Department of Zoology, Stockholm University, Stockholm SE 10691, Sweden.
Ecology. 2009 Dec;90(12):3406-17. doi: 10.1890/08-1138.1.
The majority of phytophagous insects are relatively specialized in their food habits, and specialization in resource use is expected to be favored by selection in most scenarios. Ecological generalization is less common and less well understood, but it should be selected for by (1) rarity of resources, (2) resource inconstancy, or (3) unreliability of resource quality. Here, we test these predictions by studying egg distribution and offspring survival in the orange tip butterfly, Anthocharis cardamines, on different host plants in Sweden over a five-year period. A total of 3800 eggs were laid on 16 of the 18 crucifers available at the field site during the five years. Three main factors explained host plant generalization: (1) a rarity of food resources in which the female encounter rate of individual crucifer plants was low and within-year phenological succession of flowering periods of the different crucifers meant that individual species were suitable for oviposition only within a short time window, which translates to a low effective abundance of individual crucifer species as experienced by females searching for host plants, making specialization on a single crucifer species unprofitable; (2) variation in food resources in which among-year variation in availability of any one host plant species was high; and (3) larval survivorship varied unpredictably among years on all host plants, thereby necessitating a bet-hedging strategy and use of several different host plants. Unpredictable larval survival was caused by variation in plant stand habitat characteristics, which meant that drowning and death from starvation affected different crucifers differently, and by parasitism, which varied by host plant and year. Hence, our findings are in agreement with the theoretical explanation of ecological generalization above, helping to explain why A. cardamines is a generalist throughout its range with respect to genera within the Cruciferae.
大多数植食性昆虫在食物习性上相对专业化，在大多数情况下，资源利用的专业化预计会受到选择的青睐。生态概括性不太常见，也不太被理解，但它应该会受到以下因素的选择：（1）资源的稀有性，（2）资源的不稳定性，或（3）资源质量的不可靠性。在这里，我们通过研究在瑞典的五年期间，橙色斑点蝴蝶（Anthocharis cardamines）在不同的寄主植物上的卵分布和后代存活率来检验这些预测。在五年期间，共有 3800 个卵产在现场可用的 18 种十字花科植物中的 16 种上。三个主要因素解释了寄主植物的概括性：（1）食物资源的稀有性，其中雌性遇到个别十字花科植物的几率较低，不同十字花科植物的年内开花期物候学演替意味着个别物种只适合在很短的时间窗口内产卵，这转化为雌性寻找寄主植物时所经历的个别十字花科物种的有效丰度较低，使得专门针对单一十字花科物种的专业化无利可图；（2）食物资源的变异性，其中任何一种寄主植物物种的年际可利用性变化很大；（3）幼虫存活率在所有寄主植物上不可预测地波动，从而需要一种风险分散策略并使用几种不同的寄主植物。不可预测的幼虫存活率是由植物种群栖息地特征的变化引起的，这意味着溺水和饥饿死亡对不同的十字花科植物有不同的影响，以及寄生现象，寄生现象因寄主植物和年份而异。因此，我们的发现与上述生态概括性的理论解释一致，有助于解释为什么 A. cardamines 在其 Cruciferae 属的范围内是一个广义种。
