In natural plant communities, one finds ample examples of both competitive and facilitative interactions. The effect of a species A on another species B is said to be competitive (facilitative) if an increase in A ’s population size reduces (enhances) the population growth rate of B . Competition may arise if two species live in the same habitat and are therefore occupying sites at the others’ expense. In turn, facilitation could happen, for example, because a plant species modifies the soil chemistry around itself in a way that makes it especially beneficial to members of another species. Is the prevalence of competitive and facilitative interactions merely a statistic associated with communities, or does it reveal other properties of interest? For instance, is it conducive to biodiversity to have either very many competitive or very many facilitative interactions within a community? In a recent study in PNAS, Losapio et al. (1) argue that the two are needed in concert. An overprevalence of certain combinations of competitive and facilitative interactions predictably leads to more plant species within a community. Every species potentially interacts with many others. Communities can therefore be viewed as interaction networks (Fig. 1) in which each species is embedded (2). This must be taken into account when pondering the potential community-wide effects of competition and facilitation. Naively, competition may be thought of as a destructive force, hindering the coexistence of species. Things are not that simple, however, because of the principle that “the enemy’s enemy is a friend.” If two species are in competition and the second one is a superior competitor, it might drive the first one extinct—unless there is a third species that is also in competition with the second, keeping it sufficiently in check for all three of them to persist. Similarly, the naive logic that … [↵][1]1Email: gyorgy.barabas{at}liu.se. [1]: #xref-corresp-1-1