An unseen foe in arthropod conservation efforts: The case of Wolbachia infections in the Karner blue butterfly

Infection by endosymbiotic bacteria is an underappreciated threat to endangered arthropods with serious implications for captive management programs. We examined the nature of Wolbachia infection in the North American endangered Karner blue butterfly, Lycaeides melissa samuelis, as a case study. Screening for Wolbachia across the range of the species confirmed widespread infection in the western half of the Karner blue’s range. Multilocus sequence typing using six genes confirmed that the infection in the western populations is attributable to a single strain of Wolbachia. This strain was also detected in the closely related Melissa blue butterfly, L. m. melissa, the presumed source of the infection. The infection in the Karner blue butterfly was perfectly correlated with the presence of a foreign mitochondrial DNA variant present in the Melissa blue butterfly, consistent with the hypothesis that the mitochondrial introgression was driven by the spread of Wolbachia. A single individual out of 71 screened from the eastern portion of the range of the Karner blue butterfly was also infected, however this infection was attributable to a different strain. Simulation models of the demographic effects of the spread of Wolbachia infection to uninfected populations and metapopulations suggest that such an infection might further reduce already small population sizes and substantially increase the probability of population extirpation. We discuss threats to other endangered arthropods in the light of this case study and make recommendations for minimizing the impact of endosymbiont infections in conservation plans, especially those including captive propagation and augmentation of endangered arthropod populations.     

Resource availability, matrix quality, microclimate, and spatial pattern as predictors of patch use by the Karner blue butterfly

Determination of which aspects of habitat quality and habitat spatial arrangement best account for variation in a species’ distribution can guide management for organisms such as the Karner blue butterfly (Lycaeides melissa samuelis), a federally endangered subspecies inhabiting savannas of Midwest and Eastern United States. We examined the extent to which three sets of predictors, (1) larval host plant (Lupinus perennis, wild lupine) availability, (2) characteristics of the matrix surrounding host plant patches, and (3) factors affecting a patch’s thermal environment, accounted for variation in lupine patch use by Karner blues at Indiana Dunes National Lakeshore, Indiana and Fort McCoy, Wisconsin, USA. Each predictor set accounted for 7-13% of variation in patch occupancy by Karner blues at both sites and in larval feeding activity among patches at Indiana Dunes. Patch area, an indicator of host plant availability, was an exception, accounting for 30% of variation in patch occupancy at Indiana Dunes. Spatially structured patterns of patch use across the landscape accounted for 9-16% of variation in patch use and explained more variation in larval feeding activity than did spatial autocorrelation between neighboring patches. Because of this broader spatial trend across sites, a given management action may be more effective in promoting patch use in some portions of the landscape than in others. Spatial trend, resource availability, matrix quality, and microclimate, in general, accounted for similar amounts of variation in patch use and each should be incorporated into habitat management planning for the Karner blue butterfly.     

The behaviour and habitat requirements of Maculinea nausithous (the dusky large blue butterfly) and M. teleius (the scarce large blue) in France

Maculinea nausithous and M. teleius are among the world's rarest butterflies. Both oviposit on the flowerheads of Sanguisorba officinalis, but spend most of their immature lives inside Myrmica spp. ant nests, where their larvae feed on ant brood. Very few colonies of these butterflies survive, and leading conservation bodies have called for urgent research into their habitat requirements: at present, too little is known for successful conservation programmes to be devised.This paper described observations made on three small bogs in France, which each supported colonies of both Maculinea in 1981. The main content is a detailed habitat analysis of each site. Studies were also made of the behaviour of both butterflies, and of the size of the population of each species on every site. From these, it was possible to identify some of the factors that make these sites suitable habitats for M. nausithous and M. teleius. It eas concluded that the abundance, and perhaps the species, of Myrmica ant was the crucial factor on each site.     

Isolation and the decline of the large blue butterfly (Maculinea arion) in Great Britain

In England Maculinea arion is on the verge of extinction and there have been many explanations for its decline. Evidence is put forward to show that at one time it was more widespread in England than is generally realised. It is argued that the fragmentation of this widespread distribution is, in itself, a prime cause of the butterfly's disappearance.     

