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.LinkDoi: 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.LinkDoi: 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.
Jenkins C.N., Sanders N.J., Andersen A.N., Arnan X., Brühl C.A., Cerda X., Ellison A.M., Fisher B.L., Fitzpatrick M.C., Gotelli N.J., Gove A.D., Guénard B., Lattke J.E., Lessard J.-P., Mcglynn T.P., Menke S.B., Parr C.L., Philpott S.M., Vasconcelos H.L., Weiser M.D., Dunn R.R. (2011) Global diversity in light of climate change: The case of ants. Diversity and Distributions. 17: 652-662.LinkDoi: 10.1111/j.1472-4642.2011.00770.x
Aim To use a fine-grained global model of ant diversity to identify the limits of our knowledge of diversity in the context of climate change. Location Global. Methods We applied generalized linear modelling to a global database of local ant assemblages to predict the species density of ants globally. Predictors evaluated included simple climate variables, combined temperature×precipitation variables, biogeographic region, elevation, and interactions between select variables. Areas of the planet identified as beyond the reliable prediction ability of the model were those having climatic conditions more extreme than what was represented in the ant database. Results Temperature was the most important single predictor of ant species density, and a mix of climatic variables, biogeographic region and interactions between climate and region yielded the best overall model. Broadly, geographic patterns of ant diversity match those of other taxa, with high species density in the wet tropics and in some, but not all, parts of the dry tropics. Uncertainty in model predictions appears to derive from the low amount of standardized sampling of ants in Asia, in Africa and in the most extreme (e.g. hottest) climates. Model residuals increase as a function of temperature. This suggests that our understanding of the drivers of ant diversity at high temperatures is incomplete, especially in hot and arid climates. In other words, our ignorance of how ant diversity relates to environment is greatest in those regions where most species occur - hot climates, both wet and dry. Mainconclusions Our results have two important implications. First, temperature is necessary, but not sufficient, to explain fully the patterns of ant diversity. Second, our ability to predict ant diversity is weakest exactly where we need to know the most, the warmest regions of a warming world. This includes significant parts of the tropics and some of the most biologically diverse areas in the world. © 2011 Blackwell Publishing Ltd.
Arnan X (2011) Hormigas cortadoras de hojas. El superorganismo supremo. Reseña bibliográfica de: The leafcutter ants. Civilization by instinct. Investigación y ciencia 420, 95.
Arnan X, López BC, Martínez-Vilalta J, Estorach M, Poyatos R (2011) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronología doi: 10.1016/j.dendro.2011.02.002.
Arnan X., Retana J., Rodrigo A., Cerdá X. (2010) Foraging behaviour of harvesting ants determines seed removal and dispersal. Insectes Sociaux. 57: 421-430.LinkDoi: 10.1007/s00040-010-0100-7
Harvesting ants can affect the regeneration of plants through at least two different processes: seed removal and seed dispersal. We analyse the role of different foraging strategies of ants on patterns of seed removal and dispersal by three Messor species with considerable differences in their foraging systems. Messor capitatus workers rarely leave the nest in well-formed columns, while the other two species form foraging trails, with M. bouvieri forming temporary trails and M. barbarus foraging on a stable system of permanent foraging trails. Overall seed intake of M. capitatus colonies is considerably less than that of the two group-foraging species. There are also differences in the size of seeds collected: M. barbarus and M. capitatus harvest similar amounts of large and small seeds, while M. bouvieri harvests small seeds more intensely than large ones, due to the smaller size of the worker caste. The three Messor species differ in the percent of seed dropping of the different seed type and in the seed dispersal distance. Moreover, M. bouvieri and M. capitatus redistributed dropped seeds preferentially in bare soil and low sparse vegetation habitats, while M. barbarus redistributed seeds mainly in the high vegetation habitat. These results show that the foraging systems of these harvesting ants determine different patterns of seed removal and dispersal and, thus, affect the abundance and redistribution of seeds in the area. © 2010 International Union for the Study of Social Insects (IUSSI).
Arnan X., Rodrigo A., Molowny-Horas R., Retana J. (2010) Ant-mediated expansion of an obligate seeder species during the first years after fire. Plant Biology. 12: 842-852.LinkDoi: 10.1111/j.1438-8677.2009.00294.x
Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade-intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate-seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant-mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population. © 2009 German Botanical Society and The Royal Botanical Society of the Netherlands.
Comas L, Arnan X, Gracia M, Retana J, Bosch J (2010) Relación entre el grado de madurez del bosque y las comunidades de himenópteros voladores y micromamíferos en el Parque Nacional de Aiguestortes i Estany de Sant Maurici. En: Proyectos de investigación en parques nacionales: 2006-2009. L. Ramírez y B. A sensio (Eds.). Organismo Autónomo de Parques Nacionales pp. 327-341.
Boet O, Arnan X (2010) Les formigues roges en els boscos de pi negre. El Portarró 28: 7-9.
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