RESUMEN
PREMISE: Ecogeographic isolation, or geographic isolation caused by ecological divergence, is thought to be of primary importance in speciation, yet is difficult to demonstrate and quantify. To determine whether distributions are limited by divergent adaptation or historical contingency, the gold standard is to reciprocally transplant species between their geographic ranges. Alternatively, ecogeographic isolation is inferred from species distribution models and niche divergence tests using widely available environmental and occurrence data. METHODS: We tested for ecogeographic isolation between two sister species of California annual wildflowers, Clarkia concinna and C. breweri, with a hybrid approach. We used niche models to predict water availability as the major axis of ecological divergence and then tested that with a greenhouse experiment. Specifically, we manipulated water availability in field soils for two populations of each species and predicted higher fitness in conditions representing home habitats to those representing the environment of each's sister species. RESULTS: Water availability and soil representing C. concinna generally increased both species' fitness. Thus, water and soil may indeed limit C. concinna from colonizing the range of C. breweri, but not vice versa. We suggest that the competitive environment and pollinator availability, which are not directly captured with either approach, may be key biotic factors correlated with climate that contribute to unexplained ecogeographic isolation for C. breweri. CONCLUSIONS: Ours is a valuable approach to assessing ecogeographic isolation, in that it balances feasibility with model validation, and our results have implications for species distribution modeling efforts geared toward predicting climate change responses.
Asunto(s)
Clarkia , Adaptación Fisiológica , Ecosistema , SueloRESUMEN
Fungal root endophytes play an important role in plant nutrition, helping plants acquire nutrients in exchange for photosynthates. We sought to characterize the progression of root colonization by arbuscular mycorrhizal fungi (AMF), dark septate endophytes (DSE), and fine root endophytes (FRE) over an alpine growing season, and to understand the role of the host plant and environment in driving colonization levels. We sampled four forbs on a regular schedule from June 26th-September 11th from a moist meadow (3535 m a.s.l) on Niwot Ridge, Rocky Mountain Front Range, CO, USA. We quantified the degree of root colonization by storage structures, exchange structures, and hyphae of all three groups of fungi. AMF and FRE percent colonization fluctuated significantly over time, while DSE did not. All AMF structures changed over time, and the degree of change in vesicles differed by plant species. FRE hyphae, AMF arbuscules and AMF vesicles peaked late in the season as plants produced seeds. AMF hyphae levels started high, decreased, and then increased within 20 days, highlighting the dynamic nature of plant-fungal interactions. Overall, our results show that AMF and FRE, not DSE, root colonization rapidly changes over the course of a growing season and these changes are driven by plant phenology and seasonal changes in the environment.