RESUMO
The existence of monodominant forests on well-drained soils in tropical regions has been widely reported. Such forests most likely result from a combination of both ecological and evolutionary factors. Under conditions of high seed and seedling mortality, vegetative reproduction could create a reproductive advantage leading to forest dominance, and profoundly affect the distribution of genetic variation in a clonal species. We investigated these effects in a low diversity forest site in Northeastern Costa Rica dominated by the species Pentaclethra macroloba, which sprouts from the root mass of fallen trees and from snapped trunks. We examined the population structure of juvenile P. macroloba growing in different soil types and across an elevational gradient. Using seven molecular markers, we genotyped 173 juvenile P. macroloba from 18 plots (six plots in seasonally inundated swamps, and 12 plots in upland non-swamp) spanning 50-300m in elevation at La Selva Biological Station and the adjacent Reserva Ecológica Bijagual in Northeastern Costa Rica. We answered two specific questions: (1) How extensive is clonal reproduction? and (2) what is the distribution of genetic diversity and structure?. We found that clonal reproduction occurred exclusively within inundated swamp areas. However, there was no significant difference between genetic diversity measures in swamp and non-swamp plots, which were both generally low when compared with other tropical forest species. Genetic structure was significant across all plots (F ST=0.109). However, genetic structure among swamp plots (F ST=0.128) was higher than among non-swamp upland plots (F ST=0.093). Additionally, spatial autocorrelation among individuals within non-swamp upland plots was significant from the 25 to 100m spatial scale, but not within swamp plots. The degree of overall genetic structure we found in P. macroloba is high for a tropical forest tree. The incidence of clonal reproduction is a contributing factor in genetic differentiation, but the high structure among plots without clonal reproduction indicates that other factors contribute as well.
La existencia de bosques monodominantes sobre suelos bien drenados en regiones tropicales ha sido ampliamente reportada. Investigaciones recientes han sugerido que tales bosques son probablemente resultado de una combinación de factores ecológicos y evolutivos. Bajo condiciones de alta mortalidad de semillas y plántulas, la reproducción vegetativa podría crear una ventaja reproductiva llevando a la dominancia del bosque, pero también podría afectar profundamente la distribución de la variación genética en especies clonales. Investigamos estos efectos en un sitio de bosque con baja diversidad de especies en el Noreste de Costa Rica que es ampliamente dominado por la especie Pentaclethra macroloba, la cual retoña de la masa de raíces de árboles caídos y de troncos partidos. Examinamos la estructura poblacional de individuos juveniles de P. macroloba creciendo en diferentes tipos de suelo y a través de un gradiente de altitud. Utilizamos siete marcadores moleculares, genotipamos 173 Pentaclethra macroloba de 18 parcelas (seis en ciénagas y 12 en ambientes no cenagosos) ubicados en un gradiente de elevación entre 50-300m en las reservas adyacentes: Reserva Biológica Bijagual y Estación Biológica La Selva, en el centro de Costa Rica. Abordamos dos preguntas específicas: (1) ¿Qué tan extensa es la reproducción clonal? y (2) ¿Cuál es la distribución de diversidad y estructura genética? Encontramos que la reproducción clonal ocurrió exclusivamente dentro de áreas cenagosas inundadas. La estructura genética fue significativa en todas las parcelas (F ST=0.109). Observamos una estructura genética más alta entre poblaciones juveniles dentro de las ciénagas (F ST=0.128) comparada con poblaciones no cenagosas en parcelas a mayor altura (F ST=0.093), con mayor autocorrelación espacial en sitios no cenagosos en el intervalo entre 25 y 100m. La presencia de reproducción clonal no afectó significativamente las medidas de diversidad entre las dos áreas, que fueron generalmente bajas comparadas con otras especies de bosque tropical. El alto grado de estructura genética en general es novedoso para un árbol de bosque tropical. La incidencia de reproducción clonal es un factor que contribuye en la diferenciación genética, pero la alta estructura en parcelas sin reproducción clonal indica que otros factores están contribuyendo también.
Assuntos
Fabaceae/genética , Estruturas Genéticas/genética , Costa Rica , Fabaceae/classificação , Fabaceae/fisiologia , Reprodução/genética , Reprodução/fisiologiaRESUMO
Ten Environmental Impact Assessment Reports (EIAR) were reviewed for projects involving alternative power plants in Mexico developed during the last twelve years. Our analysis focused on the methods used to assess the impacts produced by hydroelectric and geothermal power projects. These methods used to assess impacts in EIARs ranged from the most simple, descriptive criteria, to quantitative models. These methods are not concordant with the level of the EIAR required by the environmental authority or even, with the kind of project developed. It is concluded that there is no correlation between the tools used to assess impacts and the assigned type of the EIAR. Because the methods to assess impacts produced by these power projects have not changed during 2000 years, we propose a quantitative method, based on ecological criteria and tools, to assess the impacts produced by hydroelectric and geothermal plants, according to the specific characteristics of the project. The proposed method is supported by environmental norms, and can assist environmental authorities in assigning the correct level and tools to be applied to hydroelectric and geothermal projects. The proposed method can be adapted to other production activities in Mexico and to other countries.