High-density Patches Research Articles

Functional Electrical Stimulation for Equine Muscle Hypertonicity: Histological Changes in Mitochondrial Density and Distribution

Functional electrical stimulation (FES) has proven to be advantageous in reducing muscle hypertonicity and reeducating muscle memory in the human population and has recently been used in horses. Six horses ranging in age from 10 to 17 years were selected for the study. Still photographs and clinical evaluations using the Modified Ashworth Scale to characterize muscle hypertonicity were performed on all horses pre- and post-FES. Functional electrical stimulation treatments were performed over a period of 8 weeks, resulting in a total of 22 treatments per horse. Biopsies pre- and post-FES treatments were obtained from the longissimus lumborum muscle of each horse. Mitochondrial density and distribution of the blinded samples pre- and post-FES were determined, and a two-sided Welch's t test was used to analyze the results. The results of the clinical evaluations and of morphometric analyses comparing pre- to post-FES muscle biopsies found: (1) a significant increase (P < .001) in the pooled mean mitochondrial density of both glycolytic and oxidative muscle fibers, (2) a significant increase (P < .001) in the subsarcolemmal mitochondrial high-density patches in oxidative muscle fibers, and (3) a significant increase (P < .001) in the subsarcolemmal mitochondrial high-density area percentages. In summary, the clinical improvements in the reduction of hypertonicity are, conceivably, related to the daily increased muscle contraction and perfusion induced by FES training. Thus, the FES protocol used in this study produced a positive effect on mitochondrial density and distribution, which in turn may help create healthier muscle tissue that is better able to function during exercise.

Genetic chimeras reveal the autonomy requirements for Vsx2 in embryonic retinal progenitor cells.

BackgroundVertebrate retinal development is a complex process, requiring the specification and maintenance of retinal identity, proliferative expansion of retinal progenitor cells (RPCs), and their differentiation into retinal neurons and glia. The homeobox gene Vsx2 is expressed in RPCs and required for the proper execution of this retinal program. However, our understanding of the mechanisms by which Vsx2 does this is still rudimentary. To define the autonomy requirements for Vsx2 in the regulation of RPC properties, we generated chimeric mouse embryos comprised of wild-type and Vsx2-deficient cells.ResultsWe show that Vsx2 maintains retinal identity in part through the cell-autonomous repression of the retinal pigment epithelium determinant Mitf, and that Lhx2 is required cell autonomously for the ectopic Mitf expression in Vsx2-deficient cells. We also found significant cell-nonautonomous contributions to Vsx2-mediated regulation of RPC proliferation, pointing to an important role for Vsx2 in establishing a growth-promoting extracellular environment. Additionally, we report a cell-autonomous requirement for Vsx2 in controlling when neurogenesis is initiated, indicating that Vsx2 is an important mediator of neurogenic competence. Finally, the distribution of wild-type cells shifted away from RPCs and toward retinal ganglion cell precursors in patches of high Vsx2-deficient cell density to potentially compensate for the lack of fated precursors in these areas.ConclusionsThrough the generation and analysis of genetic chimeras, we demonstrate that Vsx2 utilizes both cell-autonomous and cell-nonautonomous mechanisms to regulate progenitor properties in the embryonic retina. Importantly, Vsx2’s role in regulating Mitf is in part separable from its role in promoting proliferation, and proliferation is excluded as the intrinsic timer that determines when neurogenesis is initiated. These findings highlight the complexity of Vsx2 function during retinal development and provide a framework for identifying the molecular mechanisms mediating these functions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13064-015-0039-5) contains supplementary material, which is available to authorized users.

Geostatistics as a tool to study mite dispersion in physic nut plantations.

