Abstract
In aquatic systems, invasive submerged macrophytes considerably alter the structure and functioning of communities, thus potentially compromising ecosystem services. The prolific spread of invasive macrophytes is often aided by vegetative fragment propagation, yet the contributions of various commonly occurring invertebrates to such fragmentation are often unquantified. In the present study, we examine fragmentary spread of invasive macrophytes by a group of shredder-herbivores, larval caddisflies. Through novel application of the comparative functional response (FR; resource use as a function of density) approach to the native case-building species Limnephilus lunatus, we compared utilisation of non-native waterweeds Elodea canadensis and E. nuttallii in mono- and polycultures. Furthermore, we quantified de-cased and cased caddisfly-induced fragment production and length changes among non-native E. canadensis, E. nuttallii, Crassula helmsii and Lagarosiphon major under two different plant orientations: horizontal (floating) versus vertical (upright) growth forms. Larval caddisflies exhibited Type II (hyperbolic) FRs towards both Elodea species, and utilised each plant at similar rates when plants were provided separately. When plant species were presented in combination horizontally, E. canadensis was significantly less utilised compared to E. nuttallii, corroborating observations in the field. De-cased larvae produced new plant fragments for all four aquatic macrophytes, whereas cased larvae fragmented plants significantly less. Elodea nuttalii and C. helmsii were fragmented the most overall. Crassula helmsii was utilised to the greatest extent when plants were horizontally orientated, and Elodea species when vertically orientated. This study identifies and quantifies a mechanism from a novel species group that may contribute to the spread of invasive macrophytes in aquatic systems. Whilst exploititative interactions are thought to impede invasion success, here we demonstrate how resource utilisation by a resident species may exacerbate propagule pressure from an invasive species.
Highlights
Freshwater ecosystems are increasingly invaded by alien species introduced accidentally or deliberately (Dudgeon et al 2006; Ricciardi 2006; Seebens et al 2017)
In L. lunatus-free controls, 100% of the original mass of both Elodea species remained at the end of the experiment
We have identified a potential mechanism that promotes the differential propagation of invasive macrophytes, depending on the plant-specific fragmentation properties
Summary
Freshwater ecosystems are increasingly invaded by alien species introduced accidentally or deliberately (Dudgeon et al 2006; Ricciardi 2006; Seebens et al 2017). Alien species can impact biodiversity and alter key ecosystem functions such as productivity, nutrient cycling and hydrology (Dudgeon et al 2006; Oreska and Aldridge 2011; Piria et al 2017; Crane et al 2020). Invasive macrophytes can form dense monotypic stands that alter physical habitat and biotic (vegetation, macroinvertebrates and fish) communities, as well as the interactions within and between these communities (Dibble et al 1996). In response to abiotic factors such as wind, waves and water currents, human
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
