Dynamic Critical Behavior of the Chayes-Machta Algorithm for the Random-Cluster Model. I. Two Dimensions

We study, via Monte Carlo simulation, the dynamic critical behavior of the Chayes-Machta dynamics for the Fortuin-Kasteleyn random-cluster model, which generalizes the Swendsen-Wang dynamics for the q-state Potts ferromagnet to non-integer q \ge 1. We consider spatial dimension d=2 and 1.25 \le q \le 4 in steps of 0.25, on lattices up to 1024^2, and obtain estimates for the dynamic critical exponent z_{CM}. We present evidence that when 1 \le q \lesssim 1.95 the Ossola-Sokal conjecture z_{CM} \ge \beta/\nu is violated, though we also present plausible fits compatible with this conjecture. We show that the Li-Sokal bound z_{CM} \ge \alpha/\nu is close to being sharp over the entire range 1 \le q \le 4, but is probably non-sharp by a power. As a byproduct of our work, we also obtain evidence concerning the corrections to scaling in static observables.Comment: LaTeX2e, 75 pages including 26 Postscript figure

Spanning forests and the q-state Potts model in the limit q \to 0

We study the q-state Potts model with nearest-neighbor coupling v=e^{\beta J}-1 in the limit q,v \to 0 with the ratio w = v/q held fixed. Combinatorially, this limit gives rise to the generating polynomial of spanning forests; physically, it provides information about the Potts-model phase diagram in the neighborhood of (q,v) = (0,0). We have studied this model on the square and triangular lattices, using a transfer-matrix approach at both real and complex values of w. For both lattices, we have computed the symbolic transfer matrices for cylindrical strips of widths 2 \le L \le 10, as well as the limiting curves of partition-function zeros in the complex w-plane. For real w, we find two distinct phases separated by a transition point w=w_0, where w_0 = -1/4 (resp. w_0 = -0.1753 \pm 0.0002) for the square (resp. triangular) lattice. For w > w_0 we find a non-critical disordered phase, while for w < w_0 our results are compatible with a massless Berker-Kadanoff phase with conformal charge c = -2 and leading thermal scaling dimension x_{T,1} = 2 (marginal operator). At w = w_0 we find a "first-order critical point": the first derivative of the free energy is discontinuous at w_0, while the correlation length diverges as w \downarrow w_0 (and is infinite at w = w_0). The critical behavior at w = w_0 seems to be the same for both lattices and it differs from that of the Berker-Kadanoff phase: our results suggest that the conformal charge is c = -1, the leading thermal scaling dimension is x_{T,1} = 0, and the critical exponents are \nu = 1/d = 1/2 and \alpha = 1.Comment: 131 pages (LaTeX2e). Includes tex file, three sty files, and 65 Postscript figures. Also included are Mathematica files forests_sq_2-9P.m and forests_tri_2-9P.m. Final journal versio

Quantifying crop pollinator-dependence and pollination deficits: the effects of experimental scale on yield and quality assessments

Many crops are known to be dependent on biotic pollination, but knowledge gaps remain regarding the extent of this dependence, how it varies between crop varieties, and the implications of biotic pollination for crop quality. Data is also lacking on the prevalence and extent of pollination deficits and the ability of the surrounding pollinator community to provide pollination services. Robust and standardised methodologies are crucial for pollination studies. However, there has been only limited research into the critical question of the appropriate scale to apply these methods. Here, we use a commercially important UK apple Malus domestica variety (Gala) to address the questions of pollinator-dependence and pollination deficits, quality benefits arising from pollination, and the implications of conducting pollination experiments at three different scales: the inflorescence, the branch, and the whole plant. We found that Gala apple production was highly dependent on biotic pollination: overall, pollinator exclusion reduced fruit set at harvest to 55% of open pollination levels, whilst supplementary pollination led to fruit set of 167%. However, significant differences were found between the inflorescence, branch, and tree experiments; with increasing scale of observation leading to a lower measure of pollinator-dependence and pollination deficit. At the inflorescence scale, fruit set at harvest was just 13% of normal levels following pollinator exclusion, whilst at the branch and tree scales it was 75% and 79% of normal levels respectively. Supplementary pollination led to fruit set of 218%, 172%, and 117% of normal rates at the inflorescence, branch, and tree scales respectively. Apple seed set was also significantly affected by pollination treatment and the extent of this effect also depended on experimental scale. These differences due to experimental scale are likely a combination of methodological, biological and crop management factors. Seed numbers were shown to be a very good indicator of a number of fruit quality parameters, with greater seed numbers resulting in greater production of Class 1 (i.e. top commercial value) fruit. It is recommended that to measure pollinator-dependence and pollination deficits, experiments are conducted at the largest scale practicable and that treatment effects are monitored until harvest to more accurately reflect final yield outcomes. For apples, growers are recommended to record seed number as part of their fruit quality monitoring programmes to give a rapid and easy to measure indication of potential pollination deficit

