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.
Retana J, Gracia M (2010) La planificación de la gestió forestal a escala de conca hidrogràfica. Silvicultura 61: 22-23.
Román-Cuesta RM, Retana J, Gracia M (2010) Caracterización del régimen de incendios forestales en el trópico Mexicano: el caso de Chiapas. En: Estado del Conocimiento de la Diversidad Biológica en Chiapas. CONABIO. CONABIO.
Weiser MD, Sanders NJ, Agosti D, Ellison AM, Fisher BL, Gibb H, Gotelli NJ, Gove AD, Gross K, Guénard B, Janda M, Kaspari M, Lessard JP, Longino JT, Majer JD , Menke SB, McGlynn TP , Parr CL , Philpott SM, Retana J, Suarez A, Vasconcelos GL (eds.) (2010) Canopy and litter ant assemblages share similar climate-species density relationships. Biology Letters 6: 769-772.
Vilà-Cabrera A, Martínez-Vilalta J, Vayreda J, Retana J (2010) Structural and climatic determinants of demographic rates of Scots pine forests across the Iberian Peninsula. Ecological Applications 21: 1162-1172, doi: 10.1890/10-0647.1.
Gracia M, Meghelli N, Comas L, Retana J (2010) Land cover changes after the creation of a national park in a mountain landscape in the Pyrenees. Regional Environmental Change 11: 349–358, doi: 10.1007/s10113-010-0138-0.
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.
Martínez-Vilalta J., Mencuccini M., Vayreda J., Retana J. (2010) Interspecific variation in functional traits, not climatic differences among species ranges, determines demographic rates across 44 temperate and Mediterranean tree species. Journal of Ecology. 98: 1462-1475.LinkDoi: 10.1111/j.1365-2745.2010.01718.x
Surprisingly little is known about the relationship between functional traits and demographic rates of tree species under field conditions, particularly for non-tropical species. We studied the interspecific relationship between key functional traits (wood density (WD), maximum tree height, specific leaf area, nitrogen (N) content of leaves, leaf size and seed mass), demographic rates (relative growth rate (RGR) and mortality rate (MR)) and climatic niche for the 44 most abundant tree species in Spain. Demographic data were derived from the Spanish Forest Inventory, a repeated-measures scheme including c. 90 000 permanent plots spread over a territory of c. 500 000 km[TD-SUP-OPEN]2. Functional traits data came primarily from a more detailed forest inventory carried out in Catalonia, NE Spain. Our study region covers a wide range of climatic conditions and, not surprisingly, the studied species differed markedly in their climatic niche. Despite that fact, our results showed that the variability in demographic rates across species was much more related to differences in functional traits than to differences in the average climate among species. Maximum tree height and, particularly, WD, emerged as key functional traits, and were the best predictors of demographic rates in our study. These two variables also mediated the marginally significant relationship between RGR and MR, suggestive of a weak trade-off between growth and survival. The main aspects of our results were not altered by the explicit incorporation of phylogenetic effects, suggesting that the observed relationships are not due to divergences between a few major clades. Synthesis. Our study gives support to the notion that variation in functional traits across species allows them to perform largely independently of climatic conditions along environmental gradients. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.
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