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Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Euphorbia characias is a common myrmecochorous plant of the western Mediterranean Basin whose seeds are dispersed by ants following fruit explosion. The variation in elaiosomes’ fatty acid composition of this species was studied at three hierarchical levels (sub-individual, individual and population) in four populations from the Iberian Peninsula. We found that differences in fruit location on the inflorescence do not seem to influence the fatty acid composition of elaiosomes, providing to each propagule an equal chance of being dispersed. However, significant differences in elaiosome fatty acid composition between individuals and populations were found for most of the compounds identified. The content of oleic acid, a key mediator in the ant–seed interaction, differed widely between populations, probably reflecting geographic variations in co-adaptation between plants and their dispersers. The finding that the fatty acid composition of E. characias elaiosomes is distinct from that of the seed itself, but very similar to that of elaiosomes from unrelated species, reinforces the idea of convergent evolution in the chemical composition of these structures. [Copyright &y& Elsevier]

• Food-chain length is an important property of food-webs in forests. • Three hypothesis might explain variation in FCL in forests. • We found support for the disturbance hypothesis arising from wild boar rooting. • Increased soil nutrient concentrations may reduce FCL in chestnut forests. • Promoting understory plant richness may increase FCL in chestnut forests. Food-chain length, or the trophic level of an apex predator, is among the most important properties of food-webs with implications for community structure, ecosystem processes and pollutant accumulation in forests. Three main hypotheses (ecosystem-size, productivity, and disturbance) have been erected to explain variation in food-chain length in freshwater ecosystems, yet the support for these hypotheses in less spatially restricted terrestrial ecosystems has not been extensively studied. Here, we used nitrogen (δ15N) and carbon (δ13C) stable isotopes to explore variation in the realized trophic positions (δ15N) of a beetle Carabus lineatus lateralis and a wasp Vespula vulgaris in 32 chestnut woodland patches in northwestern Spain, while accounting for the insects' relative mobility by using inferences based on δ13C. We used five potential predictors of ecosystem-size productivity, seven of disturbance and six covariates in anticipation that biological assemblages in woodlands might be influenced by ecosystem-size productivity, and from a change from the human management to a much-increased activity of ecosystem engineers, especially wild boar. Our results provided support for the disturbance hypothesis and suggested that the beetle FCL seems to be more affected by wild boar disturbance than by human-forest management, possibly due to increased forest cover and to rural abandonment in recent decades. Moreover, we found a negative association between the wasp FCL and the ecosystem-size productivity hypothesis, as indicated by the plant Ellengberg's indicator value for nitrogen, which contrasts to the hypothesis that ecosystem-size productivity should increase FCL. Our findings are discussed in relation to: (1) differences in intensity and frequency between human- and wild boar-induced disturbances; (2) the diets and mobilities of the two predators; and (3) the near lack of hard ecological boundaries in terrestrial ecosystems, such as chestnut woodlands. [ABSTRACT FROM AUTHOR]

• Streams may promote non-riparian forest diversity, including arthropods. • Rural abandonment increases structural vegetation development. • Tall and diverse understories promoted several groups of arthropods. • High tree richness was negatively associated with many arthropod measures. • Effects of stream distance on arthropods largely depended on vegetation structure. Streams are likely to be increasingly important for the conservation of non-riparian forest diversity with increased aridity due to climate change in many parts of the world. However, the importance of streams as promoters of non-riparian forest diversity has not been explored in detail. Given the likely stronger effect of surrounding habitats on open forests, we examined chestnut woodlands in northern Spain (n = 32) to explore the contribution of streams to variation in arthropod measures. We captured 5,490 arthropods (21 orders and 60 families) from which we calculated total abundance and richness and the abundance of trophic guilds. Vegetation structure at the tree and understory levels often made the largest independent contributions to explained variation in arthropod numbers and effects suggested alterations in arthropods' food-web. Negative effects of stream-distance on taxon richness and the abundance of predators, omnivores and phytophages seemed to be largely mediated by vegetation structure. The exception was a strong univariate inverse association between the abundance of aerial predators and stream distance, possibly because wasps might be exploiting riverine habitats. Overall, effects of stream-distance were weaker for ground than for aerial arthropod groups. Moreover, arthropod numbers were greater at sites with low tree species richness and tall and species-rich understories, raising concerns for the ecological consequences of the abandonment of traditional forest practices in these woodlands. There are likely to be advantages for arthropod diversity and ecosystem services (e.g. pest control, nutrient cycling, pollination) if non-riparian forests are managed in a way that depends on stream-distance. Inferences may improve with a more complete knowledge of the biology of poorly studied groups, such as flies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Irrigation and fertilization create a spatial gradient in water and organic matter availability. • Soil macroinvertebrate communities beneath the trees differed from those located one meter away. • Beneath the trees, there was a higher number of detritivores and predators. • Species beneath the trees seem to rely more on plant-based resources than those located further away. • We delimited two food webs at one-meter scale that are mostly compartmentalized. Soil macroinvertebrates play a central role in ecosystem processes such as decomposition and nutrient cycling, but the extent to which macroinvertebrate food web structure varies within ecosystems is basically unknown. Here, we examined changes in plant and macroinvertebrate community composition at increasing distances from trees within a citrus grove, following a gradient in organic matter and water availability created by the localized fertilization and irrigation of citrus trees. In addition, we analysed stable isotope signatures (δ 13C and δ 15N) of soil, plants, and macroinvertebrates to investigate changes in trophic structure within the grove. The macroinvertebrate community near the tree trunks had a higher number of detritivores and predators than the community located farther away. After correcting the isotope values of macroinvertebrates by their isotopic baseline, a spatial shift in trophic structure emerged: macroinvertebrates near the trunks had lower δ 13C-values than those located farther away (i.e., they apparently relied more on plant- based resources). This pattern is attributable to species only found near the trunks. In contrast, species distributed across the studied area showed no differences in their isotopic signatures across space, suggesting that they are connecting otherwise two compartmentalized food webs. A reduction in organic matter and water availability at increasing distances from trees is the most parsimonious explanation of the observed isotopic gradient in soil and plants, and this may, in turn, be responsible for the observed changes in food web composition and structure. This study shows that spatial variability in macroinvertebrate soil food webs can be present at scales as small as one meter if spatial variability in environmental factors is high enough. [ABSTRACT FROM AUTHOR]

Abstract: Pre-dispersal seed predators can have a severe impact on the reproductive output of their hosts, which can translate into negative effects on population dynamics. Here we compared the losses due to specialist and generalist insect seed predators in two Euphorbia species, a rare (Euphorbia welwitschii) and a common one (Euphorbia characias). Pre-dispersal losses to specialist seed-wasps (Eurytoma jaltica) and generalist hemipterans (Cydnus aterrimus and Dicranocephalus agilis) were on average higher for the rare E. welwitschii than for its widespread congener. In both Euphorbia species, the variation in losses to specialist and generalist seed predators was not related with traits indicative of plant size, fecundity, or isolation. Nevertheless, the temporal variation in losses to seed-wasps seemed to be intimately associated with the magnitude of yearly variation in fruit production. The impact of seed-wasps and hemipterans on the reproductive output of both Euphorbia species was additive, though there was evidence for infochemical-mediated interference at the fruit level. The moderate levels of seed predation in E. welwitschii, together with the results from the comparative analysis with its widespread congener, suggest that insect seed predation is not a causal effect of plant rarity. [Copyright &y& Elsevier]