Decrease In Grazing Pressure Research Articles

Soil quality indicators along a degradation gradient in central Iran: comparison of two regions with contrasting grazing systems

ABSTRACT Soil degradation poses serious environmental problems and requires quantitative assessment. This study aimed to investigate the soil properties in rangelands with different management conditions. Based on the assessment of soil erosion, vegetation cover, vegetation composition, and vegetation vigor, 56 sites were selected in rangelands with moderate, poor, and very poor conditions located in 15 grazing-free areas and one wildlife refuge region. Soil samples (0–10 cm layer) were collected from these sites through a systematic-random method to compare their physical and chemical properties. Results showed that soil organic carbon (OC) and total nitrogen content were significantly different between sites with different range conditions. The mean weight diameter of water-stable aggregates and structural stability index in moderate rangelands were 1.56 mm and 3.98%, respectively, and declined towards more degraded rangeland (i.e. 0.84 mm and 0.83%). Grazing-free rangelands exhibited a relatively larger OC deficit; hence specific management measures and control of grazing are required to enhance the quality of soil in these sites. This study highlighted the role of organic matter in preserving soil structural stability. Increasing protection level of rangelands and decreasing grazing pressure may preserve soil quality and combat desertification in these arid regions.

Identifying causes of low persistence of perennial ryegrass (Lolium perenne) dairy pasture using the Basic Grassland model (BASGRA)

AbstractRecent years have seen a decline in herbage production and tiller populations in New Zealand's perennial ryegrass (Lolium perenne) dairy pastures. One hypothesis is that modern genotypes are less suited to the warmer, drier weather experienced under changing climate patterns. In this study, a combination of long‐term trial data (2011–2017) and a process‐based pasture model (BASGRA) was used to explore the causes and possible mitigation of the observed production and population loss at three sites (dryland sites in Northland and Waikato and an irrigated site in Canterbury). Bayesian calibration was used to identify the model parameter sets that were consistent with the trial data and to identify differences in plant morphology and responses between sites. The model successfully simulated the observed differences in tiller numbers between the dryland sites, where populations and production declined rapidly after the second year and the irrigated site where populations and production were maintained. Analysis of the model calibrations along with preliminary scenario simulations suggests that increased tiller mortality associated with drought was the main cause of persistence failure at the dryland sites and that decreasing grazing pressure or breeding for tolerance to higher temperatures may not be successful in preventing this.

Mining as a catalyst of overgrazing resulting in risk of forest retreat, Erdenet Mongolia

This paper provides information on long-term suppression of natural forest regeneration due to the livestock grazing in the vicinity of one of the world largest open-pit ore mine close the city of Erdenet in Mongolia. The area is characterized by high concentration of herder’s households where the 52% were found only up to 1 km distance from the forest edge. Forest grazing causes extensive damage to seedlings and significant reduction of their growth. Within the 30–99 cm height category, up to 61% Larix sibirica, 90% Betula platyphylla and 68% Populus tremula individuals are grazingdamaged. L. sibirica and P. tremula seedlings with heights over 99 cm were absent, and no individuals of any species were found within 136–200 cm height category. In addition to the seedlings, only 7 or more meters high L. sibirica individuals are found in the forest structure, which means the absence of successfully growing forest regeneration for at least 40 years. In 2017, the defoliation of L. sibirica, reaching locally up to 100%, occurred in the stands east of the mine. Total defoliation represents a high risk of mortality of affected individuals. The stands cannot be successfully regenerated under the conditions of current intensive grazing. Mine metal stocks are calculated to provide for at least another 25 years of mining. Over that time, neither significant population decline nor decreasing grazing pressure on forests can be expected. If effective protection measures are not implemented, there is a risk of transforming threatened forest into steppe.