Spatial distribution studies in pest management identify the locations where pest attacks on crops are most severe, enabling us to understand and predict the movement of such pests. Studies on the spatial distribution of two mite species, however, are rather scarce. The mites Polyphagotarsonemus latus and Tetranychus bastosi are the major pests affecting physic nut plantations (Jatropha curcas). Therefore, the objective of this study was to measure the spatial distributions of P. latus and T. bastosi in the physic nut plantations. Mite densities were monitored over 2 years in two different plantations. Sample locations were georeferenced. The experimental data were analyzed using geostatistical analyses. The total mite density was found to be higher when only one species was present (T. bastosi). When both the mite species were found in the same plantation, their peak densities occurred at different times. These mites, however, exhibited uniform spatial distribution when found at extreme densities (low or high). However, the mites showed an aggregated distribution in intermediate densities. Mite spatial distribution models were isotropic. Mite colonization commenced at the periphery of the areas under study, whereas the high-density patches extended until they reached 30 m in diameter. This has not been reported for J. curcas plants before.

Comparison of the influence of patch-scale and meadow-scale characteristics on flow within seagrass meadows: a flume study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 516:49-59 (2014) - DOI: https://doi.org/10.3354/meps10873 Comparison of the influence of patch-scale and meadow-scale characteristics on flow within seagrass meadows: a flume study A. Adhitya1,5,*, T. J. Bouma1, A. M. Folkard2, M. M. van Katwijk3, D. Callaghan4, H. H. de Iongh5, P. M. J. Herman1 1Royal Netherlands Institute for Sea Research (NIOZ), PO Box 140, 4400 AC Yerseke, the Netherlands 2Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, UK 3Department of Environmental Science, Institute for Wetland and Water Research, Faculty of Science, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands 4School of Civil Engineering, University of Queensland, Brisbane, Queensland 4072, Australia 5Institute of Environmental Sciences, CML/Conservation Biology, Van Steenis gebouw, Einsteinweg 2, PO Box 22333 CC Leiden, The Netherlands *Corresponding author: achmad.adhitya@nioz.nl ABSTRACT: Hydrodynamic processes are an important agent of stress and facilitation in seagrass meadows, but little is known about the effects of the common phenomenon of heterogeneity of seagrass meadows on their interactions with hydrodynamic processes. To address this gap in knowledge, 4 heterogeneous configurations of Posidionia oceanica mimics were analyzed in a laboratory flume. The 4 configurations were created by placing 4 boards of mimics, i.e. 2 with high shoot density (~1100 shoots m-2) and 2 with low shoot density (~400 m-2), in different patterns (checkerboard, parallel, dense-sparse, and sparse-dense). Our results show that volumetric flow rate through each canopy, which is an indicator of the rate of supply of resources transported by the flow, tended to be greater in the low-density patches, regardless of the configuration. We also found that the Reynolds stress component τRe was positive in the lower-density patches (indicating that horizontal momentum was being transferred into the patch) and negative in the high-density patches (indicating that horizontal momentum was being transferred upwards out of the patch). Our results suggest that in resource-limited environments, hydrodynamic processes favor the growth of lower-density patches in heterogeneous seagrass meadows, thereby causing meadows to become more homogeneous over time. KEY WORDS: Seagrass · Posidionia oceanica · Hydrodynamics · Heterogeneity · Patches · Shoot density Full text in pdf format PreviousNextCite this article as: Adhitya A, Bouma TJ, Folkard AM, van Katwijk MM, Callaghan D, de Iongh HH, Herman PMJ (2014) Comparison of the influence of patch-scale and meadow-scale characteristics on flow within seagrass meadows: a flume study. Mar Ecol Prog Ser 516:49-59. https://doi.org/10.3354/meps10873 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 516. Online publication date: December 03, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Habitat selection in a deceptive predator: maximizing resource availability and signal efficacy

