No abstract

In extensive low input farming and in agroforestry systems, the importance for biodiversity of managed productive fields with respect to unmanaged marginal habitats that occupy a low proportion of farm surface, is still poorly understood, contrasting with the well-known key importance of marginal habitats in intensive systems. We analyzed the importance of open and wood pastures and marginal habitats for species richness of Iberian dehesas in Central-Western Spain. We sampled 155 plots classified into 9 general habitat categories: wood pastures (n = 41 plots); open pastures dominated by annual plants (n = 11), by perennial plants (n = 15) and co-dominated by annuals and perennial plants (n = 16); shrublands (n = 19); agricultural crops (n = 12); herbaceous strips (n = 10); woody strips (n = 11); and water bodies (n = 10). In each plot we measured the abundance and species richness of four taxonomic groups: vascular plants, bees, spiders, and earthworms. We detected 431 plant species (37 ± 2.5 CI 95 in 100 m 2 on average), 60 bee species (3.1 ± 1.1 in 600 m 2 ), 128 spider species (7.4 ± 1.2 in 1.5 m 2 ) and 18 earthworm species (2.5 ± 1.0 in 0.27 m 2 ) in 145 sampling plots. Wood pastures supported fewer species of spiders and earthworms at the plot level, but more plants and earthworm species at the landscape level than open pastures. The low proportion of shared species among habitats and among plots within each habitat type, and the high proportion of species found in unique plots or habitats indicated that every habitat contributes to farm biodiversity. Overall, our extensive survey confirms the hypothesis that the high diversity of dehesas depends on the coexistence within farms of a wide mosaic of habitats, including marginal habitats, which seemed to harbor a disproportionately high number of species as compared to their small extent. Results support policy measures for the maintenance of farm keystone structures such as linear features, small wood/shrub patches and ponds, and reveal that these measures should not be exclusively applied to more intensive farming systems.

Aim To investigate the ecophysiological traits allowing persistence of a subtropical relict tree (Prunus lusitanica L.) under a dry Mediterranean climate at the eroding edge of its range.Location A glasshouse for the study under controlled conditions and two marginal populations located in riparian forests of central Spain and exposed to summer drought, in contrast to subtropical populations that grow in mountain cloud forests.Methods Two experiments were conducted to assess tolerance to the abiotic conditions found in riparian habitats. In a glasshouse experiment, gas-exchange and light-use parameters were measured to evaluate seedling responses to a factorial combination of irradiance (60%, 10%, 2% and 0.5% full sun) and moisture (well watered control and drought stress). In a parallel field experiment, irradiance and soil moisture were measured as predictors of seedling survival at two sites in which half the seedlings were subjected to a threefold increase in summer precipitation by adding water every 10 days.Results Soil moisture strongly determined survival both in the glasshouse and in the two field sites. In the field, periodic addition of water failed to increase survival. Water-use efficiency (WUE) increased with drought. Seedlings did not tolerate deep shade (2-0.5%) and their performance and survival were better when exposed to moderate (10%) or high (60%) irradiance. The effect of water stress on seedling performance was stronger at moderate irradiance, moderate at high irradiance and negligible at very low light. Seedling size (height and number of leaves) attained after 1 month of experimental treatments had a positive effect on survival at the end of the summer, hence greater survival was not achieved at the expense of vertical growth.Main conclusions While studies in Macaronesia have shown that P. lusitanica occupies a wide range of moisture conditions along mountain slopes, it behaves as an obligate riparian species in dry peripheral populations. Intolerance to deep shade and tolerance to moderate and high irradiance allow the species to grow in small and moist gaps, or in treeless river sections. Despite the species' low range filling in marginal, drought-prone regions, long-term persistence might have been achieved through shifts to riparian habitats serving as local refuges.

Hoverflies are frequently used as biodiversity indicators and are targets of ecological studies across Europe. How hoverfly diversity responds to ecological variables is essential for species and habitat conservation. The present study is a first attempt to assess the hoverfly diversity of deciduous woodlands of Pyrenean oak (Quercus pyrenaica) in La Vera (Central-Western Spain), a habitat in need of conservation and a region that is poorly known in terms of hoverflies. Hoverflies were sampled with hand net in a mature-woodland site, a young-woodland site, and two close-by grassland sites. A higher number of species and individuals was recorded in woodland sites than in grassland sites, with only two species exclusive to the grasslands and thus, suggesting that woodland sites might be acting as a hoverfly reservoir and source. The proportion of species with phytophagous and saprophagous larvae in woodland sites was higher than outside the woodlands, probably due to a higher availability of resources in woodland sites for phytophagous and saprophagous species. The mature woodland was found to have a higher number of species and individuals than the young woodland, possibly due to the presence of grassy clearings and rotting materials in the trees of the mature woodland. The highest number of species was found in the predatory guild (Syrphinae), and smaller-bodied species within this guild were found to be more frequent in grassland than in woodland sites; possible explanations for this result are discussed. Further investigation is required to confirm and expand the results and conclusions found in this initial study on the hoverfly community of the poorly studied Q. pyrenaica woodlands of Central-Western Spain.

Insect herbivory decreases plant fitness by constraining plant growth, survival and reproductive output. Most studies on the effects of herbivory in trees rely on correlational inter-individual comparisons and could, thus, be affected by confounding factors linked to both herbivory and plant performance. Using the Mediterranean Holm oak (Quercus ilex) as a study model, we followed an experimental approach in which leaf-feeding insects (mainly Lepidoptera caterpillars) were excluded from some shoots in all study trees. Shoots subjected to herbivore exclusion exhibited lower defoliation rates and produced more acorns than control shoots. Defoliation constrained shoot growth throughout the study period, but had no effect on the number of female flowers produced per shoot. Acorn production was, however, lower in control shoots due to their higher abortion rates, and also to their greater mortality risk during summer drought, as shoots with fewer leaves were less likely to survive. Plant reaction to herbivory inhibits certain physiological pathways involved in plant growth, which, together with the effects of physical damage, reduces the amount and efficiency of the photosynthetic tissue. This increases their vulnerability to environmental stresses, such as water deficit, which limit resource assimilation. Defoliation is likely a key factor affecting oak regeneration, as it may be a significant source of seed loss prior to pre-dispersal acorn predation. Further experimental studies could help to elucidate its effects in contrasting environments. In Mediterranean regions, the harsher droughts predicted by climate change models could worsen the effects of insect herbivory on oak reproductive output.