Effects of Climate Change at Treeline: Lessons from Space-for-Time Studies, Manipulative Experiments, and Long-Term Observational Records in the Central Austrian Alps

This review summarizes the present knowledge about effects of climate change on conifers within the treeline ecotone of the Central Austrian Alps. After examining the treeline environment and the tree growth with respect to elevation, possible effects of climate change on carbon gain and water relations derived from space-for-time studies and manipulative experiments are outlined. Finally, long-term observational records are discussed, working towards conclusions on tree growth in a future, warmer environment. Increases in CO2 levels along with climate warming interact in complex ways on trees at the treeline. Because treeline trees are not carbon limited, climate warming (rather than the rising atmospheric CO2 level) causes alterations in the ecological functioning of the treeline ecotone in the Central Austrian Alps. Although the water uptake from soils is improved by further climate warming due to an increased permeability of root membranes and aquaporin-mediated changes in root conductivity, tree survival at the treeline also depends on competitiveness for belowground resources. The currently observed seedling re-establishment at the treeline in the Central European Alps is an invasion into potential habitats due to decreasing grazing pressure rather than an upward-migration due to climate warming, suggesting that the treeline in the Central Austrian Alps behaves in a conservative way. Nevertheless, to understand the altitude of the treeline, one must also consider seedling establishment. As there is a lack of knowledge on this particular topic within the treeline ecotone in the Central Austrian Alps, we conclude further research has to focus on the importance of this life stage for evaluating treeline shifts and limits in a changing environment.

Vegetation responses to seasonal weather conditions and decreasing grazing pressure in the arid Succulent Karoo of South Africa

The Succulent Karoo biome is a renowned centre of biodiversity and endemism in the arid winter rainfall region of South Africa that is threatened by climate change. On 20 permanently marked plots within a biodiversity observatory, species richness and cover were assessed annually from 2002 to 2017 during the growing season. We were interested, firstly, in whether the vegetation showed any trends in response to the strong decrease in grazing pressure, which occurred at the beginning of the monitoring period, and secondly, in the effect of seasonal climate on the vegetation. We analysed the responses of species richness and cover in four life forms to seasonal rainfall and the standardised precipitation–evapotranspiration index (SPEI) using linear mixed-effect models. Time had a positive effect on richness of annual species and a negative effect on cover of shrubs and annuals, which increased in response to SPEI and less strongly to rainfall during autumn and winter. Habitat did not have any effect and geophytes and perennial herbs did not show any significant response. The importance of SPEI during autumn and winter is discussed in relation to potential germination cues and the projected decrease in rainfall and increase in temperature during these seasons.

Assessing the effects of grazing on variations of vegetation NPP in the Xilingol Grassland, China, using a grazing pressure index

The objective of this study was to map and discriminate variations of vegetation net primary production (NPP) from the effects of precipitation variability and thereby identify the effects of grazing on NPP variations in the Xilingol Grassland. Satellite-based simulations of NPP collected over 14-year period and residuals method were used to normalize the effects of interannual precipitation on NPP. A fixed-size moving-window method was developed in this paper to quantify the annual grazing pressure (defined as grazing pressure index, GPI) on the regional scale, using vegetation cover images from 2001 to 2014. Temporal and spatial analysis methods were conducted to show patterns and trends of GPI and NPP residuals (NPPres), and further to examine the effects of grazing pressure changes on variations of NPPres. Our results showed 80.7% of the study area experienced increasing NPPres and 18.5% with significantly increasing trends (p < 0.05). 76.7% of the study area showed decreasing grazing pressure, and 11.8% of areas experienced significantly decreasing trends (p < 0.05), with a small patches scattered distribution pattern. The negative correlations between NPPres and GPI were found in 94.6% of the study area, and 41.9% with significant correlation (p < 0.05); and long-term decreasing grazing pressure had positive impacts on vegetation NPP. They indicate grazing is a main driving factor of variations in vegetation NPP other than precipitation in Xilingol Grassland. The spatial patterns and temporal trends of NPPres, grazing pressure and responses of NPPres to grazing pressure changes varied among three main grassland types.

