Contrasting patterns of insect herbivory and predation pressure across a tropical rainfall gradient

One explanation for the extraordinarily high tree diversity of tropical lowland forests is that it is maintained by specialized natural enemies such as insect herbivores, which cause distance- and density-dependent mortality. Insect herbivory could also explain the positive correlation between tree species richness and rainfall if herbivory increases with rainfall, is higher on locally abundant versus rare species, and is not limited by predation pressure at wet sites. To test these predictions, insect herbivory and predation pressure on insect herbivores were quantified across a neotropical rainfall and tree species richness gradient, and herbivory was investigated in relation to local tree abundances. Insect herbivory on leaves (folivory) decreased strongly and significantly with rainfall, while predation pressure was significantly higher at the wetter site. Herbivores were more likely to attack abundant tree species, but herbivore damage levels were not related to tree species abundance. Insect folivores might contribute to local tree species coexistence in our system, but seem unlikely to drive the positive correlation between tree species richness and rainfall. The unexpected and contrasting patterns of herbivory and predation we observed support the need for a multi-trophic perspective to understand fully the processes contributing to diversity and ecosystem functioning

Higher predation risk for insect prey at low latitudes and elevations

Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution

Plasticity of plant silicon and nitrogen concentrations in response to water regimes varies across temperate grassland species

1. Temperate grasslands exhibit strong spatial and temporal variation in water regimes. Thus, grassland plants experience potentially stressful water regimes, which may influence their tissue silicon (Si) and nitrogen (N) concentrations. Plant Si and N concentrations play important ecological roles in temperate grasslands, for example, by influencing plant performance and herbivory, yet comparisons of species' responses to a broad range of water regimes, including drought, waterlogging and flooding, are lacking. 2. We conducted a mesocosm experiment with 10 temperate grassland species of two life-forms (grasses and forbs) exposed to four different soil water regimes (drought, a benign control, waterlogged and flooded conditions), and analysed their Si and N concentrations. 3. Grasses showed lower Si concentrations under drought and flooding compared to the benign control and the highest concentrations emerged under waterlogging. Overall, plant Si responses of grasses were more uniform, while in forbs, responses varied both in direction and magnitude across species. For N concentrations, all species and life-forms showed the highest concentrations under drought compared to the benign control, while half of the species exhibited decreasing concentrations under waterlogging and/or flooding. The water regimes, especially waterlogging and flooding, induced changes in species rankings of plant Si and N concentrations, with stronger shifts in forbs than in grasses. 4. Our results indicate that spatial and temporal variation of water regimes may influence plant Si and N concentrations in temperate grassland species. Plant Si responses to water regimes might be highly species-specific in forbs but more similar in grasses, whereas plant N responses are likely to be relatively uniform across species and life-forms. 5. The strong plasticity in plant Si and N concentrations we observed might have pervasive consequences for ecological processes, such as herbivory

Data from: Contrasting patterns of insect herbivory and predation pressure across a tropical rainfall gradient

One explanation for the extraordinarily high tree diversity of tropical lowland forests is that it is maintained by specialized natural enemies such as insect herbivores, which cause distance and density dependent mortality. Insect herbivory could also explain the positive correlation between tree species richness and rainfall if herbivory increases with rainfall, is higher on locally abundant versus rare species, and is not limited by predation pressure at wet sites. To test these predictions, insect herbivory and predation pressure on insect herbivores were quantified across a Neotropical rainfall and tree species richness gradient, and herbivory was investigated in relation to local tree abundances. Insect herbivory on leaves (folivory) decreased strongly and significantly with rainfall, while predation pressure was significantly higher at the wetter site. Herbivores were more likely to attack abundant tree species, but herbivore damage levels were not related to tree species abundance. Insect folivores might contribute to local tree species coexistence in our system, but seem unlikely to drive the positive correlation between tree species richness and rainfall. The unexpected and contrasting patterns of herbivory and predation we observed support the need for a multi-trophic perspective to understand fully the processes contributing to diversity and ecosystem functioning

Weissflog_et_al._Caterpillar_data

Field data collected in June 2014 across the Isthmus of Panama. Artificial plasticine caterpillars were used to measure predation pressure. 100 caterpillars were set out in three 1-ha forest sites following procedures as described in Roslin et al. 2017 (Science)

Data from: Higher predation risk for insect prey at low latitudes and elevations

Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution