Market partitioning and the geometry of the resource space

Operations such as integration or modularization of databases can be considered as operations on database universes. This paper describes some operations on database universes. Formally, a database universe is a special kind of table. It turns out that various operations on tables constitute interesting operations on database universes as well.

Organisational niche boundaries in the n-space

The paper investigates organizational boundary spanning from the point of view of neighborhood relations. Neighborhood is defined with the closeness of organizations' resource utilization patterns. The key resource is the clientele's demand for organizational outputs (products, party programs, membership, etc.). Demand is characterized qualitatively by n taste descriptors that span an n-dimensional resource space. Organizational niche boundaries may take different forms and size. To avoid niche overlap over boundaries, organizations can configure in the resource space in different clusterings. Which are the densest arrangements that allow for the coexistence of maximal number of organizations? How can these coexisting neighborhoods build up? How do competition, new entry and the number of immediate neighbors change around the niche boundary with space dimension? The paper applies results of the sphere packing problem in n-dimensional geometry to answer these questions.

Market partitioning and the geometry of the resource space

This article gives a new explanation for generalist and specialist organizations' coexistence in crowded markets. It addresses organizational ecology's resource-partitioning theory, which explains market histories with scale economies and crowding, and it shows that some main predictions of this theory can be restated in terms of structural properties of the N-dimensional Euclidean space. As resource-space dimensionality increases, the changing niche configurations open opportunities for specialists. The proposed approach draws upon the sphere-packing problem in geometry. The model also explains new observations, and its findings apply to a range of crowding and network models in sociology.</p

Time- and depth-wise trophic niche shifts in Antarctic benthos

Climate change is expected to affect resource-consumer interactions underlying stability in polar food webs. Polar benthic organisms have adapted to the marked seasonality characterising their habitats by concentrating foraging and reproductive activity in summer months, when inputs from sympagic and pelagic producers increase. While this enables the persistence of biodiverse food webs, the mechanisms underlying changes in resource use and nutrient transfer are poorly understood. Thus, our understanding of how temporal and spatial variations in the supply of resources may affect food web structure and functioning is limited. By means of C and N isotopic analyses of two key Antarctic benthic consumers (Adamussium colbecki, Bivalvia, and Sterechinus neumayeri, Echinoidea) and Bayesian mixing models, we describe changes in trophic niche and nutrient transfer across trophic levels associated with the long- and short-term diet and body size of specimens sampled in midsummer in both shallow and deep waters. Samplings occurred soon after the sea-ice broke up at Tethys Bay, an area characterised by extreme seasonality in sea-ice coverage and productivity in the Ross Sea. In the long term, the trophic niche was broader and variation between specimens was greater, with intermediate-size specimens generally consuming a higher number of resources than small and large specimens. The coupling of energy channels in the food web was consequently more direct than in the short term. Sediment and benthic algae were more frequently consumed in the long term, before the sea-ice broke up, while consumers specialised on sympagic algae and plankton in the short term. Regardless of the time scale, sympagic algae were more frequently consumed in shallow waters, while plankton was more frequently consumed in deep waters. Our results suggest a strong temporal relationship between resource availability and the trophic niche of benthic consumers in Antarctica. Potential climate-driven changes in the timing and quality of nutrient inputs may have profound implications for the structure of polar food webs and the persistence of their constituent species, which have adapted their trophic niches to a highly predictable schedule of resource inputs