Rangeland management impacts on the properties of clayey soils along grazing gradients in the semi-arid grassland biome of South Africa

The grassland biome of South Africa is a major resource for livestock farming; yet the soils of these rangelands are stressed differently by various management systems. The aim of this study was to investigate how basic soil properties respond to different management systems. For this purpose we sampled rangeland management systems under communal (continuous grazing), commercial (rotational grazing) and land reform (mixture of grazing systems) farming. Within each of these systems a grazing gradient was identified with decreasing grazing pressure with increasing distance to the water points. Results showed that communal farms with continuous grazing were generally depleted in the respective nutrient stocks. The depletion increased with rising grazing pressure. Along that line there was a breakdown of macroaggregates with losses of the C and N stored therein. However, the commercial farms also exhibited a decline of macroaggregates and their associated C content nearby the water points. Aggregate fractionation is a sensitive indicator for detecting the beginning of soil degradation in this biome; yet, degradation was less pronounced under the rotational grazing of the commercial farms than under communal property right conditions. Hence, soil analyses confirm that fences and appropriate grazing periods are needed to manage these rangelands sustainably.

Impact of a simulated oil spill on benthic phototrophs and nitrogen‐fixing bacteria in mudflat mesocosms

Coastal and estuarine ecosystems are highly susceptible to crude oil pollution. Therefore, in order to examine the resilience of benthic phototrophs that are pivotal to coastal ecosystem functioning, we simulated an oil spill in tidal mesocosms consisting of intact sediment cores from a mudflat at the mouth of the Colne Estuary, UK. At day 21, fluorescence imaging revealed a bloom of cyanobacteria on the surface of oiled sediment cores, and the upper 1.5 cm thick sediment had 7.2 times more cyanobacterial and 1.7 times more diatom rRNA sequences when treated with oil. Photosystem II operating efficiency (Fq'/Fm') was significantly reduced in oiled sediments at day 7, implying that the initial diatom-dominated community was negatively affected by oil, but this was no longer apparent by day 21. Oil addition significantly reduced numbers of the key deposit feeders, and the decreased grazing pressure is likely to be a major factor in the increased abundance of both diatoms and cyanobacteria. By day 5 concentrations of dissolved inorganic nitrogen were significantly lower in oiled mesocosms, likely resulting in the observed increase in nifH-containing, and therefore potentially dinitrogen-fixing, cyanobacteria. Thus, indirect effects of oil, rather than direct inhibition, are primarily responsible for altering the microphytobenthos.

Dynamics of cyanobacteria–ciliate grazer activity in bitrophic and tritrophic microcosms

Direct and indirect interactions among components of bitrophic and tritrophic commu- nities were studied using laboratory microcosms. The filamentous cyanobacterium Phormidium sp., capable of inducible defence, was used as the primary producer. Phormidium reacts to ciliate attacks by withdrawing inside a polysaccharide envelope, overproducing exopolysaccharide material and remaining in dense and compact clumps. All of these defences are induced by the ciliate Pseudomi- crothorax dubius, a specialised grazer of filamentous cyanobacteria, representing the second trophic level in our system. The gymnostomatid ciliate Homalozoon vermiculare, which preys on Pseudomi- crothorax but does not directly affect cyanobacteria, was the top predator within the microcosm com- munity. The experiment showed that Homalozoon, very effective in a simple bitrophic cascade, had little effect on its prey when Phormidium was introduced into the system. Under grazer pressure, the cyanobacterium defended itself against the grazer by creating clumps of entangled filaments that also served as refuges for Pseudomicrothorax from Homalozoon. The prey ciliate Pseudomicrothorax reacts to cyanobacterial defence by increasing its encystation rate. Gradually decreasing grazing pressure resulted in a diminished Phormidium defence reaction, which enabled Pseudomicrothorax to resume feeding on filaments. Changing the extent of induced defence in Phormidium thus resulted in the stabilisation of the microcosm community.

