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Random Disturbance (random + disturbance)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Metapopulation Extinction Risk under Spatially Autocorrelated Disturbance

CONSERVATION BIOLOGY, Issue 2 2005
A. S. KALLIMANIS
patrón espacial de perturbación; simulaciones espacialmente explícitas; SLOSS; umbral de extinción Abstract:,Recent extinction models generally show that spatial aggregation of habitat reduces overall extinction risk because sites emptied by local extinction are more rapidly recolonized. We extended such an investigation to include spatial structure in the disturbance regime. A spatially explicit metapopulation model was developed with a wide range of dispersal distances. The degree of aggregation of both habitat and disturbance pattern could be varied from a random distribution, through the intermediate case of a fractal distribution, all the way to complete aggregation (single block). Increasing spatial aggregation of disturbance generally increased extinction risk. The relative risk faced by populations in different landscapes varied greatly, depending on the disturbance regime. With random disturbance, the spatial aggregation of habitat reduced extinction risk, as in earlier studies. Where disturbance was spatially autocorrelated, however, this advantage was eliminated or reversed because populations in aggregated habitats are at risk of mass extinction from coarse-scale disturbance events. The effects of spatial patterns on extinction risk tended to be reduced by long-distance dispersal. Given the high levels of spatial correlation in natural and anthropogenic disturbance processes, population vulnerability may be greatly underestimated both by classical (nonspatial) models and by those that consider spatial structure in habitat alone. Resumen:,Los modelos recientes de extinción generalmente muestran que la agregación espacial de hábitat reduce el riesgo de extinción debido a una recolonización más rápida de sitios vacíos por extinción local. Extendimos la investigación para incluir la estructura espacial en el régimen de perturbación. Desarrollamos un modelo metapoblacional espacialmente explícito en el que el patrón espacial tanto del hábitat como de los regímenes de perturbación podía variar aleatoriamente de fractal a completamente agregado (bloque) y con una amplia gama de distancias de dispersión. El incremento de la agregación espacial de la perturbación generalmente incrementó el riesgo de extinción. El riesgo relativo que enfrentan poblaciones en paisajes diferentes fue muy variable, dependiendo del régimen de perturbación. Con perturbación aleatoria, la agregación espacial de hábitat redujo el riesgo de extinción, como en estudios anteriores. Sin embargo, cuando la perturbación estaba autocorrelacionada espacialmente, esta ventaja se eliminaba o invertía debido a que las poblaciones en hábitats agregados están en riesgo de extinción masiva por eventos perturbadores a escala gruesa. Los efectos de patrones espaciales sobre el riesgo de extinción tendieron a reducirse por la dispersión de larga distancia. Debido a los altos niveles de correlación espacial en los procesos naturales y humanos de perturbación, la vulnerabilidad puede estar enormemente subestimada tanto por modelos clásicos (no espaciales) como por los que sólo consideran la estructura espacial del habitat. Los modelos que consideran la estructura espacial del hábitat solo subestiman el riesgo en comparación con modelos que consideran la estructura especial de la perturbación. [source]

Spatial dynamics of regeneration in a conifer/broad-leaved forest in northern Japan

JOURNAL OF VEGETATION SCIENCE, Issue 5 2000
Yasuhiro Kubota
Ohwi (1972) Abstract. This study deals with stand dynamics over a 6-yr period in a conifer/broad-leaved mixed forest in Hokkaido, northern Japan. The annual rates of gap formation and recovery were 81.3 m2/ha and 66.7 m2/ha, respectively and turnover time of the canopy was 125 yr. The recruitment processes of the component species in this cool-temperate forest were governed by different canopy types: gap, canopy edge and closed canopy. Magnolia obovata regenerated in canopy edges, and Acer mono and Prunus ssiori regenerated in canopy edges and gaps. The results suggested that the mosaic structure made up of closed canopy, canopy edge and gap was related to various regeneration niches. Abies sachalinensis had high mortality rates, initiating gap expansion. The transition probabilities from closed canopy or canopy edge to gap for deciduous broad-leaved trees were lower than for A. sachalinensis, which implies that the difference in degeneration patterns of conifer and broad-leaved canopies contributes to the heterogeneity of spatial structure in the mixed forests. Spatial dynamics were determined by a combination of gap expansion by A. sachalinensis (neighbour-dependent disturbance) and gap formation by deciduous broad-leaved trees (random disturbance). [source]

Regulated Quality Diffusion Revisited

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 4 2001
Andreas J. Novak
In many manufacturing applications, the regulation of a quality process to attain a given target is of central interest. In a recent paper, Liu and Nam (1999) present a model of optimal quality regulation. The underlying quality process evolves due to regulation actions and superimposed random disturbances. Optimal regulation is sought as to minimize the regulation costs and the mean squared deviation from the desired target over a finite time horizon. Unfortunately the model is incorrectly analyzed in Liu and Nam (1999), and we therefore present the correct results in the following paper. [source]

Which traits promote persistence of feral GM crops?

OIKOS, Issue 1 2005
Part 2: implications of metapopulation structure
Transgenes may spread from crops into the environment via the establishment of feral populations, often initiated by seed spill from transport lorries or farm machinery. Locally, such populations are often subject to large environmental variability and usually do not persist longer than a few years. Because secondary feral populations may arise from seed dispersal to adjacent sites, the dynamics of such populations should be studied in a metapopulation context. We study a structured metapopulation model with local dispersal, mimicking a string of roadside subpopulations of a feral crop. Population growth is assumed to be subject to local disturbances, introducing spatially random environmental stochasticity. Our aim is to understand the role of dispersal and environmental variability in the dynamics of such ephemeral populations. We determine the effect of dispersal on the extinction boundary and on the distribution of persistence times, and investigate the influence of spatially correlated disturbances as opposed to spatially random disturbances. We find that, given spatially random disturbances, dispersal slows down the decline of the metapopulation and results in the occurrence of long-lasting local populations which remain more or less static in space. We identify which life history traits, if changed by genetic modification, have the largest impact on the population growth rate and persistence times. For oilseed rape, these are seed bank survival and dormancy. Combining our findings with literature data on transgene-induced life history changes, we predict that persistence is promoted by transgenes for oil-modifications (high stearate or high laurate) and, possibly, for insect resistence (Bt). Transgenic tolerance to glufosinate herbicide is predicted to reduce persistence. [source]