Trade-offs between seed size and biotic interactions contribute to coexistence of co-occurring species that vary in fecundity

Despite theoretical advances, the ecological factors and functional traits that enable species varying in seed size and fecundity to coexist remain unclear. Given inherent fecundity advantages, why don’t small-seeded species dominate communities?

In perennial grasslands, we evaluated whether small-seeded species are less tolerant of competition from the community dominant bunchgrass than large-seeded species but also less vulnerable to seed predation by mice. We also explored whether trade-offs involving competitive tolerance include two other functional traits, height and leaf mass per area (LMA). We added seeds of 17 forb species to plots where bunchgrass competition and rodent seed predation were manipulated across sites varying in bunchgrass productivity and thus competitive intensity. Seeds were added at densities mimicking interspecific variation in fecundity among target species.

Standardizing for differences in fecundity (i.e. seed input; which enabled us to evaluate inher...