The history and ethnobotany of bracken

The fossil record shows that Pteridium has been present in all the temperate stages of the Quaternary, but that for most of this period it formed a component of the herb layer of deciduous woodlands. Bracken did not begin to reach its present abundance and importance until widespread forest clearance began with the arrival of Neolithic man about 5000 years ago. Some of the factors that have played a role in the history of bracken are illustrated by a discussion of the spread of bracken in Scotland that occurred contemporaneously with the change from cattle- to sheep-farming in the 18th century. It is shown that man has played a dominant role in influencing the spread of bracken in Scotland, but that bracken was considered of great positive economic value. The ethnobotany of bracken is discussed, and it is suggested that it was once an important source of potash for the glass, soap and bleaching industries. The use of the plant as fuel, thatch, litter, compost and food, and for medicinal purposes is considered, and mention is made of various minor uses of the plant. Unfortunately it is difficult to estimate the amount of bracken consumed by these various employments, but it is suggested that the increased abundance of the plant may have been exaggerated because what was once a useful resource has now become a pest.     

Effects of the litter layer of Pteridium aquilinum on seed banks under experimental restoration

Questions: Does the litter layer of Pteridium aquilinum (bracken) act as a barrier to certain species in the seed bank? Does bracken control/restoration treatment affect seed transfer through the litter layer? Location: Five experiments at three sites across the UK covering two major vegetation types; acid‐grassland and heath‐land. Methods: At each experiment a range of bracken control and vegetation restoration treatments were applied for about ten years. The seed bank was sampled in both the bracken litter and the soil. The cover (%) of each species in the vegetation and the bracken litter abundance (cover and depth) was also estimated. Results: The bracken litter layer acts as an inert barrier as it contained a large proportion of seeds available in the litter‐soil profile (38%– 67% of the total). Bracken litter depth and cover also influenced significantly the seed bank composition in both the bracken litter and the soil. These effects were site‐specific, and species‐specific. The application of treatments changed significantly the balance between seed inputs and outputs in the bracken litter layer for some species. This was either a positive or negative response relative to the untreated control plots. Conclusion: For heathland and acid‐grassland restoration, the bracken litter layer may be an important seed source, but it must be disturbed particularly before seed addition.     

An Untidy Cover: Invasion of Bracken Fern in the Shifting Cultivation Systems of Southern Yucatán, Mexico

In land change science studies, a cover type is defined by land surface attributes, specifically including the types of vegetation, topography and human structures, which makes it difficult to characterize land cover as discrete classes. One of the challenges in characterizing a land-cover type is to distinguish variability within the class from actual land-cover transformation. The spread of plant invasions in tropical systems is affected by seasonal variations and disturbances such as agricultural activities and fires, making it difficult to determine the spread through thematic classifications. In this paper, we estimate the changes in spatial extent and seasonal variation of bracken fern invasion in Southern Yucatán from 1989 to 2005 by using a linear mixture model (LMM), a widely used method in the classification of remotely sensed data. The results show an increase in areas affected by bracken from 40 km² in 1989 to almost 80 km² in 2000. Lower estimates of the invasion resulted from data acquired at the end of the dry season (March–May), when bracken mixes with secondary vegetation or is removed by fires. The accuracy of the maps is estimated through the use of sketch maps of farmer's parcels and field data collected from 2000 to 2001. Understanding the spatial distribution and annual variability of bracken fern cover in the region is critical to determining the relation between disturbances such as fire and forest recovery. Using LMM may enhance this understanding by giving a more accurate picture of the extent and distribution of bracken fern invasion.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp     

Is vitellogenin an ancestor of apolipoprotein B-100 of human low-density lipoprotein and human lipoprotein lipase?

Vitellogenin, an ancient animal protein, is the major yolk protein of eggs, where it is used as a food source during embryogenesis. Here it is shown that vitellogenins, including those from the invertebrates Caenorhabditis elegans and Drosophila melanogaster, contain domains that are homologous with parts of apolipoprotein B-100 (apoB-100) of human low-density lipoprotein and human lipoprotein lipase. As vitellogenins are likely to have been used by invertebrates during embryogenesis well before the circulation of lipids appeared in vertebrates, it is suggested that copies of a precursor gene, serving a function similar to vitellogenin, were modified to code for part of apoB-100 and lipoprotein lipase in vertebrates. In addition to providing a link between invertebrates and vertebrates for proteins involved in lipid transport, these homologies suggest new functions for vitellogenin other than being a yolk food for the developing embryo.     

