人类活动效应对物种多样性影响的动力模拟——以洪湖湿地生境毁坏对水鸟物种多样性的影响为例

提出了随时间变化的人类活动效应对物种多样性影响的多物种竞争非自治动力模式,并以洪湖为例模拟了湿地水鸟物种多样性对人类活动效应（生境持续毁坏）的响应过程。模拟发现：对于强．强物种,生境的持续破坏使得湿地水鸟的物种多度大幅度减小,并发生优势种群的更替;对于弱-弱物种,将导致大批的弱物种种群迅速灭绝,而余下的弱物种种群将做准周期振荡;尽管停止对湿地生境的持续毁坏,仍会使一批弱物种种群继续走向灭绝,并且使得原来最强的几个种群最终灭绝。物种灭绝对生境毁坏的这种时间滞后性,即破碎的生境中存在着一些“活死者”,必须引起自然保护学家的关注,否则会低估了实际处于灭绝边缘的物种的数目,从而影响正确的物种保护决策的制订。     

集合种群动态对栖息地毁坏时空异质性的响应

栖息地毁坏既有时间异质性,也有空间异质性,而以往的研究往往只关注其中的一种。将两种不同的异质性共同引入到元胞自动机中,模拟了集合种群动态对栖息地毁坏时空异质性的响应。发现,在随机离散的栖息地毁坏下,由于物种的迁移繁殖力受栖息地毁坏的影响很大,迁移繁殖力弱而竞争力强的物种先灭绝。在连续的栖息地毁坏下,物种的迁移繁殖力受栖息地毁坏的影响较小,物种的灭绝由竞争力和迁移繁殖力共同决定:在有绝对优势种的群落里,种间竞争显著,弱物种先灭绝,而在没有绝对优势种的群落里,种间竞争较小,则以强物种先灭绝。因此,随机毁坏不利于强物种续存,而连续毁坏则不利于具有绝对优势种群的群落里的弱物种续存。在实际开发某一栖息地时,根据集合种群结构和被保护的对象采取相应的开发模式。     

不同生境毁坏速度下的物种灭绝机制

已有似Levins的多物种模型,在研究生境毁坏的影响时,一方面主要集中在对瞬间毁坏影响的研究,另一方面主要研究生境毁坏对强物种影响的研究。在Tilman的多物种竞争共存模型的基础上,同时考虑了生境毁坏直接效应和生境毁坏时间异质性,提出了全新的普适的多物种竞争共存的非自治动力模式。通过模拟物种灭绝对不同速度的生境毁坏时间异质性的响应发现：（1）物种灭绝既存在强物种由强到弱的灭绝,也存在弱物种由弱到强的灭绝。同时,弱物种灭绝机制进一步分为弱物种瞬间集体灭绝,以及较长时间由弱到强的灭绝。（2）生境毁坏速度越快,物种灭绝的时间越短,弱物种灭绝的越多,因此,生境毁坏速度越慢,越有利于弱物种的长期续存。（3）最强物种的多度越大,强-强物种抵御生境毁坏的能力越强,而弱-弱物种抵御生境毁坏的能力越弱,集体灭绝的弱-弱物种就越多。最强物种的多度大的群落（如温带森林）,主要发生的是弱-弱物种灭绝,而最强物种多度小的群落（如热带雨林）同时发生强-强和弱-弱物种的灭绝。因此,争对不同结构的集合种群,不同的保护对象,应采取不同的管理策略。     

集合种群强物种种群的演化特性

大量的数值模拟研究表明;(1)集合种群里最强物种种群对栖息地占有率相对较少时,较小的栖息地毁坏率就可以导致该最强物种种群与其它奇数物种种群一起退化;(2)而最强物种种群对栖息地占有率相对较多则是导致集合种群里弱物种种群集体灭绝的内因;(3)当栖息地的毁坏率大于最强物种种群对栖息地的占有率时,最强物种种群将先灭绝而使得弱物种种群进化为强物种种群或新的更强的强物种种群。     

生境变化对集合种群系统生态效应的影响

通过大量的数值模拟发现 :生境恢复或扩展将导致集合种群的强弱序由自然数的顺序规律演变为奇数种群强 -偶数种群弱 ,同时集合种群里的最优秀种群将迅速扩张、发展为更为强大的最优势种。而当生境遭受到破坏 (毁坏 ) ,集合种群里的最优秀种群将迅速地伦为最弱者。如果栖息地的毁坏率大于集合种群优势种对栖息地的占有率 ,不仅集合种群里的优势种群将不可避免地灭绝 ,伴随最优秀种群走向灭绝的种群依次还有第二、第三、第四强等的种群。同时 ,将导致集合种群的强弱序由自然数的顺序规律演变为偶数种群强 -奇数种群弱。     

