Die Versuche mit ausl?ndischen Holzarten in den bayerischen Staatswaldungen

Ohne Zusammenfassung     

Maximum likelihood and Bayesian approaches to stock assessment when data are questionable

This study examines the use of age-structured maximum likelihood and Bayesian approaches for stock assessment of the Namibian monkfish, Lophius vomerinus, resource with questionable data, in which time series are short, abundance indices are variable, and research data conflict with commercial data. Bayesian approaches with both noninformative and informative priors are investigated to determine if they enhance estimation stability. Three data scenarios are assessed: commercial and research survey data, research survey data only, and commercial data only. Both statistical approaches show that resource abundance has decreased with exploitable biomass estimated at approximately 44% of pristine levels. The maximum likelihood and the Bayesian approach with noninformative priors result in similar estimates. As the abundance data contained little information pertaining to possible density dependence within the stock–recruit relationship, only a Bayesian approach with informative priors reduces uncertainty in the steepness parameter h. Estimated management quantities are sensitive both to the set of data sources and whether prior information was informative or not. The strengths of the Bayesian approach include the integration of prior information with uncertain data, the exploration of data conflicts, and the ability to show the uncertainty in estimates of management parameters. Its weakness is that estimation stability is dependent on the choice of priors, which alters some posterior distributions of management quantities.     

Towards an ultimate explanation for mixed‐species shoaling

The formation of social groups has important impacts on fitness for many animal species, with differences in group compositions resulting in a range of fitness outcomes for individuals. Recent interest in mixed‐species grouping, which extends from a large body of literature invested in understanding single‐species grouping, highlights novel complexities of group formation which relate to phenotypic, behavioural and physiological differences that naturally exist between species. Among fishes, mixed‐species shoaling is a common form of social grouping behaviour displayed across a range of marine and freshwater ecosystems. Research explaining mixed‐species shoaling shows some overlap with explanations for single‐species shoaling; however, it also demonstrates that distinct differences between species give rise to unique cost‐benefit trade‐offs which need to be incorporated into conceptual models of mixed‐species shoaling behaviour. Unique predation related trade‐offs may arise from inefficiency of the confusion effect, variation in vigilance between species and unequal species‐preferences shown by predators, whilst unique foraging‐related trade‐offs may arise from diet partitioning, variations in foraging behaviour and differences in competitive abilities between species. We review the literature on fitness outcomes associated with mixed‐species shoaling and present a new theoretical framework to explain the cost‐benefit trade‐offs for individuals within mixed‐species shoals. The framework incorporates both trade‐offs arising from differences between species and those arising from group size, the former having been largely ignored due to a focus on single‐species shoaling. Our framework is designed to inform future research striving to explain mixed‐species shoaling behaviour.     

Effect of carotenoids and background colour on the skin pigmentation of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

Three 2‐factor experiments were conducted to determine the effects of background colour and synthetic carotenoids on the skin colour of Australian snapper Pagrus auratus. Initially, we evaluated the effects on skin colour of supplementing diets for 50 days with 60 mg kg^?1 of either astaxanthin (LP; Lucantin^® Pink), canthaxanthin (LR; Lucantin^® Red), apocarotenoic acid ethyl ester (LY; Lucantin^® Yellow), selected combinations of the above or no carotenoids and holding snapper (mean weight=88 g) in either white or black cages. In a second experiment, all snapper (mean weight=142 g) from Experiment 1 were transferred from black to white, or white to white cages to measure the short‐term effects of cage colour on skin L^*, a^* and b^* colour values. Skin colour was measured after 7 and 14 days, and total carotenoid concentrations were determined after 14 days. Cage colour was the dominant factor affecting the skin lightness of snapper with fish from white cages much lighter than fish from black cages. Diets containing astaxanthin conferred greatest skin pigmentation and there were no differences in redness (a^*) and yellowness (b^*) values between snapper fed 30 or 60 mg astaxanthin kg^?1. Snapper fed astaxanthin in white cages displayed greater skin yellowness than those in black cages. Transferring snapper from black to white cages increased skin lightness but was not as effective as growing snapper in white cages for the entire duration. Snapper fed astaxanthin diets and transferred from black to white cages were less yellow than those transferred from white to white cages despite the improvement in skin lightness (L^*), and the total carotenoid concentration of the skin of fish fed astaxanthin diets was lower in white cages. Diets containing canthaxanthin led to a low level of deposition in the skin while apocarotenoic acid ethyl ester did not alter total skin carotenoid content or skin colour values in snapper. In a third experiment, we examined the effects of dietary astaxanthin (diets had 60 mg astaxanthin kg^?1 or no added carotenoids) and cage colour (black, white, red or blue) on skin colour of snapper (mean weight=88 g) after 50 days. Snapper fed the astaxanthin diet were more yellow when held in red or white cages compared with fish held in black or blue cages despite similar feed intake and growth. The skin lightness (L^* values) was correlated with cage L^* values, with the lightest fish obtained from white cages. The results of this study suggest that snapper should be fed 30 mg astaxanthin kg^?1 in white cages for 50 days to increase lightness and the red colouration prized in Australian markets.     

