Effect of Forest Fragmentation on Genetic Diversity and Mating System in a Tropical Tree, Pithecellobium elegans

Genetic diversity, population differentiation, and temporal variation in outcrossing rates were examined for Pithecellobium elegans , a Neotropical rain forest canopy tree. Several forest fragments and a large reserve (1500 ha) were compared for several population genetic parameters. For eight populations sampled on the Atlantic coastal plain of Costa Rica, allozyme heterozygosity (0.13), polymorphism (35%), and effective number of alleles (1.24) were similar to values reported for other tropical tree species that occur at similar densities of less than one individual per hectare. These measures of genetic variation were lowest in populations of the smallest size, farthest from the reserve, and more isolated from other populations. Differentiation among samples collected in small forest fragments and the reserve population accounted for 10% of the total genetic variation observed. There was a positive relationship between the level of differentiation of populations from the reserve population and their distance from the reserve. Though predominantly an annually flowering species, the number of trees in flower at any one time varied from 80% of observed trees to only 6%. Outcrossing rates did not differ for two episodes in which the proportions of flowering trees were 33% and 80%. But periods of low density of flowering adults resulted in poor seed crops or failure to set fruit for many individuals. Population size at many sites will be effectively decreased because of the variation in flowering. Fragmentation of what was once a large, continuous forested area is resulting in genetic erosion of small, isolated populations of Pithecellobium elegans .     

Roads,Interrupted Dispersal,and Genetic Diversity in Timber Rattlesnakes

Abstract: Anthropogenic habitat modification often creates barriers to animal movement, transforming formerly contiguous habitat into a patchwork of habitat islands with low connectivity. Roadways are a feature of most landscapes that can act as barriers or filters to migration among local populations. Even small and recently constructed roads can have a significant impact on population genetic structure of some species, but not others. We developed a research approach that combines fine‐scale molecular genetics with behavioral and ecological data to understand the impacts of roads on population structure and connectivity. We used microsatellite markers to characterize genetic variation within and among populations of timber rattlesnakes (Crotalus horridus) occupying communal hibernacula (dens) in regions bisected by roadways. We examined the impact of roads on seasonal migration, genetic diversity, and gene flow among populations. Snakes in hibernacula isolated by roads had significantly lower genetic diversity and higher genetic differentiation than snakes in hibernacula in contiguous habitat. Genetic‐assignment analyses revealed that interruption to seasonal migration was the mechanism underlying these patterns. Our results underscore the sizeable impact of roads on this species, despite their relatively recent construction at our study sites (7 to 10 generations of rattlesnakes), the utility of population genetics for studies of road ecology, and the need for mitigating effects of roads.     

Long-Term Effects of Group-Selection Timber Harvesting on Abundance of Forest Birds

Abstract:  Relatively few studies have examined the ecological effects of group-selection timber harvesting, and nearly all have been short-term and have lacked experimental manipulations that allow pre- and posttreatment comparisons. We have been documenting the effects of a group-selection timber harvest on bird abundance in a Maine forest for 24 years (preharvest, 1983–1987; postharvest, 1988–2006). Here we characterized the trends in bird abundance over the first 20 years of the study in the managed and control halves of the 40-ha study area. Species responses to the group-selection harvest were idiosyncratic, but in general the mature-forest bird community was retained and species dependent on early successional habitat temporarily (≤8 years) benefited. The Eastern Wood-Pewee ( Contopus virens ) , Winter Wren ( Troglodytes troglodytes ) , Pine Warbler ( Dendroica pinus ) , and White-throated Sparrow ( Zonotrichia albicollis ) increased in abundance in the managed half of the study area following timber harvest, whereas the Veery ( Catharus fuscescens ) decreased. The Black-and-White Warbler ( Mniotilta varia ) , Nashville Warbler ( Vermivora ruficapilla ) , and Common Yellowthroat ( Geothlypis trichas ) responded positively to harvesting, as indicated by decreases in abundance in the control area and more protracted declines or stable abundances in the managed area. This study constitutes the longest experimental investigation to date of the effects of a group-selection harvest on birds and thus provides important information on the strength, direction, and duration of temporal changes in bird populations following forest management.     

