Deciphering the effects of disperser assemblages and seed mass on patterns of seed dispersal in a rodent community          下载免费PDF全文

Aleksandra WRÓBEL  Rafał ZWOLAK 《Integrative zoology》2017,12(6):457-467

The sizes of both seed dispersers and seeds are traits that are likely to interact to influence seed fate in many synzoochoric plant species. Here, we examined whether members of a granivorous rodent community consisting of species of different body size vary in their effectiveness as seed dispersers, and how this relationship may be altered by seed size. We marked northern red oak (Quercus rubra) acorns with plastic tags and placed them in size‐selective rodent exclosures. The exclosures allowed differential access of rodent groups based on different body size: (i) small (e.g. Peromyscus spp.); (ii) small and medium (e.g. Tamias striatus); and (iii) small, medium and large (e.g. Sciurus carolinensis) species of rodents. Acorn removal did not differ among exclosure types, but more seeds were missing when removed by small rodents, probably because of larderhoarding. The treatments did not influence the relative frequency of acorn consumption. However, small rodents cached considerably fewer and partially ate more acorns than the other 2 groups. The mean dispersal distance was the longest for cages with medium openings, intermediate for cages with large openings and the shortest for cages with small openings. Acorn mass positively affected the probability of caching and this relationship was unaffected by exclosure type. In conclusion, granivorous rodents of different body sizes strongly differed in their interactions with acorns, with small rodents acting primarily as acorn predators and medium and large species contributing significantly more to dispersal of red oaks.  相似文献   

Response of microbial diversity to C:N:P stoichiometry in fine root and microbial biomass following afforestation     

Chengjie?Ren  Ji?Chen  Jian?Deng  Fazhu?Zhao  Xinhui?HanEmail author  Gaihe?YangEmail author  Xiaogang?Tong  Yongzhong?Feng  Shelby?Shelton  Guangxin?Ren 《Biology and Fertility of Soils》2017,53(4):457-468

Soil samples were collected in June and October from areas with three land-use types, i.e., Robinia pseudoacacia L. (RP), Caragana korshinskii Kom. (CK), and abandoned land (AL), of which the former two were afforested areas, whereas the latter was not. These areas were converted from similar farmlands 40 years prior. Illumina sequencing of 16S rRNA gene and fungal ITS gene was used to analyze soil bacterial and fungal diversity. Additionally, plant communities, soil properties, fine root biomass, and C, N, and P levels in fine root and microbial biomass were estimated. Compared to AL, the C:N:P stoichiometry in fine root and microbial biomass in the afforested lands was synchronously changed, especially the N:P ratio. Soil microbial diversities were affected by afforestation and were more related to N:P ratio than C:P and C:N ratios. Moreover, Alpha-proteobacteria, Gamma-proteobacteria, and Bacteroidetes were significantly more abundant in afforested soils than in the AL soil, and the abundances of Actinobacteria, Chloroflexi, Cyanobacteria, and Nitrospirae ranked as AL > RP or CK. For fungal taxa, Ascomycota abundance responded positively to afforestation, whereas Basidiomycota abundance responded negatively. Changes of soil microbial taxa were significantly correlated with the N:P ratio in fine root and microbial biomass, which explained 54.1 and 55% of the total variation in bacterial and fungal taxa, respectively. Thus, our results provide evidence that compositions of soil microbial communities are linked to the N:P ratio in the plant-soil system.  相似文献   

Glycemic and Insulinemic Responses Are Affected by Age of Horse and Method of Feed Processing     

Brian D. Nielsen  Cara I. O'Connor-Robison  Holly S. Spooner  Jason Shelton 《Journal of Equine Veterinary Science》2010