Many animals deceive prey by presenting a deceptive signal that lures prey into close proximity. These predators are predicted to select habitats that maximize the efficacy of their deceptive signal and offer high levels of prey traffic. The orchid mantis Hymenopus coronatus preys upon pollinators that are deceived by the predator’s resemblance to a flower. Habitat patches that contain flowers can offer orchid mantises high levels of insect activity, yet may be detrimental to the success of their deceptive signaling strategy. Currently 2 exclusive hypotheses—previously applied to deceptive flowers—predict the interaction between signaling efficacy under different flower densities. Increased competition for pollinators from nearby flowers suggests that orchid mantis signals should be more effective when in isolation from flowers (remote habitats hypothesis). Alternatively, orchid mantises may benefit from increased insect activity when near flowers (magnet species hypothesis). We found that orchid mantises had no preference for inhabiting flowers over leafy vegetation. They were also no more effective in attracting prey when sitting upon flowers compared to when in isolation from flowers. However, field experiments revealed that the density of flowers in their immediate vicinity did have an effect on orchid mantis attractiveness. Mantises were visited by more flying insects when in patches of high flower density, suggesting that they benefit from the magnet species effect. Co-occurring flowers do not negatively impact the efficacy of the orchid mantis’ deceptive signal and areas with high densities of flowers may allow them access to high levels of prey availability.

Evolution of positive and negative density-dependent dispersal.

Understanding the evolution of density-dependent dispersal strategies has been a major challenge for evolutionary ecologists. Some existing models suggest that selection should favour positive and others negative density-dependence in dispersal. Here, we develop a general model that shows how and why selection may shift from positive to negative density-dependence in response to key ecological factors, in particular the temporal stability of the environment. We find that in temporally stable environments, particularly with low dispersal costs and large group sizes, habitat heterogeneity selects for negative density-dependent dispersal, whereas in temporally variable environments, particularly with high dispersal costs and small group sizes, habitat heterogeneity selects for positive density-dependent dispersal. This shift reflects the changing balance between the greater competition for breeding opportunities in more productive patches, versus the greater long-term value of offspring that establish themselves there, the latter being very sensitive to the temporal stability of the environment. In general, dispersal of individuals out of low-density patches is much more sensitive to habitat heterogeneity than is dispersal out of high-density patches.

Trade-off between safety and feeding in the sea anemone Anthopleura aureoradiata

After a physical disturbance, such as a predatory stimulus, several marine organisms withdraw into a refuge to ensure survival. Consequently, they cannot engage in other essential activities. Re-emergence reflects a trade-off between avoidance of disturbance and lost feeding opportunities. The New Zealand sea anemone (Anthopleura aureoradiata) avoids predators by withdrawing its tentacles into its upper body. In a field experiment, responses of 480 A. aureoradiata to a physical disturbance were studied at three locations to assess the influence of the following factors on hiding time: physical contact with a neighbour; density of nearby conspecifics; total density per pool; and body size. Withdrawal times were significantly shorter for anemones in contact with a conspecific, occurring in high-density patches or of larger size. These patterns are consistent with rapid re-emergence being stimulated by competition for food from immediate neighbours and/or a lower risk of predation when in groups (i.e. a dilution effect), with larger size also potentially reducing vulnerability to predation.

Optimizing a spontaneously contracting heart tissue patch with rat neonatal cardiac cells on fibrin gel.

Engineered cardiac tissues have been constructed with primary or stem cell-derived cardiac cells on natural or synthetic scaffolds. They represent a tremendous potential for the treatment of injured areas through the addition of tensional support and delivery of sufficient cells. In this study, 1-6 million (M) neonatal cardiac cells were seeded on fibrin gels to fabricate cardiac tissue patches, and the effects of culture time and cell density on spontaneous contraction rates, twitch forces and paced response frequencies were measured. Electrocardiograms and signal volume index of connexin 43 were also analysed. Patches of 1-6 M cell densities exhibited maximal contraction rates in the range 305-410 beats/min (bpm) within the first 4 days after plating; low cell density (1-3 M) patches sustained rhythmic contraction longer than high cell density patches (4-6 M). Patches with 1-6 M cell densities generated contractile forces in the range 2.245-14.065 mN/mm3 on days 4-6. Upon patch formation, a paced response frequency of approximately 6 Hz was obtained, and decreased to approximately 3 Hz after 6 days of culture. High cell density patches contained a thicker real cardiac tissue layer, which generated higher R-wave amplitudes; however, low-density patches had a greater signal volume index of connexin 43. In addition, all patches manifested endothelial cell growth and robust nuclear division. The present study demonstrates that the proper time for in vivo implantation of this cardiac construct is just at patch formation, and patches with 3-4 M cell densities are the best candidates. Copyright © 2014 John Wiley & Sons, Ltd.

