Many seeds are buoyant and can be dispersed by water. Seeds may also have specialized structures that allow them to cling to animals. Cheatgrass seeds, for example, possess barbs on the caryopses that attach to animal fur. Finally, seeds can remain viable after passing through the digestive tracts of animals. Once eaten, these seeds can be dispersed over potentially large areas by birds, cattle, horses, and other mammals.
Humans activities are another important vector for seed dispersal.
For example, cultivation has promoted the spread of exotics. A number of exotic plants were intentionally introduced into RMNP area for use as cultivars or as ornamentals before the area became a National Park. More recently, exotic plants have been introduced as part of erosion control programs, or accidentally by park visitors. For example, spotted knapweed was found in one of the RMNP campgrounds and was likely brought in by park visitors. Exotic plants continue to be unintentionally introduced and dispersed in RMNP by clinging to clothing and mud on hiking boots, and by attaching to motor vehicles.