<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaChapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> Spartinageese preference in <str<strong>on</strong>g>the</str<strong>on</strong>g> first experiment was based <strong>on</strong>differences in defensive chemistry between native S. foliosaand hybrid Spartina, <str<strong>on</strong>g>the</str<strong>on</strong>g>y would presumably still be able touse those cues in <str<strong>on</strong>g>the</str<strong>on</strong>g> sec<strong>on</strong>d trial. We also measureddifferences in <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> material that geese discarded toexplore <str<strong>on</strong>g>the</str<strong>on</strong>g> idea that geese might discard a greaterproporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid if defensive chemistry was a cue.However, we measured no significant differences indiscarded material between native and hybrid Spartina.Our results parallel o<str<strong>on</strong>g>the</str<strong>on</strong>g>r studies <str<strong>on</strong>g>of</str<strong>on</strong>g> factors influencinggoose grazing. Earlier work by Buchsbaum et al. (1981)with eastern Canada geese (Branta canadensis canadensis)suggested that geese can detect defensive compounds suchas ferulic acid in lawn grass. Their results suggest thatphenolics at relatively high c<strong>on</strong>centrati<strong>on</strong>s could beimportant in grazing preferences. O<str<strong>on</strong>g>the</str<strong>on</strong>g>r studies havegenerally found less support for <str<strong>on</strong>g>the</str<strong>on</strong>g> role <str<strong>on</strong>g>of</str<strong>on</strong>g> phenolicsinfluencing goose grazing. A study with greater snow geese(Anser caerulescens atlantica) tested <str<strong>on</strong>g>the</str<strong>on</strong>g> influence <str<strong>on</strong>g>of</str<strong>on</strong>g> water,fiber, phenolic and protein c<strong>on</strong>tent am<strong>on</strong>g grass species andfound that <strong>on</strong>ly water c<strong>on</strong>tent was important (Gauthier andBedard 1991). Ano<str<strong>on</strong>g>the</str<strong>on</strong>g>r study using barnacle geese (Brantaleucopsis) found that feeding preferences <str<strong>on</strong>g>of</str<strong>on</strong>g> geese were bestcorrelated with water and nitrogen c<strong>on</strong>tent, although <str<strong>on</strong>g>the</str<strong>on</strong>g>relati<strong>on</strong>ship with water was str<strong>on</strong>ger (Owen et al. 1977).Coleman and Boag (1987) found that for western Canadageese n<strong>on</strong>-structural carbohydrate and not fiber or proteinc<strong>on</strong>tent was <str<strong>on</strong>g>the</str<strong>on</strong>g> best predictor <str<strong>on</strong>g>of</str<strong>on</strong>g> preferences am<strong>on</strong>g foragespecies. Structural compounds such as cellulose have alsobeen found to be poorly digested by geese relative toproteins and soluble carbohydrates (Buchsbaum et al. 1986).The c<strong>on</strong>clusi<strong>on</strong>s from our study are generally c<strong>on</strong>sistent with<str<strong>on</strong>g>the</str<strong>on</strong>g>se o<str<strong>on</strong>g>the</str<strong>on</strong>g>r studies that found little evidence for a str<strong>on</strong>g rolefor defensive chemicals such as phenolics in determining <str<strong>on</strong>g>the</str<strong>on</strong>g>observed preferences and str<strong>on</strong>ger influences <str<strong>on</strong>g>of</str<strong>on</strong>g> structuralcompounds, nitrogen and water c<strong>on</strong>tent. Interestingly,native S. foliosa has a lower carb<strong>on</strong> to nitrogen (C:N) ratio(more protein, less cellulose) relative to hybrid Spartina(Tyler et al. 2007), and also has a less coarse physicalstructure and presumably higher water c<strong>on</strong>tent.In summary, our results suggest that Canada geese maybe influencing <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> spread <str<strong>on</strong>g>of</str<strong>on</strong>g> hybrid Spartina in <str<strong>on</strong>g>the</str<strong>on</strong>g>central porti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> San Francisco Bay. The eventual loss <str<strong>on</strong>g>of</str<strong>on</strong>g>native S. foliosa due to <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid invasi<strong>on</strong>, at least in someporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> San Francisco Bay, could also have negativec<strong>on</strong>sequences for foraging by removing a potentiallyimportant food source. The intense and highly selectivegrazing <strong>on</strong> native Spartina and almost total avoidance <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>hybrid results from a str<strong>on</strong>g preference for <str<strong>on</strong>g>the</str<strong>on</strong>g> native that isapparently based <strong>on</strong> structural ra<str<strong>on</strong>g>the</str<strong>on</strong>g>r than chemicaldifferences.ACKNOWLEDGMENTSOur greatest thanks to J. Black, Humboldt StateUniversity, for many informative discussi<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> geese andgrazing, his very generous assistance and collaborati<strong>on</strong> with<str<strong>on</strong>g>the</str<strong>on</strong>g> HSU captive goose facility and his help with permitting,logistics, and procedures