Variability within the 10-year pollen rain of a seasonal neotropical forest and its implications for paleoenvironmental and phenological research

Análisis de la lluvia de polen en un fragmento de bosque subandino en Colombia

Resumen Se llevó a cabo un análisis de la lluvia de polen y su relación con la vegetación en un fragmento de bosque subandino en la cordillera Oriental Colombiana entre los 1.500 a 2.400 msnm. Transectos tipo RAP fueron llevados a cabo para realizar el inventario de la flora. Dentro de cada transecto se recolectaron muestras de musgos de forma aleatoria, los cuales fueron procesados en el laboratorio, con el fin de obtener datos de lluvia de polen. Con base en los conteos e identificación de los granos de polen y vegetación, se realizaron diagramas polínicos, estimaciones de diversidad y fue establecida la lluvia de polen y su relación con la vegetación. Análisis Clúster y de correspondencia sin tendencia (DCA) fueron elaborados para determinar la presencia de asociaciones ecologicas de polen vinculados con la altura. Un total de 66 palinomorfos fueron identificados, siendo el hábito arbóreo dominante. Los sitios ubicados a 2.100 y 2.400 msnm presentaron mayor diversidad con respecto al polen. El Clúster y el DCA marcan tres agrupaciones compuestas por especies que generan una posible línea divisoria entre el bosque subandino bajo del alto, con lo cual se generan nuevos resultados que pueden ser usados en las interpretaciones paleoecológicas.

Effects of tree architecture on pollen dispersal and mating patterns in Abies pinsapo Boiss. (Pinaceae)

Plant architecture is crucial to pollination and mating in wind-pollinated species. We investigated the effect of crown architecture on pollen dispersal, mating system and offspring quality, combining phenotypic and genotypic analyses in a low-density population of the endangered species Abies pinsapo. A total of 598 embryos from three relative crown height levels (bottom, middle and top) in five mother plants were genotyped using eleven nuclear microsatellite markers (nSSRs). Paternity analysis and mating system models were used to infer mating and pollen dispersal parameters. In addition, seeds were weighed (N = 16 110) and germinated (N = 736), and seedling vigour was measured to assess inbreeding depression. Overall, A. pinsapo shows a fat-tailed dispersal kernel, with an average pollen dispersal distance of 113-227 m, an immigration rate of 0.84-26.92%, and a number of effective pollen donors (Nep ) ranging between 3.5 and 11.9. We found an effect of tree height and relative crown height levels on mating parameters. A higher proportion of seeds with embryo (about 50%) and a higher rate of self-fertilization (about 60%) were found at the bottom level in comparison with the top level. Seed weight and seedling vigour are positively related. Nevertheless, no differences were found in seed weight or in seedling-related variables such as weight and length of aerial and subterranean parts among the different relative crown height levels, suggesting that seeds from the more strongly inbred bottom level are not affected by inbreeding depression. Our results point to vertical isotropy for outcross-pollen and they suggest that self-pollen may ensure fertilization when outcross-pollen is not available in low-density population.

Millennial-scale temperature change velocity in the continental northern Neotropics

Climate has been inherently linked to global diversity patterns, and yet no empirical data are available to put modern climate change into a millennial-scale context. High tropical species diversity has been linked to slow rates of climate change during the Quaternary, an assumption that lacks an empirical foundation. Thus, there is the need for quantifying the velocity at which the bioclimatic space changed during the Quaternary in the tropics. Here we present rates of climate change for the late Pleistocene and Holocene from Mexico and Guatemala. An extensive modern pollen survey and fossil pollen data from two long sedimentary records (30,000 and 86,000 years for highlands and lowlands, respectively) were used to estimate past temperatures. Derived temperature profiles show a parallel long-term trend and a similar cooling during the Last Glacial Maximum in the Guatemalan lowlands and the Mexican highlands. Temperature estimates and digital elevation models were used to calculate the velocity of isotherm displacement (temperature change velocity) for the time period contained in each record. Our analyses showed that temperature change velocities in Mesoamerica during the late Quaternary were at least four times slower than values reported for the last 50 years, but also at least twice as fast as those obtained from recent models. Our data demonstrate that, given extremely high temperature change velocities, species survival must have relied on either microrefugial populations or persistence of suppressed individuals. Contrary to the usual expectation of stable climates being associated with high diversity, our results suggest that Quaternary tropical diversity was probably maintained by centennial-scale oscillatory climatic variability that forestalled competitive exclusion. As humans have simplified modern landscapes, thereby removing potential microrefugia, and climate change is occurring monotonically at a very high velocity, extinction risk for tropical species is higher than at any time in the last 86,000 years.