Global regime shift dynamics of catastrophic sea urchin overgrazing

A pronounced, widespread and persistent regime shift among marine ecosystems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin overgrazing in a well-studied Australian system demonstrates a discontinuous regime shift, which is of particular management concern as recovery of desirable macroalgal beds requires reducing grazers to well below the initial threshold of overgrazing. Generality of this regime-shift dynamic is explored across 13 rocky reef systems (spanning 11 different regions from both hemispheres) by compiling available survey data (totalling 10 901 quadrats surveyed in situ) plus experimental regime-shift responses (observed during a total of 57 in situ manipulations). The emergent and globally coherent pattern shows urchin grazing to cause a discontinuous ‘catastrophic’ regime shift, with hysteresis effect of approximately one order of magnitude in urchin biomass between critical thresholds of overgrazing and recovery. Different life-history traits appear to create asymmetry in the pace of overgrazing versus recovery. Once shifted, strong feedback mechanisms provide resilience for each alternative state thus defining the catastrophic nature of this regime shift. Importantly, human-derived stressors can act to erode resilience of desirable macroalgal beds while strengthening resilience of urchin barrens, thus exacerbating the risk, spatial extent and irreversibility of an unwanted regime shift for marine ecosystems.     

北京百花山野生岩生植物资源及其开发利用

对百花山地区的岩生植物资源进行了初步调查。调查结果显示：北京百花山地区的岩生植物资源非常丰富,大约有25科56属74种,其中很多岩生植物不但拥有较高的观赏价值,而且还具有很强的抗性。在此基础上,对这些岩生植物的园林应用价值进行了分析和评价,并对我国野生岩生植物资源的开发利用提出了一些建议。     

Rock Biofertilizers with Acidithiobacillus on Sugarcane Yield and Nutrient Uptake in a Brazilian Soil

The experiment was conducted with the aim to evaluate the effects of biofertilizers with phosphate and potash rocks and soluble fertilizers (Triple super phosphate and potassium chloride) in chemical attributes of a Brazilian tableland soil grown with sugarcane. The experiment was arranged in a completely randomized factorial design 2 × 4 × 3 + 1, with four replicates. Two varieties of sugarcane, three sources of P and K mixture (natural apatite + natural biotite; P + K biofertilizers with Acidithiobacillus and P + K chemical fertilizers) were applied in four levels. A control treatment with no P and K fertilization (P₀K₀) was added for comparative purposes. Significant differences between varieties were observed in all analyzed parameters, with better results when applied the recommended levels of biofertilizers and chemical fertilizers. Stalk fresh matter increased with fertilizers and biofertilizers applications, especially when applied in levels near recommendation. Total N, total P and total K in stalk dry matter increased significantly when biofertilizers were applied. The results indicate potential use of biofertilizers that may be used as P source; however, long-term studies are necessary due to soil pH reductions and its possible adverse effects.     

Onset of maturity in male southern rock lobsters Jasus edwardsii in Tasmania,Australia

Summary

The reproductive contribution of male southern rock lobsters Jasus edwardsii has recently become of interest for managing this fishery as changes to the length of seasonal closures have shifted fishing effort towards males. To assess size at onset of maturity, a total of 387 male southern rock lobsters Jasus edwardsii were collected using baited traps from four of the eight fishery regions around the Tasmanian coast during July and August 2000. Sizes at onset of maturity in these samples were estimated by examining the vasa deferentia for evidence of the commencement of spermatid production. In addition, the total combined weight of the vasa deferentia and testis was compared with body size (as a gonad somatic index, GSI). Estimates of size at onset of maturity from the two methods were similar, although estimates from GSI appeared to have broader confidence limits. Although these physiological indices of maturity do not necessarily translate to functional maturity, they indicate that maturity is well below that of the legal minimum size of 110 mm carapace length used for managing the fishery (all estimates by either method for length at 50% sample maturity ≤70 mm carapace length). Production of sperm by males occurs below the size at onset of maturity of females from the same region and spatial patterns in maturity estimated by onset of spermatid production were similar to those of females.     

Habitat preferences and habitat restoration options for small‐bodied and juvenile fish species in the northern Murray–Darling Basin

Degradation of instream habitats in the northern Murray–Darling Basin has occurred through numerous stressors, including siltation, clearing of bankside vegetation, intrusion of livestock and impacts of pest species. A better understanding of habitat preferences of native fish species could help guide future instream habitat restoration actions. The habitat choices of seven native fish species, juvenile Murray Cod (Maccullochella peelii), juvenile Golden Perch (Macquaria ambigua ambigua), juvenile Silver Perch (Bidyanus bidyanus), adult Murray–Darling Rainbowfish (Melanotaenia fluviatilis), adult Olive Perchlet (Ambassis agassizii), adult Un‐specked Hardyhead (Craterocephalus stercusmuscarum fulvus) and adult carp gudgeons (Hypseleotris spp.) were tested in preference troughs to help inform potential habitat restoration actions in the Condamine catchment. Each species was given a choice between pair combinations of open sandy habitat, submerged macrophytes, emergent plants and rocky rubble. Habitat preferences varied between species. Murray Cod, Golden Perch, carp gudgeons and Olive Perchlets preferred structure over open sandy habitat, whilst juvenile Silver Perch, Un‐specked Hardyhead and Murray–Darling Rainbowfish did not avoid open sandy habitats. Juvenile Murray Cod preferred rocky rubble habitat over all other habitat choices. Use of complex rock piles to provide nursery habitat for Murray Cod populations is a potential restoration option. Introduction of rock could also benefit Golden Perch and carp gudgeons. Use of emergent plants, submerged macrophytes and rocky rubble for habitat restoration all appear to have merit for one or more species of small‐bodied fishes or juvenile stages of larger sized fishes. Rocky rubble or floating attached macrophytes could be viable restoration options in areas too turbid to establish submerged macrophytes. These habitat interventions would complement existing actions such as re‐snagging and provision of fish passage to assist with sustainable management of native fish populations.     

