Gonzalez thinks a lot about this sort of thing. An ecologist who studies the causes of biodiversity loss and how to prevent them, he has spent much of his career researching landscape connectivity—the degree to which animals are able to move within and between patches of habitat. Every species has a daily and seasonal pattern of movement, and distinct methods of crisscrossing a landscape to find food, water, shelter, and mates. But the myriad ways humans have sliced up, paved over, and otherwise radically reorganized Earth’s terrain impact species’ ability to get where they need to go to survive. Now, climate change is raising the stakes while throwing up new obstacles: Some species will need to migrate increasingly long distances to find suitable homes. One recent study found that in the U.S., only 41 percent of existing “natural” areas are sufficiently connected to enable species to follow the environmental conditions they need.

Back in the 1600s, what is now the urban metropolis of Montreal was a vast forest teeming with wildlife—including deer, moose, and beaver—whose presence was partly what enabled humans to thrive there. Today, though, few non-human species can cross—much less inhabit—this concrete island. Even far outside the city itself, forests and wetlands are giving way to suburban sprawl. The same is true in fast-growing cities around the world.

Gonzalez, who is tall and reedy and speaks with an accent from his native England, has spent the better part of a decade studying how his Canadian home appears from the viewpoint of other animals. Since 2011, he and members of his McGill lab have been assembling maps of “how each creature perceives the landscape”—which patches of land a bear, a nuthatch, a marten, or a frog can and cannot use.

Gonzalez, like most ecologists, believes keeping landscapes connected, and reconnecting isolated fragments, is crucial to safeguarding the planet’s biodiversity. Over the past few decades, a “connectivity” movement has been building momentum, slowly and quietly. The most audacious and high-profile North American project is the 25-year-old Yellowstone to Yukon Conservation Initiative, or Y2Y, an effort to protect the ecological health of a vast, rugged slice of the U.S. and Canada. In Europe, Natura 2000 is a network of protected areas stretching across roughly 18 percent of the EU.

The movement is beginning to gain the attention of lawmakers, too. A group of six Northeastern U.S. governors and five eastern Canadian premiers recently signed a resolution recognizing the importance of landscape connectivity. This fall, a working group will meet to discuss how to prevent further forest fragmentation on a regional scale.

But while many efforts to link natural areas and create “corridors” for animal movement focus on large swaths of land, and the large mammals, such as bears and wolves, that use them, Gonzalez is concerned about areas more densely populated by humans—cities, suburbs, exurban expanses of advancing asphalt. He argues that protecting and restoring linked areas of green space, around and even within cities such as Montreal, is key to saving species from extinction, to enhancing the quality of urban life for humans, and to improving our understanding of how the natural world is shifting around us.