Response of ant functional composition to fire

Arnan X., Cerda X., Rodrigo A., Retana J. (2013) Response of ant functional composition to fire. Ecography. 36: 1182-1192.
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Doi: 10.1111/j.1600-0587.2013.00155.x

Resum:

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.

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Post-fire invasion and subsequent extinction of Conyza spp. in Mediterranean forests is mostly explained by local factors

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.
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Doi: 10.1111/wre.12040

Resum:

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.

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