Optimal decision rules for herring gulls

A measure of fitness applicable to herring gull (Larus argentatus) life histories is introduced and related to short-term risks which depend on behaviour. This allows calculations of the relationship between fitness and behaviour if one can measure the risks an animal takes behaving in particular ways in specified situations. This method is used to evaluate the fitness of herring gulls during the incubation period at Walney Island, U.K. Two causes of egg mortality are considered, death by predation and death by exposure, and the latter is shown to be less important than the former. The chances of death by predation depend on the number of adults present on the territory and are estimated to be approximately 0·045 eggs per h if no parents are present on territory, 3·5×10^?4 eggs per h if one parent is present and 6·7×10^?4 eggs per h if two parents are present. Adult death by starvation is assumed to occur when energy reserves are exhausted; however a fitness cost is incurred if an animal maintains excess energy reserves. To restrict the number of behaviour sequences examined to manageable proportions, attention is restricted to the behaviour sequences that result from decision rules in which feeding occurs when energy reserves fall below a set point. Then optimal behaviour is characterized by (1) energy reserves maintained between 500 and 1200 kcal; (2) complementarity of mates' feeding preferences such that at least one of the pair feeds at a refuse tip; (3) parental desertion of offspring if energy reserves fall below 200 kcal; (4) parents spending the minimum possible time together on territory. These results are shown by sensitivity analysis to be insensitive to parameter errors in the model. Treating these characteristics of optimal behaviour as predictions about actual behaviour reveals that predictions 1 and 2 are correct, and prediction 4 is wrong. An experiment was designed to test prediction 3 by estimating the fat reserves of life birds and measuring how long each would continue incubation in the absence of its mate. Fatter birds did continue incubation for longer though the quantitative detail did not match prediction 3 exactly. Thus two aspects of behaviour tally with our calculation as to what is optimal, but one does not. This conclusion is discussed.     

Morphological variation in the horse: defining complex traits of body size and shape

Horses, like many domesticated species, have been selected for broad variation in skeletal size. This variation is not only an interesting model of rapid evolutionary change during domestication, but is also directly applicable to the horse industry. Breeders select for complex traits like body size and skeletal conformation to improve marketability, function, soundness and performance in the show ring. Using a well-defined set of 35 measurements, we have identified and quantified skeletal variation in the horse species. We collected measurements from 1215 horses representing 65 breeds of diverse conformation such as the American Miniature, Shetland Pony, Arabian Horse, Thoroughbred, Shire and Clydesdale. Principal components analysis has identified two key dimensions of skeletal variation in the horse. Principal component 1 is positively correlated with every measurement and quantifies overall body size. Principal component 2 captures a pattern of bone widths vs. lengths and thus quantifies variation in overall bone thickness. By defining these complex skeletal traits, we have created a framework for whole genome association studies to identify quantitative trait loci that contribute to this variation.     

The extended Moran effect and large-scale synchronous fluctuations in the size of great tit and blue tit populations

1. Synchronous fluctuations of geographically separated populations are in general explained by the Moran effect, i.e. a common influence on the local population dynamics of environmental variables that are correlated in space. Empirical support for such a Moran effect has been difficult to provide, mainly due to problems separating out effects of local population dynamics, demographic stochasticity and dispersal that also influence the spatial scaling of population processes. Here we generalize the Moran effect by decomposing the spatial autocorrelation function for fluctuations in the size of great tit Parus major and blue tit Cyanistes caeruleus populations into components due to spatial correlations in the environmental noise, local differences in the strength of density regulation and the effects of demographic stochasticity. 2. Differences between localities in the strength of density dependence and nonlinearity in the density regulation had a small effect on population synchrony, whereas demographic stochasticity reduced the effects of the spatial correlation in environmental noise on the spatial correlations in population size by 21.7% and 23.3% in the great tit and blue tit, respectively. 3. Different environmental variables, such as beech mast and climate, induce a common environmental forcing on the dynamics of central European great and blue tit populations. This generates synchronous fluctuations in the size of populations located several hundred kilometres apart. 4. Although these environmental variables were autocorrelated over large areas, their contribution to the spatial synchrony in the population fluctuations differed, dependent on the spatial scaling of their effects on the local population dynamics. We also demonstrate that this effect can lead to the paradoxical result that a common environmental variable can induce spatial desynchronization of the population fluctuations. 5. This demonstrates that a proper understanding of the ecological consequences of environmental changes, especially those that occur simultaneously over large areas, will require information about the spatial scaling of their effects on local population dynamics.     