Effects of increased pCO2 and temperature on the North Atlantic spring bloom. III. Dimethylsulfoniopropionate

The CLAW hypothesis argues that a negative feedback mechanism involving phytoplank- ton-derived dimethylsulfoniopropionate (DMSP) could mitigate increasing sea surface temperatures that result from global warming. DMSP is converted to the climatically active dimethylsulfide (DMS), which is transferred to the atmosphere and photochemically oxidized to sulfate aerosols, leading to increases in planetary albedo and cooling of the Earth's atmosphere. A shipboard incubation experiment was con- ducted to investigate the effects of increased temperature and pCO2 on the algal community structure of the North Atlantic spring bloom and their subsequent impact on particulate and dissolved DMSP con- centrations (DMSPp and DMSPd). Under 'greenhouse' conditions (elevated pCO2; 690 ppm) and elevated temperature (ambient + 4°C), coccolithophorid and pelagophyte abundances were significantly higher than under control conditions (390 ppm CO2 and ambient temperature). This shift in phytoplankton com- munity structure also resulted in an increase in DMSPp concentrations and DMSPp:chl a ratios. There were also increases in DMSP-lyase activity and biomass-normalized DMSP-lyase activity under 'green- house' conditions. Concentrations of DMSPd decreased in the 'greenhouse' treatment relative to the con- trol. This decline is thought to be partly due to changes in the microzooplankton community structure and decreased grazing pressure under 'greenhouse' conditions. The increases in DMSPp in the high tem- perature and greenhouse treatments support the CLAW hypothesis; the declines in DMSPd do not.

Direct and Indirect Effects of the Fungicide Carbendazim in Tropical Freshwater Microcosms

Direct and indirect effects of the fungicide carbendazim on ecosystem structure and functioning were studied < or =8 weeks after application (nominal concentrations: 0, 3.3, 33, 100, and 1000 microg/L) to outdoor microcosms in Thailand. Direct effects on macroinvertebrates are discussed in detail in a separate article. The present article presents the effects on other end points and discusses the hypothesized ecologic effect chain. Negative treatment effects on the zooplankton community were only recorded for the highest carbendazim treatment (NOEC(community) = 100 microg/L). The rotifer Keratella tropica, cladocerans (Moina micrura, Ceriodaphnia cornuta, and Diaphanosoma sp.), and cyclopoid copepods were decreased or even eliminated at this treatment level. The decrease in zooplankton and macroinvertebrate abundances was accompanied by an increase in numbers of several tolerant invertebrates, presumably caused by a release from competition and predation. The death of sensitive invertebrates probably also led to an overall decreased grazing pressure because increased levels of chlorophyll-a and bloom of the floating macrophyte Wolffia sp. were noted. The increase in primary producers is discussed to be the probable cause of changes in physicochemical water conditions, eventually resulting in an anoxic water layer during the last 3 weeks of the experiment. This is likely to have resulted in decreased invertebrate abundances noted in that period. Furthermore, the decreased decomposition of Musa (banana) leaves observed 8 weeks after application is considered to be the indirect effect of a decreased microbial activity resulting from these anoxic water conditions, rather than a direct toxic effect of carbendazim.

A map-based method for exploring responses to different levels of grazing pressure at the landscape scale

At the beginning of the last century European landscapes were a mosaic of open and forested habitats formed by centuries of human use. During the 20th century, however, this mosaic was altered. Changes in grazing pressure from domestic animals have been suggested as one of the drivers of these alterations. This paper presents a methodology developed to calculate an index of potential grazing pressure change at the landscape level. Information about location, type and number of grazing animals is used to produce detailed Geographical Information System (GIS) maps of potential grazing pressure change. Spatial information from these maps can then be geographically linked to vegetation maps such that the effect of grazing pressure changes on vegetation can be statistically analyzed. This methodology was applied to a Norwegian mountain landscape to test if decreased grazing pressure by domestic animals leads to woodland establishment in open habitats. Canonical Correspondence Analyzes (CCA) were performed and the results showed significant effects. Decreased grazing pressure increased the probability of woodland establishment in heathlands. The methodology described in this paper might be a useful tool in planning strategies both for conservation efforts and sustainable resource use.

