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基于能量平衡模型的食物网关键种识别研究
Identifying Keystone Species in Food Webs Based on An Energy-budget Model
【作者】 赵磊;
【导师】 张化永;
【作者基本信息】 华北电力大学(北京) , 能源环境工程, 2017, 博士
【摘要】 当前地球生态系统面临物种灭绝加速、多样性丢失严重等突出问题。由于物种互相联系并构成了复杂的食物网,某个物种的灭绝所带来的影响很可能会沿着食物网传递出去,并造成一系列的次生灭绝,使得本已日益严重的多样性丢失问题雪上加霜。因此,准确地识别食物网中的关键物种,不仅有助于探索生态系统对物种灭绝的响应机制,更有利于确定物种保护的优先级,以便于将有限的资源投入到最关键的位置。本研究首先收集并分析了包含物种间碳流动的食物网数据,从中筛选出20个食物网作为论文研究的对象。一方面,分析食物网的拓扑结构,利用传统的拓扑方法研究特定序列的物种移除所引发的次生灭绝,以研究不同物种在食物网结构上的重要性。另一方面,基于食物网中的能量平衡模式,构建动力学模型以刻画食物网中不同物种的生物量变化,并模拟不同的移除序列所引发的次生灭绝,以研究不同物种在功能上的重要性。这些移除序列包含了四个不同尺度的物种重要性指标,包括考虑物种自身属性的基于生物量的指标,考虑物种间营养连接的基于权重和间接影响的指标,考虑特定营养模块的基于物种对模块参与度的指标,考虑子网络的基于物种到其它子网络距离的指标。这四类指标由小到大,层层递进,从不同的角度研究了物种重要性的排序和关键物种的检测。研究结果如下:(1)在拓扑分析和动力学分析中,基于最大生物量的物种移除比基于最小生物量的移除造成了更多的次生灭绝和对食物网稳定性的损害,表明生物量大的物种在维持食物网结构和功能上均发挥了重要的作用。传统的度中心性指标在拓扑分析中表现良好,但在动力学分析中不能有效的度量物种的重要性。(2)考虑连接权重或间接作用的序列移除比传统的仅考虑物种连接数的序列移除造成了更多的次生灭绝和更多稳定性的损害,表明考虑权重或间接作用的指标比传统的连接数指标在度量物种重要性方面更为有效。这一结论在拓扑分析和动力学分析中是一致的。(3)在拓扑分析和动力学分析中,基于物种对模块资源参与度的序列移除产生的次生灭绝比随机移除显著多,而基于物种对集团被捕食者和集团捕食者的序列移除产生的次生灭绝与随机移除没有显著差异。这表明对模块的资源参与度高的物种在维持食物网结构和功能方面更为重要,而对模块的被捕食者和捕食者参与度高的物种未显示出重要性。(4)在拓扑分析和动力学分析中,基于物种到子网络最短距离的序列移除比基于最大距离的序列移除及随机移除所产生的次生灭绝要多,对食物网稳定性的损害也更为显著。这表明不同子网络连接处的物种在维持食物网整体结构和功能方面更为重要。(5)比较食物网对不同移除序列的抵抗能力,发现在拓扑分析中,定向连接度高的食物网即连接更为紧密的食物网对于物种灭绝的抵抗能力更强;在动力学分析中,物种数更多的食物网对物种灭绝的抵抗能力更弱,定向连接度和加权连接度高的食物网对于物种灭绝的抵抗能力更强。本论文在四个不同尺度提出了全新的度量物种重要性的指标,并利用拓扑方法和动力学方法对这些指标进行了验证。这些指标的提出为生物多样性保护策略的指定提供了一定的参考价值。本文还证明了传统的度中心性指标可用于度量物种的结构重要性,但在度量物种功能重要性方面没有效果。这一结论表明了前人关于食物网中心性的研究可能高估了度中心性的重要性。另外,本文基于物种之间的碳流动数据构建了食物网动力学模型,其模型参数均由实际数据计算得出,因此在未来的理论研究工作中具有极大的应用价值。
【Abstract】 Currently our Earth’s ecosystems are suffering several serious problems,such as the accelerating rate of species extinctions and the biodiversity loss.Prior studies point out that we have entered what has been described as the Sixth Great Extinction.Species are not isolated,but connected with each other into complex food webs.The effects of the extinction of a species could spread along the food web and trigger the cascading extionctions,i.e.secondary extioncions.This would undoubtedly worsen the already severe problem of biodiversity loss.Therefore,identifying the keystone species in food webs correctly would be helpful in understanding the underly mechanisms of the response of ecosystems to species loss.It can further help determining the priority of species to be conserved,and increase the efficient allocation of limited resources.This study firstly gathered and analyzed the food web data of carbon flux,with 20 food webs selected as the objects of the study.The classical topological approach was applied to simulate the secondary extinctions in different deletion sequences and investigate the structure importance of different species.Then,a dynamic model based on energy budget was built up to depict the biomass change of species in the food webs.The secondary extioncions in different deletion sequences were recorded based on the dynamical simulations,in order to investigate the functional importance of different species.These deletion sequences reflect several importance indices at four different scales,including the biomass which is based on species traits,the indices considering trophic link weight and indirect effects which is based on the interactions between species,the contribution of species to trophic modules,and the distance of species to other compartments.These four groups of indices investigate the importance of species importance and detect the