生境变化对集合种群系统生态效的影响

通过大量的数值模拟发现：生境恢复或扩展将导致集合种群的强弱序由自然数的顺序规律演变为奇数种群强－偶数种群弱,同时集合种群里的最优秀种群将迅速扩张,发展为更为强大的最优势种,而当生境遭受到破坏（毁坏）,集合种群里的最优秀种群将迅速地伦为最弱者,如果栖息地的毁坏率大于集合种群优势种对栖息地的占有率,不仅集合种群里的优势种群将不可避免地灭绝,伴随最优秀种群走向灭绝的种群依次还有第二、第三、第四强等的种群。同时将导致集合种群的强弱序由自然数的顺序规律演变为偶数种群强－奇数种群弱。     

物种灭绝对不同时间尺度栖息地毁坏响应的空间模拟

人类活动所引起的栖息地毁坏已成为当前物种多样性丧失的最主要的原因之一。空间显含模型相对于空间隐含模型来说,更加接近于现实,因此,通过元胞自动机,模拟了物种多样性对万年、千年、百年时间尺度人类活动所引起的栖息地毁坏的响应。研究结果表明：万年时间尺度上,物种是由强到弱的灭绝;而在千年时间尺度上,物种灭绝的序受集合种群结构的影响较大;在百年时间尺度上。物种由于栖息地毁坏过于剧烈和迅速,来不及作出响应。在栖息地完全毁坏时集体灭绝。因此,物种灭绝序不只是受竞争-侵占均衡机制的影响,还受不同时间尺度（不同速率）栖息地毁坏的影响。以及集合种群结构的影响。     

似Allee效应对2-物种集合种群竞争动态的影响

集合种群具有与局域种群Allee效应相似的现象被称为似Allee效应.将似Allee效应引入2-竞争物种集合种群系统,建立了具有似Allee效应的2-物种集合种群演化动态模型.大量的数值模拟表明:(1)似Allee效应导致集合种群水平上两竞争物种构成的系统具有多个平衡态;(2)似Allee效应使竞争共存物种无法续存甚至全部灭绝,即使种群具有很高的初始斑块占有率,并且最终平衡态随初始斑块占有率变化而改变;(3)似Allee效应可能使竞争排斥物种共同灭绝,且效应越强,物种存活时间越短;但似Allee效应不会增强强物种对弱物种的排斥强度,反而可能使强物种变为弱物种,弱物种变为强物种,其具有与栖息地毁坏类似的影响种群竞争等级排序的作用;(4)似Allee效应对竞争集合种群续存是一个不稳定的干扰因素,微小的变化都将引起系统平衡态的剧变.但对于已经达到平衡态的集合种群系统,似Allee效应对强弱种群多度起到调节与制约的作用,有助于平衡态集合种群的稳定与共存,这一结论更完整的揭示了似Allee效应在竞争集合种群系统发展的不同阶段所起的不同作用.以上这些结论对物种保护及集合群落的管理具有重要的指导意义.     

Allee效应对具有生境恢复的集合种群的影响

Allee效应与种群的灭绝密切相关,其研究对生态保护和管理至关重要。Allee效应对物种续存是潜在的干扰因素,濒危物种更容易受其影响,可能会增加生存于生境破碎化斑块的濒危物种的死亡风险,因此研究Allee效应对种群的动态和续存的影响是必要的。从包含由生物有机体对环境的修复产生的Allee效应的集合种群模型出发,引入由其他机制形成的Allee效应,建立了常微分动力系统模型和基于网格模型的元胞自动机模型。通过理论分析和计算机模拟表明:(1)强Allee效应不利于具有生境恢复的集合种群的续存;(2)生境恢复有利于种群续存;(3)局部扩散影响了集合种群的空间结构、动态行为和稳定性,生境斑块之间的局部作用将会减缓或消除集合种群的Allee效应,有利于集合种群的续存。     

