Functional diversity among seed dispersal kernels generated by carnivorous mammals

Abstract

Knowledge of the spatial scale of the dispersal service provided by important seed dispersers (i.e. common and/or keystone species) is essential to our understanding of their role on plant ecology, ecosystem functioning and, ultimately, biodiversity conservation. Carnivores are the main mammalian frugivores and seed dispersers in temperate climate regions. However, information on the seed dispersal distances they generate is still very limited. We focused on two common temperate carnivores differing in body size and spatial ecology – red fox (Vulpes vulpes) and European pine marten (Martes martes) – for evaluating possible functional diversity in their seed dispersal kernels. We measured dispersal distances using colour-coded seed mimics embedded in experimental fruits that were offered to the carnivores in feeding stations (simulating source trees). The exclusive colour code of each simulated tree allowed us to assign the exact origin of seed mimics found later in carnivore faeces. We further designed an explicit sampling strategy aiming to detect the longest dispersal events; as far we know, the most robust sampling scheme followed for tracking carnivore-dispersed seeds. We found a marked functional heterogeneity among both species in their seed dispersal kernels according to their home range size: multimodality and long-distance dispersal in the case of the fox and unimodality and short-distance dispersal in the case of the marten (maximum distances = 2846 and 1233 m, respectively). As a consequence, emergent kernels at the guild level (overall and in two different years) were highly dependent on the relative contribution of each carnivore species. Our results provide the first empirical evidence of functional diversity among seed dispersal kernels generated by carnivorous mammals. Moreover, they illustrate for the first time how seed dispersal kernels strongly depend on the relative contribution of different disperser species, thus on the composition of local disperser assemblages. These findings provide a key starting point for understanding and modelling plant population processes that include mammal-mediated seed dispersal, such as connectivity, range expansion and colonization.