Changing land management of lowland wet grasslands of the UK: impacts on snipe abundance and habitat quality

AbstractSnipe Gallinago gallinago breeding on lowland wet grasslands in England have undergone widespread and dramatic declines in abundance and distribution since at least the 1970s. There are many potential drivers of the decline but reductions in habitat quality, driven by land management, are often proposed as a contributing factor in the historical declines of breeding waders. Breeding snipe are now restricted to a few key places such as nature reserves and environmentally sensitive areas where management for breeding waders is implemented. On average, populations have continued to decline, even in these key areas, though population trends vary from a decline of 98% to an increase of 61% between the early 1990s and 2006. We examined the relationship between regional variation in snipe population trends and soil conditions, other habitat features and land management. Snipe were more likely to persist in fields where the soil conditions were wet and soft. Fields are wetter and softer now than in the early 1990s and management influenced these conditions. Soil softness increased with decreasing grazing pressure and increasing surface flooding. Soil moisture increased with surface flooding and was higher in organic soils. Changes in field condition were consistent with decreases in grazing pressure and increases in surface flooding. In spite of habitat condition being altered in a way that should have been beneficial to snipe, the numbers have continued to decline. Thus, it is unlikely that the measures of habitat condition examined here have been the driver of the decline and other factors must be involved. Research efforts should now focus on alternative explanations of the decline, for example, changes in other key aspects of habitat quality such as prey abundance, or changes in snipe productivity or mortality.

Direct and indirect effects of an antifouling biocide on benthic microalgae and meiofauna

When multitrophic, natural communities are exposed to a contaminant, indirect, food-web mediated effects may become as important as direct toxic effects. In this study the antifouling agent copper pyrithione (CPT) was used as a model toxicant to study toxic effects on microphytobenthos (MPB) and meiofauna, as well as on the interaction between them. The hypothesis was that exposure to CPT will decrease meiofaunal grazing pressure and that this effect would result in increased primary production and biomass of MPB. Two laboratory experiments (16 and 29days long) were performed, using natural sediment that was exposed to both acute and repeated exposure of CPT (final dose 5 nmol CPT per g dry weight sediment). Variables measured included light utilization efficiency of MPB (PAM fluorometry), primary production ( 14C-uptake), chl a content of the sediment, algal composition, meiofauna biomass and meiofaunal grazing pressure on MPB ( 14C-incubations). Although CPT, added as a single dose or repeatedly, affected both MPB and meiofauna, no strong mechanistic evidence for a top-down control was found. The clearest direct CPT effects were seen for MPB function (light utilization efficiency and primary production), while algal biomass and composition were only marginally affected. MPB recovered rapidly from the toxicant exposure, a finding that verified the conclusion from previous experiments that the MPB community is highly resilient. The magnitude of the direct response of the microalgae depended on whether the total dose of CPT was added as one initial dose or divided between several additions; effects were larger after one initial dose. Although meiofauna biomass decreased at CPT exposure in both experiments, this decline was not reflected in decreased grazing pressure on MPB. Meiofauna grazed between 1 and 12% of the algal biomass per day. The lack of a clear top-down effect from CPT on MPB could have several both biological and methodological reasons, such as low sensitivity of the meiofaunal species to CPT, and a combination of simultaneously operating bottom-up and top-down effects from CPT.

Size-dependent growth rates in eukaryotic and prokaryotic algae exemplified by green algae and cyanobacteria: comparisons between unicells and colonial growth forms

The size dependency of maximum growth rates was investigated in cyanobacteria and in green algae (Chlorophyta). Both unicellular and colony-forming species were included in the study. Significant allometric relationships were found between size and maximum growth rate for both cyanobacteria and green algae. The size-dependent growth could be described by the same scaling exponent in both cyanobacteria and green algae, but in both cyanobacteria and green algae only unicells evinced size-dependent growth rates-there was no relationship between colony size and growth rate in colonial forms of cyanobacteria and green algae. It is concluded that the colonial growth form represents an evolutionary adaptation to escape the negative effects of size-dependent growth, while retaining the positive effects of increased size, e.g. a decreased grazing pressure.