for behavioral studies. We alsothank HSU students E. Bjerre and K. Spragens for <str<strong>on</strong>g>the</str<strong>on</strong>g>irgenerous assistance with followup experiments, aviarylogistics and Spartina care. We also thank S. Nort<strong>on</strong>, N.Rayl, U. Mahl, N. Christiansen and C. Love for help withfield grazing studies, plant collecti<strong>on</strong>s, sample processingand data entry.REFERENCESAyres, D.R., D. Garcia-Rossi, H.G. Davis, and D.R. Str<strong>on</strong>g1999. Extent and degree <str<strong>on</strong>g>of</str<strong>on</strong>g> hybridizati<strong>on</strong> between exotic(Spartina alterniflora) and native (S. foliosa) cordgrass(Poaceae) in California, USA determined by random amplifiedpolymorphic DNA (RAPDs). Molecular Ecology 8:1179-1186.Ayres D.R., D.L. Smith, K. Zaremba, S. Klohr, and D.R.Str<strong>on</strong>g. 2004. Spread <str<strong>on</strong>g>of</str<strong>on</strong>g> exotic cordgrasses and hybrids(Spartina sp.) in <str<strong>on</strong>g>the</str<strong>on</strong>g> tidal marshes <str<strong>on</strong>g>of</str<strong>on</strong>g> San Francisco Bay,California, USA. Biological Invasi<strong>on</strong>s 6: 221-231.Banks, R.C., C. Cicero, J.L. Dunn, A.W. Kratter, P.C. Rasmussen,J.V. Remsen, J.D. Rising, and D.F. Stotz. 2004.Forty-fifth supplement to <str<strong>on</strong>g>the</str<strong>on</strong>g> American Ornithologists'Uni<strong>on</strong> Check-list <str<strong>on</strong>g>of</str<strong>on</strong>g> North American Birds. Auk 121:985-995.Buchsbaum, R., I. Valiela, and J. Teal. 1981. Grazing byCanada geese and related aspects <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> chemistry <str<strong>on</strong>g>of</str<strong>on</strong>g> saltmarsh vegetati<strong>on</strong>. Col<strong>on</strong>ial Waterbirds 4: 126-131.Buchsbaum, R., J. Wils<strong>on</strong>, and I.Valiela. 1986. Digestibility<str<strong>on</strong>g>of</str<strong>on</strong>g> plant c<strong>on</strong>stituents by Canada geese and Atlantic Brant.Ecology 67: 386-393.Coleman, T.S., and D.A. Boag. 1987. Canada goose foods:<str<strong>on</strong>g>the</str<strong>on</strong>g>ir significance to weight gain. Wildfowl 38: 82-88.Cohen, A.N., and J.T. Carlt<strong>on</strong>. 1998. Accelerating invasi<strong>on</strong>rate in a highly invaded estuary. Science 279: 555-558.Daehler, C.C., and D.R. Str<strong>on</strong>g. 1997. Reduced herbivoreresistance in introduced smooth cordgrass (Spartina alterniflora)after a century <str<strong>on</strong>g>of</str<strong>on</strong>g> herbivore-free growth.Oecologia 110: 99-108.Faber, R.M. 2000. Good intenti<strong>on</strong>s g<strong>on</strong>e awry. CaliforniaCoast and Ocean 16: 14-17.Gauthier, G., and J. Bedard. 1991. Experimental tests <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>palatability <str<strong>on</strong>g>of</str<strong>on</strong>g> forage plants in greater snow geese. Journal<str<strong>on</strong>g>of</str<strong>on</strong>g> Applied Ecology 28: 491-500.Lang, A., and J.M. Black. 2001. Foraging efficiency in BarnacleGeese Branta leucopsis: a functi<strong>on</strong>al resp<strong>on</strong>se tosward height and an analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> sources <str<strong>on</strong>g>of</str<strong>on</strong>g> individualvariati<strong>on</strong>. Wildfowl 52: 7-20.Levin, L.A., C. Neira, and E.D. Grosholz. 2006. <strong>Invasive</strong>cordgrass modifies wetland trophic functi<strong>on</strong>. Ecology 87:419-432.- 195 -
Chapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> Spartina<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaNeira, C., L.A. Levin, and E.D. Grosholz. 2005. Benthicmacr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunal communities <str<strong>on</strong>g>of</str<strong>on</strong>g> three Spartina-hybrid invadedsites in San Francisco Bay, with comparis<strong>on</strong> to uninvadedhabitats. Marine Ecology Progress Series292:111-126.Neira, C., E.D. Grosholz, L.A. Levin, and R. Blake. 2006.Mechanisms generating modificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> benthos followingtidal flat invasi<strong>on</strong> by a Spartina (alterniflora X foliosa)hybrid. Ecological Applicati<strong>on</strong>s 16:1391-1404.Neira, C., L.A. Levin, E.D. Grosholz, and G. Mendoza.2007. The influence <str<strong>on</strong>g>of</str<strong>on</strong>g> invasive Spartina growth phases<strong>on</strong> associated macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunal communities. Biological Invasi<strong>on</strong>s9:975-993.Owen, M., M. Nugent, and N. Davies. 1977. Discriminati<strong>on</strong>between grass species and nitrogen-fertilized vegetati<strong>on</strong>by young Barnacle Geese. Wildfowl 28:21-26.Poole, A. (Editor). 2005. The birds <str<strong>on</strong>g>of</str<strong>on</strong>g> North America <strong>on</strong>line:http://bna.birds.cornell.edu/BNA/. Cornell Laboratory <str<strong>on</strong>g>of</str<strong>on</strong>g>Ornithology, Ithaca, NY.Tyler, A.C., J.G. Lambrinos, and E.D. Grosholz. 2007. Nitrogeninputs promote <str<strong>on</strong>g>the</str<strong>on</strong>g> spread <str<strong>on</strong>g>of</str<strong>on</strong>g> an invasive marshgrass. Ecological Applicati<strong>on</strong>s 17:1886-1898.- 196 -
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