Herbivory on Temperate Rainforest Seedlings in Sun and Shade: Resistance, Tolerance and Habitat Distribution

Abstract

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.

High Tolerance to Salinity and Herbivory Stresses May Explain the Expansion of Ipomoea Cairica to Salt Marshes

“…The growth of plants in habitats with more than one stress factor may be particularly negatively influenced due to interactions between the stress factors. For example, herbivory decreased seedling survival and growth of temperate rainforest species in the shade, but this did not happen in the sun [69]. Previous studies revealed that the salinity tolerance of invaders is important because it may help to relate physiological tolerance to distribution limits in the field [70].…”

How does herbivory affect individuals and populations of the perennial herb Paeonia officinalis?

“…In shady habitats, plants are supposed to be more vulnerable to herbivory because of either higher nutritive value or lower secondary-compound content (Henriksson et al, 2003;Koricheva et al, 1998b;Moran and Showler, 2005;Roberts and Paul, 2006). Differences in herbivory rate along a light gradient are not only due to differences in plant resistance or tolerance to herbivory, but also to variations in phytophagous insect abundance (Louda and Rodman, 1996;Saldago-Luarte and Gianoli, 2010). We detected in open habitats a higher herbivory rate for two morphological stages, seedlings and reproductive plants, but no significant differences between habitats were obvious for small and large vegetative plants.…”

Effect of light environment on intra-specific variation in herbivory in the carnivorous plantPinguicula moranensis(Lentibulariaceae)

“…For example, higher damage has been reported in plants of shaded habitats (Maiorana 1981;Niesenbaum 1992). In contrast, higher herbivory has been observed in open sunny sites (Lincoln & Mooney 1984;Louda et al 1987;Salgado-Luarte & Gianoli 2010).…”