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Szilagyi, A., Scheuring, I., Edwards, D. P., Orivel, J., & Yu, D. W. (2009). The evolution of intermediate castration virulence and ant coexistence in a spatially structured environment. Ecol. Lett., 12(12), 1306–1316.
Abstract: Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we construct a spatially explicit model of the symbiosis between the ant-plant Cordia nodosa and its two, protecting ant symbionts, Allomerus and Azteca. Allomerus is also a castration parasite, preventing fruiting to increase colony fecundity. Limiting the dispersal of Allomerus and host plant selects for intermediate castration virulence. Increasing the frequency of the mutualist, Azteca, selects for higher castration virulence in Allomerus, because seeds from Azteca-inhabited plants are a public good that Allomerus exploits. These results are consistent with field observations and, to our knowledge, provide the first empirical evidence supporting the hypothesis that spatial structure can reduce castration virulence and the first such evidence in a natural landscape for either mortality or castration virulence.
Keywords: Cooperation; evolution of virulence; host-pathogen; mutualism; myrmecophyte; parasite; rock-paper-scissors; spatial games; tolerance; trade-off
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Cohen, M. C. L., Behling, H., Lara, R. J., Smith, C. B., Matos, H. R. S., & Vedel, V. (2009). Impact of sea-level and climatic changes on the Amazon coastal wetlands during the late Holocene. Veg. Hist. Archaeobot., 18(6), 425–439.
Abstract: Wetland dynamics in northern Brazil during the Holocene were studied by pollen analysis and AMS radiocarbon dating of three cores. Near the Amazon mouth region, covered mainly by primary Amazon coastal forest and herbaceous vegetation, the pollen record indicates the dominance of mangroves between 4800 and 1100 cal yr B.P. A contraction of the mangrove area and an expansion of herbaceous and fern vegetation occurred between 1100 and 750 cal yr B.P. The period between 750 and 200 cal yr B.P. is characterized by an expansion of mangrove and a decrease in herbaceous and fern vegetation. This trend continued until the present. On Atalaia Island, the sediment core indicates a period with poor pollen preservation between 830 and 630 cal yr B.P. Between 630 and 330 cal yr B.P., mangroves expanded. Later, up to 45 cal yr B.P., the mangrove area decreased and the herbaceous vegetation expanded. During the last hundred years, the relative sea-level rise most probably favored the mangrove expansion as far as the topographically highest sector on this island, while the herbaceous vegetation decreased. The pollen data from Agua Preta Lake indicate dry conditions, as reflected by the poor pollen preservation between 390 and 240 cal yr B.P. Between 240 and 60 cal yr B.P., restinga and Amazon coastal forest with palms dominated this region. For the last 120 years, the record indicates an expansion of the mangrove area. However, recent confinement of mangrove development to the topographically highest area, and the loss of mangrove areas on the lowest surfaces have led to a net loss of mangrove coverage during the last decades.
Keywords: Mangrove; Marajo Island; Pollen analysis; Sea-level
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Campillo, F., & Rossi, V. (2009). Convolution Particle Filter for Parameter Estimation in General State-Space Models. IEEE Trans. Aerosp. Electron. Syst., 45(3), 1063–1072.
Abstract: The state-space modeling of partially observed dynamical systems generally requires estimates of unknown parameters. The dynamic state vector together with the static parameter vector can be considered as an augmented state vector. Classical filtering methods, such as the extended Kalman filter (EKF) and the bootstrap particle filter (PF), fail to estimate the augmented state vector. For these classical filters to handle the augmented state vector, a dynamic noise term should be artificially added to the parameter components or to the deterministic component of the dynamical system. However, this approach degrades the estimation performance of the filters. We propose a variant of the PF based on convolution kernel approximation techniques. This approach is tested on a simulated case study.
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Seymour, R. S., Gibernau, M., & Pirintsos, S. A. (2009). Thermogenesis of three species of Arum from Crete. Plant Cell Environ., 32(10), 1467–1476.
