Tailoring biocontrol to maximize top-down effects: on the importance of underlying site fertility

摘要: The degree to which biocontrol agents impact invasive plants varies widely across landscapes, often for unknown reasons. Understanding this variability can help optimize species management while also informing our understanding of trophic linkages. To address these issues, we tested three hypotheses with contrasting predictions regarding the likelihood success. (1) effort hypothesis: populations are regulated primarily by top-down effects, predicting that increased efforts alone (e.g., more individuals a given agent or time since release) will enhance (2) relative fertility bottom-up nutrient enrichment increase dominance invasives and thus reduce success, regardless efforts. (3) fertility-dependent effects only regulate if weak. It predicts greater but in low-nutrient sites. test hypotheses, surveyed 46 sites states prior releases Galerucella beetles, most common used against purple loosestrife (Lythrum salicaria). We found strong support hypothesis, as success occurred efforts, low-fertility This result held early stage metrics (higher abundance) ultimate outcomes (decreased plant size abundance). Presence grass Phalaris arundinacea was inversely related abundance, suggesting biocontrol-based reductions made secondary invasion P. likely. Our data suggest be prioritized future monitoring account variation site work mitigate it. introduce new framework integrates findings conflicting patterns previously reported from other systems, proposing unimodal relationship whereby availability enhances hampers it high-nutrient results represent one first examples depending on fertility, has potential inform decisions entire regions among systems.