Knapweed and leafy spurge don't have many fans in these parts. Nobody makes the drive from Texas to pose with them and post the photos on Instagram. Invasive species aren't usually something to celebrate, because they can wreak havoc on native ecosystems in ways impossible to undo. But other invaders have gotten a much warmer welcome. One listener wonders why some non-native species – like brown trout and rainbows – are so valued in Montana.

Mountain goat populations have been on the decline in Montana for 70 years. Researchers are working to learn more about the nimble climbers, which means going where the goats go – and that's easier said than done. But no mountain is too high, no weather too extreme to stop us from answering this week's question: What happened to the mountain goat population in the Bitterroot Mountains?

In the wilds of Montana, you might find yourself in awe at the sight of a grizzly bear lumbering down a trail in Glacier Park, or entranced by the sounds of an elk bugling in the mist at dawn. But this week on The Big Why, a listener wants to know more about the not-so-wild critters eating our gardens, popping up in front of our cars and sleeping in our yards. What's life like for urban deer?

If you've spent much time in Missoula, you've probably gotten turned around in the "Slant Streets" at least once. If you've lived there long enough, you've probably heard sensational tales of strife and betrayal surrounding the origin of the Garden City’s most geographically confused neighborhood. We're here to set the record straight. It’s the saga of the Slant Streets, on The Big Why.