12903 research outputs found
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A review of time of planting in strawberry: yields are higher with early to intermediate plantings
No full textTime of planting affects the productivity of crops. A review was conducted to determine the effect of time of planting on the performance of strawberry plants in warm locations (n = 42 experiments). Additional information was collated on the relationship between yield, temperature and the size of the nursery plants and their carbohydrates. There were linear (n = 23) or quadratic relationships (n = 7) between yield and the time of planting. In the linear relationships,
yields decreased as planting was delayed. In the quadratic relationships, optimum yields occurred with an intermediate planting, with lower yields with an earlier or a later planting. There was a quadratic relationship between yield and the time of planting when the first planting was in early September in the Northern Hemisphere or in early March in the Southern Hemisphere. Low yields with early plantings were associated with small plants, few stored reserves and inadequate temperatures in the nursery. Low yields with later plantings were associated with a short production season. Research is required to determine if earlier plantings are required in subtropical areas to reduce the impacts of global warming. The relationship between yield and temperatures in the nurseries needs to be explored further
Genome-wide evaluation of Scylla serrata (giant mud crab) population structure between and within two continental shelf regions of northern Australia
No full textContext
Offshore spawning and larval distribution of the wide ranging Scylla serrata (giant mud crab) provides genetic connectivity potential across large spatial scales.
Aims
We examined the genetic connectivity of S. serrata between and within two large continental shelves of northern and eastern Australia, to inform fisheries assessment and management.
Methods
Over 300 individuals were sampled from 14 locations, within 6 oceanographic regions, across the 2 continental shelves, providing 40,364 single nucleotide polymorphisms (SNPs) for analysis.
Key results
Results indicated a single genetic stock along the eastern continental shelf of Australia with no evidence of north to south structuring. A separate genetic stock on the northern continental shelf of Australia was indicated, with evidence supporting a degree of east–west structuring of S. serrata populations within the Gulf of Carpentaria.
Conclusions
The spatial extent of genetically connected S. serrata metapopulations is likely dependent on the oceanographic features of a region. The spatial scale of S. serrata stocks should be assessed on a case-by-case basis, confirmed by empirical evidence (e.g. SNP analysis) given connectivity is likely dependent on regional oceanographic conditions.
Implications
The outcomes of this study have implications for management of fished S. serrata stocks, especially where fishing mortality may (or may not) have effects beyond the jurisdiction of interest
Factors affecting methane production of composite and crossbred cattle grazing tropical and subtropical pastures in Northern Australia
No full textUnderstanding the factors affecting variation in methane (CH4) production rate among individual animals is an essential step in developing methane phenotypes to enable genomic selection for lower CH4 emissions. GreenFeed units (C-Lock inc., Rapid City, SD, USA) are an increasingly popular method for recoding methane production of grazing cattle. GreenFeed units take short-term breath measurements (of several minutes duration) when visited by cattle. Our aim was twofold 1) understand the factors associated with variation in CH4 production records from grazing beef cattle across tropical and sub-tropical cattle grazing regions and 2) given these factors and frequencies of visitation, determine trial length necessary to derive accurate phenotypes for genomic prediction. In total 5 trials were conducted across 3 locations resulting in repeated measurements on 328 mixed sex cattle. Factors including test day, trial location, hour of visit and pipe temperature had a significant effect on CH4 production. GreenFeed unit contributed a significant proportion of the total variation in methane emissions, across both intraday and daily methane production (P < 0.05). Testing the effect of trial length ranging from 5 and 52 days, showed that within-animal variation slightly decreased with repeated observations. However, the addition of cattle not previously recorded increased between animal variation, this slowed post 30 days. The optimal trial length balancing maximising cattle recorded, and repeated observations, was 28 days resulting in 20,440 visits from 324 cattle
Enhancing green bean crop maturity and yield prediction by harnessing the power of statistical analysis, crop records and weather data
No full textClimate change impacts require us to reexamine crop growth and yield under increasing temperatures and continuing yearly climate variability. Agronomic and agro-meteorological variables were concorded for a large number of plantings of green bean (Phaseolus vulgaris L.) in three growing seasons over several years from semi-tropical Queensland. Using the Queensland government’s SILO meteorological database matched to sowing dates and crop phenology, we derived planting specific agro-meteorological variables. Linear and nonlinear statistical models were used to predict duration of vegetative and pod filling periods and fresh yield using agro-meteorological variables including thermal time, radiation and days of high temperature stress. High temperatures over 27.5∘C and 30∘C in the pod fill period were associated with a lower fresh bean yield. Differences between specific bean growing sites were examined using our bespoke open source software to derive agro-meteorological variables. Agronomically informed statistical models using production data were useful in predicting time of harvest. These methods can be applied to other commercial crops when crop phenology dates are collected
