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141.
1. Stream ecosystems exhibit a highly consistent dendritic geometry in which linear habitat units intersect to create a hierarchical network of connected branches.
2. Ecological and life history traits of species living in streams, such as the potential for overland movement, may interact with this architecture to shape patterns of occupancy and response to disturbance. Specifically, large-scale habitat alteration that fragments stream networks and reduces connectivity may reduce the probability a stream is occupied by sensitive species, such as stream salamanders.
3. We collected habitat occupancy data on four species of stream salamanders in first-order (i.e. headwater) streams in undeveloped and urbanised regions of the eastern U.S.A. We then used an information–theoretic approach to test alternative models of salamander occupancy based on a priori predictions of the effects of network configuration, region and salamander life history.
4. Across all four species, we found that streams connected to other first-order streams had higher occupancy than those flowing directly into larger streams and rivers. For three of the four species, occupancy was lower in the urbanised region than in the undeveloped region.
5. These results demonstrate that the spatial configuration of stream networks within protected areas affects the occurrences of stream salamander species. We strongly encourage preservation of network connections between first-order streams in conservation planning and management decisions that may affect stream species. 相似文献
2. Ecological and life history traits of species living in streams, such as the potential for overland movement, may interact with this architecture to shape patterns of occupancy and response to disturbance. Specifically, large-scale habitat alteration that fragments stream networks and reduces connectivity may reduce the probability a stream is occupied by sensitive species, such as stream salamanders.
3. We collected habitat occupancy data on four species of stream salamanders in first-order (i.e. headwater) streams in undeveloped and urbanised regions of the eastern U.S.A. We then used an information–theoretic approach to test alternative models of salamander occupancy based on a priori predictions of the effects of network configuration, region and salamander life history.
4. Across all four species, we found that streams connected to other first-order streams had higher occupancy than those flowing directly into larger streams and rivers. For three of the four species, occupancy was lower in the urbanised region than in the undeveloped region.
5. These results demonstrate that the spatial configuration of stream networks within protected areas affects the occurrences of stream salamander species. We strongly encourage preservation of network connections between first-order streams in conservation planning and management decisions that may affect stream species. 相似文献
142.
SEARLE LINDA M.; CHAMBERLAIN KEITH; RAUSCH THOMAS; BUTCHER DENNIS N. 《Journal of experimental botany》1982,33(5):935-942
[Methylene-14C]-3-indolylmethylglucosinolate (14C-IMG) was convertedin vitro to [methylene-14Cl-3-indolylacetonitrile (14C-IAN)by myrosinase over a pH range of 4.0-6.0 and this conversionwas enhanced by ferrous ions. Other products of the reactionincluded 3-indolylmethanol, 3, 3'-diindolylmethane and ascorbigenA. Trace amounts of 14C-IAN were produced non-enzymically from14C-IMG in the presence of ferrous ion over a similar pH range.Furthermore, swede tissues (Brassica napus cv. Danestone) infectedwith Plasmodiophora brassicae Woron. could convert 14C-IMG to14C-IAN. These results were consistent with the hypothesis thatthe overgrowth symptoms of the clubroot disease are caused bythe conversion of IMG to the auxin precursor IAN. 相似文献
143.
DNA extracted from simian adenovirus SA7 can induce tumours in hamsters and is infectious in tissue culture1,2. We now have evidence that fragments of the SA7 genome can initiate tumours in newborn hamsters. 相似文献
144.
LINDA D. JONES ELIZABETH HODGSON TREVOR WILLIAMS STEVE HIGGS PATRICIA A. NUTTALL 《Medical and veterinary entomology》1992,6(3):261-265
Tick saliva (or salivary gland extract) potentiates the transmission of Thogoto (THO) virus to uninfected ticks feeding on a non-viraemic guinea-pig. This phenomenon has been named saliva activated transmission (SAT). To investigate the potential of different haematophagous arthropods to mediate SAT, guinea-pigs were infested with uninfected R.appendiculatus Neumann nymphs and inoculated with THO virus and salivary gland extract (SGE) derived from a range of ixodid (metastriate and prostriate) or argasid ticks, or mosquitoes; control guinea-pigs were inoculated with virus alone. Enhancement of THO virus transmission was observed only when SGE was derived from metastriate ticks. Comparison with the vector potential of these various arthropod species revealed that enhancement of THO virus transmission was specific for ticks which were competent vectors of the virus. The data indicate a correlation between vector competence and the ability of haematophagous arthropods to mediate SAT of THO virus. 相似文献
145.
The patterns of rainfall in the Serengeti Ecosystem, Tanzania 总被引:3,自引:1,他引:2
M. NORTON-GRIFFITHS D. HERLOCKER † LINDA PENNYCUICK ‡ 《African Journal of Ecology》1975,13(3-4):347-374
146.
