Table 2 Some of the fundamental ways that organisms can be grouped into collections

Embedded in the same system(s)

• Proximity in time and space to nuclear blast

• Bird arrival times to summer breeding grounds

Engaging in the same processes

• Non-feeding nutrient exchange

• Coordinated behaviors in a social setting (e.g., calling behaviors in response to predators)

• Interactions (host-symbiont; competition)

Sharing common descent

• Genetic similarity

• Member of a genetically connected population

• Phylogenetic relationships

Sharing similar morphology, physiology, behavior (whether by descent or convergence)

• Flight

• Fossorial locomotor pattern

• Countercurrent respiration

• Quorum sensing in bacteria

Socially constructed characteristics

• Membership in an organization

• Legal status

• Education level