Model predictions using empirical data from five sites
To illustrate how evolutionary effects may vary in real ecosystems, we used available data (Germanet al. 2012) on the decomposition kinetic parameters from five sites of increasing latitude and decreasing mean annual temperature (Costa Rica, California, West Virginia, Maine, and Alaska, Fig. 4). We evaluated non-evolutionary and evolutionary responses for each site under three levels of competition asymmetry (as quantified by the local competitive advantage to producers, c 0) (Fig. 4a-h). Under our baseline scenario, EVO effects correlate strongly with mean annual temperature, even more so for low competition asymmetry (Fig. 4i). Stronger EVO effects occur in colder sites, as found in the general analysis (Fig. 3a). In contrast, the non-evolutionary response does not correlate with mean annual temperature (Fig. 4a). As a result, a temperate site such as Maine exhibits a weak non-evolutionary response that can be strongly amplified by evolution, whereas the warm Costa Rica site shows a strong non-evolutionary response that is little affected by evolution.
These results are quantitatively attenuated but qualitatively unaffected when microbial mortality increases moderately with temperature (Fig. 4b, f, j). With a stronger effect of temperature on microbial mortality, all sites show the evolutionary buffering effect (Fig. 4k) found in the general analysis (Fig. 3c). The intensity of evolutionary buffering is independent of the sites’ mean annual temperature, whereas it varies significantly with competition asymmetry (Fig. 4k). Under the temperature-dependent MGE scenario, non-evolutionary and evolutionary responses are reduced in magnitude compared to the baseline scenario (Fig. 4d, h), particularly in cold sites. However, in these sites, EVO effects are enhanced dramatically (Fig. 4l). Thus, in a site as cold as Alaska, a significant evolutionary loss of soil carbon is predicted, whereas the non-evolutionary-driven loss of soil carbon would be negligible (Fig. 4l).