Stream macroinvertebrate assemblage uniformity and drivers in a tropical bioregion

Abstract

Summary Understanding spatial and environmental drivers of undisturbed stream assemblages is important for separating natural and human‐induced changes, but has rarely been attempted for an entire tropical bioregion. We sampled riffle macroinvertebrate assemblages and measured associated biophysical variables in post‐wet and dry seasons from 68 streams of orders 1–5 across the Australian Wet Tropics, a small bioregion (18 497 km2) defined by its warm moist climate and closed‐forest vegetation. As climate and landscape were relatively uniform across the bioregion, we predicted that assemblages would be similar, with turnover (beta diversity) unrelated to distance, and with composition determined mainly by habitat. We identified 93 higher taxa. Density and richness of macroinvertebrates were greatest in the dry season because of habitat contraction and minimal flow disturbance. Richness was greatest in higher order streams. Relative abundance and richness of functional groups showed minor effects of catchment, lithology and stream order, and a positive relationship with altitude for richness of collectors, predators and shredders, and for abundance of shredders. Distance‐based linear modelling showed that among‐assemblage differences were explained by landscape‐scale variables (9.5% of the variation), stream size (13.0%), riparian characteristics (9.6%), water quality (4.6%), substratum (21.1%) and organic resources (22.4%); for models of individual taxa and functional groups, habitat and organic‐resource variables also predominated. Similarities among site assemblages differed little among catchments and there was no relationship between pairwise similarities of catchments and their geographical distances. Nestedness analysis confirmed that samples and catchment groupings were nested subsets of the total set of samples. Across the Australian Wet Tropics, uniformity of assemblages (identified to family or above) conformed to the bioregional classification, probably as a result of the great age of the region. The habitat variables that most influenced macroinvertebrate assemblages support the idea that a suite of biophysical influences is common to stream macroinvertebrate assemblages globally.

Hydrology, hydraulics and scale influence macroinvertebrate responses to disturbance in tropical streams

“…In PNG, flows have high day-to-day variability but low monthly variability (Yule and Pearson 1996) (Table 2). The AWT study sites were Birthday and Yuccabine Creeks in the uplands, and Pixies Creek in the lowlands, all having characteristics of other AWT low-order forest streams (Pearson et al 2017). The PNG sites were lowland low-order forest streams, Tam Creek and Creek 115, tributaries of the Ok Tedi River, which had similar characteristics to the AWT streams, apart from their contrasting hydrographs.…”

Environmental and spatial drivers of oligochaeta metacommunities structure along the Paraguay‐Paraná fluvial system

“…to these categories. Regarding benthic invertebrates, there is extensive evidence that organic matter content in sediments and granulometry are master variables affecting their distributions in large rivers (e.g., Blettler et al, 2016;Ezcurra de Drago et al, 2007;Pearson et al, 2017;Takeda & Fujita, 2004;Wantzen et al, 2014). For this reason, we consider that, at least for Oligochaeta, the upper catchment presents more heterogeneous habitats than higher order rivers.…”

Urbanisation alters fatty acids in stream food webs

“…The significant increase in Σω3 FAs and EPA proportions in shredders indicated that periphyton growth, and their FAs, increased on leaf litter and/or transported matter, as catchment urbanisation increased (Guo, Kainz, Valdez, Sheldon, & Bunn, ). An increase in proportions of Σω3 FAs and EPA of periphyton and macroinvertebrates may seem like beneficial responses to urbanisation, but these possibly could be outweighed by the negative and well‐documented effects of altered habitat, hydrology, and other stressors on the biomass and diversity of periphyton and macroinvertebrate communities (Hoyle, Kilroy, Hicks, & Brown, ; Moore & Palmer, ; Pearson et al., ; Roy, Rosemond, Paul, Leigh, & Wallace, ; Smucker & Detenbeck, ). Sensitive periphyton and macroinvertebrate taxa that thrive in minimally‐impacted systems are replaced by those with faster growth rates or higher P content under greater nutrient availability and by those more tolerant to altered habitat and deteriorated water quality (King et al., ; Morse, Wollheim, Benstead, & McDowell, ; Stevenson, Hill, Herlihy, Yuan, & Norton, ; Tsoi, Hadwen, & Fellows, ).…”