Habitat selection and diet of Great Snipe Gallinago media during breeding

The Great Snipe Gallinago media is considered to be an endangered species. This paper examines its food and habitat use on a sub-alpine/low-alpine breeding area in central Norway. It was estimated that earthworms constitute more than 90% of Great Snipe food (by weight). Feeding birds selected the low herb willow scrub vegetation community and to a lesser degree eutrophic fen. Birds did not selectively feed on eutrophic dwarf birch/juniper heath despite it being the third most used vegetation community by virtue of its extent. Although soil penetrability, vegetation cover and earthworm density varied across vegetation communities, Great Snipe selected sites with similar habitat characteristics in different vegetation communities. Great Snipe seemed to select for an optimal combination of soil penetrability and earthworm density, and for medium scrub cover. Nests were found in a broad range of vegetation communities, but only low herb willow scrub was selectively used. However, an equal number of nests was found in eutrophic fen due to its larger extent. Dense vegetation cover around nests and short flushing distance of incubating females indicate low sensitivity to disturbance. We consider the Great Snipe to be a food and habitat specialist, requiring habitats rich in sub-surface invertebrates to breed. This may explain its scattered distribution in Scandinavia, and may render it vulnerable to habitat modification and loss.     

Birds,Cattle, and Bracken Ferns: Bird Community Responses to a Neotropical Landscape Shaped by Cattle Grazing Activities

Large areas of tropical moist forests have been converted to cattle pastures, generating complex landscapes where different habitats are represented by small patches with an uneven spatial distribution. Here, we describe how bird communities respond to the different elements present in a livestock landscape that was originally dominated by tropical moist forest. We surveyed six habitats: open pastures, pastures with shrubs, early‐ and middle‐secondary forests, mature forest, and pastures invaded by bracken ferns (Pteridium aquilinum). Bird diversity was high in secondary and mature forests, and low in fern‐invaded sites and open pastures. Fern‐dominated sites had the lowest bird species richness, and trophic guild diversity of all habitats. Habitat structure affected both bird species richness and densities in similar ways. Tree species richness was the habitat attribute that had a bigger positive effect on bird species richness. Bird community structure varied among sampled habitats, separating habitats in two major groups (forests and pastures). Our data indicate that bracken fern‐invaded pastures were the worst habitat condition for avian communities. To increase bird diversity, we recommend to eliminate or manage bracken fern and to increase shrub and tree cover in open pastures to provide food resources and shelter for birds. Finally, we encourage the maintenance of secondary and mature forest remnants as a strategy to conserve resident birds within a landscape dominated by livestock activities.     

Vitamin content of four marine microalgae. Potential use as source of vitamins in nutrition

Summary Certain marine microalgae contain water-and lipid-soluble vitamins and can be used as food supplements or food ingredients. A number of vitamins are present in higher concentrations in the microalgae than in conventional foods traditionally considered rich in them. Ingestion of relatively small quantities of microalgae can cover the requirements for some vitamins in animal nutrition, including human nutrition, while supplementing others. Marine microalgae can thus be considered to represent a non-conventional source of vitamins or a vitamin supplement for animal or human nutrition.     

