Do different life-history strategies promote coexistence among native and exotic annual plants: 17-years of annual plant coexistence in semiarid Chile

Background/Question/Methods .

In unpredictable and temporally variable environments, evolution should select for life-history strategies to survive challenging times and to capitalize on times of resource availability. In semiarid environments, variability in the frequency and strength of rainfall pulses controls annual plant recruitment. Under such circumstances bet-hedging strategies favor strategies that spread the risk of mortality and favor long-term reproductive success. Evolutionarily and geographically unrelated species could develop similar strategies, in which case the processes that favor persistence and recruitment of native species could also promote the establishment and persistence of exotic species. At our long-term site in semiarid Chile we assessed whether native and exotic annual species expressed similar or contrasting bet-hedging traits, and if such strategies promoted coexistence under the highly variable precipitation regime driven by El Niño Southern Oscillations. We analyzed this variability using a proxy of long-term fitness for the two most common native and exotic annual plant species. We analyzed seed densities in soil samples collected over a 17-year period, and experimentally assessed the impact of the maternal environment (availability of water and nutrients) on the percentage of seeds germinating as well as on the mean and variability of seed sizes and dormancies.

Results/Conclusions . 

Native and exotic species at this site displayed different and complementary life-history and bet-hedging strategies in terms of seed size, latency, and germination probabilities. These strategies are conservative in which a low variable number of seeds were produced independent of the quality of the environment where maternal native plants grew (high or low water). In contrast, both exotic species had low germination fractions, which meant that their strategy is to produce many dormant seeds that would germinate in different years. Seeds from plants that grew in unfavorable maternal environments were smaller than seeds produced by plants from favorable maternal environments. These differences in strategies may be associated with contrasting evolutionary exposure to variable precipitation and allow native and exotic species to have different germination responses to environmental conditions. Given these differences, inter-annual variability in rainfall provides temporal windows that allow species with these complementary life history strategies to coexist.  Invasive species at this site may be successful in part because “establishment filters” have excluded those species whose life history traits are too similar to those of existing native species.