Effects of annual grass senescence on NH4 and N-glycine uptake by blue oak (Quercus douglasii) seedlings and soil microorganisms in California oak woodland

Annual grasses are stronger competitors for available soil N than blue oak seedlings and soil microorganisms. However, little is known about the dynamics of N competition during annual grass senescence. We conducted a field experiment in a California oak woodland to study effects of annual grass senescence on N uptake by grasses, blue oak seedlings and soil microorganisms. Labeled N was applied at the beginning of April, May and of June in the form of ¹⁵NH₄⁺ or ¹⁵N-glycine. Plants and soils were harvested after 5 days (¹⁵NH₄⁺ and ¹⁵N-glycine treatments) and after 26 days (¹⁵NH₄⁺ treatment only). We evaluated effects of N form, season and labeling period on N competition among oak seedlings, annual grasses and soil microorganisms. N forms did not affect competition among grasses, oak seedlings and soil microorganisms, but more ¹⁵N was incorporated into the soil organic N pool in the ¹⁵N-glycine treatments than in the ¹⁵NH₄⁺ treatments. There were no seasonal (May vs June) effects on ¹⁵N recovery in blue oak seedlings and soil microorganisms. Plant samples from April harvest were lost. In June, when grasses were senescing, more ¹⁵N was found in the soil inorganic pool than in May. Extremely dry soils in June may have limited inorganic N availability to oak seedlings and soil microorganisms. After 26-day labeling period, ¹⁵N recovery in blue oak seedlings and the soil organic N pool significantly increased, while ¹⁵N recovery in both the soil microbial and inorganic N pools decreased compared to the 5-day labeling period. Although blue oak seedling biomass changed little from early May to late June, N concentrations in oak roots increased 53%. In contrast, annual grass biomass peaked in May, and then decreased rapidly. Our results suggest that blue oak seedlings and annual grasses have different temporal competitive abilities. Blue oak seedlings appear to have a long-term strategy for N competition. Blue oaks take up N slowly but steadily, increasing N uptake from 5 to 26 days. This extended time period has a greater positive effect on N uptake than does reduced grass uptake caused by senescence.     

Effects of sewage sludge and copper enrichment on both soil mesofauna community and decomposition of oak leaves (Quercus suber) in a mesocosm

A laboratory mesocosm experiment was performed to study the effects of copper-enriched sewage sludge application on a mesofauna community. For 12 weeks, characteristics and changes in this defined and artificial mesofauna community structure were monitored as well as the dynamics of leaf litter decomposition. The mesofauna community comprised six species of Collembola (Folsomia fimetaria, Isotomurus prasinus, Lepidocyrtus cyaneus, Mesaphorura macrochaeta, Parisotoma notabilis, Protaphorura armata), two species of acari Oribatida (Achipteria coleoptrata, Adoristes sp.), one species of acari Gamasida (Hypoaspis aculeifer) and one species of enchytraeid (Enchytraeus crypticus). Three treatments included the addition of 22 g dry weight (DW) sludge spiked with 0, 200 and 1,000 mg Cu kg^?1 DW sludge in each mesocosm, and one treatment had 66 g DW sludge spiked with 1,000 mg Cu kg^?1 DW sludge added in each mesocosm. Copper, complexed with sludge due to a favourable pH, had no effect on community and litter parameters when added to low amount of sludge. In contrast, tripling the sludge dose in addition to a high dose of Cu changed in time the sludge and leaf chemical composition as well as mesofauna community structure. Responses of the mesofauna to this treatment differed between species. The abundance of species such as I. prasinus, L. cyaneus, M. macrochaeta and P. notabilis decreased, whereas the abundance of H. aculeifer increased and became dominant.     

