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.
Eklof A., Jacob U., Kopp J., Bosch J., Castro-Urgal R., Chacoff N.P., Dalsgaard B., de Sassi C., Galetti M., Guimaraes P.R., Lomascolo S.B., Martin Gonzalez A.M., Pizo M.A., Rader R., Rodrigo A., Tylianakis J.M., Vazquez D.P., Allesina S. (2013) The dimensionality of ecological networks. Ecology Letters. 16: 577-583.EnllaçDoi: 10.1111/ele.12081
How many dimensions (trait-axes) are required to predict whether two species interact? This unanswered question originated with the idea of ecological niches, and yet bears relevance today for understanding what determines network structure. Here, we analyse a set of 200 ecological networks, including food webs, antagonistic and mutualistic networks, and find that the number of dimensions needed to completely explain all interactions is small (
Filella I., Primante C., Llusia J., Martin Gonzalez A.M., Seco R., Farre-Armengol G., Rodrigo A., Bosch J., Penuelas J. (2013) Floral advertisement scent in a changing plant-pollinators market. Scientific Reports. 3: 0-0.EnllaçDoi: 10.1038/srep03434
Plant-pollinator systems may be considered as biological markets in which pollinators choose between different flowers that advertise their nectar/pollen rewards. Although expected to play a major role in structuring plant-pollinator interactions, community-wide patterns of flower scent signals remain largely unexplored. Here we show for the first time that scent advertisement is higher in plant species that bloom early in the flowering period when pollinators are scarce relative to flowers than in species blooming later in the season when there is a surplus of pollinators relative to flowers. We also show that less abundant flowering species that may compete with dominant species for pollinator visitation early in the flowering period emit much higher proportions of the generalist attractant β-ocimene. Overall, we provide a first community-wide description of the key role of seasonal dynamics of plant-specific flower scent emissions, and reveal the coexistence of contrasting plant signaling strategies in a plant-pollinator market.
Lazaro-Gonzalez A., Arnan X., Boulay R., Cerda X., Rodrigo A. (2013) Short-term ecological and behavioural responses of Mediterranean ant species Aphaenogaster gibbosa (Latr. 1798) to wildfire. Insect Conservation and Diversity. 6: 627-638.EnllaçDoi: 10.1111/icad.12018
Fire greatly affects plant and animal biodiversity. There is an extensive body of literature on the effects of fire on insect communities, in which a large variability of responses has been observed. Very few studies, however, have addressed functional responses at the species level, information that would greatly enhance our understanding of the impact of fire at higher organisational levels. The aim of this study is to analyse the short-term ecological and behavioural responses of the Mediterranean ant Aphaenogaster gibbosa to fire-induced environmental changes. We compared aspects of the abiotic and biotic environment relevant to this species, as well as differences in colony foraging behaviour, on unburnt and burnt plots in a Mediterranean area that was affected by a wildfire. Our results showed that fire modified plant cover around nests and daily cycles of soil temperature close to the nest. Although there were no significant differences in food quantity, food quality (particularly seed composition) was different between unburnt and burnt plots. In accordance with these environmental changes, we found significant differences in the daily activity rhythms and diet composition of A. gibbosa between unburnt and burnt plots. Overall, these differences did not result in significant changes in overall foraging activity and efficiency, allowing ant colonies to maintain the same food intake regardless of the habitat they occupied. We conclude that A. gibbosa uses behavioural plasticity to modify its foraging strategy in recently burnt environments and thus survive post-fire conditions. © 2013 The Royal Entomological Society.
Pino J., Arnan X., Rodrigo A., Retana J. (2013) Post-fire invasion and subsequent extinction of Conyza spp. in Mediterranean forests is mostly explained by local factors. Weed Research. 53: 470-478.EnllaçDoi: 10.1111/wre.12040
This work explored the invasion patterns of Conyza species in Mediterranean pine forests after fire and identified their main correlates through a temporal study approach. We hypothesised that wildfires might favour Conyza spp. invasion in these forests, but only transiently and depending on fire regime. We recorded Conyza spp. invasion and subsequent extinction in plots from species' occurrence and cover in vegetation surveys. We also explored the association of Conyza spp. presence and cover with a set of climatic, landscape and local (plot) factors using GLZ and GLM. We assessed changes in significant factors over time with a Wilcoxon test for paired samples. Evidence for Conyza spp. establishment was found in two-thirds of the study plots, with an invasion peak 2 years after fire. Local factors related to resource availability, including high fire severity, low soil stoniness and total vegetation cover and high herbaceous cover, were significantly correlated with Conyza occurrence in plots at the invasion peak. However, Conyza cover was always low (≤6%) and populations did not persist more than several years, thus becoming rarer as plant cover increased. Landscape and climatic factors showed no association with Conyza occurrence. In conclusion, wildfires favour transient invasion of European Mediterranean pine forests by Conyza spp. Invasion is mostly enhanced by local fire severity and constrained by subsequent vegetation recovery, while it is poorly explained by climate and landscape, either current or historical. © 2013 European Weed Research Society.
Quevedo L., Arnan X., Rodrigo A. (2013) Selective thinning of Arbutus unedo coppices following fire: Effects on growth at the individual and plot level. Forest Ecology and Management. 292: 56-63.EnllaçDoi: 10.1016/j.foreco.2012.12.007
In recent years, several Mediterranean forests subject to fire are becoming increasingly dominated by the resprouter species Arbutus unedo L. (strawberry tree). However, there is little information available about the management of these areas, and it is not clear if the approaches utilized for other, more abundant Mediterranean resprouter species such as Quercus ilex and Quercus cerrioides would produce similar results for A. unedo. In this study, performed in the NE Iberian Peninsula, we analyzed the effect of two post-fire treatment types, selective thinning and selective thinning plus understory clearing, on the growth of retained A. unedo resprouts and the new resprouting induced by the treatment itself. Treatment effects were analyzed at both the individual and plot level. Our results showed that, in the short term, retained resprouts on treated trees grew more in height and diameter (absolute and relative) than those on control trees, with no differences seen between treatment types. In the intermediate term, all the strawberry trees occurring on treated plots grew longer, and this growth was greater in plots that had been both thinned and cleared. New, induced resprouts were unaffected by the type of treatment applied. In contrast to other studies, we failed to find a negative relationship between the degree of induced resprouting and retained resprout growth We therefore conclude that, irrespective of understory clearing, the selective thinning of A. unedo improves coppice vertical structure. Retained resprouts grow more in diameter and will thus more rapidly become exploitable as firewood and timber. Also, the tree is kept free of dead fuel, reducing the risk of spreading fire. © 2012 Elsevier B.V.
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