Exotic grasses and nitrate enrichment alter soil carbon cycling along an urban–rural tropical forest gradient

Urban areas are expanding rapidly in tropical regions, with potential to alter ecosystem dynamics. In particular, exotic grasses and atmospheric nitrogen (N) deposition simultaneously affect tropical urbanized landscapes, with unknown effects on properties like soil carbon (C) storage. We hypothesized that (H1) soil nitrate (NO₃^?) is elevated nearer to the urban core, reflecting N deposition gradients. (H2) Exotic grasslands have elevated soil NO₃^? and decreased soil C relative to secondary forests, with higher N promoting decomposer activity. (H3) Exotic grasslands have greater seasonality in soil NO₃^? vs. secondary forests, due to higher sensitivity of grassland soil moisture to rainfall. We predicted that NO₃^? would be positively related to dissolved organic C (DOC) production via changes in decomposer activity. We measured six paired grassland/secondary forest sites along a tropical urban‐to‐rural gradient during the three dominant seasons (hurricane, dry, and early wet). We found that (1) soil NO₃^? was generally elevated nearer to the urban core, with particularly clear spatial trends for grasslands. (2) Exotic grasslands had lower soil C than secondary forests, which was related to elevated decomposer enzyme activities and soil respiration. Unexpectedly, soil NO₃^? was negatively related to enzyme activities, and was lower in grasslands than forests. (3) Grasslands had greater soil NO₃^? seasonality vs. forests, but this was not strongly linked to shifts in soil moisture or DOC. Our results suggest that exotic grasses in tropical regions are likely to drastically reduce soil C storage, but that N deposition may have an opposite effect via suppression of enzyme activities. However, soil NO₃^? accumulation here was higher in urban forests than grasslands, potentially related to of aboveground N interception. Net urban effects on C storage across tropical landscapes will likely vary depending on the mosaic of grass cover, rates of N deposition, and responses by local decomposer communities.     

A spatial analytical approach for selecting reintroduction sites for burbot in English rivers

1. Availability of suitable habitat is a prerequisite for species reintroduction success, and to ensure population persistence, investigations of a species’ habitat utilisation throughout its life history should be conducted as part of a feasibility study. 2. Habitat utilisation models for burbot, Lota lota, developed using data from field studies conducted in France and Germany and information from the literature were used to assess the feasibility of reintroducing burbot into rivers of its former native range in eastern England. 3. Per cent tree roots, aquatic vegetation and flow types were important predictors of adult burbot abundance. Furthermore, the habitat utilisation models were supplemented with information from the literature, which suggested that off‐channel habitat such as wetlands and backwaters is important for spawning and nursery stages. 4. An assessment of the habitat availability in the rivers of the burbot’s former native range using variables related to spawning and nursery and adult life stages showed that although adult habitat was widely distributed, the availability of spawning and nursery habitat was less abundant, potentially limiting successful reestablishment. 5. Potential suitable habitat was concentrated in the central and southern areas of the species’ former English distribution. Overall, rivers of the burbot’s former range potentially afford suitable habitat to sustain a reintroduced population. However, sites should be preferentially selected on the basis of having appropriate spawning and nursery areas.     

Effect of ante- and postmortem hide clipping on the microbiological quality and safety and ultimate pH value of beef carcasses in an EC-approved abattoir

Aims:  Effect of ante- and postmortem hide clipping on the microbiological quality of beef carcasses. Methods and Results:  Bovine carcasses (362) were tested for indicator micro-organisms and the presence of pathogens. Prior to slaughter, hide cleanliness of each animal was categorized on a scale of 1–5 (clean to dirty). Lowest mean aerobic colony counts (ACC) (log₁₀ 3·0 CFU cm⁻²) came from carcasses where clipping had been performed in lairage, antemortem. ACC from animals clipped online (log₁₀ 3·2 CFU cm⁻²) were significantly higher (P < 0·05) than those clipped in lairage, but comparable to those carcasses from Category 1 and 2 animals. There were no significant differences in the detection of pathogens from any of the carcass groups. Ultimate pH values for carcasses from Category 3 and 4 animals showed clipping animals in lairage, as opposed to online, resulted in a small, but significant increase (P < 0·05) in pH value (mean pH 5·66 and 5·59, respectively). Conclusions:  Hide clipping does not adversely affect microbiological quality of carcasses, although higher ultimate pH values indicate increases in antemortem stress. Significance and Impact of the Study:  Hide clipping carcasses both ante- and postmortem appears to be an effective intervention to minimize transfer of hide microflora to carcasses during slaughtering operations. Online clipping offers advantages for animal welfare and improves safety for operatives.