Collective action for the conservation of on-farm genetic diversity in a center of crop diversity: an assessment of the role of traditional farmers' networks

"This project explored the possible role of collective action among small-scale farmers in managing and maintaining genetic resources in a center of crop diversity. It focused on the local institutions that ensure the supply of seed of diverse maize landraces to small-scale farmers in the Central Valleys of Oaxaca, Mexico. The key hypothesis was that the medium-to-long-term supply of a diverse set of varieties to any individual small-scale maize farmer depends on an agreement among a group of farmers to manage and supply the seed of these landraces to each other, if the need arises, and that this constitutes a form of collective action. Six communities were studied, three of them in-depth. Methodologies used included in-depth semi-structured interviews with key informants, focus group discussions, and a tracer study—following the flows of seed among different farmers. The results show that, while there is a well-developed local seed supply system based on sets of social relationships and involving multiple types of transactions, there is no evidence of collective action. Most farmers rely on and prefer to select and save seed from their own harvests. There are seed flows, however, and most seed transactions take place among people with social links, but not within a well-defined group. There are no specialized suppliers of seed, either individuals or groups. Most transactions are bilateral and while the most common transaction is the sale and purchase of seed, this is not done for profit but out of a sense of moral obligation. The system is based on the creation of trust, which is needed because seed is not transparent—that is, it is not possible to fully predict the plant phenotype that may result from a given seed simply by looking at the seed. Farmers demand different types of maize and they believe that there is a strong genotype-by-environment interaction, hence “foreign” maize types may not be appropriate for them. At the same time, farmers also find occasional experimentation beneficial and believe that they can slowly modify the characteristics of “foreign” landraces. In this system, there are strong incentives to be conservative, but also to try new landraces and experiment. The local seed system of these farmers is resilient but able to innovate as well. Interventions to support the conservation of landraces on farm, based on specialized networks for seed that rely on collective action, may not work.." Author's AbstractCentral America, Europe and North America, Small farmers, Collective action, Informal seed systems, Crop diversification, Seed supply, Trust,

The effects of neonicotinoid seed treatments on farmland birds

Neonicotinoids are the most common group of agricultural insecticides used worldwide, with seed treatments accounting for a large proportion of applications. Since neonicotinoids were introduced to the agricultural market, concerns have been raised regarding their effect on non-target organisms, and in the last 5 years avian-related research has gained momentum. However, the extent and impact of neonicotinoid exposure in free-living birds, particularly farmland communities, remains poorly understood. Here, data were collected for agricultural plant material and multiple species of farmland bird from neonicotinoid-treated fields, to assess the exposure pathway associated with seed treatments. Biological samples were obtained from 15 species of bird to measure levels of exposure and data were collected to investigate whether there were associated physiological sub-lethal effects. Long-term data sets for neonicotinoid use and bird populations were also modelled to assess the impact of seed treatments on farmland bird species over the last 21 years. Seed treatments were found to be a significant source of exposure for farmland birds. Exposure was confirmed in 9% of individuals pre-sowing, compared to 68% of individuals post-sowing, and 30% of species overall. Exposure was found to be associated with one physiological parameter, which could be detrimental to bird health. There was no consistent evidence to suggest that dietary exposure to neonicotinoid seed treatments has impacted bird populations historically, however three bird species warrant further investigation in this regard. These data suggest that current risk assessment and insecticide product safety protocols do not effectively safeguard farmland bird communities from neonicotinoid exposure during sowing, and imply that exposure may be widespread in bird communities where neonicotinoids are in use. Results obtained here highlight the need for field-based data in ecotoxicological risk assessments and should be considered in relation to any future systemic insecticide seed treatments

The floodplain meadows of Soomaa National Park, Estonia. Vegetation - Dispersal - Regeneration

In the years 1998-2000 various aspects of the vegetation ecology and plant population dynamics of the floodplain meadows of the Soomaa National Park in Estonia were studied. Based on phytosociological methods the floodplain meadows and related communities were surveyed and habitat parameters like groundwater dynamics and soil properties were recorded. The survey of 171 relevés resulted in the description of 15 meadow, reed and sedge communities. These ranged from dry communities on sandy ridges, mesic communities in lower but well drained sites, moist communities on poorly drained sites of the central floodplains to wet communities on the lowest and frequently inundated sites. Most of these communities can conveniently be placed in the established syntaxonomical system, at least at the level of alliances. True meadow communities of the Arrhenatheretalia and Molinietalia were easily recognizable but showed distinct properties setting them apart from their Central European counterparts. Communities with Sesleria caerulea were found to be unique to the Baltic area but could be placed inside the Molinion. In a set of three experimental studies various aspects of the regeneration dynamics of floodplain plants were assessed. Seed traps were used to study the composition of the local seed rain, in a seed sowing study the germination of ten species in different gap types was investigated and a third study examined the role of seed bank and seed rain in the colonization of artificial gaps. Data were also analyzed in view of the role of plant traits and functional groups. 140 seed traps were placed at 28 sample locations along three transects. 34423 seeds of ca. 76 species were collected during one year of sampling; the distribution of species was highly skewed with only five species accounting for 84 % of the total seed count, median seed density was 6579 seeds/sqm. Approximately half of the seed rain originated from the direct neighborhood of the seed traps but only very few species came from outside the studied transects; those were either wind-dispersed or water-dispersed. Temporal variation of seed rain was considerable with three distinct peaks in the course of one year. The distribution of plant traits showed substantial variation between seed rain and vegetation. Generally, wind- and water-dispersed species were more important in the seed rain whereas animal-dispersed species and those without apparent dispersal agent were more prominent in the vegetation. Multivariate analysis revealed that established vegetation, seed rain and different vegetation types were each characterized by a distinct combination of vegetative and generative traits. Ten species typical of the Soomaa floodplain meadows were sown into experimental plots with different disturbance treatments and into the undisturbed vegetation. Most of the studied species were able to germinate and establish in the experimental plots; emergence rate in the first year generally declined in the order bare soil > bryophytes > litter removed > intact vegetation. No significant differences between treatments were found for establishment after three years and for survival; however, both values tended to be lowest in intact vegetation. In some species, however, survival tended to be higher in the semi-open conditions, which is discussed in terms of sheltering effects. Implications of seed sowing studies for habitat restoration are discussed and it is suggested that deliberate (re-)introduction of species by seed may be a valuable method to overcome seed limitation. 20 plots with three treatments were set up to study the role of seed rain and seed bank in the re-colonization of gaps in the meadow vegetation. Soil inversion was used to measure the seed rain; exclusion of the seed rain by nylon mesh allowed the assessment of the seed bank. A disturbed but uncovered plot and an undisturbed control received input from both seed bank and seed rain. 4363 seedlings of 61 species were identified in the plots. The seed bank generally was four to five times richer in both species and seeds than the seed rain. Similarity between the established vegetation and the seedling assemblages was very low. Analysis of life history traits suggested that both established vegetation and seedling assemblages were characterized by unique sets of plant traits. The data collected for the functional analysis of the experimental results was also used for a general assessment of trait distribution and functional group differentiation of the grassland vegetation as a whole. Correlation analysis showed that a number of traits like clonal growth, reproductive mode, guild membership, seed number and weight etc. were inter-correlated. These correlations are explained in terms of general bio-physical constraints and trade-offs. A cluster analysis of a trait matrix of 135 floodplain species resulted in nine morphologically and functionally defined groups of species

