# 3.2: Populations

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## Section Hook

Roadkill, we’ve all seen it on the roadside. It is just one very unfortunate outcomes of our extensive road networks. Roads, especially freeways and busy highways, also break apart habitats. When habitats are broken up into smaller pieces it weakens wildlife populations which need to move freely across landscapes for resources, refuge, and mates. Over long time scales, these fragmented habitats decrease species diversity, weaken species population gene pools, and can lead to extirpation (elimination of local population(s)) and extinction. As a result of numerous studies, ecologists have found one solution, wildlife crossings (aka green corridors or wildlife corridors). Wildlife crossings look like an underpass or overpass. However, they are filled with dirt and plants to look more natural. These crossings enable wildlife populations to move more freely, and safely, across landscapes all over the globe.

Figure $$\PageIndex{a}$$: A newly constructed wildlife overpass over a Singapore highway. Image by Benjamin P. Y-H. Lee (licensed under CC-BY-4.0)

Populations are interacting and interbreeding groups of individuals from the same species in a common area. The study of population ecology focuses on population size and the factors that regulate population growth.