The objective of this study was to examine age-related differences in glycemic and insulinemic responses of horses that were fed various feedstuffs, with particular attention to method of feed processing. A 16 × 16 Latin square design was used with eight 2-year-olds and eight mature Arabians. Horses were maintained on a roughage diet and were subjected to a glycemic response test once weekly. A control treatment consisted of an oral dextrose drench (0.25 g dextrose/kg of BW). Ten treatments consisted of variously processed feed ingredients fed at the rate of 1.5 g/kg of BW. Five other treatments were commercial feeds of a proprietary nature and are not reported. Fasting blood samples were taken once a week for 16 weeks. Thirty minutes later, another baseline sample was taken and horses were administered their respective treatment. Further blood samples were taken every 30 minutes through four hours. Samples were analyzed for glucose and insulin concentrations. Differences in glucose response between 2-year-olds and mature horses were minimal. However, mature horses had a higher insulin response (P < .01) suggesting young horses had greater insulin sensitivity. Additionally, differences (P < .05) existed between treatments with pelleted steam-processed corn having the highest glycemic response and cracked corn the lowest. Results from this study confirm that mature horses have reduced insulin sensitivity and that both glycemic and insulinemic responses are altered with feed processing techniques. Thermal processing produces the greatest response; however, a low glycemic response may not be desirable if starch escapes into the hindgut.  相似文献   

Current control methods for diamondback moth and other brassica insect pests and the prospects for improved management with lepidopteran-resistant Bt vegetable brassicas in Asia and Africa     

D. Grzywacz  A. Rossbach  A. Rauf  D.A. Russell  R. Srinivasan  A.M. Shelton 《Crop Protection》2010

The diamondback moth (DBM), Plutella xylostella (L.), remains a major pest of brassica crops worldwide. DBM has been estimated globally to cost US$ 1 billion in direct losses and control costs. Chemical control of this pest remains difficult due to the rapid development of resistance to insecticides and to their effect on natural enemies. These problems are especially severe in South Asia and Africa where lack of knowledge, limited access to newer and safer insecticides, and a favourable climate result in DBM remaining a serious year-round pest which substantially increases the cost and uncertainty of crop production. Despite these problems, application of synthetic insecticides remains overwhelmingly the most common control strategy. Biologically-based efforts to control DBM in Africa and Asia have focused strongly on parasitoid introductions. However, despite the identification and deployment of promising parasitoids in many regions, these efforts have had limited impact, often because farmers continue early-season spraying of broad-spectrum insecticides that are lethal to parasitoids and thus exacerbate DBM outbreaks. A significant driver for this pattern of insecticide use is the presence of aphids and other pests whose appearance initiates inappropriate spraying. Despite often extensive training of producers in farmer field schools, many growers seem loath to discard calendar or prophylactic spraying of insecticides. The introduction of an IPM technology that could replace the use of broad-spectrum insecticides for DBM and other key Lepidoptera is crucial if the benefits of parasitoid introduction are to be fully realised. The deployment of DBM-resistant brassicas expressing proteins from Bacillus thuringiensis could help to break this cycle of insecticide misuse and crop loss, but their deployment should be part of an integrated pest management (IPM) package, which recognises the constraints of farmers while addressing the requirement to control other Lepidoptera, aphids and other secondary pests.  相似文献   

Persistence of depleted abalones in marine reserves of central California     

Fiorenza Micheli  Andrew O. Shelton  Seth M. Bushinsky  Alice L. Chiu  Alison J. Haupt  Kimberly W. Heiman  Carrie V. Kappel  Margaret C. Lynch  Rebecca G. Martone  Robert B. Dunbar  James Watanabe 《Biological conservation》2008,141(4):1078-1090

We evaluated the persistence and possible recovery of two depleted marine mollusks, the red (Haliotis rufescens) and black abalone (H. cracherodii), in central California, USA. Monitoring over 32-years did not reveal increasing or decreasing trends in red abalone abundances and sizes over the past three decades, in the absence of harvesting. Comparisons between marine reserves protected for at least 25 years and sites with open public access showed significant difference in size structure for black abalone, with individuals greater than 8 cm in shell length comprising 14–37% of animals in reserves and 2–11% at open-access sites, and a trend for greater abundances of red abalone within reserves. Despite no increasing trends, protection in one of the no-take reserves, the Hopkins marine life refuge (HMLR), has led to persistence of red abalone populations over multiple generations, at average densities of 0.2 individuals/m². At other locations, both within the HMLR and elsewhere, red abalone densities are lower than at the location where long-term studies were conducted (av. 0.03 animals/m²), and an order of magnitude lower than for black abalone (av. 0.4 animals/m²). These results suggest that continued fishery closure and protection in no-take reserves are effective tools for allowing persistence of abalone populations, though there are no signs of recovery to levels comparable to those preceding fisheries collapse. Such failure to recover is most likely associated with high natural mortality and possibly continued illegal take, but not with processes underlying low abalone population levels elsewhere, including food or habitat limitation, recruitment failure, or disease. Linking current structure and trends to specific processes is a crucial first step towards devising focused strategies for conserving and re-building depleted marine populations.  相似文献   

