THE KEYSTONE SPECIES CONCEPT - VARIATION IN INTERACTION STRENGTH IN A ROCKY INTERTIDAL HABITAT
THE KEYSTONE SPECIES CONCEPT - VARIATION IN INTERACTION STRENGTH IN A ROCKY INTERTIDAL HABITAT
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DOI：
10.2307/2937163
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发表时间：
1994-08-01
影响因子：
6.1
通讯作者：
YAMADA, SB
中科院分区：
文献类型：
--
作者：
MENGE, BA;BERLOW, EL;YAMADA, SB
关键物种概念的有用性和普遍性最近受到质疑。我们研究了原始主要捕食者海星 Pisaster ochraceus 与其主要猎物贻贝（贻贝（Mytilus californianus 和 M. trossulus））之间相互作用强度的变化。这项研究是由于俄勒冈州中部海岸的两个低地带地点——锅炉湾（BB）和草莓山（SH）的群落结构差异而引发的。 SH 的捕食者，尤其是海星，比 BB 的体型更大、数量更多。此外，SH 地区的固着动物更为丰富，而大型植物则较少。在两个地点的暴露于波浪的地点，捕食者更加丰富，而在SH，暴露于波浪的地点的固着无脊椎动物更加丰富，并且在波浪保护的地点沙覆盖率较高。为了检验捕食强度的变化解释了其中一些差异的假设，我们检查了两个地点的高波和低波暴露位置处的海星-贻贝相互作用。通过确定移植到低潮间带有或没有海星的大地块（18-163 M2）中的贻贝成群（每团 50 只贻贝，壳长 4-7 厘米）的存活率来量化捕食强度。通过确定相同大地块中标记样方中的猎物再定殖率来量化捕食效应。通过检查以米为单位（在样地内的移植物之间）、10米（在每个地点的每次暴露内的重复样地之间）、100米（在地点内的波浪暴露之间）和10000米（在地点之间）尺度的捕食来量化相互作用强度的空间变化。通过在 1990 年和 1991 年进行实验来评估时间变化。通过量化塑料网球（收集器）的招募密度和单独标记的移植贻贝的生长，分别评估猎物（贻贝）招募和生长与群落结构差异之间的关系，在每个地点 x 暴露 x 潮汐水位组合，持续 4 年。捕食强度在所有空间尺度上变化很大。在两个最大的空间尺度（数十公里、数百米），移植贻贝的存活率和猎物重新定植的差异取决于海星丰度随地点、波浪暴露、猎物招募和生长的变化，以及在SH保护下的沙埋程度。当海星稀少时，两个最小尺度（米、十米）的变化较大，而当海星丰富时，变化较小。移植的贻贝在暴露于波浪的 SH 中 2 周内死亡率为 100%，但在受波浪保护的 BB 中则超过 52 周。仅在暴露于 SH 波的部位检测到海星对猎物重新定植的影响。在这里，猎物的招募和生长异常高，贻贝 M. trossulus 在 9 个月内入侵并统治了太空。 14个月后，在没有皮萨斯特的情况下，海螺的大小和数量都增加了，阻止了贻贝数量的增加。在其他地点 x 暴露组合中没有发生类似的变化，显然是因为猎物招募量低，也可能是由于海螺对幼体的捕食。长期结果表明，与华盛顿州一样，海星会阻止大型成年加州海星入侵潮间带下部区域，但仅限于暴露于波浪的地点，而不是受波浪保护的地点。因此，观察到三种不同的捕食模式：（1）海星在暴露于波浪的岬角上进行强烈的基石捕食； (2) 海星、海螺和可能的其他捕食者在受波浪保护的海湾中进行较弱的分散捕食，(3) 在经常被沙子掩埋的受波浪保护的地点进行较弱的捕食。在四个暴露于波浪的岬角（我们的两个在俄勒冈州，另外两个在华盛顿州）的可比实验结果，以及这些和其他西海岸岬角上的群落之间的相似性表明，基石捕食广泛发生在该系统中。然而，受波浪保护的栖息地的结果表明，这种情况并不普遍。在俄勒冈州，关键捕食显然取决于猎物产量高的条件（即补充和生长），而当猎物产量低时发生分散捕食，当环境压力高时发生弱捕食。将我们的结果与其他海洋和非海洋栖息地的例子相结合表明，需要考虑更广泛的模型，而不仅仅是关键捕食。一组扩展模型的预测和解释价值取决于识别区分它们的因素。尽管证据有限，但对 17 个例子的调查表明（1）基石捕食显然无法通过先前提出的 11 个差异中的任何一个来区分关键捕食和分散捕食，但（2）可以通过猎物生产率来区分。此外，（3）对竞争性优势猎物的差异捕食并不能区分关键系统和非关键系统，因为这种相互作用发生在两种类型的群落中。相反，对优势猎物的差异性捕食明显区分了强捕食群落和弱捕食群落。虽然关键的捕食概念已经并将继续有用，但需要更广泛地关注测试和开发更通用的社区监管模型。
The usefulness and generality of the keystone species concept has recently been questioned. We investigated variation in interaction strength between the original keystone predator, the seastar Pisaster ochraceus, and its primary prey, mussels (Mytilus californianus and M. trossulus). The study was prompted by differences in community structure at two low zone sites along the central Oregon coast, Boiler Bay (BB) and Strawberry Hill (SH). Predators, especially seastars, were larger and more abundant at SH than at BB. Further, sessile animals were more abundant and macrophytes were less abundant at SH. Predators were more abundant at wave-exposed sites at both sites, and at SH, sessile invertebrates were more abundant at the wave-exposed location and sand cover was high at the wave-protected location. To test the hypothesis that variation in predation strength explained some of these differences, we examined the seastar-mussel interaction at locations with high and low wave exposure at both sites. Predation intensity was quantified by determining the survival of mussels in clumps (50 mussels per clump, shell length 4-7 cm) transplanted to large plots (18-163 M2) with or without seastars in the low intertidal zone. Predation effects were quantified by determining prey recolonization rates in marked quadrats in the same large plots. Spatial variation in interaction strength was quantified by examining predation at scales of metres (among transplants within plots), 10's of metres (between replicate plots within each exposure at each site), 100's of metres (between wave