Towards a mechanistic understanding of variation in aquatic food chain length revealed by meta-analysis

Ecologists have long sought to understand the forces determining food
chain lengths (FCLs). Multiple hypotheses have proposed a diverse array of
potential environmental determinants of FCL, typically including ecosystem
size, resource productivity, and disturbance. Yet, many empirical studies
have found that FCL responses to these environmental variables can be
positive as well as negative. To explain such mixed responses, we develop
a simple yet comprehensive, site-occupancy dynamic framework for complex
food webs by integrating multiple environmental drivers. With the
competition-colonization tradeoff among basal species, our model shows
that increasing ecosystem size results in a monotonic increase in FCL as a
whole, while FCL displays a non-linear, oscillatory response to resource
productivity or disturbance in benign environments. These predictions are
generally supported by our meta-analysis of an empirical dataset compiled
from diverse aquatic ecosystems. Therefore, this unifying framework offers
a novel mechanistic explanation for observed variation in FCLs driven by
multiple environmental factors.

长期以来，生态学家一直致力于探究决定食物链长度（Food Chain Lengths, FCL）的核心驱动因子。诸多假说已提出了一系列潜在的食物链长度环境决定因子，通常涵盖生态系统规模、资源生产力与干扰作用。然而，大量实证研究发现，食物链长度对这些环境变量的响应既可能为正，也可能为负。为解释这种矛盾的响应结果，我们整合多种环境驱动因子，构建了一个简洁而全面的复杂食物网位点占据动态框架。通过纳入基位物种（basal species）间的竞争-定殖权衡（competition-colonization tradeoff）关系，我们的模型显示：整体而言，生态系统规模的扩大会导致食物链长度呈单调递增趋势；而在良性环境中，食物链长度对资源生产力或干扰作用则呈现出非线性的振荡响应。我们对来自多样水生生态系统的实证数据集开展的荟萃分析（meta-analysis），总体上支持了上述预测结果。因此，这一统一框架为多种环境因子所驱动的食物链长度变异提供了全新的机理解释。