Variation in juvenile steelhead (Oncorhynchus mykiss) dispersal in relation to age and growth performance

Volitional dispersal is a ubiquitous strategy characteristic of species across major faunal groups. Dispersal during the juvenile life stage is of interest because early performance can be critical for determining future success (survival/reproduction). For salmonids, dispersal can influence local density, competition, individual growth and survival, though drivers of dispersal at meso-scales are rarely quantified. Here, we evaluate dispersal of tagged juvenile steelhead (Oncorhynchus mykiss) through habitat units in extended stream reaches (500 m) at sites across a watershed from July to October 2017. Our aim was to quantify the frequency and spatial extent of dispersal, identify links to biotic and abiotic factors, evaluate the implications for individual growth and test for associations between dispersal and migration initiation. Dispersal rates varied between sites, but were consistently higher for age 1+ than for age 0 steelhead (avg. 21% vs. 6% respectively). Age 1+ dispersal probability was positively correlated with time between recapture events and body mass, and negatively correlated with growth rate, maximum temperature experienced and age 1+ density. At sites where there appeared to be growth benefits to remaining sedentary compared to moving, proportionally fewer fish performed dispersal. We found no links between dispersal and timing or probability of migration initiation the following spring. Our results support the hypothesis that although dispersal over intermediate scales (10–1,000 m) might be rare, it could be an important strategy that permits fish to seek out better opportunities (foraging, shelter or otherwise) in underutilised areas.     

Effects of natural barriers on the spillover of a marine mollusc: implications for fisheries reserves

• 1. The movement of organisms and dispersal of propagules is fundamental to the maintenance of populations over time. However, the existence of barriers, created through the spatial configuration of habitats, may significantly affect dispersal patterns and thus influence community dynamics and resource sustainability.
• 2. Within marine environments unstructured or open habitats may form partial or complete ecological barriers due to elevated risk of predation or physical stresses associated with them. The existence and effects of such barriers may be of particular importance when considering the establishment of marine protected areas with a fisheries enhancement focus.
• 3. In this paper, the spillover of post‐settlement queen conch (Strombus gigas) from a protected area in the Turks and Caicos Islands is investigated. It is hypothesized that the reserve boundaries overlap with a series of shallow, sand habitats that effectively enclose the protected population, reducing the spillover of conch into the adjacent fished areas.
• 4. To test this, density gradient maps for juvenile and adult conch populations were constructed using underwater visual survey data at 68 sites within and surrounding the protected area. These maps illustrate very low densities coinciding with poor, shallow sand habitats along the two marine boundaries of the reserve where spillover is expected to take place.
• 5. These sand habitats are thought to create ecological barriers to a slow, sedentary gastropod largely due to their shallowness (physical stresses of solar exposure or anoxia) and lack of food reducing the tendency of individuals to move across these areas, despite the 10‐times higher density of adult queen conch observed in the protected area compared with outside.

Copyright © 2003 John Wiley & Sons, Ltd.     

新疆特殊农田生态赤眼蜂田间自然扩散的初步研究

在新疆棉花、加工番茄等特殊农田生态环境和种植模式下,螟黄赤眼蜂(Trichogramma chilonis)在田间自然扩散呈现随距离延长、寄生卵量递减的趋势,螟黄赤眼蜂在棉田、玉米田和加工番茄田扩散有效距离为8～10 m,最远扩散15 m,田间温湿度和风向等环境条件对螟黄赤眼蜂田间扩散和寄生影响作用明显,田间温度偏高和相对湿度偏低不利于螟黄赤眼蜂的寄生,下风口螟黄赤眼蜂寄生率明显高于上风口.     