Microalgal productivity, community composition, and pelagic food web dynamics in a subtropical, turbid salt marsh isolated from freshwater inflow

Carbon entering the food web originating from microalgal productivity may be as important to salt marsh consumers as carbon originating from vascular plant production. The objective of this study was to further our understanding of the role played by microalgae in salt marshes. We focused on microalgal productivity, community dynamics, and pelagic food web linkages. Across three consecutive springs (2001–2003), we sampled the upper Nueces Delta in southeast Texas, United States; a shallow, turbid system of ponds and elevated vegetated areas stressed by low freshwater inflow and salinities ranging from brackish (11) to hypersaline (300). Despite high turbidity and low external nutrient loadings, microalgal productivity was on the order of that reported for vascular plants. Primary productivity in surface waters ranged from 0 to 2.02 g C m−2 d−1 and was usually higher than primary productivity associated with the benthos, which ranged from 0 to 1.14 g C m−2 d−1. This was likely due to high amounts of wind-driven resuspended sediment limiting production at greater depths. Most of the water column microalgal biovolume seemed to originate from the benthos and was comprised mostly of pennate diatoms. But true phytoplankton taxa were also observed, which included cryptomonads, chlorophyhtes dinoflagellates, and cyanobacteria. Succession from r-selected to K-selected taxa with the progression of spring, a common phenomena in aquatic systems, was not observed. Codominance by both potentially edible and less edible taxa was found. This was likely due to decreased grazing pressure on r-selected taxa as salinity conditions became unfavorable for grazers. In addition to a decoupled food web, reduced primary and net productivity, community respiration, and microalgal and zooplankton population densities were all observed at extreme salinities. Our findings suggest that a more accurate paradigm of salt marsh functioning within the landscape must account for microalgal productivity as well as production by vascular plants. Because the value of microalgal productivity to higher trophic levels is taxa specific, the factors that govern microalgal community structure and dynamics must also be accounted for. In the case for the Nueces Delta, these factors included wind mixing and increasing salinities.

Response of zooplankton and phytoplankton communities to creosote-impregnated Douglas fir pilings in freshwater microcosms.

Creosote has been used extensively as an industrial wood preservative for the protection of marine pilings, railway ties, and utility poles and is a common source of polycyclic aromatic hydrocarbons (PAHs) into aquatic environments. At present, there is little information by which to judge the potential for creosote leached from impregnated pilings to cause toxicity to biota in aquatic environments. The objective of the current study was to assess the effects of creosote on zooplankton and phytoplankton populations in freshwater microcosms in relation to changes in the concentration and composition of PAHs leached from creosote-impregnated Douglas fir pilings during an 83-day exposure period. The study consisted of single microcosms containing one half, one, two, three, four, and six treated pilings. Two microcosms that received untreated pilings were used as controls. The total surface area of pilings in each microcosm was normalized by adding the appropriate number of untreated pilings. Samples were collected periodically between -14 and 83 days pre- and postexposure to determine aqueous concentrations of 15 priority PAHs and to assess the response of zooplankton and phytoplankton communities. Plankton community response to creosote was analyzed using principle responses curves. Peak aqueous concentrations of sigmaPAH occurred at day 7, ranging from 7.3 to 97.3 microg/L. Zooplankton abundance decreased in all microcosms after introduction of the impregnated pilings, with the magnitude of response varying as a function of aqueous creosote concentration. Using inverse regression, a no-observed-effect concentration for the zooplankton community of 11.1 microg/L was estimated. In contrast, algal abundance and diversity increased in all treatments between 7 and 21 days and attained levels up to twice that in control microcosms. This trend most likely reflected decreased grazing pressure because of the decrease in zooplankton populations, but it may also have reflected growth stimulation resulting from exposure to various constituents within the creosote mixture. Our results indicate that creosote leached from impregnated pilings deployed under typical conditions (e.g., wharves) may cause transient toxicity to benthic or limnetic communities shortly after deployment, but this likely poses few long-term risks to aquatic freshwater plankton communities.