Influence of Habitat Patchiness on Genetic Diversity and Spatial Structure of a Serpentine Endemic Plant

Abstract: Conservation of rare plant species often involves small, local populations dispersed within apparently suitable habitat. We used enzyme electrophoresis to study genotypic diversity in 32 populations of Calystegia collina , a self-incompatible clonal plant endemic to serpentine substrate in northern California's Coast Range. Genotypic diversity within a population was a good predictor of seed set by randomly marked flowers. Ramets from the most abundant genotypes in a population were most likely to produce flowers, but flowers from abundant genotypes were less likely to produce seed capsules than were flowers from rarer genotypes. These results are consistent with previous findings that reproductive success in C. collina is limited by the availability of compatible pollen. On small serpentine outcrops supporting only one or two populations, C. collina did not show reduced genotypic diversity or heterozygosity compared with populations on large outcrops supporting many populations. Instead, genotypic diversity and outcrop size had strong but independent influences on reproductive success. Although large serpentine outcrops contain more populations and provide better conditions for flower and seed production, significant diversity of unique genotypes clearly exists in isolated serpentine outcrops. Our findings suggest that plant conservation strategies must take into account the natural distribution of populations. The effects of habitat fragmentation on C. collina and other plant species that occur naturally in small, discrete patches may be unlike those that have been documented in more recently fragmented species.     

Influence of Forest Fragmentation on Community Structure of Frogs and Lizards in Northeastern Costa Rica

Abstract:  To better understand responses of reptiles and amphibians to forest fragmentation in the lowland Neotropics, we examined community and population structure of frogs and lizards in the fragmented landscape surrounding La Selva Biological Station in the Sarapiquí region of northeastern Costa Rica. We used diurnal quadrats and nocturnal transects to sample frogs and lizards in nine forest fragments (1–7 ha each) and La Selva (1100 ha). Species richness in all fragments combined was 85% of that found in La Selva with comparable sampling effort. Richness varied from 10 to 24 species among forest fragments, compared with 36 species at La Selva. Lizard density was higher and frog density was lower in forest fragments than in La Selva. Community composition varied among sites and by fragment size class, and species occurrence was nested with respect to fragment area. Isolation and habitat variables did not significantly affect species richness, composition, or nestedness. We classified 34% of species as fragmentation sensitive because they were absent or occurred at low densities in fragments. Nevertheless, the relatively high diversity observed in the entire set of fragments indicates that preserving a network of small forest patches may be of considerable conservation value to the amphibians and reptiles of this region.     

Public Timber Supply, Market Adjustments, and Local Economies: Economic Assumptions of the Northwest Forest Plan

Abstract:  The Northwest Forest Plan in the Pacific Northwest sought to stabilize local economies, including local employment and income, by stabilizing the flow of wood fiber from public forests. This is also a common forest management objective in other regions and countries. Because this economic strategy ignores basic market adjustments, it is likely to fail and to unnecessarily damage forest ecosystems. Application of basic economic principles on how markets operate significantly changes the apparent efficacy of efforts to manage local economies by managing timber supply. The emphasis on timber supply tends to ignore the dominant role that the demand for wood fiber and wood products, rather than wood-fiber supply, plays in determining levels of harvest and production. Contemporary economics indicates that markets tend to operate to offset reductions in wood-fiber supply. This significantly moderates the economic cost of reducing commercial timber harvest in the pursuit of environmental objectives. In addition, contemporary economic analysis indicates that the economic links between natural forests and local communities are much broader than simply the flow of commercially valuable logs to manufacturing facilities. At least in the United States, the flow of environmental services from natural forests has increasingly become an amenity that has drawn people and economic activity to forested areas. Attractive site-specific qualities, including those supported by natural forests, can potentially support local economic development even in the face of reduced timber harvests. These market-related adjustments partially explain the Northwest Forest Plan's overestimation of the expected regional impacts associated with reduced federal timber supply and the ineffectiveness of the plan's efforts to protect communities by stabilizing federal timber supply.     