exposures within locations), and 10 000's of metres (between sites). Temporal variation was evaluated by performing the experiments in 1990 and 1991. The relation between prey (mussel) recruitment and growth to differences in community structure was evaluated by quantifying recruitment density in plastic mesh balls (collectors) and growth of individually marked transplanted mussels, respectively, at each site x exposure x tide level combination each month for 4 yr.Predation intensity varied greatly at all spatial scales. At the two largest spatial scales (10's of kilometres, 100's of metres), differences in both survival Of transplanted mussels and prey recolonization depended on variation in seastar abundance with site, wave exposure, prey recruitment and growth, and at SH protected, the extent of sand burial. Variation at the two smallest scales (metres, 10's of metres) was high when seastars were scarce and low when seastars were abundant. Transplanted mussels suffered 100% mortality in 2 wk at wave-exposed SH, but took > 52 wk at wave-protected BB. Seastar effects on prey recolonization were detected only at the SH wave-exposed site. Here, where prey recruitment and growth were unusually high, the mussel M. trossulus invaded and dominated space within 9 mo. After 14 mo, whelks, which increased in both size and abundance in the absence of Pisaster, arrested this increase in mussel abundance. Similar changes did not occur at other site x exposure combinations, evidently because prey recruitment was low and possibly also due to whelk predation on juveniles. Longer term results indicate that, as in Washington state, seastars prevent large adult M. californianus from invading lower intertidal regions, but only at wave-exposed, not wave-protected sites. Thus, three distinct predation regimes were observed: (1) strong keystone predation by seastars al wave-exposed headlands; (2) less-strong diffuse predation by seastars, whelks, and possibly other predators at a wave-protected cove, and (3) weak predation at a wave-protected site buried regularly by sand.Comparable experimental results at four wave-exposed headlands (our two in Oregon and two others in Washington), and similarities between these and communities on other West Coast headlands suggest keystone predation occurs broadly in this system. Results in wave-protected habitats, however, suggest it is not universal. In Oregon, keystone predation was evidently contingent on conditions of high prey production (i.e., recruitment and growth), while diffuse predation occurred when prey production was low, and weak predation occurred when environmental stress was high. Combining our results with examples from other marine and non-marine habitats suggests a need to consider a broader range of models than just keystone predation. The predictive and explanatory value of an expanded set of models depends on identifying factors distinguishing them. Although evidence is limited, a survey of 17 examples suggests (1) keystone predation is evidently not distinguished from diffuse predation by any of 11 previously proposed differences, but (2) may be distinguished by rates of prey production. Further, (3) differential predation on competitively dominant prey does not distinguish keystone from nonkeystone systems, since this interaction occurs in both types of community. Instead, differential predation on dominant prey evidently distinguishes strong-from weak-predation communities. While the keystone predation concept has been and will continue to be useful, a broadened focus on testing and developing more general models of community regulation is needed.