Effect of Moniliformis moniliformis density on distribution within the definitive host population (Rattus norvegicus)

The population dynamics of Moniliformis moniliformis was studied in ‘free-ranging’ laboratory rats, Rattus norvegicus, presented with different relative density levels of M. moniliformis in cockroaches, Periplaneta americana. Changes in selected population parameters of the negative binomial distribution were evaluated as indicators of changes in aggregation. A significant increase in the degree of aggregation of parasites occurred as a result of the increase in relative density of infective stages available to the rats. This increase in aggregation was due to the increase in over-dispersion that occurred in female rats only. The degree of aggregation in females was found to be significantly higher than that in males at both treatment levels. The best indicators of the degree of aggregation were found to be the ratio of the variance to the relative density and the ratio of the log-variance to log-relative density. Changes in k were not correlated with changes in over-dispersion or the relative density.     

基于高光谱特征的雅氏落叶松尺蠖虫口密度估算

[目的]多年来,蒙古高原典型落叶松害虫雅氏落叶松尺蠖Eeannis jacobssoni发生频繁,使森林生态系统遭到严重破坏.虫口密度可直接描述森林虫害严重程度,进而及时、快速获得害虫虫口密度信息显得极为重要.本研究旨在依据雅氏落叶松尺蠖暴发区的落叶松光谱实测数据和虫口密度数据,构建基于高光谱特征的虫口密度估算方法.[...     

Effect of sedimentological and hydrodynamical changes in the intertidal areas of the Oosterschelde estuary (SW Netherlands) on distribution,density and biomass of five common macrobenthic species: Spio martinensis (Mesnil), Hydrobia ulvae (Pennant), Arenicola marina (L.), Scoloplos armiger (Muller) and Bathyporeia sp.

In order to evaluate the impact of the construction of the storm-surge barrier and secondary dams on macrobenthos of the tidal flats in the Oosterschelde (SW Netherlands), changes in distribution, density and biomass of five common species (Spio martinensis, Hydrobia ulvae, Arenicola marina, Scoloplos armiger and Bathyporeia sp) were analysed.Data on macrobenthos were collected from 1979 to 1989 on five different tidal flats. Changes in sediment texture and hydrodynamic factors during the construction and after the completion of the coastal engineering project were taken into account.Three severe winters in a row caused more disturbance in the population of the main predator of S. armiger than did the hydrodynamical changes. A temporary prolongation of the emersion time (in 1986 and 1987) caused a temporary decrease in juvenile A. marina. But afterwards they still occupy the same nursery grounds. Increased wave action on the edges of the flats probably created new niches for Bathyporeia sp. and Spio martinensis, replacing other benthic species.It is not yet clear what has caused the decline of H. ulvae in many places in the Oosterschelde estuary. Parasitic infestation is one of the possibilities.