Food or furniture: Separating trophic and non‐trophic effects of Spanish moss to explain its high invertebrate diversity

Abstract

Foundation species are typically suggested to enhance community diversity non‐trophically by increasing habitat structure and mitigating physical stress, while their trophic role is considered of minor importance. Yet, there is little experimental evidence on the relative importance of trophic and non‐trophic effects and the interaction with patch size. Here, we transplanted different festoon sizes of living Tillandsia usneoides (Spanish moss) and structural mimics assessing the trophic and non‐trophic roles of this habitat‐forming epiphyte in mediating the invertebrate community. Compared to bare branches, mimics enhanced species and feeding guild richness and abundances, but living festoons even more so, demonstrating that trophic and non‐trophic effects jointly stimulated the community. Specifically, our results show that, independent of patch size, 40% of the total species richness and 46% of total guild richness increase could be contributed to habitat structure alone, while Spanish moss trophically stimulated these metrics by another 60% and 54%. As detritivores were particularly enhanced in living festoons, our findings suggest that trophic stimulation occurred primarily through the provisioning of Spanish moss detritus. Our results highlight that foundation species can facilitate their associated communities through both trophic and non‐trophic pathways, calling for studies addressing their indirect trophic role via the brown food web.

Positive cascading effects of epiphytes enhance the persistence of a habitat‐forming macroalga and the biodiversity of the associated invertebrate community under increasing stress

“…In our study, a large biomass of J. rubens , which forms finely branched structures on H. incurva , could have increased organic matter retention, thereby improving habitat quality for detritivores and omnivores. In contrast with studies from terrestrial systems (Angelini & Silliman, 2014; Borst et al., 2019), predators were not facilitated by epiphytes in our study. This could be explained by the fact that most of the predators are highly motile and could be, therefore, considered as transient components of the assemblage supported by H. incurva .…”

“…Dominance of detritivores, which feed on organic matter and transfer it to higher trophic levels, is often reported in epiphyte assemblages, suggesting that detritus‐based food webs mediate carbon transfer in systems with high epiphyte cover (Angelini & Silliman, 2014; Borst et al., 2019; Piazzi et al., 2018). For instance, Borst et al.…”

“…For instance, Borst et al. (2019) demonstrated that the epiphyte bromeliad T. usneoides , on the oak Q. virginiana , by serving as important food source in the form of detritus, increased the abundance of detritivores and omnivores, with subsequent cascading positive effects on predators. In our study, a large biomass of J. rubens , which forms finely branched structures on H. incurva , could have increased organic matter retention, thereby improving habitat quality for detritivores and omnivores.…”

Heterogeneity within and among co-occurring foundation species increases biodiversity

“…functions) to animals, create stronger facilitation cascades than non-living secondary FS. Living secondary FS likely promoted biodiversity because they are edible and produce detritus, thereby supporting both consumer and decomposer-based communities, and by modifying local conditions through metabolic process including gas exchange and excretion 23 , 38 , 57 . Nevertheless, even mimics of secondary FS had positive effects on biodiversity, highlighting the universal importance of habitat space in affecting biodiversity 2 , 40 .…”

Foundation Species Abundance Influences Food Web Topology on Glass Sponge Reefs

“…Many of these studies were either correlative or theoretical papers that assumed that the foundation species was unpalatable to or not consumed by most community members. An experimental study that used habitat mimics to separate the importance of trophic and non-trophic interactions found that both types of interactions were important for structuring communities (Borst et al, 2019). Consequently, the importance of foundation species' trophic interactions in structuring food webs is unclear.…”