†These authors formed the core team behind the Technical Comment. The remaining authors are listed alphabetically according to their first name. Affiliations located after Acknowledgements.Abstract Kubelka et al. (Science, 9 November 2018, p. 680-683) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.
Main textClimate change affects organisms in a variety of ways (1-4), including through changes in interactions between species. A recent study (5, referred to as "the Authors") reports that a specific type of trophic interaction, namely depredation of shorebird nests, increased globally over the past 70 years. The Authors state that their results are "consistent with climateinduced shifts in predator-prey relationships". They also claim that the historical perception of a latitudinal gradient in nest predation, with the highest rates in the tropics, "has been recently reversed in the Northern Hemisphere, most notably in the Arctic." They conclude that "the Arctic now represents an extensive ecological trap… for migrating birds, with a predicted negative impact on their global population dynamics". These conclusions have far-reaching implications, for evolutionary and population ecology, and for shorebird conservation and related policy decisions (6). Therefore, such claims require robust evidence, strongly supported by the data. Here we dispute this evidence.First, the Authors graphically show non-linear, spatio-temporal variation in predation rates (their Fig. 2AB and 3), and suggest that in recent years, predation has strongly increased in North temperate and especially Arctic regions, but less so in other areas. However, they only statistically test for linear changes in predation rates over time for all regions combined, and for each geographical region (their Table S2) or period (before-and after-2000; their Table S6) separately. To substantiate their conclusions, the Authors should have presented statistical evidence for an interaction between region/latitude and year/period on predation rate. Moreover, their analyses control for spatial auto-correlation, but failed to model nonindependence of data from the same site (pseudo-replication).Using the Authors' data, we ran a set of mixed-effect models, structurally reflecting their results depicted in their Fig. 2AB and 3, but including location as a random factor (Table 1, (7)). These analyses show (a) that much of the variation in nest predation rate is explained by study site (>60%, compared to species: <5%), implying a reduced effective sample size, (b) that all regions -except the South temperate -show similar predation rates, and (c) that nest predation rates increase over time similarly across all geographical areas (Fig. 1A-F). Linear models without interaction terms are much better supported than non-linear ...
