High Animal Density Research Articles

TERRESTRIAL HABITAT SELECTION AND STRONG DENSITY‐DEPENDENT MORTALITY IN RECENTLY METAMORPHOSED AMPHIBIANS

To predict the effects of terrestrial habitat change on amphibian populations, we need to know how amphibians respond to habitat heterogeneity, and whether habitat choice remains consistent throughout the life-history cycle. We conducted four experiments to evaluate how the spatial distribution of juvenile wood frogs, Rana sylvatica (including both overall abundance and localized density), was influenced by habitat choice and habitat structure, and how this relationship changed with spatial scale and behavioral phase. The four experiments included (1) habitat manipulation on replicated 10-ha landscapes surrounding breeding pools; (2) short-term experiments with individual frogs emigrating through a manipulated landscape of 1 m wide hexagonal patches; and habitat manipulations in (3) small (4-m2); and (4) large (100-m2) enclosures with multiple individuals to compare behavior both during and following emigration. The spatial distribution of juvenile wood frogs following emigration resulted from differences in the scale at which juvenile amphibians responded to habitat heterogeneity during active vs. settled behavioral phases. During emigration, juvenile wood frogs responded to coarse-scale variation in habitat (selection between 2.2-ha forest treatments) but not to fine-scale variation. After settling, however, animals showed habitat selection at much smaller scales (2-4 m2). This resulted in high densities of animals in small patches of suitable habitat where they experienced rapid mortality. No evidence of density-dependent habitat selection was seen, with juveniles typically choosing to remain at extremely high densities in high-quality habitat, rather than occupying low-quality habitat. These experiments demonstrate how prediction of the terrestrial distribution of juvenile amphibians requires understanding of the complex behavioral responses to habitat heterogeneity. Understanding these patterns is important, given that human alterations to amphibian habitats may generate extremely high densities of animals, resulting in high density-dependent mortality.

Control of Medusahead (Taeniatherum caput-medusae) Using Timely Sheep Grazing

Medusahead is among the most invasive grasses in the western United States. Selective control of this noxious winter annual grass is difficult in California grasslands, as many other desirable annual grasses and both native and nonnative broadleaf forbs are also important components of the rangeland system. Intensive grazing management using sheep is one control option. This study was designed to determine the optimal timing for sheep grazing on heavily infested medusahead sites, and to evaluate the changes in species composition with different grazing regimes. Midspring (April/May) grazing reduced medusahead cover by 86 to 100% relative to ungrazed plots, regardless of whether it was used in combination with early spring or fall grazing. Early spring (March) or fall (October to November) grazing, alone or in combination, was ineffective for control of medusahead. In addition, midspring grazing increased forb cover, native forb species richness, and overall plant diversity. At the midspring grazing timing, medusahead was in the “boot” stage, just prior to exposure of the inflorescences. The success of this timely grazing system required high animal densities for short periods. Although this approach may be effective in some areas, the timing window is fairly narrow and the animal stocking rates are high. Thus, sheep grazing is unlikely to be a practical solution for management of large medusahead infestations.Nomenclature:Medusahead, Taeniatherum caput-medusae (L.) Nevski ELYCA.

Could a big gut be too costly for muskoxen ( Ovibos moschatus) in their first winter?

Young mammalian herbivores are more vulnerable to harsh winter conditions than adults, especially among large circumpolar species like the muskox ( Ovibos moschatus). We compared feeding responses of muskox calves (body mass 95 kg) with those of mature, non-reproductive females (body mass 227 kg) in mid-winter when air temperatures fell to −40 °C. Food intakes (1.8–2.2 kg digestible dry matter (DM) d −1), digesta fill (27–32 kg wet mass) and digestibility of hay (52–58% of DM; 49–55% of gross energy) were similar between age groups even though calves were much smaller than adults. Calves fed more frequently (12 vs. 8 feeding bouts per day) and thus spent more time feeding each day than adults (387 vs. 343 min per day). High mass-specific food intakes of calves indicate higher requirements for maintenance of body tissue than adults, which could be related to a larger intestinal tract in young muskoxen. Notably, cows and calves maintained a constant body mass throughout, indicating that they were feeding at maintenance levels and that the relatively higher intakes of calves were not related to growth. Together, these data suggest that limited food availability due to snow cover or high animal density may reduce the survival of muskoxen in their first winter.