Location of capture sufficiently characterises lifetime growth trajectories in a highly mobile fish
No full textVariation in somatic growth plays a critical role in determining an individual’s body size and the expression of its life history. Understanding the environmental drivers of growth variation in mobile organisms such as fishes can be challenging because an individual’s growth expression integrates processes operating at different spatial and temporal scales. Traditionally, otolith (ear stone) based growth analyses have focussed on temporal environmental variation by assuming an individual spends its whole life at its capture location. This approach ignores the movement potential of individuals and thus the role of spatio-temporal variation in conditions experienced. Here, we develop a modelling framework that incorporates individual movement information reconstructed via the analysis of chemical tracers in otoliths. We assess whether consideration of movement histories is important to estimating growth of a mobile freshwater fish, golden perch (Macquaria ambigua) at three spatial resolutions: basin-scale, reach-scale (movement-exclusive), and reach-scale (movement-inclusive). The predictive capacity of annual growth models slightly improved from the basin to the reach spatial scales (inclusive or exclusive of movement histories). Contrary to expectations, incorporating individual movement information, did not improve our ability to describe growth patterns. Golden perch growth was linked to the magnitude of and variation in spring, summer, and previous-year (antecedent) discharge, and spring temperature. The direction and magnitude of these effects was, however, dependent on life stage. Adults benefitted strongly from any increase in discharge or temperature, whereas juveniles benefitted only from increased summer discharge and grew slower in years characterised by wetter and warmer springs. We suggest that, for highly mobile fish like golden perch and in the absence of fine, ‘within reach’ scale biological data, coarser ‘reach-scale’ environmental variation may adequately describe individual growth trajectories
Interception of exotic ants and survey of the ant fauna at Gaoming Port, China
No full textGlobalization of trade and tourism has promoted the dispersal of exotic animals and plants around the world. Quantifying the invasion of exotic insects resulting from overseas trade is essential for national and international risk assessments. Seaports are important hubs for the arrival of exotic insects and a pathway for the invasion of alien species. Analyzing the interception data of exotic species at seaports and investigating the surrounding areas can improve our understanding and limit the risks of biological invasions. In this study, we examined the diversity of ant species associated with different shipping commodities and the origin of exotic ants arriving at Gaoming Port, China, during 2014–2017. In addition, we surveyed the ant communities at the port using bait and pitfall traps. We found 609 records of ants that were intercepted from foreign imports over a four years period, with most originating from Southeast Asian countries. Dolichoderus thoracicus and other species belonging to this genus were the most frequently intercepted species, accounting for 35.79% of interceptions. Solenopsis spp., Anoplolepis gracilipes and several other species presenting significant risks to ecosystems, agriculture, forestry and human health were also intercepted on several occasions. Field surveys showed that Solenopsis invicta was the dominant ant species in the seaport ant community, which also harbored other known tramp species, such as Tapinoma melanocephalum and Paratrechina longicornis. This study indicates that there is high probability of the introduction of foreign ants through seaports. Strengthening quarantine work and monitoring at and near ports is helpful for reducing the risks of the establishment and spread of exotic ants during the early phases of invasion associated with ports. © This article is distributed under a Creative Commons Attribution License CCBY4.
The Global Perception and Understanding of Vibration and Acoustics in Timber Structures
No full textMass timber buildings are becoming more common globally, but challenges remain, particularly with timber’s performance when exposed to low-frequency vibration and acoustics. Timber’s lower density compared to concrete and steel results in lower natural frequencies comparatively that can be excited more easily by footfall induced events. If unmanaged, this could lead to occupant discomfort and at times structural issues. However, it is not suggested that mass timber floors are non-conformant, instead the concern and drive behind the author’s research has been the overly conservative design practices that may be occurring as a result. This could lead to excessive material usage, and costly builds when proposing mass timber.
