 -- Herborg et al. (2007 Ecol Applic)

Predicted distribution of crab in North America Apparent risk corresponds with amount of ballast dumped (propagule pressure) and with environmental suitability; red is high risk. Herborg et Herborg al. (2007) Applications et. Ecological al. (2007 Ecol Applic)

Propagule Pressure • number of introduction events • number of propagules introduced per event • condition of the propagules Propagule pressure is a logical first step toward predicting invasion risk Colonization Pressure • related to propagule pressure, but it refers to the number of species introduced

Invasions related to Economy Size The more you trade internationally, the more you expose yourself to species from other countries that come in either intentionally (stocked) or accidentally (ballast water) Hulme (2009) Journal of Applied Ecology

Propagule Pressure Determines Invasion Risk Probability of Establishment Number of Propagules/Events • Increased PP increases establishment probability by reducing demographic stochasticity (Simberloff 2009) • Increased number of release events increases establishment probability by reducing environmental stochasticity (Simberloff 2009)

Reducing Propagule Pressure Reduces Risk benefit Probability of Establishment Number of Propagules • If we can reduce PP we can reduce risk by putting some of the species present into a situation where they suffer from demographic stochasticity

More Invasions Expected with more Invaders Introduced Colonization Pressure birds on islands random data Aliens Established e 1: in l 1 Aliens Introduced (% of total available) Lockwood et al. (2009) Diversity & Distributions

Native butterfly species distribution in Ecuador Williamson and Gaston (2005) J. Animal Ecology common rare Species Rank A few species are super abundant (upper left), and many are very, very rare (lower right). If I randomly collect 20 individuals, they will be dominated by individuals from the common group, and perhaps there will be no rare species. If I collect 2000 individuals, we expect some of the rare ones to show up.

As I sample a community, I first pick up common species, and with further sampling start to slowly add rarer species until the curve saturates and all species are represented As I sample a community more and more, the mean abundance of each species collected increases linearly large inoculation small inoculation Lockwood et al. (2009) Diversity & Distributions Because colonization pressure levels off, but mean propagule pressure does not, the curve flows upward

Propagule Pressure and Colonization Pressure large release moderate release small release Lockwood et al. (2009) Diversity & Distributions

Propagule Pressure and Colonization Pressure Low demographic stochasticity High demographic stochasticity • With high propagule release: a large number of AIS and high propagule pressure for each (low demographic stochasticity). • With low propagule release: few species present, and all are present at low density and suffer from demographic problems • 2 large benefits from reducing propagule release: fewer AIS, lower densities of each

Relationship between Propagule Pressure and Colonization Pressure Data for ballast water and sediments sampled from ships coming into Canada. Ships are required to flush at sea and take on midocean water, which has fewer species and lower abundances, thus risk should be lower. Briski et al. (2012), Proc. Roy. Soc. B

Invertebrates in ships’ ballast tanks on the Great Lakes Pre-regulation Post-regulation 18000 14000 Invertebrate 10000 Density (Mean + S. E. 4000 individuals. m-3) All Species 4000 Risky Species 3000 2000 1000 0 0 Ballast water exchange reduces density and diversity of species capable of colonizing the Great Lakes, and no new invasions have been reported Bailey et al. (2011) Environmental Science and Technology

Determinants of Invasion Success 1) Hayes & Barry (2008, Biol. Invas. ) reported invasion success determined by: • climate/habitat match • history of invasiveness • propagule pressure 2) Colautti et al. (2006, Biol. Invas. ) reported invasion success determined by: • propagule pressure • history of invasiveness • physiological tolerance (fishes) • disturbance