Arnan X., Ferrandiz-Rovira M., Pladevall C., Rodrigo A. (2011) Worker size-related task partitioning in the foraging strategy of a seed-harvesting ant species. Behavioral Ecology and Sociobiology. 65: 1881-1890.EnllaçDoi: 10.1007/s00265-011-1197-z
Messor bouvieri is a seed-harvesting ant species in which workers forage in trails from the nest to a search area. A previous observation of seed transfer events between workers returning to the nest suggested potential task partitioning. In this study, we describe seed transportation and analyze the role of task partitioning in the foraging strategy of this species in terms of seed intake efficiency in relation to costs and benefits based on transport speed and task reliability. We assess the harvesting efficiency of task partitioning by comparing cooperative seed transport (CST) and individual seed transport (IST) events. Our results show task partitioning in the form of a sequence of transfer events among workers going from the search area to the nest. Importantly, and despite the weak worker polymorphism of this species, this sequence involved workers of different sizes, with seeds usually being passed along from smaller to larger workers. In addition, we show that small workers are better at finding seeds (spend less time finding a seed), and large workers are better at transporting them (were faster when walking back to the nest and lost fewer seeds). However, we failed to demonstrate that workers of different sizes are specialized in performing the task in which they excel. Overall, sequential CST in M. bouvieri results in a greater seed intake because seed search time decreases and task reliability increases, compared to IST. The determinants and adaptive benefits of CST are discussed. © 2011 Springer-Verlag.
Arnan X., Rodrigo A., Retana J. (2011) What are the consequences of ant-seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?. Oecologia. 167: 1027-1039.EnllaçDoi: 10.1007/s00442-011-2034-9
Strong interactions between dry-fruited shrubs and seed-harvesting ants are expected in early successional scrubs, where both groups have a major presence. We have analysed the implications of the seed characteristics of two dry-fruited shrub species (Coronilla minima and Dorycnium pentaphyllum) on seed predation and dispersal mediated by harvester ants and the consequences of these processes on spatio-temporal patterns of plant abundance in a heterogeneous environment. We found that large C. minima seeds were collected much more (39%) than small D. pentaphyllum seeds (2%). However, not all of the removed seeds of these plant species were consumed, and 12.8% of the seeds were lost along the trails, which increased dispersal distances compared with abiotic dispersal alone. Seed dropping occurred among all microhabitats of the two plant species, but especially in open microhabitats, which are the most suitable ones for plant establishment. The two plant species increased their presence in the study area during the study period: C. minima in open microhabitats and D. pentaphyllum in high vegetation. The large size of C. minima seeds probably limited the primary seed dispersal of this species, but may have allowed strong interaction with ants. Thus, seed dispersal by ants resulted in C. minima seeds reaching more suitable microhabitats by means of increasing dispersal distance and redistribution among microhabitats. In contrast, the smaller size of D. pentaphyllum seeds arguably allows abiotic seed dispersal over longer distances and colonization of all types of microhabitats, although it probably also limits their interaction with ants and, consequently, their redistribution in suitable microhabitats. We suggest that dyszoochory could contribute to the success of plant species with different seed characteristics in scrub habitats where seeds are abundantly collected by seed-harvesting ants. © 2011 Springer-Verlag.
Espelta J.M., Arnan X., Rodrigo A. (2011) Non-fire induced seed release ina weakly serotinous pine: Climatic factors, maintenance costs or both?. Oikos. 120: 1752-1760.EnllaçDoi: 10.1111/j.1600-0706.2011.19570.x
The advantages of canopy seed retention (serotiny) for plants inhabiting fire-prone ecosystems are well documented. However, very few species are completely serotinous and non-fire induced opening of serotinous fruits is commonly observed (weak serotiny). Two non-mutually exclusive causes are envisaged to contribute to this process: mechanical changes in serotinous fruits mediated by climatic conditions (e.g. drought) or the costs of maintenance for the plant of these long-lasting structures. However, their relative contribution to the spontaneous opening of serotinous fruits remains elusive as well as the consequences for the build-up of the canopy seed bank and inter-individual differences in serotiny. In this study we monitored the dynamics of cone production and cone opening in the weakly serotinous Pinus halepensis for five years (2004-2008), including two severe drought episodes (2005, 2006). Drought decreased the production of conelets, increased the abortion of immature cones, reduced the seed quality in the cohorts of cones produced during these years, and increased the opening of serotinous cones. During the first drought episode, a higher proportion of serotinous cones opened in those pines bearing a larger crop of younger cones. This suggests that not only passive changes induced by drought but also competition among cones for resources (e.g. water) might be involved in this process. The opening of serotinous cones in pines bearing more cones made inter-individual differences in the size of the canopy cone bank to narrow or even to reverse from 2004 to 2008. These results may help to understand the decrease in serotiny when pines grow and accumulate more cones and the large inter-individual variability in the degree of serotiny observed in P. halepensis forests. In addition, the negative effects of drought episodes for the size of the canopy cone bank and the seeds contained can be an unexplored cause of post-fire regeneration constraint. © 2011 The Authors.
Retana J, Arnan X, Arianoutsou M, Barbati A, Kazanis D, Rodrigo A (2011) Post-fire Management of non-serotinous pine forests. In: Post-fire management and restoration of southern European forests (Moreira F, Arianoutsou M, Corona P & De las Heras J eds). Managing Forest Ecosystems Series, Vol. 24. Springer, pp. 329. ISBN 978-94-007-2207-1.
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