(2018) Yearly fluctuations of flower landscape in a Mediterranean scrubland: Consequences for floral resource availability. . : -.EnllaçDoi: https://doi.org/10.1371/journal.pone.0191268
Doblas-Miranda, E., Alonso, R., Arnan, X., Bermejo, V., Brotons, L., de las Heras, J., Estiarte, M., Hódar, J.A., Llorens, P., Lloret, F., López-Serrano, F.R., Martínez-Vilalta, J., Moya, D., Peñuelas, J., Pino, J., Rodrigo, A., Roura-Pascual, N., Valladares, F., Vilà, M., Zamora, R., Retana, J. (2017) A review of the combination among global change factors in forests, shrublands and pastures of the Mediterranean Region: Beyond drought effects. Global and Planetary Change. 148: 42-54.EnllaçDoi: 10.1016/j.gloplacha.2016.11.012
Osorio-Canadas, S., Arnan, X., Rodrigo, A., Torné-Noguera, A., Molowny, R., Bosch, J. (2016) Body size phenology in a regional bee fauna: A temporal extension of Bergmann's rule. Ecology Letters. : 0-0.EnllaçDoi: 10.1111/ele.12687
Quevedo L., Arnan X., Rodrigo A. (2015) Post-fire forestry management improves fruit weight and seed set in forest coppices dominated by Arbutus unedo L.. Forest Ecology and Management. 345: 65-72.EnllaçDoi: 10.1016/j.foreco.2015.02.030
In Mediterranean ecosystems, post-fire forestry management practices are often used to improve forest structure and to reduce the risk of fire in coppices of resprouting species. Such practices enhance tree growth (i.e., height), probably because they release resources. On the one hand, resource release may stimulate reproduction. On the other hand, tree species that are regenerating after a fire may already face a delay in reproduction, and this delay may be lengthened if species mainly invest these additional resources in growth. Within this theoretical framework, it is poorly understood how different forest management practices affect the reproductive abilities of forest species. In this study, we analyzed the effect of two post-fire forestry treatments (selective thinning of resprouts and selective thinning of resprouts plus understory clearing) on a Mediterranean coppice dominated by the resprouter species Arbutus unedo L.; in particular, we examined how the treatments affected this species' reproductive ability (flower and fruit production at the tree and stand level, as well as fruit characteristics). Our results show that the treatments had no effects on the number of flowers and mature fruits per individual. Meanwhile, mature fruit dry mass and seed set were greater in plots that had been both thinned and cleared than in control plots and plots that had only been thinned. This pattern was reversed for seed abortion rate: it was lower in plots that had been thinned and cleared. The dry mass of developed seeds did not differ among treatments. At the stand level, the percentage of strawberry trees that flowered, the percentage of strawberry trees that bore fruit, the dry biomass of mature fruits per hectare, and the number of developed seeds per hectare were not affected by these treatments. Other studies have shown that these two forest management practices can improve the vertical and horizontal structure of A. unedo coppices that are regenerating post fire; this study demonstrates that selective thinning does not modify the species' reproductive success and, such practice when combined with understory clearing might enhance it. Consequently, these forestry practices might ensure the natural regeneration of populations of this species, as well as the availability of food for local fauna. It is thus highly recommended that such practices be used to manage coppices dominated by resprouter species following fire, especially in situations where the growth of the forest canopy has stagnated and/or reproduction of forest species has been delayed. © 2015 Elsevier B.V.
Arnan X., Escola A., Rodrigo A., Bosch J. (2014) Female reproductive success in gynodioecious Thymus vulgaris: Pollen versus nutrient limitation and pollinator foraging behaviour. Botanical Journal of the Linnean Society. 175: 395-408.EnllaçDoi: 10.1111/boj.12173
Gynodioecy is a dimorphic breeding system in which female individuals coexist with hermaphroditic individuals in the same population. Females only contribute to the next generation via ovules, and many studies have shown that they are usually less attractive than hermaphrodites to pollinators. Several mechanisms have been proposed to explain how females manage to persist in populations despite these disadvantages. The 'resource reallocation hypothesis' (RRH) states that females channel resources not invested in pollen production and floral advertisement towards the production of more and/or larger seeds. We investigated pollination patterns and tested the RRH in a population of Thymus vulgaris. We measured flower display, flower size, nectar production, visitation rates, pollinator constancy and flower lifespan in the two morphs. In addition, we measured experimentally the effects of pollen and resource addition on female reproductive success (fruit set, seed set, seed weight) of the two morphs. Despite lower investment in floral advertisement, female individuals were no less attractive to pollinators than hermaphrodites on a per flower basis. Other measures of pollinator behaviour (number of flowers visited per plant, morph preference and morph constancy) also showed that pollinators did not discriminate against female flowers. In addition, stigma receptivity was longer in female flowers. Accordingly, and contrary to most studies on gynodioecious species, reproductive success of females was not pollen limited. Instead, seed production was pollen limited in hermaphrodites, suggesting low levels of cross-pollination in hermaphrodites. Seed production was resource limited in hermaphrodites, but not in females, thus providing support for the RRH. © 2014 The Linnean Society of London.
