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。     

人类周期性活动对物种多样性的影响及其预测

人类活动通过作用于栖息地而影响着物种的种群动态,从而影响着物种多样性的变化。首次提出了不同时间尺度人类周期性活动干扰下的多物种竞争动力模式,模拟了千年时间尺度,物种多样性对人类周期性活动的响应过程,开展了人类周期性活动所导致的物种多样性的量的变化的预测研究。有关模拟和预测结果表明:在人类周期性活动的作用下,物种多度变化对栖息地变化的响应也做准周期振荡;同时人类活动强度越大,物种多度振荡的幅度也越大;并且在栖息地减少过程中,人类周期性活动对物种多样性的影响幅度要小于栖息地扩充过程中的。在一个完整的周期内,并没有物种的灭绝,只是物种的多度和强弱关系变化很大。当人类周期性活动仅持续1/4个周期时,最强的几个物种将灭绝,而其它物种做准周期振荡,但振幅相对较小。     

物种多样性对栖息地毁坏时间异质性的响应

栖息地毁坏是物种多样性丧失最重要的因素之一.通过多物种竞争共存的非自治动力模型,利用香农多样性指数,研究并比较了不同结构集合种群群落的物种多样性对不同程度和不同速度的栖息地毁坏时间异质性的响应.结果表明:在栖息地瞬间毁坏下,物种多样性先快速下降,之后得到一定程度的恢复,最终在下降中走向平衡;在栖息地持续完全毁坏下,栖息地毁坏速度对物种多样性随累积栖息地毁坏率变化的影响,只有在最强物种多度 (q)较小时比较明显,而在q较大时较小;对于栖息地持续部分毁坏,栖息地毁坏速度只影响物种多样性振荡的幅度,而不影响其变化的最终结果,并且速度越快,物种多样性振荡幅度越大,越不利于群落的稳定.     

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.     

物种演化对人类活动作用下不同性质栖息地毁坏的响应

栖息地毁坏是物种多样性减少的首要因素之一, 因此研究物种演化对栖息地毁坏的响应是非常必要的。而栖息地的毁坏又有瞬间毁坏和持续毁坏两种, 以往对栖息地毁坏的研究集中在瞬间毁坏上, 而该文则是通过N_物种 竞争共存模型分析对比了物种演化对栖息地瞬间毁坏和持续毁坏的响应特征。研究发现 :不同性质的栖息地毁坏都会导致物种强弱关系的变化, 并非如通常所认为的强物种将免于遭受物种灭绝的威胁, 也不是强物种首先灭绝, 而是因集合种群结构的不同而异。在热带雨林群落, 瞬间毁坏下物种演化一般经历了强迫适应和恢复上升阶段, 而持续毁坏下物种得不到恢复, 只能持续衰退, 在较长一段时间内持续毁坏比瞬间毁坏更有利于物种的续存 ;而在温带森林群落, 瞬间毁坏下物种演化一般经历强迫适应, 恢复上升和准周期振荡, 最后平衡, 而持续毁坏下物种只能持续衰退, 出现了在栖息地持续毁坏率小于瞬间毁坏率时, 物种的栖息地占有率却小于瞬间毁坏时的占有率。     

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。     

栖息地毁坏与动物物种灭绝关系的模拟研究

利用多个物种共存模式模拟了不同情况下的不同动物种群演化的动力学特性,研究结果表明：（1）由于栖息地的毁坏所导致的动手的种灭绝是依赖于对物种死亡率和有关平衡态的假设的,不同的假设下,既使栖息地的破坏率相同,灭绝的物种可能是竞争能力最强的若干物种,也可能是竞争能力相对较弱的若干物种,既不象传统的物种进化理论所认为的必是弱的物种先灭绝,也不象Tilman等人所认为的一定是最强的若干物种先灭绝;（2）如果弱的物种具有较高的平均死亡率,则当栖息地受到一定的毁坏时,将有较多强的物种灭绝,而且物种灭绝时间将大大缩短;（3）在物种死亡率不变的情形下,物种在未受毁坏栖息地上的平衡态和大占有率pl^0,将有利于物种的生存。     

