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1

Effects of conspecific and heterospecific residents on patterns of immigration in two species of voles

100%
McGuire B., Oli M. K., Getz L. L.
Acta Theriologica
|
2009
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tom 54
|
nr 4
321-332
Studies with birds have shown that presence and density of resident conspecifics and heterospecifics can influence patterns of habitat selection. There have been few studies on the effects of social cues on rates of immigration in mammals. We report results from a long-term live trapping study of immigration in two species of voles, Microtus ochrogaster Wagner, 1842 and Microtus pennsylvanicus Ord, 1815, in bluegrass habitat in east-central Illinois, USA. We compare immigration into control sites from which no individuals of either species were removed with immigration into experimental sites from which either conspecifics or heterospecifics were removed. We focus on characteristics of immigrants and rates of immigration in relation to density in destination habitats. Within each species, immigrants into control and removal sites were similar with respect to body mass and reproductive condition, indicating no major differences in the physical condition of immigrants into sites with established populations and sites without established populations. For both species, density of conspecifics at a site positively influenced rate of immigration at that site. Density of heterospecifics at destination sites did not significantly influence rate of immigration for either species. These results suggest that site selection by dispersing M. ochrogaster and M. pennsylvanicus is characterized by conspecific attraction.
2

The influence of immigration on demography of sympatric voles

100%
Getz L. L., Oli M. K., Hofmann J. E., McGuire B.
Acta Theriologica
|
2005
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tom 50
|
nr 3
We studied the influence of immigration on the dynamics ofMicrotus ochrogaster Wagner, 1842 andM. pennsylvanicus Ord, 1815 populations in alfalfa, bluegrass, and tallgrass prairie in east-central Illinois for 25 years. The numbers of immigrants in a site were positively correlated with overall population densities of the species in the vicinity of the study sites and within the study site. Population density of the other species was not correlated with immigration of either species. Immigrants did not differ significantly from residents with respect to sex-ratio and reproductive condition. Persistence of immigrantM. pennsylvanicus was lower than that of resident adults in all three habitats, while that of immigrantM. ochrogaster was lower than that of resident adults in alfalfa, where the species was most abundant. Neither the absolute number of immigrants nor the proportion of the population composed of immigrants indicated an effect of immigrants on among- and within-habitat differences in demography and population fluctuations of either species. Immigrants may have been an important factor in maintenance ofM. pennsylvanicus in alfalfa, a low-quality habitat, but the influence of immigration on the dynamics of populations inhabiting other habitats was insubstantial.
3

Vole population dynamics: factors affecting peak densities and amplitudes of annual population fluctuations of Microtus pennsylvanicus

100%
Getz L. L., Oli M. K., Hofmann J. E., McGuire B.
Acta Theriologica
|
2007
|
tom 52
|
nr 2
We studied factors affecting peak densities and amplitudes of fluctuation during 20 annual population fluctuations ofMicrotus pennsylvanicus Ord, 1815 in alfalfa and bluegrass habitats over a 25-year period. Survival was correlated with population density over the 25 years and was the most consistent variable associated with stoppage of population growth. Although not correlated with population density over the 25 years, a decline in the proportion of reproductively active adult females contributed to cessation of growth of population fluctuations that peaked in late autumn-winter, and to cessation of growth of eight of eleven population fluctuations that peaked during summer-early autumn. We conclude variation in survival to be the primary factor affecting peak densities and amplitudes of population fluctuation ofM. pennsylvanicus.
4

Demography of fluctuating prairie vole populations: comparison of demographic variables among phases of fluctuations

100%
Getz L. L., Oli M. K., Hofmann J. E., McGuire B.
Acta Theriologica
|
2007
|
tom 52
|
nr 3
We tested for differences in the proportion of reproductively active males and females, proportion of the population composed of young and immigrants, and monthly survival (total, adult, young) among phases (trough, increase, and decline) and among habitats (alfalfa, bluegrass, and tallgrass) of 30 population fluctuations ofMicrotus ochrogaster Wagner, 1842 over 25 years in east-central Illinois USA. Total population survival and survival of adults and young were greatest during the increase phase, among fluctuations, irrespective of habitat. The proportion of reproductively active adult males and females was lowest during the decline phase, an effect of lower reproduction during the winter. These results suggest that phase-specific changes in survival were the primary demographic factor driving population fluctuations ofM. ochrogaster in our study sites. We conclude that small-scale spatially different population fluctuations may be explained by the same mechanisms that explain fluctuations within a population.
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