Geomorphic transience moderates topographic controls on tropical canopy foliar traits

Tropical ecosystems that exist on mountainous terrain harbour enormous species and functional diversity. In addition, the morphology of these complex landscapes is dynamic. Stream channels respond to mountain uplift by eroding into rising rock bodies. Many local factors determine whether channels are actively downcutting, in relative steady‐state, or aggrading. It is possible to assess the trajectory of catchment‐level landscape evolution utilising lidar‐based models, but the effect of these trajectories on biogeochemical gradients and organisation of canopy traits across climatic and geochemical conditions remain uncertain. We use canopy trait maps to assess how variable erosion rate within catchments influence hillslope controls on canopy traits across Mt. Kinabalu, Borneo. While foliar nutrient content generally increased along hillslopes, these relationships were moderated by catchment responses to changing erosion pressure, with active downcutting associated with greater turnover in canopy traits along hillslopes. These results provide an understanding of geomorphic process controls on forest functional diversity.     

粤北石漠化地区植被退化过程及其建模

在粤北石漠化地区选取不同石漠化阶段的样地,运用面上调查和定位观测相结合的方法,研究石漠化地区植被退化及构建其理论模型.结果表明:随石漠化程度的加深,粤北石漠化土地的植物群落结构越来越趋于简单,植被演替趋势为(黄连木、苎麻、黄荆、三裂叶野葛)→(黄连木、青蒿、野菊)→(五节芒、野古草、牛筋草)→黄叶凤尾藓,群落层片从4层变为1层,物种减少比例从0→14％ →46％→86％,土壤有机质、全氮、速效氮、速效磷和速效钾含量也随石漠化程度的加深呈极显著下降.植被演替退化可以用不同物种关于某种资源的竞争模型来描述,由此建立了粤北石漠化地区植被退化的模型.     

Conditional female strategies influence hatching success in a communally nesting iguana

The decision of females to nest communally has important consequences for reproductive success. While often associated with reduced energetic expenditure, conspecific aggregations also expose females and offspring to conspecific aggression, exploitation, and infanticide. Intrasexual competition pressures are expected to favor the evolution of conditional strategies, which could be based on simple decision rules (i.e., availability of nesting sites and synchronicity with conspecifics) or on a focal individual's condition or status (i.e., body size). Oviparous reptiles that reproduce seasonally and provide limited to no postnatal care provide ideal systems for disentangling social factors that influence different female reproductive tactics from those present in offspring‐rearing environments. In this study, we investigated whether nesting strategies in a West Indian rock iguana, Cyclura nubila caymanensis, vary conditionally with reproductive timing or body size, and evaluated consequences for nesting success. Nesting surveys were conducted on Little Cayman, Cayman Islands, British West Indies for four consecutive years. Use of high‐density nesting sites was increasingly favored up to seasonal nesting activity peaks, after which nesting was generally restricted to low‐density nesting areas. Although larger females were not more likely than smaller females to nest in high‐density areas, larger females nested earlier and gained access to priority oviposition sites. Smaller females constructed nests later in the season, apparently foregoing investment in extended nest defense. Late‐season nests were also constructed at shallower depths and exhibited shorter incubation periods. While nest depth and incubation length had significant effects on reproductive outcomes, so did local nest densities. Higher densities were associated with significant declines in hatching success, with up to 20% of egg‐filled nests experiencing later intrusion by a conspecific. Despite these risks, nests in high‐density areas were significantly more successful than elsewhere due to the benefits of greater chamber depths and longer incubation times. These results imply that communal nest sites convey honest signals of habitat quality, but that gaining and defending priority oviposition sites requires competitive ability.     

Effect of Mineral Phosphate Solubilization on Biological Nitrogen Fixation by Diazotrophic Cyanobacteria

The ability of two diazotrophic cyanobacteria Westiellopsis prolifica and Anabaena variabilis were examined to solubilize extracellular insoluble tricalcium phosphate (TCP) and Mussorie rock phosphate (MRP). The two strains exhibited a differential response to insoluble forms of phosphorus used. W. prolifica showed better growth in presence of MRP while A. variabilis proliferated better in presence of TCP. Biological nitrogen fixation measured in terms of acetylene reduction (AR) activity showed significant variation among the concentrations of TCP or MRP and time of incubation. W. prolifica and A. variabilis showed maximum AR activity on 14 and 21 days of incubation respectively. In general AR activity in presence of MRP was always less than that in presence of TCP at all concentrations. Among the two cyanobacteria A. variabilis was best in terms of P-solubilization and nitrogen fixation and TCP (20 mg P l⁻¹) was the best source of insoluble P rather than MRP or K₂HPO₄.