Yashchenko Varvara, Fossen Erlend Ignacio, Kielland Øystein Nordeide, Einum Sigurd
Centre for Biodiversity Dynamics, Department of Biology, NTNU, Norwegian University of Science and Technology, Realfagbygget, NO-7491, Trondheim, Norway.
J Anim Ecol. 2016 Jul;85(4):1070-7. doi: 10.1111/1365-2656.12515. Epub 2016 Apr 21.
Population density has recently been suggested to be an important factor influencing metabolic rates and to represent an important 'third axis' explaining variation beyond that explained by body mass and temperature. In situations where population density influences food consumption, the immediate effect on metabolism acting through specific dynamic action (SDA), and downregulation due to fasting over longer periods, is well understood. However, according to a recent review, previous studies suggest a more general effect of population density per se, even in the absence of such effects. It has been hypothesized that this results from animals performing anticipatory responses (i.e. reduced activity) to expected declines in food availability. Here, we test the generality of this finding by measuring density effects on metabolic rates in 10 clones from two different species of the zooplankton Daphnia (Daphnia pulex Leydig and D. magna Straus). Using fluorescence-based respirometry, we obtain high-precision measures of metabolism. We also identify additional studies on this topic that were not included in the previous review, compare the results and evaluate the potential for measurement bias in all previous studies. We demonstrate significant variation in mass-specific metabolism among clones within both species. However, we find no evidence for a negative relationship between population density and mass-specific metabolism. The previously reported pattern also disappeared when we extended the set of studies analysed. We discuss potential reasons for the discrepancy among studies, including two main sources of potential bias (microbial respiration and declining oxygen consumption due to reduced oxygen availability). Only one of the previous studies gives sufficient information to conclude the absence of such biases, and consistent with our results, no effect of density on metabolism was found. We conclude that population density per se does not have a general effect on mass-specific metabolic rate.
最近有人提出，种群密度是影响代谢率的一个重要因素，并且代表着一个重要的“第三轴”，能够解释除体重和温度所解释的变异之外的其他变异。在种群密度影响食物消耗的情况下，通过特定动力作用（SDA）对代谢产生的直接影响以及因长期禁食导致的下调作用，都是很容易理解的。然而，根据最近的一篇综述，先前的研究表明，即使在没有这些影响的情况下，种群密度本身也有更普遍的影响。据推测，这是由于动物对预期食物可利用性的下降做出了预期反应（即活动减少）。在这里，我们通过测量两种不同种类的浮游动物水蚤（蚤状溞Leydig和大型溞Straus）的10个克隆体的密度对代谢率的影响，来检验这一发现的普遍性。使用基于荧光的呼吸测量法，我们获得了高精度的代谢测量值。我们还识别了先前综述中未包括的关于该主题的其他研究，比较了结果并评估了所有先前研究中测量偏差的可能性。我们证明了两个物种内克隆体之间的质量比代谢存在显著差异。然而，我们没有发现种群密度与质量比代谢之间存在负相关关系的证据。当我们扩展分析的研究集时，先前报道的模式也消失了。我们讨论了研究之间存在差异的潜在原因，包括潜在偏差的两个主要来源（微生物呼吸和由于氧气可利用性降低导致的氧气消耗下降）。之前只有一项研究提供了足够的信息来得出不存在此类偏差的结论，并且与我们的结果一致，未发现密度对代谢有影响。我们得出结论，种群密度本身对质量比代谢率没有普遍影响。