恩诺沙星对土壤微生物群落代谢功能多样性的影响（Effects of Enrofloxacin on the Functional Diversity of Soil Microbial Communities）

为了评价恩诺沙星(Enrofloxacin)对土壤微生物群落的影响,借助BIOLOG检测法比较了不同浓度恩诺沙星影响下的土壤微生物的群落特征.结果表明,加药组土壤微生物的丰富度指数和多样性指数显著低于空白对照组,且药物浓度越高丰富度和多样性越小.用药后第3d、14d,恩诺沙星含量0.1～100μg·g-1使土壤微生物群落代谢功能多样性显著降低(p<0.05);第35d,恩诺沙星含量10～100μg·g-1使土壤微生物群落代谢功能多样性显著降低,随着药物作用的时间延长,药物含量0.01～1μg·g-1组土壤微生物群落代谢功能多样性与空白对照组之间的差异变小.     

Impacts of Roads and Hunting on Central African Rainforest Mammals

Abstract:  Road expansion and associated increases in hunting pressure are a rapidly growing threat to African tropical wildlife. In the rainforests of southern Gabon, we compared abundances of larger (>1 kg) mammal species at varying distances from forest roads and between hunted and unhunted treatments (comparing a 130-km² oil concession that was almost entirely protected from hunting with nearby areas outside the concession that had moderate hunting pressure). At each of 12 study sites that were evenly divided between hunted and unhunted areas, we established standardized 1-km transects at five distances (50, 300, 600, 900, and 1200 m) from an unpaved road, and then repeatedly surveyed mammals during the 2004 dry and wet seasons. Hunting had the greatest impact on duikers ( Cephalophus spp. ), forest buffalo ( Syncerus caffer nanus ), and red river hogs ( Potamochoerus porcus ), which declined in abundance outside the oil concession, and lesser effects on lowland gorillas ( Gorilla gorilla gorilla ) and carnivores. Roads depressed abundances of duikers, sitatungas ( Tragelaphus spekei gratus ), and forest elephants ( Loxondonta africana cyclotis ), with avoidance of roads being stronger outside than inside the concession. Five monkey species showed little response to roads or hunting, whereas some rodents and pangolins increased in abundance outside the concession, possibly in response to greater forest disturbance. Our findings suggest that even moderate hunting pressure can markedly alter the structure of mammal communities in central Africa. Roads had the greatest impacts on large and small ungulates, with the magnitude of road avoidance increasing with local hunting pressure.     

Fish Faunas of the African Great Lakes: Origins, Diversity, and Vulnerability

The largest African Great Lakes, Tanganyika, Malawi, and Victoria, which have the richest lacustrine fish faunas of any of the world's lakes, provide a unique comparative series for studies of evolutionary mechanisms, community ecology, and fish behavior. Their colorful littoral fishes are also known to aquarists worldwide. This paper examines the origins of their fish diversity, looking at the history of the lakes, colonization from river systems, and evolution of endemic faunas within each lake. All three lakes support fisheries of great socioeconomic importance for the rapidly rising human populations. The paper also examines the vulnerability of the faunas to fishing pressures and introductions of exotic species. In Malawi and Victoria, bottom-trawling has altered the cichlid species composition. The loss of an estimated 200 taxa of endemic cichlid species from Lake Victoria's fauna, following introductions of exotic fishes (tilapias and predatory centropomid Lates ) 40 years ago, stresses the need to protect the unique fish faunas in Lakes Tanganyika and Malawi.     

Effects of Fragmentation of Araucarian Vine Forest on Small Mammal Communities

Abstract: Habitat loss and fragmentation are major threats to the survival of forest-dependent fauna. We examined the abundance of small mammal species in forests, corridors, remnants of araucarian vine forest, and Araucaria cunninghamii plantations and pastures. None of the forest mammal species persisted following conversion of forest to pasture. Plantations supported lowered abundances of a subset of forest species that were mainly habitat generalists with respect to their occurrence in different floristic types of undisturbed native forest. Within plantations, an increased subcanopy cover was associated with a more forest-like small mammal assemblage. Species' responses to habitat fragmentation varied. The floristic habitat generalists were largely tolerant of habitat fragmentation, their abundance being similar in forests, corridors, and remnants, and were capable of persisting in remnants a few hectares in area. Floristic habitat specialists were vulnerable to habitat fragmentation and thus were abundant in continuous forest, were less abundant in corridors, and were generally absent from remnants. Species that avoid the corridor matrix and are therefore constrained to the corridor may be disadvantaged by the linearity of the habitat, consistent with the predictions of central-place foraging theory. Although small remnants and corridors provide habitat for some species, those that are more specialized in their use of undisturbed habitat types require the retention or reestablishment of large intact areas.     