Effects of habitat management on heathland response to atmospheric nitrogen deposition

A field experiment was carried out to investigate the impact of four different management treatments on the response of Calluna-dominated heathland to nitrogen additions of 0 or 30 kg ha⁻¹ yr⁻¹ at a lowland heath in Surrey, England. Post-management Calluna regeneration, growth and canopy development were significantly affected by both the form of management and by nitrogen addition. The effect of nitrogen on shoot growth was lower, in absolute terms, in those plots which had undergone more intensive management treatments. Seedling establishment was higher in plots which received a simulated accidental burn treatment, reflecting the greater proportion of bare ground and the high degree of physical disturbance associated with this treatment. Invasion by Deschampsia seedlings was increased by nitrogen addition, particularly in simulated accidental burn plots. In the long term, the need to maintain a low nutrient environment to favour Calluna dominance, particularly in the face of elevated nitrogen deposition, favours the use of managements which result in the export of a significant proportion of the organic nitrogen stores. However, further study is required to ensure that initial enhancement of seedling invasion by grass and other species, associated with these more intense managements, does not outweigh the long term benefits of associated nutrient removal.     

生境和施肥对棉田节肢动物群落结构的影响

采用不同的生境和施肥组合方法,研究生境复杂性和施肥对棉田节肢动物群落结构的影响,以期为棉田害虫生态防治提供理论依据。生境复杂性设棉田未覆盖稻草(A1)与覆盖稻草(A2)2种方式,施肥设复合肥90 kg(N).hm 2(B1)、复合肥90 kg(N).hm 2添加沼肥90 kg(N).hm 2(B2)、复合肥90 kg(N).hm 2添加尿素90 kg(N).hm 2(B3)3种方式。每个小区采取平行线跳跃法抽取10株棉花,每周一次调查每株棉花上和植株周围0.25 m2地表部分所有节肢动物种类数量和个体数量。结果表明,蜘蛛类(Araneae)个体数[A2(391.1±70.1)头.10株1,A1(226.8±29.3)头.10株1]、优势种天敌星豹蛛(Pardosa astrigera)个体数[A2(171.7±13.3)头.10株1,A1(59.3±9.8)头.10株1]、蜘蛛类优势集中性(A20.527±0.089,A10.258±0.049)、害虫类多样性(A21.459±0.067,A11.245±0.249)覆草生境极显著高于未覆草生境。害虫类均匀度(A20.635±0.040,A10.588±0.100)覆草生境显著高于未覆草生境。害虫类个体数[A2(772.4±206.9)头.10株1,A1(1 156.4±243.7)头.10株1]]、目标害虫棉大卷叶螟(Syleptahn derogate)个体数[A2(320.8±80.6)头.10株1,A1(659.5±254.8)头.10株1]、害虫类优势集中性(A20.311±0.029,A10.400±0.107)、蜘蛛类多样性(A20.997±0.169,A11.584±0.138)、蜘蛛类均匀度(A20.536±0.073,A10.803±0.052)覆草生境极显著低于未覆草生境。施肥方式极显著影响了害虫类个体数[B1(1 015.3±344.1)头.10株1,B2(714.0±152.2)头.10株1,B3(1 164.0±168.9)头.10株1]、棉大卷叶螟个体数[B1(552.0±253.8)头.10株1,B2(280.6±63.7)头.10株1,B3(638.0±256.0)头.10株1]、害虫类优势集中性(B10.370±0.055,B20.282±0.022,B30.414±0.111)、害虫类多样性(B11.324±0.228,B21.511±0.066,B31.222±0.200)、蜘蛛类多样性(B11.167±0.374,B21.418±0.373,B31.286±0.262)、害虫类均匀度(B10.600±0.039,B20.683±0.043,B30.550±0.081);显著影响了蜘蛛类优势集中性(B10.457±0.175,B20.353±0.167,B30.368±0.123)、蜘蛛类均匀度(B10.613±0.160,B20.701±0.130,B30.695±0.168)、捕食性昆虫类多样性(B11.190±0.153,B21.496±0.179,B31.474±0.125)。生境与施肥对害虫类个体数、棉大卷叶螟数个体数、害虫类优势集中性、害虫类多样性、害虫类均匀度的交互作用极显著,生境与施肥对蜘蛛物种数的交互作用显著。棉田覆草改善优势种天敌星豹蛛的生存环境,显著提高对棉大卷叶螟的控制效果;复合肥添加沼肥不利于棉大卷叶螟种群数量的增长。     

