Woody plant invasion in grassland ecosystems is a worldwide phenomenon, and biotic interactions as competition and predation have been invoked as a possible barrier to woody encroachment in many ecosystems. We evaluated the role of rodents as seed predators in Pampean grasslands, and we assessed the differences in removal by rodents between one native species, Prosopis caldenia (Caldén) and one exotic species, Gleditisia triacanthos (Honey locust). The experiment was conducted at different phases of the rodent population cycle in two grassland communities, a remnant of a native grassland and a post agriculture grassland (old field). The amount of seed loss caused by predation was estimated by a bait‐removal experiment in foraging stations. We estimated the frequency of foraging stations with consumption, the overall amount of seed predation and the individual rate of seed predation. The total amount of seed removal and the individual rate of seed removal were higher for P. caldenia than for G. triacanthos, in the native grassland than in the old field, and in autumn when rodent density was maximum. Overall, the role of rodents on woody seed removal varied according to the plant species and depending on the local conditions that vary through time and space.

The goal of this work was to determine how the foraging behaviour of Akodon azarae changes with predation risk and food availability in cropfield borders of Buenos Aires, Argentina. Our hypotheses were that A. azarae has a greater foraging efficiency in safe areas than in risky ones and that the foraging behaviour of A. azarae also depends on the level of resources. We measured giving-up densities (GUDs) and food consumption twice a year in artificial foraging patches (bottles with known amounts of millet seed) in covered and open areas and with two different levels of seed abundance. In both periods, GUDs were lower in the covered areas than in the open ones independently of food level. Consumption increased with food level in covered areas but not in open areas. Based on these results, we conclude that A. azarae appears to maximize its consumption depending on predation risk.

In Florida, the Cuban Treefrog (Osteopilus septentrionalis) is a superb colonist and appears to be a significant driver of amphibian community dynamics. Decline of native anurans has been linked to possible competition with adult O. septentrionalis but interactions during the larval stage are largely unknown. Rearing O. septentrionalis tadpoles along with two native anurans, the Squirrel Treefrog (Hyla squirella) and the Southern Toad (Bufo terrestris) in both experimental artificial ponds and laboratory aquaria, the role of competition as the mechanism driving the dynamics of invaded amphibian communities in Florida was examined. Also examined was the role of priority effects and variation between pond locations in altering interactions between O. septentrionalis and native anuran larvae. Interspecific competition was strong during the larval stage; the presence of O. septentrionalis reduced larval performance and survival of native anurans. Pond location alone had little effect on interspecific interactions, but priority effects were strong. Pond location and priority effects acted together to influence species interactions. The selective influence of different interaction modifiers acted to increase or decrease the impacts of exotic species on native taxa.