Inconsistent responses of conservation biocontrol to landscape structure: new insights from a network-based review.

Abstract

Conservation biological control (CBC) has been an active research topic for the last two decades and is now one of the key ways being explored to develop agroecological production systems. Using broad concepts and indicators, recent reviews and meta-analyses have highlighted major inconsistencies in the responses of CBC to landscape structure, revealing their context-dependent nature. To decipher these relations, we reviewed the scientific literature (50 articles) using (i) an original ontology allowing us to navigate across the different terms and concepts used in this literature, and (ii) a network-based methodology to describe the scattering, completeness and generalizability of scientific knowledge on CBC. An interactive version of this network is available online. Our results highlight the strong information scattering caused by the variety of indicators used to describe both landscape structure and CBC. We observe trade-offs between the use of coarse concepts classically used in meta-analysis (e.g. landscape complexity) and the non-convergence of results (ambiguity). The network analysis points out consistantly less information ambiguity when considering sub-networks focused on trophic chains than in the full information network, without losing connectance. We suggest that effects of landscape structure may be different between trophic chains because of specific selection pressures associated to cropping systems. Our novel review procedure offers a relatively simple but powerful complementary approach to classical meta-analysis to explore ecological patterns. It highlights that crop trophic chain probably represents the adequate ecological unit to investigate landscape-CBC relationship. Designing pest suppressive landscapes while favoring farmland biodiversity will imply considering multiple crop trophic chains responding differently to landscape structure. Therefore, we recommend to assess the level of CBC at both crop field and landscape scales to inform decisions on the best individual or collective strategy to adopt.