The trade of live crustaceans in Portugal: space for technological improvements

Abstract Barrento, S., Marques, A., Pedro, S., Vaz-Pires, P., and Nunes, M. L. 2008. The trade of live crustaceans in Portugal: space for technological improvements. – ICES Journal of Marine Science, 65: 551–559. In Portuguese coastal areas, crabs and lobsters maintained alive until prepared for the table are commercially and economically very important. The trade in live crustaceans, mostly imported animals, is an interlinked and complex chain, from fishing, collection, holding facilities, and transportation, to the end-consumer, the various facilities playing a key role. Along the chain, animals can be affected by several stressors, inducing high mortality with consequent economic loss, and contributing to unsustainable exploitation of the resource. A survey was developed to characterize storage, transportation, and handling issues affecting various crustaceans at Portuguese holding facilities. In all, 22 facilities were identified and categorized by activity and water supply system. Despite the wide variation in their infrastructure, there were no major differences in mortality rate of crustaceans between importers, wholesalers, and exclusively retailers. At all facilities, Necora puber, Cancer pagurus, and Carcinus maenas had higher rates of mortality and shorter duration of captivity than Maja spp., Homarus sp., Panulirus regius, or Palinurus sp. Overall, the main problems identified were technical issues related to careless handling, high animal density, and the varying physiological needs of each species.

Impacts of savanna trees on forage quality for a large African herbivore

Recently, cover of large trees in African savannas has rapidly declined due to elephant pressure, frequent fires and charcoal production. The reduction in large trees could have consequences for large herbivores through a change in forage quality. In Tarangire National Park, in Northern Tanzania, we studied the impact of large savanna trees on forage quality for wildebeest by collecting samples of dominant grass species in open grassland and under and around large Acacia tortilis trees. Grasses growing under trees had a much higher forage quality than grasses from the open field indicated by a more favourable leaf/stem ratio and higher protein and lower fibre concentrations. Analysing the grass leaf data with a linear programming model indicated that large savanna trees could be essential for the survival of wildebeest, the dominant herbivore in Tarangire. Due to the high fibre content and low nutrient and protein concentrations of grasses from the open field, maximum fibre intake is reached before nutrient requirements are satisfied. All requirements can only be satisfied by combining forage from open grassland with either forage from under or around tree canopies. Forage quality was also higher around dead trees than in the open field. So forage quality does not reduce immediately after trees die which explains why negative effects of reduced tree numbers probably go initially unnoticed. In conclusion our results suggest that continued destruction of large trees could affect future numbers of large herbivores in African savannas and better protection of large trees is probably necessary to sustain high animal densities in these ecosystems.

Ecological Recycling Agriculture to Reduce Nutrient Pollution to the Baltic Sea

ABSTRACT HELCOM (Helsinki Commission) has adopted a programme with a vision of a healthy Baltic Sea Environment, with diverse biological components functioning in balance, resulting in good environmental status and supporting a wide range of sustainable human economic activities. HELCOM assessments presented in the Stakeholder Conference plan of 2007 clearly show that problems with eutrophication exist in most of the sub-basins of the Baltic and that good environmental status has not been achieved. Agriculture is responsible for a large share of the leaching of nutrients to watercourses, including groundwater lakes and finally the sea. The analysis of data presented in this paper concludes that specialized agriculture with its separation of crop and animal production results in a high load of nitrogen and phosphorus to the Baltic Sea. This agricultural specialization took place throughout the Scandinavian countries after World War II and has resulted in farms with a high density of animals and great surpluses of plant nutrients concentrated to certain regions. Examples from Sweden are presented in this paper. This trend of increasing products per animal and per hectare on fewer farms and a higher surplus of nutrients on each of them is continuing in Sweden and is likely to spread to new EU member countries within the Baltic Sea drainage area with the probable consequence of increasing nutrient loads. Ecological Recycling Agriculture (ERA) is defined as an agriculture system based on local and renewable resources that integrate animal and crop production on each farm or farms in close proximity. As a result a large part of the nutrient uptake in the fodder is effectively recycled. This in effect means that each farm strives to be self-sufficient in fodder production, which in turn limits animal density and ensures a more even distribution of animals geographically. This study of 12 Swedish farms confirms earlier results that agriculture based on these principles of ecological recycling can lead to a decrease in the potential emission of reactive nitrogen by half as well as a significant reduction in the accumulation and loss of reactive phosphorus. Application of these agricultural principles throughout the Baltic region in all EU countries would result in the halving of reactive nitrogen losses and minimizing losses of reactive phosphorus. In this way the goals, set by the states of the region, could be met and the process leading to the worst-case scenario of greatly increased nutrient loads to the Baltic Sea could be stopped.

