Population models with environmental stochasticity

Two discrete population models, one with stochasticity in the carrying capacity and one with stochasticity in the per capita growth rate, are investigated. Conditions under which the corresponding Markov processes are null recurrent and positively recurrent are derived.     

Dynamics of intestinal coccidia in peak density Microtus agrestis, Microtus oeconomus and Clethrionomus glareolus populations in Finland

Study of seasonal changes in the occurrence of Eimeria spp. in Microtus agrestis, Clethrionomys glareolus and Microtus oeconomus populations in Finland showed distinct seasonal variation in all three host species: the peaks occurred in both prevalence and density of infection in early autumn. The low prevalence and density of eimerian infections before and during the main crash of vole populations in late winter indicate that these organisms, although potentially pathogenic, do not significantly contribute to the drastic decline in cyclic vole populations.     

Structural heterogeneity and spatial autocorrelation in a natural mature Pinus sylvestris dominated forest

The tree species composition, vertical stratification and patterns of spatial autocorrelation at the tree and quadrate (25 × 25 m) scales were studied in a natural mature PinuS sylvestris dominated forest in eastern Finland. For the analyses we mapped the locations and dimensions of trees taller than 10 m in a 9 ha (300 × 300 m) area, and within this area we mapped all trees taller than 0.3 m on a core plot of 4 ha (200 × 200 m). The overall tree size distribution was bimodal. the dominant layer and the understory forming the peak frequencies. Pinus sylvestris dominated the main canopy, together with scattered Betula pendula and Picea abies. Alnus incana, Populus tremula, Salix caprea, Sorbus aucuparia and Juniperus communis occurred only in the under- and middlestories. Autocorrelation analysis (semivarianee) of tree size variation revealed spatial patterns, which were strongly dependent on the size of trees included in the analysis. When all living trees, including the understory regeneration, were taken into account, the autocorrelation pattern ranged up to 35 m inter-tree distances, reflecting the spatial scale of understory regeneration patches. Competitive interaction among middle- and upperstory trees (height>10 m) had contrasting effects on autocorrelation pattern depending on spatial scale. At the fine scale, dominant trees suppressed their smaller close neighbors (asymmetric competition), which was shown as increased tree size variation at small inter-tree distances (<2 m). At slightly larger inter-tree distances, specifically among large trees of similar size, competition was more symmetrical, which resulted in decreased tree size variation at these inter-tree distances (3–4 m). This effect was seen most clearly in the dominant trees, there being a clear autocorrelation pattern in tree size up to inter-tree distances of ～4 m. At the quadrate scale (25 × 25 m) the analysis revealed high local variation in structural characteristics such as tree height diversity (THD), tree species diversity (H) and autocorrelation of tree height. The analysis suggests that naturally developed P. sylvestris forests exhibit complex small-scale patterns of structural heterogeneity and spatial autocorrelation in tree size. These patterns may be important for stand-scale habitat diversity and can have aggregated effects on ecosystem dynamics at larger spatial scales though their influence on the spread of disturbance and regeneration after disturbance.     

Structure of Cytokine Hydrophobic Cores

Diagrams were constructed that describe, using a common frame of reference, the interactions that occur within the hydrophobic cores of the left-handed four-helix bundles of interleukin-2, -4, -5, granulocyte/macrophage-, granulocyte-, macrophage-colony-stimulating factor, β- and γ-interferon, growth hormone, and leukemia inhibitory factor. Based on the assumption that the topologies of the ligand-receptor complexes are similar, analogous patterns were obtained from these diagrams and lead to the detailed comparison of the hydrophobic cores. These patterns were then used to obtain pairwise rigid-body superpositions among all of the four-helix bundles: values of the root-mean-square deviations (Cα-atoms) over the four α-helices of the bundles range from 1.14 Å to 3.22 Å. Two distinct groups are formed after clustering based on structural superposition of the ten cytokines.     

The effect of two growth forms of Norway spruce on stand development and radiation interception: a model analysis

Summary Development of tree and canopy structure, and interception of photosynthetically active radiation (PAR) were studied in two model stands of Norway spruce consisting of trees with rapid versus slow site capture. The tree models were derived using Burger's (1953) sample tree material, from which two subpopulations of dominant trees were selected using the rate of horizontal site capture of the tree crowns as the criterion of division. The development of stand structure and interception of PAR were simulated in the two model canopies. The simulation period covered the period from tree age 15–80 years. The average development of the trees in the two subpopulations proved to be very different. The rapidly expanding trees were characterized by low mean within-crown needle area density and a long crown. The slowly expanding trees were smaller but had a higher mean within-crown needle area density. Up to approximately 40 years of age the stand of rapidly expanding trees contained more leaf area and intercepted more radiation than the stand of slowly expanding trees, when canopy cover was held constant. After 40 years of age this relationship was reversed due to the subsequent decline of leaf area in the stand of rapidly expanding trees and the increase in leaf area in the stand of slowly expanding trees. The biological relevancy and silvicultural implications of the simulated patterns of tree and stand development are discussed.     

The use of fallout 137Cs and 239,240Pu for dating of lake sediments

The distribution of ¹³⁷Cs and ^239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of ¹³⁷Cs and ^239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950's can be estimated from the ¹³⁷Cs and ^239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg^–1 dry wt for ¹³⁷Cs and ^239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for ¹³⁷Cs and ^239,240Pu in the lakes investigated. A slight migration of ^239,240Pu and ¹³⁷Cs was found and the migration of ¹³⁷Cs seems to be higher than that of ^239,240Pu. The advantages of ¹³⁷Cs dating method are rapidity and simplicity. ^239,240Pu is preferable when the sample size is small. The agreement found between ¹³⁷Cs and ^239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years.     

Immunohistochemical demonstration of carbonic anhydrase

Summary Rabbits were immunized using human erythroxyte carbonic anhydrase B (HCA B) purified. by the modified methods of Armstrong et al. (1966) and Bernstein and Schraer (1972). The globulin fraction was isolated by ammonium sulphate precipitation. The anti-HCA B globulin was specific, when judged using the double diffusion technique of Ouchterlony and immunoelectrophoresis. No cross reaction with human erythrocyte carbonic anhydrase C was found, but cross reactions with erythrocyte carbonic anhydrase from rat, mouse and guinea pig were observed. Fluorescein isothiocyanate conjugated goat anti-rabbit globulin was used for the localization of HCA B in tissue sections and erythrocytes on slides.