Granivores and Restoration: Implications of Invasion and Considerations of Context-dependent Seed Removal

Granivores are important components of sagebrush communities in western North America. These same regions are being altered by the invasion of the exotic annual Bromus tectorum (cheatgrass) that alters physical and biological dynamics in ways that appear to promote its persistence. This research directly relates to the restoration of B. tectorum-dominated systems in two inter-related ways. First, because these landscapes have large quantities of seeds applied during restoration, it is important to determine the major granivore communities in intact sagebrush communities and in nearby cheatgrass-dominated communities. Second, it is important to develop an understanding of patterns of seed harvest by granivores. In addition to the data chapters there are two review chapters; Chapter 1 highlights factors contributing to seed removal and Chapter 7 provides ecologically based techniques that could minimize the negative consequences of granivores during ecological restoration. Common groups of ants showed increased abundances; uncommon species and functional groups were generally negatively impacted by cheatgrass (Chapter 2). Conversely, rodents were negatively impacted by conversion to cheatgrass (Chapter 4). Ant seed removal was highly context-dependent (Chapter 3), depending on the background vegetation (large-scale among-patch effects), foraging distance from the nest mound (small-scale among-patch effects), and the presence of other seed species in mixture (within-patch effects). In addition, cheatgrass provided associational resistance to native seeds in mixture, meaning the presence of cheatgrass increased native seed survival. In Chapter 5 a novel statistical technique in the ecological sciences showed that rodents have marked preferences for some seeds over others and that more seeds were removed in sagebrush compared to cheatgrass-dominated sites, although associational effects among seed mixtures were not detected. In Chapter 6 we show that the amount of seed harvested depended on both intraspecific and interspecific seed density. B. tectorum seeds had associational susceptibility (increased harvest) in the presence of native seeds. Although the reciprocal effect may occur, we did not find statistical support for it. These sets of studies are not only of basic ecological interests, but are also important for developing management strategies for restoration of these degraded lands

Fast Multi-Scale Community Detection based on Local Criteria within a Multi-Threaded Algorithm

Many systems can be described using graphs, or networks. Detecting communities in these networks can provide information about the underlying structure and functioning of the original systems. Yet this detection is a complex task and a large amount of work was dedicated to it in the past decade. One important feature is that communities can be found at several scales, or levels of resolution, indicating several levels of organisations. Therefore solutions to the community structure may not be unique. Also networks tend to be large and hence require efficient processing. In this work, we present a new algorithm for the fast detection of communities across scales using a local criterion. We exploit the local aspect of the criterion to enable parallel computation and improve the algorithm's efficiency further. The algorithm is tested against large generated multi-scale networks and experiments demonstrate its efficiency and accuracy.Comment: arXiv admin note: text overlap with arXiv:1204.100

Defining and Evaluating Network Communities based on Ground-truth

Nodes in real-world networks organize into densely linked communities where edges appear with high concentration among the members of the community. Identifying such communities of nodes has proven to be a challenging task mainly due to a plethora of definitions of a community, intractability of algorithms, issues with evaluation and the lack of a reliable gold-standard ground-truth. In this paper we study a set of 230 large real-world social, collaboration and information networks where nodes explicitly state their group memberships. For example, in social networks nodes explicitly join various interest based social groups. We use such groups to define a reliable and robust notion of ground-truth communities. We then propose a methodology which allows us to compare and quantitatively evaluate how different structural definitions of network communities correspond to ground-truth communities. We choose 13 commonly used structural definitions of network communities and examine their sensitivity, robustness and performance in identifying the ground-truth. We show that the 13 structural definitions are heavily correlated and naturally group into four classes. We find that two of these definitions, Conductance and Triad-participation-ratio, consistently give the best performance in identifying ground-truth communities. We also investigate a task of detecting communities given a single seed node. We extend the local spectral clustering algorithm into a heuristic parameter-free community detection method that easily scales to networks with more than hundred million nodes. The proposed method achieves 30% relative improvement over current local clustering methods.Comment: Proceedings of 2012 IEEE International Conference on Data Mining (ICDM), 201