Karenia brevis red tides,brevetoxins in the food web,and impacts on natural resources: Decadal advancements

As recently as a decade ago, Karenia brevis red tides and their effects on animal resources in the Gulf of Mexico were principally perceived as acute blooms that caused massive fish kills. Although occasional mortalities of higher vertebrates were documented, it has only been in the past decade that conclusive evidence has unequivocally demonstrated that red tides and their brevetoxins are lethal to these organisms. Brevetoxins can be transferred through the food chain and are accumulated in or transferred by biota at many trophic levels. The trophic transfer of brevetoxins in the food web is a complex phenomenon, one that is far more complicated than originally conceived. Unexplained fish kills and other animal mortalities in areas where red tide is endemic are being increasingly linked with post-bloom exposures of biota to brevetoxins. Mass mortality events of endangered Florida manatees (Trichechus manatus latirostris) follow a consistent spatial and temporal pattern, occurring primarily in the spring in southwestern Florida. Persistent blooms can also cause a cascade of environmental changes, affecting the ecosystem and causing widespread die-offs of benthic communities. Ongoing fish kills from sustained blooms can lead to short-term declines in local populations. Although animal populations in areas where red tide is endemic are unquestionably at risk, it remains to be determined to what extent populations can continue to recover from these sustained effects.     

Bracken invasion in Scotland

Summary

For the first time, estimates of the amount of sparse bracken on open land, the amounts of bracken under tree cover and the amounts in linear features are made. These data were used to predict the areas of Scotland most at risk from invasion from patch edges, from sparse patches becoming dense and from invasion along linear features. Computer models show that if the climate warms over the next 50 yr as predicted, then bracken growth will increase and the amount of hill land suitable for invasion by bracken will increase. On some sites where bracken is being controlled, it is reduced in cover and other ground vegetation is becoming established. However, we cannot ensure that when bracken is controlled that the control is always effective and that appropriate vegetation will become established. Some generalized rules have been derived to help in the selection of sites likely to show the most benefit from control treatment.     

Control of bracken

Mechanical methods of bracken control are now being replaced by the use of chemicals. Trials indicate the value of asulam and glyphosate in reducing frond numbers of bracken when sprayed in late July or early August in the west of Scotland. There is still a need to find a bracken eradicant chemical rather than a control chemical. Research is also required to investigate the results of removing the bracken cover on the ecology of the treated areas. The effects of sudden exposure of the hitherto protected grass to extremes of climate are not known.     

Simulation of bracken cover in forested areas in Victoria in response to season,overstorey and fire conditions

Abstract A computer-based model is presented that brings together the existing knowledge about the dynamics of bracken in eucalypt forests in south-eastern Australia. The average length of the growing season, the timing and extent of logging, and the timing and severity of fire are major inputs to the model. The model is predominantly deterministic, but has a stochastic environmental component. The model is validated with four independent sets of data. The model successfully predicts the trends in the data. The interactions between bracken, other understorey species and eucalypt regeneration are explored with the model. The likely effect of different silvicultural and fire management practices on the cover of bracken are investigated using the model. Year to year variation can mask the effects of disturbance if bracken cover is viewed in any one year in isolation. Bracken cover trends can only be seen over a period of 10 years or more. The model reinforces the importance of site productivity as measured by length of growing season and the degree of tree removal on bracken cover.     

The significance of vertebrates in the structure and functioning of ecosystems

A review of published data on the ecology of terrestrial vertebrates and, partly, fishes is used as a basis to show that their communities have only a weak relationship to the structure of phytocenoses. Unlike plants, vertebrates actively choose preferable biotopes and do not die off upon transition between the stages of succession. The role of vertebrates in the functioning of ecosystems is determined by their contribution to matter and energy turnover and effect on the structure of ecosystems of different ranks. The transfer of matter and energy in food chains accelerates their turnover, and the distribution of excrements and corpses within the ranges of animal activity and migrations modulates the pattern of matter and energy fluxes over the Earth’s surface. The spread of plant diaspores by animals and the burrowing and feeding activities of first-order consumers give rise to microsuccessions within macrosuccession stages, thereby contributing to the diversity of vegetation. In some cases, the activities of first-order consumers may result in the cessation of succession.     

