Variation in fruit and seed dimensions is better explained by dispersal system than by leaf size in a tropical rainforest.

PREMISE: Variation in fruit and seed traits could originate from selection pressures exerted by frugivores or other ecological factors (adaptive hypotheses) and developmental constraints (by-product hypotheses) or chance. METHODS: We evaluated fruit and leaf traits for nearly 850 plant species from a rainforest in Tinigua Park, Colombia. Through a series of linear regressions controlling for the phylogenetic signal of the traits (minimum N = 542), we tested (1) whether the allometry between seed width and length depends on seed dispersal system (Mazer and Wheelwright's adaptive hypothesis of allometry for species dispersed in the guts of animals = endozoochory) and (2) whether fruit length is associated with leaf length (i.e., Herrera's by-product hypothesis derived from the assumption that both organs develop from homologous structures). RESULTS: We found a strong negative allometric association between seed width and length for seeds of endozoochorous species, as expected; but also, for anemochorous species. We found a positive relationship between fruit and leaf length, but this relationship was not evident for zoochorous species. Fruit size was highly correlated with seed size. CONCLUSIONS: The allometry between seed length and width varied among dispersal systems, supporting that fruit and seed morphology has been modified by interactions with frugivores and by the possibility to rotate for some wind dispersed species. We found some support for the hypothesis on developmental constraints because fruit and leaf size were positively correlated, but the predictive power of the relationship was low (10-15%).

PREMISA: La variación en los rasgos de frutos y semillas de las plantas podría tener su origen en las presiones de selección ejercidas por los frugívoros u otros factores ecológicos (hipótesis adaptativas), así como en limitaciones del desarrollo (hipótesis de subproductos) o en el azar. MÉTODOS: Nosotros evaluamos rasgos de frutos y hojas en cerca de 850 especies de plantas de un bosque húmedo tropical en el Parque Nacional Natural Tinigua, Colombia. Usando una serie de regresiones lineales que controlan por la señal filogenética de dichos rasgos (mínimo N = 542), nosotros probamos (1) si la alometría entre el ancho y largo de la semilla depende del sistema de dispersión de la semilla (i.e., hipótesis adaptativa de Mazer y Wheelwright; en la que se espera una alometría negativa para especies dispersadas por endozoocoria) y (2) si el largo del fruto está asociado con el largo de la hoja (i.e., la hipótesis del subproducto de Herrera derivada de la suposición de que ambos órganos se desarrollan a partir de estructuras homólogas). RESULTADOS: Nosotros encontramos una fuerte asociación alométrica negativa entre el ancho y el largo de las semillas para las semillas de las especies endozoócoras, como era de esperar; pero también, para las especies anemócoras. Nosotros también hallamos una relación positiva entre el largo del fruto y de la hoja, pero esta relación no fue evidente para las especies endozoócoras. Detectamos que el tamaño del fruto esta altamente correlacionado con el tamaño de la semilla. CONCLUSIONES: La alometría entre el largo y el ancho de la semilla varió entre sistemas de dispersión, lo que sugiere que la morfología de frutos y semillas ha sido moldeada por interacciones con frugívoros en el caso de las semillas endozoócoras y por la posibilidad de rotar para algunas especies dispersadas por el viento. Aunque el poder predictivo de la relación entre el tamaño del fruto y de la hoja fue bajo (10-15%), nosotros encontramos un apoyo moderado a la hipótesis sobre las limitaciones del desarrollo, ya que el tamaño del fruto y de la hoja estaban correlacionados positivamente.

Influence of Arthropod and Fruit Abundance on the Dietary Composition of Highland Colombian Woolly Monkeys (Lagothrix lagotricha lugens).

The woolly monkey's (Lagothrix lagotricha) diet consists primarily of fruits, and for some populations fruit availability predicts its frequency in the diet. Woolly monkeys also eat new leaves, flowers, seeds and arthropods, but it is unclear whether arthropods are consumed in proportion to their environmental availability. We tested the hypothesis that arthropod consumption by woolly monkeys depends on availability. We studied a group of woolly monkeys for 10 months in 2013-2014, in Cueva de los Guácharos National Park, Colombia, in order to test the hypothesis that arthropod consumption by woolly monkeys depends on availability. We carried out surveys of plant phenology each month for 10 months to estimate fruit productivity, and every 2 months we also surveyed 3 canopy substrates (leaves, mosses and bromeliads) to quantify variation in arthropod biomass. During this time, we also quantified the diet of a woolly monkey group. The items most consumed were fruits (60%), followed by arthropods (24%), leaves (13%) and miscellaneous other items (3%). Arthropod biomass in the canopy did not vary considerably over the 10 months (0.014-0.037 g/g substrate) but was lower at the end of the second rainy season. A positive correlation was found between availability and entomophagy, but only when arthropods were relatively abundant. We did not find a relationship between arthropod and fruit feeding frequencies. Our results indicate that arthropods are prevalent in the diet of the woolly monkeys due to their abundance in Andean forest canopies.