Abstract
BackgroundLong-distance seed dispersal (LDD) has strong impacts on the spatiotemporal dynamics of plants. Large animals are important LDD vectors because they regularly transport seeds of many plant species over long distances. While there is now ample evidence that behaviour varies considerably between individual animals, it is not clear to what extent inter-individual variation in behaviour alters seed dispersal by animals.MethodsWe study how inter-individual variation in the movement and feeding behaviour of one of Europe’s largest herbivores (the red deer, Cervus elaphus) affects internal seed dispersal (endozoochory) of multiple plant species. We combine movement data of 21 individual deer with measurements of seed loads in the dung of the same individuals and with data on gut passage time. These data serve to parameterize a model of passive dispersal that predicts LDD in three orientations (horizontal as well as upward and downward in elevation).With this model we investigate to what extent per-seed probabilities of LDD and seed load vary between individuals and throughout the vegetation period (May–December). Subsequently, we test whether per-seed LDD probability and seed load are positively (or negatively) correlated so that more mobile animals disperse more (or less) seeds. Finally, we examine whether non-random associations between per-seed LDD probability and seed load affect the LDD of individual plant species.ResultsThe studied deer dispersed viable seeds of at least 62 plant species. Deer individuals varied significantly in per-seed LDD probability and seed loads. However, more mobile animals did not disperse more or less seeds than less mobile ones. Plant species also did not differ significantly in the relationship between per-seed LDD probability and seed load. Yet plant species differed in how their seed load was distributed across deer individuals and in time, and this caused their LDD potential to differ more than twofold. For several plant species, we detected non-random associations between per-seed LDD probability and seed load that generally increased LDD potential.ConclusionsInter-individual variation in movement and feeding behaviour means that certain deer are substantially more effective LDD vectors than others. This inter-individual variation reduces the reliability of LDD and increases the sensitivity of LDD to the decline of deer populations. Variation in the dispersal services of individual animals should thus be taken into account in models in order to improve LDD projections.
Highlights
Long-distance seed dispersal (LDD) has strong impacts on the spatiotemporal dynamics of plants
Our study shows that variation in the movement and feeding behaviour of red deer individuals has profound effects on the long-distance seed dispersal (LDD) of a variety of plant species
We found that inter-individual variation in the movement and feeding behaviour of red deer has a profound effect on LDD of a variety of plant species
Summary
Long-distance seed dispersal (LDD) has strong impacts on the spatiotemporal dynamics of plants. Large animals are important LDD vectors because they regularly transport seeds of many plant species over long distances. For sessile plants, seed dispersal is the “premier spatial demographic process” [1]. Long-distance dispersal (LDD) is of particular interest with regards to the preservation of biodiversity, as it plays a pivotal role in linking local populations within a meta-population [3, 6,7,8,9], allowing the colonisation of new habitat and facilitating migration and gene flow [3, 7,8,9]. Research into ungulate mediated zoochory has mostly focussed on extrinsic determinants of seed dispersal. These can be broadly divided into being either ‘seed-focussed’ or ‘vector-focussed’. Studies of vector-focussed determinants almost always aggregate vectors at the level of species [4, 12, 15, 17, 28, 29], populations [13] or functional groups [16] and seek the drivers of average vector behaviour
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