Interactions of slope and canopy of herbage of three herbage species on transport of faecal indicator bacteria by rain splash

The movement of faecal pathogens from land to surface and ground‐water are of great interest because of the public and livestock health implications. Knowledge of canopy structure and how it might be managed to help mitigate nutrient and pathogen movement in pasture is needed to create management practices that balance livestock production with environmental benefits. An experiment was conducted using a rainfall‐simulating device to test whether canopy structure of species common to pastures in Appalachia, USA could be managed to influence dispersion of faecal pathogens. Seven pots (30‐cm diameter) of white clover, orchardgrass and perennial ryegrass were lined up on horizontal and sloping surfaces under a rainfall simulator. The centre pot was inoculated at the soil surface with 4 × 10¹⁰ faecal coliform bacteria (FC) just before rainfall simulation started. The species were maintained under short, moderate and tall canopy management treatments. White clover exhibited the greatest rates of lateral and vertical dispersion of FC into the canopy, especially in the short canopy management treatment following 30 min of rainfall (about 40 mm). Low concentrations of faecal coliform bacteria also dispersed into the canopies of the grass species but the differences in concentration of FC between the grass species were not different. When the proportion of white clover in a pasture is high, the canopy should be relatively taller to reduce the likelihood of infection associated with faecal coliform‐contaminated herbage.     

Plant‐frugivore interactions in an intact tropical forest in north‐east Thailand

Fleshy‐fruited plants in tropical forests largely rely on vertebrate frugivores to disperse their seeds. Although this plant–animal interaction is typically considered a diffuse mutualism, it is fundamental as it provides the template on which tropical forest communities are structured. We applied a mutualistic network approach to investigate the relationship between small‐fruited fleshy plant species and the fruit‐eating bird community in an intact evergreen forest in northeast Thailand. A minimum of 53 bird species consumed fruits of 136 plant species. Plant‐avian frugivore networks were highly asymmetrical, with observed networks filling 30% of all potential links. Whereas some of the missing links in the present study might be due to undersampling, forbidden links can be attributed to size constraints, accessibility and phenological uncoupling, and although the majority of missing links were unknown (58.2%), many were probably due to a given bird species being either rare or only a very occasional fruit eater. The most common frugivores were bulbuls, barbets and fairy‐bluebirds, which were responsible for the majority of fruit removal from small fleshy fruited species in our system. Migratory birds seemed to be a minor component of the plant‐frugivore networks, accounting for only 3% of feeding visits to fruiting trees; they filled 2% of the overall potential networks. The majority of interactions were generalized unspecific; however, Saurauia roxburghii Wall. appeared to be dependent on flowerpeckers for dispersal, while Thick‐billed Pigeons were only seen to eat figs.     

Dispersal of invasive Phytolacca americana seeds by birds in an urban garden in China

Although seed dispersal is a key process determining the regeneration and spread of invasive plant populations, few studies have explicitly addressed the link between dispersal vector behavior and seedling recruitment to gain insight into the invasion process within an urban garden context. We evaluated the role of bird vectors in the dispersal of pokeweed (Phytolacca americana), a North American herb that is invasive in urban gardens in China. Fruiting P. americana attracted both generalist and specialist bird species that fed on and dispersed its seeds. The generalist species Pycnonotus sinensis and Urocissa erythrorhyncha were the most frequent dispersers. Seedling numbers of P. americana were strongly associated with the perching behavior of frugivorous birds. If newly recruited bird species use seedling‐safe perching sites, the P. americana will regenerate faster, which would enhance its invasive potential. Based on our observations, we conclude that the 2 main bird vectors, P. sinensis and U. erythrorhyncha, provide potential effective dispersal agents for P. americana. Our results highlight the role of native birds in seed dispersal of invasive plants in urban gardens.     

