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Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators

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ABSTRACT

Predators not only consume prey but exert nonconsumptive effects in form of scaring, consequently disturbing feeding or reproduction. However, how alternative food sources and hunting mode interactively affect consumptive and nonconsumptive effects with implications for prey fitness have not been addressed, impending functional understanding of such tritrophic interactions. With a herbivorous beetle, two omnivorous predatory bugs (plant sap as alternative food, contrasting hunting modes), and four willow genotypes (contrasting suitability for beetle/omnivore), we investigated direct and indirect effects of plant quality on the beetles key reproductive traits (oviposition rate, clutch size). Using combinations of either or both omnivores on different plant genotypes, we calculated the contribution of consumptive (eggs predated) and nonconsumptive (fewer eggs laid) effect on beetle fitness, including a prey density‐independent measure (c:nc ratio). We found that larger clutches increase egg survival in presence of the omnivore not immediately consuming all eggs. However, rather than lowering mean, the beetles generally responded with a frequency shift toward smaller clutches. However, female beetles decreased mean and changed clutch size frequency with decreasing plant quality, therefore reducing intraspecific exploitative competition among larvae. More importantly, variation in host plant quality (to omnivore) led to nonconsumptive effects between one‐third and twice as strong as the consumptive effects. Increased egg consumption on plants less suitable to the omnivore may therefore be accompanied by less searching and disturbing the beetle, representing a “cost” to the indirect plant defense in the form of a lower nonconsumptive effect. Many predators are omnivores and altering c:nc ratios (with egg retention as the most direct link to prey fitness) via plant quality and hunting behavior should be fundamental to advance ecological theory and applications. Furthermore, exploring modulation of fitness traits by bottom‐up and top‐down effects will help to explain how and why species aggregate.

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Individual egg survival within clutches (a‐c) in relation to clutch size for both plant genotypes (Loden, 78183) and omnivore treatments (AN = A. nemorum, OM = O. marginalis). Proportion of surviving beetle eggs is jittered to increase visibility, and the lines show the model prediction with bootstrapped confidence limits. The lowest figure (d) shows the overall mean of all three treatments. Black circles show the mean (± SD) survival per clutch (open) and per cumulative number of eggs on a plant (closed). Capital letters indicate differences between treatments, and lowercase letters differences between genotypes (p < .05; Tukey's test)
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ece32828-fig-0004: Individual egg survival within clutches (a‐c) in relation to clutch size for both plant genotypes (Loden, 78183) and omnivore treatments (AN = A. nemorum, OM = O. marginalis). Proportion of surviving beetle eggs is jittered to increase visibility, and the lines show the model prediction with bootstrapped confidence limits. The lowest figure (d) shows the overall mean of all three treatments. Black circles show the mean (± SD) survival per clutch (open) and per cumulative number of eggs on a plant (closed). Capital letters indicate differences between treatments, and lowercase letters differences between genotypes (p < .05; Tukey's test)

Mentions: The egg survival in clutches (Table 1: M5) and the survival of all eggs on a plant (Table 1: 1 M7) in the presence of A. nemorum depended on the plant genotype, with lower survival on Loden (Figure 3). Egg survival was generally lower in the second part of the experiment and did not differ significantly between treatments (Figure 4a–c) although, again, it was higher for 78183 than for Loden (per clutch and per eggs on plant; Figure 4d). During the second part of the experiment, we found a tendency for genotype to have an effect on the egg survival in clutches and a significant interaction between clutch size and treatment (Table 1 1: M6). This interaction, and the interaction between clutch size and genotype in the first part (Table 1: M5), can be attributed to survival increasing with clutch size for the 1 AN 1 OM treatment (Figure 4) and for genotypes 78183 and 78021 (Figure 3), respectively. Egg survival was generally lower in the second part of the experiment which we attribute to the use of third instars of O. marginalis, as mentioned previously.


Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators
Individual egg survival within clutches (a‐c) in relation to clutch size for both plant genotypes (Loden, 78183) and omnivore treatments (AN = A. nemorum, OM = O. marginalis). Proportion of surviving beetle eggs is jittered to increase visibility, and the lines show the model prediction with bootstrapped confidence limits. The lowest figure (d) shows the overall mean of all three treatments. Black circles show the mean (± SD) survival per clutch (open) and per cumulative number of eggs on a plant (closed). Capital letters indicate differences between treatments, and lowercase letters differences between genotypes (p < .05; Tukey's test)
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Related In: Results  -  Collection

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ece32828-fig-0004: Individual egg survival within clutches (a‐c) in relation to clutch size for both plant genotypes (Loden, 78183) and omnivore treatments (AN = A. nemorum, OM = O. marginalis). Proportion of surviving beetle eggs is jittered to increase visibility, and the lines show the model prediction with bootstrapped confidence limits. The lowest figure (d) shows the overall mean of all three treatments. Black circles show the mean (± SD) survival per clutch (open) and per cumulative number of eggs on a plant (closed). Capital letters indicate differences between treatments, and lowercase letters differences between genotypes (p < .05; Tukey's test)
Mentions: The egg survival in clutches (Table 1: M5) and the survival of all eggs on a plant (Table 1: 1 M7) in the presence of A. nemorum depended on the plant genotype, with lower survival on Loden (Figure 3). Egg survival was generally lower in the second part of the experiment and did not differ significantly between treatments (Figure 4a–c) although, again, it was higher for 78183 than for Loden (per clutch and per eggs on plant; Figure 4d). During the second part of the experiment, we found a tendency for genotype to have an effect on the egg survival in clutches and a significant interaction between clutch size and treatment (Table 1 1: M6). This interaction, and the interaction between clutch size and genotype in the first part (Table 1: M5), can be attributed to survival increasing with clutch size for the 1 AN 1 OM treatment (Figure 4) and for genotypes 78183 and 78021 (Figure 3), respectively. Egg survival was generally lower in the second part of the experiment which we attribute to the use of third instars of O. marginalis, as mentioned previously.

View Article: PubMed Central - PubMed

ABSTRACT

Predators not only consume prey but exert nonconsumptive effects in form of scaring, consequently disturbing feeding or reproduction. However, how alternative food sources and hunting mode interactively affect consumptive and nonconsumptive effects with implications for prey fitness have not been addressed, impending functional understanding of such tritrophic interactions. With a herbivorous beetle, two omnivorous predatory bugs (plant sap as alternative food, contrasting hunting modes), and four willow genotypes (contrasting suitability for beetle/omnivore), we investigated direct and indirect effects of plant quality on the beetles key reproductive traits (oviposition rate, clutch size). Using combinations of either or both omnivores on different plant genotypes, we calculated the contribution of consumptive (eggs predated) and nonconsumptive (fewer eggs laid) effect on beetle fitness, including a prey density&#8208;independent measure (c:nc ratio). We found that larger clutches increase egg survival in presence of the omnivore not immediately consuming all eggs. However, rather than lowering mean, the beetles generally responded with a frequency shift toward smaller clutches. However, female beetles decreased mean and changed clutch size frequency with decreasing plant quality, therefore reducing intraspecific exploitative competition among larvae. More importantly, variation in host plant quality (to omnivore) led to nonconsumptive effects between one&#8208;third and twice as strong as the consumptive effects. Increased egg consumption on plants less suitable to the omnivore may therefore be accompanied by less searching and disturbing the beetle, representing a &ldquo;cost&rdquo; to the indirect plant defense in the form of a lower nonconsumptive effect. Many predators are omnivores and altering c:nc ratios (with egg retention as the most direct link to prey fitness) via plant quality and hunting behavior should be fundamental to advance ecological theory and applications. Furthermore, exploring modulation of fitness traits by bottom&#8208;up and top&#8208;down effects will help to explain how and why species aggregate.

No MeSH data available.


Related in: MedlinePlus