Departure mechanisms for host search on high-density patches by the Meteorus pulchricornis.

Less attention has been paid to the parasitoid–host system in which the host occurs in considerably high density with a hierarchical patch structure in studies on time allocation strategies of parasitoids. This study used the parasitoid Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) and the Oriental leafworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) as the parasitoids–host model system to investigate patch-leaving mechanisms as affected by the high-host density, hierarchical patch structure, and foraging behaviors on both former and current patches. The results showed that three out of eight covariates tested had significant effects on the patch-leaving tendency, including the host density, ovipositor insertion, and host rejection on the current patch. The parasitoid paid more visits to the patch with high-density hosts. While the patch with higher host densities decreased the leaving tendency, the spatial distribution of hosts examined had no effect on the leaving tendency. Both oviposition and host rejection decreased the patch-leaving tendency. The variables associated with the former patch, such as the host density and number of ovipositor insertions, however, did not have an effect on the leaving tendency. Our study suggested that M. pulchricornis females may use an incremental mechanism to exploit high-density patches to the fullest.

Spatial distribution patterns of the soft corals Alcyonium acaule and Alcyonium palmatum in coastal bottoms (Cap de Creus, northwestern Mediterranean Sea)

Current knowledge on the abundance and distribution patterns of different soft coral species is relatively limited when compared to other benthic suspension feeders such as gorgonians and hard coral species. To overcome this scarcity of information, the distribution patterns of the soft corals Alcyonium acaule and Alcyonium palmatum were investigated in northwestern Mediterranean benthic communities over a wide geographical (60 km of coastline) and bathymetrical (0–70 m depth) extent using a remotely operated vehicle. A. acaule was the most abundant species in the study area with highest recorded density of 18 col m−2 found at depths of 35–45 m in areas that are directly exposed to strong near-bottom currents. Conversely, A. palmatum was only found as scattered solitary colonies at greater depths in soft bottoms, with maximum density of 2.4 col m−2. Medium and large colonies of A. acaule were preferentially found on sloping and vertical rocky bottoms where they form dense patches. High-density patches of A. acaule were preferentially found on vertical rocky bottom, while isolated colonies were preferentially observed on coralligenous substrata as well as on flat soft and maerl substrates. A. acaule biomass distribution showed highest values between 40 and 45 m depth, and between 60 and 65 m depth. This suggests that deeper populations are formed by colonies that are bigger than the equivalent shallower ones. Although both species are almost genetically identical, ecologically they are very different. For this reason, conservation plans should consider the differential ecological traits shown by these two soft coral species.

Observation of 3D defect mediated dust acoustic wave turbulence with fluctuating defects and amplitude hole filaments

We experimentally demonstrate the direct observation of defect mediated wave turbulence with fluctuating defects and low amplitude hole filaments, from a 3D self-excited plane dust acoustic wave in a dusty plasma by reducing dissipation. The waveform undulation is found to be the origin for the amplitude and the phase modulations of the local dust density oscillation, the broadening of the sharp peaks in the frequency spectrum, and the fluctuating defects. The corrugated wave crest surface also causes the observed high and low density patches in the transverse (xy) plane. Low oscillation amplitude spots (holes) share the same positions with the defects. Their trajectories in the xyt space appear in the form of chaotic filaments without long term predictability, through uncertain pair generation, propagation, and pair annihilation.

