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).