An Ecosystem Model with Evolutionary Adaptive Trophic Structure

Philip J. Underwood<br>Doctorate of Philosophy<br>The School of Environmental Sciences<br>University of East Anglia<br>September 2013 <br>We live in an era of rapid change in ecosystems and their environments, that all scales up to the global. The contemporary view is that the interactions between life and the environment are bidirectional: the environment creates life and life creates the environment. However, most ecosystem models have an inbuilt rigidity such that the degrees to which they can mimic structural change in response to environmental cues is very limited. In an effort to capture the plasticity of life we present a new theoretical individual-based ecosystem model in the context of previous classical and experimental modelling approaches. The aim is to develop a deeper understanding of the factors determining trophic structure. The individual-based approach permits the inclusion of traits to model heritable attributes. Population-level models implement a mean-fi eld approximation that led to the competitive exclustion principle. The addition of a trait to de ne speci c feeding strategy permits the model exploration of this problem. Life history theory predicts that reduced juvenile mortality selects for delayed maturity and decreased reproductive effort, and reduced adult mortality will select for the opposite. Through the inclusion of a different trait to represent relative parental investment in offspring, we explore the predictions of life history theory and hypotheses for clutch size.

菲利普·J·安德伍德（Philip J. Underwood）<br>哲学博士<br>东安格利亚大学（University of East Anglia）环境科学学院<br>2013年9月<br>我们正处于生态系统及其生存环境快速变化的时代，此类变化的尺度可延展至全球范围。当前学界普遍认为，生命与环境之间存在双向交互作用：环境塑造生命，同时生命也会改造其生存环境。然而，绝大多数生态系统模型存在内在刚性，使其在响应环境信号以模拟生态系统结构变化方面的能力极为有限。为刻画生命的可塑性，本文在回顾既往经典建模与实验建模范式的基础上，提出了一种全新的基于个体的生态系统模型（individual-based ecosystem model）。本研究旨在更深入地解析决定生态系统营养结构的各类因素。基于个体的建模范式允许引入性状参数以刻画生物的可遗传属性。种群水平的模型通常采用平均场近似，由此推导出竞争排除原理（competitive exclusion principle）。通过引入表征特定取食策略的性状参数，本模型可对该问题展开探索。生活史理论（life history theory）预测：幼体死亡率降低会在自然选择下催生延迟成熟与繁殖投入降低的策略，而成体死亡率降低则会引发相反的演化方向。通过引入表征后代相对亲本投入的另一类性状参数，本研究对生活史理论的相关预测以及窝卵数（clutch size）相关假说展开了验证与探索。