植物群落物种共存机制的研究进展

摘要/Abstract

摘要：

物种共存是由进化、历史及生态尺度上的过程决定的。现存的理论从不同的尺度探讨了植物群落物种共存的可能机制，本文阐述了其中几种重要的理论。种库理论在进化和历史尺度上解释了植物物种共存的形成原因。在生态尺度上，虽然传统的生态位理论受到质疑，但是更新生态位理论和资源比率% 异质性假说越来越受到重视；竞争共存理论认为具有相似竞争能力或能够避免竞争排斥的植物物种可以共存。在非平衡条件下，生物和非生物因素对植物物种共存也有显著影响，它们一方面作用于竞争优势种，使竞争优势向稀有种转移，另一方面可以创造生境时空异质性，为生态位分化提供机会。生态漂变学说认为群落中物种的组成不断变化，物种的共存和分布由随机因素决定。这些植物群落物种共存理论各有所长，互相补充。应用现代科学技术进行研究，结果必将促进人们对植物物种共存问题的深刻理解。

Abstract:

Abstract Species coexistence, a key question in plant community ecology, means the abundance or the number of species occurring in a certain time at a given community. Zobel emphasized that species coexistence should be determined by the processes of the evolutionary, historical and ecological scale. So far, many theories explaining the mechanisms of species coexistence at certain levels and under particular conditions exist. This review outlines some important theories, such as species pool hypothesis, regeneration niche theory, and competition theory, to elucidate species coexistence.

The term “species pool” was introduced to indicate that a set of species is potentially capable of coexisting in a particular community. Species pool plays an important role in species coexistence and abundance. The species pool theory proposed that the number of species occupying a certain habitat should be determined by characteristics of the particular habitat. The larger the area that a habitat type occupies, the greater the opportunity for speciation, and hence the larger the number of available species adapted to that particular habitat. Further, the availability of species also depends on historical processes at a bio-geographical scale, which determine the migration of species among regions, and the dispersal of species between and within local populations. Species pool theory explains the origination of species coexistence on evolutionary scale, but itself works in ecological scale.

Since traditional niche theory cannot effectively explain the numerous species coexisting in tropical forest and temperate grasslands, alternative niche theories are blooming. The regeneration niche theory is, in principle, a compromise between the niche differentiation and balanced competition, thus the species differing in their requirements for seed production, dispersal, germination and so on can coexist. Resource ratio/heterogeneity hypothesis, a promising theory, gives the possible solution by considering ratios of limiting nutrients to their absolute amounts.

Competitive species can coexist. If the species have similar competitive abilities, competitive exclusion might not occur at all, or occur at such a low frequency that it takes a long time for compensatory processes (eg. evolutionary change) to operate. Some factors, such as disturbance and herbivory, can mainly influence the dominant species, thus shifting competitive advantage to inferior species, and there are more chances for the superior and inferior species to coexist. The storage effect, where reproductive potential can be “stored” through unfavorable periods, promotes the coexistence of competing species under fluctuating environmental conditions. The distribution pattern of species, patchiness of environment and resource, and harsh and fluctuating conditions can also favor the competing coexistence of species.

Under non-equilibrium circumstance, species coexistence can be mediated by two main factors. One is disturbance, which interrupts the development of communities, prevents resource exploitation by overgrowth species, and avoids competitive exclusion. In the meantime, disturbances can create temporal and spatial heterogeneity, and provide new resource axes for niche differentiation. The other is the biotic agent. Biotic interactions among and within nutritional ranks can affect the coexistence of competing species. Janzen-Connell suggests that host-specific pests reduce recruitment of conspecific adults where conspecific seed density is greatest, thus free space is occupied by other plant species, which is density- or distance-dependent. The herbivore’s action can change the growth rate, growth form and growth rhythm of plants so that plant species produce the capture ability of resources and competing ability (exploiting resources or enduring resource stress). In addition, microorganisms play some role in plant species coexistence.

The unified neutral theory, seeking to unify both the number of species in a community and the distribution of the relative abundances of those species, assumes that every individual in every species in a biological community is identical, and that the total abundance of all species is fixed. All changes in distribution and abundance occur because of purely random variation in births, deaths, migration and speciation. This theory can accurately predict many attributes of ecological communities — particularly the distribution of abundances of tree species.

All the above mechanisms for plant species coexistence are not incompatible, but complementary, and it seems that plant species coexist within a community for different reasons. More investigation should be carried out on these reasons.

侯继华, 马克平. 植物群落物种共存机制的研究进展. 植物生态学报, 2002, 26(增刊): 1-8

HOU Ji-Hua, MA Ke-Ping. ON MECHANISMS OF SPECIES COEXISTENCE IN PLANT COMMUNITIES. Chinese Journal of Plant Ecology, 2002, 26(增刊): 1-8

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植物群落物种共存机制的研究进展

ON MECHANISMS OF SPECIES COEXISTENCE IN PLANT COMMUNITIES

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