Testing biological hypotheses in site occupancy models: a Bayesian approach

The occupancy rate of a target species in a region divided in quadrats (or sites) is defined as the proportion of quadrats occupied by this species. This is a key quantity in site occupancy models which typically remains unknown after the data are collected, because the probability of detecting a target species in a given quadrat is < 1. Implementing tests on occupancy rates leads to a quite unusual situation, because an occupancy rate is not a statistical parameter, but a function of a discrete process partially observed. To deal with that difficulty, we adopt a Bayesian view within which the treatment of such tests turns out to be natural. We develop our approach for discrete-time site occupancy data, and we illustrate it by testing if the occupancy rate of a bird species increases over time (colonization test). A Bayesian model averaging is implemented to deal with the fact that several plausible models are viewed for the data at hand. We state a closed-form expression for the posterior probability of each model. The posterior probability of the null hypothesis (under a given model) is obtained by implementing a data augmentation algorithm. Finally, from a variety of examples, we show that the Bayesian methodology allows us to address a wide range of questions about occupancy

The peasants in turmoil: Khmer Rouge, state formation and the control of land in northwest Cambodia

Over the past 15 years, northwest Cambodia has seen dramatic agrarian expansion away from the central rice plain into the peripheral uplands fuelled by peasant in-migration. Against this background, we examine the nature of relations between the peasantry and the state. We first show the historical continuities of land control processes and how the use of violence in a post-conflict neoliberal context has legitimised ex-Khmer Rouge in controlling land distribution. Three case studies show the heterogeneity of local level sovereignties, which engage the peasants in different relations with authority. We examine how these processes result in the construction of different rural territories along the agricultural frontier and argue that, in this region of Cambodia, the struggles between Khmer Rouge and neoliberal modes of land control are central to state formation processes

The Ultramassive White Dwarf EUVE J1746-706

We have obtained new optical and extreme ultraviolet (EUV) spectroscopy of the ultramassive white dwarf EUVE J1746-706. We revise Vennes et al.'s (1996a, ApJ, 467, 784) original estimates of the atmospheric parameters and we measure an effective temperature of 46,500 +/- 700 K and a surface gravity log g = 9.05 +/- 0.15 (~1.2 M_o), in agreement with Balmer line profiles and the EUV continuum. We derive an upper limit on the atmospheric abundance of helium of He/H = 1.3 x 10^{-4} and a neutral hydrogen column density in the local interstellar medium N_HI = 1.8 +/- 0.4 x 10^{19} cm^{-2} from the EUV spectrum. Our upper limit corresponds to half the helium abundance observed in the atmosphere of the ultramassive white dwarf GD 50. We discuss the possibility that EUVE J1746-706 represents an earlier phase of evolution relative to GD 50 and may, therefore, help us understand the origin and evolution of massive white dwarfs.Comment: 6 pages, 4 postscript figures, uses aastex, to be published in ApJ Letter