Imagine you have a large circular area of native forest. All the populations living there are essentially homogenous, some species might form small groups but overall they can all interact directly, share the same resources, and mix genetic information.

Now humans come in, and instead of one continuous piece of land, you have segments of native forest surrounded by roads or semi-urban pathways. You can then imagine the populations as segmented bubbles.

This model of bubbles of native land surrounded by human landmarks is a tool ecology can use to predict how populations develop and interact. There are a lot of different permutations depending on size, biome, types of obstacles, and so on. But one of the most basic analysis you can do is detect bubbles that act as "sources" and bubbles that act as "drains" or "sinks". A source is a bubble with an excess of individuals, those are likely to cross the obstacles in their way and find themselves into other bubbles, supplying new individuals. Drains are bubbles where due to insufficient numbers, human activity or other factors, a species can't sustain a good number of individuals by themselves - they need immigrants from other bubbles.

This dynamic between sources providing new individuals and drains is fundamental for a metapopulation to exist even when the area is severely degraded by human activity. Imagine your well kept backyard providing bees to your neighbor with a sub-optimal one, for instance. This new metapopulation of bees is stable, even though the environment isn't ideal.