Worker Health and Safety in Concentrated Animal Feeding Operations

A trend in consolidating livestock and poultry operations into concentrated animal feeding operations (CAFOs) potentially increases farm worker exposure to the hazards associated with high animal density conditions. The two main contributors of documented injury (fatal and non-fatal) are related to accidents with machinery and animals. Tractor rollovers are the leading accident in the area of farming machinery issues; kicks, bites, and workers being pinned between animals and fixed objects are non-machinery issues typically caused by inadequate precautions taken in the vicinity of livestock. These types of accidents are well documented; however, recommended safety strategies continue to be studied to reduce the risks and numbers of injuries associated with both machines and animals. Unlike accidents involving machinery and animals, air emission exposure and potential health effects from CAFOs are not well documented. CAFOs have the potential to show higher gaseous and particulate matter emissions compared to smaller farms. Pollutants like hydrogen sulfide, ammonia, volatile organic compounds, particulate matter, and endotoxin are emitted on CAFOs and can potentially affect worker health. These specific air emissions, their sources, and some of their harmful capabilities have been identified, and regulations have been implemented to create improved work environments on CAFOs. Despite such precautions, farm workers continue to report respiratory health symptoms related to their work environment. Air pollutant exposure and its health effects on farm workers require focused research to arrive at improved safety strategies that include mitigation techniques and protective gear to minimize adverse effects of working in CAFOs.

Assessment of management-related risk factors for paratuberculosis in Danish dairy herds using Bayesian mixture models

Transmission of Mycobacterium avium subsp. paratuberculosis (Map) to susceptible animals is primarily considered to occur via faeces and milk originating from infectious cows. However, studies of factors resulting in increased transmission of Map are difficult to perform due to a long and unpredictable incubation period and inaccurate diagnostic tests. A multi-level Bayesian mixture model has been shown to predict the infection status of an individual cow more precisely than traditional cut-off based methods used for interpretation of diagnostic test-information, thereby increasing the precision of the diagnostic information. The objective of our study was to assess management-related risk factors for within-herd transmission of Map. Management-related risk factors were recorded in 97 Danish dairy herds. Twenty-six months following that recording, the antibody status of all lactating cows ( n = 7410) in the same herds was measured by the use of an ELISA. A multi-level Bayesian mixture model was used to assess the association between the probability of infection of individual cows and 41 herd-level management-related risk factors using univariable analyses. In this model, the continuous OD value was used to estimate the probability of infection, corrected for known animal covariates and laboratory factors. The statistical significance of the potential risk factors was assessed by calculating odds ratios and their 95% credibility posterior intervals. Four significant risk factors were identified: housing of cows in bed stalls compared to housing in tie stalls; low level of hygiene in the feeding area of calving areas; low amounts of straw in the bedding of the calving area; high animal density among young stock >12 months of age. Surprisingly, the hygiene level in the calving area was not found to affect the odds of infection.

