Sighting frequency and food habits of the leopard tortoise, Geochelone pardalis, in northern Tanzania

Sighting frequency and food habits of the leopard tortoise (Geochelone pardalis) were studied in northern Tanzania from October 1993 to June 1996. Sighting frequency varied significantly between protected (0.22 mhr^?1) and unprotected sites (0.59 mhr^?1), and between Arusha (0.27 mhr^?1) and Serengeti sites (0.56 mhr^?1). The tortoise diet comprised mostly plants (97.8%) and rarely inorganic matter (2.2%). A total of 47 plant species from 21 families was eaten. Forbs made up 74.5% of the plant items and monocots the remainder. Succulents contributed 51.0% of the plant items eaten while grasses and legumes accounted for 16.8% and 13.5%, respectively. Some plant items were eaten more frequently than their occurrence in the habitats.     

Macroinvertebrate species and assemblages in the headwater streams of the River Tyne,northern England in relation to land cover and other environmental variables

The macroinvertebrate species and assemblages of headwater streams of the River Tyne catchment in northern England were classified and their relationship with environmental variables based on stream structure, water acidity, distance from source and land cover investigated using constrained ordination and logistic regression. Fuzzy classification of data from 322 stream sites generated five assemblages. Stream structure, quantified as an exposure index, was found to be the most important environmental variable, with water acidity also important. Distance from source and land cover had less influence on species and assemblage distribution. A considerable amount of variation in assemblage distribution was explained using a two-variable logistic regression with stream structure (exposure index) and water acidity (pH) in a template. Site structure and water acidity appeared to be related to drift, geology and topography with little anthropogenic influence. The applicability of the habitat template concept for explaining the distribution of stream macroinvertebrates is discussed.     

Growth and carapacial colour variation of the leopard tortoise, Geochelone pardalis babcocki, in northern Tanzania

Observations were made of growth rate and variation in colour pattern of the leopard tortoise ( Geochelone pardalis babcocki ) in northern Tanzania between October 1993 and June 1996. Growth rate differed significantly between tortoises, with immature animals (6.9 ± 1.4 mm month⁻¹) and females (5.7 ± 1.3 mm month⁻¹) exhibiting higher rates of growth than adult animals (2.9 ± 0.8 mm month⁻¹) and males (3.2 ± 1.1 mm month⁻¹), respectively. The faster growth rate in immature animals suggested that growth rate declined with age. The difference in growth rates between the sexes was ascribed to sexual dimorphism, adult females being larger and therefore growing faster than males.
The carapacial colour pattern observed in the northern Tanzanian tortoises was generally similar to that described elsewhere in the species' range. The colour pattern varied between Arusha and Serengeti District tortoises. Animals at the Arusha sites tended to be sparsely coloured (55.6%) compared to the Serengeti tortoises, which had a buff colouration with radiating spots (89.3%).; The sparse colouration provides effective camouflage in the drier Arusha habitats, as does the buff colouration with black spots in the wetter, darker habitats in the Serengeti.     

The influence of wetlands in regulating water quality in the Seronera River,Serengeti National Park,Tanzania

The distribution of temperature, salinity, visibility and dissolved oxygen was sampled from 1996 to 2002 at sites along the Seronera River. The minimum temperature decreased with distance upstream. The salinity increased up-river where occasionally hypersaline conditions prevailed. Dissolved oxygen was highly variable spatially and temporally, depending on both the level of eutrophication by animal dung and the presence of wetlands that help filter the excess nutrients. During the study period, fringing, freshwater wetlands have generally been degraded and in some cases destroyed, and this has been accompanied by significantly decreased oxygen levels, sometimes nearing anoxic conditions. Also during this period, saltwater wetlands have increased, and since wildlife impacted these wetlands little, dissolved oxygen levels remained high throughout. Visibility was highest in areas fringed by wetlands.This revised version wa published online in March 2005 with corrections to the issue cover date.     

