Stream mosses as chemically‐defended refugia for freshwater macroinvertebrates

Abstract

Marine and terrestrial studies show that small, sedentary herbivores that utilize plants as both food and habitat can gain enemy-free space by living on hosts that are chemically defended from larger, generalist consumers. Although large herbivores are increasingly recognized as important consumers of macrophytes in freshwater communities, the potential indirect effects of herbivory on plant-associated macroinvertebrates have rarely been studied. Here, we show that the large, generalist consumers in a riverine system, Canada geese, Branta canadensis , and crayfish, Procambarus spiculifer , both selectively consumed riverweed, Podostemum ceratophyllum , over an aquatic moss, Fontinalis novae-angliae, even though moss comprised 89% of the total plant biomass on riverine rocky shoals. Moss supported twice as many plant-associated macroinvertebrates as riverweed, suggesting that it might provide a spatial refuge from consumption by these larger consumers. Bioassay-guided fractionation of moss extracts led to the isolation of a C 18 acetylenic acid, octadeca-9,12-dien-6-ynoic acid, that deterred crayfish feeding. In contrast to results with Canada geese and crayfish, both the amphipod Crangonyx gracilis and the isopod Asellus aquaticus consumed significant amounts of moss but rejected riverweed in laboratory feeding assays. Moreover, neither amphipod nor isopod feeding was deterred by the crude organic extract of Fontinalis , suggesting that these mesograzers tolerate or circumvent the chemical defenses that deterred larger consumers. Thus, herbivory by large, generalist herbivores may drive freshwater plant community structure towards chemically defended plants and favor the ecological specialization of smaller, less mobile herbivores on unpalatable hosts that represent enemy-free space.

Bryophytes as food: comparative consumption and utilization of mosses by a generalist insect herbivore

“…This study offers strong evidence that mosses are chemically defended against generalist herbivores, corroborating other studies (Davidson et al., 1989, 1990; Parker et al., 2007), and suggesting mosses should be given much more attention in the field of plant–insect interactions. Secondary chemicals of mosses have been largely ignored by chemical ecologists and agricultural entomologists, but they might offer novel pathways of defense that have proved effective over evolutionary timescales.…”

“…Most previous work on chemical defenses of bryophytes has implicated phenolic compounds, which tend to be soluble in water (Davidson et al., 1989; Liao, 1993; Glime, 2006). However, Parker et al. (2007) thoroughly explored the bioactivity of extracts of the aquatic moss F. novae‐angliae , and found that hexane‐ and chloroform‐soluble fractions were deterrent to stream herbivores, but water‐soluble fractions showed no activity.…”

“…Glime (2006) reviewed previous work and presented several original studies pointing toward the importance of phenolic compounds in deterring herbivory by molluscs and isopods. Parker et al. (2007) found evidence that the aquatic moss Fontinalis novae‐angliae Sull.…”

Aquatic Plant Dynamics in Lowland River Networks: Connectivity, Management and Climate Change

“…There are many complex co-evolving biotic interactions [106][107][108]. We only tested here for the effect of green algae cover on vascular plants.…”

Influence of bryophyte biomass and organic matter quantity on the abundance and richness of oligochaetes in forest streams with different phytophysiognomies in southeastern Brazil

“…The bryophytes associated with stones in low-order lotic environments accumulate particulate organic matter (Habdija et al, 2004) and are used as substrate for colonization of periphyton (Stream Bryophyte Group, 1999), providing food and shelter against the water current (Rosa et al, 2011(Rosa et al, , 2013Rodrigues et al, 2013) and refuge from predators (Glime and Clemons, 1972;Parker et al, 2007;Alvarez and Peckarsky, 2013) for various species of aquatic invertebrates. Several studies (Percival and Whitehead, 1929;Suren, 1993;Linhart et al, 2002;Tokeshi and Arakaki, 2012) have shown that these plants contribute to the dimensional complexity of the habitat within the stream flow, because they increase the surface area that can be colonized, resulting in a positive variation in the density and diversity of invertebrates.…”