DOI: 10.5061/dryad.h70rxwdqq
title: Trout and invertebrate assemblages in stream pools through wildfire and drought

description: Climate change is increasing the frequency, severity, and extent of
 wildfires and drought in many parts of the world, with numerous
 repercussions for the physical, chemical, and biological characteristics
 of streams. Yet information on how these perturbations affect top
 predators and their impacts on lower trophic levels in streams is limited.
 The top aquatic predator in southern California streams is native
 Oncorhynchus mykiss, the endangered southern California steelhead trout
 (trout). To examine relationships among the distribution of trout,
 environmental factors, and stream invertebrate resources and assemblages,
 we sampled pools in 25 stream reaches that differed in the presence (9
 reaches) or absence (16 reaches) of trout over 12 years, including 8
 reaches where trout were extirpated during the study period by drought or
 post-fire flood disturbances. Trout were present in deep pools with high
 water and habitat quality. Invertebrate communities in trout pools were
 dominated by a variety of medium-sized collector-gatherer and shredder
 invertebrate taxa with non-seasonal life cycles, whereas tadpoles and
 large, predatory invertebrates (Odonata, Coleoptera, Hemiptera (OCH)),
 often with atmospheric breather traits, were more abundant in troutless
 than trout pools. Structural equation modeling (SEM) of the algal-based
 food web indicated a trophic cascade from trout to predatory invertebrates
 to collector-gatherer taxa and weaker direct negative trout effects on
 grazers; however, both grazers and collector-gatherers also were
 positively related to macroalgal biomass. SEM also suggested that
 bottom-up interactions and abiotic factors drove the detritus-based food
 web, with shredder abundance being positively related to leaf litter
 (CPOM) levels, which, in turn, were positively related to canopy cover and
 negatively related to flow. When compared to the literature, these results
 emphasize the context dependency of trout effects on prey communities and
 the relative importance of top-down versus bottom-up interactions on food
 webs, contingent on environmental conditions (flow, light, nutrients,
 disturbances) and the abundances and traits of component taxa.
 Invertebrate assemblage structure changed from a trout to a troutless
 configuration within a year or two after trout were lost owing to
 post-fire scouring flows or drought. Increases in OCH abundance after
 trout were lost were much more variable after drought than after fire. The
 reappearance of trout in one stream where they were lost resulted in
 quick, severe reductions in OCH abundance. These results indicate that
 climate-change induced disturbances can result in the extirpation of a top
 predator, with cascading repercussions for stream communities and food
 webs.  This study also emphasizes the importance of preserving or
 restoring refuge habitats, such as deep, shaded, perennial, cool stream
 pools with high habitat and water quality, to prevent the extirpation of
 sensitive species and preserve native biodiversity during a time of
 climate change. 
description: Sampling of stream invertebrates, observations of trout, and
 measurements of stream abiotic factors.<br>
description: # Trout and invertebrate assemblages in stream pools through wildfire and
 drought Spreadsheets
 (datasets) are organized by type of analyses (multivariate versus
 univariate) and the data used for specific analyses (Multivariate:
 non-metric multi-dimensional scaling (NMS), multi-response permutation
 procedure (MRPP), Indicator Species Analysis (ISA); Univariate: Mixed
 effects models, structural equation models, linear regression, or Analysis
 of Variance (ANOVA) and Tukey's HSD test). The initial ReadMe file
 for multivariate versus univariate analyses shows the focus of analyses,
 the data file (spreadsheet) used for each analysis, the statistical
 analysis performed, the figure associated with each analysis, and the
 number of site-times used in each analysis and, in the case of the
 univariate analyses, the months and years included in analyses. Two
 additional spreadsheets include a ReadMe file dealing with the methods and
 references for assigning traits to collected taxa and a file showing the
 trait designations for collected taxa. ## Description of the data and file
 structure * Multivariate: Data files containing site-time names and the
 absolute abundances (number/30 standard sweeps) of invertebrate taxa,
 followed by codes for stream and time categories and values for abiotic
 measurements. * Univariate: Data files contain site-time names; stream,
 time, and burn codes; t and values of environmental variables, and the
 absolute abundances (number/30 standard sweeps) of invertebrates belonging
 to different traits or taxonomic groups. * Taxa traits: A compendium of
 the traits assigned to collected taxa. Variables and methods are either
 spelled out or defined in the ReadMe Taxa Traits file.