Invasive willows drive instream community structure

Abstract

1. Exotic invasive species are known to influence taxonomic communities and ecological processes. Few studies have examined the impact on taxonomic communities across trophic levels because it is time consuming and requires a wide range of identification skills. 2. Here, we examined the impacts of invasive willow trees (Salix spp.) on microbial and macroinvertebrate composition using a combination of high resolution ecogenomic and classical approaches. Aquatic communities were compared and contrasted between stream reaches with and without willow infestation in three temperate Australian streams. 3. Willows significantly altered in-stream fungal, algal and macroinvertebrate communities. Macroinvertebrate diversity was similar between riparian types. Willow-infested sites were characterised by lower macroinvertebrate abundance and Australian biotic index scores, indicating the presence of taxa generally more tolerant to pollution. 4. At invaded sites, grazers were replaced by generalist collector-gatherer taxa and the proportions of macroinvertebrate functional-feeding groups (FFG) were altered such that the primary trophic pathway was changed from an autotrophic algal-based pathway to a heterotrophic, detrital-based pathway. 5. Riparian invasion by willows may change the primary source of energy from autotrophy to heterotrophy in small streams, with knock-on effects on community structure across trophic levels.

The impacts of invasive ecosystem engineers in freshwaters: A review

“…The variety of negative impacts of invasive species on freshwater ecosystems are well documented (e.g. Beatty et al, ; Coffman, Ambrose, & Rundel, ; McInerney et al, ; Tables , ). However, when invasive species are also ecosystem engineers, they have the capacity to change environmental conditions to suit their own needs (Cuddington, Wilson, & Hastings, , Table , Figure ), and reduce suitability for native species (e.g.…”

“…Willows ( Salix spp.) are one example and form thickets in rivers that alter flow and erosion patterns (Boulton et al, ), with their extensive root mats changing benthic habitat structure (Jayawardana, Westbrooke, Wilson, & Hurst, ; McInerney et al, ), as well as benthic invertebrate and microbial community composition (McInerney et al, ; McInerney & Rees, ; Read & Barmuta, ). Ecosystem engineers such as emergent macrophytes may also establish feedback loops that increase their dominance (Figure ).…”

Partitioning of macroinvertebrate communities in a large New Zealand river highlights the role of multiple shore‐zone habitat types

“…Riprap can also reduce wood recruitment and shade along river edges (Reid & Church, ; Massey, Biron, & Choné, ), although in this study, the combination of willow and riprap negated this effect. Shade along willow‐lined reaches, coupled with deciduous leaf fall, can be important bottom‐up drivers of macroinvertebrate community structure along vegetated shore‐zones, mediated by food‐web factors such as organic matter breakdown and algal growth, as reported in Australian streams by McInerney et al (). Finally, riprap can be characterized by higher water velocity than other habitat types (e.g., Massey et al, ; Pander et al, ), but in this study, this was not evident at sampling points likely due to eddies created by large rocks upstream.…”

Spatial prioritization for widespread invasive species control: Trade‐offs between current impact and future spread

“…Willows pose a significant threat to biodiversity within the region. Willows increase shade and water turbidity and change the chemical composition of freshwater streams, impacting water quality, freshwater invertebrates, and fish (McInerney et al, 2016). Willows also outcompete native plants, disrupting native vegetation communities and habitat for riparian species such as lizards and frogs (Cremer, 2003).…”