Population density and the intensity of paternity assurance behaviour in a monogamous wader: the Curlew Numenius arquata

We compared paternity assurance behaviour and related displays in high (1.6 pairs perkm²) and low (6.7 pairs per km²) density populations of the Curlew Numenius arquata breeding on arable farmland in western Finland. There was little evidence of individuals pursuing extra-pair copulations or males exhibiting paternity assurance behaviour. Furthermore, there was no variation in the frequency of intrusions or in the intensity of paternity assurance behaviour relative to lay date. However, intrusions and approaches to the pair female by extra-pair males were more frequent at high breeding density, and pair males remained closer to their female, followed her more and exhibited a higher frequency of copulatory behaviours in the high-density population. Therefore, high breeding density appeared to increase opportunities for individuals to copulate outside the pair-bond and resulted in more intense male paternity guards. Male song flight displays were also more frequent in the high-density population. Territorial absences by males were infrequent in both areas. The increased frequency of intrusions and interactions between non-pair individuals (male-male and male-female) at high density were probably the major factors in explaining area differences in the intensity of paternity assurance and territorial behaviour.     

Long-term microtine dynamics in north Fennoscandian tundra: the vole cycle and the lemming chaos

Densities of microtine rodents in two habitat complexes in the tundra of Finnmarks-vidda, Norwegian Lapland, were studied during 1977-89 by means of snap trapping (Small Quadrat Method) Predator populations were studied by mapping breeding raptors and by snow-tracking small mustelids During 1977-85, snow-trackmg was conducted only during peak and decline years, whereas during 1986-89, snow-tracking was conducted every winter (November-December) and live-trapping (in August) was used as an additional method
Lowland vole populations had regular density fluctuations with peaks in 1978-79. 1982-84 and 1987-88 Highland vole populations fluctuated less regularly and at lower over-all densities Highland lemming populations had two outbreaks, in 1978 and 1988, ending in abrupt winter crashes In the lowland, outbreak levels were reached only in 1978 All microtine declines in relatively productive lowland habitats were accompanied by intense activity of small mustelids. whereas avian predators were common only in 1983 Lowland declines also showed clear between-habitat asynchrony they started in areas with an exceptional abundance of productive habitats and then spread to more barren areas These lowland data are consistent with the hypothesis of a mustelid-microtine limit cycle, although also several other hypotheses remain unrefuted The highland lemming data suggest a simple exploiter-victim interaction between lemmings and the vegetation     

Habitat use of small mustelids in north Fennoscandian tundra: a test of the hypothesis of patchy exploitation ecosystems

The habitat use of small mustelids in a tundra area in Norwegian Lapland was studied chiefly by means of snow-tracking 1986-89 Stoats showed strong peference to a habitat complex immediately beneath the thrust line of the Scandes, with exceptional abundance of luxuriant habitats, whereas weasel activity was more evenly spread over the lowland tundra Mustelid activity on the high tundra above the thrust line was consistently low Within each subarea. stoat activity was concentrated to the most luxuriant habitats Similar preferences were shown by weasels on the lowland but not in the vicinity of the thurst cliff Daily movements of both species varied from local (c 200 m) to extensive (up to 4 km), no consistent interspecific differences in travel distances could be observed
The results largely conform to the hypothesis of patchy exploitation ecosystems (T Oksanen 1990a), according to which predator activity tends to "spill over' from luxuriant habitats, capable of supporting predator populations, to adjacent barren ones, due to despotic behavior within and between species and due to opportunistic predation by transient predators However, predator activity in barren habitats during the crash winter could not be explained by these mechanisms alone A third mechanism - breakdown of habitat preferences of predators during crash phases of a cyclic prey population - was thus introduced     

Trophic levels and trophic dynamics: A consensus emerging?

There are three clearly different views on trophic levels. The systems-ecological tradition sees trophic levels as relatively discrete and well-defined units whose interactions cannot be derived from interactions between constituent populations. The reductionist population-ecological tradition sees trophic levels as inappropriate abstractions that cannot be used in formulating predictive theories. The tradition of trophic dynamics sees the first three trophic levels of autotroph-based ecosystems as reasonable abstractions, useful in formulating predictive theories, but devoid of properties that could not be directly extrapolated from those of constituent populations. Recent literature suggests that the first two schools are converging towards the viewpoints of the third, though the latter has also been modified by the interaction.     

The Liver Cells in Acute Starvation and Refeeding

A series of 52 young male white laboratory mice were starved for a maximum of five days, and 45 normally fed animals were used as controls. A group of experimental animals and a corresponding control group were sacrificed after two, three, and four days' starvation and after six, 12 and 17 days' refeeding. Even after two days the animals had lost weight, and the liver cells had diminished highly significantly. A return to the initial values was noted after 12 days' refeeding. In the experimental animals a strong negative correlation was noted between the cell count per field and body weight (r =–0.712, b =–7.520), while no such correlation was observed for the controls. The volume of the liver cells was reduced by 61.7 %, the volume of their nuclei by 16.2 % after four days' starvation. After two to three days' starvation the liver cells often showed a slight accumulation of fat. Mitoses were frequent in the liver cells during the stage of regeneration, when the cells had attained the same size as in the controls.     

Fatty Tissue in Starved Lambs a Histoquantitative and Statistical Study

The kidney fat was histologically examined of 27 spontaneously dead lambs of which 14 had starved. The lambs were born with mature fat, but in young animals a starvation period of more than 24 hrs. reduced the fat tissues and changed its cells towards the embryonal type built up of preadipocytes. These cells were smaller than the mature fat cells. Nucleus was large, round and situated in the centre of the cell. The slight eosinophilic, strongly diminished cytoplasm was some granulated and had some small fat droplets. The starvation changes of fat cells did not depend on the weight of animals or on the age of lambs less than two weeks.     

Attachment and detachment of bacteria on surfaces with tunable and switchable wettability

Controlling accumulations of unwanted biofilms requires an understanding of the mechanisms that organisms use to interact with submerged substrata. While the substratum properties influencing biofilm formation are well studied, those that may lead to cellular or biofilm detachment are not. Surface-grafted stimuli-responsive polymers, such as poly (N-isopropylacrylamide) (PNIPAAm) release attached cells upon induction of environmentally-triggered phase changes. Altering the physicochemical characteristics of such polymeric systems for systematically studying release, however, can alter the phase transition. The physico-chemical changes of thin films of PNIPAAm grafted from initiator-modified self-assembled monolayers (SAMs) of ω-substituted alkanethiolates on gold can be altered by changing the composition of the underlying SAM, without affecting the overlying polymer. This work demonstrates that the ability to tune such changes in substratum physico-chemistry allows systematic study of attachment and release of bacteria over a large range of water contact angles. Such surfaces show great promise for studying a variety of interactions at the biointerface. Understanding of the source of this tunability will require further studies into the heterogeneity of such films and further investigation of interactions beyond those of water wettability.