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    Esa 2013 presentation (final) Esa 2013 presentation (final) Presentation Transcript

    • Latitudinal variation in tritrophic interactions associated with native and exotic genotypes of Phragmites australis Warwick Allen, Randee Young, Ganesh Bhattarai, Jordan Croy, and James Cronin Louisiana State University wallen7@lsu.edu Laura Meyerson University of Rhode Island
    • Invasive Species • One of the world’s worst environmental problems • Enemy-release hypothesis (Elton 1958) is a wellsupported mechanism explaining invasion success 1) Decreased herbivory in introduced range relative to native range 2) Greater impact of herbivores on natives than exotics in introduced range • Influence of higher trophic levels has been ignored (Harvey et al. 2010) Hyalopterus pruni and predator
    • Latitudinal Gradients • Theory predicts that species interactions increase in strength towards the tropics Interaction Strength • Little is known about how mechanisms of invasion success may change over broad spatial scales Latitude
    • Latitudinal Gradients • Little is known about how mechanisms of invasion success may change over broad spatial scales • Theory predicts that species interactions increase in strength towards the tropics Herbivory Chemical defense • Mixed results in empirical studies (Moles et al. 2011 meta-analysis) • Latitudinal gradients in species interactions may alter invasion success Physical defense
    • Phragmites australis (common reed) • Tall perennial grass • Virtually worldwide distribution • Found in brackish and freshwater marshes, pond edges, ditches, and other disturbed wet areas
    • Phragmites australis (common reed) • Multiple native and invasive genotypes in North America • Exotic genotype M ( ) from Europe (mid 1800s) forms extensive monocultures – Known invasion history • Gulf genotype I ( ) prevalent 25 yrs. a in the south • Native genotypes (all others) widespread but declining 100 yrs. 50 yrs. Exotic Gulf All others native Modified from Saltonstall (2002)
    • Gallers: Lipara spp. (Chloropidae) • Introduced from Europe L. rufitarsis • Specialists on P. australis – L. rufitarsis – L. pullitarsis – L. similis L. similis • Inquilines (commensals) and natural enemies Calamoncosis sp. Anthomyza sp. L. pullitarsis • Galls inhibit flowering 100% of time – Damage quantified as proportion of stems infested – Biological control potential?
    • Research Objectives 1. Examine distribution of Lipara spp. in North America 2. Test for the presence and direction of latitudinal gradients in herbivory, parasitism, predation, and commensalism 3. Compare patterns of species interactions between P. australis genotypes to investigate implications for invasion success 4. Explore the potential of Lipara spp. as biological control agents of invasive P. australis
    • Methods: Field Survey • 120 sites sampled in NA (M, I, and native genotypes) • 21 sites in Europe Exotic (M) Gulf (I) Native
    • Lipara spp. and Associates Survey • 26 sites with Lipara spp. present in NA • Data collected: – Infestation rate (Europe also) – Flowering frequency – Stems reared or dissected (Lipara species, predation/parasitism rate, inquilines) – Lipara and associates performance (body mass) L. rufitarsis and inquiline
    • Lipara spp. Distribution Lipara present Exotic (M) Gulf (I) Native Lipara absent Exotic (M) Gulf (I) Native
    • Lipara spp. Distribution Lipara present Exotic (M) Gulf (I) Native Lipara absent Exotic (M) Gulf (I) Native
    • Lipara spp. Distribution Lipara present Exotic (M) Gulf (I) Native Lipara absent Exotic (M) Gulf (I) Native
    • Lipara spp. Latitudinal Gradients Proportion of stems galled by Lipara spp. • Infestation rate increases with latitude Native Exotic (M) 0.6 Genotype – F1, 24 = 20.813, P < 0.001 Latitude – F1, 24 = 8.509, P = 0.008 0.5 0.4 R² = 0.261 0.3 Enemy release 0.2 R² = 0.276 0.1 0 36 37 38 39 40 41 Site Latitude 42 43 44 45
    • Lipara spp. Infestation Rate • Higher in NA native and invasive genotypes than Europe Proportion of stems galled by Lipara spp. 0.4 a F2, 44 = 31.483, P < 0.001 Error bars = 95% CI 0.35 0.3 0.25 0.2 b 0.15 0.1 0.05 c 0 North America Native North America Invasive (M) Europe (M) Phragmites australis genotype/location
    • Lipara rufitarsis body mass • Body mass marginally higher in L. rufitarsis developing on native P. australis genotypes • Body mass decreases marginally with latitude F1, 17 = 3.509, P = 0.078 Error bars = 95% CI 2.5 2 1.5 1 0.5 0 Native Invasive (M) Phragmites australis genotype Native Invasive (M) 2.9 Mean weight per individual (mg) Mean weight per individual (mg) 3 2.7 F1, 17 = 3.720, P = 0.071 2.5 2.3 R² = 0.082 2.1 R² = 0.405 1.9 1.7 1.5 36 38 40 Latitude 42 44
    • Lipara spp. Parasitism/Predation • Parasitism/predation by arthropods – 0% in NA – 26% on L. rufitarsis in UK (Reader 2003) – 19% on L. rufitarsis and 22% on L. similis in Germany (Tscharntke 1994) – Europe species rich in parasitoids (Nartshuk 2006) *
    • Proportion of Lipara spp. galls containing inquilines Lipara spp. Inquilines • Inquiline frequency of occurrence Calamoncosis sp. Anthomyza sp. 0.6 F1, 18 = 0.427, P = 0.552 Error bars = 95% CI 0.5 0.4 0.3 0.2 0.1 0 Native Invasive (M) Phragmites australis genotype • Follows pattern of infestation rate of Lipara spp. Proportion of Lipara spp. galls containing inquilines • Latitudinal pattern but no difference between genotypes 0.9 F1, 18 = 48.982, P < 0.001 0.8 0.7 R² = 0.796 Native Invasive (M) 0.6 0.5 R² = 0.679 0.4 0.3 0.2 0.1 0 36 38 40 42 Latitude 44 46
    • Conclusions • Lipara species currently restricted to eastern US – L. rufitarsis common from NC-ME, L. similis abundant in Northeast, L. pullitarsis only in Mid-Atlantic • Latitudinal gradients present in herbivory, inquiline frequency, and possibly performance • Enemy release from Lipara spp. may contribute to P. australis invasion success in NA – Biological control using Lipara spp. unlikely to succeed • Higher trophic levels not influencing invasion success – Lack of natural enemies may explain higher infestation rates relative to Europe
    • Future Directions • Common garden experiment – Test if patterns found in field survey have a genetic basis – Examine traits underlying oviposition preference – URI common garden (>200 P. australis populations from NA) • L. rufitarsis galls collected from nearby field site and spread throughout garden
    • • Cronin Lab – – – – Ganesh Bhattarai Anthony Chow Forrest Dillemuth Heidi Stevens • Undergraduates – – – – – – Acknowledgements Randee Young Jordan Croy Ray Andrews Allison Hunt April Simmons Patrick Mooney • Land Owners – – – – – – – – Mackay Island National Wildlife Refuge Palm Beach County Parks Department Rockefeller Wildlife Refuge Alice Welford Pettipaug Yacht Club Rachel Carson National Wildlife Refuge The Nature Conservancy Estell Manor State Park • Committee/Advisors – – – – – – Jim Cronin Kyle Harms Mike Stout James Geaghan Laura Meyerson Bret Elderd • Funding Sources – NSF (DEB 1050084) – LEEC – LSU BioGrads
    • Questions?