Keystone (architecture) in the context of "Book of Mormon"

A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. The concept was introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. Some keystone species, such as the wolf and lion, are also apex predators.

The role that a keystone species plays in its ecosystem is analogous to the role of a keystone in an arch. While the keystone is under the least pressure of any of the stones in an arch, the arch still collapses without it. Similarly, an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.It became a popular concept in conservation biology, alongside flagship and umbrella species. Although the concept is valued as a descriptor for particularly strong inter-species interactions, and has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems.

In architecture, a vault (French voûte, from Italian volta) is a self-supporting arched form, usually of stone or brick, serving to cover a space with a ceiling or roof. As in building an arch, a temporary support is needed while rings of voussoirs are constructed and the rings placed in position. Until the topmost voussoir, the keystone, is positioned, the vault is not self-supporting. Where timber is easily obtained, this temporary support is provided by centering consisting of a framed truss with a semicircular or segmental head, which supports the voussoirs until the ring of the whole arch is completed.

The Mycenaeans (ca. 1800–1050 BC) were known for their tholos tombs, also called beehive tombs, which were underground structures with conical vaults. This type of vault is one of the earliest evidences of curved brick architecture without the use of stone arches, and its construction represented an innovative technique for covering circular spaces.

An ogee (/oʊˈdʒiː/ /ˈoʊdʒiː/) is an object, element, or curve—often seen in architecture and building trades—that has a serpentine- or extended S-shape (sigmoid). Ogees consist of a "double curve", the combination of two semicircular curves or arcs that, as a result of a point of inflection from concave to convex or vice versa, have ends of the overall curve that point in opposite directions (and have tangents that are approximately parallel).

First seen in textiles in the 12th century, the use of ogee elements—in particular, in the design of arches—has been said to characterise various Gothic and Gothic Revival architectural styles. The shape has many such uses in architecture from those periods to the present day, including in the ogee arch in these architectural styles, where two ogees oriented as mirror images compose the sides of the arch, and in decorative molding designs, where single ogees are common profiles (see opening image). The term is also used in marine construction, particularly in shipbuilding, where ogee curves are used in hull design to improve hydrodynamics.The word was sometimes abbreviated as o-g as early as the 18th century, and in millwork trades associated with building construction, ogee is still sometimes written similarly (e.g., as O.G.).

Centring, centre, centering, or center is a type of falsework: the temporary structure upon which the stones of an arch or vault are laid during construction. Until the keystone is inserted an arch has no strength and needs the centring to keep the voussoirs in their correct relative positions. A simple centring without a truss is called a common centring. A cross piece connecting centring frames is called a lag or bolst.

Centring is normally made of wood timbers, a relatively straightforward structure in a simple arch or vault; but with more complex shapes involving double curvature, such as a dome or the bottle-shaped flue in a Norman-period kitchen, clay or sand bound by a weak lime mortar would be used. Shaping could be done by eye, perhaps with the help of a template, then stones or bricks laid against it. On larger works like a 19th-century pottery kiln this was impractical. The structure would be built round a post acting as a datum, and each course of stonework would be set at a distance from the datum.

A corbel arch (or corbeled / corbelled arch) is an arch-like construction method that uses the architectural technique of corbeling to span a space or void in a structure, such as an entranceway in a wall or as the span of a bridge. A corbel vault uses this technique to support the superstructure of a building's roof.

A corbel arch is constructed by offsetting successive horizontal courses of stone (or brick) beginning at the springline of the walls (the point at which the walls break off from verticality to form an arc toward the apex at the archway's center) so that they project towards the archway's center from each supporting side, until the courses meet at the apex of the archway (often the last gap is bridged with a flat stone). For a corbeled vault covering, the technique is extended in three dimensions along the lengths of two opposing walls.