Even though, there are varies of animals in the temperate grassland, there are examples of the competitive exclusion principle. According to http://wiki.answers.com/Q/How_is_the_species_diversity_related_to_the_stability_of_an_ecosystem, species diversity can affect this biome When you have more than one species in a given niche, then if one species declines for whatever reason, there are other species which can replace it, and the ecosystem as a whole remains functional. It has been demonstrated that genetic erosion is a major problem in grassland in the UK. Contrary to many suggestions in the literature on genetic erosion, continuing progress by breeders in further improving cultivars is not highlighted as an obvious factor, and genetic distances between cultivars may even be improving, although the evidence to date is only circumstantial. The most severe past problems are probably the simplification of the agricultural grassland system and the failure of many past collecting expeditions to sample populations in a manner appropriate to their biology and ecotypic variation. The most severe ongoing problems are probably the continuing contamination of native populations with genes from improved varieties and the continuing loss of "landraces" or traditional permanent grassland. The combination of past and present problems suggests that current ex situ collections probably hold only a small proportion of the diversity that used to exist in situ, and that the rate of genetic erosion in situ is similar to that that stimulated mass collecting of other crops in the 1970s and 1980s.For all species characteristic of grassland that can be readily improved, the number of native populations has decreased through being replaced with sown cultivars. Native species whose distribution spans a range of different grassland types have suffered a reduction in the genetic distance between populations through the loss of ecotypes associated with disappearing grassland communities. The same probably also applies to ecotypic variation associated with different soil types and management types that are disappearing through soil amelioration and intensive management, although definitive evidence is not available on this. Native Lolium perenne, and possibly also other native species that are also in the genepools of widely used improved cultivars, have suffered major genetic erosion through introgression with cultivars disrupting the genetic structure of the native populations
http://apps3.fao.org/wiews/Prague/Paper7.jsp