scholarly journals A fencing experiment on a high-density population of Microtus townsendii

1977 ◽  
Vol 55 (7) ◽  
pp. 1166-1175 ◽  
Author(s):  
Rudy Boonstra ◽  
Charles J. Krebs
Keyword(s):  
Survival Rate ◽  
Breeding Season ◽  
Population Regulation ◽  
Control Area ◽  
High Density ◽  
Low Density ◽  
Vole Population ◽  
Sharp Decline ◽  
Density Population ◽  
Microtus Townsendii

If dispersal is prevented, a low-density vole population will increase to unusually high densities. A mouse-proof fence was constructed around a vole population that had already reached high density and both this population and one on a control area were live-trapped from January 1975 to November 1975. The population on the control remained at peak densities. The enclosed population increased to even higher density once the breeding season had started and had a higher survival rate than the control population. By midsummer the enclosed population had severely overgrazed the vegetation and went into a sharp decline. Dispersal losses from the control were estimated at 32% for males and 31% for females in these high-density populations. Microtus townsendii populations thus responded to a fence in a manner similar to that of other species that have been studied. This experiment indicates the importance of dispersal to population regulation in voles even at peak densities.

scholarly journals Anatomy and physiology of Cattail as related to different population densities

2015 ◽  
Vol 33 (1) ◽  
pp. 01-12 ◽  
Author(s):  
F.F. CORRÊA ◽  
R.H. MADAIL ◽  
S. BARBOSA ◽  
M.P. PEREIRA ◽  
E.M. CASTRO ◽  
...  
Keyword(s):  
Growth Rate ◽  
High Density ◽  
Root Anatomy ◽  
Low Density ◽  
Typha Angustifolia ◽  
Anatomy And Physiology ◽  
Shoot Ratio ◽  
Root Shoot Ratio ◽  
Apoplastic Barriers ◽  
Density Population

The objective of this work was to evaluate the effects of the population density of Typha angustifolia plants in the anatomical and physiological characteristics. Plants were collected from populations of high density (over 50% of colonization capacity) and low density (less than 50% of colonization capacity) and cultivated under controlled greenhouse conditions. Plants from both populations were grown in plastic trays containing 4 L of nutritive solution for 60 days. At the end of this period, the relative growth rate, leaf area ratio, net assimilatory rate, root/shoot ratio, leaf anatomy, root anatomy, and catalase and ascorbate peroxidase activities were evaluated. Plants from high density populations showed increased growth rate and root/shoot ratio. Low density populations showed higher values of stomatal index and density in leaves, as well as increased palisade parenchyma thickness. Root epidermis and exodermis thickness as well as the aerenchyma proportion of high density populations were reduced, these plants also showed increased vascular cylinder proportion. Only catalase activity was modified between the high and low density populations, showing increased values in low density populations. Therefore, different Typha angustifolia plants show differences in its anatomy and physiology related to its origins on high and low density conditions. High density population plants shows increased growth capacity related to lower apoplastic barriers in root and this may be related to increased nutrient uptake capacity.

An experimental study of the behavior of blue grouse (Dendragapus obscurus). I. Differences between the founders from three populations

1975 ◽  
Vol 53 (9) ◽  
pp. 1222-1237 ◽  
Author(s):  
Arthur T. Bergerud ◽  
H. Dennis Hemus
Keyword(s):  
Vancouver Island ◽  
Mirror Image ◽  
High Density ◽  
The Other ◽  
Low Density ◽  
Single Population ◽  
High Density Population ◽  
Dendragapus Obscurus ◽  
Field Workers ◽  
Density Population

In 1970 the authors compared the behavior of two low-density populations of blue grouse (Dendragapus obscurus) with the behavior of a high-density population on Vancouver Island. They then introduced individuals from these populations onto four islands and compared the behavior of these founders in 1971 and 1972.One island received founders from all three populations, while the other three islands each received founders from a single population. Birds from two low-density populations were quite observable, and displayed frequently when approached by field workers, both at their capture sites on Vancouver Island and in different habitats on the release sites on islands. The high-density population was much less observable, and displayed less frequently than did the two low-density populations, both at the capture sites and on the release islands. Male founders from the low-density populations were more aggressive in interacting with their mirror image than were males from the high-density population. Male founders from the high-density population dispersed less from the release sites, had smaller territories, and settled closer together than did males from the two low-density populations. These findings are consistent with the view that animals have a form of behavior that spaces them out as numbers rise, and so prevents unlimited increase in numbers.

