Because of their wide-ranging nature, long-term conservation strategies designed to protect carnivore populations by necessity must target large, diverse, and often ecologically important areas, all of which include many other species. Carnivores therefore can be effective surrogates or umbrella species for broader biodiversity conservation planning. Some species, including wolves, lions, and sea otters, are also keystone species, meaning their presence is a critical element to the structure and functioning of their ecosystems. This might manifest as predators influencing the behavior of potential prey by increasing the risk they might be attacked, thereby increasing the activity of these species. Through direct predation, they can also directly impact the abundance of prey, and the diversity and composition of animal and plant communities, through a process known as a trophic cascade. Other species, particularly mesocarnivores such as river otters, pine martens, and Canada lynx, can serve as effective indicator or sentinel species. This means their presence may be indicative of an ecosystem’s relative health, including a food web less impacted by people and pollutants, or the integrity of an ecosystem over a large geographical area.