The whole is greater than the sum of its parts
Breaking Apart the Rainforest
Habitat fragmentation is the process by which one large habitat is broken up into many smaller ones. As a rule it is better not to do this because animals often need to move to find food and mates, and dividing up habitats means animals may either have to move across potentially dangerous areas to find what they need, or not be able to find it at all.
Life on the Edge
Once the forest canopy is broken up like this, it is also vulnerable to "edge effects" such as fluctuations in sunlight levels, temperature and other factors that would normally only affect the very outer edge of the forest. This lack of stability severely impacts species that are highly evolved to exist in the interiors of rainforests, and makes it easier for other species that don't normally occur, like rats, to invade.
Study after study shows that once forests are fragmented they are deforested more quickly, both by increased numbers of people who can now move among the gaps, but also by wildfires which are made more prevalent by edge effects.