The existence of an Allee effect in populations of Porcellio scaber (Isopoda: Oniscidea)

An Allee effect occurs when at low densities there is a positive relationship between density and fitness leading to a higher probability of extinction. One circumstance in which it may arise is when isolated individuals are less effective in modifying their environment in a favourable way than groups of individuals. In this paper we use Porcellio scaber to test the hypothesis that the fitness correlate of growth rate will vary as a function of density not just due to the negative effects of increasing interference competition whilst foraging at higher densities, but also positively at lower densities due to isolated individuals spending more time and energy searching for other individuals with which to aggregate whilst sheltering.Below densities of 70 m^–2 relative growth rates increased as a function of density, above 70 m^–2 growth rate decreased with increasing density. Time spent walking and searching increased at lower densities. These behavioural observations, together with the original observations on water loss and oxygen consumption made by Allee [1], are used to interpret the curvilinear growth rate response to density as an example of a component Allee effect, which is discussed in relation to the importance of aggregation as an adaptation to the terrestrial environment in the Oniscidea.     

Organic Matter Dynamics,Aggregation, and Carbon Sequestration in Mine Tailings Amended with Humic Substances

Mechanisms of macroaggregation, carbon dynamics, and carbon sequestration were investigated in degraded mine tailings. Humic substances (HSs), wheat straw, lime, and their various combinations were added to the mine tailings and then incubated at 20 °C for 24 weeks. A significant increase (up to 79%) of water‐stable macroaggregates was observed in the HS‐amended tailings after the incubation. During the macroaggregation, 20–33% sand of the mine tailings was bound by HS‐derived active carbon pool. The organic carbon concentration of the macroaggregates significantly increased in the HS‐amended mine tailings compared to the control. Mineral‐associated organic matter carbon derived from the HSs was mainly responsible for the increased concentration of macroaggregate carbon and the increased amount of macroaggregates as well. This active pool of added organic matter was sequestered in aggregates during the process of macroaggregation and thus improved the structure of the mine tailings.     

不同放牧强度下门源草原毛虫在高寒草甸上的空间分布

按照放牧强度递增的顺序在高寒矮嵩草草甸上选取冬季自由放牧、轻牧、中牧、重牧4个样地,每个样地随机选取10个0.5m×0.5m的样方,对每个样方中的植被高度、盖度、虫口密度、毛虫的垂直分布高度等指标进行测定,根据空间分布指数对不同放牧强度下门源草原毛虫幼虫的空间分布情况进行分析。结果表明,适度的放牧干扰会增大门源草原毛虫的虫口密度,过度放牧则可抑制该物种密度的增大。门源草原毛虫在水平和垂直两个方向上均呈现聚集分布。放牧干扰不会改变该物种的聚集分布特征,但可通过对其食物及生境的作用,影响其聚集程度。     

Soil physical responses to cattle grazing cover crops under conventional and no tillage in the Southern Piedmont USA

Grazing of cover crops in grain cropping systems can increase economic return and diversify agricultural production systems, but the environmental consequences of this intensified management have not been well documented, especially under different tillage systems. We conducted a multiple-year investigation of how cover crop management (grazed and ungrazed) and tillage system [conventional (CT; initial moldboard plowing and thereafter disk tillage) and no tillage (NT)] affected soil physical properties (bulk density, aggregation, infiltration, and penetration resistance) on a Typic Kanhapludult in Georgia. Responses were determined in two cropping systems: summer grain/winter cover crop and winter grain/summer cover crop. Soil bulk density was reduced (P = 0.02) with CT compared with NT to a depth of 30 cm at the end of 0.5 year, but only to a depth of 12 cm at the end of 2, 2.5, and 4.5 years. Grazing of cover crops had little effect on soil bulk density, except eventually with 4.5 years of management. Water-stable macroaggregation was reduced (P ≤ 0.01) with CT compared with NT to a depth of 12 cm at all sampling times during the first 2.5 years of evaluation. Stability of macroaggregates in water was unaffected by grazing of cover crops in both tillage systems. Across 7 sampling events during the first 4 years, there was a tendency (P = 0.07) for water infiltration rate to be lower with grazing of cover crops (5.6 mm min⁻¹) than when ungrazed (6.9 mm min⁻¹), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0–10 cm (P = 0.001) and the difference was greater in ungrazed than in grazed systems (P = 0.06). Biannual CT operations may have alleviated any surface degradation with animal traffic, but the initially high level of soil organic matter following long-term pasture and conversion to cropland with NT may have buffered the soil from any detrimental effects of animal traffic. Overall, the introduction of cattle to consume the high-quality cover crop forage did not cause substantial damage to the soil.     

