Response of grazers to sudden nutrient pulses in oligotrophic versus eutrophic conditions
Response of grazers to sudden nutrient pulses in oligotrophic versus eutrophic conditions
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贫营养与富营养条件下食草动物对突然营养脉冲的反应
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
S. Connell
中科院分区：
文献类型：
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作者：
B. Russell;S. Connell
食草动物可以消耗更多的营养丰富的藻类比营养贫乏的藻类，这种觅食行为可能会抵消营养素升高对藻类栖息地的负面影响。了解这一现象可能有助于理解为什么某些地区在养分负荷突然增加（例如风暴事件的径流）时比其他地区具有更大的持久性和恢复力。我们使用3个连续的野外实验来测试并随后接受以下假设：在强烈的食草性制度下（1）软体动物减少暴露于高营养物的机会性藻类（草皮）的更大百分比覆盖，因此这些藻类的生物量比暴露于环境营养物的藻类少，（2）暴露于高营养物的草皮吸引更大密度的食草性动物，和（3）当背景营养负荷通常较低（环境营养条件）时，暴露于富营养藻类突然增加的食草动物比当它们较高（富营养条件）时更多地减少藻类生物量。至关重要的是，这些影响在贫营养条件下更大，这表明在营养浓度通常较低的系统中，食草动物对突发营养事件的反应会更大。然而，食草动物无法控制增加藻类生长时，营养富集发生在一个较长的时间（即富营养化条件）。这些观察结果支持这样一种观点，即食草动物可能在易受人类活动影响的系统中发挥有用的作用，在短期内降低水质（即短期内增加养分供应），但这种机制可能不足以减少富营养化的长期影响。
Herbivores can consume more nutrient rich algae than nutrient poor algae, and such foraging behaviour may counter the negative effects of elevated nutrients on algal habitats. Under- standing this phenomenon may be useful in understanding why some localities have greater persis- tence and resilience than others in the face of sudden increases in nutrient loads (e.g. run-off from storm events). We used 3 successive field experiments to test, and subsequently accept, the hypo- theses that under intense regimes of herbivory (1) molluscs reduce a greater percentage cover of opportunistic algae (turfs) exposed to elevated nutrients, and consequently these algae have less bio- mass than those exposed to ambient nutrients, (2) turfs exposed to elevated nutrients attract greater densities of herbivores, and (3) grazers exposed to sudden increases in nutrient rich algae reduce algal biomass more when background nutrient loads are normally low (ambient nutrient conditions) than when they are high (enriched nutrient conditions). Critically, these effects were greater under oligotrophic conditions, suggesting that the response of grazers to sudden nutrient events would be greater in systems where nutrient concentrations are usually low. However, grazers were not able to control increased algal growth when nutrient enrichment occurred over a longer period (i.e. eutrophic conditions). These observations support the idea that grazers may provide useful functions in systems susceptible to human activities that reduce water quality over short periods (i.e. short-term increase in nutrient availability), but that this mechanism may not be sufficient to reduce the long- term effects of eutrophication.