Contrasting diel patterns in vertical movement and locomotor activity of whale sharks at Ningaloo Reef

Activity patterns of animals often relate to environmental variables such as food availability and predation pressure. Technological advances are providing us with new tools to monitor and better understand these activity patterns. We used animal-attached data loggers recording acceleration and depth to compare activity patterns and vertical habitat use of whale sharks (Rhincodon typus) at Ningaloo Reef, Western Australia. Whale sharks showed a moderate reverse diel vertical migration but exhibited a clear crepuscular pattern in locomotory activity. Peak activity occurred at sunset, whereas vertical movement peaked prior to this. Typical ram surface filter feeding could be identified and occurred primarily during sunset and the first hours of night. At such times, direct observations indicated whale sharks were feeding on tropical krill swarms. Kinematic analysis of postural data and data from vertical movement suggests that whale sharks at Ningaloo spend ~8 min per day actively ram surface filter feeding. Considering the high biomass present in krill schools, it is estimated that whale sharks at Ningaloo have a similar energy intake as those at other aggregation sites. Diel patterns in activity and diving behaviour suggest that whale sharks have tuned their diving behaviour in anticipation of the formation of these high-density patches which appear to only be periodically, but predictably available at sunset. Our results confirm that diel patterns in vertical habitat selection and vertical movements do not necessarily reflect patterns in activity and foraging behaviour. Direct quantification of activity and behaviour is required in gaining accurate representation of diel activity patterns.

Monitoring Strategy for Eight Amphibian Species in French Guiana, South America

Although dramatic amphibian declines have been documented worldwide, only few of such events have been quantitatively documented for the tropical forests of South America. This is due partly to the fact that tropical amphibians are patchily distributed and difficult to detect. We tested three methods often used to monitor population trends in amphibian species in a remote lowland tropical forest of French Guiana. These methods are capture-mark-recapture (CMR), estimation of the number of calling males with repeated counts data and distance sampling, and rates of occupancy inferred by presence/absence data. We monitored eight diurnal, terrestrial amphibian species including five Dendrobatidae and three Bufonidae. We found that CMR, the most precise way of estimating population size, can be used only with two species in high density patches where the recapture rate is high enough. Only for one of the species (Dendrobates tinctorius), a low coefficient of variation (CV = 0.19) can be achieved with 15 to 20 capture events. For dendrobatid species with day-calling males, audio surveys yield a better probability of detection with only 8 audio surveys needed; quantitative estimates can be achieved by computing the number of calling males inferred from audio counts or distance sampling analysis. We therefore suggest that an efficient monitoring protocol for Neotropical amphibian species should include a combination of sighting and audio techniques, and we discuss the need of implementing a large-scale monitoring in order to provide a baseline for comparison with future changes.

Monitoring the fishing process in the sea urchin diving fishery of Galicia

Abstract Fernández-Boán, M., Freire, J., Parma, A. M., Fernández, L., and Orensanz, J. M. 2013. Monitoring the fishing process in the sea urchin diving fishery of Galicia – ICES Journal of Marine Science, 70: 604–617. The assessment and management of small-scale benthic fisheries requires attention to the spatial structure of stocks and patterns of effort allocation. Spatial information helps in the interpretation of fisheries data, and is required for designing spatially explicit management strategies, often prescribed in the case of benthic fisheries. Monitoring of boats with GPS, combined with port interviews, was evaluated as an approach to investigate the spatial pattern of fishing intensity and catch per unit of effort (CPUE) in the sea urchin (Paracentrotus lividus) diving fishery from Galicia, Spain. Fishing opportunities (FOs), relatively small regions of high fishing intensity, were identified and mapped at a fine scale. New FOs were first visited at an approximately constant rate. Concentration analysis shows that effort intensity was not uniformly distributed within FOs. CPUE did not exhibit a significant trend throughout the season, either at the scale of the aggregated fishery or within individual FOs. Catch per area and area covered per unit of diving time were inversely related, indicating that fishers stay longer in high-density patches. While abundance is the primary driver of effort allocation, other factors contributing to suitability were identified. Based on these results, we discuss realistic options for the monitoring of this and comparable fisheries.

