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Fine-scale plant defence variability increases top-down control of an herbivore
Functional Ecology ( IF 4.6 ) Pub Date : 2021-04-20 , DOI: 10.1111/1365-2435.13808 Ryan L. Paul 1 , Ian S. Pearse 2 , Paul J. Ode 1
中文翻译：
精细尺度的植物防御变异性增加了对食草动物的自上而下的控制
更新日期：2021-04-20
Functional Ecology ( IF 4.6 ) Pub Date : 2021-04-20 , DOI: 10.1111/1365-2435.13808 Ryan L. Paul 1 , Ian S. Pearse 2 , Paul J. Ode 1
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- Herbivore populations are regulated by a combination of plant defences and natural enemies. While plant defence can suppress herbivore populations, these defences can also adversely affect natural enemies, thereby releasing herbivores from top-down control.
- Over their life spans, herbivores and their natural enemies may experience substantial variation in plant defence. Recent studies have demonstrated that individual herbivores feeding on diets containing variable concentrations of plant toxins suffer substantially reduced fitness compared to herbivores feeding on a constant toxin concentration, even when both groups of herbivores experience equivalent means. However, the impacts of defence variability on natural enemies and top-down control of herbivores are unknown.
- Using artificial diets, we independently manipulated the mean concentration and variation of a plant toxin experienced by individual Trichoplusia ni caterpillars and its parasitoid Copidosoma floridanum. Additionally, by combining the performance of individual caterpillars on different constant diet concentrations of toxin, we were able to estimate the effect of toxin variability between herbivores using nonlinear averaging.
- Increases in the mean toxin concentration in the diet of parasitized T. ni hosts decreased the fitness of C. floridanum, while variance in individual diets did not impact parasitoid fitness, even though both mean and variance decreased the fitness of T. ni caterpillars. Increased variability in encountered plant defences suppressed individual herbivore fitness with no perceptible cost to top-down control. At the population level, however, increased variability between individual herbivore diets decreased the success of parasitoids relative to herbivores, thus reducing the strength of top-down control.
- Our study highlights the importance of defence variability at different scales in regulating herbivore performance. Variability in plant defence has the potential to reduce herbivore populations through a combination of bottom-up and top-down effects, but only at small spatial scales experienced by individual herbivores.
中文翻译：
精细尺度的植物防御变异性增加了对食草动物的自上而下的控制
- 食草动物种群受植物防御和天敌的共同调控。虽然植物防御可以抑制食草动物种群，但这些防御也会对天敌产生不利影响，从而使食草动物摆脱自上而下的控制。
- 在它们的一生中，食草动物和它们的天敌可能会经历植物防御的巨大变化。最近的研究表明，与以恒定毒素浓度为食的食草动物相比，以含有不同浓度植物毒素的饮食为食的食草动物个体的适应度显着降低，即使两组食草动物的平均水平相同。然而，防御变异性对天敌和食草动物自上而下控制的影响尚不清楚。
- 使用人工饮食，我们独立操纵了个体Trichoplusia ni毛虫及其寄生蜂Copidosoma floridanum经历的植物毒素的平均浓度和变化。此外，通过结合个体毛毛虫对不同恒定饮食浓度毒素的表现，我们能够使用非线性平均来估计食草动物之间毒素变异性的影响。
- 寄生的T. ni宿主饮食中平均毒素浓度的增加降低了C. floridanum的适应性，而个体饮食的差异不影响寄生蜂的适应性，即使平均值和方差都降低了T. ni毛虫的适应性。遇到的植物防御的可变性增加抑制了个体食草动物的适应性，而自上而下的控制没有明显的成本。然而，在种群水平上，个体食草动物饮食之间变异性的增加降低了寄生蜂相对于食草动物的成功率，从而降低了自上而下控制的强度。
- 我们的研究强调了不同尺度的防御变异在调节食草动物表现方面的重要性。植物防御的可变性有可能通过自下而上和自上而下效应的组合减少食草动物种群，但仅限于个体食草动物所经历的小空间尺度。
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