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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.

No MeSH data available.


Mean (±SE) clutch size and eggs laid on individual plants by two Phratora vulgatissima females on four different Salix genotypes (S. dasyclados: Gudrun, Loden; S. viminalis: 78183, 78021) and the presence of omnivores (Control = only leaf beetles, AN = Anthocoris nemorum, OM = Orthotylus marginalis) for the first (a, c) and second (b, d) parts of the experiment. Lowercase letters indicate differences between genotypes and uppercase letters differences between overall means (±SD) of treatments (p < .05; Tukey's test)
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ece32828-fig-0001: Mean (±SE) clutch size and eggs laid on individual plants by two Phratora vulgatissima females on four different Salix genotypes (S. dasyclados: Gudrun, Loden; S. viminalis: 78183, 78021) and the presence of omnivores (Control = only leaf beetles, AN = Anthocoris nemorum, OM = Orthotylus marginalis) for the first (a, c) and second (b, d) parts of the experiment. Lowercase letters indicate differences between genotypes and uppercase letters differences between overall means (±SD) of treatments (p < .05; Tukey's test)

Mentions: The omnivore treatments had no effect, but plant genotype strongly modulated the mean clutch size of P. vulgatissima (Table 1: M1, M2) with the S. viminalis genotype 78021 associated with the largest clutches (Figure 1a) in the presence of A. nemorum in the first part of the experiment. In the second part of the experiment, the mean clutch size did not differ between treatments, but seemed to resemble the genotype‐specific sizes recorded during the first part. In general, clutches were larger if more eggs were laid on a plant and this relationship became increasingly stronger in the presence of A. nemorum in the first part (Figure S1) and tended to be stronger on the Loden genotype compared to 78183 in the remaining omnivore treatments (Figure S2).


Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators
Mean (±SE) clutch size and eggs laid on individual plants by two Phratora vulgatissima females on four different Salix genotypes (S. dasyclados: Gudrun, Loden; S. viminalis: 78183, 78021) and the presence of omnivores (Control = only leaf beetles, AN = Anthocoris nemorum, OM = Orthotylus marginalis) for the first (a, c) and second (b, d) parts of the experiment. Lowercase letters indicate differences between genotypes and uppercase letters differences between overall means (±SD) of treatments (p < .05; Tukey's test)
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ece32828-fig-0001: Mean (±SE) clutch size and eggs laid on individual plants by two Phratora vulgatissima females on four different Salix genotypes (S. dasyclados: Gudrun, Loden; S. viminalis: 78183, 78021) and the presence of omnivores (Control = only leaf beetles, AN = Anthocoris nemorum, OM = Orthotylus marginalis) for the first (a, c) and second (b, d) parts of the experiment. Lowercase letters indicate differences between genotypes and uppercase letters differences between overall means (±SD) of treatments (p < .05; Tukey's test)
Mentions: The omnivore treatments had no effect, but plant genotype strongly modulated the mean clutch size of P. vulgatissima (Table 1: M1, M2) with the S. viminalis genotype 78021 associated with the largest clutches (Figure 1a) in the presence of A. nemorum in the first part of the experiment. In the second part of the experiment, the mean clutch size did not differ between treatments, but seemed to resemble the genotype‐specific sizes recorded during the first part. In general, clutches were larger if more eggs were laid on a plant and this relationship became increasingly stronger in the presence of A. nemorum in the first part (Figure S1) and tended to be stronger on the Loden genotype compared to 78183 in the remaining omnivore treatments (Figure S2).

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.