Effects of Karst Forest Degradation on Pulmonate and Prosobranch Land Snail Communities in Sabah, Malaysian Borneo

Abstract:  Limestone (karst) outcrops in Southeast Asia are rich in land snails. Certain groups of land snails, in particular Prosobranchia species, are restricted to limestone and show a high degree of short-range endemism. Karst habitats are, however, seriously degraded by quarrying, logging, agriculture, and burning. The effect of these disturbances on land snail fauna is unknown, so we studied paired primary and secondary forest localities on six separate limestone hills in Sabah, Malaysian Borneo. Land snails were sampled with a standard protocol and identified to species level. More than 16,000 individuals, belonging to 74 species, were recorded. In most sites, snail diversities did not differ between disturbed and undisturbed plots. However, pulmonate snails were significantly more abundant at disturbed localities than prosobranch snails, whereas abundances for both groups were similar at undisturbed sites. Because Prosobranchia contain many site-endemic species, our findings suggest that continued exposure to these disturbances will eventually lead to extinctions in this group.     

2种短周期工业用材林种植恢复过程对林内小气候的影响

在广西南宁市北郊的杉木林采伐迹地上,经过炼山清理,营造厚荚相思林和尾巨桉林以及灌草坡自然恢复3种植被类型,分别对主要气象要素进行连续4 a的对比观测.结果表明:(1)厚荚相思林和尾巨桉林内太阳辐[射]照度日平均值分别为126.6和90.8 W·m-2,分别占灌草坡植被的50.4%和36.1%;并随着林龄增大林内太阳辐[射]照度呈波浪式下降趋势.(2)厚荚相思林和尾巨桉林内年平均空气温度和地面温度分别比灌草坡植被降低0.7～0.8和1.8～2.7 ℃,并随着林龄增大温度逐渐降低.2种林分各年份空气相对湿度比灌草坡植被提高1～3百分点;并随着林龄增大而使林分内的增湿作用越明显.(3)2种短周期工业用材林种植恢复到5年生时,对林内小气候的调节作用已达到了成熟林分的水平,且厚荚相思林优于尾巨桉林.     

Using Genetic Profiles of African Forest Elephants to Infer Population Structure,Movements, and Habitat Use in a Conservation and Development Landscape in Gabon

Conservation of wide‐ranging species, such as the African forest elephant (Loxodonta cyclotis), depends on fully protected areas and multiple‐use areas (MUA) that provide habitat connectivity. In the Gamba Complex of Protected Areas in Gabon, which includes 2 national parks separated by a MUA containing energy and forestry concessions, we studied forest elephants to evaluate the importance of the MUA to wide‐ranging species. We extracted DNA from elephant dung samples and used genetic information to identify over 500 individuals in the MUA and the parks. We then examined patterns of nuclear microsatellites and mitochondrial control‐region sequences to infer population structure, movement patterns, and habitat use by age and sex. Population structure was weak but significant, and differentiation was more pronounced during the wet season. Within the MUA, males were more strongly associated with open habitats, such as wetlands and savannas, than females during the dry season. Many of the movements detected within and between seasons involved the wetlands and bordering lagoons. Our results suggest that the MUA provides year‐round habitat for some elephants and additional habitat for others whose primary range is in the parks. With the continuing loss of roadless wilderness areas in Central Africa, well‐managed MUAs will likely be important to the conservation of wide‐ranging species. Utilización de Perfiles Genéticos de Elefantes Africanos para Inferir su Estructura Poblacional, Movimientos y Uso del Hábitat en un Paisaje con Conservación y Desarrollo en Gabón Resumenfgs