Species richness matters for the quality of ecosystem services: a test using seed dispersal by frugivorous birds

Abstract

The positive link between biodiversity and ecosystem functioning is a current paradigm in ecological science. However, little is known of how different attributes of species assemblages condition the quality of many services in real ecosystems affected by human impact. We explore the links between the attributes of a frugivore assemblage and the quantitative and qualitative components of its derived ecosystem service, seed dispersal, along a landscape-scale gradient of anthropogenic forest loss. Both the number and the richness of seeds being dispersed were positively related to frugivore abundance and richness. Seed dispersal quality, determined by the fine-scale spatial patterns of seed deposition, mostly depended on frugivore richness. In fact, richness was the only attribute of the frugivore assemblage affecting the probability of seed dispersal into deforested areas of the landscape. The positive relationships between frugivore richness per se (i.e. independent of frugivore abundance and composition) and all components of seed dispersal suggest the existence of functional complementarity and/or facilitation between frugivores. These links also point to the whole assemblage of frugivores as a conservation target, if we aim to preserve a complete seed dispersal service and, hence, the potential for vegetation regeneration and recovery, in human-impacted landscapes.

Geographic consistency in the seed dispersal patterns of Taxus baccata L. in the Iberian Peninsula

“…As the main driver of seed flow, frugivorous birds play a pivotal role for yew populations, however carnivorous mammals should not be neglected since they contribute to the recolonization process through long distance dispersal (Escribano-Avila et al, 2012). Conservation and management practices should focus on maintaining a frugivore assemblage as diverse as possible to allow for complementary seed dispersal (García & Martínez, 2012;Escribano-Avila et al, 2014), thus increasing the chance for a seed to reach favourable conditions and acus preferentially forage around the focal trees, sometimes in big flocks (T. iliacus), and fly short distances towards the neighbouring microhabitats (Martínez et al, 2008), thus most likely dispersing the seeds within forest patches. On the other hand, Turdus viscivorus tends to fly long distances and hence would disperse a substantial amount of seeds among forest patches (Jordano & Schupp, 2000;Martínez et al, 2008;Morales et al, 2013).…”

Disentangling habitat use by frugivorous birds: Constant interactive effects of forest cover and fruit availability

“…between birds foraging in the same tree). In fact, the relative abundances of the different thrush species are frequently correlated in our study system (García & Martínez 2012), suggesting interspecific facilitation rather than competition at the population level (see also Saracco et al 2004). …”

“…For the better management of spatial information, the plot was subdivided into 440 20 × 20 m cells. Previous studies have proven that the size of the study plot and cells are appropriate in terms of extent and grain, respectively, for studying variability in habitat cover and fruit abundance, with cell size representing a relevant scale for bird habitat use and heterogeneity in seed rain patterns (García & Martínez 2012;García et al 2013;Martínez & García 2014). The study was carried out over four consecutive years: the autumn-winter seasons of 2008-09, 2009-10, 2010-11 and 2011-12 (hereafter, respectively 2008, 2009, 2010 and 2011).…”

“…The abundance of birds per cell was calculated as the cumulative number of birds detected in each cell during the season divided by the total observation time for each cell, calculating the number of birds per 10 h of observation. Bird abundance resulting from these censuses lead to an estimation of total frugivore activity throughout the season for the different cells of the study plot (García & Martínez 2012;García et al 2013). For detailed information on the methodology of bird censuses see Appendix A (see also García & Martínez 2012;García et al 2013).…”

“…Previous studies in the same system have described seed rain patterns and their variability between years and through the landscape (Herrera, Morales, & García 2011;García et al 2013;García & Martínez 2012;Martínez & García 2014). Nevertheless, we still lack a proper understanding of the ecological mechanisms (i.e.…”