A reconsideration of natural dispersal distances of the pine pathogen Dothistroma septosporum

The natural spread of Dothistroma septosporum, the causal agent of a foliar disease of pines, was investigated at three sites in the south of England using trap plants. The pathogen is considered to be primarily rain‐splash dispersed, but this study shows that it can be spread many hundreds of metres from an inoculum source, demonstrating that dispersal is not solely via rain splash. The maximum distance the pathogen was recorded from any infection source was in excess of 1400 m, over five times the distance defined in the only previous work of this kind. Consequently, a reassessment of forest and production nursery management practices is called for, as these assume that the pathogen only spreads naturally over limited distances. Detection of the pathogen on trap plants over 100 m from the inoculum source was, in most cases, only possible using quantitative real‐time PCR diagnosis. The entire diagnostic procedure, from DNA extraction to amplification, was able to detect a minimum of approximately 17 D. septosporum cells in a pine needle sample, assuming only a moderate DNA extraction efficiency of 30%.     

9种风传杂草种子的扩散能力及传播策略

[目的]研究9种风传杂草种子的扩散能力及传播策略。[方法]以9种杂草种子为试验材料,研究其传播能力(沉降速度、水平移动距离)及其与种子形态结构之间的相关性。[结果]就9种种子整体而言,种子的沉降速度与水平移动距离呈极显著负相关。菊科植物种子的沉降速度与果长、毛长呈正相关,而禾本科植物种子的沉降速度与二者呈负相关;菊科植物种子的水平移动距离与果长、毛长呈负相关,而禾本科植物种子的水平移动距离与二者呈正相关,说明菊科植物和禾本科植物种子的传播策略不同,而这种传播策略往往与植物本身生存环境有关。禾本科植物具有横向传播优势。[结论]该研究可为深入了解种子的传播机制以及杂草的入侵防治提供理论依据。     

辽东栎的繁殖体及其与种群更新的关系

就辽东栎的种子雨及其传播动力、种子传播后的命运、种子萌发、幼苗建立、实生更新对动物捕食的适应和萌生特性等方面进行了简要综述,并对未来研究的发展方向进行了展望。辽东栎种子是多种脊椎动物和鸟类的食物资源,种子萌发和幼苗形成期间的捕食压力导致其实生更新困难,但捕食动物对种子的搬运和埋藏对辽东栎种群更新和扩散具有重要意义;光照和水分对辽东栎的种子萌发和幼苗建立都具有重要影响,在森林管理工作中,适当干扰 (例如择伐) 对辽东栎的种子萌发、幼苗生长与存活以及种群更新都是有利的。较强的萌生能力对维持辽东栎的遗传多样性和种群活力具有重要的生态学意义;在强干扰条件下,萌生作为辽东栎通过从种子、幼苗、幼树到成年植株过程中的更新瓶颈的途径,是辽东栎实现种群更新的主要对策。     

Effects of insect infestation on rodent‐mediated dispersal of Quercus aliena: results from field and enclosure experiments

Rodents influence plant establishment and regeneration by functioning as both seed predators and dispersers. However, these rodent–plant interactions can vary significantly due to various environmental conditions and the activity of other insect seed predators. Here, we use a combination of both field and enclosure (i.e. individual cage and semi‐natural enclosure) experiments, to determine whether rodents can distinguish sound seeds from those infested with insects. We also demonstrate how such responses to insects are influenced by food abundance and other environmental factors. We presented rodents with 2 kinds of Quercus aliena seeds (sound and insect‐infested seeds) in a subtropical forest in the Qinling Mountains, central China, from September to November of 2011 to 2013. The results showed that rodents preferred to hoard and eat sound seeds than infested seeds in the field and semi‐natural enclosure, while they preferred to eat infested seeds over sound seeds in the individual cages. In addition, both hoarding and eating decisions were influenced by food abundance. Rodents hoarded more sound seeds in years of high food abundance while they consumed more acorns in years of food shortage. Compared with field results, rodents reduced scatter‐hoarding behavior in semi‐natural enclosures and ate more insect‐infested seeds in smaller individual cages. These results further confirm that rodents distinguish infested seeds from non‐infested seeds but demonstrate that this behavior varies with conditions (i.e. environment and food abundance). We suggest that such interactions will influence the dispersal and natural regeneration of seeds as well as predation rates on insect larvae.