美國《國家科學(xué)院院刊》（PNAS）日前刊登了題為《區域異質(zhì)性的代價(jià)以及生態(tài)群落多樣性》的研究論文，提出了一個(gè)與以往不同的生物多樣性假說(shuō)。
　　1平方米的草地上如何能包含幾十種植物物種？什么因素決定了一個(gè)生態(tài)系統中的物種數量？這兩個(gè)問(wèn)題無(wú)論對于理解自然還是對于自然生態(tài)系統對人類(lèi)的價(jià)值，都具有很重要的意義。自然生態(tài)系統所提供的服務(wù)和產(chǎn)品超過(guò)地球上全部的GDP。近50年來(lái)，傳統的生態(tài)學(xué)理論認為，在特定的區域可以共存的物種數量隨著(zhù)棲息地環(huán)境條件異質(zhì)性的升高而增加。來(lái)自耶路撒冷的學(xué)者Omri Allouche和Michael Kalyuzhny在一項研究中對這項傳統假設進(jìn)行了重新檢驗。研究指出，在異質(zhì)性的環(huán)境（其中存在著(zhù)多種不同類(lèi)型棲息地）中，每個(gè)物種擁有更少的資源和更不適宜的環(huán)境，使這些物種更加容易走向滅絕。這導致另一種假設：過(guò)度的棲息地異質(zhì)性可能減少物種的數量。
　　研究人員利用數學(xué)分析和生態(tài)系統實(shí)證分析方法對此項假設進(jìn)行了檢驗。該假設的預測檢驗是采用元分析的方法，數據來(lái)源于世界各地的數十個(gè)動(dòng)植物物種的數據庫。通過(guò)分析發(fā)現，理論和數據分析都支持新的假設，即棲息地異質(zhì)性可能提高物種滅絕的速度。

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PNAS發(fā)表論文摘要（英文）

Area–heterogeneity tradeoff and the diversity of ecological communities

For more than 50 y ecologists have believed that spatial heterogeneity in habitat conditions promotes species richness by increasing opportunities for niche partitioning. However, a recent stochastic model combining the main elements of niche theory and island biogeography theory suggests that environmental heterogeneity has a general unimodal rather than a positive effect on species richness. This result was explained by an inherent tradeoff between environmental heterogeneity and the amount of suitable area available for individual species: for a given area, as heterogeneity increases, the amount of effective area available for individual species decreases, thereby reducing population sizes and increasing the likelihood of stochastic extinctions. Here we provide a comprehensive evaluation of this hypothesis. First we analyze an extensive database of breeding bird distribution in Catalonia and show that patterns of species richness, species abundance, and extinction rates are consistent with the predictions of the area–heterogeneity tradeoff and its proposed mechanisms. We then perform a metaanalysis of heterogeneity–diversity relationships in 54 published datasets and show that empirical data better fit the unimodal pattern predicted by the area–heterogeneity tradeoff than the positive pattern predicted by classic niche theory. Simulations in which species may have variable niche widths along a continuous environmental gradient are consistent with all empirical findings. The area–heterogeneity tradeoff brings a unique perspective to current theories of species diversity and has important implications for biodiversity conservation.