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Snäll, T., Ribeiro Jr., P. J. and Rydin, H. 2003. Spatial occurrence and colonisations in patch-tracking metapopulations: local conditions versus dispersal. -Oikos 103: 566-578.We studied the relative importance of local variables and dispersal for the occurrence and colonisation of the epiphytic bryophytes Orthotricum speciosum (spore dispersed), and O. obtusifolium (spore and asexual gemmae) on aspen trees ('patches') in two forest landscapes (one old-growth and one fragmented) using multiple logistic regression. The relative importance of dispersal was quantified as the reduction of residual deviance for a connectivity variable. In modelling dispersal, we assumed that trees with low local abundance were recent colonisations, and that trees with high local abundance were diaspore sources for colonisation. The occurrence of O. speciosum in the fragmented landscape was most affected by shading, but also by connectivity, aspen diameter and vitality. In the old-growth landscape, connectivity was the single most important variable for recent colonisations, but its effect was lower than the sum of the effects of all local environmental variables. The occurrence of O. obtusifolium in the fragmented landscape was related to similar variables but the relative importance of these variables was different, and connectivity did not affect the probability of a recent colonisation in this species. We describe the epiphyte-tree system in the patch-tracking metapopulation model. In this model colonisations are distance dependent, but in contrast to the classical metapopulation model local extinctions are caused by deterministic patch destruction -once the epiphyte has colonised the tree it remains until the tree dies.Theoretical (Tilman and Kareiva 1997, Bascompte and Solé 1998, Keymer et al. 2000 and empirical work on animals (Hanski 1994a) and plants (Husband and Barrett 1996, Freckleton andWatkinson 2002) have shown that the spatial structure of the landscape and metapopulation processes are important in explaining the regional dynamics of species.Conceptual models have been formulated to generalise species dynamics in landscapes. In the models, the landscape is simplified to patches surrounded by inhabitable matrix. Whereas the metapopulation model sensu Harrison and Taylor (1997; 'classical metapopulation') assumes species colonisations of patches and extinctions from patches, the source-sink model (Pulliam 1988) further introduces local population demography, and its main message is that source patches are required for long-term species persistence. The remnant species model (Eriksson 1996) emphasises that some plant species disperse over time rather than space through periods of poor patch quality. The only model assuming a spatial dynamics of the patches is the habitat-tracking metapopulation model (Thomas 1994). Thomas (1994) argued that metapopulation dynamics must be superimposed on a dynamic environmental mosaic in order to understand the dynamics of a large number of organisms. This was implemented in Overton's (...

A new approach to dengue vector surveillance based on permanent egg-collection using a modified ovitrap and

We introduce two characteristics for stationary and isotropic marked point proces- ses, "E"("h") and "V"("h"), and describe their use in investigating mark-point interactions. These quantities are functions of the interpoint distance "h" and denote the conditional expectation and the conditional variance of a mark respectively, given that there is a further point of the process a distance "h" away. We present tests based on "E" and "V" for the hypothesis that the values of the marks can be modelled by a random field which is independent of the unmarked point process. We apply the methods to two data sets in forestry. Copyright 2004 Royal Statistical Society.

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