Experimental Tests of Priority Effects and Light Availability on Relative Performance of Myriophyllum spicatum and Elodea nuttallii Propagules in Artificial Stream Channels

Abstract

Submersed macrophytes have important ecological functions in many streams, but fostering growth of beneficial native species while suppressing weedy invasives may be challenging. Two approaches commonly used in management of terrestrial plant communities may be useful in this context: (1) altering resource availability and (2) establishing desirable species before weeds can invade (priority effects). However, these approaches are rarely used in aquatic systems, despite widespread need for sustainable solutions to aquatic weed problems. In artificial stream channels in California, USA, I conducted experiments with asexual propagules of non-native invasive Myriophyllum spicatum (Eurasian watermilfoil) and native Elodea nuttallii (western waterweed) to address the questions: (1) How does light availability affect relative performance of the two species?; (2) Does planting the native earlier than the invasive decrease survival or growth rate of the invasive?; and (3) Do light level and priority effects interact? The relative performance between E. nuttallii and M. spicatum had an interesting and unexpected pattern: M. spicatum had higher growth rates than E. nuttallii in the zero and medium shade levels, but had similar performance in the low and high shade levels. This pattern is most likely the result of E. nutallii’s sensitivity to both very low and very high light, and M. spicatum’s sensitivity to very low light only. Native priority did not significantly affect growth rate or survival of M. spicatum, possibly because of unexpectedly poor growth of the E. nuttallii planted early. This study suggests that altering light levels could be effective in reducing growth of an invasive macrophyte, and for changing the competitive balance between a native and a non-native species in the establishment phase. Further investigations into the use of priority effects and resource alteration for submersed macrophyte management are warranted, given their mixed results in other (limited) studies.

Shade provided by riparian plants and biotic resistance by macrophytes reduce the establishment of an invasive Poaceae

“…Byun, de Blois & Brisson 2013;Ulrich & Perkins 2014). On the other hand, a lack of effects of early arrivals on invasive growth was found by Zefferman (2015), indicating that the lack of biotic resistance was unlikely to be sufficient if the invasive species grew quickly or if the natives were grazed, as observed in her experiment. In another experiment, natives planted a priori had positive effects on invasive germination, but negative effects on their final biomass (Mason, French & Jolley 2013).…”

“…In the context of invasion biology, some investigations have shown that planting native plants before invasive species arrive may provide resistance to invasion (Byun, de Blois & Brisson 2013;Ulrich & Perkins 2014), but others have found that the early arrival of natives did not reduce invasibility (e.g. Mason, French & Jolley 2013;Zefferman 2015). Thus, the role of priority effects on invasibility is still an open question.…”

“…light) and the biotic resistance provided by native plants that arrive early on invasive macrophytes are poorly known (e.g. Mason, French & Jolley 2013;Zefferman 2015).…”

Ambrosia artemisiifolia control in agricultural areas: effect of grassland seeding and herbivory by the exotic leaf beetle Ophraella communa

“…Studying the role of priority in shaping community composition can address management activities and the choice of native plant assemblages able to inhibit invasive plant species (Zefferman 2015).…”

Historical contingency and spatial processes rather than ecological niche differentiation explain the distribution of invasive goldenrods (Solidago and Euthamia)

“…plant community composition of the new territory, specifically the presence of interacting species, availability of suitable space and resources, and the time a population has been established (Putten et al 2013;Vannette and Fukami 2014;Marchante et al 2015;Young et al 2015). Numerous studies of species' interactions indicate that the order of arrival into an ecosystem, the so-called priority effect (Shulman et al 1983), can influence local community assembly (Fukami 2010;Grman and Suding 2010;Kardol et al 2013;Putten et al 2013;Zefferman 2015;Fraser et al 2015). As a result, ecological contingencies can govern the success of colonisation of dispersing individuals and limit the distribution of invasive species (Ricklefs 2010;Fraser et al 2015).…”