动物与植物种子更新的关系Ⅱ．动物对种子的捕食、扩散、贮藏及与幼苗建成的关系

植物的繁殖体总是面临来自各类生物（如昆虫、脊椎动物、真菌）的捕食风险。因动物捕食引起的种子死亡率影响植物的适合度、种群动态、群落结构和物种多样性的保持。种子被捕食的时间和强度成为植物生活史中发芽速度、地下种子库等特征的主要选择压力,而种子大小、生境类型等因素也影响动物对植物种子的捕食。捕食者饱和现象被认为是植物和种子捕食者之间的高度协同进化作用的结果,是限制动物破坏种子、提高被扩散种子存活率的一种选择压力。大部分群落中的大多数植物种子被动物扩散。种子扩散影响种子密度、种子被捕食率、病原体攻击率、种子与母树的距离、种子到达的生境类型以及建成的植株将与何种植物竞争,从而影响种子和幼苗的存活,最终影响母树及后代植物的适合度。种子被动物扩散后的分布一般遵循负指数分布曲线,大多数种子并没有扩散到离母树很远的地方。捕食风险、生境类型、植被盖度均影响动物对种子的扩散。植物结实的季节和果实损耗的过程也体现了其对扩散机会的适应。许多动物有贮藏植物种子的行为。动物贮藏植物繁殖体的行为,一方面调节食物的时空分布,提高了贮食动物在食物缺乏期的生存概率;另一方面也为种子萌发提供了适宜条件,促进了植物的扩散。于是,植物与贮食动物形成了一种协同进化关系,这种关系可能是自然界互惠关系（mutualism)的一种。影响幼苗存活和建成的因子包括种子贮蒇点的微生境、湿度、坡向、坡度、林冠盖度等。许多果食性动物吃掉果肉后,再将完好的种子反刍或排泄出来。种子经动物消化道处理后,发芽率常有所提高。     

Predators and avian community organization: an experiment in a semi-desert grassland

Summary We provide experimental evidence that predators are a major factor organizing a community of granivorous grassland birds (mostly emberizid finches). Our focus is not on the lethal effects of predators, but on the simple idea that (i) birds will not settle where they perceive a high risk of predation, and (ii) species differ in their perception of the safety of woody vegetative cover due to differences in antipredator escape behavior. Consistent with this idea is the fact that the composition of this grassland community responds markedly to minor manipulations in the distribution of woody cover. In particular, with the addition of cover to open grasslands, species with cover-dependent escape tactics increase in abundance, while the abundance of cover-independent species decreases greatly; this decrease may reflect aggression from cover-dependent species, but evidence suggests that some cover-independent species may actively avoid cover-rich areas per se. Non-predatory effects of cover, most notably those concerning food resources and microclimate, appear unable to explain these results. Predators may influence many communities of terrestrial vertebrates via species-specific responses to cover.     

Recovery of Moorland Vegetation after Aerial Spraying of Bracken (Pteridium aquilinum (L.) Kuhn) with Asulam

Bracken (Pteridium aquilinum) is a major weed of seminatural vegetation in Great Britain, as in many other countries. As a consequence, large areas have been subject to control with the intention of restoring the former vegetation. The use of aerial spraying with asulam, a narrow spectrum, carbamate herbicide, has become a common method of control. However, its long‐term efficacy has not been assessed in terms of either controlling the bracken or in producing suitable restored habitats. This study undertook such an assessment by comparing the results of a 2002 survey of the sites subject to bracken control by aerial spraying of asulam with previous (1990/1991 and 1994) surveys of the same sites. This showed that a single application of asulam was effective in eradicating bracken (<1% cover remaining) on a third of sites. However, on 10% of the sites, the bracken had regenerated completely (cover >80%) and on the remainder it was still present in patches (>20% of quadrats), often at high density. More than half the sprayed sites had seen good recovery of moorland vegetation, the target of the restoration, because they were now classified as having upland heathland vegetation within the National Vegetation Classification. Considerable amounts of bracken control are grant aided as part of agri‐environment schemes. These schemes should be adapted to encourage good practice, namely, intensive follow‐up treatment by spraying any emerging fronds, and to encourage treatment of previously sprayed areas rather than spraying of new areas in order to protect previous investment of grant aid.     

