Diamond, Jared M. 1975.

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Diamond, Jared M. 1975. The Island dilemma. Lessons of modern biogeographical studies for the design of natural reserves. Biol. Conserv. (7):129-146


A system of natural reserves, each surrounded by altered habitat, resembles a system of islands from the point of view of species restricted to natural habitats. Recent advances in island biogeography may provide a detailed basis for understanding what to expect of such a system of reserves. The main conclusions are as follows:

  1. The number of species that a reserve can hold at equilibrium is a.function of its area and its isolation. Larger reserves, and reserves located close to other reserves, can hold more species.
  2. If most of the area of a habitat is destroyed, and a fraction of the area is saved as a reserve, the reserve will initially contain more species than it can hold at equilibrium. The excess will gradually go extinct. The smaller the reserve, the higher will be the extinction rates. Estimates of these extinction rates for bird and mammal species have recently become available in a few cases.
  3. Different species require different minimum areas to have a reasonable chance of survival.

Some geometric design principles are suggested in order to optimise the function of reserves in saving species.


Sistemas reservas naturales, c/u rodeado de hábitats alterados ≈ sistema de islas-hábitat en un mar de alteración. Análisis de biogeografía insular predice, con ejemplos de tasas para mamíferos y aves:

  1. ∑spp sostenibles en una reserva = ƒ(área, aislamiento). Reservas más grandes/más cercanas a otras similares tienen más spp
  2. si 100-X% de un hábitat es destruido y X % es protegido, reserva perderá spp hasta equilibrio. Entre más pequeña reserva > tasa de extinción.
  3. Spp ≠ requieren ≠ áreas mínimas para tener probabilidades razonables de supervivencia.

Comentario: Alumnos de E. O. Wilson, Simberloff y Abele, 1976 y quienes dieron apoyo experimental a la Tbi, plantean un punto de vista diferente. Ver más comentarios en dicha ficha.

Diseños geométricos y factores determinantes

Hay una ilustración mejor para este resumen (ver Biblios Magdalena 130806); también otras referencias aún no wikizadas. v. gr.,

  • J. J. Ramírez, 1989. Variación vertical del fitoplancton y parámetros fisico-químicos en cuatro embalses del oriente antioqueño y su relación con el área, edad, altitud, y tiempo de residencia medio del agua. Tesis de Maestría, Universidad de Antioquia, Medellín.
  • Simberloff, Daniel y Lawrence G. Abele. 1982. Refuge design an island biogeographic theory: effects of fragmentation. Am. Nat. 120(1):41-50.

Cole's theoretical conclusion that one large site generally contains more species than several small ones [(SLOSS question)] is falsified by data in the literature, as is his contention that exceptions will only occur when the species in the sites are but a small fraction of those in the species pool. For a variety of taxa, for a number of different habitat types, and for a wide range of sizes of the biota as a fraction of the pool, either there is no clear best strategy, or several small sites are better than one large site. Since there are numerous idiosyncratic biological considerations, plus a number of nonbiological ones that bear heavily on refuge design, it is unlikely that a general reductionist model can generate useful predictions or advice on this matter.

Suggested geometric principles, derived from island biogeographic studies, for the design of natural reserves. In each of the six cases labelled, species extinction rates will be lower for the reserve design on the upper cell than for the reserve design on the lower cell. (fig. 7., Diamond, 1975, ligeramente modificada)