The effect of a combination of permanent breeding cage and low housing density on the reproductive success of farmed blue foxes

Social factors are known to affect the reproduction of many canids both in the wild and in farms. For example, reproduction in farmed silver foxes is regulated by social stress; foxes seem to benefit from noncramped housing conditions and permanent breeding cages. However, no comparable studies have been carried out in farmed blue foxes. The aim of our experiment was to create an alternative, improved, economically viable and practical housing solution for blue foxes. Therefore, we compared reproductive performance of blue foxes in permanent breeding cages with low animal densities (L group, N = 79) and traditional housing with its changing social environment with high animal density (H group, N = 74). The reproductive data from the L and H groups were compared separately for primiparous and multiparous vixens because the reproductive performance in primiparous vixens was substantially lower ( P < 0.001) than in multiparous vixens. Altogether, 41 and 39% of the primiparous vixens in the H and L group whelped ( P > 0.05), but only 28 and 34%, respectively, weaned at least one cub ( P > 0.05), i.e., 72 and 66% of the primiparous vixens did not reproduce in the H and L group, respectively ( P > 0.05). The total reproductive performance, expressed as cubs at weaning per breeding female, was 1.7 ± 3.5 for the H and 1.6 ± 2.9 for the L group ( P > 0.05). In the primiparous vixens, the only statistically significant difference observed between the two housing systems was that the onset of oestrus occurred five days earlier in the H than in the L group ( P < 0.05). All multiparous vixens in the L group exhibited oestrus compared to 94% in the H group ( P > 0.05). Furthermore, there was a nonsignificant (ns) trend for fewer barren females (9% versus 17%), more successfully reproducing vixens (83% versus 74%) and a higher number of live-born cubs (10.9 ± 4.7 versus 9.4 ± 3.9) in the L than in H group in the multiparous vixens (for all P > 0.05). This resulted in 1.7 and 1.4 cubs more per breeding and per mated vixen, respectively, at weaning in the L group (7.3 ± 5.0) compared to the H group (5.6 ± 4.2), but also this difference was nonsignificant. Although our present results lack statistical significance, they are promising enough to encourage field experiments with sufficiently large number of animals to prove or disprove these preliminary findings that lower housing density and permanent breeding cage, together or separately, may enhance reproduction particularly in multiparous blue fox vixens.

Antibodies againstLeptospiraspp. in Captive Collared Peccaries, Peru

To the Editor: Leptospirosis is endemic to tropical South America and is a major public health problem for persons living in some regions of the Amazon Basin (1–3). For local inhabitants, the collared peccary (Tayassu tajacu) represents a major source of meat and income and is one of the most hunted species. As a result, several farms are attempting to produce captive collared peccaries (4). Although spirochetes have been isolated from bats, marsupials, and rodents in the Peruvian Amazon (5), local popular game animals have not been tested. From May through December 2003, 96 collared peccaries from 4 experimental farms in 2 Amazonian provinces of Peru (Loreto and Ucayali) were surveyed for antibodies against Leptospira spp. Although the initial stock of each farm came from the wild, most animals had been born in captivity, remained on their respective farms, and had no contact with animals from the different farms. Blood samples were taken from animals that were born or maintained on the farm for ≥6 months, were in good physical condition, and showed no signs of disease. Samples that had been hemolyzed or otherwise contaminated were discarded, leaving optimal samples from 96 animals (sex ratio 1:1, 71% ≥1 year of age). The microscopic agglutination test was performed with a panel of 24 antigens belonging to 17 serogroups of Leptospira spp. used for screening surveys at the National Leptospirosis Reference Laboratory. An additional distinct strain, obtained from a febrile human patient in the Peruvian Amazon and provisionally designated as Var10, was added (2). Serum samples were considered positive if they had 50% agglutination and titers >100 (6). Chi-square tests were used for statistical comparisons of sex and age; significance was set at p<0.05. Among the screened samples, 64.6% reacted to 15 serovars (strains) that belong to 11 serogroups (Table). Seroprevalence did not differ significantly in relation to sex or age. Var10 was the most prevalent (56.2%) strain. This strain was isolated from a human patient in Iquitos (Loreto, Peru) and involved in recent outbreaks in the northern Peruvian Amazon (2); its taxonomic classification is pending. In terms of its distribution, 32 peccaries had positive results for Var10 only; 12 serum samples were reactive to >1 known serogroup. Leptospira sp. Var10 reacted mainly with serogroups Australis and Hebdomadis. Maximum titers were 6,400 for serogroup Tarassovi and 3,200 for Icterohaemorraghiae. High seroprevalence (15.6%) against serogroup Australis (serovar bratislava) has been reported in collared peccaries and in feral and domestic pigs (7,8) Table Prevalence of antileptospiral agglutinins per positive serogroup in captive collared peccaries, Peruvian Amazon, May 2003–Dec 2003* Seroprevalence on the farm in Loreto (n = 27) was 100%. At this farm, peccaries are kept near aquatic species and numerous ponds of stagnant water, which provide an ideal environment for the development of Leptospira spp. Because of recent human leptospirosis outbreaks in the area (2), 3 of the peccary caretakers were tested for antibodies against Leptospira spp.; their results were negative. Although similar to animals described in previous reports (7,9), none of the sampled animals showed evidence of disease at the time of sampling; however, absence of clinical disease does not exclude the possibility of subclinical or past infections. Furthermore, the high prevalence of antibodies to multiple serotypes suggests a wide exposure to Leptospira spp. Despite reports that suggest the collared peccary could act as a reservoir for Leptospira spp. (7,9), the finding of high antibody titers in some individual animals could indicate that collared peccaries are incidental rather than reservoir hosts. However, the prevalences found at 4 distant farms also indicate that this species could play some role in the maintenance and spread of leptospirosis in the Amazon Basin. Multiple titers to different serovars or serogroups in the same serum sample are common with serologic testing and difficult to interpret. Multiple titers can result from cross-reactions between different serovars or from true multiple infections (10). Regardless, serologic tests are only indicative of exposure to leptospires. Further efforts are necessary to isolate lepstospires from the urine or renal tissue of collared peccaries to confirm the presence of spirochetes and their potential dissemination into the environment. Our findings indicate that persons who have contact with collared peccaries and their products, particularly animal caretakers, researchers, hunters, and game traders, are at risk for zoonotic disease (3). Because further wildlife production in the Peruvian Amazon is expected, movement of animals and high animal densities could increase the chances of spirochete transmission within and between the farms. Therefore, precautions should be taken to limit the potential risks for leptospirosis transmission to domestic animals and humans.

