Weis Jerome J, Madrigal Daniel S, Cardinale Bradley J
Department of Ecology, Evolution & Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
PLoS One. 2008 Jul 30;3(7):e2825. doi: 10.1371/journal.pone.0002825.
One of the most common questions addressed by ecologists over the past decade has been--how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called 'transgressive overyielding'). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to 'complementary' use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments.
METHODOLOGY/PRINCIPAL FINDINGS: Experimental units were comprised of patches containing either homogeneous nutrient ratios (16:1 nitrogen to phosphorus (N:P) in all patches) or heterogeneous nutrient ratios (ranging from 4:1 to 64:1 N:P across patches). After allowing 6-10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a 'selection effect'--where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community--was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments.
CONCLUSIONS/SIGNIFICANCE: Our study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use.
在过去十年中，生态学家们提出的最常见问题之一是——物种丰富度如何影响群落生物量的产生？最近的实验总结表明，物种丰富度往往会提高广泛营养级组和生态系统中的生物量产量；然而，多样化混养的生物量很少超过群落中最具生产力的单一物种的生物量（这种现象称为“超产”）。一些人推测，缺乏超产现象是因为实验通常在过于简单、同质的环境中进行，在这种环境中，物种几乎没有机会表现出导致“互补”利用资源从而提高生物量产量的生态位差异。我们在实验室实验中对这一假设进行了检验，在该实验中，我们在同质和异质营养环境中操纵淡水藻类的丰富度。
方法/主要发现：实验单元由含有同质营养比（所有斑块中氮与磷（N:P）的比例为16:1）或异质营养比（斑块间N:P比例从4:1到64:1）的斑块组成。在允许藻类生长6 - 10代后，我们发现藻类物种丰富度在同质和异质环境中对生物量生产的影响相似。尽管五个藻类物种中的四个对营养异质性表现出强烈反应，但在两种环境中都是单一物种主导藻类群落。因此，“选择效应”——即多样性使竞争优势物种被纳入并主导群落生物量的机会最大化——是丰富度在同质和异质环境中影响生物量的主要机制。
结论/意义：我们的研究表明，空间异质性本身不足以产生生物多样性对生产力的强烈影响。相反，异质性必须与斑块间物种相对适合度的变化相结合，以便空间生态位分化产生互补的资源利用。
