Ecological infrastructures and organic farmingeffects on beneficial arthropod communities in Mediterranean traditional crops

Resumen

The current scenario of global threats to biodiversity coupled with the growing concern about the long-term sustainability of agroecosystems has led to the development of measures including the maintenance of ecological focus areas such as non-cropped habitats or the promotion of environmentally friendly agricultural practices such as organic farming. Under this scenario of biodiversity loss, the preservation of ecological infrastructures is crucial to maintain ecosystem functions and to deliver ecosystem services such as pollination or biological control of pests, which largely determine agricultural productivity and food security. In addition, the development of reliable evaluation schemes is essential to assess the status of biodiversity. In agroecosystems, ecological infrastructures contribute heavily to enhance biodiversity and underlying services, and their contribution depends on their ecological quality. Based on the questionnaire by Boller et al. (2004) for temperate areas, we propose a reliable tool for evaluating the ecological quality of woodland patches, hedges and grass strips associated with Mediterranean agroecosystems (simplified questionnaire). Since management practices and organism composition vary across geographical regions, the implementation of evaluation tools adapted to other geographical regions is deemed necessary. The development of the simplified questionnaire followed a five-steps' approach: (i) application of the Boller's questionnaire in the field; (ii) Boller's questionnaire adaptation; (iii) development of the simplified questionnaire through the assessment and simplification of Boller's questionnaire; (iv) evaluation of the simplified questionnaire effectiveness; (v) proposal of plant indicator species associated to the different quality levels obtained from applying the simplified questionnaire, as an additional tool for quality assessment that complements such questionnaire. A total of 482 ecological infrastructures were evaluated in La Rioja (Spain) in 2014. We point out that the assessment tool based on simplified questionnaire is straightforward and easy to apply by both experts and non-experts. We also propose the simplified questionnaire development procedure as a guide to create evaluation questionnaires adapted to other ecological infrastructure types. The role that ecological infrastructures such as hedges or strips have in enhancing functionally important groups has been reasonably well investigated in temperate areas. However, it is much less documented in agroecosystems from the Mediterranean basin, even though this area has been identified as a biodiversity hotspot for conservation priorities. We analyzed, in a study developed during 2014 in a traditional vineyard agroecosystem in La Rioja (Northern Spain), the beneficial arthropod communities across four types of linear ecological infrastructures: woodland hedges, rosaceous hedges, grass strips and flower strips. We investigated the value of these elements as a source of predators, parasitoids and pollinators. We show that the abundance, richness and distribution of families of each functional group is determined by features characterizing the different types of those infrastructures. Ecological infrastructures with a suitable level of structural diversity constitute an important reservoir of predators. On the other hand, parasitoids and pollinators were limited by the availability of hosts, pollen and nectar resources. Flower strips, less complex infrastructures that offer a high amount of floral resources, benefited communities of both parasitoids and pollinators. Within arthropods, spiders are generalist predators that are considered important components of biodiversity in vineyard ecosystems, where they can play a prominent role in the natural control of pest populations. Nevertheless, the influence that ecological infrastructures have on driving spider assemblages in Mediterranean vineyard agroecosystems is practically unknown. The spider assemblages across woodland hedges, rosaceous hedges, grass strips and flower strips were analyzed in a study conducted in La Rioja. These assemblages were examined across three levels of organization (taxon, guild and body-size group). Abundance and richness of spiders were higher in more structurally diverse infrastructures. The response to habitat type differed among guilds but, overall, higher densities of spiders from different guilds were found in hedges. Body-size groups had a more balanced distribution in strips and hedges with higher levels of structural diversity. Due to the variability in habitat preferences found among the different functionally important taxa of predators, parasitoids and pollinators, we highlight the importance of preserving different types of ecological infrastructures across vineyard agroecosystems to maintain well-structured assemblages of beneficial arthropods and maximize underlying services. Our results suggest that it is also crucial to preserve complex and heterogeneous ecological infrastructures to maintain diversified spider assemblages. In addition to the role that ecological infrastructures have in the maintenance of the biodiversity in agroecosystems, some of the negative effects of agricultural intensification on biodiversity can be counteracted by the implementation of the more sustainable management practices that organic farming uses. In terrestrial ecosystems, both land use and topographic features are important filters in shaping taxa distribution. It is essential to identify which factors significantly drive changes in populations in order to maximize the abundance and richness of beneficial arthropods and the underlying services across agroecosystems. We examined beneficial arthropod communities to disentangle the extent to which predators, parasitoids, and pollinators are conditioned by local field management (organic vs. conventional management) and topographic features (hillside aspect). Beneficial arthropod communities were assessed in traditional cherry orchards in western Spain. Overall, dominant or most representative parasitoid and pollinator taxa benefited from organic management, whereas predators showed a more heterogeneous pattern due to their varying responses to habitat characteristics. Topographic features, although being a factor for some of the studied groups, did not strongly affect beneficial arthropod communities. We additionally explored the response of spider community to the farming system (organic and conventional) and the hillside aspect (sunny or shady) from a taxonomical, behavioral, and morphological perspective. Spiders were identified to family and classified in body size classes. According to their foraging behavior, spiders were additionally sorted in guilds and, for a selected family of each guild, morphological traits were measured on each individual. Spider traits and composition are determined both by local factors derived from farming system, as well as by climate conditions associated to the hillside aspect. In taxonomical terms, spiders benefit from organic farming and by the shady aspect. However, from a guild perspective, spiders respond more heterogeneously to such factors, with strong variations among different feeding behaviors. Additionally, morphological traits within guilds vary in response to management practices that constitute conditioning disturbance events for each guild, resulting in filtering small individuals. Our results indicate that the effects of farming system on beneficial arthropods are not easily predictable. Due to the variability in habitat preferences found among different functionally important taxa, we highlight the importance of continuing to unravel the specific responses of beneficial arthropods to local management practices. Furthermore, differences in taxonomical, behavioral, and morphological responses of spiders to habitat properties highlight the importance of examining their assemblages from different perspectives.