Browsing by Author "Salgado-Luarte, Cristian"

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    Herbivores Modify Selection on Plant Functional Traits in a Temperate Rainforest Understory
    (2012) Salgado-Luarte, Cristian; Gianoli, Ernesto
    There is limited evidence regarding the adaptive value of plant functional traits in contrasting light environments. It has been suggested that changes in these traits in response to light availability can increase herbivore susceptibility. We tested the adaptive value of plant functional traits linked with carbon gain in contrasting light environments and also evaluated whether herbivores can modify selection on these traits in each light environment. In a temperate rainforest, we examined phenotypic selection on functional traits in seedlings of the pioneer tree Aristotelia chilensis growing in sun (canopy gap) and shade (forest understory) and subjected to either natural herbivory or herbivore exclusion. We found differential selection on functional traits depending on light environment. In sun, there was positive directional selection on photosynthetic rate and relative growth rate (RGR), indicating that selection favors competitive ability in a high-resource environment. Seedlings with high specific leaf area (SLA) and intermediate RGR were selected in shade, suggesting that light capture and conservative resource use are favored in the understory. Herbivores reduced the strength of positive directional selection acting on SLA in shade. We provide the first demonstration that natural herbivory rates can change the strength of selection on plant ecophysiological traits, that is, attributes whose main function is resource uptake. Research addressing the evolution of shade tolerance should incorporate the selective role of herbivores.
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    Herbivory may modify functional responses to shade in seedlings of a light-demanding tree species
    (2011) Salgado-Luarte, Cristian; Gianoli, Ernesto
    P>1. The ability to display functional responses to shading, i.e. phenotypic changes that enhance plant performance in low light, is fundamental for plant success in forest communities. Herbivory may constrain plant functional responses to shading and this could explain the often observed lower plant tolerance of herbivore damage in the shade.
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    Herbivory on Temperate Rainforest Seedlings in Sun and Shade: Resistance, Tolerance and Habitat Distribution
    (2010) Salgado-Luarte, Cristian; Gianoli, Ernesto
    Differential herbivory and/or differential plant resistance or tolerance in sun and shade environments may influence plant distribution along the light gradient. Embothrium coccineum is one of the few light-demanding tree species in the temperate rainforest of southern South America, and seedlings are frequently attacked by insects and snails. Herbivory may contribute to the exclusion of E. coccineum from the shade if 1) herbivory pressure is greater in the shade, which in turn can result from shade plants being less resistant or from habitat preferences of herbivores, and/or 2) consequences of damage are more detrimental in the shade, i.e., shade plants are less tolerant. We tested this in a field study with naturally established seedlings in treefall gaps (sun) and forest understory (shade) in a temperate rainforest of southern Chile. Seedlings growing in the sun sustained nearly 40% more herbivore damage and displayed half of the specific leaf area than those growing in the shade. A palatability test showed that a generalist snail consumed ten times more leaf area when fed on shade leaves compared to sun leaves, i.e., plant resistance was greater in sun-grown seedlings. Herbivore abundance (total biomass) was two-fold greater in treefall gaps compared to the forest understory. Undamaged seedlings survived better and showed a slightly higher growth rate in the sun. Whereas simulated herbivory in the shade decreased seedling survival and growth by 34% and 19%, respectively, damaged and undamaged seedlings showed similar survival and growth in the sun. Leaf tissue lost to herbivores in the shade appears to be too expensive to replace under the limiting light conditions of forest understory. Following evaluations of herbivore abundance and plant resistance and tolerance in contrasting light environments, we have shown how herbivory on a light-demanding tree species may contribute to its exclusion from shade sites. Thus, in the shaded forest understory, where the seedlings of some tree species are close to their physiological tolerance limit, herbivory could play an important role in plant establishment.
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    Trade-off between plant resistance and tolerance to herbivory: Mechanical defenses outweigh chemical defenses
    (2023) Salgado-Luarte, Cristian; Gonzalez-Teuber, Marcia; Madriaza, Karina; Gianoli, Ernesto
    Plant resistance includes mechanical and chemical defenses that reduce herbivory, whereas plant tolerance reduces the fitness impact of herbivory. Because defenses are costly and investing in both resistance and tolerance may be superfluous, trade-offs among them are expected. In forest ecosystems, the mechanical strengthening of leaves is linked both to shade adaptation and antiherbivore defenses, but it also compromises resource uptake, therefore limiting regrowth following damage, suggesting a trade-off between mechanical defenses and tolerance. We tested for the resistance-tolerance trade-off across 11 common tree species in a temperate rainforest and explored mechanistic explanations by measuring chemical and mechanical defenses. Herbivory damage was negatively associated with leaf toughness and fiber content, whereas there was no significant relationship between herbivory and secondary metabolites (flavonols, gallic acid, tannins, and terpenoids). We detected a resistance-tolerance trade-off, as expected. We found a negative relationship between mechanical defenses and tolerance, estimated as the survival ratio between experimentally damaged and undamaged seedlings. Tolerance and secondary metabolites showed no significant association. Results suggest that selective forces other than herbivory acting on defensive traits can favor a resistance-tolerance trade-off. Therefore, plant adaptation to contrasting light environments may contribute to the evolution of resistance-tolerance trade-offs.