The natural regulation of giant tortoise populations on Aldabra Atoll: recruitment

1979 ◽  
Vol 286 (1011) ◽  
pp. 177-188 ◽  
Keyword(s):  
High Density ◽  
Annual Rainfall ◽  
Egg Mass ◽  
First Year ◽  
Low Density ◽  
Isolated Populations ◽  
High Density Population ◽  
Density Area ◽  
Low Density Area ◽  
Density Population

The reproductive ecology of the giant tortoise ( Geochelone gigantea Schweigger) in three isolated populations was studied for 2 years on Aldabra Atoll. Density-dependent recruitment was demonstrated. Nest destruction in the low density area was dependent on the density of mature females providing a mechanism for regulating population size. Increases in annual rainfall and the resultant increase in food availability induced an increase in mean egg mass in the low density area (and thereby total hatchling production), whereas in the high density population mean clutch size, mean egg mass, total number of nests and total hatchling production all increased significantly. Large eggs produced large hatchlings which survived better during the first year than hatchlings from small eggs. Hatchling mortality was 94 and 81 % in the first year in the high and low density populations respectively. Recruitment into the 5 year age class (after which predation is considered negligible) had almost ceased in the high density population compared with 0.44 per 100 breeding females per year in the low density population.

Seasonal home range size and philopatry in two northern white-tailed deer populations

2000 ◽  
Vol 78 (11) ◽  
pp. 1930-1940 ◽  
Author(s):  
Louis Lesage ◽  
Michel Crête ◽  
Jean Huot ◽  
A Dumont ◽  
Jean-Pierre Ouellet
Keyword(s):  
Home Range Size ◽  
High Density ◽  
Home Ranges ◽  
Low Density ◽  
Adult Males ◽  
High Density Population ◽  
Wintering Areas ◽  
N 93 ◽  
Density Population ◽  
Competition For Resources

From 1994 to 1997, we compared summer and winter space utilisation by two white-tailed deer (Odocoileus virginianus) populations wintering in adjacent areas in southeastern Quebec characterised by deep snow cover. One population lived at low density (10 deer/km2) with access to abundant forage in winter (127 000 twigs/ha), whereas for the other, high-density population (20 deer/km2), forage availability was reduced (68 000 twigs/ha). Because of intraspecific competition for resources, we predicted that deer in the high-density population would have smaller home ranges, would exhibit greater philopatry, and would be more likely to disperse. Deer from both populations occupied summer home ranges that were similar in size (1182 ha for adult males; 1102 ha for adult females; 6033 ha for yearling males; 2528 ha for yearling females) but much larger than home ranges observed elsewhere in North America. The high-density population showed a higher level of philopatry than the low-density population during winter but not during summer. Most deer remained migratory during the study (n = 93) but 4 of the 5 that dispersed were from the high-density population. We speculate on the ability of white-tailed deer populations facing severe winters to adapt to using large home ranges in summer. Our results shed light on how wintering areas appear and expand.

The effect of other organisms on the survival rate of Aphodius tasmaniae Hope (Scarabaeidae) in the lower south east of South Australia.

1962 ◽  
Vol 10 (4) ◽  
pp. 617 ◽  
Author(s):  
DA Maelzer
Keyword(s):  
Survival Rate ◽  
High Mortality ◽  
South Australia ◽  
High Density ◽  
The Other ◽  
Low Density ◽  
Competition For Food ◽  
Lower South

The survival rate of the univoltine species Aphodius tasmaniae in improved pastures in the lower south-east of South Australia is influenced by individuals of the same species (i.e. by density) and by individuals of many other species. The species is distributed patchily with areas of high density interspersed with more extensive areas of low density. In the areas of high density, competition for food occurs and larvae may "fight". Such fights result in deaths, but there is little evidence of high mortality resulting from competition and little evidence that "density-induced combat" governs the number of the species. Of the other species which influence A. tasmaniae it is considered that the entomophagous fungus Cordyceps aphodii Mathieson is the only one which, in conjunction with water in winter, causes a sufficiently variable mortality from year to year to contribute significantly towards changes in numbers of A. tasmaniae from generation to generation.

Experimental alteration of sex ratios in populations of Microtus townsendii, a field vole

1978 ◽  
Vol 56 (1) ◽  
pp. 17-27 ◽  
Author(s):  
J. A. Redfield ◽  
M. J. Taitt ◽  
C. J. Krebs
Keyword(s):  
Population Regulation ◽  
Sex Ratios ◽  
Field Vole ◽  
Vole Population ◽  
Partial Removal ◽  
Male Density ◽  
Experimental Alteration ◽  
Two Populations ◽  
Microtus Townsendii

Sex ratios in two populations of Microtus townsendii were experimentally manipulated toward 80% males and 20% males over a 2-year period. The demography of these manipulated populations was changed very little in comparison with a control population with 50% males. Neither survival, breeding, nor growth were related to the density of voles of the same sex. All populations had restricted immigration and the recruitment of females was more tightly regulated than recruitment of males. The number of young voles recruited per pregnancy is inversely related to female density on all areas, and not related to male density. The survival rate of juveniles was influenced more by the females than by the males.Microtus townsendii seems to fit the model of a species in which spacing behavior is sex specific, so that the partial removal of one sex has virtually no effect on the other sex. We need to determine the factors that restrict the entrance of recruits into a vole population. These experiments suggest that the role of females in the restriction on juvenile survival and female recruitment could be critical for vole population regulation.

