ABSTRACT: Individuals rarely have equal competitive abilities, with body size being one of the most important attributes affecting the mechanism (i.e. exploitative and interference) and consequences of competition. Competitive interactions within size-structured populations are complex and can have major implications for population dynamics, community structure and evolutionary processes. Destructive grazing of kelp beds by the green urchin Strongylocentrotus droebachiensis creates barrens where high-quality food is scarce and intraspecific competition may have an important role in structuring populations. In this study, we experimentally identified the mechanisms underlying size-asymmetric competition between small, medium, and large size classes of the green urchin. A field-based mesocosm experiment showed that small and medium sea urchins grew less and produced smaller gonads when competing for food with large conspecifics. Surprisingly, when food was provided ad libitum but large urchins were present, small individuals’ growth and foraging behavior were reduced, providing strong evidence for interference competition between small and large sea urchins. Interactions between medium and large sea urchins were, however, more influenced by exploitative competition, suggesting that sea urchins shift ontogenetically from a situation of intense interference competition to one dominated by exploitative competition. The size structure of the population can thus determine the relative importance of interference and exploitative competition. In turn, the importance of interference competition may influence size structure by inhibiting the growth of smaller urchins, a pattern consistent with the prediction of theoretical models. The consideration of size-asymmetric competitive interactions can lead to a better understanding of population size structure and dynamics.

中文翻译：

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规模结构化种群的种内竞争：关键海洋草食动物干扰竞争重要性的个体发生转变

摘要：个体很少具有同等的竞争能力，而体型是影响竞争机制（即剥削和干扰）和竞争后果的最重要属性之一。规模结构人口内部的竞争互动非常复杂，可能会对人口动态，社区结构和进化过程产生重大影响。绿色顽童强壮海藻droebachiensis对海藻床的破坏性放牧在缺乏优质食物的地区造成贫瘠，种内竞争可能在构造种群方面起重要作用。在这项研究中，我们通过实验确定了绿色小顽童的小，中和大尺寸类别之间尺寸不对称竞争的潜在机制。一项基于野外的介观实验表明，中小海胆在争夺具有大体型的食物时，生长速度变慢，性腺也变小。出人意料的是，当随意提供食物但有大顽童存在时，小个体的生长和觅食行为就会减少，这为大小海胆之间的干扰竞争提供了有力的证据。但是，中型和大型海胆之间的相互作用更受剥削性竞争的影响，这表明海胆在遗传上已从激烈的干扰竞争转变为以剥削竞争为主的情况。因此，人口规模结构可以确定干扰和剥削竞争的相对重要性。反过来，干扰竞争的重要性可能会通过抑制小顽童的生长而影响尺寸结构，这种小顽童的模式与理论模型的预测相符。规模不对称竞争相互作用的考虑可以使人们更好地了解人口规模的结构和动态。干扰竞争的重要性可能会通过抑制较小的海胆的生长而影响尺寸结构，这种模式与理论模型的预测相符。规模不对称竞争相互作用的考虑可以使人们更好地了解人口规模的结构和动态。干扰竞争的重要性可能会通过抑制较小的海胆的生长而影响尺寸结构，这种模式与理论模型的预测相符。规模不对称竞争相互作用的考虑可以使人们更好地了解人口规模的结构和动态。