Data from: Evolution of resource use along a gradient of stress leads to increased facilitation

The stress-gradient hypothesis (SGH) posits that the relative importance
of facilitative interactions versus negative interactions increases as
levels of abiotic stress increase. Originally formulated in empirical
studies of plant populations, in recent years the SGH has been found to
describe how interactions change in response to stress in a wide range of
species including algae, mussels and moths. However, there has been little
theory attempting to predict patterns from first principles in relation to
different types of interactions. Here, we use mathematical models of
microbial populations to investigate whether patterns consistent with the
SGH arise when species interact through resource use and allelopathy.
Evolution alters the degree to which competition for resource use versus
facilitation (cross-feeding) occurs. Our results are consistent with the
SGH; species interactions evolve to be more facilitative as average stress
intensifies. This occurs because at greater stress the species evolve to
become specialists on either of the two resources thereby decreasing
overlap in resource use and increasing facilitation through cross-feeding.
In addition, the production of toxic allelopathic compounds decreases as
stress intensifies due to density-dependent effects. Our results suggest
that the SGH could arise through fundamental interactions that are common
to many organisms and therefore that the SGH could be a more widespread
phenomenon than previously recognised.