Elmer C. Birney

Importance of Vegetative Cover to Cycles of Microtus Populations

A hypothesis is presented that a site-dependent threshold level of vegetative cover is necessary for a population of Microtus to increase in numbers sufficiently to undergo a multi-year cycle. The hypothesis is supported by results of studies in grassland habitats in the tallgrass prairie of Oklahoma and Minnesota, the mixed grass prairie of South Dakota, and the shortgrass prairie of Colorado. Levels of cover below the threshold sometimes support resident, breeding populations of voles. Levels above the threshold may influence amplitude, duration, and synchrony of Microtus cycles.

Parental care and mating system of the prairie vole, Microtus ochrogaster

Summary1.The mating system of prairie voles (Microtus ochrogaster) was investigated by experimentally manipulating the sexual composition of vole societies, thereby providing each vole with a variety of mating choices.2.In male-female pairs, both parents appeared to contribute equally to the care of young, with the exception of lactation. Paternal activities included nest and runway construction, food caching, and grooming, retrieving, and brooding the young.3.Voles in 26 of 27 societies mated monogamously; those in the other group mated polygynously.4.Nonreproductive voles in the experimental societies generally lived in communal groups. Communal groups are known to occur in field populations of prairie voles, but it is not known if they exist during periods of reproductive activity.5.We address the questions of the adaptive significance of voles living communally and we consider the relationship between communal voles and dispersing voles in nature. The results of this study were interpreted relative to four mating systems that may be associated with paternal care in mammals. We conclude that M. ochrogaster is basically monogamous; a verbal model is presented for the evolution of monogamy in this species.

Structure and Productivity of Grassland Small Mammal Communities Related to Grazing-Induced Changes in Vegetative Cover

Effect of grazing on the structure and productivity of small mammal communities in four types of North American grasslands is examined quantitatively using data collected during a 4-year period. Small mammal communities in tallgrass and montane grasslands appear more affected by grazing and the subsequent reduction in vegetative cover (=total above-ground standing crop of plants) than do small mammal communities in shortgrass and bunchgrass grasslands. This trend is evident when small mammals in grazed versus ungrazed habitats are compared with regard to mean community biomass, annual community respiration, production, and consumption, mean species diversity and evenness, proportional species and functional group composition, seasonal dynamics of community biomass, and temporal variation in proportional species composition. These results lend further support to the hypothesis that the general composition of grassland small mammal communities is determined primarily by structural attributes of the habitat.

Small Mammal Community Structure in North American Grasslands

The structure of small mammal communities in nine North American grassland types is examined quantitatively utilizing data collected during a 4-year period. Small mammals in each grassland type are divided into groups according to species, size, reproductive strategy, life form, seasonality of activity, and diet. Observed spatio-temporal patterns of faunal composition are related to differences in structure of the different grassland ecosystems. The structural differences identified as being most important are primarily those related to latitudinal and moisture gradients. Temporal variability of small mammal community composition is characteristic of all grassland types. The degree of temporal variability is not easily related to structural differences of the grasslands studied.

EFFECT OF LIGHT INTENSITY ON ACTIVITY PATTERNS OF PATAGONIAN LEAF-EARED MICE, PHYLLOTIS XANTHOPYGUS

Abstract The effect of light intensity on activity was investigated in a study of captive leaf-eared mice, Phyllotis xanthopygus. This nocturnal mouse lives in rocky outcrops but forages in open areas with little vegetative cover. Primary predators are raptors and canids, all of which are expected to have increased hunting success under higher levels of moonlight. Because of this correlation between light intensity and predation risk, we predicted that increased light intensity during the dark period would result in decreased nocturnal activity. Data were collected continuously for 3 days under varying light intensities and were analyzed using cosinor analysis to estimate parameters describing the activity rhythm (mesor, amplitude, and acrophase). Number of diurnal activity bouts increased after exposure to light intensities similar to full moonlight (3.0 lux). Total activity of mice in middle (1.5 lux) and high (3.0 lux) light treatments was depressed as evinced by significantly lower mesor and amplitude estimates compared with those of mice in control conditions (0.0 lux). The acrophase also was significantly different between the control and the 2 treatment groups.

