Influence Of Spatial Structure Research Articles

Influence of spatial structure on pathogen colonization and extinction: a test using an experimental metapopulation

The Linum marginale–Melampsora lini plant–pathogen interaction has been studied extensively with regard to its epidemiology and population genetic structure (host resistance and pathogen virulence) in a natural metapopulation. In this study, this system was used in an experimental metapopulation approach to investigate explicitly how the distance (degree of isolation) between local population patches influences disease dynamics within a growing season, as well as the genetic structure of pathogen populations through stochastic colonization and extinction processes. The experimental design centred on four replicate sets of populations, within which patches were spaced at increasingly greater distances apart. Each patch consisted of an identical set of host and pathogen genotypes, with each pathogen genotype having the ability to attack only one of four host‐resistance types. Over the 2 years of the experiment, the results showed clear ‘boom‐and‐bust’ epidemic patterns, with the strongest determinant of disease dynamics within a growing season being the identity of particular host–pathogen genotypic combinations. However, there were also significant effects of spatial structure, in that more isolated patches tended to exhibit lower levels of disease during epidemic peaks than patches that were close together. Extinction of pathogen genotypes from individual populations was positively related to the severity of disease during preceding epidemic peaks, but negatively related to the level of disease present at the final census prior to overwintering. The probability of recolonization of pathotypes into populations during the second growing season was most strongly related to the distance to the nearest neighbouring source population in which a given pathotype was present. Overall, these results highlight the importance of spatial scale in influencing the numerical and genetical dynamics of pathogen populations.

Interactions between landscape structure and animal behavior: the roles of heterogeneously distributed resources and food deprivation on movement patterns

To examine how resource distributions affect the movement behaviors of fed and food-deprived Eleodes extricata Say darkling beetles (Coleoptera: Tenebrionidae), we experimentally manipulated the dispersion of food to create clumped, random, and uniform distributions in an otherwise homogeneous 25-m2 experimental field landscape. Quantitative measures of the tortuosity, net linear displacement, overall path length, and velocity of beetle movement pathways showed that food-deprived beetles generally moved more slowly and over shorter distances than did fed beetles. This effect was mediated by the spatial distribution of food, however; food distributed randomly over the landscape evoked more tortuous paths over larger overall distances. The foraging movements of food-deprived beetles were most different from those of fed individuals in treatments with randomly distributed food resources. These results show that the influence of spatial structure on individuals depends not only on the arrangement of pattern but also on the function that the structure plays. Thus, 'spatial structure' is defined not only by physical characteristics of the landscape but also by how that structure is used by animals.

Misspecification in Spatial Interaction Models: Further Results

Commonly used models for data on flows between sets of origins and destinations may often be misspecified because of a failure to account for the influence of spatial structure and other factors that affect flows. General expressions for the bias in parameter estimates that arises from such misspecification are derived for the most usual methods of estimation.

The influence of spatial structure and socio-economic factors on migration rates

Willis K. G. (1972) The influence of spatial structure and socio-economic factors on migration rates. A case study: Tyneside 1961–1966, Reg. Studies 6, 69–82. The 1961 and 1966 Census indicate wide variations in migration rates per 1000 population, though precise analysis is hampered by census tabulation by local authority areas. Numerous theoretical studies have emphasized the importance of the structure of space in which migration occurs, but these have lacked practical application in Britain. From examination of rates on Tyneside, it is shown that spatial structure has a negligible influence on composite migration rates, economic and social factors accounting for most of the variance. A method of analysing a matrix of inter-local authority migration is proposed by which the relative importance of space over localized areas is indicated. Non-linear models are suggested as more applicable in analysing the size and composition of migration streams.

Air travel, spatial structure, and gravity models

This paper is a continuation of some previous investigations 2 into the influence of spatial structure on spatial interaction. R takes as its point of departure two of the implicit assumptions of the gravity model: i) uniformity among cities of the effects that their populations have on intercity travel and 2) the lack of effect of spatial structure on such travel. Despite shortcomings the gravity model 3 has been a useful integrative approach in the search for regularity in spatial phenomena: linking in a common mold movements through s~ace of travelers, shoppers, and migrants, 4; commodities within countries, o; and international trade between countries. 6 In most investigations utilizing this model masses of all terminals of movements under study are implicitly taken to have effects of the same magnitudel a single coefficient, b, is taken to measure the effect of terminal masses on interspatial flows as in (MiMj) b