Obligate
Required or necessary; describing organisms that must live in a particular way and cannot survive otherwise. The opposite of facultative.
Used in the Books
This term appears in 4 chapters:
"The plant has evolved floral structures precisely matched to the moth's anatomy. The relationship is obligate: neither species can reproduce without the other. This tight co-evolution produced intricate reciprocal adaptations, but it also creates **fragility..."
"...illion birds in that single flock alone - possibly the most abundant bird species in North America, perhaps the world. Passenger pigeons were social obligates: they required massive flocks for successful breeding. The noise, movement, and density of millions of birds triggered hormonal changes essential for..."
"...tion**: Many mutualisms evolve increasing interdependence where partners become unable to survive independently, eliminating defection possibilities. Obligate mutualisms - where neither partner can complete its life cycle without the other - represent extreme interdependence. Examples include fig-fig wasp ..."
"...t visit those specific plants. Fig wasps (Agaonidae) are the extreme case. Each fig species (Ficus) is pollinated by a single wasp species in an obligate mutualism - the wasp can only reproduce in that fig, and the fig can only be pollinated by that wasp."
Biological Context
An obligate parasite can only survive by parasitizing a host. Obligate anaerobes die in the presence of oxygen. Obligate mutualists cannot survive without their partner. The term indicates an absolute requirement, not a preference.