Organisms on the move in the Americas

Patchen Barss
Image of Bird from Amazon

How did the bird species of the Amazon become so diverse?

What accounts for the astounding biodiversity of the Amazon? How can an escaped fish threaten entire ecosystems?  Why did a long-idle vine suddenly become the scourge of the east? Here, three UTSC researchers tackle the questions of how organisms move—or not—and what we can do about them.

The diverse Amazon

The Amazon region of South America is home to 10 per cent of the world’s known biodiversity. Either speciation (the process by which new species arise) happens quickly there, or species survive longer, allowing for an unparalleled build-up of diversity. It turns out speciation rates are actually very slow in the Amazon, but extinction rates are even slower. One of the drivers of speciation in the region has long been speculated to be the Amazon River itself. In many places, the river is too wide for small birds to fly across. Divided by water, the theory goes, bird populations on each side split off into separate species. The trouble is, the forests that the birds call home extend all the way to the Amazon’s headwaters, where gene exchange can happen freely.

Biologist Jason Weir now suspects that bird speciation took place during a period of forest shrinkage – when the forest was smaller, the river truly split it in two. When the forest regrew, it became an open question whether a divided (bird) house had led to permanent speciation. This is a question Weir continues to research.

Carp invasion

In 1966, an important Asian carp escaped into the wild from a government research facility in Arkansas. So began an invasion of North American waterways that continues to this day. They devour and destroy local vegetation, and push indigenous fish species to extinction.

Regulations, electrical fences, barriers and poisons have all failed to keep the carp from spreading across the United States. While this fish got its North American start in warmer waters, Nicholas Mandrak says the four species of Asian carp that are currently chewing up the underwater scenery, could very easily adjust to Canada’s climate.

He not only tracks the movement of carp through rivers, canals and lakes, but he also advises the federal government on strategies to beat back the invasion—using tools that come with exotic names such as pressure devices, sonic boomers, bubble barriers, CO2 barriers.

The sudden spread of dog-strangling vine

Putting down roots should mean you’re no longer on the move, but two vicious species of swallowwort plant, known colloquially and collectively as “dog-strangling vine” have been doing nothing but picking up speed since they first dug into Ontario soil in the 1800s.

For more than a century, the vine basically idled in the areas where farmers first introduced it. Then, in the second half of the 20th century, it began to spread, scattering its downy milkweed-like seeds far and wide on the wind. The vine now covers large swaths of eastern USA and Canada and it’s moving west.

Urban forest conservation researcher Marc Cadotte says there are still some local habitats that haven’t been invaded, but they won’t likely last long. The vine can grow taller than a human being, and can grow densely enough to choke out other plants. Among other things, Cadotte is investigating a Ukrainian “biocontrol” moth that could slow or stop the spread of this vine. In its caterpillar stage, the Hypena moth appears to survive exclusively on dog-strangling vines—this moth has shown great promise in being able fend off the invasion without affecting native species.