Inconsistent responses of carabid beetles and spiders to land-use intensity and landscape complexity in north-western Europe

Reconciling biodiversity conservation with agricultural production requires a better understanding of how key ecosystem service providing species respond to agricultural intensification. Carabid beetles and spiders represent two widespread guilds providing biocontrol services. Here we surveyed carabid beetles and spiders in 66 winter wheat fields in four northwestern European countries and analyzed how the activity density and diversity of carabid beetles and spiders were related to crop yield (proxy for land-use intensity), percentage cropland (proxy for landscape complexity) and soil organic carbon content, and whether these patterns differed between dominant and non-dominant species. 90 % of individuals respectively. We found that carabids and spiders were generally related to different aspects of agricultural intensification. Carabid species richness was positively related with crop yield and evenness was negatively related to crop cover. The activity density of non-dominant carabids was positively related with soil organic carbon content. Meanwhile, spider species richness and non-dominant spider species richness and activity density were all negatively related to percentage cropland. Our results show that practices targeted to enhance one functionally important guild may not promote another key guild, which helps explain why conservation measures to enhance natural enemies generally do not ultimately enhance pest regulation. Dominant and non-dominant species of both guilds showed mostly similar responses suggesting that management practices to enhance service provisioning by a certain guild can also enhance the overall diversity of that particular guild

Addressing pollination deficits in orchard crops through habitat management for wild pollinators

There is increasing evidence that farmers in many areas are achieving below maximum yields due to insufficient pollination. Practical and effective approaches are needed to maintain wild pollinator populations within agroecosystems so they can deliver critical pollination services that underpin crop production. We established nesting and wildflower habitat interventions in 24 UK apple orchards and measured effects on flower-visiting insects and the pollination they provide, exploring how this was affected by landscape context. We quantified the extent of pollination deficits and assessed whether the management of wild pollinators can reduce deficits and deliver improved outcomes for growers over 3 years. Wildflower interventions increased solitary bee numbers visiting apple flowers by over 20%, but there was no effect of nesting interventions. Other pollinator groups were influenced by both local and landscape-scale factors, with bumblebees and hoverflies responding to the relative proportion of semi-natural habitat at larger spatial scales (1000 m), while honeybees and other flies responded at 500 m or less. By improving fruit number and quality, pollinators contributed more than £16 k per hectare. However, deficits (where maximum potential was not being reached due to a lack of pollination) were recorded and the extent of these varied across orchards, and from year to year, with a 22% deficit in output in the worst (equivalent to ~£14 k/ha) compared to less than 3% (equivalent to ~£2 k/ha) in the best year. Although no direct effect of our habitat interventions on deficits in gross output was observed, initial fruit set and seed set deficits were reduced by abundant bumblebees, and orchards with a greater abundance of solitary bees saw lower deficits in fruit size. The abundance of pollinators in apple orchards is influenced by different local and landscape factors that interact and vary between years. Consequently, pollination, and the extent of economic output deficits, also vary between orchards and years. We highlight how approaches, including establishing wildflower areas and optimizing the ratio of cropped and non-cropped habitats can increase the abundance of key apple pollinators and improve outcomes for growers