Abstract: Inflorescences of arum lilies have a three-part spadix with a scent-producing, sterile appendix above two bands of fertile male and female florets. The appendix and male florets are thermogenic, but with different temporal patterns. Heat-production was measured in Arum concinnatum, A. creticum and A. idaeum. The male florets of A. concinnatum showed a 3 d continuous episode of thermogenesis with three waves, and the appendix warmed in a single, 6 h episode. Maximum fresh-mass-specific CO2 production rate was 0.17 μmol s(-1) g(-1) to achieve a 10.9 degrees C temperature elevation by the appendix, and 0.92 μmol s(-1) g(-1) to achieve a 4.8 degrees C elevation by male florets. Reversible, physiological temperature regulation was not evident in either tissue. Respiration increased with tissue temperatures with Q(10) values of 1.8-3.9, rather than less than 1.0 as occurs in thermoregulatory flowers. Experimental step changes in temperature of appendix and male floret tissues also failed to show thermoregulatory responses. The patterns of thermogenesis therefore appear to be fixed by the temporal sequence of blooming. Thermogenesis in the alpine species, A. creticum and A. idaeum, was significantly lower than in the lowland A. concinnatum, possibly related to difficulty in raising floral temperature in their cold and windy habitat.
Keywords: Araceae; arum lily; inflorescence; pollination; temperature regulation
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Gloor, M., Phillips, O. L., Lloyd, J. J., Lewis, S. L., Malhi, Y., Baker, T. R., et al. (2009). Does the disturbance hypothesis explain the biomass increase in basin-wide Amazon forest plot data? Glob. Change Biol., 15(10), 2418–2430.
Abstract: Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential-power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.
Keywords: Amazon rainforest; carbon sink; disturbance; mortality; power law
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Campillo, F., Rakotozafy, R., & Rossi, V. (2009). Parallel and interacting Markov chain Monte Carlo algorithm. Math. Comput. Simul., 79(12), 3424–3433.
Abstract: In many situations it is important to be able to propose N independent realizations of a given distribution law. We propose a strategy for making N parallel Monte Carlo Markov chains (MCMC) interact in order to get an approximation of an independent N-sample of a given target law. In this method each individual chain proposes candidates for all other chains. We prove that the set of interacting chains is itself a MCMC method for the product of N target measures. Compared to independent parallel chains this method is more time consuming. but we show through examples that it possesses many advantages. This approach is applied to a biomass evolution model. (C) 2009 IMACS. Published by Elsevier B.V. All rights reserved.
Keywords: Markov chain Monte Carlo method; Interacting chains; Hidden Markov model
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Seymour, R. S., White, C. R., & Gibernau, M. (2009). Endothermy of dynastine scarab beetles (Cyclocephala colasi) associated with pollination biology of a thermogenic arum lily (Philodendron solimoesense). J. Exp. Biol., 212(18), 2960–2968.
Abstract: Cyclocephala colasi beetles are facultative endotherms that spend most of their adult lives inside the inflorescences of Philodendron solimoesense, where ambient temperature (T-a) averages about 28 degrees C due to floral thermogenesis. Measurements of respiration within a range of T-a showed that active beetles became spontaneously endothermic at T-a below 28 degrees C but were rarely endothermic above it. There was no evidence of endothermy within the inflorescences, indicating that activities in the floral chamber can occur without the high energy expense of endothermy. Bouts of endothermy occurred at lower T-a in respirometer chambers mainly in the evening, when the insects normally fly from one inflorescence to another, and during the night, when they normally eat and mate within the inflorescence. Patterns of endothermy in individual episodes were studied in non-flying beetles with respirometry and infrared thermal imaging. Heat was generated in the thorax by oscillatory waves of respiration that were coupled with thoracic temperature (T-th) increases. Stationary beetles could regulate T-th at about 33 degrees C independently of T-a between 16 and 29 degrees C. At T-a=20 degrees C, this represents a 116-fold increase in metabolic rate over resting, ectothermic values. Endothermy was clearly a requirement for flight, and beetles departing inflorescences warmed to about 30 degrees C before take-off. During flight, T-th was dependent on T-a, decreasing from 37 to 28 degrees C at T-a of 37 to 20 degrees C, respectively. The lowest T-a at which flight could occur was about 20 degrees C. Thermal conductance of stationary, endothermic beetles increased at higher metabolic rates, probably because of increased ventilatory heat loss.
Keywords: beetle; endothermy; pollination biology; Cyclocephala; Philodendron
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Leroy, C., Sabatier, S., Wahyuni, N. S., Barczi, J. F., Dauzat, J., Laurans, M., et al. (2009). Virtual trees and light capture: a method for optimizing agroforestry stand design. Agrofor. Syst., 77(1), 37–47.