Characteristics of Dispersing Meadow Voles Microtus pennsylvanicus

A population of meadow voles Microtus pennsylvanicus in Minnesota exhibiting annual rather than multiannual fluctuations in density was studied. To characterize voles of different movement patterns, data on sex, age, reproductive condition and genotype at two polymorphic loci (Tf arid LAP) were collected in summer (n = 1323) and autumn (n = 1191) during 2 consecutive years. Three movement patterns were identified: (1) dispersers were those voles that moved onto grids from which all trapped Microtus were removed; (2) residents were those voles found on the same grid during at least two trapping periods; (3) movers were those voles known to move long distances within a population. The following conclusions were drawn. (1) Dispersers differed from residents most consistently by being more likely to be young. Although dispersers also differed from residents both reproductively and genetically, the differences were not consistent for all age-sex groups throughout the study. (2) Movers were an identifiable subset of residents that differed from dispersers and other residents during summer by being more likely to be adult males. (3) During the breeding season, female residents were the most stable subset of the population, whereas adult males tended to move long distances within the population. Young females tended to disperse close to the time of initiating reproductive activity; young males tended to disperse as nonreproductives. During the nonbreeding season, dispersers were more nearly a random subset of residents. INTRODUCTION Dispersal, movement away from home resulting in at least temporary transience for an individual (Lidicker, 1975), can have both demographic and evolutionary effects in populations (for review see Gaines and McClenaghan, 1980). Evolutionarily, it affects gene flow and thus patterns of genetic change within and between populations (Anderson, 1970; Endler, 1977; Levin, 1976; Weins, 1976). In addition, the adaptive advantage of dispersal is unclear. Dispersers presumably encounter some or all of a multitude of risks inherent in traversing unfamiliar habitat. If dispersal is adaptive to individuals, then reproductive benefits such as outbreeding, finding new resources and avoiding aggression from conspecifics must on average outweigh the risks (Lidicker, 1962, 1975). Alternatively, dispersal behavior may not be adaptive to individuals; theoretically, it can evolve by parental manipulation (Hamilton and May, 1977) or by group selection (Van Valen, 1971). From the point of view of population biology, dispersal is of interest for two basic reasons. First, dispersal patterns may correlate with other life history characteristics (e.g., lifespan, age to first reproduction, and habitat, Pianka, 1970); thus, information on dispersal can aid in understanding the life history pattern of a population (Fairbairn, 1978). Secondly, dispersal can affect population density (Krebs and Myers, 1974; Lidicker, 1978; Finerty, 1980) and may alter the social structure of populations in such a way as to affect density (Charnov and Finerty, 1980). To test two hypotheses regarding dispersal in a population of Microtus pennsylvanicus, we established removal grids in both optimal and suboptimal habitat of a noncyclic population of M. pennsylvanicus in Minnesota. The objective of the research was to characterize voles of differing movement patterns (dispersers, movers and residents) with regard to sex, age, reproductive condition and genotype at the transferrin and Present address: BSCS, Box 930, Boulder, Colo. 80027. 2To whom reprint requests should be addressed.

Plants, small mammals, and the hierarchical landscape classifications of Patagonia

Assemblages of plants were studied at 14 sites in northern Patagonia corresponding to localities at which we (Monjeau et al. 1997) earlier studied the relationship between small mammal assemblages and landscape classifications. This allowed us to test predictions that both plants and small mammals correspond to the more inclusive hierarchical landscape divisions but that plants track better than small mammals the less inclusive divisions. Species presence or absence of plants at each locality was used in a series of multivariate analyses and compared by correlation analysis with those generated from small mammal species data. Assemblages of both plants and small mammals corresponded to the upper divisions, which are based on climatic and geomorphological features, but small mammal assemblages did not correspond to the lower divisions of the landscape classifications. Three factors are considered as explanations for the observed differences between plants and small mammals: a) small mammal habitat is determined more by plant growth form than by plant species; b) trophic level differences between the two groups; and c) species pool size affects the resolution of microhabitat correspondence. Our data indicate that both plant assemblages and small mammal assemblages respond to climatic and geomorphological features, which is in contrast to the paradigm that mammal assemblages simply follow plant assemblages. We also attempted to reconcile classification systems in Patagonia by proposing a nomenclatural system based on a hierarchical classification. In the system proposed, ecoregion is the lowest division small mammal assemblages can recognize in Patagonia. Finally, we conclude that the hierarchical nature of landscapes based on a holistic view of environments reflects real entities that are not just the perceptions of landscape ecologists.