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。     

不同栖息地状态下外来种入侵及对本地种生存影响的模拟

外来种入侵引起的生态及经济问题日益严重,人类活动导致大规模栖息地持续变化的背景下,外来种的入侵过程及本地物种多样性的演化更为复杂.在Tilman多物种共存模型基础上,建立了栖息地持续变化条件下的外来种入侵干扰模式,分别模拟了栖息地不变、持续毁坏及持续恢复条件下的外来种入侵及对本地物种多样性的生态影响.模拟结果表明:(1)拓殖率小(入侵性弱)的外来种不能成功定殖,栖息地的持续变化对其没有任何影响.(2)拓殖率增大的外来种入侵过程复杂,栖息地持续毁坏导致其灭绝时间相比于栖息地不变时明显推迟,栖息地持续恢复使其灭绝提前;一定时间内持续增加栖息地可以减小此类外来种入侵危害.(3)拓殖率足够大的外来种能够成功定殖,快速定殖-扩散的入侵过程不会因栖息地毁坏而迅速改变,其响应具有时间滞后性;栖息地持续恢复也有利于其迅速蔓延,占有率呈线性疯狂增长.(4)在具有外来种入侵的本地生态系统中,栖息地持续改变(增加或减少)对本地物种多样性的发展均不利.     

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。     

Extinction debt in source-sink metacommunities

In an increasingly modified world, understanding and predicting the consequences of landscape alteration on biodiversity is a challenge for ecologists. To this end, metacommunity theory has developed to better understand the complexity of local and regional interactions that occur across larger landscapes. While metacommunity ecology has now provided several alternative models of species coexistence at different spatial scales, predictions regarding the consequences of landscape alteration have been done exclusively for the competition-colonization trade off model (CC). In this paper we investigate the effects of landscape perturbation on source-sink metacommunities. We show that habitat destruction perturbs the equilibria among species competitive effects within the metacommunity, driving both direct extinctions and an indirect extinction debt. As in CC models, we found a time lag for extinction following habitat destruction that varied in length depending upon the relative importance of direct and indirect effects. However, in contrast to CC models, we found that the less competitive species are more affected by habitat destruction. The best competitors can sometimes even be positively affected by habitat destruction, which corresponds well with the results of field studies. Our results are complementary to those results found in CC models of metacommunity dynamics. From a conservation perspective, our results illustrate that landscape alteration jeopardizes species coexistence in patchy landscapes through complex indirect effects and delayed extinctions patterns.     

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。     

基于栖息地恢复对群落不同种群演化影响的模拟

通过建立基于栖息地恢复的多种群演化动力学模式,模拟了不同群落结构的不同物种种群的演化特点。模拟结果发现了两类灭绝机制,揭示了(1)小规模栖息地的恢复对群落中的弱小物种的影响是非常有限的,不会给弱小物种种群带来灭绝风险。大幅度的栖息地增加几乎使所有的物种种群都在最初数百年中内都有出现一定的增加,特别是竞争能力最强的物种,其幅度的增加最为显著,但次最强的物种种群可能会在千年左右灭绝。群落内幸存的种群将经历3个阶段迅速壮大(增加)阶段震荡阶段稳定阶段;(2)存在着协同现象,栖息地减少所导致种群的协同演化规律与栖息地恢复所导致的种群的演化规律两者之间既有共同点,又有不同点。毁坏是一种破坏,大规模的栖息地的恢复对已适应于破坏后新环境的某些物种也可能是一种威胁,这类似于生态入侵的初始阶段。     

The competitive dynamics of metapopulations subject to the Allee-like effect

It is well recognized that individuals of many species can benefit from the presence of conspecifics, a concept broadly referred to as the Allee effect. At the metapopulation level, there is an analogous but essentially different phenomenon called the Allee-like effect that leads to metapopulation extinction thresholds at low habitat occupancy. But so far not adequate attention has been paid to this phenomenon. In this paper, the Allee-like effect is introduced into a metapopulation model of one species and also that of a three-state two-species competitive system. Phase plane analysis is used to investigate the dynamics of these models. We demonstrate that the Allee-like effect alone could lead to multiple stable states in three-state two-species competitive systems at the metapopulation level, and the number of stable states decrease as the Allee-like effect becomes more severe. Severe Allee-like effects may make coexistence impossible and may even lead to the extinction of both species even if their initial habitat occupancies are high and suitable habitats are enough. It is especially noticeable that depending on their initial conditions one species may exclude the other one that subjects to a weaker Allee-like effect than the former, while the second species always excludes the first one when both species are assumed to be in the absence of the Allee-like effect. We also investigate the habitat destructive effect on the Allee-like system mentioned above. Research indicates that the existence of the Allee-like effect makes a metapopulation more susceptible to habitat destruction. All in all, the Allee-like effect is probably a destabilizing factor that, together with habitat destruction, would affect the continuous existence of species. These conclusions may have important implications for conservation and metacommunity organization.     

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.     

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.