The effect of oral oxidised copper wire on liver copper in farmed red deer

Twenty-two weaner red deer stags grazed on a marginally copper-deficient property were used to evaluate the effect on liver copper levels of log oxidised copper wire particles given orally. The deer were assigned to two groups on the basis of pre-trial liver copper levels, and grazed together for the duration of the trial from March to October. Liver biopsies were collected from treated and control deer on six occasions at monthly intervals and were analyzed for copper content.

Mean liver copper in the treated group rose from pre-treatment levels of 101.8μmol/kg to a peak of 849.6μmol/kg two months after copper administration. Thereafter, levels fell steadily until six months after administration when they averaged 84.8μmol/kg. The mean liver copper content of untreated deer rose from 102.7μmol/kg at the commencement of the trial, peaked at 255.3μmol/kg after two months, fell to 103μmol/kg one month later and remained low thereafter. The liver copper content in treated deer was significantly higher than for control deer for the duration of the study (p<0.0l for months 1–4 and 6, p <0.05 for month 5).

It is concluded that log oxidised copper wire particles acted to provide adequate liver copper stores for up to five months in deer grazed on a marginally copper-deficient property.     

A climatic analysis method for expert systems assisting tree species introductions

There is a need for improved methods to suggest whether a particular tree species is worth testing at a new location. A method is proposed which compares the climatic similarity of a potential new location with conditions within a species natural distribution, and identifies if similar sites exist. When information is available, climatic comparisons can also be made with successful sites of introduction outside the natural range. A program is described which carries out these comparisons and Eucalyptus citriodora is analysed as an example. It is concluded that the method offers advantages over systems which describe climatic requirements simply as ranges of suitable conditions. The importance of soil factors is recognised and ways in which these could be analysed along with climatic factors are noted. The integration of the similarity analysis into existing databases or its development as part of a complete expert system are discussed.     

Continuous monitoring of pop hole usage by commercially housed free-range hens throughout the production cycle

Free-range laying hens are able to move between the indoor house and range through exits termed pop holes. The aim of this study was to examine the proportion of the flock that used the pop holes and to identify patterns of movement throughout the flock cycle. Four flocks of free-range hens each of 1500 birds were studied. Ten per cent of each flock were tagged with RFID (radio-frequency identification) transponders and their pop hole activity studied throughout the production cycle. Within two weeks of tagging at 25, 35, 45, 55 and 65 weeks of age, approximately 80 per cent of the tagged birds were seen in the pop holes and 50 per cent of the tagged birds were seen on 80 per cent of the days available to them after tagging. Within the flock, subpopulations of birds could be identified: those that never ventured to the pop holes (approximately 8 per cent), those that used the pop holes very infrequently (approximately 8 per cent), those that sat in the pop holes (approximately 4 per cent), and those that used the pop holes frequently (approximately 80 per cent). There was an effect of age of the birds, time of day and daily mean temperature on pop hole usage. Additional factors affecting activity on particular days were wind speed, rainfall and hours of sunshine. The findings show that a significant proportion of the flock accesses the pop holes on a regular basis with only a very small proportion preferring to stay in the house.