All field-collected actinorhizae examined on Comptonia peregrina and Myrica pensylvanica in Maine are spore negative

1989 ◽  
Vol 67 (5) ◽  
pp. 1460-1464 ◽  
Author(s):  
Christa R. Schwintzer
Keyword(s):  
Soil Ph ◽  
Host Selection ◽  
Positive Root ◽  
Root Nodules ◽  
Tree Cover ◽  
Nitrogen Fixing ◽  
Selection Of ◽  
Myrica Pensylvanica

The occurrence of spore-negative and spore-positive root nodules of Comptonia peregrina (sweet fern) and Myrica pensylvanica (bayberry) was examined in Maine, as well as the distribution of these nitrogen-fixing shrubs and selected characteristics of the environments in which they occur. Thirty-one widely distributed sweet fern sites were examined, and 16 of these were sampled intensively. The 16 sites were relatively open with < 30% tree cover, and their soil was coarse textured with pH ranging from 3.8 to 6.1. Bayberry nodules were examined at eight sites. All eight sites had the same characteristics as those of sweet fern except that soil pH ranged from 3.4 to 7.4. All nodules on both sweet fern and bayberry were spore negative. One possible explanation is host selection of spore-negative Frankia strains.

Resource selection by grazing herbivores on post-fire regrowth in a West African woodland savanna

2007 ◽  
Vol 34 (2) ◽  
pp. 77 ◽  
Author(s):  
Erik Klop ◽  
Janneke van Goethem ◽  
Hans H. de Iongh
Keyword(s):  
Resource Selection ◽  
West African ◽  
Tree Cover ◽  
Resource Selection Functions ◽  
Risk Of Predation ◽  
Savanna Fires ◽  
Grass Sward ◽  
Burnt Areas ◽  
Good Visibility ◽  
Selection Of

The preference of grazing herbivores to feed on grass regrowth following savanna fires rather than on unburnt grass swards is widely recognised. However, there is little information on which factors govern patterns of resource selection within burnt areas. In this study, we attempted to disentangle the effects of different habitat and grass sward characteristics on the utilisation of post-fire regrowth by nine species of ungulates in a fire-dominated woodland savanna in north Cameroon. We used resource-selection functions based on logistic regression. Overall, the resource-selection functions identified the time elapsed since burning as the most influential parameter in determining probability of use by ungulates, as most species strongly selected swards that were recently burned. This pattern might be related to nutrient levels in the grass sward. In addition, most species selected areas with high grass cover and avoided grass swards with high amounts of dead stem material. This is likely to increase bite mass and, hence, intake rates. The avoidance of high tree cover by some species may suggest selection for open areas with good visibility and, hence, reduced risk of predation. Body mass seemed to have no effect on differential selection of post-fire regrowth, irrespective of feeding style.

scholarly journals Development of the nitrogen-fixing and protein-synthesizing apparatus of bacteroids in pea root nodules

1979 ◽  
Vol 562 (3) ◽  
pp. 515-526 ◽  
Author(s):  
T. Bisseling ◽  
R.C. Van Den Bos ◽  
M.W. Weststrate ◽  
M.J.J. Hakkaart ◽  
A. Van Kammen
Keyword(s):  
Root Nodules ◽  
Nitrogen Fixing ◽  
Pea Root

Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths

Parasitology ◽  
1995 ◽  
Vol 111 (4) ◽  
pp. 531-536 ◽  
Author(s):  
A. Saul
Keyword(s):  
Genetic Drift ◽  
Computer Model ◽  
Genetic Heterogeneity ◽  
Host Selection ◽  
Selection Pressure ◽  
Intestinal Helminths ◽  
Infection Rates ◽  
Stochastic Fluctuations ◽  
Stochastic Simulation Model ◽  
Selection Of

SUMMARYA stochastic simulation model of the transmission and maintenance of genetic heterogeneity in the absence and presence of external selection pressures is presented for polygamous intestinal helminths such as Ascaris. The model assumes that the density distribution of the adult parasites is highly aggregated and that density-dependent effects on fecundity are important. The model gives rise to stable infection rates in the host. Where the parasite population contains genetic heterogeneity, with the exception of stochastic fluctuations which models genetic drift, the ratio of the different alleles remained constant over extended periods of time. This result contrasts with that of an earlier analytical model (Anderson, R. M., May, M. R. & Gutpa S. (1989) Parasitology 99, S59–S79), in which uneven mating probabilities for the different combinations of worm possible in a host was postulated to inevitably lead to fixation of the most abundant allele. New results suggest that in spite of the restricted choice of mating available to a worm in the confines of a host, selection pressure always leads to enrichment of the parasites carrying resistant alleles.

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