集合种群空间混沌的模拟研究以及Allee效应、拥挤效应与捕食效应对空间模式的影响

集合种群的空间模式研究是当今生态学的核心问题之一。本研究利用常微分动力系统以及基于网格模型的元胞自动机模型对Allee效应、拥挤效应以及捕食作用集合种群的空间分布模式做了全面的模拟研究。Allee效应描述当种群水平低于某一阈值时会发生由生殖成功几率下降造成的种群负增长率,而拥挤效应是指当种群密度过高时引起的个体性为异常从而达到调节种群增长率的作用。文章组建了3个空间确定性模型：局部作用模型(CIM)、距离敏感模型(DSM)和集合种群捕食模型(MMP)。局部作用模型显示在一维生境中空斑块形成金字塔状,二维模型显示出明显的动态拟周期性以及由空间混沌所形成的异质性。距离敏感模型可导致由迁移个体中密度制约强度决定的集合种群大小复杂动态与种群密度的双峰分布。这些结果说明动态行为的复杂性,不仅可用于表征研究物种的特性,而且可以表明该物种的续存能力与灭绝风险。集合种群捕食模型是概率转换空间模型,利用该模型得出了依赖于模型参数和生境尺度的白组织种群概率空间分布模式。模拟的结果表明,系统的内在机制和这种白组织模式导致捕食者形成集团型不明显的“捕食小组”或“杀手小组”,并具有较高扩散力．但却包括侵占率低、灭绝率高的特点。而使猎物种群形成高集团性、高侵占率、低灭绝率、低扩散力的种群集团。这种特点又使捕食者种群在生境中处于中心地带,而使猎物种群形成在捕食者和生境边缘间的环状分布。这些结果还说明了尺度对于生态学的研究是至关重要的,不同的尺度将产生不同的系统模式。     

Population size dependence, competitive coexistence and habitat destruction

1. Spatial dynamics can lead to coexistence of competing species even with strong asymmetric competition under the assumption that the inferior competitor is a better colonizer given equal rates of extinction. Patterns of habitat fragmentation may alter competitive coexistence under this assumption.
2. Numerical models were developed to test for the previously ignored effect of population size on competitive exclusion and on extinction rates for coexistence of competing species. These models neglect spatial arrangement.
3. Cellular automata were developed to test the effect of population size on competitive coexistence of two species, given that the inferior competitor is a better colonizer. The cellular automata in the present study were stochastic in that they were based upon colonization and extinction probabilities rather than deterministic rules.
4. The effect of population size on competitive exclusion at the local scale was found to have little consequence for the coexistence of competitors at the metapopulation (or landscape) scale. In contrast, population size effects on extinction at the local scale led to much reduced landscape scale coexistence compared to simulations not including localized population size effects on extinction, especially in the cellular automata models. Spatially explicit dynamics of the cellular automata vs. deterministic rates of the numerical model resulted in decreased survival of both species. One important finding is that superior competitors that are widespread can become extinct before less common inferior competitors because of limited colonization.
5. These results suggest that population size–extinction relationships may play a large role in competitive coexistence. These results and differences are used in a model structure to help reconcile previous spatially explicit studies which provided apparently different results concerning coexistence of competing species.     

Responses of Metapopulation Dynamics to Two Different Kinds of Habitat Destruction Caused by Human Activities

Habitat destruction can be classified into instantaneous destruction and continuous destruction by the different ways of human destroying habitat. Previous studies, however, always focused on instantaneous destruction. In this study, we develop a universal model, Multi-time scale N-species model, to study and compare the responses of metapopulation dynamics to both kinds of habitat destruction. The model explores that: (1) under instantaneous habitat destruction, species extinction is determined by the proportion of habitat destruction (D) and the structure of metapopulation (q). When D>q, species will go extinct ranked from the best competitor to the worst. When D≤ q, no species will go extinct, but the equilibrium abundances of odd-ranked competitors will decrease, and the equilibrium abundances of even-ranked competitors will increase; (2) under continuous destruction, species extinction is dependent on the speed of habitat destruction and the metapopulation structure. The higher the speed of habitat destruction and the bigger q are, the earlier species go extinct. Usually, there are two possible mechanisms of species extinction: one is that all species go extinct collectively following complete destruction, and the other is that species go extinct in ranked competitive order from best to worst, and the survivals, if they exist, will go extinct collectively following complete destruction. The oscillation amplitudes of inferior competitors are so large as to increase the probability of stochastic extinction under instantaneous destruction. Therefore, it is relatively propitious for the persistence of rare species under slow and continuous destruction, especially when continuous destruction stops.     

破碎栖息地中物种灭绝机制

栖息地毁坏既会直接降低物种多度,又会间接地降低物种迁移繁殖力,同时还会改变原有的种间平衡.尽管已有研究表明栖息地毁坏是物种灭绝的主要原因之一,但是尚未揭示破碎的栖息地中物种灭绝的驱动机制.通过元胞自动机模拟了物种灭绝对栖息地毁坏空间异质性响应的基础上,进一步研究了栖息地毁坏和种间竞争对物种灭绝的影响.结果发现:强物种的灭绝主要来自栖息地毁坏,而弱物种的灭绝,在随机毁坏下,主要由栖息地毁坏与种间竞争共同决定,而在边缘毁坏下则主要由种间竞争所引起的.栖息地毁坏与种间竞争共同引起的物种灭绝的时间非常短,而栖息地毁坏或种间竞争所引起的物种灭绝时间则较长.     