Behavior Webs of Piscivores at Subtropical Live-Bottom Reefs

Direct visual and acoustic observations at subtropical reefs off the southeast united states and northeast Gulf of mexico revealed a complex web of behavioral interactions within and between mid-water and demersal guilds of piscivorous fishes. While mixed-species groups of mid-water and demersal piscivores stalked and attacked common prey species independently, facilitative behaviors between mid-water and demersal piscivores were common in each region. In the latter case, prey reduced nearest neighbor distances and retreated toward the seafloor during predatory attacks by mid-water fishes. Demersal fishes subsequently attacked and consumed prey in these ephemeral high density patches. Aggregations of fishes in other trophic guilds, unassociated with predation events, modified movements of prey fishes and provided camouflage for piscivores that occurred within and along the periphery of those aggregations. Demersal piscivores often assumed the role of mid-water piscivores when the abundance of mid-water piscivores was low and when demersal piscivores were larger than mid-water species. Young-of-the-year great barracuda, Sphyraena barracuda (edwards, 1771), also assumed this role, generally when other piscivores were absent. Such behavioral interactions appear to be common in these communities. If predator-prey relationships are regularly facilitated by these types of mixed-species interactions, such facilitative behaviors may be important in terms of population processes (e.g., yielding increases in prey consumption with resultant increases in growth rate, and fecundity). A framework for testing such predictions provides a pathway for assessing the population consequences of such interactions.

Predator‐mediated interactions between preferred, alternative and incidental prey in the arctic tundra

Apparent competition between prey is hypothesized to occur more frequently in environments with low densities of preferred prey, where predators are forced to forage for multiple prey items. In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density. Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce. To test this hypothesis, we measured predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across three summers with variable lemming abundance. Predation risk on artificial shorebird nests was positively related to goose nest density, and this relationship was strongest at low lemming abundance when predation risk increased by 600% as goose nest density increased from 0 to 12 nests ha−1. Camera monitoring showed that activity of arctic foxes, the most important predator, increased with goose nest density. Our data support our incidental prey hypothesis; when preferred prey decrease in abundance, predator mediated apparent competition via aggregative response occurs between the alternative and incidental prey items.

Estructura y productividad de una población silvestre de Physaria mendocina (Brassicaceae). Implicancias para su desarrollo como cultivo oleaginoso

Population structure and seed yield of a wild stand of Physaria mendocina (Brassicaceae). Implications for its development as an oilseed crop: Wild stands of the perennial forb Physaria mendocina (syn Lesquerella mendocina, Brassicaceae), are uncommon, small and inconspicuous. This species, native to the Monte desert, is being evaluated as a new oil-seed crop for arid lands. We evaluated a wild population in the Lihue Calel National Park (La Pampa, Argentina) for three years: 2000, 2001, and 2002. The aims of our study were: 1) to characterize the spatial distribution, density and size structure of this population, and 2) to analyze the relationship between population structure and individual plant seed-production. The relationship between population structure and productivity was evaluated using path analysis. We found an aggregated spatial distribution pattern, with patches of high and low density. The proportion of larger size individuals increased in low density patches, respect to those in with high density in which prevailed smaller individuals. Smaller plants had less biomass accumulation and seed production, and had a greater below ground allocation, in relation to larger plants. Individual total biomass was the main determinant of the observed variation in seed-yield in relations to plant size, while harvest index was very stable across the range of plant diameter. The understanding of functional mechanics of seed production should aid in the conservation of wild stands, and in the domestication of this perennial species.

