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Distance Decay (distance + decay)
Selected AbstractsDistance Decay of Tree Species Similarity in Protected Areas on Terra Firme Forests in Colombian AmazoniaBIOTROPICA, Issue 5 2009Álvaro Duque ABSTRACT In this study, we investigated the pattern of floristic similarity as a function of geographical distances and environmental variability in well-drained uplands (terra firme) in Colombian Amazonia. The study site comprised three National Natural Parks, Tinigua, Chiribiquete, and Amacayacu, located in different geological units that represent a soil fertility gradient linked to parental materials. Differences in species richness between sites were compared using rarefaction analysis. A clear floristic transition appeared in the east,west direction following a soil fertility gradient along the first PCoA axis. In multiple regression analyses based on distance matrices, both geographical distances and geology explained 64 percent of the total floristic variation. Geographical distances alone accounted for 12 percent of variation in floristic similarities among plots, while geology alone accounted for 1 percent, and the joint effect of both explained 51 percent of the floristic variation. The species richness trend supports the existence of a latitudinal corridor southward of the geographical Equator in the Amazon basin, where tree diversity reaches the maximum expected values. A coupled effect of stochastic dispersal limitation and habitat specialization would certainly appear to be an appropriate explanation for tree species turnover in terra firme forests in Colombian Amazonia, strongly emphasizing that competition and neutrality must be supplementary rather than mutually exclusive processes. This result pinpoints the effect of dispersal on floral mixing as an ongoing active process for structuring tree communities in NW Amazonia, and the size of the reserves as a relevant issue to protect rare species from extinction by chance. [source] The wealth of species: ecological communities, complex systems and the legacy of Frank PrestonECOLOGY LETTERS, Issue 3 2007Jeffrey C. Nekola Abstract General statistical patterns in community ecology have attracted considerable recent debate. Difficulties in discriminating among mathematical models and the ecological mechanisms underlying them are likely related to a phenomenon first described by Frank Preston. He noted that the frequency distribution of abundances among species was uncannily similar to the Boltzmann distribution of kinetic energies among gas molecules and the Pareto distribution of incomes among wage earners. We provide additional examples to show that four different ,distributions of wealth' (species abundance distributions, species,area and species,time relations, and distance decay of compositional similarity) are not unique to ecology, but have analogues in other physical, geological, economic and cultural systems. Because these appear to be general statistical patterns characteristic of many complex dynamical systems they are likely not generated by uniquely ecological mechanistic processes. [source] Not everything is everywhere: the distance decay of similarity in a marine host,parasite systemJOURNAL OF BIOGEOGRAPHY, Issue 2 2009Ana Pérez-del-Olmo Abstract Aim, We test the similarity,distance decay hypothesis on a marine host,parasite system, inferring the relationships from abundance data gathered at the lowest scale of parasite community organization (i.e. that of the individual host). Location, Twenty-two seasonal samples of the bogue Boops boops (Teleostei: Sparidae) were collected at seven localities along a coastal positional gradient from the northern North-East Atlantic to the northern Mediterranean coast of Spain. Methods, We used our own, taxonomically consistent, data on parasite communities. The variations in parasite composition and structure with geographical and regional distance were examined at two spatial scales, namely local parasite faunas and component communities, using both presence,absence (neighbour joining distance) and abundance (Mahalanobis distance) data. The influence of geographical and regional distance on faunal/community divergence was assessed through the permutation of distance matrices. Results, Our results revealed that: (1) geographical and regional distances do not affect the species composition in the system under study at the higher scales; (2) geographical distance between localities contributes significantly to the decay of similarity estimated from parasite abundance at the lowest scale (i.e. the individual host); (3) the structured spatial patterns are consistent in time but not across seasons; and (4) a restricted clade of species (the ,core' species of the bogue parasite fauna) contributes substantially to the observed patterns of both community homogenization and differentiation owing to the strong relationship between local abundance and regional distribution of species. Main conclusions, The main factors that tend to homogenize the composition of parasite communities of bogue at higher regional scales are related to the dispersal of parasite colonizers across host populations, which we denote as horizontal neighbourhood colonization. In contrast, the spatial structure detectable in quantitative comparisons only, is related to a vertical neighbourhood colonization associated with larval dispersal on a local level. The stronger decline with distance in the spatial synchrony of the assemblages of the ,core' species indicates a close-echoing environmental synchrony that declines with distance. Our results emphasize the importance of the parasite supracommunity (i.e. parasites that exploit all hosts in the ecosystem) to the decay of similarity with distance. [source] Finding a serial burglar's home using distance decay and conditional origin,destination patterns: a test of empirical Bayes journey-to-crime estimation in the HagueJOURNAL OF INVESTIGATIVE PSYCHOLOGY AND OFFENDER PROFILING, Issue 3 2009Richard Block Abstract Can we tell where an offender lives from where he or she commits crimes? Journey-to-crime estimation is a tool that uses crime locations to tell us where to search for a serial offender's home. In this paper, we test a new method: empirical Bayes journey-to-crime estimation. It differs from previous methods because it utilises an ,origin,destination' rule in addition to the ,distance decay' rule that prior methods have used. In the new method, the profiler not only asks ,what distances did previous offenders travel between their home and the crime scenes?' but also ,where did previous offenders live who offended at the locations included in the crime series I investigate right now?'. The new method could not only improve predictive accuracy, it could also reduce the traditional distinction between marauding and commuting offenders. Utilising the CrimeStat software, we apply the new method to 62 serial burglars in The Hague, The Netherlands, and show that the new method has higher predictive accuracy than methods that only exploit a distance decay rule. The new method not only improves the accuracy of predicting the homes of commuters,offenders who live outside their offending area,it also improves the search for marauders,offenders who live inside their offending area. After presenting an example of the application of the technique for prediction of a specific burglar, we discuss the limitations of the method and offer some suggestions for its future development. Copyright © 2009 John Wiley & Sons, Ltd. [source] ERSA Conference participation: does location matter?PAPERS IN REGIONAL SCIENCE, Issue 4 2006Jouke Van Dijk conference participation; distance decay; conference location Abstract., This article analyses participation in the annual European congresses of the Regional Science Association (ERSA) from 1998 through 2003. We formulate goals that the ERSA conferences should aim at and based on these aims we formulate hypotheses about conference participation. In the empirical part we test hypotheses with regard to the spatial distribution of the participants over countries, the distribution of the frequency of attendance among the participants, and the presence of distance decay in participation. All hypotheses are confirmed. We also pay attention to the relation between the frequency of attendance and distance. In the conclusions we derive implications for future conferences. [source] | |||||||||||||