An improved assay for l-gulonolactone oxidase

Abstract A rapid quantitative assay for l -gulonolactone oxidase in mammalian liver is described. It involves solubilizing the enzyme by homogenizing liver in a solution containing sodium deoxycholate. Recovery of enzyme is greater than in procedures utilizing whole homogenates or those in which microsomes are isolated by differential centrifugation. The effects on enzyme activity of various conditions of sampling and storing liver prior to analysis were determined.

EVOLUTION OF AN ENZYME SYSTEM: ASCORBIC ACID BIOSYNTHESIS IN MONOTREMES AND MARSUPIALS

L-ascorbic acid, vitamin C for those species dependent on an exogenous source, is a physiologically essential molecule for all multicellular animals. Nevertheless, some species of birds and mammals lack and apparently have lost the capacity to synthesize it. Some vertebrate species synthesize it in liver, some in kidney, and some in both. It has been the goal of our research for several years to understand the evolution of the ascorbic acid pathway in vertebrates, as a model for the study of (1) regressive (=streamlining) evolution, (2) tissue locus shifts in biochemical pathways, and (3) the operation of selection on the ability of animals to regulate the production of an essential molecule. We here present data on the activity and tissue locus of L-gulonolactone oxidase (GLO) (EC1.1.3.8) in the Monotremata and Marsupialia and integrate these data into an hypothesis of the evolution of ascorbate biosynthesis in vertebrates. GLO catalyzes the final step, conversion of L-gulonolactone to L-ascorbic acid, in the pathway by which the latter is synthesized from D-glucose (Dagley and Nicholson, 1970; Chatterjee, 1973a). Although few species of most higher taxa have been examined, invertebrates (Gupta et al., 1972; Chatterjee, 1973b), teleost fish (Chatterjee, 1973a; Andrews and Murai, 1975), some birds (Chaudhuri and Chatterjee, 1969), and a few mammals (Chatterjee, 1973a), appear to lack GLO, and thus are unable to synthesize ascorbate. Lungfish (D. E. Dykhuizen, pers. comm.), amphibians, reptiles, and most birds are reported to have GLO in the kidney whereas eutherian mammals and some birds have it in the liver (Chatterjee, 1973a). We recently demonstrated (Birney et al., 1979) GLO activity in kidney of monotremes and in both liver and kidney in bandicoots and in some macropods. Prior to that report, the Virginia opossum (Didelphis virginiana) was the only noneutherian mammal studied, and it was believed to be capable of synthesizing ascorbate in liver on the basis of dehydrogenation of L-gulonolactone as determined histologically (Nakajima et al., 1969). The basic evolutionary relationship and times of divergence for the three major groups of mammals, Prototheria, Metatheria, and Eutheria, are reasonably well understood (Hopson and Crompton, 1969; Crompton and Jenkins, 1973; Lillegraven, 1974; Clemens, 1977). Furthermore, Ride (1964), Kirsch (1977a, 1977b), and Kirsch and Calaby (1977) have greatly enhanced our knowledge of the evolutionary relationships within the Marsupialia. Thus we feel that the relationships of the major groups of mammals discussed herein are adequately known so that we can superimpose the pattern of GLO activity on this phylogeny and initiate an understanding of the evolution of the biochemical system involved by proposing and evaluating some preliminary hypotheses.

Variation of l-gulonolactone oxidase activity in placental mammals

Abstract 1. 1. The activity of l -gulonolactone oxidase (EC 1.1.3.8) in livers of 49 species of eutherian mammals varied intraspecifically among individuals; coefficients of variation were 0.2 to 0.4 in many species. 2. 2. Differences observed in l -gulonolactone oxidase activity among strains of laboratory rats and domestic rabbits are probably genetically controlled. 3. 3. Pronounced sex differences in l -gulonolactone oxidase activity were found in some species, particularly in the genera Peromyscus, Reithrodontomys and Onychomys. 4. 4. Mormota monax exhibited seasonal variation in l -gulonolactone oxidase somewhat like that previously observed in Sylvilagus floridanus; no such seasonal variation was found in Sciurus carolinensis. 5. 5. Hibernation did not affect l -gulonolactone oxidase activity in Spermophilus tridecemlineatus. 6. 6. In four species of rodents, Microtus ochrogaster, Tylomys panamensis, Octodon degus and Sigmodon hispidus, l -gulonolactone oxidase activity was not affected by the level of dietary ascorbate.