Influence of enclosure size and animal density on fecal cortisol concentration and aggression in Père David’s deer stags

We investigated the impact of enclosure size and animal density on behavior and adrenocortical secretion in Père David’s deer in Dafeng Nature Reserve, China. From February 15 to April 16 in 2004, we conducted two experiments. First, we studied maintenance behavior and conflict behavior of Père David’s deer stags in a large enclosure (200 ha) with low animal density (0.66 deer/ha) and a small display pen (0.75 ha) with high animal density (25.33 deer/ha). The maintenance behavior we recorded included standing, locomotion, foraging and rest. During the behavioral observations, we collected fresh voided fecal samples from the stags periodically, and analyzed the fecal cortisol concentrations in those samples using radioimmunoassay technique. Second, we monitored the fecal cortisol concentrations of one group of stags (12 deer lived in an enclosure of 100 ha) before and after transferred into a small pen (0.5 ha). We found that in the first experiment: (1) there were significant differences in standing and rest whereas no significant differences of locomotion and foraging between the free-ranging group and the display group; (2) frequency of conflict behavior in the display group was significantly higher than those in the free-ranging group; and (3) fecal cortisol concentration of the display group (326.17 ± 16.98 ng/g dry feces) was significantly higher than that of the free-ranging group (268.98 ± 15.21 ng/g dry feces). In the second experiment, there was no significant difference of the fecal cortisol concentrations among sampling days, but the mean fecal cortisol concentration of the day after transferring (337.46 ± 17.88 ng/g dry feces) was significantly higher than that of the day before transferring (248.44 ± 7.99 ng/g dry feces). Comparison with published findings, our results indicated that enclosure size and animal density affect not only behaviors, but also adrenocortical secretion in Père David’s deer. Small living space with high animal density may impose physiological stress to captive Père David’s deer. Moreover, long-term physiological stress and increase of conflict behavior may subsequently affect survival and reproduction of the deer.