LINDA HANFORD 《Ecological Entomology》1974,126(1):1-40
Udinia, an Ethiopian coccid genus, is redefined and a key is given to the thirteen species now recognised: bruncki sp. n. , catori (Green) comb. n. [= Lecanium subhirsutum Newstead syn. n. ], farquharsoni (Newstead) [= U.exoleta (De Lotto) syn. n. ], glabra De Lotto, ikoyensis sp. n. , lobayana (Balachowsky & Ferrero) comb. n. , newsteadi sp. n. , nigeriensis sp. n. , pattersoni sp. n. , paupercula De Lotto, pterolobina De Lotto, scitula De Lotto, setigera (Newstead). Five species are described as new and three species are redescribed and for these lectotypes are designated. The morphological characters used are discussed and listed and intraspecific variations shown by two of the species are tabulated. The distribution of all the species is recorded on two maps and the literature dealing with associations between ants and Udinia and related coccid genera is briefly reviewed. 相似文献
147.
MICHAEL J. LINKE ALAN A. ASHBAUGH JUDITH V. KOCH LINDA LEVIN REIKO TANAKA PETER D. WALZER 《The Journal of eukaryotic microbiology》2009,56(1):58-65
ABSTRACT. We examined the effects of surfactant protein A (SP-A), a collectin, on the interaction of Pneumocystis murina with its host at the beginning, early to middle, and late stages of infection. Pneumocystis murina from SP-A wild-type (WT) mice inoculated intractracheally into WT mice (WTS -WTR ) adhered well to alveolar macrophages, whereas organisms from SP-A knockout (KO) mice inoculated into KO mice (KOS -KOR ) did not. Substitution of WT mice as the source of organisms (WTS -KOR ) or recipient host macrophages (KOS -WTR ) restored adherence to that found with WTS -WTR mice. In contrast, when immunosuppressed KO and WT mice were inoculated with P. murina from a homologous source (KOS -KOR , WTS -WTR ) or heterologous source (WTS -KOR , KOS -WTR ) and followed sequentially, WTS -KOR mice had the highest levels of infection at weeks 3 and 4; these mice also had the highest levels of the chemokine macrophage inflammatory protein-2 and neutrophils in lavage fluid at week 3. Surfactant protein-A administered to immunosuppressed KOS -KOR mice with Pneumocystis pneumonia for 8 wk as a therapeutic agent failed to lower the organism burden. We conclude that SP-A can correct the host immune defect in the beginning of P. murina infection, but not in the middle or late stages of the infection. 相似文献
148.
A screening method is described whereby potato plants are grown in soil in closed plastic containers in the dark, producing root systems upon which potato cyst nematodes can reproduce. Tubers are planted in John Innes No. 2 compost at 30% moisture and inoculated with an egg suspension. The canisters are held at 20°C for 7 wk after which, visible developing females are counted. This method of screening is more rapid, economical and produces data as reproducible as those from conventional pot tests. The value of the test for detecting resistance early in a potato breeding programme is discussed. 相似文献
149.
THOMAS FROST LINDA GRAHAM JOAN ELIAS MARK HAASE DONALD KRETCHMER & JAMES KRANZFELDER 《Freshwater Biology》1997,38(2):395-399
1. A previously undescribed symbiotic relationship is reported between the freshwater sponge Corvomeyenia everetti , which occurs throughout eastern North America, and a yellow-green alga.
2. Ultrastructural and pigment analyses place the algal endosymbiont within the class Eustigmatophyceae in the division Heterokontophyta.
3. The relationship of the alga with C. everetti appears to be specific and it contributes significantly to the energy budget of the host.
4. Although the growth form of C. everetti is very similar to other freshwater sponges that usually have green-algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and sponges in the development of symbiotic associations in fresh water. 相似文献
2. Ultrastructural and pigment analyses place the algal endosymbiont within the class Eustigmatophyceae in the division Heterokontophyta.
3. The relationship of the alga with C. everetti appears to be specific and it contributes significantly to the energy budget of the host.
4. Although the growth form of C. everetti is very similar to other freshwater sponges that usually have green-algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and sponges in the development of symbiotic associations in fresh water. 相似文献
150.
LINDA PENNYCUICK 《African Journal of Ecology》1975,13(1):65-87
Data on the monthly distributions of the Serengeti migratory wildebeest population between June 1960 and May 1973 have been analysed. It has been shown that the population performs an annual migration, spending the wet season on the Serengeti plains, then moving west towards Lake Victoria at the beginning of the dry season, and later north to the northern extension of the Serengeti National Park or into the Masai Mara Game Reserve in Kenya. The wildebeest return to the plains as soon as the rain begins, but if this is delayed they may move south-west from the northern areas into the corridor first. Annual differences in the pattern of the migration can be correlated with differences in rainfall. The rainfall affects particularly the timing of the movements of the wildebeest on and off the plains, and the extent to which they utilize the northern areas. A large increase in the size of the population over the years studied has resulted in a greater utilization of the northern areas. It has been shown that about half the total range of the wildebeest population is outside the boundaries of the Serengeti National Park, and it is therefore important that these areas should be protected if such a large population is to survive. 相似文献