RESUMEN

Topography is a factor that can significantly affect the diversity and the distribution of trees species in tropical forests. Aniba perutilis, a timber species listed as vulnerable to extinction, is widely distributed in Andean forest fragments, especially in those with highly variable topography. Based on field surveys and logistic regression analyses, we studied the population structure and the effect of highly variable topography on the spatial distribution of this tree in three protected forest fragments in the central Andes of Colombia. Individuals of A. perutilis were mainly found on mountain ridges and hills with gentle slopes; no individuals were found in valleys. Using a species distribution model with presence/absence data, we showed that the available habitat for A. perutilis is significantly smaller than the extension of the fragments and much smaller than the extension of the currently protected areas. Our results have important implications for the conservation ofA. perutilis and likely for other threatened Andean tree species, which can also have locally restricted distributions due to highly variable local topography.

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RESUMEN

Topography is a factor that can significantly affect the diversity and the distribution of trees species in tropical forests. Aniba perutilis, a timber species listed as vulnerable to extinction, is widely distributed in Andean forest fragments, especially in those with highly variable topography. Based on field surveys and logistic regression analyses, we studied the population structure and the effect of highly variable topography on the spatial distribution of this tree in three protected forest fragments in the central Andes of Colombia. Individuals of A. perutilis were mainly found on mountain ridges and hills with gentle slopes; no individuals were found in valleys. Using a species distribution model with presence/absence data, we showed that the available habitat for A. perutilis is significantly smaller than the extension of the fragments and much smaller than the extension of the currently protected areas. Our results have important implications for the conservation of A. perutilis and likely for other threatened Andean tree species, which can also have locally restricted distributions due to highly variable local topography.

La topografía es un factor que puede afectar considerablemente la diversidad y la distribución de las especies de árboles tropicales. Aniba perutilis, una especie de árbol maderable vulnerable a la extinción, está ampliamente distribuida en fragmentos de bosques andinos, especialmente en aquellos con topografía altamente variable. A partir de trabajo de campo y análisis de regresión logística, estudiamos la estructura de la población y los efectos de la topografía sobre la distribución espacial de este árbol en tres fragmentos de bosque en la cordillera central de Colombia que actualmente se encuentran protegidos. Los individuos de A. perutilis se encontraron principalmente en los filos de montaña y colinas con gradientes topográficos suaves; no se encontraron individuos en los valles. A partir de un modelo de distribución de especies usando datos de presencia/ausencia, mostramos que el hábitat disponible para A. perutilis es considerablemente más pequeño que la extensión de los fragmentos y mucho más reducido que la extensión actual de las áreas protegidas. Nuestros resultados tienen implicaciones importantes para la conservación de A. perutilis y probablemente otras especies de árboles andinos amenazados, los cuales pueden estar restringidos de forma similar debido a la variabilidad topográfica local.

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Habitat degradation and fragmentation are expected to reduce seed dispersal rates by reducing fruit availability as well as the movement and abundance of frugivores. These deleterious impacts may also interact with each other at different spatial scales, leading to nonlinear effects of fruit abundance on seed dispersal. In this study we assessed whether the degradation and fragmentation of southern Chilean forests had the potential to restrict seed dispersal the lingue (Persea lingue) tree, a fleshy-fruited tree species. Of five frugivore bird species, the austral thrush (Turdus falcklandii) and the fire-eyed diucon (Xolmis pyrope) were the only legitimate seed dispersers as well as being the most abundant species visiting lingue trees. The results showed little or no direct effect of habitat fragmentation on seed dispersal estimates, possibly because the assemblage of frugivore birds was comprised habitat-generalist species. Instead, the number of fruits removed per focal tree exhibited an enhanced response to crop size, but only in the more connected fragments. In the fruit-richer fragment networks, there was an increased fragment-size effect on the proportion of fruits removed in comparison to fruit-poor networks in which the fragment size effect was spurious. We suggest that such nonlinear effects are widespread in fragmented forest regions, resulting from the link between the spatial scales over which frugivores sample resources and the spatial heterogeneity in fruiting resources caused by habitat fragmentation and degradation.