太行山区不同农业景观生境的蜘蛛群落结构特征及其影响因子

为探索太行山区农业景观中不同生境类型对蜘蛛多样性的影响,采用陷阱法对河北省武安市西部太行山区5种类型生境(核桃林、玉米地、苹果-芍药套作园、次生林、绿海花廊景观带)的地表蜘蛛多样性进行调查。通过分析5种类型生境中蜘蛛多样性分布及其与局部生境因子的相关关系,探讨半自然生境对蜘蛛的保护作用。结果表明:人为干扰会显著降低生境中蜘蛛丰富度和多度;增加植被群落结构的复杂程度会使生境中蜘蛛丰富度显著增加,而蜘蛛的多度显著降低;蜘蛛的多度随生境中枯落物厚度的增加而增加。其中核桃林的蜘蛛Shannon-Wiener多样性显著高于其他4种类型生境,核桃林、次生林和绿海花廊的蜘蛛丰富度显著高于苹果-芍药套作园和玉米地,苹果-芍药套作园和绿海花廊的蜘蛛多度显著高于其他3种生境。玉米地、苹果园-芍药套作和绿海花廊中蜘蛛的群落组成具有较高相似性,而核桃林与次生林中蜘蛛群落结构具有较高异质性。地表枯落物厚度是影响当地蜘蛛群落结构的最主要因素。研究区在农业景观与自然景观的过渡区种植核桃林、苹果-芍药套作园和绿海花廊间作板栗,对蜘蛛多样性的保护都有积极作用;不同的生境因子与不同蜘蛛群落的关系不同,如狼蛛偏向人为干扰较大的苹果-芍药套作园和绿海花廊景观带,所以生产管理时要结合特有的生境条件,对相应的蜘蛛进行合理的保护和高效的利用。研究结果对当地的农业景观生境管理和生物多样性保护具有指导意义。     

Effects of grazing practices and fossorial rodents on a winter avian community in Chihuahua, Mexico

Chihuahuan Desert grasslands are important wintering grounds for grassland and shrub-adapted birds. Many species belonging to these assemblages are currently exhibiting population declines. One area recognized for its importance to biological diversity, including grassland birds, is the Janos-Nuevo Casas Grandes black-tailed prairie dog (Cynomys ludovicianus) complex in northwestern Chihuahua, Mexico, an area containing 58 colonies with 30,000 ha of prairie dogs. This is one of the largest remaining prairie dog complexes and the only intact complex in the Chihuahuan Desert. In its current condition, a large percentage of this complex is of reduced value to wildlife. Overgrazing on communal (ejido) lands has resulted in areas being comprised of annual grasses and forbs. The density of active prairie dog burrows and banner-tailed kangaroo rat (Dipodomys spectabilis) mounds as well as avian diversity and abundance were lower on ejido lands than an adjacent private ranchland with and without prairie dogs. Few avian species used overgrazed portions of the prairie dog colony. Community similarity among plot types was low due to different management practices and differences on and off colony. To retain, and in many instances restore the biological diversity of this important region it is essential to work with local ejidos on grazing management.     

Effects of fire temperature on the physical and chemical characteristics of the ash from two plots of cork oak (Quercus suber)

