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Patterns and drivers of insect herbivory in tropical forests
Forests, especially tropical forests, influence and provide numerous processes and ecosystem services important for maintaining ecosystems, biodiversity, and human well-being worldwide. They influence for instance the global hydrological cycle, serve as carbon sinks, and provide various products use...
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| Format: | Doctoral Thesis |
| Language: | English |
| Published: |
Philipps-Universität Marburg
2024
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| Subjects: | |
| Online Access: | PDF Full Text |
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| Summary: | Forests, especially tropical forests, influence and provide numerous processes and ecosystem services important for maintaining ecosystems, biodiversity, and human well-being worldwide. They influence for instance the global hydrological cycle, serve as carbon sinks, and provide various products used by humans (e.g., wood and food). Herbivory in forests is mainly caused by insects and influences several ecosystem functions such as nutrient cycles and carbon sequestration. Furthermore, it affects the composition and characteristics of the local plant community. Plants, in turn, respond to herbivory with evolved avoidance- or protection strategies that can influence the plant’s palatability and thus herbivory. Besides biotic factors, abiotic factors such as precipitation or nutrients shape herbivory. As a result, insect herbivory in forests varies in space and time resulting in complex and non-static patterns. Understanding the herbivory of insect communities and the factors influencing them is crucial for predicting and mitigating possible changes under the pressure of climate- and land-use change. To improve the understanding of herbivory patterns and their underlying mechanisms, I investigated both the herbivory of insect communities and insect herbivore dynamics and their relations to plant
traits as well as several abiotic variables in tropical montane forests of southern Ecuador.
In Chapter 1, I examine spatial differences in community herbivory between the canopy and the woody understory of two different forest types (mountain rainforest and mountain dry forest) and refer the results to a global comparison of canopy-understory herbivory patterns based on a literature survey. The results showed that vertical herbivory patterns are scale-dependent, as the worldwide comparison revealed no significant differences between the vertical forest strata, while the two south Ecuadorian forest types exhibited significant forest type-specific differences. This indicates that the variation in herbivory between forests might be larger than within forests.
Chapter 2 focuses on the general importance of various leaf traits for community herbivory patterns in a tropical mountain rainforest. In this study, no clear relationship was found between leaf traits and community herbivory, and the variability within traits was mainly at the species level. These results could indicate either a bias caused by the temporal mismatch of sampling
leaf traits and community herbivory and the actual event of herbivory or that other environmental factors are more important in structuring community herbivory than leaf traits.
Chapter 3 describes the effects of various leaf traits on the abundance and mean body mass of the most dominant herbivorous feeding guilds: leaf- and rostrum chewers. The results match the previous study since they show no consistent relations between certain traits and herbivores but feeding guild-specific dynamics for both abundance and mean body mass.
Overall, my thesis highlights the complexity of biotic and abiotic mechanisms underlying herbivore- and herbivory patterns of insect communities in tropical forests. I was able to provide an impetus to reconsider the importance of leaf traits for insect herbivory on a community level and point out that not only an appropriate selection of leaf traits is required, but also the large intra- and interspecific variation of traits must be considered when analyzing community
herbivory. Thus, although much research is still needed to fill the gaps, I can conclude that the importance of certain environmental factors for community herbivory depends on both the composition and characteristics of the target community and on space and time. |
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| DOI: | 10.17192/z2024.0239 |