Differences in sensitivity to the fungal pathogen Batrachochytrium dendrobatidis among amphibian populations

Contributing to the worldwide biodiversity crisis are emerging infectious diseases, which can lead to extirpations and extinctions of hosts. For example, the infectious fungal pathogen Batrachochytrium dendrobatidis (Bd) is associated with worldwide amphibian population declines and extinctions. Sensitivity to Bd varies with species, season, and life stage. However, there is little information on whether sensitivity to Bd differs among populations, which is essential for understanding Bd‐infection dynamics and for formulating conservation strategies. We experimentally investigated intraspecific differences in host sensitivity to Bd across 10 populations of wood frogs (Lithobates sylvaticus) raised from eggs to metamorphosis. We exposed the post‐metamorphic wood frogs to Bd and monitored survival for 30 days under controlled laboratory conditions. Populations differed in overall survival and mortality rate. Infection load also differed among populations but was not correlated with population differences in risk of mortality. Such population‐level variation in sensitivity to Bd may result in reservoir populations that may be a source for the transmission of Bd to other sensitive populations or species. Alternatively, remnant populations that are less sensitive to Bd could serve as sources for recolonization after epidemic events.     

Effects of Agricultural Cultivation on Demographics of Southern High Plains Amphibians

Abstract:  Anthropogenic disturbance of landscapes surrounding wetlands is considered a factor in local and global amphibian declines. Few data exist on the effects of agricultural cultivation of wetland watersheds on amphibians, and results from previous studies are contradictory. Our objective was to test the effects of general anthropogenic land use (cultivation vs. grassland) on the demographics of seven species and three age classes of amphibians in the Southern High Plains of Texas. We partially enclosed 16 playa wetlands (4 per land use per year) with drift fences and pitfall traps and monitored relative daily abundance and diversity from 16 May to 17 October 1999 and 19 April to 18 August 2000. In general, relative abundance (i.e., average daily capture) of New Mexico and plains spadefoots (  Spea multiplicata, S. bombifrons ) was greater at cropland than grassland playas; the abundance of other species and diversity of the amphibian assemblage was not affected by land use. Also, abundance generally was greater in 1999 than 2000 for metamorph spadefoots and barred tiger salamanders ( Ambystoma tigrinum mavortium ). Differences in spadefoot abundance between land-use types may have been related to low species-specific vagility, resulting in increased nestedness within disturbed landscapes and reduced abundance of a potential keystone intraguild predator in cropland playas. The yearly difference in amphibian abundance was likely related to annual precipitation, which influenced wetland hydroperiod. Agricultural cultivation surrounding wetlands is associated with the increased abundance of some amphibian species, but other demographic and fitness parameters—such as temporal demographics, body size, and diet diversity—may be negatively affected.     

Extending the Dewanji and Kalbfleisch model to incorporate marker data

The model of Dewanji and Kalbfleisch for the estimation of time to tumour onset from a serial-sacrifice experiment is extended to include a marker state prior to the onset of the tumour. There are two versions of the model, one where a tumour is allowed to develop without the onset of marker, the other where a tumour develops after the marker but in which the marker later becomes unobservable.     

Threatened Peripheral Populations in Context: Geographical Variation in Population Frequency and Size and Sexual Reproduction in a Clonal Woody Shrub

Abstract:  Geographically peripheral populations of widespread species are often the focus of conservation because they are locally rare within political jurisdictions. Yet the ecology and genetics of these populations are rarely evaluated in a broader geographic context. Most expectations concerning the ecology and evolution of peripheral populations derive from the abundant-center model, which predicts that peripheral populations should be less frequent, smaller, less dense, and have a lower reproductive rate than central populations. We tested these predictions and in doing so evaluated the conservation value of peripheral populations for the clonal shrub Vaccinium stamineum L. (Ericaceae, deerberry), which is listed as threatened in Canada. Based on 51 populations sampled from the center to the northern range limits over 2 years, population frequency and size declined toward the range limit, but ramet density increased. Sexual reproductive output varied widely among populations and between years, with many populations producing very few seeds, but did not decline toward range margins. In fact seed mass increased steadily toward range limit, and this was associated with faster germination and seedling growth, which may be adaptive in seasonal northern environments. Our results did not support the prediction that clonal reproduction is more prevalent in peripheral populations or that it contributed antagonistically to the wide variation in seed production. Peripheral populations of V. stamineum are as productive as central populations and may be locally adapted to northern environments. This emphasizes the importance of a broad geographical perspective for evaluating the ecology, evolution, and conservation of peripheral populations.     