Abstract: In agroforestry systems, the distribution of light transmitted under tree canopies can be a limiting factor for the development of intercrops. The light available for intercrops depends on the quantity of light intercepted by tree canopies and, consequently, on the architecture of the tree species present. The influence of tree architecture on light transmission was analysed using dynamic 3D architectural models. The architectural analysis of Acacia mangium and Tectona grandis was performed in Indonesian agroforestry systems with trees aged from 1 to 3 years. 3D virtual trees were then generated with the AmapSim simulation software and 3D virtual experiments in which tree age, planting density, planting pattern and pruning intensity varied were reconstructed in order to simulate light available for the crop. Canopy closure of trees was more rapid in A. mangium than in T. grandis agroforestry systems; after 3 years the quantity of light available for A. mangium intercrops was three times lower than under T. grandis. Simulations with A. mangium showed that practices such as pruning and widening tree spacing enable to increase the total transmitted light within the stand. On T. grandis, modification of the tree row azimuth resulted in changes in the spatial and seasonal distribution of light available for the intercrops. These results are discussed in terms of agroforestry system management.
Keywords: Acacia mangium; Tectona grandis; Agroforestry; Light interception; Plant architecture; Simulation; 3D virtual plant
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Vedel, V., Brena, C., & Arthur, W. (2009). Demonstration of a heritable component of the variation in segment number in the centipede Strigamia maritima. Evol. Dev., 11(4), 434–440.
Abstract: Here we address the question of how arthropod segment number may evolve by reporting the results of further work on the model system Strigamia maritima. Recently, we showed that there was a plastic component of the variation in segment number within this species; now we demonstrate that there is also a heritable component. This is important because it enables a connection to be made between the known latitudinal trend among species of geophilomorph centipedes ( more segments at lower latitudes) and the parallel trend within them. This latter trend is best documented in S. maritima but is also known in several other species. However, while a general connection between the inter- and intraspecific trends can now be made, deciding upon a specific hypothesis of the nature of the selection involved is still problematic. We provide two alternative hypotheses, one based on the temperature-related plasticity in segment number being adaptive, the other based on it being nonadaptive.
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Flores, O., Rossi, V., & Mortier, F. (2009). Autocorrelation offsets zero-inflation in models of tropical saplings density. Ecol. Model., 220(15), 1797–1809.
Abstract: Modelling the local density of tropical saplings can provide insights into the ecological processes that drive species regeneration and thereby help predict population recovery after disturbance. Yet, few studies have addressed the challenging issues in autocorrelation and zero-inflation of local density. This paper presents Hierarchical Bayesian Modelling (HBM) of sapling density that includes these two features. Special attention is devoted to variable selection, model estimation and comparison. We developed a Zero-Inflated Poisson (ZIP) model with a latent correlated spatial structure and compared it with non-spatial ZIP and Poisson models that were either autocorrelated (Spatial Generalized Linear Mixed, SGLM) or not (generalized linear models, GLM). In our spatial models, local density autocorrelation was modeled by a Conditional Auto-Regressive (CAR) process. 13 explicative variables described ecological conditions with respect to topography, disturbance, stand structure and intraspecific processes. Models were applied to six tropical tree species with differing biological attributes: Oxandra asbeckii, Eperua falcata, Eperua grandiflora, Dicorynia guianensis, Qualea rosea, and Tachigali melinonii. We built species-specific models using a simple method of variable selection based on a latent binary indicator. Our spatial models showed a close correlation between observed and estimated densities with site spatial structure being correctly reproduced. By contrast, the non-spatial models showed poor fits. Variable selection highlighted species-specific requirements and susceptibility to local conditions. Model comparison overall showed that the SGLM was the most accurate explanatory and predictive model. Surprisingly, zero-inflated models performed less well. Although the SZIP model was relevant with respect to data distribution, and more flexible with respect to response curves, its model complexity caused marked variability in parameter estimates. In the SUM, the spatial process alone accounted for zero-inflation in the data. A refinement of the hypotheses employed at the process level could compensate for distribution flaws at the data level. This study emphasized the importance of the HBM framework in improving the modelling of density-environment relationships. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Hierarchical Bayesian Modelling; Conditional Auto-Regressive model; Variable selection; Zero-Inflated Poisson; Posterior predictive; Paracou; French Guiana
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