Habitat destruction and the extinction debt revisited: The Allee effect

Habitat destruction, often caused by anthropogenic disturbance, can lead to the extinction of species at an unprecedented rate. It is important, therefore, to consider habitat destruction when assessing population viability. Another factor often ignored in population viability analysis, is the Allee effect that adds to the risk of populations already on the verge of extinction. Understanding the Allee effect on species dynamics and response to habitat destruction has intrinsic value in conservation prioritization. Here, the Allee effect was considered in a multi-species hierarchical competition model. Results showed that species persistence declines dramatically due to the Allee effect, and certain species become more susceptible to habitat destruction than others. Two extinction orders emerged under habitat destruction: either the best competitor becomes extinct first or the best colonizer first. The extinction debt and order, as well as the time lag between habitat destruction and species extinction, were found to be determined by species abundance and the intensity of the Allee effect.     

How species diversity responds to different kinds of human-caused habitat destruction

Human-caused habitat destruction, the major cause of species diversity losses, can be classified into two basic types, instantaneous destruction and continuous destruction. Thus, a universal model should be established to simulate and forecast the effects of different kinds of habitat destruction on species diversity during different historical periods. In this paper, we explore a multi-time-scale n-species model to study and compare species responses to instantaneous and continuous destruction. We find that (1) under instantaneous destruction, there are two different mechanisms of species extinction: one is a time-delayed deterministic extinction of superior competitors in order from the best to the poorest; the other is the extinction in a short time of inferior competitors. The survivors will experience three phases: decline, adjustment, and equilibrium. (2) When the total amounts of habitat destruction for both instantaneous and continuous cases are equal, the oscillation amplitudes of species abundances under instantaneous destruction are much greater than under continuous destruction, especially for inferior competitors, which make inferior competitors under instantaneous destruction more prone to stochastic extinction. Therefore instantaneous destruction is more detrimental to the survival of inferior competitors. (3) Under continuous destruction with habitat eventually being destroyed completely, there also are two types of species extinction mechanisms: the first is extinction in order from the best competitors to the poorest before complete destruction; the second is collective extinction due to complete destruction.     

Spatial heterogeneity, source-sink dynamics, and the local coexistence of competing species

Patch occupancy theory predicts that a trade-off between competition and dispersal should lead to regional coexistence of competing species. Empirical investigations, however, find local coexistence of superior and inferior competitors, an outcome that cannot be explained within the patch occupancy framework because of the decoupling of local and spatial dynamics. We develop two-patch metapopulation models that explicitly consider the interaction between competition and dispersal. We show that a dispersal-competition trade-off can lead to local coexistence provided the inferior competitor is superior at colonizing empty patches as well as immigrating among occupied patches. Immigration from patches that the superior competitor cannot colonize rescues the inferior competitor from extinction in patches that both species colonize. Too much immigration, however, can be detrimental to coexistence. When competitive asymmetry between species is high, local coexistence is possible only if the dispersal rate of the inferior competitor occurs below a critical threshold. If competing species have comparable colonization abilities and the environment is otherwise spatially homogeneous, a superior ability to immigrate among occupied patches cannot prevent exclusion of the inferior competitor. If, however, biotic or abiotic factors create spatial heterogeneity in competitive rankings across the landscape, local coexistence can occur even in the absence of a dispersal-competition trade-off. In fact, coexistence requires that the dispersal rate of the overall inferior competitor not exceed a critical threshold. Explicit consideration of how dispersal modifies local competitive interactions shifts the focus from the patch occupancy approach with its emphasis on extinction-colonization dynamics to the realm of source-sink dynamics. The key to coexistence in this framework is spatial variance in fitness. Unlike in the patch occupancy framework, high rates of dispersal can undermine coexistence, and hence diversity, by reducing spatial variance in fitness.     

Coexistence in metacommunities: a tree-species model

Simple patch-occupancy models of competitive metacommunities have shown that coexistence is possible as long as there is a competition-colonization tradeoff such as that of superior competitors and dispersers. In this paper, we present a model of competition between three species in a dynamic landscape, where patches are being created and destroyed at a different rate. In our model, species interact according to a linear non-transitive hierarchy, such that species Y(3) outcompetes and can invade patches occupied by species Y(2) and this species in turn can outcompete and invade patches occupied by the inferior competitor Y(1). In this hierarchy, inferior competitors cannot invade patches of species with higher competitive ability. Analytical results show that there are regions in the parameter space where coexistence can occur, as well as regions where each of the species exists in isolation depending on species' life-history traits associated with their colonization abilities and extinction proneness as well as with the dynamics of habitat patches. In our model, the condition for coexistence depends explicitly on patch dynamics, which in turn modulate the limiting similarity for species coexistence. Coexistence in metacommunities inhabiting dynamic landscapes although possible is harder to attain than in static ones.