Temporal and nonlinear dispersal patterns of Ludwigia hexapetala in a regulated river
Rivers are vulnerable to biological invasion due to hydrologic connectivity, which facilitates post-entry movement of aquatic plant propagules by water currents. Ecological and watershed factors may influence spatial and temporal dispersal patterns. Field-based data on dispersal could improve risk assessment models and management responses. Ludwigia hexapetala, an invasive emergent macrophyte, provides a case study for understanding dispersal patterns throughout a watershed. The species spreads via hydrochory and is increasingly imposing detrimental ecological and economic impacts within watersheds of the United States and Europe. We investigated morphology of shoot fragments and their dispersal in the Russian River watershed of California, capturing shoot fragments of L. hexapetala during repeated summer surveys at five locations in the river and quantifying their morphological traits that predict establishment success. Highly variable capture counts suggest the importance of pulse disturbance events in local dispersal of L. hexapetala. Unexpectedly, dispersing propagule pressure was nonlinear, with more shoot fragments captured in the middle rather than lower river. Captured fragments in the middle river were twice the length of fragments captured in the lower river and bore 83% more stem nodes, characteristics associated with greater establishment success. Our results support development of spatially targeted management, outreach, and prevention efforts that could lead to decreased propagule pressure in the watershed.
KeywordsAquatic plants Hydrochory Propagule pressure Plant invasions Riverine wetlands Watershed ecology
This research was supported by the US Army Corps of Engineers, Engineer Research and Development Center, Aquatic Plant Control Research Program, Vicksburg, Mississippi, USA. M. Skaer Thomason received support from the USDA-ARS Pathways program for graduate student development, and a subsequent USDA post-doctoral appointment. We thank Rebecca Drenovsky, Eric Wolanski and anonymous reviewers for comments that improved the manuscript. We thank Caryn J. Futrell for chemical laboratory analyses, and Sonoma County Water Agency for technical input and access to sites. We thank Shannon Burke, Malia Forbert, Caryn J. Futrell, Alex Pluchino, and Rachel Stump for assistance in the field and laboratory.
- Boedeltje G, Bakker JP, Bekker RM, Van Groenendael JM, Soesbergen M (2003) Plant dispersal in a lowland stream in relation to occurrence and three specific life-history traits of the species in the species pool. J Ecol 91:855–866. https://doi.org/10.1046/j.1365-2745.2003.00820.x CrossRefGoogle Scholar
- Grewell BJ, Netherland MD, Skaer Thomason MJ (2016a) Establishing research and management priorities for invasive water primroses (Ludwigia spp.). ERDC/EL TR-16-2. US Army Corps of Engineers Research and Development Center, Environmental Laboratory, VicksburgGoogle Scholar
- Grewell BJ, Skaer Thomason MJ, Futrell CJ, Iannucci M, Drenovsky RE (2016b) Trait responses of invasive aquatic macrophyte congeners: colonizing diploid outperforms polyploid. AoB Plants 8:plw014. https://doi.org/10.1093/aobpla/plw014
- Haury J, Druel A, Cabral T, Paulet Y, Bozec M, Coudreuse J (2014) Which adaptations of some invasive Ludwigia spp. (Rosidae, Onagraceae) populations occur in contrasting hydrological conditions in western France? Hydrobiologia 737:45–56. https://doi.org/10.1007/s10750-014-1815-7 CrossRefGoogle Scholar
- Levine JM, Murrell DJ (2003) The community-level consequences of seed dispersal patterns. Annu Rev Ecol Evol Syst 34:549–574. https://doi.org/10.1146/annurev.ecolsys.34.011802.132400 CrossRefGoogle Scholar
- Merritt DM, Wohl EE (2002) Processes governing hydrochory along rivers: hydraulics, hydrology, and dispersal phenology. Ecol Appl 12:1071–1087. https://doi.org/10.1890/1051-0761(2002)012[1071:PGHARH]2.0.CO;2 CrossRefGoogle Scholar
- Nelson N (1944) A photometric adaptation of the Somogyi method for determination of glucose. J Biol Chem 153:375–380Google Scholar
- Pollen-Bankhead N, Thomas RE, Gurnell AM, Liffen T, Simon A, O’Hare MT (2011) Quantifying the potential for flow to remove the emergent aquatic macrophyte Sparganium erectum from the margins of low-energy rivers. Ecol Eng 37:1779–1788. https://doi.org/10.1016/j.ecoleng.2011.06.027 CrossRefGoogle Scholar
- US Geological Survey (2017) National Water Information System. https://waterdata.usgs.gov/nwis
- Wagner WL, Hoch PC, Raven PH (2007) Revised classification of the Onagraceae. Syst Bot Monogr 83:1–240Google Scholar