Twenty-Five Years of Population Fluctuations of Microtus ochrogaster and M. Pennsylvanicus in Three Habitats in East-Central Illinois

Abstract

Populations of 2 species of arvicoline rodents, the prairie vole (Microtus ochrogaster) and meadow vole (M. pennsylvanicus), were monitored monthly in alfalfa, bluegrass, and tallgrass prairie habitats in east-central Illinois from 1972 through 1997. Alfalfa provides very highquality preferred food and poor vegetative cover for both vole species, whereas bluegrass provides intermediate food and vegetative cover. Preferred food resources were very low, especially for M. ochrogaster, and vegetative cover was very dense in tallgrass prairie. Maximum and mean population densities of M. ochrogaster were highest in alfalfa, intermediate in bluegrass, and lowest in tallgrass prairie. Populations of M. ochrogaster displayed synchronous 3-to 4-year multiannual cycles in all 3 habitats. Cycles were most pronounced in alfalfa, less pronounced in bluegrass, and barely discernible in tallgrass prairie. Food availability seems more important than vegetative cover for the success of M. ochrogaster. Densities of M. pennsylvanicus generally were very low in bluegrass and alfalfa habitats, both of which contained an abundance of preferred food plants. When M. pennsylvanicus was present in abundance in these 2 habitats, populations displayed annual or erratic fluctuations. Densities of M. pennsylvanicus were much higher in tallgrass prairie than in the other 2 habitats. Although vegetative cover seems more important than food availability for the success of M. pennsylvanicus, no evidence existed for population cycles in tallgrass prairie. We found no synchrony among population fluctuations of the 2 species of voles in the 3 habitats.

Balancing selection maintains polymorphisms at neurogenetic loci in field experiments

“…Changes in population density (40,41) can impact components of fitness through intraspecific competition (e.g., for food, mates, and territories). Competitive interactions for resources are often resolved by an individual's level of aggression, a behavior regulated by Avpr1a and Oxtr (13,47).…”

“…Assessing the role of sex follows the predominantly sexually divergent roles adopted by loci within the vasopressin-oxytocin pathway: variation in V1aR density in the brain typically is associated with the expression of behaviors in males that include spatial memory, mating behavior, offspring care, and aggressiveness (5,15,37), whereas variation in OTR density in the brain is associated more with female behaviors, such as maternal aggression, mother-infant bonding, and same-sex social interactions (30,38,39). Quantifying whether there is an interaction between genotype and population density is an extension of the ecology of many species, notably the prairie vole (40) and the bank vole (41), whose populations naturally experience periodic fluctuations in density that alter the extent of intraspecific competition, e.g., for food and breeding territories (41). Bank voles experience a decrease in reproductive success and survival probability as population density increases, and thus environmental heterogeneity can favor alternate genotypes (42).…”

The influence of immigration on demography of sympatric voles

“…The estimates of population densities and fluctuations within each site reported by Getz et al (2001) were used in our analyses. We also estimated overall ("metapopulation") monthly densities of each species in the general study area by averaging the monthly population densities of all study sites ( Fig.…”

“…Each month a 2-day prebaiting period was followed by a 3-day trapping session (Getz et al 2001). All study sites were trapped for three days each month; traps were checked at 0800 h and 1500 h. See Getz et al (2001) for details of the field protocol. At first capture, we toe-clipped all animals (2 toes on each foot) for individual identification.…”

From dispersal to landscapes: progress in the understanding of population dynamics

“…Examples are the species of Microtus in Illinois (Getz et al 1987(Getz et al , 2001, and the long-term pattern of density changes among the rodents in northern Sweden (Hörnfeldt 1994, Niklasson et al 1995. Even more challenging to conventional approaches was the discovery that various populations of the same species could vary in demographic behavior over space.…”