Research On Dynamical Stability And Key-stone Species Identification Of Complex Food Web

The dynamic stability and key-stone species identification of complex food webs are the frontier and hotspot in ecology filed.In this thesis,three complex food webs with different degrees of complexity were analyzed,via establishing differential dynamic model of food web to study the chaotic dynamics and quantitatively determining the chaos of food web by using Lyapunov exponent spectrum and Lyapunov dimension.Based on the comparison on the change of chaotic properties of food webs before and after species removal,the species of food webs were sorted by the difference of Lyapunov dimension;then,the sub webs in food webs were decomposed with each species as the core,and the key-stone species and the 'key clusters' of each food web were determined by analyzing the complexity of the sub webs and comparing the Lyapunov dimension of the original food web.The results can be described as follows:(1)The chaotic characteristics of complex food webs enhance with the increase of species numbers.The impact of species removal on the food web of high complexity is far less than that of low complexity.The removal of specific species in the food web of low complexity will cause dramatic change of the food web dynamic properties,while the food web of high complexity does not show such phenomenon,indicating that the dynamic stability of the food web may become stronger with the increase of the food web chaotic complexity.(2)Bidirectional recognition may occur in the recognition of key-stone species based on chaotic dynamics,that is,the food web may demonstrate key species as"stable factor"(the difference of Lyapunov dimension is positive)which maintains the stability of food web or as "unstable factor"(the difference of Lyapunov dimension is negative)" which makes the food web exhibiting more complex changes.Such bidirectional recognition was rarely found in previous studies,and this study reveals the rule of bidirectional recognition on the chaotic dynamics of food webs.(3)The simulations where species removal is adopted for the food web find that the chaotic characteristics of the sub-webs containing key species may also be weak,indicating that the key species and the core species of the "key cluster" are not exactly the same.The "key cluster" is not necessarily composed of the sub-webs of the key species,and multiple species which are not key in the food web can also produce an important "key cluster".Based on the chaotic dynamics of the food web dynamic model,this thesis investigated the importance ranking of the species in the food web,explored the food web dynamic stability and identified the key species.revealed the changing rule of the complex food web on the chaotic characteristics,providing a theoretical basis for key-stone species conservation and ecological balance maintenance in ecosystems.