Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Edited by James A. Estes, University of California, Santa Cruz, CA, and approved July 2, 2015 (received for review January 31, 2015)
Article Figures & SI
Figures
- Fig. 1.
Plastic ingestion by seabirds as reported in the literature (1962–2012). (A) Frequency of individuals with plastic fragments in their digestive system per species–study combination. (B) Proportion of individuals in each species–study combination having plastic in their digestive system with time. Plot shows median and quartiles, with bars extending to 1.5 times the interquartile range. (C) Date of first discovery of plastic ingestion for seabird species across all species identified in the literature review.
- Fig. 2.
The expected number of seabird species ingesting plastic and driving factors. Predictions are at the 1 × 1 degree scale. (A) The expected number of species ingesting plastic based on predictions from a generalized linear mixed model, using a random effect to represent taxa-specific ingestion rates (n = 186). (B) The expected number of species ingesting plastic, as in A, but based on a generalized linear model using fixed effects for taxa-specific ingestion rates (n = 92). (C) Modeled concentration of marine debris in the world’s oceans on a log scale. (D) Species richness for seabirds considered in this study, based on data from Birdlife International (32).
Tables
A. Incidence of plastic in individual seabirds within a study Fixed Effects Random Effects Term Coefficient Estimate Standard Error Z value Pr(>|z|) Number of groups Model Term Grouping Variable Variance Intercept −3.08 0.61 −5.03 4.87E-07 59 Intercept Reference 4.30 Year* 1.76 0.38 4.58 4.63E-06 57 Intercept Genus 8.61 Method Lavage 0.24 0.31 0.76 0.45 57 Year* Genus 0.92 Method Bolus −0.29 0.37 −0.79 0.43 Method Necropsy −0.29 0.25 −1.19 0.24 B. Chance of identifying a species that has ingested plastic Fixed Effects Random Effects Term Coefficient Estimate Standard Error Z value Pr(>|z|) Number of groups Model Term Grouping Variable Variance Intercept 1.32 0.57 2.30 0.021 59 Intercept Reference 0.48 Year* 0.80 0.29 2.73 0.0063 57 Intercept Genus 2.55 Method Lavage −1.71 0.86 −1.99 0.046 57 Year* Genus 0.019 Method Bolus −0.93 1.20 −0.78 0.44 Method Necropsy −1.36 0.55 −2.48 0.013 ↵* Year is centered and rescaled for analysis, (year – 1982.365)/10.43.
- Table 2.
Analysis of the predictive power of debris exposure for predicting ingestion rates reported in the scientific literature
A. Comparison of model adequacy B. Parameters for the best model Model AIC Coefficient Coefficient Std. Error Pr(>|z|) DSGT 2656.8 Intercept −96.88 6.41 < 2e−16 SGT 2679.0 Weighted Mean 0.0032 0.0007 1.1e−06 DGT 2688.3 Body Size 2.72 0.47 7.5e−09 DSG 2871.9 G Aphrodroma −1.64 0.74 2.6e−02 SG 2900.1 G Calonectris −1.78 0.30 4.3e−09 GT 2904.1 G Cyclorrhynchus 3.33 0.20 < 2e−16 DG 2910.9 G Fratercula 0.56 0.21 8.9e−03 G 3180.2 G Fulmarus 1.26 0.23 3.9e−08 DT 4778.5 G Oceanodroma 1.43 0.36 8.6e−05 DST 4780.5 G Pachyptila 1.08 0.35 1.9e−03 ST 5473.2 G Pelagodroma 2.77 0.51 7.0e−08 T 5513.0 G Phoebastria −5.46 1.27 1.6e−05 DS 6010.9 G Procellaria −2.06 0.47 1.4e−05 D 6117.3 G Pseudobulweria −3.24 1.02 1.5e−03 S 6158.6 G Pterodroma −1.35 0.24 1.2e−08 0 7982.2 G Spheniscus −11.78 2.05 9.7e−09 G Thalassarche −7.24 1.04 3.4e−12 Year 0.047 0.003 < 2e−16 Method L −7.11 1.02 3.0e−12 Method LN −2.64 0.29 < 2e−16 Method N 0.44 0.09 1.1e−06 Note that genera and sampling methods that did not have significant coefficients are not reported for brevity. Note that the reference genus is Aethia, which is represented in the data by 3 species sampled in Alaska, and is included in the intercept term in the model. Coefficients for genera included in the analysis are preceded by a “G” and italicized. D, debris exposure; G, genus; S, body weight; T, starting year of the study; 0, intercept only model. Sampling method codes are: L, lavage; N, necropsy.
Data supplements
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Plastic in seabirds is pervasive and increasing
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