Maron John L, Marler Marilyn
Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA.
Am Nat. 2008 Jul;172 Suppl 1:S18-33. doi: 10.1086/588303.
Theory and empirical work have demonstrated that diverse communities can inhibit invasion. Yet, it is unclear how diversity influences invader impact, how impact varies among exotics, and what the relative importance of diversity is versus extrinsic factors that themselves can influence invasion. To address these issues, we established plant assemblages that varied in native species and functional richness and crossed this gradient in diversity with resource (water) addition. Identical assemblages were either uninvaded or invaded with one of three exotic forbs: spotted knapweed (Centaurea maculosa), dalmatian toadflax (Linaria dalmatica), or sulfur cinquefoil (Potentilla recta). To determine impacts, we measured the effects of exotics on native biomass and, for spotted knapweed, on soil moisture and nitrogen levels. Assemblages with high species richness were less invaded and less impacted than less diverse assemblages. Impact scaled with exotic biomass; spotted knapweed had the largest impact on native biomass compared with the other exotics. Although invasion depressed native biomass, the net result was to increase total community yield. Water addition increased invasibility (for knapweed only) but had no effect on invader impact. Together, these results suggest that diversity inhibits invasion and reduces impact more than resource additions facilitate invasion or impact.
理论和实证研究表明，多样化的群落能够抑制外来物种入侵。然而，目前尚不清楚多样性如何影响入侵者的影响，外来物种之间的影响如何变化，以及多样性相对于自身能够影响入侵的外在因素的相对重要性。为了解决这些问题，我们建立了本地物种和功能丰富度不同的植物组合，并将这种多样性梯度与资源（水）添加相结合。相同的组合要么未被入侵，要么被三种外来杂草之一入侵：斑点矢车菊（Centaurea maculosa）、达尔马提亚亚麻荠（Linaria dalmatica）或直立委陵菜（Potentilla recta）。为了确定影响，我们测量了外来物种对本地生物量的影响，对于斑点矢车菊，还测量了其对土壤湿度和氮水平的影响。物种丰富度高的组合比多样性较低的组合受到的入侵和影响更小。影响程度与外来生物量成正比；与其他外来物种相比，斑点矢车菊对本地生物量的影响最大。虽然入侵降低了本地生物量，但最终结果是增加了群落总产量。添加水增加了入侵性（仅针对矢车菊），但对入侵者的影响没有作用。综合来看，这些结果表明，多样性抑制入侵并减少影响的程度超过了资源添加促进入侵或影响的程度。
