RESUMEN
PREMISE OF THE STUDY: Darwin first proposed that species with larger ecological breadth have greater phenotypic variation. We tested this hypothesis by comparing intraspecific variation in specific leaf area (SLA) to species' local elevational range and by assessing how external (abiotic) filters may influence observed differences in ecological breadth among species. Understanding the patterns of individual variation within and between populations will help evaluate differing hypotheses for structuring of communities and distribution of species. METHODS: We selected 21 species with varying elevational ranges and compared the coefficient of variation of SLA for each species against its local elevational range. We examined the influence of external filters on local trait composition by determining if intraspecific changes in SLA with elevation have the same direction and similar rates of change as the change in community mean SLA value. KEY RESULTS: In support of Darwin's hypothesis, we found a positive relationship between species' coefficient of variation for SLA with species' local elevational range. Intraspecific changes in SLA had the same sign, but generally lower magnitude than the community mean SLA. CONCLUSIONS: The results indicate that wide-ranging species are indeed characterized by greater intraspecific variation and that species' phenotypes shift along environmental gradients in the same direction as the community phenotypes. However, across species, the rate of intraspecific trait change, reflecting plastic and/or adaptive changes across populations, is limited and prevents species from adjusting to environmental gradients as quickly as interspecific changes resulting from community assembly.
Asunto(s)
Fenómenos Ecológicos y Ambientales , Variación Genética , Modelos Biológicos , Altitud , Colorado , Modelos Lineales , Hojas de la Planta/anatomía & histología , Estaciones del Año , Especificidad de la EspecieRESUMEN
La distribución de la especies es usualmente relacionada con la magnitud de la plasticidad fenotípica (PF). Con el fin de examinar la posible relación entre la magnitud de la PF y la amplitud ecológica en respuesta a la disponibilidad de luz, este trabajo evaluó la PF a través de la ontogenia en clones de Lippia alba y Lippia origanoides, especies congenéricas que presentan diferencias en su distribución. Clones de cada especie fueron distribuidos aleatoriamente en tres tratamientos, baja (33%), media (53%), y alta (100%) disponibilidad lumínica. Se evaluó la PF de caracteres morfológicos y de asignación de biomasa a través de la ontogenia por medio de un análisis de varianza (ANAVA) y la comparación interespecífica se realizó a través del índice de plasticidad fenotípica (RDPI). L. alba y L. origanoides presentaron variación de la plasticidad a través de la ontogenia en varios de los caracteres estudiados. La comparación interespecífica a través del RDPI mostró que la mayor PF de L. alba sobre L. origanoides en algún estado de la ontogenia no fue consistente ni uniforme a través de esta. Estos resultados sugieren una débil asociación entre la magnitud de la PF en respuesta a la disponibilidad lumínica. Además, indican que la mayor distribución de L. alba, se debe a un mayor desempeño en la tasa de crecimiento relativa y consecuentemente a una mayor acumulación de biomasa total, que posiblemente, le permiten alcanzar rápidamente su madurez sexual y así la colonización de nuevas áreas.
The distribution of the plant species is usually related to the magnitude of the phenotypic plasticity (PF). With the purpose of to stablish the possible relationship between the magnitude of the PF and the ecological breadth in response to light availability, the PF during the ontogeny in clones of Lippia alba and Lippia origanoides was evaluated. Both species are congeneris and show differences in their distribution. Three random treatments of light availability were set up, low (33%), medium (53%), and high (100%). The PF of morphologic and biomass allocation traits was evaluated during the ontogeny in clones of L. alba and L. origanoides through the ANOVA and the interspecific comparison were carried out through relative distance plasticity index (RDPI). L. alba and L. origanoides displayed variation of the plasticity through the ontogeny in several of the studied traits. The interspecific comparison through RDPI showed that the PF greather of L. alba in comparison to L. origanoides in some state of the ontogeny was not consistent nor uniform. These results suggest a lack association between the magnitudes of the PF in response to the availability of light. Additionally this indicate that the greater distribution of L. alba could be cause by a greater performance in the relative rate of growth and the greater accumulation of total biomass, therefore, it would likely contribute L. alba to reach its sexual maturity faster and the colonization of new areas.
RESUMEN
Individual physiological response to complex environments is a major factor in the ecological breadth of species. This study compared individual patterns of both long-term and short-term response to controlled, multifactorial environments in four annual Polygonum species that differ in field distribution (P. cespitosum, P. hydropiper, P. lapathifolium, and P. persicaria). To test long-term response, instantaneous net photosynthetic rate and stomatal conductance were measured in situ on one full-sib replicate from five inbred lineages from each of five field populations per species, raised in all possible combinations of low or high light; dry, moist, or flooded soil; and poor or rich nutrient status. Short-term plastic adjustment to changes in light level was examined by switching individual plants of the four species from one of six multifactorial growth environments to the contrasting light environment, and measuring assimilation rates 1 h after transfer. The Polygonum species differed significantly in their patterns of long-term photosynthetic response to particular resources and resource combinations. The species known to have relatively broad ecological distributions (P. persicaria and P. lapathifolium) maintained high photosynthetic performance in a variety of moisture and nutrient environments when grown in high light, while the more narrowly distributed P. hydropiper maintained such functional levels only if given both high light and ample macronutrients. P. cespitosum, a species limited to shaded habitats, maintained low photosynthetic rates across the environmental range. Complex differences among the species in instantaneous water use efficiency (WUE) reflected their highly specific and to some extent independent patterns of photosynthetic and stomatal response to the multifactorial environments. The species also differed significantly in short-term physiological adjustment to changes in light level. Plants of P. persicaria and P. cespitosum reached 78% and 98%, respectively, of their maximum photosynthetic rates 1 h after transfer from low to high light, but P. hydropiper and P. lapathifolium plants reached only c. 60% of their maximum rates. When switched from high to low light, P. persicaria and P. cespitosum plants maintained 64-76% of their maximum rates, while P. hydropiper and P. lapathifolium plants decreased photosynthetic rates sharply to less than 50% of their maximum rates. These results indicate that the latter two species will be less able to maintain effective functional levels in variable light environments, a result consistent with their distributions in the field.