Trends in fishery resource utilisation on the Great Fish Estuary

Potts, W.M., Cowley, P.D., Corroyer, B. & Næsje, T.F. 2005. Trends in fishery resource utilisation on the Great Fish Estuary. - NINA Report 50. 34pp. The Great Fish Estuary, located in the Eastern Cape Province, is becoming an increasingly popular fishing venue. A resource utilisation study consisting of a series of roving creel interview surveys was conducted in the estuary between March 200 I and February 2002 and between October 2003 and September 2004. During interviews with resource users, demographic informat ion as well as catch, effort, bait, duration of the fishing trip and number of rods/lines were obtained. Recreational shore fishers dominat ed during both study periods (54 %, both periods), followed by subsistence fishers (40 % - 1st st udy period, 23 % - 2nd study period) and recreat ional boat fishers (5 % - 1st study period, 23 % - 2nd st udy period). The increase in recreational boat fishers between the two study periods, was most probably attributed to the increased sampling on weekend days during the second study period and to the improved infrastructure at the Fish River Diner Caravan Park. Spotted grunter (Pomadasys commersonnii) and dusky kob (Argyrosomus japonicus) dominated the catches during both st udy periods. The overall catch per unit effort was lower during the second (0.19 fish/angler-hour) than during the first (0.22 fish/angler-hour) study period, while the distribution of fishing effort was more widespread during the second study period than in the fi rst . The total fishing effort during the second study period was twice as high (122 044 hrs), while the total catch was only o ne third higher (18 978 fish) than in the first study period (60 436 hrs and 12 752 fish, respectively). Results from the two study periods were used to make recommendations for the design of future estuarine fishery surveys. While the study showed a variety of short -term fluctuations, long term monitoring studies are recommended to examine trends in the Great Fish Estuary fisheries and other estuarine fisheries in South Africa. Subsistence fishery, recreational fishery, bait fishery, datacollection protocols, managemen

Preface: Linefish resilience in the Anthropocene

No Abstrac

The physiological role of AT1 receptors in the ventrolateral medulla

Neurons in the rostral and caudal parts of the ventrolateral medulla (VLM) play a pivotal role in the regulation of sympathetic vasomotor activity and blood pressure. Studies in several species, including humans, have shown that these regions contain a high density of AT1 receptors specifically associated with neurons that regulate the sympathetic vasomotor outflow, or the secretion of vasopressin from the hypothalamus. It is well established that specific activation of AT1 receptors by application of exogenous angiotensin II in the rostral and caudal VLM excites sympathoexcitatory and sympathoinhibitory neurons, respectively, but the physiological role of these receptors in the normal synaptic regulation of VLM neurons is not known. In this paper we review studies which have defined the effects of specific activation or blockade of these receptors on cardiovascular function, and discuss what these findings tell us with regard to the physiological role of AT1 receptors in the VLM in the tonic and phasic regulation of sympathetic vasomotor activity and blood pressure

Editorial overview: recommendations for the promotion of a resilient linefishery in the Anthropocene

‘Linefish’ is a uniquely South African term used to describe marine fishes that are captured using hook and line. The South African linefishery is a complex socio-ecological system that has a considerable impact on the coastal marine environment while generating social and economic benefits for commercial, small-scale and recreational fishers. Like many fisheries, this complex system is under threat from the combined impacts of increasing levels of exploitation and climate change associated with the Anthropocene. The Southern African Marine Linefish Symposium (SAMLS) provides a platform for linefish scientists, managers, conservation officers, individuals from nongovernmental organisations, and other stakeholders to meet and exchange knowledge about the state and development of linefisheries. This overview discusses some of the long-term trends in linefish research during the last five symposia and highlights salient outcomes of the 5th SAMLS, which was held in July 2019. While the recovery and management success for some of South Africa’s commercial linefish species are recognised, the lack of policy and management in the recreational sector will not only undermine the implementation of the country’s new small-scale fisheries policy, but also the resilience of the socio-ecological system. To promote a resilient linefishery in the Anthropocene it is recommended that the fishery policies be strengthened to cover all sectors in the linefishery and that the general principles of the ecosystem approach to fisheries, including the incorporation of the human dimension and the implementation of co-management, are promoted. Improved communication between fishers, scientists, and managers is necessary, and recreational permit revenue should be used for research and monitoring to improve the management and stock assessment of species important to the recreational and small-scale sectors. Keywords: line fishing, Linefish Management Protocol, management, research priorit