Lignin signatures show the effects of changes in heather and bracken cover on the composition of organic matter in a moorland soil profile

Bracken (Pteridium aquilinum) is aggressively displacing heather (Calluna vulgaris) on many moorlands in Britain. We investigated the use of lignin derivatives to identify the distribution of soil organic matter (SOM) derived from bracken in moorland soil profiles formed under heather. Phenylpropanoids extracted from recently senesced litters, roots and SOM, using alkaline CuO oxidation, showed distinct signatures for bracken and heather, with vanillyl moieties dominating bracken litter extracts and vanillyl and syringyl dominating heather litter extracts. Ratios of vanillyl and syringyl concentrations characterised the SOM derived from heather and bracken better than the concentrations of the individual moieties. The analysis showed up to a depth of 5 cm under pure bracken cover, and at the interface between heather and bracken, the SOM was largely derived from bracken litter but below that depth SOM was apparently derived from heather. The use of these methods to identify the plant origin of SOM not only enables understanding the effects of changing vegetation cover on organic matter dynamics in moorland soils but could also facilitate management techniques in moorland/heathland restoration which involve the removal of comparatively nutrient-rich SOM derived from bracken. Received: 30 November 1997 / Accepted: 11 April 1998     

Use of indigenous knowledge for rapidly assessing trends in biodiversity: a case study from Chiapas, Mexico

In order to evaluate the usefulness of rapid surveys of indigenous knowledge for assessing trends in biodiversity, a case study was undertaken in two rural communities, Juznajab and Muquenal, in Chiapas, Mexico. This involved the use of a variety of rapid rural appraisal (RRA) and participatory rural appraisal (PRA) techniques, including semi-structured interviews, transect walks and participatory mapping. These approaches were used in conjunction with analysis of land use maps and aerial photographs to evaluate recent changes in vegetation cover and abundance of utilised species. In both communities, the extent of forest cover was considered by local people to have declined substantially in recent decades, with an annual decline in forest cover of 0.3% and 0.6% estimated by local people in Juznajab and Muquenal, respectively. Results from RRA indicated that this has been accompanied by significant declines in the abundance of useful species. In Juznajab 60% and 79%, and in Muquenal 96% and 85% of plants and animal species, respectively, were considered to have declined within living memory. These declines appear to result from over-utilization as well as habitat changes. For example, most of the tree species used for timber and the animal species used for meat were considered to have declined substantially in both communities. These results indicate that indigenous knowledge is potentially a valuable source of information about biodiversity trends, which could be assessed during Rapid Biodiversity Assessments and incorporated into the process of resource management by local communities. However, the contradictions recorded between assessments of vegetation change by local people and data obtained from other sources indicates the need for caution in the use of indigenous knowledge for this purpose.     

Collective decision-making and behavioral polymorphism in group living organisms

Collective foraging in group living animal populations displaying behavioral polymorphism is considered. Using mathematical modeling it is shown that symmetric, spatially homogeneous (food sources are used equally) and asymmetric, spatially inhomogeneous (only one food source is used) regimes can coexist, as a result of differential amplification of choice depending on behavioral type. The model accounts for recent experimental results on social caterpillars not only confirming this coexistence, but also showing the relationship between the two types of regime and the ratio of active to inactive individuals.     

ARTHROPODS THAT PREY ON VERTEBRATES

1. Many arthropods are predators of vertebrates: four orders of the class arachnida, six orders of insecta, five orders of crustacea and one order of chilopoda include species that have been reported to eat vertebrates. At the population level, some arthropods are responsible for significant mortality among some vertebrates.
2. Arthropods are well equipped for this type of predation; many are larger than vertebrates (approximately 20% of the vertebrate fauna of eastern North America is less than 10 cm in length), they may hunt in social groups and many have toxins or other adaptations that increase predatory efficiency.
3. Several arthropod predators and vertebrates may be involved in cross predation, the species eating each other. The switch in the role of predator and prey occurs during 'ontogenetic reversal' as the vertebrate grows from small and vulnerable to large and predaceous. Cross predation decreases the future risk for one's self or offspring.
4. The opportunity for arthropod predation on vertebrates exists in many communities, but a review of some food webs catalogued by Cohen (1978) indicates that this particular link may be easily overlooked. Some arthropods should be investigated as potential predators of vertebrates.
5. The information available from the analysis of feeding interactions in a community should be an important link between field and theoretical ecology; however, most food webs are probably underestimates of the complexity that is commonplace.