Activity of root voles (Microtus oeconomus) under snow: social encounters synchronize individual activity rhythms

Microtine rodents usually display short-term activity rhythms synchronized by light. Social interactions have also been suggested to act as a zeitgeber, entraining individual activity, but evidence supporting this is scarce. In areas with a permanent snow cover during winter, small rodents spend most of the time in the subnivean space, between the snow cover and the ground, where they most likely are unaffected by otherwise dominating photoperiodic cues. The subnivean space, however, is fragmented, and this limits movement and may isolate individuals living just a few meters apart. These conditions provide excellent opportunities to test for the existence of social synchronization. During two winters, I experimentally decreased the subnivean fragmentation by placing out a network of corrugated aluminium sheets on the ground before snowfall, thus increasing the potential for movement and social interaction within the subnivean space. Other areas were left as controls. Intensive PIT-tag monitoring in the subnivean system provided individual activity data of root voles (Microtus oeconomus) without disturbing normal activity. The data revealed that microtines under snow displayed a free-running activity rhythm and that the activity was evenly distributed throughout the 24-h day, indicating a lack of photo-entrainment. Despite this lack of light, interacting individuals were synchronous, and pairwise synchrony decreased with decreasing potential for social interactions. These results suggest that social interactions indeed entrain microtine activity. Several possible adaptive advantages of the synchrony of microtine rodent activity have been proposed, and these theories are discussed in light of the result presented.     

Experimental Study on the Effects of Population Density of Bloodsucking Mosquito (Aedes communis Deg.) Larvae on Their Biological Characteristics

Results of laboratory experiments on the effects of population density of Aedes communis Deg. larvae on their growth, survival, and sex ratio are presented. At the highest density, larval mortality increased by factors of 1.5 and 2.2, the duration of preimaginal development increased significantly, and the weight of pupae was 11 and 14.7% smaller than in low-density populations. The sex ratio was the same in both cases. The absolute numbers and the biomass of insects per cultivation vessel were greater in high-density populations.     

Monitoring of Orchid Populations in a Unique Area of Their Concentration in the Middle Urals

The abundance, density, structure, and dynamics of the populations of 11 rare orchid species are characterized on the basis of observations carried out in the eastern foothills of the Middle Urals from 1991 to 2002. The pattern of changes in the age structure of populations belonging to different ecobiomorphs is revealed. The concept of vegetatively oriented and generatively oriented age spectra of populations is proposed.     

Modelling strategies for the management of the critically endangered Carpentarian rock-rat (Zyzomys palatalis) of northern Australia

The Carpentarian rock-rat (Zyzomys palatalis) is a critically endangered endemic rodent known from only four sandstone gorges in the southeast Gulf of Carpentaria, Northern Territory, Australia. These gorges harbour thickets of monsoon rainforest and broadleaf woodland, surrounded by a Eucalypt savanna matrix. The long-term persistence of Z. palatalis is threatened by altered fire regimes, grazing by feral animals and stock, weed intrusion, and the stochastic hazards associated with small, fragmented populations. To assess the relative importance of these threats and develop practical management options, a population and habitat simulation model was developed, based on the best existing data. Population viability was predicted to be highly sensitive to the frequency of hot, late dry-season fires. Progressive habitat degradation (due predominantly to intense late dry-season fires) is likely to substantially reduce population size and lead to the probable extinction of the species within the next 100 years. The most effective management strategy to counteract this threat would be regular, controlled, fuel reduction burns in the vegetation around the gorge entrances during the early dry season. Establishing a new population (through translocation of captive-bred individuals) would not appreciably reduce extinction risk, but could provide valuable additional data on the impact of threats, if conducted as an adaptive management experiment.     

洞庭湖垸内灾害风险区湖垸高效生态农业模式研究

为了协调好防灾减灾与农业可持续发展的关系,运用灾害学、循环经济学以及农业、林业、牧业、水产、生态、系统工程等学科交叉的理论与方法,将灾害防控技术体系、先进的农业生产方式及生产技术体系与高效生态农业结构的优化机理融为一体,设计了垸內居民区庭院循环经济型灭虫防病技术集成模式,垸内生产区水陆循环经济型血防治鼠避洪耐涝技术集成模式,并分别在典型区域进行了示范,试验表明：与传统生产方式相比,生态、经济、社会三大效益十分显著。同时认为,在建设好优势农产品生产基地的基础上,积极创造条件,发展与之相配套的商品服务体系和市场体系,促进粮、猪、油、麻、渔等产品的精、深加工,延伸产业链,增加产品附加值,提升模式的综合效益,进而推进湖垸农业产业化。