Caut S., Jowers M.J., Arnan X., Pearce-Duvet J., Rodrigo A., Cerda X., Boulay R.R. (2014) The effects of fire on ant trophic assemblage and sex allocation. Ecology and Evolution. 4: 35-49.EnllaçDoi: 10.1002/ece3.714
Fire plays a key role in ecosystem dynamics worldwide, altering energy flows and species community structure and composition. However, the functional mechanisms underlying these effects are not well understood. Many ground-dwelling animal species can shelter themselves from exposure to heat and therefore rarely suffer direct mortality. However, fire-induced alterations to the environment may change a species' relative trophic level within a food web and its mode of foraging. We assessed how fire could affect ant resource utilization at different scales in a Mediterranean forest. First, we conducted isotopic analyses on entire ant species assemblages and their potential food resources, which included plants and other arthropods, in burned and unburned plots 1 year postfire. Second, we measured the production of males and females by nests of a fire-resilient species, Aphaenogaster gibbosa, and analyzed the differences in isotopic values among workers, males, and females to test whether fire constrained resource allocation. We found that, in spite of major modifications in biotic and abiotic conditions, fire had little impact on the relative trophic position of ant species. The studied assemblage was composed of species with a wide array of diets. They ranged from being mostly herbivorous to completely omnivorous, and a given species' trophic level was the same in burned and unburned plots. In A. gibbosa nests, sexuals had greater δ15N values than workers in both burned and unburned plots, which suggests that the former had a more protein-rich diet than the latter. Fire also appeared to have a major effect on A. gibbosa sex allocation: The proportion of nests that produced male brood was greater on burned zones, as was the mean number of males produced per nest with the same reproductive investment. Our results show that generalist ants with relatively broad diets maintained a constant trophic position, even following a major disturbance like fire. However, the dramatically reduced production of females on burned zones compared to unburned zones 1 year postfire may result in considerably reduced recruitment of new colonies in the mid to long term, which could yield genetic bottlenecks and founder effects. Our study paves the way for future functional analyses of fire-induced modifications in ant populations and communities. © 2013 The Authors.
Quevedo L., Arnan X., Boet O., Rodrigo A. (2014) Post-fire selective thinning of Arbutus unedo L. coppices keeps animal diversity unchanged: The case of ants. Annals of Forest Science. 71: 897-905.EnllaçDoi: 10.1007/s13595-014-0381-5
Context: In the Mediterranean area, different post-fire management strategies are used for coppices of resprouting species to promote a more regular forest structure, enhance plant growth, and reduce fire risk. However, the effects of these management treatments on forest-associated fauna are unknown, which in turn could be limiting their beneficial effects.Aims: The aim of this work was to determine whether forest management of a recently burned area dominated by a vigorous resprouting tree species (Arbutus unedo L.) affects ant communities.Methods: Ant communities, sampled using pitfall traps, were examined from unmanaged and selective thinning coppices of A. unedo. Ants are here used as bioindicators of ecosystem health and surrogates for other animal groups.Results: Very limited effects of these post-fire management strategies on the structure and composition of ant communities were found. The lack of effects could be due to the reported small changes in physical conditions among treatments; or either, the most sensitive ant species to these post-fire management treatments might be the same ones affected by fire and, consequently, the ant species that would potentially be affected most were no longer in the study area.Conclusion: The lack of any significant effects caused by these post-fire management practices on the associated fauna of A. unedo coppices points out the suitability of these treatments in these circumstances. © 2014, INRA and Springer-Verlag France.
