Ecological interactions of herbivory and predation in various terrestrial ecosystems

Heveakore MARAIA

Doctoral thesis

The reciprocal effect of leaf traits and herbivore communities along latitudinal and vertical gradients

Abstract:

My thesis investigates ecological interactions, especially herbivory and predation related to herbivorous insect along gradients in various terrestrial ecosystems - including islands vs. mainland, along latitudinal gradient in tropical and temperate forests, and in their vertical gradients, and finally in fire-mammal dominated ecosystems in subtropical savanna. The thesis examines tri-trophic interactions, specifically within plants, arthropod herbivores, and insectivorous predator dynamics, to explore how both biotic (top-down as well as bottom-up) and abiotic factors influence herbivory patterns. Through manipulative experiments, multi-site and multi-trophic studies, the research provides novel and valuable insights into the roles of plant defences, clines in herbivory, herbivory rate and accumulation and seasonality affecting herbivory damage. The first chapter (Chapter I) evaluates the effects of vertebrate and invertebrate predators on herbivory across elevational gradients on island vs. mainland, where plant defences are expected to play different roles. Chapter I reveals that vertebrate predators are more effective in controlling herbivory damage on islands than on the mainland. The second chapter (Chapter II) examines how seasonality, microclimate, and leaf traits influence insect herbivory along a vertical gradient in a tropical rainforest of Papua New Guinea. The novelty of this chapter is in the focus on herbivory rate on marked leaves, revisited for nearly a year, along a complete vertical gradient in tropical forest. The third chapter (Chapter III) investigates insect herbivory in a South African savanna-forest mosaic, highlighting how herbivory caused by chewing and mining insects varies with plant traits, mammal herbivores' density, and fire frequency across rainfall gradients. Very importantly, this chapter represents one of very few studies focusing on insect herbivory in savanna, finding it to be an important yet neglected topic. The final chapter (Chapter IV) explores insect herbivory across a latitudinal gradient, emphasising the varying effects of seasonality in temperate and tropical forests. Chapter IV represents a robust study rejecting the hypothesis, that insect herbivory is stronger/higher in tropical than in temperate forests. In Chapter IV, I argue that difference needs to be made between studies surveying standing herbivory vs. herbivory rate. Overall, my thesis study enhances the understanding of complex ecological interactions between herbivorous insect and plants and deepens our knowledge of how environmental factors shape the interplay between them and between the predators of insect, and the overall role of herbivory of terrestrial ecosystems. Besides other contributions to science, the thesis provides measures of standing herbivory damage and herbivory rates for many woody plant species, from various parts of the globe, representing thus another valuable contribution to other researchers.

Keywords

Insect herbivory, Papua New Guinea, latitudinal gradient, altitudinal gradient, mainland, tri-trophic interactions, arthropods, chewing herbivores, Kakoba Research Crane, New Guinea's tropical rainforest, vertical forest gradients, Plant-herbivore interactions, predation pressure, exclosure experiments, predator exclusion, oceanic islands, arthropod herbivory damage, insect-plant interactions, leaf chewers, leaf miners, savanna-forest mosaic, South Africa ungulates, temperate forests, seasonality, scientific research cranes, forest types, plant species diversity

Language used: English

Date on which the thesis was submitted / produced: 8. 1. 2025

Thesis defence

• Supervisor: Mgr. Kateřina Sam, Ph.D.

UNIVERSITY OF SOUTH BOHEMIA IN ČESKÉ BUDĚJOVICE

Faculty of Science

Doctoral programme / field:
Ecosystem Biology and Ecology / Ecosystem Biology and Ecology