Dolphins are a home range species and live in fission fusion societies. A home range is a non-defended area that an animal or group of animals of the same species moves through regularly. Ranges tend to overlap, although species may temporally avoid each other by calling and marking their location. Fission fusion refers to the fact that some groupings are very fluid and temporary, but others are more stable and last much longer. Food availability, predation pressures, and reproductive condition are variable factors which, along with sex, age, and kinship that determine the grouping of dolphins (Bearzi 1997).
Seasonal Variation: The fish that dolphins prey on are a variable superabundant resource, but the distribution and available quantity of food constantly changes as the fish themselves move. Dolphins do not defend territories because they must be free to follow their prey where ever it swims. Dolphins seasonally utilize different areas of their year round home ranges (Barros 1998). Throughout the year, shallower habitats have more abundant prey than deep waters. During the warm seasons tiger sharks were found in shallow habitats twice as often as in deeper waters. Deeper waters were frequented during the warm seasons, when shark predation was very high in shallow waters, and dolphins lived in shallower waters during the cold months when predation risks were lower (Heithaus 2002).
Individual Variation: Some dolphins stay in one area for several years, especially in coastline regions. These semi-perminant groups are called local communities. "Visiting" extra-community dolphins are often sighted, showing that although some dolphins exhibit sight fidelity, others are more roaming (Bearzi 1997). Two distinct patterns of association were observed between females; they were either in bands, groups of two or three, or solitary. Solitary individuals had larger home ranges and banded individuals were more restricted to shallower coastline areas. Males were observed in both pairs and solitary patterns. Solitary and pair males were not seen associating even when their home ranges overlapped. Male home ranges are larger than female ranges, likely due to increased access to females for breeding (Quintana-Rizzo 2001).
Activity Variation: Feeding groups were significantly smaller than traveling and socializing groups. Large feeding groups could be more advantageous only when pray is more abundant or schooling. By varying the size of their groups with activity, dolphins are able to get food with less competition and still have the protection and assistance with small calves that a larger group provides (Bearzi 1997). Resting groups were larger than foraging groups, giving the resting dolphins more eyes for protection and fewer mouths when they are trying to eat (Heithaus 2002).
Sex Variation: see social relationships