Isotopic assessment of fog drip water contribution to vegetation during dry season in Junshan wetland,northern Dongting Lake

Stable isotopes ²H and ¹⁸O of fog drip water, lake water, soil profiles, and vegetation leaves in Junshan wetland of East Dongting Lake, China, were investigated to estimate the contribution of fog drip water to wetland vegetation. Because of its recycled terrestrial meteoric water source, fog drip water is characterized by isotopic compositions that plot above the local meteoric water line (LMWL). Lake water undergoes intense evaporation owing to its low water volume and long residence time. The isotopic compositions of soil water suggest that it is recharged by both recent rainfall and fog drip water. A binary mixing model shows that approximately 16% of unsaturated soil water originates from continuous recharge by fog drip water, reaching 31% in surface soil where the vegetation roots are mainly distributed. Inspired by the literatures on acidification of intercepted clouds and fog as the major factor in forest die-back in Europe, the findings in this study inform future investigations into the relationships between fog water deposition and wetland degradation especially in heavily industrialized foggy areas.     

Reduced snow cover changes nitrogen use in canopy and understory vegetation during the subsequent growing season

Plant and Soil - We examined how mechanical management of invasive macrophyte, Typha × glauca alters plant-soil interactions underlying carbon processes and nutrient cycling, which are...     

Towards an ecohydrology-based restoration of the Usangu wetlands and the Great Ruaha River, Tanzania

An open channel flow model, calibrated against field data, suggests that cattle intrusion in the eastern Usangu wetlands, as well as both dry and wet weather irrigation upstream, are responsible for the seasonal drying out of the Great Ruaha River (GRR) downstream. This human-induced change has severe socio-economic implications downstream, including hindering hydroelectricity production, as well as a devastating impact on the Ruaha National Park (RNP) ecosystem that is now shifting from wet tropics to dry tropics. To ensure sustainable development, governance is urgently needed for the Usangu catchment in a way that is compatible with ecohydrology principles for the sustainable use of water resources. In order to do that, perennial flow must be restored to the GRR. For this to happen this study suggests that all the livestock must be removed from the eastern Usangu wetlands and dry weather irrigators must return at least 25% (∼4 m³ s⁻¹) of the water to the river.     

基于马尔科夫链模型的长江源区土地覆盖格局变化特征

利用长江源区1986、2000与2014年3期的遥感影像,结合实地野外考察获得该地区在这3个时间点的土地覆盖类型图。根据各时期之间的土地覆盖格局的变化确定土地类型之间的转移概率,进一步完成对该地区马尔科夫链模型的构建、检验与预测。结果表明:1986—2014年,长江源区的土地覆盖格局的变化特征符合马尔科夫过程,通过马尔科夫链模型能够对该地区的覆盖格局变化过程进行有效的模拟;长江源区的土地覆被退化趋势明显,湿地、中高覆盖草地等面积不断下降,裸地、沙地以及低覆盖草地等面积则一直在增加;2000年以后,由于三江源区自然保护区的建立以及降水量的增加等因素影响,长江源区的植被退化状况得到明显改善。     

萧氏松茎象种群发生与植被盖度的关系

在江西赣州发生萧氏松茎象HylobitelusxiaoiZhang危害的松林内 ,对不同虫株率松林灌木层群落多样性和植被盖度进行测定 ,在此基础上对松林的虫株率分 3次 ( 1 1月 ,次年 5月和次年 8月 )进行调查 ,最后结合各调查因子组建了萧氏松茎象种群发生量预测模型 ,植被盖度与虫口密度间存在显著相关性 ,虫口密度随植被盖度降低而减少 ,不同月份间虫口密度间均达到极显著水平。进一步对各因子进行多元回归分析 ,得到线性回归方程 :Y =-2 0 62 6+1 41 7T2 +0 2 3 3T1 -0 1 4 1G ;逐步回归分析得到最优回归方程Y=-0 0 91 1 +1 2 5 82 ,R =0 992 ,P <0 0 1。由逐步回归方程可知 ,次年 5月份虫口密度与次年 8月份虫日密度关系最为密切。     

