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

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

Highly concentrated bitumen emulsions. A state of the art, review of experimental results

Les emulsions concentrades o altament concentrades de betum són un camp molt poc estudiat avui en dia. El treball és un estat de l'art de tots els papers que hi ha sobre aquest tema desde el mètode tradicional fins el HIPR (High Internal Phase Ratio)

Parallel functional differentiation of an invasive annual plant on two continents.

Rapid local adaptation frequently occurs during the spread of invading species. It remains unclear, however, how consistent, and therefore potentially predictable, such patterns of local adaptation are. One approach to this question is to measure patterns of local differentiation in functional traits and plasticity levels in invasive species in multiple regions. Finding consistent patterns of local differentiation in replicate regions suggests that these patterns are adaptive. Further, this outcome indicates that the invading species likely responds predictably to selection along environmental gradients, even though standing genetic variation is likely to have been reduced during introduction. We studied local differentiation in the invasive annual plant Erodium cicutarium in two invaded regions, California and Chile. We collected seeds from across strong gradients in precipitation and temperature in Mediterranean-climate parts of the two regions (10 populations per region). We grew seeds from maternal families from these populations through two generations and exposed the second generation to contrasting levels of water and nutrient availability. We measured growth, flowering time and leaf functional traits across these treatments to obtain trait means and plasticity measures. We found strong differentiation among populations in all traits. Plants from drier environments flowered earlier, were less plastic in flowering time and reached greater size in all treatments. Correlations among traits within regions suggested a coordinated evolutionary response along environmental gradients associated with growing season length. There was little divergence in traits and trait intercorrelations between regions, but strongly parallel divergence in traits within regions. Similar, statistically consistent patterns of local trait differentiation across two regions suggest that local adaptation to environmental gradients has aided the spread of this invasive species, and that the formation of ecotypes in newly invaded environments has been relatively consistent and predictable

Diversidad genética intra-poblacional de plantas trepadoras y árboles en un bosque templado en Chile central

The climbing habit is a key innovation in angiosperm evolution: climbing plant taxa have greater species richness than their non-climbing sister groups. It is considered that highly diversified clades should show increased among-population genetic differentiation. Less clear is the expected pattern regarding within-population genetic diversity in speciose lineages. We tested the hypothesis of greater within-population genetic diversity in climbing plants compared to trees in a temperate forest in central Chile. The assumption underlying this hypothesis is that higher among-population differentiation in climbers compared to trees should reflect higher genetic diversity as well. AFLP markers from 167 individual plants from 14 species (seven climbers and seven trees) were used to estimate the following indices of within-population genetic diversity: mean unbiased expected heterozygosity (HE), percentage of polymorphic loci (PPL), Shannon information index (I), and the effective number of alleles (NE). Overall, within-population genetic diversity did not differ between climbing plants and trees. The HE for climbing plants was slightly higher than that of trees (0.247 vs. 0.231), and PPL was higher in trees (93.6) than in climbers (81.8), but these differences were not statistically significant. Both I and NE were very similar for both groups. The expected greater genetic diversity in climbers might have been counterbalanced by tree-related ecological factors that turned to be relevant in the species assemblages studied. Results of this preliminary study should be further confirmed with a broader approach including several forest sites and larger sample sizes.El hábito trepador es una innovación clave en la evolución de las angiospermas: los taxa de plantas trepadoras poseen mayor riqueza de especies que sus grupos hermanos no-trepadores. Se considera que clados altamente diversificados debieran mostrar mayor diferenciación genética entre poblaciones. Menos claro es el patrón esperado respecto a la diversidad genética al interior de las poblaciones en linajes especiosos. Evaluamos la hipótesis de mayor diversidad genética intrapoblacional en plantas trepadoras en comparación con árboles en un bosque templado en Chile central. El supuesto detrás de esta hipótesis es que la mayor diferenciación poblacional en las trepadoras, comparadas con los árboles, debiera reflejar una mayor diversidad genética también. Marcadores AFLP de 167 plantas individuales de 14 especies (siete trepadoras y siete árboles) fueron usados para estimar los siguientes índices de diversidad genética intra-poblacional: heterocigosidad esperada media (HE), porcentaje de loci polimórficos (PPL), índice de información de Shannon (I), y el número efectivo de alelos (NE). En general, la diversidad genética intra-poblacional no difirió entre plantas trepadoras y árboles. La HE para plantas trepadoras fue levemente mayor a la de los árboles (0,247 vs. 0,231), y el PPL fue más alto en árboles (93,6) que en trepadoras (81,8), pero estas diferencias no fueron estadísticamente significativas. Tanto I como NE fueron muy similares en ambos grupos. La mayor diversidad genética esperada en trepadoras puede hacer sido contrarrestada por factores ecológicos particulares a los árboles que resultaron ser relevantes en los ensambles de especies estudiados. Los resultados de este estudio preliminar debieran ser confirmados con una aproximación a mayor escala, incluyendo varios sitios en el bosque y mayores tamaños muestrales

Data from: Herbivores modify selection on plant functional traits in a temperate rainforest understory

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

Effects of simulated herbivory on <i>Embothrium coccineum</i> seedlings in sun and shade sites.

<p>Open bars: undamaged seedlings; hatched bars: seedlings subjected to 50% leaf damage. Bars show results 10 months after inflicting damage. <b>A</b>) Seedling survival (proportions, ± SE). <b>B</b>) Seedling relative growth rate, RGR (cm cm⁻¹ day⁻¹, ± SE). Bars sharing a letter are not significantly different (Tukey HSD test).</p

Analysis of variance of the effects of leaf damage and light environment on survival and growth of <i>Embothrium coccineum</i> seedlings.

<p>Analysis of variance of the effects of leaf damage and light environment on survival and growth of <i>Embothrium coccineum</i> seedlings.</p

Table S1 Study species and their features from Tolerance to herbivory and the resource availability hypothesis

Table S1. Study species, their minimum light requirement (MLR, % canopy openness; the 10th percentile of distribution across the light gradient in the forest*), leaf lifespan (yearsȹ), leaf toughness (kN m-1) and data of the tolerance experiment: height of experimental seedlings (cm) and sample size (half were assigned to control and half to damage treatments, see text for details)

Herbivory pressure and plant resistance in <i>Embothrium coccineum</i> seedlings from contrasting light environments.

<p>A) Index of herbivory, IH (± SE) on seedlings in sun (white bar) and shade environments (gray bar) in a southern temperate rainforest. Means were significantly different (P<0.001; t-test). B) Leaf area consumed (% ± SE) by the generalist snail <i>Helix aspersa</i> in a 48 h no-choice palatability test with leaves from seedlings grown in sun (white bar) and shade (black bar) sites. Means were significantly different (P<0.005; Mann-Whitney U test).</p