Environmental Sustainability and Social Desirability Issues in Pig Feeding

Feeding pigs used to be a means of managing domestic resources that may otherwise have been wasted into valuable animal protein. Feeding pigs thus was a form of husbandry. Following recent rapid industrial development, pig rearing has changed from extensive to intensive, but this transformation has been associated with major concerns. The concentration of large amounts of pig manure in small arrears is environmentally hazardous. Moreover, high densities of animals in intensive production systems also impose a health threat for both animals and humans. Furthermore, the use of growth promoters and preventive medicines for higher production efficiencies, such as in-feed antibiotics, also induces microbial resistance thus affects human therapeutics. In addition, consumers are questioning the ethics of treating animals in intensive production systems. Animal welfare, environmental and bio-safe issues are re-shaping the nature of pig production systems. Feeding pigs thus involves not only the consideration of economic traits, but also welfare traits and environmental traits. Thus, a focus on technological feasibility, environmental sustainability and social desirability is essential for successful feeding operations. Feeding pigs now involves multiple projects with different sustainability goals, but goal conflicts exist since no pattern or scenario can fulfill all sustainability goals and the disagreements are complicated by reduced or even no use of in-feed antibiotics. Thus it is difficult to feed pigs in a manner that meets all goals of high quality, safe product, eco- and bio-sustainability, animal welfare and profit. A sustainable pig production system thus requires a prioritization of goals based on understanding among consumers, society and producers and needs to view from both a local and global perspective.

Effects of scattering layer composition, animal size, and numerical density on the frequency dependence of volume backscatter

The mesopelagic boundary community around the Hawaiian Islands is a land-associated, sound scattering layer that undergoes diel migrations with both a vertical and horizontal component. A video camera system was developed to quantitatively examine the numerical density, size, and taxonomic composition of micronekton. The camera system was combined with a four-frequency vessel-mounted echosounder system (38, 70, 120, and 200 kHz) to document the full migration range of micronekton and describe the changes in composition and density throughout their diel migration. Migrating animals split into multiple, distinct layers at night with differences in micronekton density, composition, and size. These differences were correlated with differences in the frequency response of volume backscatter. The relationship between these variables and backscatter intensity relationship between frequencies is complex. The results suggest strong partitioning of habitat by these animals in space and time, which, along with the high densities of animals, indicate that competition is important in driving the behavior and structuring the community.

The comparative biodiversity of seven globally important wetlands: a synthesis

The species diversity data of seven globally important wetlands (Canadian peatlands, Florida Everglades, Pantanal, Okavango Delta, Sundarban, Tonle Sap, and Kakadu National Park) were compared. The available data for most groups of lower plants and animals are insufficient for a comparative analysis. Data on vertebrates and higher plants are more complete and show high species diversity. The large habitat diversity allows the coexistence of amphibious species with many immigrants from connected deepwater and terrestrial habitats. Several of these immigrant species find an important permanent refuge in the wetlands; some use the wetlands as periodic habitats. All wetlands are important habitats for long-distance migratory bird species. The species composition reflects the biogeography of the respective regions, e.g. the high diversity of large ungulates characteristic for Africa is also found in the Okavango Delta in Botswana, and the high fish species diversity typical for South America is also reflected in the Pantanal in Brazil. The number of endemic species in most wetlands is low, except in the Everglades. The low numbers are explained to some extent by the dramatically changing paleo-climatic conditions that increased extinction rates, but also by the connection with large river systems that act as migratory and transport routes for species from large catchment areas and hinder the genetic isolation of wetland populations. The high number of endemic species in the Everglades is explained in part by its isolation on a peninsula. The relatively low nutrient status of most wetlands does not negatively affect species diversity and often leads to high animal densities. Large populations of endangered or rare species in all wetlands contribute to the great value of these areas for biodiversity protection. All wetlands are subjected to an increasing degree to human pressure through, e.g. water abstraction, changes in the natural flood regime, land reclamation, pollution, over-utilization of natural resources, and poaching. High habitat diversity and a pronounced natural disturbance regime make some of the wetlands vulnerable to invasion by exotic species, as shown for the Everglades. All studied wetlands are at least in part protected by national and international conventions. This provides perspectives for long-term protection only to a limited extent because of major environmental changes in their surroundings. Further strong efforts are required to match protection and sustainable use of the wetlands proper with management activities in their catchments.