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Population structure and environmental relationships of the tropical tree Nectandra rudis (Lauraceae), a rare species in western Mexico. The tree N. rudis is a rare species from western Mexico of which community and population features are unknown. We studied a population in an altitudinal gradient, from 550-1,850 m above sea level in the Sierra de Manantlan, Jalisco, Mexico. We established four 60x48 m sample sites at vertical distances of 100 m along this altitudinal gradient. Within each plot, ten 100 m2 circular sub-sampling units were randomly located. At each unit, we recorded diameter at breast height (dbh) and tree height for all woody vegetation > or =2.5 cm dbh. Basal area, tree density, frequency, species richness and importance values per species and plot. We estimated the vertical structure (total tree height) and diameter( as M=5log(10)N) for all N. rudis individuals. A direct ordination through Canonical Correspondence Analysis was done, involving amongst other species, edaphic and environmental data matrices. The record of 44 N. rudis individuals, in seven out the 56 plots sampled, represents the most septentrional record for the species and the first in Western Mexico. Its density and basal area represented 4.5 % and 8.7 % respectively of the total estimated for the community. The greatest importance values were observed at 1 650 m above sea level. The population structure of N. rudis is structured into five diameter categories in an inverse "J" shaped distribution. This is a typical behavior observed to occur in the Lauraceae, which produces big seeds of short viability that germinate when there is high soil moisture content. The species tend to form dense seedling banks although only a reduced number of them are able to survive. Species richness varies from 27 to 39 at plot level; the greatest importance values for the plots on which N. rudis was found, corresponds to Urera verrucosa (Liebm.) V.W. Steinm., N. rudis, Ficus sp., Beilschmiedia manantlanensis Cuevas y Cochrane, amongst others. Canonical Correspondence Analysis suggests that environmental variables such as rooted trees, crown cover, litter depth and soluble magnesium are the more significant explanatory variables for the distribution and abundance of N. rudis.

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RESUMEN

Population structure and environmental relationships of the tropical tree Nectandra rudis (Lauraceae), a rare species in western Mexico. The tree N. rudis is a rare species from western Mexico of which community and population features are unknown. We studied a population in an altitudinal gradient, from 550-1,850 m above sea level in the Sierra de Manantlan, Jalisco, Mexico. We established four 60x48 m sample sites at vertical distances of 100 m along this altitudinal gradient. Within each plot, ten 100 m2 circular sub-sampling units were randomly located. At each unit, we recorded diameter at breast height (dbh) and tree height for all woody vegetation > or =2.5 cm dbh. Basal area, tree density, frequency, species richness and importance values per species and plot. We estimated the vertical structure (total tree height) and diameter( as M=5log(10)N) for all N. rudis individuals. A direct ordination through Canonical Correspondence Analysis was done, involving amongst other species, edaphic and environmental data matrices. The record of 44 N. rudis individuals, in seven out the 56 plots sampled, represents the most septentrional record for the species and the first in Western Mexico. Its density and basal area represented 4.5 % and 8.7 % respectively of the total estimated for the community. The greatest importance values were observed at 1 650 m above sea level. The population structure of N. rudis is structured into five diameter categories in an inverse "J" shaped distribution. This is a typical behavior observed to occur in the Lauraceae, which produces big seeds of short viability that germinate when there is high soil moisture content. The species tend to form dense seedling banks although only a reduced number of them are able to survive. Species richness varies from 27 to 39 at plot level; the greatest importance values for the plots on which N. rudis was found, corresponds to Urera verrucosa (Liebm.) V.W. Steinm., N. rudis, Ficus sp...

Nectandra rudis es una especie rara en el occidente de México. Analizamos la población y la comunidad donde se desarrolla, en la Sierra de Manantlan, Jalisco, México. Establecimos cuatro parcelas de 60x48 m con diferencias altitudinales de 100 m entre sí. En cada una seleccionamos aleatoriamente diez círculos de 100 m2 cada uno, en los cuales medimos los diámetros normales y las alturas de las especies leñosas con diámetro ≥2.5 cm. Para cada especie y por parcela determinamos el área basal, la densidad, la frecuencia, la riqueza de especies y los valores de importancia. Establecimos la estructura vertical y diamétrica de N. rudis. Hicimos una ordenación directa con la matriz de especies y las variables edáficas y ambientales. El registro de N. rudis en la Sierra de Manantlán representa el primer registro para el occidente de México y el más septentrional del taxon. La población se estructura en cinco categorías diamétricas y genera una curva en forma de “J” invertida. La riqueza de especies en las parcelas donde se encuentra N. rudis, varía de 27 a 39, y los mayores valores de importancia son para Urera verrucosa, N. rudis y Ficus sp. La ordenación directa permite postular a la presencia de árboles caídos, la cobertura, la profundidad del horizonte superficial y el magnesio soluble, como los factores ambientales de mayor influencia en la distribución y abundancia de N. rudis.

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