Habitat and density-dependent growth of the sea urchin Paracentrotus lividus in Galicia (NW Spain)

We studied the small-scale spatial variability in the growth of Paracentrotus lividus in two populations in Galicia (NW Spain) by reading growth rings. A tetracycline marking experiment was carried out to verify that the rings form annually. The growth rings were read by two independent readers in order to estimate the uncertainty involved in assigning the age. Of the six growth models evaluated (Tanaka, von Bertalanffy, Gompertz, Richards, logistic and Jolicoeur) the Tanaka function obtained the best fit to the data. This function predicts unlimited growth and a maximum growth rate of 15.00 (±0.97 SE) mm·year−1 at 3.09±0.10years old, which progressively decreases at older ages. However, habitat characteristics lead to intrapopulation variations in this general function. Recruitment seems to occur mainly in shallow waters (≤4m) and when the sea urchins reach 50mm (approximately 4years old) they migrate to deeper areas. Sea urchins larger than 50mm that stayed in shallow waters grew at a rate between 0.41 and 0.43mm·year−1 less than the sea urchins that moved to depths of 8 and 12m. The population density also influenced the growth, and individuals older than 4years had higher growth rates in high-density patches than in low-density areas. This could be due to the better environmental conditions in aggregation areas, that is, better protection against waves and predators and/or more abundant food.

Effect of Tuber Density and Trifloxysulfuron Application Timing on Purple Nutsedge (Cyperus rotundus) Control

Herbicides are the basis for conventional management of purple nutsedge, one of the world's most troublesome weeds. However, as concern rises over their environmental impact, farmers are being required to reduce herbicide usage. Herbicide efficacy is strongly affected by weed growth stage and density at application, and when herbicides are applied under optimal conditions, low rates can provide maximal control efficacy (CE). Therefore, this study aimed to determine the time window for control of purple nutsedge using a low rate of herbicide, based on an effective degree days (EDDs) model, at low (one tuber) and high (10 tubers) densities. Two experiments were performed under field conditions, in the summers of 2009 and 2010. Rate of 3.75 g a.i. ha−1trifloxysulfuron was applied once on each of five individual application dates. The growth of both treated and untreated plots was evaluated by means of leaf cover area (LCA) and biomass, which were then used to establish the time window for control. Results showed differences in both growth parameters between low and high tuber densities. The high-density patches reached LCA and fresh biomass values of 1,367 g and 1.12 m2, respectively, compared to 604 g and 0.69 m2, respectively, in the lower density patches. The favorable control periods based on biomass and LCA for the lower density patches were set to later dates than those for the higher density patches, 626 EDD compared to 483 EDD for biomass, and 786 EDD compared to 502 EDD for LCA, respectively. Although differences between the biomass- and LCA-based favorable control periods were observed at both tuber densities, the computed linear relations between the two growth parameters enabled adjusting them and setting the appropriate control period.

Spatial and temporal dynamics of Sorghum halepense patches in maize crops

Andújar D, Barroso J, Fernández‐Quintanilla C &amp; Dorado J (2012). Spatial and temporal dynamics of Sorghum halepense patches in maize crops. Weed Research52, 411–420.SummaryPatches of Sorghum halepense of various sizes and densities were artificially created in a maize field. Spatial and temporal patch expansion was monitored during 4 years. The results show that the patches expanded in the same direction of field traffic, with little or no displacement in all the other directions. Apparently, tillage was the main mechanism for dispersal of S. halepense rhizomes, with seeds playing a minor role in dispersal. The spatial growth pattern was characterised by a compact spread of the original patch and by the appearance of small patches at various distances from the primary source, which tended to merge with each other and with the original source. This type of pattern indicates an ‘infiltration’ invasion strategy. The initial patch size significantly influenced their growth rate; small patches grew proportionately faster than larger patches. The initial plant density had a significant influence on the temporal dynamics; low density patches increased up to 130 shoots m−2, the same upper level reached by high density patches. Sorghum halepense seems to be an excellent target for site‐specific weed management (SSWM), with compact patches expanding slowly and in a highly predictable way. However, new foci detached from the original source can expand quickly and could invade the whole field in a relatively short time. Early detection and management of small patches should contribute to improve SSWM practices.