Cork oak, (Quercus suber) is widely distributed in the Mediterranean region, an area subject to frequent fires. The ash produced by burning can have impacts on the soil status and water resources that can differ according to the temperature reached during fire and the characteristics of the litter, defined as the dead organic matter accumulated on the soil surface prior to the fire. The aim of this work is to determine the physical and chemical characteristics of ash produced in laboratory experiments to approximate conditions typical of fires in this region. The litter of Quercus suber collected from two different plots on the Iberian Peninsula, Mas Bassets (Catalonia) and Albufeira (Portugal), was combusted at different temperatures for 2 h. We measured Mass Loss (ML per cent), ash colour and CaCO₃ content, pH, Electrical Conductivity (EC) and the major cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) released from ash slurries created by mixing ash with deionized water. The results showed that ML per cent is higher at all temperatures in Albufeira samples compared to Mas Bassets samples, except at 550°C, and the rate of loss increases faster with temperature than the Mas Bassets samples. At 150°C the ash colour is yellowish, becoming reddish at 200–250°C and black at 300°C. Above 400°C the ash is grey/white. This thermal degradation is mostly observed in Albufeira litter. The formation of CaCO₃ was identified at a lower temperature in Albufeira litter. At temperatures < 300°C, pH and EC values are lower, rising at higher temperatures, especially in Albufeira slurries. The concentration of cations at lower temperatures does not differ substantially from the unburned sample except for Mg²⁺. The cation concentration increases at medium temperatures and decrease at higher temperatures, especially the concentration of divalent cations. The monovalent cations showed a larger concentration at moderate temperatures, mainly in Albufeira ash slurries. The analysis of the Ca:Mg ratio also showed that for the same temperature, a higher severity results for Albufeira litter. Potential negative effects on soil properties are observed at medium and higher temperatures. These negative effects include a higher percentage of mass loss, meaning more soil may be exposed to erosion, higher pH values and greater cation release from ash, especially monovalalent cations (K⁺, Na⁺) in higher proportions than the divalent ions (Ca²⁺, Mg²⁺), that can lead to impacts on soil physical properties like aggregate stability. Furthermore, the ions in ash may alter soil chemistry which may be detrimental to some plants thus altering the recovery of these ecosystems after fire. Low intensity prescribed fire can be a useful tool to land management in these sites, due to the reduced effects of fire temperatures on the physical and chemical properties of surface litter, and can reduce the risk of high temperature wildland fires by reducing fuel loadings. From the perspective of water resources, lower fire temperatures produce fewer impacts on the chemistry of overland flow and there is less probability that the soil surface will be eroded. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of environmental characteristics of aquaculture sites on the quality of cultivated Newfoundland blue mussels (Mytilus edulis)

This study examined (1) the effects of seasonal and annual environmental characteristics (temperature, chlorophyll content, salinity, microbial water quality, and algal lipid composition) in four aquaculture locations on the quality (meat content, shell size, and microbial and lipid compositions) of cultivated blue mussels and (2) the optimum harvest time for premium-quality mussels. Seasonal and annual temperature fluctuation of the seawater in the aquaculture sites significantly (P < 0.05) affected their salinity, microbial content, and algal fatty acid compositions, which in turn affected the quality attributes of cultivated mussels. The optimum growth period in terms of meat content (4-5 g) and shell size (50-60 mm) can be achieved within 1 year of cultivation. Because the cultivated mussels examined in this study never reached the maximum microbial load limits (10(5) or log 5 colony-forming units/g of meat), they can be harvested throughout the year. Meanwhile, no significant (P > 0.05) annual changes were observed in total omega-3 polyunsaturated fatty acids content of cultivated mussels. Nonetheless, the optimum harvest time may be April-June for eicosapentaenoic acid (EPA) rich mussels and September-October for docosahexaenoic acid (DHA) rich mussels in terms of fatty acid proportions; however, June may be the best month for the highest concentrations of both EPA and DHA.     

管理措施及土壤因子对5种农田生境地表蜘蛛群落多样性的影响

以往的研究表明有机管理有利于生物多样性保护,但在不同农业生境类型中是否都存在这个结论呢?基于此问题,本研究在一个多生境的有机管理农场与一个相邻的多生境常规集约化管理农区,采用陷阱法进行蜘蛛取样,对比有机和常规管理措施下大棚菜地、果园、稻田田埂、露天田块及农田边界等5种生境类型的农田蜘蛛多样性的差异,并分析土壤因子对蜘蛛多样性的影响。研究发现:1)有机管理与常规管理的蜘蛛物种数没有显著差异,但有机管理的果园中蜘蛛个体数比常规管理的果园中多139%,且差异显著。同一管理措施下,仅常规管理农田区的农田边界蜘蛛个体数和物种数分别显著高于其他生境均值104%和59%。2)有机管理农场比常规管理农田的蜘蛛物种组成差异略大,且在有机管理下不同生境间的蜘蛛群落组成差异更明显。3)土壤因子中有机质、全氮、全磷含量等对蜘蛛群落结构有显著影响,但对蜘蛛个体数和物种数没有显著影响,仅土壤Cu含量和蜘蛛个体数呈显著负相关。在本研究中虽然有机管理和土壤因子对蜘蛛多样性有一定影响,但不同生境间管理强度、植被结构等差异对蜘蛛多样性的影响更大。因此,发展多种农业生境类型的有机农业可提升物种β多样性。同时,在常规集约化管理农区,保留农田边界等半自然生境、适当减少化肥和农药等投入、降低农田内部的管理强度、防止土壤重金属污染等措施均有助于保护蜘蛛多样性。     