Optimization of experimental infection protocols for the estimation of genetic parameters of resistance to White Spot Syndrome Virus (WSSV) in Penaeus ( Litopenaeus) vannamei

Two infection protocols, individual oral (IO) and waterborne infection (WB), were evaluated to challenge Penaeus ( Litopenaeus) vannamei with White Spot Syndrome Virus (WSSV). Five different batches of full and half-sib families were infected experimentally and tested for growth performance under commercial growth conditions. The genetic variance for WSSV resistance was estimated using a linear sire–dam repeatability model that considers test-day survival as the dependent variable. The heritability estimates using the IO protocol ranged from 0.01 ± 0.00 to 0.02 ± 0.01, whereas the heritability estimates using the WB infection protocol were not significantly different from zero. The genetic correlations measured as the product moment correlation between full-sib family breeding values for resistance to WSSV and harvest body weight in ponds were unfavourable in three of the five batches and favourable in one of them. The dosage of WSSV was better controlled with IO oral infection than with other methods, with all animals being exposed to approximately the same risk of infection at the same time. This should improve the accuracy of the genetic parameters and hence improve the accuracy of the breeding values. It should, however, be noted that once the outbreak was established and the mortalities began, the shape and the magnitude of the slope of the mortality curves showed little difference in the infection pattern between batches irrespective of the dosage and infection protocol, and in most of the cases the cumulative mortality was greater than 80%. The main reason for this is probably the high densities of animals in the tanks needed for the genetic evaluations.

Extreme diel horizontal migrations by a tropical nearshore resident micronekton community

The mesopelagic boundary community around the Hawaiian Islands is a land-associated, sound-scattering layer that undergoes diel migrations with both a vertical and horizontal component. To understand horizontal migration, it is important to understand the full cycle of migration and to determine which animals undertake these movements and which do not. We developed a video camera system to quan- titatively examine the numerical density, size, and tax- onomic composition of micronekton. We combined the camera system with vessel-mounted echosounders to document the full migration range of micronekton and describe the changes in composition and density throughout their diel migration. Onshore horizontal movement is limited to waters deeper than 23 m. Off- shore, horizontal migration seems to cease between 9 and 11 km from the shoreline. Some animals in the mesopelagic boundary community undertake horizon- tal migrations of at least 11 km roundtrip each night. This impressive migration indicates that there must be a substantial benefit to horizontal migration. The migrating animals split into multiple, distinct layers at night with differences in micronekton density, compo- sition, and size. Myctophid fishes are the most abun- dant component of the horizontally migrating layers. Large myctophids are the first to migrate into and last to leave the shallow water areas. During the day, the layers merge into a single layer at 400 m depth or deeper. At night, there is evidence of strong partition- ing of habitat by these animals in space and time, which—along with the high densities of animals— suggests that competition is important in driving the behavior of, and structuring, the community.

Response of wheat to additional nitrogen fertilizer application after pig slurry on over-fertilized soils

Pig slurry is a valuable nutrient resource but constitutes a waste disposal problem in areas of high animal density. In the semiarid area of Pla d’Urgell, in the Ebro Valley, North-East Spain, irrigated crops receive large amounts of nutrients in the form of manure and mineral fertilizers. We studied the effect of pig slurry and additional side-dress mineral fertilizers on irrigated wheat, Triticum aestivum L., on a coarse loam soil, with high soil P and K levels. Yields increased by 62.3% when using pig slurry. The application of ammonium sulfate nitrate sidedress did not significantly increase wheat production. The average apparent recoveries were higher for potassium (88.7%) than for nitrogen (51.3%) and phosphorus (36.3%). Greater amounts of soil NO3-N were measured over the four growing seasons, which was consistent with the amount of N applied. Macronutrient and micronutrient uptake was significant higher for pig slurry treatments, but only small differences were found between the pig slurry and pig slurry plus ammonium sulfate nitrate treatments. The unfertilized treatment showed significantly lower soil P, K, Cu and Zn content than pig slurry treatments; 34%, 21%, 34%, and 26% respectively. These findings could be used to develop a nutrient management plan based on knowledge of soil test results and crop nutrient removal. This could help to improve the use of pig slurry and mineral fertilizers on limited available land areas and prevent the accumulation of potentially toxic elements in soils and the export of nutrients through agricultural drainage.

