Connecting the dots: an invariant migration corridor links the Holocene to the present

Abstract

Numerous species undergo impressive movements, but due to massive changes in land use, long distance migration in terrestrial vertebrates has become a highly fragile ecological phenomenon. Uncertainty about the locations of past migrations and the importance of current corridors hampers conservation planning. Using archeological data from historic kill sites and modern methods to track migration, we document an invariant, 150 km (one-way) migration corridor used for at least 6000 years by North America's sole extant endemic ungulate. Pronghorn (Antilocapra americana) from the Greater Yellowstone Ecosystem, like other long distant migrants including Serengeti wildebeest (Connochaetes taurinus) and Arctic caribou (Rangifer tarandus), move nearly 50 km d-1, but in contrast to these other species, rely on an invariant corridor averaging only 2 km wide. Because an entire population accesses a national park (Grand Teton) by passage through bottlenecks as narrow as 121 m, any blockage to movement will result in extirpation. Based on animation of real data coupled with the loss of six historic routes, alternative pathways throughout the 60,000 km2 Yellowstone ecosystem are no longer available. Our findings have implications for developing strategies to protect long distance land migrations in Africa, Asia and North America and to prevent the disappearance of ecological phenomena that have operated for millennia.

Figure 1

Migration routes (yellow, existing; turquoise, extirpated) of pronghorn in and adjacent to the Greater Yellowstone Ecosystem in relation to yellowstone (YNP) and Grand Teton (GTNP) national parks. Yellow line thickness reflects relative susceptibility to loss. The inset (box) highlights study region of invariant migratory corridor in the upper Green River basin (see figure 2).

Figure 2

The migration corridor between GTNP and winter ranges in the upper Green River basin of Wyoming. Dots reflect ca 11 450 points of 10 colour coded adult female pronghorn. Insets (a–c) reflect geographical bottlenecks (yellow circles) and locations along migration route. Enhanced imagery in (c) depicts rivers (green) to east and west of Trapper's Point hunting site where 6000 year old pronghorn bones were recovered.