The timing of frugivore‐mediated seed dispersal effectiveness

Abstract

The seed dispersal effectiveness framework allows assessing mutualistic services from frugivorous animals in terms of quantity and quality. Quantity accounts for the number of seeds dispersed and quality for the probability of recruitment of dispersed seeds. Research on this topic has largely focused on the spatial patterns of seed deposition because seed fates often vary between microhabitats due to differences in biotic and abiotic factors. However, the temporal dimension has remained completely overlooked despite these factors-and even local disperser assemblages-can change dramatically during long fruiting periods. Here, we test timing effects on seed dispersal effectiveness, using as study case a keystone shrub species dispersed by frugivorous birds and with a fruiting period of 9 months. We evaluated quantity and quality in different microhabitats of a Mediterranean forest and different periods of the fruiting phenophase. We identified the bird species responsible for seed deposition through DNA barcoding and evaluated the probability of seedling recruitment through a series of field experiments on sequential demographic processes. We found that timing matters: The disperser assemblage was temporally structured, seed viability decreased markedly during the plant's fruiting phenophase, and germination was lower for viable seeds dispersed in the fruiting peak. We show how small contributions to seed deposition by transient migratory species can result in a relevant effectiveness if they disperse seeds in a high-quality period for seedling recruitment. This study expands our understanding of seed dispersal effectiveness, highlighting the importance of timing and infrequent interactions for population and community dynamics.

Seed dispersal by dispersing juvenile animals: a source of functional connectivity in fragmented landscapes

“…20%); hence, the wild olive is virtually the only fruit species in the matrix [3]. The avian frugivore assemblage in this landscape is dominated by migratory species [20], the Sardinian warbler being the main resident species inhabiting the forest.…”

“…With this, we aimed at increasing sample sizes because DNA-barcoding identification generally fails (PCR failure) in 5 -10% of samples [3,20,21]. Conversely, we generally collected just a subsample of the seeds in the forest when seed traps received many seeds of certain plant species [20]. A detailed description of this section is available in the electronic supplementary material.…”

“…Lett. 15: 20190264 frugivore species responsible for dispersal events [3,20,21]. This approach allowed us to know the contribution (%) of Sardinian warblers to the magnitude of seed deposition, for different seed species and periods of the year, quantified in the seed traps we placed in the forest and matrix of our study landscape.…”

Introduction: Special issue on species interactions, ecological networks and community dynamics – Untangling the entangled bank using molecular techniques

“…The findings regarding particular interactions range from insight into emergent features such as levels of specialization in ecological interaction networks (Clare et al, ; Doña, Proctor, et al, ; Doña, Serrano, et al, ; Koskinen et al, ; Sepp et al, ) to the role of individual seed dispersers in seed dispersal networks. As a case in point, González‐Varo, Arroyo, and Jordano () are able to show how much of an ecological function (seed dispersal) is concentrated to particular species at particular points in time. Migratory bird species may only be passing through an area, but still be main agents of seed dispersal for particular plants.…”

“…Migratory bird species may only be passing through an area, but still be main agents of seed dispersal for particular plants. This emphasizes the need for resolving variation in network structure through time, for which molecular techniques are ideally placed (González‐Varo et al, ).…”