Habitat Complexity in Aquatic Microcosms Affects Processes Driven by Detritivores

Abstract

Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure. Here, we focussed on how complexity of artificial habitat (plastic plants), in microcosms, influenced short-term processes driven by three aquatic detritivores. The effects of habitat complexity on leaf decomposition, production of fine organic matter and pH levels were explored by measuring complexity in three ways: 1. as the presence vs. absence of habitat structure; 2. as the amount of structure (3 or 4.5 g of plastic plants); and 3. as the spatial configuration of structures (measured as fractal dimension). The experiment also addressed potential interactions among the consumers by running all possible species combinations. In the experimental microcosms, habitat complexity influenced how species performed, especially when comparing structure present vs. structure absent. Treatments with structure showed higher fine particulate matter production and lower pH compared to treatments without structures and this was probably due to higher digestion and respiration when structures were present. When we explored the effects of the different complexity levels, we found that the amount of structure added explained more than the fractal dimension of the structures. We give a detailed overview of the experimental design, statistical models and R codes, because our statistical analysis can be applied to other study systems (and disciplines such as restoration ecology). We further make suggestions of how to optimise statistical power when artificially assembling, and analysing, ‘habitat complexity’ by not confounding complexity with the amount of structure added. In summary, this study highlights the importance of habitat complexity for energy flow and the maintenance of ecosystem processes in aquatic ecosystems.

From individuals to communities: Habitat complexity affects all levels of organization in aquatic environments

“…Several methods were devised to measure habitat provisioning by the different types of HC, including fractal dimension (Tokeshi & Arakaki, 2012) and habitat heterogeneity (Carvalho & Barros, 2017), and to specify HC quantity (Dibble & Thomaz, 2006) and quality (Warfe et al, 2008). Fractal dimension can describe the dimensionality of the environment (Flores et al, 2016; Grutters et al, 2015). Various indices can quantify habitat provisioning by macrophyte beds using their architecture (Lillie & Budd, 1992) or interstitial distance between structures like stems or branches (Dibble et al, 1996).…”

Hasse diagrams as a visual aid for linear models and analysis of variance

“…There is no evidence that any larger model does any better. Example 14 (Habitat complexity) Flores et al (2016) describe some experiments to investigate how habitat complexity affects biodiversity. In one experiment, the treatments were all combinations of levels of two factors.…”

“…The anova for one of the responses given by Flores et al (2016) gives the scaled Hasse diagram in Figure 20. To avoid confusion, two models have not been named.…”