A multi-scale analysis of species-environment relationships: rare moths in a pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) community

Community level analyses of species-environment relationships can provide critical information for conservation planners. A comprehensive analysis of the factors that influence species distributions should include variables measured at multiple scales because species-environment relationships are known to vary with the scale of observation. The pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) communities, or pine barrens, of the northeastern USA are severely threatened by development and fire suppression. They also provide critical habitat for many species of rare moths. We used partial canonical correspondence analysis to assess the relative effects of three levels of environmental variables (plot, patch, and landscape) on the distribution and abundance of 10 species of rare moths in a pine barrens community in southeastern Massachusetts, USA. We also used a set of spatial variables to quantify and partial out the effects of spatial autocorrelation of species composition among sampling locations. All three levels of environmental factors combined, independent of spatial factors, accounted for virtually half (48.4%) of the total variation in the moth community. Sequential partitioning of the variance explained by each level of environmental factors indicated that landscape level factors explained more than twice as much variance as plot and patch level factors. Another environmental model that included only landscape level variables explained 53% of the total variation in the moth community. Patch density and percentage of the landscape comprised of open and sparse canopy, scrub oak habitats were the most significant variables. These results suggest that the presence of scrub oak habitat within relatively large, heterogeneous landscape mosaics may be more important for the maintenance of many rare pine barrens associated moth populations than plot or patch level characteristics.     

A multi-scale analysis of species-environment relationships: breeding birds in a pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) community

Analyses of species-environment relationships are critically needed to guide conservation of many declining species. Comprehensive investigations of these relationships must incorporate environmental variables at multiple spatial scales since species responses to the environment vary with the scale of observation. We used partial canonical correspondence analysis to associate a bird assemblage in a threatened pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) community in Plymouth County, Massachusetts, USA, with plot, patch, and landscape level variables. The first level of analysis partitioned the amount of variance in the bird community explained by plot, patch, and landscape factors from that explained by spatial autocorrelation. The second level partitioned the amount of variance explained by plot, patch, and landscape factors alone and in combination. All three levels of environmental variables together accounted for 43% of the variance in the species data and only 5% of the variance was explainable by spatial factors alone. Landscape level factors accounted for a slightly larger amount of the explained variation (12%) than plot (11%) or patch (8%) level factors. We also examined the cumulative fit of each species to the plot, patch, and landscape partial models. Nine species of regional and/or national conservation concern had distributions that fit one model considerably better than the others. The Great Crested Flycatcher (Myiarchus crinitus) and Black-and-white Warbler (Mniotilta varia) were predominantly associated with plot level factors; the Whip-poor-will (Caprimulgus vociferus) was predominantly associated with patch level factors; and the Purple Finch (Carpodacus purpureus), Gray Catbird (Dumetella carolinensis), Scarlet Tanager (Piranga olivacea), Ovenbird (Seiurus aurocapillus), Brown Thrasher (Toxostoma rufum), and Eastern Kingbird (Tyrannus tyrannus) were predominantly associated with landscape level factors. This study suggests that focusing conservation efforts at the landscape level would provide the most effective protection for the largest number of sensitive species.     

