Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regime (cheatgrass, "Bromus tectorum"), nutrient cycling (smooth cordgrass "Spartina alterniflora"), and hydrology ("Tamarix") in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass, "Spartina alterniflora", threatens the existence of California cordgrass ("Spartina foliosa") in San Francisco Bay. Invasive species cause competition for native species and because of this 400 of the 958 endangered species under the Endangered Species Act are at risk.