Unit of Animal Ecology, University of Potsdam, Potsdam, Germany.
Oecologia. 2011 Nov;167(3):623-33. doi: 10.1007/s00442-011-2008-y. Epub 2011 May 20.
Indirect resource competition and interference are widely occurring mechanisms of interspecific interactions. We have studied the seasonal expression of these two interaction types within a two-species, boreal small mammal system. Seasons differ by resource availability, individual breeding state and intraspecific social system. Live-trapping methods were used to monitor space use and reproduction in 14 experimental populations of bank voles Myodes glareolus in large outdoor enclosures with and without a dominant competitor, the field vole Microtus agrestis. We further compared vole behaviour using staged dyadic encounters in neutral arenas in both seasons. Survival of the non-breeding overwintering bank voles was not affected by competition. In the spring, the numbers of male bank voles, but not of females, were reduced significantly in the competition populations. Bank vole home ranges expanded with vole density in the presence of competitors, indicating food limitation. A comparison of behaviour between seasons based on an analysis of similarity revealed an avoidance of costly aggression against opponents, independent of species. Interactions were more aggressive during the summer than during the winter, and heterospecific encounters were more aggressive than conspecific encounters. Based on these results, we suggest that interaction types and their respective mechanisms are not either-or categories and may change over the seasons. During the winter, energy constraints and thermoregulatory needs decrease direct aggression, but food constraints increase indirect resource competition. Direct interference appears in the summer, probably triggered by each individual's reproductive and hormonal state and the defence of offspring against conspecific and heterospecific intruders. Both interaction forms overlap in the spring, possibly contributing to spring declines in the numbers of subordinate species.
间接资源竞争和干扰是种间相互作用的广泛发生机制。我们研究了两种物种，北方小型哺乳动物系统内这两种相互作用类型的季节性表达。季节因资源可利用性、个体繁殖状态和种内社会系统而异。我们使用活捕方法监测了有和没有优势竞争物种（草地田鼠）的 14 个实验种群中银行田鼠（Myodes glareolus）的空间利用和繁殖情况。在两个季节中，我们还在中性竞技场中使用 staged dyadic encounters 比较了田鼠的行为。非繁殖越冬的银行田鼠的存活率不受竞争影响。在春季，竞争种群中雄性银行田鼠的数量而非雌性的数量显著减少。在有竞争者的情况下，银行田鼠的家域范围随着田鼠密度的增加而扩大，表明存在食物限制。基于相似性分析的季节间行为比较表明，存在避免与对手进行代价高昂的攻击的行为，而这种行为与物种无关。夏季的相互作用比冬季更具攻击性，并且异种种间相遇比同种种间相遇更具攻击性。基于这些结果，我们认为相互作用类型及其各自的机制不是非此即彼的类别，并且可能随季节而变化。在冬季，能量限制和热调节需求减少了直接攻击，但食物限制增加了间接资源竞争。直接干扰出现在夏季，可能是由每个个体的生殖和激素状态以及对同种和异种种群入侵者的后代的防御触发的。这两种相互作用形式在春季重叠，可能导致春季次要物种数量下降。
