Plant species richness and community composition
affect insect diversity. Despite the unimodal model often
used to describe relationships between diversity and
productivity (Grime 1973; Rosenzweig 1992; Abrams
1995), an increase in plant diversity could monotonically
improve ecosystem productivity (Tilman et al. 1996;
Hooper et al. 2005). Ecosystem productivity could
potentially enhance diversity at higher trophic levels and
likewise increase the diversity of herbivorous insscts,
parasites and predators (Hunter and Price 1992; Siemann
1998; Siemann et al. 1998). An increase in plant diversity
would have a stronger positive effect on species richness
at higher tropical levels. However, a recent review found
that lower trophic species responded more strongly to
an increase in plant diversity than higher trophic levels
in grassland (Scherber et al.2010). Increases in plant
diversity would decrease the effects of biological invasion,
pathogen and hyperparasitism (Scherber et al.2010). This
pattern also means that increasing plant diversity could
potentially enhance ecosystem stability (Tilman et al.
2006).