Relación entre la composición florística y los nutrientes del suelo en comunidades de palmas del Chocó biogeográfico en Colombia y Ecuador

En ecología una de las preguntas más importantes es: ¿cuáles son los factores ambientales que explican la alta diversidad de especies de plantas en los bosques tropicales? En este trabajo, se estudiaron las comunidades de palmas y su relación con los nutrientes del suelo en dos localidades del Chocó biogeográfico. Específicamente, se investigó: (1) cómo varían los nutrientes del suelo entre las dos localidades; (2) cuál es la relación entre los nutrientes del suelo y la composición florística de palmas; (3) cuáles son los nutrientes más importantes que explican la variación en la composición florística de las comunidades de palmas; y (4) cómo varía la abundancia de las especies dominantes de sotobosque y de dosel a lo largo del gradiente de concentración de los nutrientes más importantes. Se realizaron 20 transectos de 500 x 5 m (5 ha), en los cuales se identificaron y contaron todos los individuos de palmas en sus diferentes estadios de crecimiento. Las muestras de suelo se tomaron en cada uno de los transectos a los 0 , 250 y 500 m. Los cationes (Al, Ca, Mg, K, P) se extrajeron con la técnica Mehlich-III y las concentraciones se analizaron con espectrometría de emisión con plasma de acoplamiento inductivo (ICP-OES). La concentración de macronutrientes se relacionó con la composición florística mediante el test de Mantel, el test parcial de Mantel, regresiones lineales y escalamiento multidimensional no métrico (NMDS). Se encontraron 9 158 individuos y 33 especies de palmas en las 5 ha cubiertas por los transectos. La composición florística presentó una correlación positiva y significativa con los nutrientes del suelo (rM = 0.63-0.69) y con la distancia geográfica entre los transectos (rM = 0.71-0.75), mientras que las variables edáficas mostraron una alta correlación con la distancia geográfica (rM = 0.72). Asimismo, se encontró una débil relación significativa entre la fertilidad del suelo y la abundancia de palmas de sotobosque, pero ninguna con las palmas del dosel. Nuestros resultados demuestran que los suelos juegan un papel importante en la composición de las comunidades de palmas a escalas locales en la región del Chocó, y que los suelos más pobres y ricos en fósforo presentan la mayor diversidad de palmas.

One of the most important questions in ecology is: which are the environmental factors that explain the high plant diversity of tropical forests? We studied the floristic composition of palm communities and their relationship to soil nutrients in two localities of the Chocó region to understand (1) how soil nutrients vary between the two localities; (2) what is the relationship between soil nutrients and palm floristic composition; (3) what are the most important nutrients that explain the variation in floristic composition of palm communities; and (4) how does the abundance of the most exuberant understory and canopy palm species vary along the concentration gradient of the most important nutrients? We established 20 transects (5 x 500 m) and identified all palm individuals of all growth stages. Soil samples were taken at each transect at the beginning, middle, and end. Macronutrients (Al, Ca, Mg, K, P) were extracted with the Mehlich-III technique and their concentrations were analyzed by inductively coupled plasma emission spectrometry (ICP-OES). We used Mantel test, partial Mantel tests, linear regressions, and non-metric multidimensional scaling to determine if the concentration of nutrients was related to the floristic composition. We found a total of 9 158 individuals and 33 species of palms in the 5 ha covered by our transects. Floristic composition had a positive and significant correlation with soil nutrients (rM = 0.63-0.69) and with geographical distance between transects (rM= 0.71-0.75), whereas the soil nutrients were highly correlated with geographical distance (rM = 0.72). We also found a small, yet significant, relationship between soil fertility and the abundance of understory palms, but no relationship with canopy palms. Our results demonstrate for the first time that soils play an important role in the composition of palm communities at local scales in the Chocó region, and that infertile and phosphorus-rich soils have the highest palm diversity.

Multiple Mantel tests and isolation-by-distance, taking into account long-term historical divergence

Mantel tests of matrix correspondence have been widely used in population genetics to examine microevolutionary processes, such as isolation-by-distance (IBD). We used partial and multiple Mantel tests to simultaneously test long-term historical effects and current divergence and equilibrium processes, such as IBD. We used these procedures to calculate genetic divergence among Eugenia dysenterica (Myrtaceae) populations in Central Brazil. The Nei's genetic distances between pairs of local populations were strongly correlated with geographic distances, suggesting an IBD process, but field observations and the geographic distribution of the samples suggest that populations may have been subjected to more complex evolutionary processes of genetic divergence. Partial Mantel regression was used to partition the effects of geographic structure and long-term divergence associated with a possible historical barrier. The R(2) of the model with both effects was 73.3%, and after the partition 21.9% of the variation in the genetic distances could be attributed to long-term historical divergence alone, whereas only 1.5% of the variation in genetic distances could be attributed to IBD. As expected, there was a large overlap between these processes when explaining genetic divergence, so it was not possible to entirely partition divergence between historical and contemporary processes.

Comparacion floristica de doce parcelas en bosque de tierra firme en la amazonia peruana

Floristic composition of twelve plots, 25 m by 25 m, was studied in the Peruvian Amazonia in order to investigate if it were possible to use a part of the flora as an indicator of the changes observed in other components of the flora. Floristic similarities among the plots were calculated using six different taxonomic or physiognomic groups: ferns, the families Melastomataceae and Myristicaceae, trees thicker than 2.5 cm diameter at breast hight (DBH), trees between 2.5 cm and 5 cm DBH, and trees thicker than 5 cm DBH. The similarities were used for agglomerati ve classifications of the plots and for analyzing the correlations among the different groups of plants with Mantel's test. The results indicate that floristic changes were similar in all of the groups and therefore every group can potentially be used as an indicator.

Um estudo da composição florística de doze parcelas de 25 m 25 m foi realizado na Amazônia peruana com o objetivo de observar a possibilidade de utilizar uma parte da flora como indicador para as alterações anotadas em outros elementos da flora. As similaridades florísticas entre as parcelas foram definidas usando seis grupos taxonômicos ou fisionômicos diferentes: fetos, as famílias Melastomataceae e Myristicaceae, árvores com diâmetro á altura do peito (DAP) maior a 2.5 cm, árvores com DAP entre 2.5 cm e 5 cm, e árvores maiores a 5 cm de DAP. As similaridades foram utilizadas para classificar as parcelas e para analisar as correlações entre os grupos diferentes de plantas com a prova de Mantel. Os resultados mostram que as alterações florísticas são similares em todos os grupos, e por isso qualquer destes grupos é capaz de servir de indicador.