Competition for inorganic and organic N by blue oak (Quercus douglasii) seedlings, an annual grass, and soil microorganisms in a pot study

Sources of competition for limited soil resources, such as nitrogen (N), include competitive interactions among different plant species and between plants and soil microorganisms (microbes). To study these competitive interactions, blue oak seedlings (Quercus douglasii) were grown alone or grown together with an annual grass, wild oats (Avena barbata) in pots containing field soil. We injected ¹⁵N-labeled ammonium, nitrate or glycine into the soil of each pot and harvested plants 5 days later. Plant shoots and roots, soil microbial N and soil KCl-extractable N were analyzed for ¹⁵N content. When oak and grass were grown together, ¹⁵N recovery from the inorganic N treatments (NH₄⁺, or NO₃⁻) was 34, 9 and 4% for the grass, microbes and oak seedlings, respectively, and only 1% remained as KCl-extractable N. ¹⁵N recovery from the glycine treatment was 18, 22, 5% for the grass, microbes and oak seedlings, respectively, and 4% remained as KCl-extractable N. When oaks were grown alone, ¹⁵N recovery by soil microbes was 21, 48 and 40% in the NO₃⁻, NH₄⁺ and glycine treatments, respectively. N forms had no effects on ¹⁵N recovery in oak seedlings (7%) and in KCl-extractable N pool (13%). In general, total N recovery by the grass was much greater than by oaks. However, on a fine root surface area or length basis, oaks exhibited higher N uptake than the grass. Our results suggest that the high rooting density and rapid growth rate of the annual grasses such as Avena barbata made them superior competitors for available soil N when compared to blue oak seedlings and to microbes. Soil microbes were better competitors for organic than inorganic N when annual grasses were present, but preferred NH₄⁺ when competing only with oak seedlings.     

Effects of mirex on the larval development of blue crab

The effects of 0.01, 0.1, 1.0 and 10.0 ppb mirex on the development of blue crabs,Callinectes sapidus, from hatching to first crab stage are described. None of the concentrations of mirex showed any appreciable effect on the larvae during the first five days. Thereafter 0.01 ppb and 0.1 ppb mirex were found to be sublethal. These concentrations had no effect on the duration of development from hatching to megalopa or from hatching to first crab stage. Concentrations of 1.0 ppb and 10.0 ppb mirex proved to be acute. No one stage of development was particularly sensitive to 0.01 ppb mirex, but in the other three concentrations some stages were more sensitive (statistically) than others. The results of residue analyses are given for larvae reared in four concentrations of mirex at different periods of development. Residues of mirex in developmental stages increased with concentration, but biological magnification was greatest in larvae reared in the lowest concentration of mirex and lowest in larvae reared in the highest concentration.     

Effects of cattle grazing on ecology and habitat of Columbia Basin pygmy rabbits (Brachylagus idahoensis)

Dramatic declines in the endangered Columbia Basin pygmy rabbit, a genetically unique population of small, burrowing rabbits in Northwestern United States, are likely the combined results of habitat degradation and fragmentation, disease, and predation. A critical component of pygmy rabbit habitat includes big sagebrush (Artemisia tridentata), which constitutes 82-99% of their winter diet and 10-50% of their summer diet. Sagebrush also forms the bulk of hiding cover around burrow sites. Across the range of pygmy rabbits, sagebrush habitat is grazed extensively by cattle. However, grazing has unknown effects on pygmy rabbits inhabiting the remaining, fragmented shrub-steppe habitat. We evaluated the effects of four grazing treatments on the distribution of pygmy rabbit burrows, diets of pygmy rabbits, and quality and quantity of vegetation at Sagebrush Flat in central Washington. Ungrazed areas contained significantly more burrows per unit area than did grazed areas. Vegetation composition and structure differed little among treatments in early summer before annual grazing by cattle. However, cattle grazing in late summer through winter removed about 50% of the grass cover, and reduced the nutritional quality (e.g., increased fiber and decreased protein) of the remaining grass. Although pygmy rabbits ate <2% grasses in winter, grasses and forbs comprised 53% of late summer diets. Because these endangered rabbits avoided grazed areas, removing cattle grazing from key habitat locations may benefit efforts to restore this rabbit in Washington.