Symbiosis is a close and long-term biological interaction between two different species. These relationships can be categorized based on whether the interaction is beneficial, harmful, or neutral to each species. Mutualism is a type of symbiosis where both species benefit. An example is the relationship between bees and flowers, where bees get food and flowers get help with pollination. Commensalism occurs when one species benefits while the other is neither helped nor harmed, such as barnacles attaching to a whale's skin. Parasitism is a relationship in which one species, the parasite, benefits at the expense of the other, the host, which is harmed. An example of this is a tick feeding on a dog. These interactions are fundamental to ecology, as they influence the survival, reproduction, and distribution of species within an ecosystem.