In insect communities, insect species richness increased as plant species richness and plant functional group richness increased, and both factors may explain how the loss of plant diversity influences higher trophic levels.
Abstract:
We experimentally separated the effects of two components of plant diversity—plant species richness and plant functional group richness—on insect communities. Plant species richness and plant functional group richness had contrasting effects on insect abundances, a result we attributed to three factors. First, lower insect abundances at higher plant functional group richness were explained by a sampling effect, which was caused by the increasing likelihood that one low‐quality group, C4 grasses, would be present and reduce average insect abundances by 25%. Second, plant biomass, which was positively related to plant functional group richness, had a strong, positive effect on insect abundances. Third, a positive effect of plant species richness on insect abundances may have been caused by greater availability of alternate plant resources or greater vegetational structure. In addition, a greater diversity of insect species, whose individual abundances were often unaffected by changes in plant spec...
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Q1. Why did the authors use it as an independent variable in analyses?
Because actual plant species richness explained more variation in every analysis of insect species richness and abundance (see also Knops et al. 1999), the authors used it as their independent variable in analyses.
Q2. What was the significance of C4 grasses in predicting insect abundances?
The importance of C4 grasses in affecting insect abundances was shown in analyses where its presence or absence replaced functional group richness as the significant variable predicting insect abundances.
Q3. What is the important factor causing lower insect abundances at higher plant diversity?
In such systems, changes in plant functional group composition may have been the most important factor causing lower insect abundances at higher plant diversity.
Q4. Why did the authors analyze differences in insect abundance in plots without C4 grasses?
Because of the strong, negative influence of C4 grasses.001 on insect abundance, the authors analyzed differences in insect abundances in plots with and without C4 grasses.
Q5. How does higher plant diversity affect insect abundances?
Higher plant diversity may then have increased insect abundances indirectly by increasing plant biomass and thus the quantity of resources for insects.
Q6. What is the effect of predators and parasitoids on insect diversity?
There was some evidence that higher predator and parasitoid diversity may have increased herbivore diversity, as would be predicted if predators and parasitoids limit the abundance of otherwise dominant herbivores (Paine 1966; Tilman and Pacala 1993; Siemann et al. 1998).
Q7. What is the relationship between insect abundance and plant species richness?
After controlling for the effects of insect abundance, herbivores and predators were the only trophic groups whose species richness showed a significant, positive relationship to plant species richness.
Q8. What was the effect of the experimental plots on insect abundance?
the experimental plots were relatively unproductive, and the availability of food resources limited insect abundances and thus species richness.