Applying community assembly rules to understanding invasion - the seed predation filter.

PEARSON, DEAN E.; HIERRO, JOSÉ L.; MARON, JOHN L.; ICASATTI, NADIA S.; CALLAWAY, RAY; RUNYON, JUSTIN; ORTEGA, YVETTE

Missoula

Encuentro; Northwest Science Meeting.; 2014

University of Montana

Exotic plant invasions have devastated native ecosystems since humans began translocating species across natural barriers. Yet we still do not fully understand how some invaders accomplish this. Theoretically, invasion outcomes should be predictable based on how individual species traits relate to community filters - independent of species origins. However, exotic species invasions commonly result in virtual monocultures, not normally found in native systems, suggesting that biological invasions challenge the premise of community assembly theory or that some invaders may break the rules that natives must follow. Here we apply community assembly theory to examine how native and exotic plants respond to a specific biotic filter, seed predation by native rodents and ants, in central Argentina and west-central Montana. We found that the in situ seed predation filter in central Argentina, a system we show is relatively resistant to invasion, was strongly biased against exotics, while the seed predation filter in Montana, a system relatively susceptible to invasion, was biased in favor of exotics. In both systems seed size largely predicted invader responses to the filter, but we also found that some strongly invasive exotics evaded the filter, possibly via chemical defenses. Applying community assembly theory to exotic plant invasions demonstrates that in situ filters can help explain the relative invasiveness of many exotic plants (particularly, weakly to moderately successful invaders) and possibly the differential invasibility of systems. However, understanding invasion outcomes for some strong invaders may require deciphering how these species evade in situ filters.