Torne-Noguera A., Rodrigo A., Arnan X., Osorio S., Barril-Graells H., Da Rocha-Filho L.C., Bosch J. (2014) Determinants of spatial distribution in a bee community: Nesting resources, flower resources, and body size. PLoS ONE. 9: 0-0.EnllaçDoi: 10.1371/journal.pone.0097255
Understanding biodiversity distribution is a primary goal of community ecology. At a landscape scale, bee communities are affected by habitat composition, anthropogenic land use, and fragmentation. However, little information is available on local-scale spatial distribution of bee communities within habitats that are uniform at the landscape scale. We studied a bee community along with floral and nesting resources over a 32 km2 area of uninterrupted Mediterranean scrubland. Our objectives were (i) to analyze floral and nesting resource composition at the habitat scale. We ask whether these resources follow a geographical pattern across the scrubland at bee-foraging relevant distances; (ii) to analyze the distribution of bee composition across the scrubland. Bees being highly mobile organisms, we ask whether bee composition shows a homogeneous distribution or else varies spatially. If so, we ask whether this variation is irregular or follows a geographical pattern and whether bees respond primarily to flower or to nesting resources; and (iii) to establish whether body size influences the response to local resource availability and ultimately spatial distribution. We obtained 6580 specimens belonging to 98 species. Despite bee mobility and the absence of environmental barriers, our bee community shows a clear geographical pattern. This pattern is mostly attributable to heterogeneous distribution of small (<55 mg) species (with presumed smaller foraging ranges), and is mostly explained by flower resources rather than nesting substrates. Even then, a large proportion (54.8%) of spatial variability remains unexplained by flower or nesting resources. We conclude that bee communities are strongly conditioned by local effects and may exhibit spatial heterogeneity patterns at a scale as low as 500-1000 m in patches of homogeneous habitat. These results have important implications for local pollination dynamics and spatial variation of plant-pollinator networks. © 2014 Torné-Noguera et al.
Arnan X., Cerda X., Rodrigo A., Retana J. (2013) Response of ant functional composition to fire. Ecography. 36: 1182-1192.EnllaçDoi: 10.1111/j.1600-0587.2013.00155.x
Little is known about the impact of disturbances on functional diversity and the long-term provisioning of ecosystem services, especially in animals. In this work we analyze the effect of wildfire on the functional composition of Mediterranean ant communities. In particular, we asked whether a) fire changes functional composition (mean and dissimilarity of trait values) at the community level; and b) such fire-induced functional modification is driven by changes in the relative abundance-dominance of species or by a replacement of species with different traits. We sampled ant communities in burned and unburned plots along 22 sites in a western Mediterranean region, and we computed two complementary functional trait composition indices ('trait average' and 'trait dissimilarity') for 12 functional traits (related to resource exploitation, social structure and reproduction) and with two different datasets varying in the way species abundance is considered (i.e. abundance and occurrence data). Our results suggest a set of functional responses that seem to be related to direct mortality by fire as well as to indirect fire-induced modifications in environmental conditions relevant for ants. Trait average of colony size, worker size, worker polymorphism and the ratio between queen and worker size, as well as the trait dissimilarity of the proportion of behaviorally dominant species and of liquid food consumption, and overall functional diversity, were higher in burned than in unburned areas. Interestingly, different patterns arise when comparing results from abundance and occurrence data. While the response to fire in trait averages is quite similar, in the case of trait dissimilarity, the higher values in response to fire are much more marked when considering occurrence rather than abundance data. Our results suggest that changes in trait average are driven at the same time by replacement of species with different traits and by changes in the relative abundance-dominance of species, while fire promotes a higher diversity of functions that is primarily driven by rare species that are functionally unique. Overall, we observed major fire-induced changes in functional composition in Mediterranean ant communities that might have relevant consequences for ecosystem processes and services. © 2013 The Authors.
Arnan X., Quevedo L., Rodrigo A. (2013) Forest fire occurrence increases the distribution of a scarce forest type in the Mediterranean Basin. Acta Oecologica. 46: 39-47.EnllaçDoi: 10.1016/j.actao.2012.10.005
Here we report how fire recurrence increases the distribution of a scarce forest type in NE Spain that is dominated by the resprouter tree species Arbutus unedo. We used a combination of GIS and field surveys to determine the effect of fire and pre-fire vegetation on the appearance of A. unedo forests. In the field, we also analyzed the factors that promote fire and lead to the appearance of A. unedo forests. Our results reveal an increased occurrence of A. unedo forests in NE Spain in recent years; this phenomenon was strongly related to fire recurrence and the vegetation type present prior to fire. Most Pinus halepensis forests that burned more than once gave rise to A. unedo forests. Our results indicate that these conversions were related to a reduction in pine density coupled with increases in the density and size of A. unedo trees due to recurrent fires. Given that fires are increasing in number and magnitude in the Mediterranean, we predict a major change in landscape structure and composition at the regional scale. © 2012 Elsevier Masson SAS.
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