keystone species from small scale to large scale and from simple to complex.The findings of these four groups of indices are listed as following:(1)In both topological and dynamical analyses,the species removal based on maximum biomass caused more secondary extinctions and more damage to food web stability than the removal based on minimum biomass.This indicates that the species with large biomass can play important role in maintaining the structures and functions of food webs.Degree centrality,one of the classical indicators,performed well in topological analyses,but it could not indicate the species importance in dynamical analyses.(2)The species removal considering link weight and indirect effects triggered more secondary extinctions and caused more damage to food web stability than the traditional indicator based on number of links.This indicates that the indices considering link weight or indirect effects performed more effective than the traditional indicator in measuring the species importance.This conclusion is consistent in both topological and dynamical analyses.(3)In both topological and dynamical analyses,species remo vals based on the contribution of species to the IGP resource generated more secondary extinctions than random deletion,while removals based on the contribution to the IGPrey or IGPredator showed no significant difference with random deletion in the numbe r of secondary extinctions.This indicates the species which contribute much to the IGP resource are crutial in maintaining the structures and functions of food webs.The species which contribute much to the IGPrey or IGPredator do no show any importance.(4)In both topological and dynamical analyses,species removals based on the shortest distance of a species to the compartments caused more secondary extincitons and more damage to food web stability than removals based on the longest distance and random removals.This indicates the species connecting different compartments would be more important in maintaining the whole structures and functions of food webs.(5)Comparing the resistance of food webs to different deletion sequences,the following findings have been achieved: in topological analyses,food webs with high directed connectance,i.e.well connected food webs,showed high resistance to species loss;in dynamical analyses,food webs with high richness showed low resistance to species loss,while food webs with high directed connectance or weighted connectance showed high resistance to species extinctions.This study proposed new indices measuring species importance at four different scales.Topological and dynamical approaches were used to test th e efficience of these indices.These new indices provide reference for the development of the strategy of biodiversity protection.This study also proved that the traditional degree centrality could be used in measuring the structure importance of species,but should not be used in measuring the functional importance.This finding suggest that the prior studies have overestimated the relative importance of degree centrality.Furthermore,a food web dynamic model has been built up based on the carbon flux between species.The parameter values of this model are calculated from the empirical data and thus should be of great application in theoretical studies in the future.
【Key words】 food web; carbon flux; keystone species; stability; deletion sequences; centrality;
- 【网络出版投稿人】 华北电力大学(北京) 【网络出版年期】2017年 12期
- 【分类号】Q148
- 【被引频次】4
- 【下载频次】507
- 攻读期成果