Fig. 1 Conceptual diagram or metamodel of major hypothesized influences on ACSP. Covariates that are external to stream ecosystems (i.e., exogenous variables) are indicated by rectangles. Covariates that are direct measures of in-stream conditions or processes (i.e., endogenous variables) are indicated by ovals. Each covariate is also recognized as one of five color-coded types (see inset key): biogeography, climate, terrestrial habitat, in-stream habitat, and community. Solid black arrows depict known causal effects among covariates. Arrow labels correspond to exemplar references [A (23, 25), B (26, 27), C (35, 94), D (22, 95), E (36, 96), F (7, 28), G (29, 33), H (34, 97)]. Parenthetic signs next to black arrow labels indicate that the relationship is expected to be positive (+), negative (−), or variable (+/−). Solid green arrows depict fundamental relationships that are expected but not explicitly documented here (e.g., the negative relationship between latitude and air temperature). Dashed arrows depict hypothesized covariation among variables.
Fig. 2 SEMs of ACSP in streams and rivers. Models include an SEM for the U.S. (A) and for global streams and rivers (B). Exogenous variables are indicated by rectangles, and endogenous variables are represented by ovals. Coefficients of determination (r2) are shown for all endogenous variables, and standardized path coefficients are shown for all modeled relationships. Positive and negative effects among variables are depicted by black and red arrows, respectively, with arrow widths proportional to effect sizes (i.e., path coefficients). In the U.S. model, significant covariance between mean annual water temperature (“Water temperature”) and the minimum average discharge that persists for 30 consecutive days (“30-day consec. flow”) is depicted by a dashed double-headed arrow. In the global model, the dashed arrow between mean annual precipitation (“Precipitation”) and mean annual water temperature indicates a nominally significant (P = 0.09) effect; all other relationships in the U.S. and global models are significant at P = 0.05. Both the U.S. and global models satisfied each of the three model fit criteria, with significant χ2 P values (U.S. = 0.06; global = 0.63), standardized root mean squared residuals (U.S. = 0.06; global = 0.02), and comparative fit index values (U.S. = 0.97; global > 0.99). Inset histograms show the distribution of natural log (ln)–transformed ACSP at U.S. and global scales. Covariate types are as shown in Fig. 1.
- Table 1 Comparison of effect sizes in univariate regression models of ACSP in U.S. streams.
Unstandardized regression slopes (b) and standardized slopes (β) are each reported with 95% confidence intervals (shown in parentheses) as well as sample sizes (n) and coefficients of determination (r2). Covariates shown in bold text have slopes (95% confidence intervals) that exclude zero and are therefore considered statistically significant.
Hypothesized effect Covariate n b β r2 Temperature Mean annual air
temperature128 1.32 (−0.11 to 2.75) 0.16 (−0.01 to 0.34) 0.02 Mean annual water
temperature107 1.32 (0.74 to 1.90) 0.39 (0.22 to 0.57) 0.15 Canopy shading % Forest cover in
catchment128 −0.56 (−1.06 to −0.06) −0.19 (−0.37 to −0.02) 0.03 Stream size Basin area 128 0.10 (0.02 to 0.19) 0.21 (0.03 to 0.38) 0.03 Mean annual discharge 102 0.04 (−0.03 to 0.11) 0.10 (−0.08 to 0.27) <0.01 Hydrology Flashiness 124 −0.23 (−0.64 to 0.19) −0.10 (−0.27 to 0.08) <0.01 CV discharge 124 −0.20 (−0.86 to 0.45) −0.06 (−0.24 to 0.13) 0.01 Minimum 30-day
consecutive flow124 1.36 (0.39 to 2.33) 0.24 (0.07 to 0.42) 0.05 Channel substrate Average sediment size
(unweighted)88 −0.10 (−0.22 to 0.02) −0.17 (−0.38 to 0.04) 0.02 Average sediment size
(weighted)88 −0.12 (−0.24 to 0.00) −0.20 (−0.41 to 0.01) 0.03 Land cover Impervious surface in
basin124 3.24 (−0.19 to 6.67) 0.16 (−0.01 to 0.34) 0.02 % Medium density
urbanization in
catchment128 3.39 (1.11 to 5.68) 0.25 (0.08 to 0.42) 0.06 % Crop cover in
catchment128 0.86 (−0.46 to 2.18) 0.11 (−0.06 to 0.29) 0.01 - Table 2 Direct and total effects of each driver on ACSP in the U.S. and global models.
Total effects are calculated as the sum of the direct and indirect effects of the predictor on the response variable.
SEM model Predictor Response Direct Total effect U.S. model Water temperature ACSP 0.39 0.39 30-day consecutive flow ACSP 0.28 0.28 Precipitation ACSP 0.18 Air temperature ACSP 0.36 Impervious cover ACSP 0.02 Watershed area ACSP 0.16 Mean elevation ACSP −0.10 Absolute latitude ACSP −0.01 Forest cover ACSP −0.08 Global model Absolute latitude ACSP 0.35 0.19 Air temperature ACSP 0.38 Mean elevation ACSP −0.19 Precipitation ACSP 0.05 Water temperature ACSP 0.47 0.47
Supplementary Materials
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/4/eaav2348/DC1
Supplementary Materials and Methods
Fig. S1. Maps of study sites included in the ACSP database.
Table S1. Data dictionary for variables included in the secondary production database for U.S. streams.
Data file S1. Citation records for all studies included in the ACSP database.
Data file S2. Complete secondary production and covariate data for all U.S. streams.
Data file S3. Secondary production and covariate data for the global streams database.
Data file S4. R code to build the U.S and global SEM models.
References (98–102)
Additional Files
Supplementary Materials
The PDF file includes:
- Supplementary Materials and Methods
- Fig. S1. Maps of study sites included in the ACSP database.
- Table S1. Data dictionary for variables included in the secondary production database for U.S. streams.
- References (98–102)
Other Supplementary Material for this manuscript includes the following:
- Data file S1 (.csv format). Citation records for all studies included in the ACSP database.
- Data file S2 (.csv format). Complete secondary production and covariate data for all U.S. streams.
- Data file S3 (.csv format). Secondary production and covariate data for the global streams database.
- Data file S4 (.txt format). R code to build the U.S and global SEM models.
Files in this Data Supplement:
