Geoscience Reference
In-Depth Information
small.Whenviewedfromanecologicalperspective,oneshouldratherimaginehow
abundant,large,healthytheropodsprobablymaintainedriver-floodplainplantcom-
munities and facilitated the growth of low-lying vegetation and forests wherever
they lived. In other words, large theropods, such as
Allosaurus
,
Acrocanthosaurus
,
Gigantosaurus
, and
Tyrannosaurus
, might have been the original “green” dino-
saurs, saving plants wherever they stalked, and hence helping the evolution of their
ecological communities.
This seemingly incongruous leap of logic is loosely based on recent research
into the effects of apex predators on riverbanks (called
riparian zones
) and forest
ecosystems, exemplified by wolves in the vicinity of Yellowstone National Park
(Wyoming).Sincethe1990sinYellowstone,wildlifebiologistsandecologistshave
examined the ecological effects of wolf reintroductions, in which wolf packs were
put back in places where they had been locally extinct for a while. One of the most
surprising results of these reintroductions was how riparian ecosystems in Yellow-
stone improved, with greater and more vigorous plant growth that approached their
recent, pre-colonial state, when wolves naturally inhabited this area. Rapid stream
erosionandfloodingalsolessened,bothdirectresultsofmoreplantsgrowingalong
stream banks.
What did this have to do with wolves, or even carnivorous dinosaurs? First,
with regard to wolves, their favorite item on the menu—one that they will pick
nearly every time if given a choice—is elk (
Cervus canadensis
). With no major
threat from predators in Yellowstone ecosystems, elk ran wild (more so), overpop-
ulating and eating much of the vegetation, including young tender plants along ri-
parian zones. Reduced numbers and heights of plants along streams meant fewer
plant roots holding down the soils, which led to accelerated erosion and flooding
around Yellowstone streams, making it tougher for new plant growth to take hold.
But once wolves were back in the neighborhood, salads that were once taken leis-
urely plummeted, riparian plant communities bounced back, and streams no longer
lost so much sediment or flooded with quite so much ferocity.