Effects of flood duration and season on germination of black,cherrybark, northern red,and water oak acorns   总被引：1，自引：0，他引：1  

Guo  Yanfei  Shelton  Michael  Lockhart  Brian R. 《New Forests》1998,15(1):69-76

Effects of flood duration (0, 10, 20, and 30 days) and season (winter and spring) on acorn germination were tested for two upland oaks [black and northern red oak (Quercus velutina Lam. and Q. rubra L.)] and two bottomland oaks [cherrybark and water oak (Q. pagoda Raf. and Q. nigra L.)]. Acorns were stratified for 30 days before flooding at a depth of 15 cm along the edge of a small pond. After flooding, acorns were sowed in sand-filled plastic cups and germinated for 40 days. Flood duration and season strongly affected radicle and epicotyl emergence of the upland oaks, but effects were generally limited to spring flooding. Embryo axes of the upland oak acorns were severely damaged with as little as 10 days of spring flooding. Almost no epicotyls developed, but radicles developed from the connective tissues between embryo axes and the cotyledons of many acorns. Spring flooding also significantly increased the percentage of decayed acorns for the upland oaks. In contrast, germination of the bottomland oaks was slightly improved by flooding during both seasons. Results demonstrated that the effects of flooding on the distribution of species within bottomlands can begin with seed storage and germination.  相似文献   

Neptune's eccentricity and the nature of the kuiper belt     

WR Ward  JM Hahn 《Science (New York, N.Y.)》1998,280(5372):2104-2106

The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units.  相似文献   

Estrogen sex-reversal of Tilapia aurea     

Kevin D. Hopkins  William L. Shelton  Carole R. Engle 《Aquaculture (Amsterdam, Netherlands)》1979,18(3):263-268

Chemical treatments were used to produce sex-reversed female (genetic male) Tilapia aurea, which can be bred to produce monosex offspring. Various combinations of estrogens, two synthetic and one natural, an antiandrogen, and a ‘pituitary blocking agent’ were orally administered to sexually undifferentiated fry. Treatment periods were 4, 5, 6 and 8 weeks. Seven of the 36 treatments produced more than 50% females (α = 0.05). Two treatments were more successful than the others: (1) 17-α-ethynylestradiol (EE) at 100 mg kg^?1 diet in combination with methallibure (ME) at 100 mg kg^?1 for 6 weeks and (2) EE-100 with ME-100 and cyproterone acetate (CA) at 100 mg kg^?1 for 6 weeks. These treatments produced fish that were 90% female. Comparisons of the treatments with and without CA indicated that CA may lessen the hormone effectiveness of the treatments. Diethylstilbestrol was as potent as EE in comparable CA treatments.  相似文献   

Neuronal Ceroid Lipofuscinosis in Rambouillet Sheep: Characterization of the Clinical Disease     

Philip R. Woods  Ralph W. Storts  Maurice Shelton  Carl Menzies 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(5):370-375

A chronic progressive, neurodegenerative disease has been identified in 4 closely related flocks of purebred Rambouillet sheep. Blindness, circling, proprioceptive deficits, reduced cognition, and poor body condition are the main clinical signs. Prominent lesions include markedly decreased cerebral size and weight, enlarged cerebral ventricles, and intraneuronal accumulations of autofluorescent pigment. Affected sheep usually die between 1 and 2 years of age. The clinical signs and postmortem findings are consistent with neuronal ceroid-lipofuscinosis.  相似文献   

Life insurance clarified.     

W M Shelton 《The Veterinary clinics of North America》1976,6(1):43-50

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