Belowground Herbivores and Ecosystem Processes

Summary

There is increasing awareness of the importance of belowground herbivores in the structure and function of ecological communities. However, experimenting with root feeders, especially to elucidate ecosystem effects, is difficult and involves techniques that may have indirect effects on the parameters of interest. Belowground insect herbivory affects many aspects of ecosystem function, particularly productivity, allocation patterns, nutrient cycling and interactions between component species. However, there is a likely general continuum of response to belowground herbivory. Low levels of root feeding possibly result in a root system that is more efficient and so may benefit the host plant; high levels of root feeding have dramatic negative impacts on plant growth, often causing plant death. At moderate levels of root herbivory, whether there is a negative, positive or no effect on plant growth is likely to be determined by other factors such as soil nutrient and water content and competition.

Root feeding changes the nutrient content of host plants, leading to increased aboveground insect herbivore growth and fecundity, resulting in changed population sizes and shifts in community structure. Recent evidence suggests that these plant-mediated interactions can also affect higher trophic levels: tephritid seed predators and their parasitoids were recorded in greater abundance on thistles subjected to root herbivory. Changes in the quality, quantity and composition of the foliage, induced by root feeding, can lead to increased litter quality, quantity and composition. This is known to impact on the size and structure of comminutor assemblages. Consequently, underground herbivory may affect decomposition, mineralization and subsequent nutrient availability.

As quoted by MoronRios et al. (1997),“Below-ground herbivores have been poorly studied regardless of their importance for the establishment and composition of plant communities”.