The aim of this study tour has then been to visit a series of practitioners related to mass timber panel production, designers/ builders of mass timber structures, and researchers focusing on the challenges related to mass timber floor vibration and acoustics
Habitat-use strategies of young barramundi (Lates calcarifer) in a heavily modified landscape
No full textBarramundi (Lates calcarifer) is a facultatively catadromous species that migrates between saltwater and fresh water to complete its life cycle. Modified riverine landscapes may limit these migratory paths and alter the environmental cues that migratory fish rely on to trigger migration. This study aims to determine the timing and prevalence of migration strategies of L. calcarifer in modified habitats and to identify the environmental parameters associated with these movements. Historical habitat use was interpreted from mean otolith Sr:Ca ratios as a proxy for ambient salinity. In this study, 27.9% (range: 16.1%–50.0% per year) of L. calcarifer exhibited catadromy, which is lower than what has been found for this species in other regions. Juvenile L. calcarifer adopted a catadromous strategy either early in life or not at all. Across the nine cohorts represented in the study, the fraction of catadromous individuals showed a moderately positive trend (r = 0.34–0.50), though not statistically significant, with wetter and cooler wet seasons. In the modified landscape of the Burdekin basin, North Queensland Australia, other factors may influence the likelihood of barramundi adopting a catadromous life strategy. Habitat connectivity is crucial for the viability of wild L. calcarifer populations and associated fisheries. Freshwater management should consider the timing required for juvenile L. calcarifer to access freshwater habitats and consider further interventions to improve habitat connectivity
Sentinel site strategy for the early detection of pest and invasive ants
No full textEarly detection of invasive ant infestations can greatly reduce resource requirements and costs associated with management. The National Electric Ant Eradication Program (NEAEP) has used a targeted surveillance strategy since its inception to focus surveillance efforts at ‘sentinel sites’ where high risk carriers of electric ant (Wasmannia auropunctata) aggregate, and/or could support pathways for extensive spread. In addition to early detection, sentinel sites can prioritise and focus future surveillance efforts when a target species is detected within a catchment. In this paper, the NEAEP sentinel site strategy is outlined, and field effort and diagnostic data reviewed. Since the financial year 2011/ 2012 the Program has surveyed a total of 290 sentinel sites. As funding to the program increased, the number of visits to sentinel sites also increased. In the last 5 years, we have detected W. auropunctata at sentinel sites 32 times and of these detections, waste transfer stations accounted for 34.21%; illegal dumping 21.05%, and plant nurseries 15.79%. After a detection at a sentinel site, proactive surveillance, focused on the sentinel site catchments, located a further 44 infested areas, with one catchment suspected to contain a population of W. auropunctata that is yet to be detected. It is believed that this sentinel site strategy can be used to detect other ant species, as evidenced by the detections of established invasive species at multiple NEAEP sentinel sites; African big-headed ant (Pheidole megacephala), and Singapore ant (Trichomyrmex destructor)
Buoyancy of Florestina tripteris seed, an invasive exotic weed of Central Western Queensland
No full textSticky florestina (Florestina tripteris DC.) (florestina) is an invasive weed present in central western Queensland. Recent higher rainfall years have aided the spread of florestina and there is potential for further increase in abundance and distribution. Florestina has several vectors for spread including vehicles, machinery, animals and waterways. Currently, the potential dispersal distance of florestina seed along waterways is unknown. This study investigated the duration of florestina seed buoyancy to determine potential dispersal distances in flowing water.
The buoyancy of florestina seeds was tested in a laboratory by placing lots of 50 seeds in 800 mL beakers containing 350 mL of water and subjecting them to various levels of agitation (no, low and high agitation). The length of time seeds remained buoyant was recorded. After an hour, 55.6% of seed remained floating in the no agitation treatment compared to 34% and 18% in the low and high agitation treatments respectively. After seven hours, 10% of seed remained floating in the no agitation, 11.6% in the low agitation and 5.6% in the high agitation. Greater than 94% of seed for all treatments had lost buoyancy within 24 hours of being placed in the water. The remaining seed stayed floating for various lengths of time with one seed still floating after eight days in the no agitation treatment. By having a greater understanding of how florestina spreads across the landscape, more effective management plans can be developed to improve land management outcomes