Chen Ke-Wei, Chen Yigen
College of Agriculture, South China Agricultural University, Guangzhou, China.
Department of Entomology and Nematology, University of California, One Shields Avenue, Davis, California, USA.
Insect Sci. 2018 Apr;25(2):337-351. doi: 10.1111/1744-7917.12399. Epub 2016 Nov 24.
The slow growth-high mortality hypothesis (SG-HG) predicts that slower growing herbivores suffer greater mortality due to a prolonged window of vulnerability. Given diverse plant-herbivore-natural enemy systems resulting from different feeding ecologies of herbivores and natural enemies, this hypothesis might not always be applicable to all systems. This is evidenced by mixed support from empirical data. In this study, a meta-analysis of the SG-HM hypothesis for insects was conducted, aiming to find conditions that favor or reject SG-HM. The analysis revealed significant within- and between-group heterogeneity for almost all explanatory variables and overall did not support SG-HM. In this analysis, SG-HM was supported when any of the following 5 conditions was met: (1) host food consisted of artificial diet; (2) herbivore growth was measured as larval mass; (3) herbivores were generalists; (4) no or multiple species of natural enemies were involved in the study; and (5) parasitoids (i.e., parasitic insects) involved in the study were gregarious. SG-HM was rejected when any of the following 5 conditions was met: (1) herbivores were from the order Hymentoptera; (2) parasitoids from more than 1 order caused herbivore mortality; (2) parasitoids were specialists; (3) parasitoids were solitary; (4) parasitoids were idiobionts or koinobionts; and (5) single species of natural enemy caused mortality of specialist herbivores. All known studies investigated herbivore mortality for a short period of their life cycle. Researchers are encouraged to monitor herbivore mortality during the entire window of susceptibility or life cycle using life tables. Studies involving multiple mortality factors (i.e., both biotic and abiotic) or multiple natural enemy species are also encouraged since herbivores in nature face a multitude of risks during the entire life cycle. More comprehensive studies may increase our understanding of factors influencing the relationships between herbivore growth and mortality.
缓慢生长-高死亡率假说（SG-HG）预测，生长较慢的食草动物由于易受伤害的时间延长，死亡率更高。鉴于食草动物和天敌不同的取食生态导致了多样的植物-食草动物-天敌系统，这一假说可能并不总是适用于所有系统。实证数据的支持情况不一就证明了这一点。在本研究中，对昆虫的SG-HM假说进行了荟萃分析，旨在找出支持或否定SG-HM的条件。分析显示，几乎所有解释变量在组内和组间均存在显著异质性，总体上不支持SG-HM。在该分析中，当满足以下5个条件中的任何一个时，SG-HM得到支持：（1）宿主食物为人工饲料；（2）以幼虫体重衡量食草动物的生长；（3）食草动物为多食性动物；（4）研究中未涉及或涉及多种天敌物种；（5）研究中涉及的寄生蜂（即寄生昆虫）为群居性。当满足以下5个条件中的任何一个时，SG-HM被否定：（1）食草动物属于膜翅目；（2）来自多个目的寄生蜂导致食草动物死亡；（2）寄生蜂为专食性动物；（3）寄生蜂为独居性；（4）寄生蜂为静止期寄生或生长期寄生；（5）单一物种的天敌导致专食性食草动物死亡。所有已知研究都只在食草动物生命周期的短时间内调查其死亡率。鼓励研究人员使用生命表在整个易受伤害期或生命周期内监测食草动物的死亡率。也鼓励开展涉及多种死亡因素（即生物和非生物因素）或多种天敌物种的研究，因为自然界中的食草动物在整个生命周期中面临多种风险。更全面的研究可能会增进我们对影响食草动物生长与死亡率之间关系的因素的理解。