植被覆盖度和归一化湿度指数对热力景观格局的影响——以广州为例

利用LANDSAT-5 TM影像提取地表温度、植被覆盖度和归一化湿度指数(NDMI)等信息,结合景观生态学方法探讨广州市不同区域城市植被和NDMI对地表温度的调节作用.结果表明:植被覆盖度、NDMI和地表温度两两之间有较强的线性相关性,但不同区域植被覆盖度、NDMI与地表温度的相关程度存在明显差异;提高相同植被覆盖度时,中心城区的降温效果最好,其次是处于中心城区北缘的近郊区;不同区域森林公园对周围热环境的影响程度不同,960～1080 m缓冲区内平均温度与公园内部平均温度之差分别为4.69℃(白云山)、1.27℃(马仔山)和0.41℃(流溪河);高植被覆盖度可增加热力景观多样性和不同景观之间的结合度,促进低温斑块内部与其他斑块如高温斑块间的能量交换,起到控制热岛效应的效果;增加环境湿度与提高植被覆盖度对热力景观格局所形成的作用相当.     

The influence of flow and other environmental factors on benthic invertebrates in the Sacramento River, U.S.A.

We examined how community composition of benthic invertebrates was related to current velocities and other environmental variables within the Sacramento River in California, USA. Invertebrates were collected in 1998 and 1999 from 10 sites over a gradient of 187 river kilometers. Canonical correspondence analysis revealed that current velocity was the most important variable explaining community composition. Other predicator variables that influenced community composition included periphyton biomass, altitude, and disturbance. Because of the importance of velocity in structuring benthic communities in this system, alterations of flow caused by changes in river regulation structures should be carefully considered.     

Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops

1 Maintenance of floral diversity throughout the growing season in vineyards in the form of summer cover crops of buckwheat (Fagopyrum esculentum Moench) and sunflower (Helianthus annus Linnaeus), had a substantial impact on the abundance of western grape leafhoppers, Erythroneura elegantula Osborn (Homoptera: Cicadellidae), and western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and associated natural enemies. 2 During two consecutive years, vineyard systems with flowering cover crops were characterized by lower densities of leafhoppers and thrips, and larger populations and more species of general predators, including spiders. 3 Although Anagrus epos Girault (Hymenoptera: Mymaridae), the most important leafhopper parasitoid, achieved high numbers and inflicted noticeable mortality of grape leafhopper eggs, no differences in egg parasitism rates were observed between cover cropped and monoculture systems. 4 Mowing of cover crops forced movement of Anagrus and predators to adjacent vines resulting in the lowering of leafhopper densities in such vines. 5 Results indicate that habitat diversification using summer cover crops that bloom most of the growing season, supports large numbers of predators and parasitoids thereby favouring enhanced biological control of leafhoppers and thrips in vineyards.     

The effect of vegetation cover on vigilance and foraging tactics in the fat sand rat Psammomys obesus

The combination of the visual obstruction and protection properties of vegetation is considered to be one of the most important factors determining the trade-off between vigilance and foraging in a prey species. In the Negev desert, diurnal fat sand rats construct their burrows in the ephemeral river beds ("wadis"), under dense and tall shrubs of Atriplex halimus, or on the open first fluvial terrace, covered with scattered low shrubs of Anabasis articulata. We tested the hypothesis that properties of the vegetation would affect the time budget of female sand rats. Sand rats spent more time aboveground, rested more, were less vigilant, and moved more slowly under the dense cover in the wadi than at the open terrace. No differences in the total foraging time were revealed, but foraging tactics varied between habitats: individuals in the wadi mainly fed aboveground, whereas those at the terrace mainly hoarded. Our results indicate that sand rats perceive the dense vegetation cover as good protection despite its visual obstructive nature, and that vigilance in Psammomys obesus is performed at the cost of resting rather than at the cost of foraging. Received: January 15, 2001 / Accepted: April 17, 2001     

The impact of over 80 years of land cover changes on bee and wasp pollinator communities in England