化学信息素对散居型东亚飞蝗聚集行为的影响

散居型是东亚飞蝗的一个重要生态型。对散居型蝗虫行为的深入研究为飞蝗的防治和预报提供重要依据。采用行为生物测定和触角电位测定（EAG）的方法对来自于群居型和散居型蝗虫的化学信息素对散居型东亚飞蝗聚集行为的影响进行了初步研究。研究结果认为,群居型蝗蝻粪便释放出的化学信息素对散居型蝗蝻有明显的聚集作用;散居型蝗蝻对所测试的不同龄期群居型蝗蝻信息素均表现出明显的电生理反应,其中粪便抽提物的电生理活性较强,散居型蝗蝻对来自于相同龄期或较高龄期的群居型蝗蝻的化学信息素的电生理反应较强,其中,雄性比雌性敏感;群居型成蝗粪便信息素抽提物对散居蝗蝻有明显的电生理活性,雄性成蝗释放出的化学信息素电生理活性较高;散居型蝗蝻对来自于散居型蝗虫的化学信息素也有一定电生理反应,但反应不明显。散居型飞蝗的行为和型变与环境中的化学信息有密切关系,进一步深入研究十分必要。     

石榴园5种主要食叶类害虫与其捕食性天敌之间的关系

为统筹利用自然天敌和通过化学措施全年综合防治石榴园害虫,对石榴园害虫及其天敌进行了系统调查,明确了江淮丘陵区石榴园主要食叶类害虫为棉蚜、小绿叶蝉、黄刺蛾、扁刺蛾和小袋蛾。采用灰色关联度分析法、生态位分析法和空间格局聚集强度指数分析法分析了主要害虫与其捕食性天敌在数、时、空方面的关系,综合排序得出:棉蚜的主要捕食性天敌是异色瓢虫、中华草蛉和八斑球腹蛛,小绿叶蝉的主要捕食性天敌是粽管巢蛛、三突花蟹蛛和草间小黑蛛,黄刺蛾的主要捕食性天敌是粽管巢蛛、锥腹肖蛸和八斑球腹蛛,扁刺蛾的主要捕食性天敌是锥腹肖蛸、八斑球腹蛛和粽管巢蛛,小袋蛾的主要捕食性天敌是三突花蟹蛛、粽管巢蛛和异色瓢虫。棉蚜种群的聚集均数λ值大于2,其聚集是本身原因引起的;而小绿叶蝉、黄刺蛾、扁刺蛾和小袋蛾及其捕食性天敌的λ值小于2,其聚集是环境中某些因子引起的。     

增长极理论与农业产业空间布局研究

为进一步解决农业资源分散、产业布局零乱等问题,进行增长极理论与农业产业空间布局研究,本研究基于增长极理论聚集和扩散效应,以武乡县、孝义市为研究对象,构建不同发展模式的农业产业空间布局.将农业产业空间布局划分为突出区位优势和主导产业的空间布局、以产业链为重要支撑空间布局、以产业园区或基地为载体空间布局和以农业产业强镇为载...     

桃蛀螟越冬幼虫在玉米田的空间格局

应用聚集度指标检验、线形回归方程检验方法研究探讨了桃蛀螟越冬幼虫在玉米田垂直方向和水平方向的空间格局。结果表明,该害虫主要在玉米秸的穗节处越冬,在垂直方向和水平方向的空间格局均为聚集分布,这种聚集主要由环境因素引起。在回归分析检验中,3种回归模型以Talor(1961)幂法则拟合效果最好。     

Assessing the impact of Diplocardia ornata on physical and chemical properties of compacted forest soil in microcosms

 The influence of compaction on Diplocardia ornata (Smith) burrowing and casting activities, soil aggregation, and nutrient changes in a forest soil were investigated using pot microcosms. Treatments included two levels each of compaction, organic matter, and earthworms. Both burrowing and casting activities were more abundant in uncompacted soil than in compacted soil. Bulk density decreased in microcosms of compacted soil containing D. ornata from 1.76 g cm^–3 to 1.49 g cm^–3 over the study period. The overall percent of aggregates in the same size classes in compacted soil was less than the percent of aggregates in uncompacted soil. The mean percent of aggregates in earthworm casts for size classes 0.25–1.00 mm was higher for compacted soil than for uncompacted soil. The reverse was true for aggregates in class sizes 2.00–4.00 mm. Soil compaction also affected soil microbial biomass carbon and soil inorganic N concentrations. These results indicate that the burrowing and casting activities of earthworms in compacted forest soils, as in soils of agricultural and pastured lands, can help ameliorate disturbed soils by improving aggregation, reducing bulk density, and increasing nutrient availability. Received: 1 September 1999     

Effect of biochar and phosphorus fertilizer application on soil fertility: soil physical and chemical properties

This study evaluated the effect of biochar and phosphorus fertilizer application on selected soil physical and chemical properties in two contrasting soil types: Rhodic Ferralsols (clay) in Thohoyandou and Leptic Cambisols (loamy sand) in Nelspruit, South Africa. Field experiments were conducted in summer and winter. Treatments consisted of a factorial combination of four biochar levels (0, 5, 10 and 20 t ha^?1) and two phosphorus fertilizer levels (0 and 90 kg ha^?1) arranged in a randomized complete block design with three replicates. Chickpea was the test crop. Soil bulk density, aggregate stability, porosity, total C, total N, C:N ratio, K and Mg were determined. Biochar (10 t ha^?1) and phosphorus increased bulk density and decreased porosity at 0–5 and 15–20 cm soil depth on a loamy sand soil in both seasons. The interaction between biochar and phosphorus increased total C and total N on a clay soil in the summer sowing. However, in the loamy sand soil, biochar (10 t ha^?1) increased total C, C:N ratio, K and Mg in the summer sowing. The effect of biochar was more evident in the loamy sand soil than the clay soil suggesting that the influence of biochar may be soil-specific.