Limits to Biodiversity (Species Packing) LB Slobodkin, State University of New York-Stony Brook, Stony Brook, NY, USA r 2001 Elsevier Inc All rights reserved This article is reproduced from the previous edition, volume 3, pp 729–738, r 2001, Elsevier Inc Glossary Chemostat Apparatus for growing microorganisms in a continually replenished medium Community A multispecific aggregation of organisms in a particular location that may interact with each other Competition More than one species utilizing one or more common resources Ecological niche The set of requirements that must be met if a particular species is to survive It is sometimes used to mean the place in which those requirements are met Ecosystem A region with more or less clear boundaries, which contains a particular set of species and may be characterized by some set of meteorological, climatological, and geochemical properties Invasive or alien species Species that have recently colonized some geographic regions different from the one in which they were initially described Isocline A line along which some property remains constant Introduction: The Biological Packing Metaphor Different locations vary conspicuously in the number of species that are present Some, like coral reefs and tropical rain forests, are famous for their high species diversity, while others, like some Alaskan forests, are notably monotonous in the number of kinds of trees that are present Differences in diversity have attracted many researchers, although as yet there is no one all-encompassing theory of species diversity In fact, the overall term ‘‘species diversity’’ seems more useful at the level of scientific policy and public relations than it is at the level of scientific discourse There are many theories and models of species diversity, which differ in their foci and assumptions The theory of species packing is concerned with one aspect of diversity, specifically the coexistence of populations of different species located in a particular space It carries elements of the concept of ‘‘species richness’’ in that the greater the species richness of a region, the more species have presumably been ‘‘packed’’ into it It also carries implications for ‘‘realized species niches’’ because it might be inferred that the more species are packed into a region, the narrower the realized niches Like so many of the terms of theoretical ecology, ‘‘species packing’’ often is used in a metaphorical sense, which can be misleading It is best to begin by analyzing the concept in a literal and elementary way The word ‘‘packing’’ has at least two meanings, which can cause confusion It may mean placing objects inside a wrapper or container without altering them, or it may mean squeezing 642 Multidimensional niche A tempero-spatial region defined by meeting a set of different requirements for viability of a particular kind of organism Niche dimensions Ranges of values of environmental measurements in an ecological niche A range of temperatures, salinities, or oxygen concentrations may be niche dimensions for a population of fish Packing The placement of objects in a container Reification The assignment of empirical reality to the referenda of a word or theory, regardless of the existence of any such referenda Species diversity The number of different species in some area of interest Global species diversity refers to all species Local species diversity refers to some geographic region such as Hawaii or New York City Species packing The study of how species on the same trophic level coexist in a limited region or container them in to a fixed-size container Contrast the packing of glass tumblers with that of pillows Tumblers are packed into a container but if they press hard against each other they shatter Pillows can be squeezed into a container and fluffed up again when they are taken out The possibility of either type of species packing presupposes some sort of container into which things are packed Is the inferred container equivalent to an environment? Does an environment have fixed geometric dimensions like a wooden box? A pond, a log, a rotting fruitFall can, in fact, be thought of as containers However, environments can be defined in ways that may have more meaning to investigators than to inhabitants Are the boundaries of a study area like La Selva, a political unit like Costa Rica, or a geographic area like Central America in some sense meaningful packing containers? We will introduce the mathematical theory of species packing, examine how the theory has been exemplified in laboratory and field experiments, and, finally, consider the implications of species packing for field observations Two Species In One Container Theory The problem of species packing was crystallized in the apparently simple question: ‘‘Why are there so many kinds of animals?’’ Thereafter there has been a continual stream of Encyclopedia of Biodiversity, Volume http://dx.doi.org/10.1016/B978-0-12-384719-5.00088-5