Spatial variation in ant and rodent post‐dispersal predation of vertebrate‐dispersed seeds

Abstract

Summary1. Post-dispersal predation of vertebrate-dispersed seeds has received little attention in the Mediterranean region. We investigated the spatial variation in post-dispersal seed predation of vertebrate-dispersed plants and its potential implications for plant diversity in fleshy fruited plant communities of southern Spain.2. An experiment was conducted in forests and open scrubland at mid-and high elevations to explore: (a) the possibility of differential seed predation by rodents and granivorous ants; (b) the spatial variation, between and within habitats, in post-dispersal seed predation and predator abundance; and (c) whether the spatial distribution of predation covaries among plant species. 3. Rodents and granivorous ants proved to be important predators of vertebratedispersed seeds, and showed significant variation in their preferences for different seed species. Granivorous ant preferences depended on seed size, as seeds heavier than 20 mg were hardly ever removed. Rodents were indifferent to seed size. 4. Sites safe from predators were more frequent at mid-elevations. In contrast to other temperate communities, successional status (open scrubland vs forest) did not determine the probability of predation, probably because ants are more important as seed predators in the early successional stages of Mediterranean habitats than in other temperate communities. The large-scale variations in the occurrence of safe sites for the seeds depended on resource abundance rather than on predator abundance. 5. We found a significant interaction in seed predation rates between microhabitat and seed species at mid-elevations, but not in high-elevation habitats, implying stronger covariance across plant species in the microhabitats adequate for recruitment (e.g. with lower predation risk) at high elevation. This pattern may contribute to the differential plant diversity at mid-and high elevations in Mediterranean fleshy fruited plant communities. Theoretical models predict that seed predators may contribute to the maintenance of species diversity if the spatial distribution of safe sites from predators is uncorrelated across plant species, as it was at mid-elevations.

Does predation contribute to tree diversity?

“…Our study failed to find evidence for either of these mechanisms, suggesting that differential predation of seeds or seedlings does not contribute to seedling bank diversity in our study system. Rey et al (2002) also found little variation in predator seed preferences across habitats in sites that coincided with lowered plant diversity. In addition, they found that rodents displayed no preference for larger-seeded species, while ants actually preferred smaller-seeded species.…”

What are the consequences of ant–seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?

“…Seeds may be predated by a wide variety of animals, but predominantly by rodents, birds and ants (Brown et al 1979;Willson 1992;. Given the major activity of granivorous ants in Mediterranean open areas, even compared to rodent activity (Hulme 1997;Rey et al 2002;Boulay et al 2009), ants are considered the major predators of dry-fruited seeds in Mediterranean ecosystems (Willott et al 2000;Azcárate et al 2005). For this reason, a strong interaction between dry-fruited shrubs and seed-harvesting ants might be expected in Mediterranean grasslands and scrublands.…”

Padrões das síndromes de dispersão de plantas em áreas com diferentes graus de pluviosidade, PE, Brasil

“…Estudos que investigam a variação dos mecanismos de dispersão ao longo dos diferentes estratos verticais no nível de comunidades são escassos, pois a maioria se detém a observar um único mecanismo, espécie, ou outros fatores locais e infl uências (Drezner et al 2001Rey et al 2002. Wikander (1984) relatou que, em uma fl oresta decídua na Venezuela, a anemocoria foi a síndrome mais relevante, principalmente no estrato superior, e a zoocoria no inferior.…”