Intensity of interference affects the distribution of house sparrows, Passer domesticus, at food patches

Interference ideal free distribution (IFD) models predict animal distributions across resource patches, taking into account the effects of resource density and competitor interference on an individual's resource intake rate. Assuming that individuals behave to maximize fitness, foragers should aggregate at patches of high resource abundance when interference is weak. However, when interference is strong, foragers should choose to reduce interference by foraging at less crowded patches, even if these patches have lower resource density. Consequently, interference IFD predicts disproportionately high animal densities at rich patches when interference is low and a more uniform distribution among patches when interference is strong. To test this prediction we observed house sparrows, Passer domesticus, at a rich and a poor patch with different seed densities. We manipulated interference by altering the size of the pair of patches: two small patches (high interference) or two large patches (low interference). Birds experienced no interference at large patches where fighting was infrequent and preferred the rich patch where foraging rates increased with bird numbers. In contrast, birds aggressively interfered with each other at small patches, and interference was higher in rich patches than in poor patches. As predicted, birds increased their use of poor patches to minimize interference, resulting in an even distribution of birds across rich and poor patches. Our results show how changes in interference with resource density can make consumer distributions independent of resource distribution, even at moderate interference intensities. Manipulating interference through patch size may provide a unique opportunity to examine the effects of competitive asymmetries on patch use.

Nutrient discharge from small agricultural catchments in Sweden

Abstract Within the Swedish Monitoring Programme for Agriculture, 27 small agricultural catchments were investigated for between 9 and 14 years (6 years for one catchment), starting in the late 1980s, to determine the impact of agricultural activities on discharge water. The catchments represent major variations in climate, soil types and farming in Sweden and hence long-term average load of total nitrogen (N) and total phosphorus (P) at stream outlets varied widely among the catchments, from 2 to 41 and from 0.1 to 0.9 kg ha −1 yr −1 , respectively. Catchments with large N loads were characterised by several factors favourable for leaching, such as mild winter climate, large precipitation, sandy or organic soils and high animal density in combination with intensive cropping systems with a low percentage of ley. Large P loads were mainly related to factors such as clay and clay loam soils, medium to high precipitation and large proportions of annual crops in the catchments. Flow-normalised time series of monthly loads of nitrate N, phosphate P and particulate P (for 24 catchments) were tested for trends. Significant downward trends were revealed for nitrate N, phosphate P and particulate P for seven, eight and three catchments, respectively, whereas, upward trends were revealed for nitrate N and particulate P for one and two catchments, respectively. Downward nitrate N trends for two catchments were correlated to smaller amounts of applied manure, especially during autumn, and to a decrease in the area of spring cereals and spring rape.

Spatial analysis of campylobacter infection in the Canadian province of Manitoba.

BackgroundThe study describes population level variations in campylobacter incidence within the Canadian province of Manitoba, and the relationship to sociodemographic and landscape related characteristics. Using data derived from the Manitoba Health Public Health Branch communicable disease surveillance database, the study applied a number of spatial and ecological techniques to visualize, explore and model campylobacter incidence for the years 1996 to 2004. Analytical techniques used in the study included spatial smoothing, the spatial scan statistic, the Gini coefficient, and Poisson regression analysis.ResultsThe study demonstrated marked and statistically significant geographic variability in the rates of campylobacter incidence in Manitoba.. The incidence of campylobacter was observed to be significantly higher in populations living in rural and agricultural areas of the province, with the highest rates occurring in populations living in proximity to high densities of farm animals (cows, pigs, chickens). The study also observed that the age specific pattern of campylobacter incidence in rural Manitoba was very different than the urban pattern, with the incidence rate in the 0–4 year age group seven times higher in rural Manitoba than in the City of Winnipeg.ConclusionThe study demonstrates the value of a deploying a diverse set of spatial techniques to better understand the dynamics of an enteric disease such as campylobacter infection. The study concludes that there may be three distinct mechanisms for the transmission of campylobacter in Manitoba which are operating simultaneously. These include broad population exposure to a centralized food system endemically infected with the campylobacter organism, exposure to local level factors such as farm animals or contaminated water, and exposure to campylobacter infection through foreign travel.