A stochastic model of seed dispersal pattern to assess seed predation by ants in annual dry grasslands

Abstract

A combined field experiment and modelling approach has been used to provide evidence that ants may be responsible for an observed lower patchiness and higher plant diversity in the neighbourhood of ant nests, within Mediterranean dry grasslands belonging to the phytosociological class Tuberarietea guttatae. The hypothesis was that seeds occurring in clumps may have an higher probability to be harvested than seeds having a scattered distribution. In order to test this hypothesis, four analysis steps have been performed. First, the seed productivity and dispersal pattern was recorded for four plant species found, either more abundant beside the ant nests (Tuberaria guttata, Euphorbia exigua) or away from the ant nests (Bromus scoparius and Plantago bellardi). Second, a stochastic model was developed to simulate the observed dispersal patterns of each studied species. Third, ten seed arranges in accordance to the distribution patterns created by the model were offered to the ants and the positions of the predated seeds was recorded. Finally, the observed pattern of seed predation was matched to models performed by different distributions of probability. Results confirmed the initial hypothesis, showing that the probability of being predated decreases with the increase of the reciprocal distance of seeds. It was concluded that the preference of ants for high concentrations of food items holds down the dominant species sufficiently to allow the subordinates to survive. The observed higher frequency of small-seeded, small-sized, or creeping therophytes close to the ant nests can be therefore seen as an example of indirect mirmecophily

Thirty years unmanaged green roofs: Ecological research and design implications

“…Along with that, the progressive increase in barochory and autochory illustrated a shift in the succession towards short-distance dispersal species. Furthermore, the establishment of ant colonies probably affected the vegetation dynamics (Guarino, Ferrario, & Mossa, 2005) as the observed increased incidence of zoochorous (myrmecochorous) species in 1999-2014 would suggest.…”

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

“…Additionally, seed aggregation may increase seed removal rate by ants (Hughes and Westoby 1990;Gorb and Gorb 2000;Guarino et al 2005). Abiotic dispersal distance is usually associated with seed size (Hoppes 1988;Sallabanks 1992;Guarino et al 2005), so that large seeds land much closer to the parent plant than smaller ones. The limited dispersal mechanisms of large C. minima seeds (Fig.…”

“…4). Therefore, seed dispersal by harvesting ants offers a number of attractive advantages to seeds, such as reduced competition from the mother plant and from individuals belonging to the same cohort (Andersen 1988;Hölldobler and Wilson 1990), the reduction of predation risk (O'Dowd and Hay 1980;Guarino et al 2005) and the colonization of new habitats (Arnan et al 2010). …”

Annual dune plant communities in the Southwest coast of Europe

“…Globally, the diversity of therophitic communities is enormous, because these communities easily change their floristic combination along ecological gradients such as climatic, soil, topographic and human disturbance-related gradients (Guarino et al 2005). After the major review from Díez-Garretas et al (2003), to extensive dune areas, especially in the North of Lisbon (Dividing Portuguese Sector, Sadensean-Dividing Portuguese Subprovince, Lusitan-Andalusian Coastal Province), the available information has been revealed to be scarce.…”