Technologies for the control of fat and lean deposition in livestock

When the ratio of lean to fat deposition is improved, so is feed conversion efficiency. Net benefits may include lower production costs, better product quality, less excretion of nitrogenous wastes into the environment, decreased grazing pressure on fragile landscapes, and reduced pressure on world feed supplies. However, finding a way to achieve these goals that is reliable, affordable, and acceptable to the majority of consumers has proved to be a major challenge. Since the European Union banned hormonal growth promoters (HGPs) 15 years ago, countries such as Australia and the United States have licensed new products for livestock production, including bovine growth hormone (GH), porcine and equine GH, and the β-agonist ractopamine. There has also been considerable research into refining these products, as well as developing new technologies. Opportunities to improve β-agonists include lessening their effects on meat toughness, reducing adverse effects on treated animals, and prolonging their duration of action. In the last regard, the combined use of a β-agonist with GH, which upregulates β-adrenoceptors, can produce an outstanding improvement in carcass composition and feed efficiency. Insulin-like growth factor-1 (IGF-1) mediates many of the actions of GH, but has proved to be of more use as a growth reporter/selection marker in pigs, than as a viable treatment. However, a niche for this product could exist in the manipulation of neonatal growth, causing a life-long change in lean:fat ratio. Another significant advance in endocrinology is the discovery of hormones secreted by muscle and fat cells, that regulate feed intake, energy metabolism, and body composition. Leptin, adiponectin and myostatin were discovered through the study of genetically obese, or double-muscled animals. Through genetic manipulation, there is potential to exploit these findings in a range of livestock species, although the production of transgenic animals is still hampered by the poor level of control over gene expression, and faces an uphill battle over consumer acceptance. There are several alternatives to HGPs and transgenics, that are more likely to gain world-wide acceptance. Genetic selection can be enhanced by using markers for polymorphic genes that control fat and lean, such as thyroglobulin, or the callipyge gene. Feed additives of natural origin, such as betaine, chromium and conjugated linoleic acid, can improve the fat:lean ratio under specific circumstances. Additionally, `production vaccines' have been developed, which alter the neuro-endocrine system by causing an auto-immune response. Thus, antibodies have been used to neutralise growth-limiting factors, prolong the half-life of anabolic hormones, or activate hormone receptors directly. Unfortunately, none of these technologies is sufficiently well advanced yet to rival the use of exogenous HGPs in terms of efficacy and reliability. Therefore, further research is needed to find ways to control fat and lean deposition with due consideration of industry needs, animal welfare and consumer requirements.

Landscape structure and food supply affect eagle owl (Bubo bubo) density and breeding performance: a case of intra‐population heterogeneity

AbstractDuring the 20th century, Mediterranean landscapes underwent extensive changes. In particular, decreasing grazing pressure combined with abandonment of agricultural uplands favoured the development of Mediterranean forests with a corresponding reduction of open habitats and landscape diversity. In some parts of the Mediterranean basin, including our study area, the reduction of open landscapes took place at the same time as a rapid decline in rabbits as a result of myxomatosis. This study assesses the impact of past changes in landscape and rabbit density on the density and the breeding performance of the eagle owl Bubo bubo, one of the largest predators of Mediterranean ecosystems. Eagle owl density, nest site structure and composition at the landscape level, diet and fecundity of 35 eagle owl nesting territories was analysed for 27 years. The study area is characterized by two distinct areas, the border of the massif and the interior, in which past changes acted differently. Eagle owls in the interior were simultaneously affected by the loss of rabbits, a shift to smaller prey, and by open areas reverting to forest. All of these factors reduced the foraging efficiency of the owls. When myxomatosis decimated the rabbit population, owls in the border area switched to other mammals, birds and fish, whereas in the interior, alternative prey were less abundant. The main impacts of reduced prey availability and landscape diversity on interior pairs were: (1) lower density of breeding pairs; (2) lower diversity in landscape structure and closer habitats; (3) lower richness and diversity in the diet; (4) later egg‐laying dates; (5) lower productivity.

A delay differential equation model on harmful algal blooms in the presence of toxic substances

The periodic nature of blooms is the main characteristic in marine plankton ecology. Release of toxic substances by phytoplankton species or toxic phytoplankton reduce the growth of zooplankton by decreasing grazing pressure and have an important role in planktonic blooms. A simple mathematical model of phytoplankton-zooplankton systems with such characteristics is proposed and analysed. As the process of liberation of toxic substances by phytoplankton species is still not clear, we try to describe a suitable mechanism to explain the cyclic nature of bloom dynamics by using different forms of toxin liberation process. To substantiate our analytical findings numerical simulations are performed and these adequately resemble the results obtained in our field study.