Change in land cover is thought to be one of the key drivers of pollinatordeclines, and yet there is a dearth of studies exploring the relationshipsbetween historical changes in land cover and shifts in pollinator communities.Here, we explore, for the first time, land cover changes in England over morethan 80 years, and relate them to concurrent shifts in bee and wasp speciesrichness and community composition. Using historical data from 14 sites acrossfour counties, we quantify the key land cover changes within and around thesesites and estimate the changes in richness and composition of pollinators. Landcover changes within sites, as well as changes within a 1 km radius outside thesites, have significant effects on richness and composition of bee and waspspecies, with changes in edge habitats between major land classes also having akey influence. Our results highlight not just the land cover changes that may bedetrimental to pollinator communities, but also provide an insight into howincreases in habitat diversity may benefit species diversity, and could thushelp inform policy and practice for future land management.     

Land cover dynamics of different topographic conditions in Beijing,China

Topographic conditions play an important role in controlling land cover dynamic processes.In this study,remotely sensed data and the geographic information system were applied to analyze the changes in land cover along topographic gradients from 1978 to 2001 in Beijing,a rapidly urbanized mega city in China.The study was based on five periods of land cover maps derived from remotely sensed data:Landsat MSS for 1978,Landsat TM for 1984,"1992,1996 and 2001,and the digital elevation model (DEM) derived from 1:250,000 topographic map.The whole area was divided into ten land cover types:conifer forest,broadleaf forest,mixed forest,shrub,brushwood,meadow,farmland,built-up,water body and bare land.The results are summarized as follows.(1) Shrub,forest,farmland and builtup consist of the main land cover types of the Beijing area.The most significant land cover change from 1978 to 2001 was the decrease of the farmland and expansion of the builtup area.Farmland decreased from 6354 to 3813 km2 in the 23 years,while the built-up area increased from 421 to 2642 km2.Meanwhile,the coverage of forest increased from 17.2% to 24.7% of the total area.The conversion matrix analysis indicated that the transformation of farmland to the built-up area was the most significant process and afforestation was the primary cause of the replacement of shrub to forest.(2) Topographic conditions are of great importance to the distribution of land cover types and the process of land cover changes.Elevation has an intensive impact on the distribution of land cover types.The area below 100 m mostly consists of farmland and built-up areas,while the area above 100 m is mainly covered by shrub and forest.Shrub has the maximum frequency in areas between 100 and 1000 m,while forest has dominance in areas above 800 m.According to the analysis of land cover changes in different ranges of elevation,the greatest change below 100 m was the process of urbanization.The process of the main land cover change occurred above 100 m was the transformation from shrub to forest.This result was consistent with the vertical change of natural vegetation distribution in Beijing.(3) Slope has a great influence on the distribution of land cover.Farmland and built-up areas are mostly distributed in fiat areas,while shrub and forest occupy steeper areas compared with other land cover types.Forest frequency increased with the increasing slope.Land cover changes differed from the slope gradients.In the plain area,the land cover change occurred as the result of urbanization.With the increasing of the slope gradient,afforestation,which converts shrub to forest,was the process of the primary land cover change.     

Human impacts on Persoonia falcata. Perspectives on post-contact vegetation change in the Keep River region, Australia, from contemporary vegetation surveys

Persoonia falcata R. Br. and Buchanania obovata Engl. seeds are consistently preserved in abundance from archaeological sites across the Keep River region from 3500 b.p. up until the contact period. Although artefacts continued to be deposited after establishment of the pastoral industry, remains of these two plant species disappear in the upper levels of all excavated deposits. The contemporary vegetation in the vicinity of these sites appears to lack P. falcata, although B. obovata remains in abundance. These observations raise questions regarding (1) the impact of changing land-use and fire regimes, (2) the impact of Aboriginal land management on particular plant species and (3) the reorientation of Aboriginal site use across the region after settlement. These issues are explored in this paper using a comparative analysis of stand structure of the contemporary vegetation around previously excavated sites, as well as from published information on recent regional fire history. Results show improved recruitment of P. falcata (that is, seedlings are recruited into adult life stages) in the only site where Aboriginal people have re-introduced customary management. Both the timing of burning and significant unburnt periods appear important to the post-contact decline and also in the future success of populations of P. falcata in the region.