scholarly journals Ancestral ecological regime shapes reaction to food limitation in the Least Killifish, Heterandria formosa

2020 ◽  
Author(s):  
Anja Felmy ◽  
Jeff Leips ◽  
Joseph Travis
Keyword(s):  
Life Histories ◽  
Food Limitation ◽  
Pathogen Transmission ◽  
High Density ◽  
Food Level ◽  
Low Density ◽  
Capita Food ◽  
Per Capita ◽  
Density Population ◽  
Density Regime

AbstractIn populations with contrasting densities of conspecifics, we often see genetically-based differences in life histories. The divergent life histories could be driven by several distinct agents of selection, including, amongst other factors, variation in per-capita food levels, the intensity of crowding-induced stress, rates of pathogen transmission, mate encounter rates, and the rates with which waste products accumulate. Understanding which selective agents act in a particular population is important as the type of agents can affect both population dynamics and evolutionary responses to density-dependent selection. Here we used a full-factorial laboratory experiment to examine whether two populations of a small live-bearing freshwater fish, characterised by high-density/low-predation or low-density/high-predation conditions, are adapted to different per-capita food levels. As expected, fish from the higher density regime handled food limitation better than those from the lower density regime. Although the lower food level resulted in slower growth, smaller body size, delayed maturation and reduced survival in both populations, especially survival to maturity showed a highly significant population x food-level interaction. At low food, 75% of fish from the low-density population died, compared to only 15% of fish from the high-density population. This difference was much smaller at high food (15% vs. 0% mortality), and was mediated, at least partly, through a larger size at birth of fish from the high-density regime. While we cannot preclude other agents of selection from operating differently in the study populations, we demonstrate that selection at higher density confers a greater ability to cope with low per-capita food availability.

scholarly journals First Report of Puccinia xanthii on Xanthium italicum in Eastern Hungary

Plant Disease ◽  
2003 ◽  
Vol 87 (12) ◽  
pp. 1536-1536 ◽  
Author(s):  
I. Dávid ◽  
P. Harcz ◽  
G. J. Kövics
Keyword(s):  
Leaf Disc ◽  
High Density ◽  
Pathogenicity Test ◽  
Low Density ◽  
Weed Species ◽  
Row Crops ◽  
First Report ◽  
High Density Population ◽  
Noxious Weed ◽  
Density Population

In 2002, in Debrecen, eastern Hungary, Puccinia xanthii Schwein. was detected on hunter burr, a geographically spreading, noxious weed species in row crops. Symptoms were found on leaves, stems, and petioles of plants collected from a competition experiment between sugarbeet and hunter burr. Density of the hunter burr population (6 plants per m2 or 20 plants per m2) influenced the rate of infection. In the low-density population, the number of rust pustules and infected leaves was lower than that in the high-density population, in which 70% infection was reached by September. First symptoms appeared at the end of July (high-density population) and in the beginning of August (low-density population) in the form of small, chlorotic raised spots on the underside of the leaves. Dark brown telia (3.8 mm in diameter or larger) developed on spots. Elliptical telia occurred at the rate of 0.02 to 2.37 pustules per cm2. Elongated pustules caused swelling and epidermal splitting on stems and petioles. Teliospores were brown, two-celled, and 35 to 56 × 15 to 21 μm, the walls were 0.8 to 1.0 μm at the side and 5 to 8 μm at the apex, the septum was 1 to 1.5 μm, and a persistant pedicel was 15 to 50 μm. Size and morphology of teliospores fit the description of P. xanthii (2). A pathogenicity test was conducted in the greenhouse (24°C with high relative humidity) according to the “leaf disc method” of Morin et al. (1) using freshly collected hunter burr leaves. Teliospores germinated immediately, producing metabasidia, and basidiospores were produced within 5 h. The first macroscopic symptoms on test plants were observed 4 days after inoculation. Approximately 8 days after inoculation, developing telia arose from the thallus and began to erupt through the epidermis. Developed teliospores on artificially inoculated plants were morphologically identical to those from leaves collected in the field. Control plants did not develop symptoms. This microcyclic rust occurs in several regions of the world, including several southern European countries. This rust is a potential biological agent for the control of Xanthium spp.; however, it can infect several cultivars of sunflower (1). To our knowledge, this is the first report of P. xanthii in Hungary. References: (1) L. Morin et al. Can. J. Bot. 71:959, 1993. (2) J. A. Parmelee. Can. J. Bot. 47:1391, 1969.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

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