Avoiding artifacts when varying the number of species in ecological models

Optimizing the landscape in grain production and identifying trade-offs between ecological benefits based on production possibility frontiers: A case study of Beijing-Tianjin-Hebei region

There are severe conflicts between grain production and ecological benefits, and how to explore the critical configurations of agricultural landscapes and natural habitats to clarify sustainable scenarios remains unclear. Thus, this study explored a transferable approach to generating the production possibility frontiers of trade-offs between grain production and ecological benefits (biodiversity, carbon sink, and water consumption) under unconstrained, ecological constraint, and agricultural and ecological constraint scenarios, and identified the threshold and safety area for landscape optimization in the Beijing-Tianjin-Hebei (BTH) region of China. When reaching the Pareto optimality of trade-off frontiers, the grain yield and biodiversity increased by 10%-17%, the grain yield and carbon sink increased by 15%-48%, and the grain yield and water consumption improved by 4%-25%. The grain production and ecological benefits were outside the safety area in the BTH region, and the landscape optimization strategy was different for each trade-off. Both the food and biodiversity security can be further improved through increasing by 2.7% of cropland in the BTH region. The land use strategy of converting 6.8% of the cropland of the BTH region into forest land can promote carbon sink security. Although the land use strategy of converting 2.3% of the cropland of the BTH region into grassland can promote water security, more effort should be focused on technological innovation. This study highlights that landscape optimization will promote landscape multifunctionality and provides quantitative landscape optimization thresholds and safety boundaries for improving grain production and ecological benefits.

Functional diversity buffers the effects of a pulse perturbation on the dynamics of tritrophic food webs

Biodiversity decline causes a loss of functional diversity, which threatens ecosystems through a dangerous feedback loop: This loss may hamper ecosystems' ability to buffer environmental changes, leading to further biodiversity losses. In this context, the increasing frequency of human-induced excessive loading of nutrients causes major problems in aquatic systems. Previous studies investigating how functional diversity influences the response of food webs to disturbances have mainly considered systems with at most two functionally diverse trophic levels. We investigated the effects of functional diversity on the robustness, that is, resistance, resilience, and elasticity, using a tritrophic-and thus more realistic-plankton food web model. We compared a non-adaptive food chain with no diversity within the individual trophic levels to a more diverse food web with three adaptive trophic levels. The species fitness differences were balanced through trade-offs between defense/growth rate for prey and selectivity/half-saturation constant for predators. We showed that the resistance, resilience, and elasticity of tritrophic food webs decreased with larger perturbation sizes and depended on the state of the system when the perturbation occurred. Importantly, we found that a more diverse food web was generally more resistant and resilient but its elasticity was context-dependent. Particularly, functional diversity reduced the probability of a regime shift toward a non-desirable alternative state. The basal-intermediate interaction consistently determined the robustness against a nutrient pulse despite the complex influence of the shape and type of the dynamical attractors. This relationship was strongly influenced by the diversity present and the third trophic level. Overall, using a food web model of realistic complexity, this study confirms the destructive potential of the positive feedback loop between biodiversity loss and robustness, by uncovering mechanisms leading to a decrease in resistance, resilience, and potentially elasticity as functional diversity declines.