No abstract

In this study we explore the relationships between demography, patterns of habitat use, and the diets selected by Lemmus and Dicrostonyx at Igloolik Island, N.W.T. The demography of both species at Igloolik is similar to that recorded at other localities, but maximal densities vary between sites and may be related to the abundance of suitable forage. Home range characteristics and patterns of habitat use in each lemming species are related to the spatial and temporal distribution of preferred foods: in summer, Lemmus uses low-lying wet meadow habitats dominated by graminoids and mosses, whereas Dicrostonyx uses mainly upland dry heaths dominated by shrubs; in winter, both species make greater use of moist transitional habitats. Although the two species differ in their patterns of resource use, these differences may be altered through interspecific and intraspecific interactions.

The acetylene reduction assay was used to examine biological nitrogen fixation in the high arctic tundra at Sarcpa Lake, Northwest Territories (68°32′ N, 83°19′ W). The highest rates of acetylene reduction (9.37 ± 3.19 μmol C2H4 m−2 h−1) were in habitats that had a high density of the legumes Oxytropis maydelliana, O. arctobia, and Astragalus alpinus. Nitrogen fixation in the wet soils along the shore of a small lake was similar (8.87 ± 4.35 μmol C2H4 m−2 h−1) because of the blue-green alga Nostoc, which associates with mosses. Free-living blue-green algae and lichens made insignificant contributions to the total nitrogen fixation budget because they were uncommon and fixed nitrogen at a slower rate. Nitrogen-fixing lichens in the area included Stereocaulon arenarium and S. rivulorum. It is concluded that legumes have a significant input to the biological nitrogen fixation budget at Sarcpa Lake.

RODGERS, A. R., and M. C. LEWIS. 1985. Diet selection in Arctic lemmings (Lemmus sibericus and Dicrostonyx groenlandicus): food preferences. Can. J. Zool. 63: 1 16 1 -1 173. Testing of hypotheses relating lemming population dynamics to their food supply requires a detailed understanding of several major components of the diet selection process such as requirements, availability, preference, and selectivity. In this study, food preferences of Arctic lemmings were determined in cafeteria trials: Lemmus preferred graminoids and moss, while Dicrostonyx preferred shrubs and herbs. The stability of these preference patterns in each species was tested in further experimental cafeteria trials. Individuals of both species were pretreated on one of several diets, and two main types of trial were conducted involving limited and unlimited availability of test foods. Naive animals of both species, born and raised in captivity on artificial diets, were also used in the trials. In all cases, preference patterns in each species were maintained, suggesting that they are strongly heritable. Comparison of preference indices to the physical and chemical characteristics of tundra plants indicates that preference patterns in both species are related primarily to macronutrients and caloric content. Differences between Lemmus and Dicrostonyx are determined by secondary compounds and the physical characteristics of the plant species preferred by each. Comparison of ingestion rates and digestibility coefficients indicate that Dicrostonyx has a greater capacity than Lemmus in dealing with the negative characteristics of plants, such as secondary compounds or the presence of plant "hairs ." ROWERS, A. R., et M. C. LEWIS. 1985. Diet selection in Arctic lemmings (Lemmus sibericus and Dicrostonyx groenlandicus): food preferences. Can. J. Zool . 63: 1 1 6 1 -1 1 73.La vkrification des hypotheses qui relient la dynamique des populations de lemmings a leurs habitudes alimentaires suppose d'abord une bonne comprkhension des principaux aspects du processus de sklection de leur nourriture: besoins, disponibilitk, prkfkrences et ~Clectivitk. Au cours de cette ktude, la prkfkrence des lemmings de l'arctique pour certains aliments a Ctk dkterminCe par des expkriences du type "cafktkria"; Lemmus prkfere les graminoi'des et les mousses, alors que Dicrostonyx prCEre les buissons et les herbackes. La stabilitk de ces prkfkrences a aussi fait l'objet d'exphiences de type "cafCtkria": plusieurs individus des deux eswces ont d'abord resu chacun un type diffkrent de nourriture, puis ont kt6 soumis a la prksence de types de nourriture divers en quantitk limitke ou en quantitk illimitke. Des animaux "nai'fs" des deux esp&ces, nks et nourris en captivitC a des rCgimes artificiels, ont semi kgalement au cours de ces exp6riences. Dans tous les cas, les prkfkrences de chaque esp&ce se sont maintenues, ce qui indique qu'elles sont fortement hkrkditaires. Les indices de prkfkrence des deux espkces ont Ct C confrontCs aux caractkristiques physiques et chimiques des pla...

Summary Genecological differentiation of leaf dissection and size in European samples of Geranium sanguineum L. is considered against a background of the ecological behaviour of this species. The differentiation is analysed using Variance Analysis and shown to be closely correlated with a community classification based on eco‐geographical indicator species; leaf dissection is correlated with the ‘continentality’ and leaf size with the ‘openness’ of the original community. The variation in both cases is ecoclinal. The importance of morphological differentiation to studies of adaptation is discussed in the light of current knowledge.