Habitat selection is the process or behavior that an animal uses to select or choose a habitat in which to live; correspondingly, plants and fungi engage in habitat selection, even though their inherent mobility is different from animals. To live in a habitat an animal must first have access to the habitat. Once the animal has access to the habitat it must be able to tolerate the conditions of the habitat and find the resources that it needs to survive in that habitat. Animals must be able to tolerate at least two kinds of factors in the habitat. These factors are abiotic factors and biotic factors. Abiotic factors are non-biological factors such as temperature, humidity, salinity and pH to name a few. Biotic factors are biological factors such as competition, predation, and disease. If both abiotic and biotic factors can be tolerated the animal must also be able to find the resources that it needs to survive. These resources include food, shelter from abiotic and biotic factors, and a mate. If an animal can not tolerate abiotic and biotic factors in a habitat or if it does not find food, shelter or a mate in that habitat, it is likely that the habitat will not be selected and the animal will leave the habitat. Habitats that are suitable for animals will often times have many animals of the same species there. This can lead to intraspecific competition. All of these things have an impact on the ecology of the animal (its distribution and abundance).
One way to determine if a habitat is suitable for an animal is to conduct a transplant experiment. In a transplant experiment animals of interest are transplanted or brought to a habitat to test that habitat for suitability. If the animal survives and reproduces in the habitat, it is concluded that the habitat was unoccupied because the animal was unable to get there or because it did not have access to the habitat. If the animal does not stay, survive, or reproduce in the habitat, it is concluded that it could be due to a lack of resources or because certain biotic and or abiotic factors are present and it can not tolerate them. A habitat that is suitable can become unsuitable if the animal's resources and or biotic and abitoic factors change. This is what often happens when we develop areas that are currently undeveloped. This causes us to see animals that we never saw in our environments before. It also can lead to a decline in the number of these animals.