Assortative mixing in networks

A network is said to show assortative mixing if the nodes in the network that have many connections tend to be connected to other nodes with many connections. We define a measure of assortative mixing for networks and use it to show that social networks are often assortatively mixed, but that technological and biological networks tend to be disassortative. We propose a model of an assortative network, which we study both analytically and numerically. Within the framework of this model we find that assortative networks tend to percolate more easily than their disassortative counterparts and that they are also more robust to vertex removal.Comment: 5 pages, 1 table, 1 figur

Ambiguity, complexity and dynamics in the membership of collaboration

This paper is concerned with the role that membership structures of inter-organizational collaborations have on the achievement of collaborative advantage in the context of tackling social issues. Based on action research involving participants in a wide variety of collaborative situations, the paper aims to explore the nature of the membership of collaborations in practice. A picture of membership is built up from two perspectives. The first considers the structure of collaboration, and argues that ambiguity and complexity in structure may be demonstrated over many dimensions. The second adds another layer of complication through exploring the dynamics of the way in which membership structures change over time. The paper concludes by examining the implications for practitioners and policy makers of this picture in terms of its effect on the design of collaborations and on the factors which tend to lead to collaborative inertia instead of collaborative advantage

The Fish Community of an East African Mangrove: Effects of Turbidity and Distance from the Sea

Mangroves are often reported as nursery grounds for fish. Fish may enter mangroves in order to avoid predators, but may not need to do so if turbidity provides a sufficient predator refuge outside the forest. This study assessed the effects of turbidity in the field and laboratory on mangrove fish community structure and behaviour. The extent to which fish penetrate into mangroves has received little attention. This study also looked at differences in fish community structure at mangrove sites near (6m) and far (200m) from the mangrove/sea boundary. Twelve field samples were taken at approximately monthly intervals from replicate 25m2 landward and seaward plots, in a Sonneratia alba stand at Gazi Bay, Kenya. A total of 25 species of fish were caught, 15 in seaward plots and 13 in landward ones. Mean abundance for all plots and sampling times was 2.15 (equivalent to 0.09 m-2). Seaward plots had a total mean abundance more than twice that of landward plots (2.75 ± 1.9 S.D. vs. 1.23 ± 0.33 S.D. respectively). There was no relationship between abundance and turbidity. Laboratory experiments showed no significant changes in behaviour of three common species in response to turbidity. The low density of fish recorded concurs with previous work, and probably reflects conditions in Gazi Bay as a whole, rather than unusual features of the mangrove environment there

Impacts of Mangrove Density on Surface Sediment Accretion, Belowground Biomass and Biogeochemistry in Puttalam Lagoon, Sri Lanka

Understanding the effects of seedling density on sediment accretion, biogeochemistry and 3 belowground biomass in mangrove systems can help explain ecological functioning and inform 4 appropriate planting densities during restoration or climate change mitigation programs. The 5 objectives of this study were to examine: 1) impacts of mangrove seedling density on surface 6 sediment accretion, texture, belowground biomass and biogeochemistry, and 2) origins of the 7 carbon (C) supplied to the mangroves in Palakuda, Puttalam Lagoon, Sri Lanka. Rhizophora 8 mucronata propagules were planted at densities of 6.96, 3.26, 1.93 and 0.95 seedlings m-2 along 9 with an unplanted control (0 seedlings m-2). The highest seedling density generally had higher 10 sediment accretion rates, finer sediments, higher belowground biomass, greatest number of fine 11 roots and highest concentrations of C and N (and the lowest C/N ratio). Sediment accretion rates,12 belowground biomass (over 1370 days), and C and N concentrations differed significantly 13 between seedling densities. Fine roots were significantly greater compared to medium and coarse 14 roots across all plantation densities. Sulphur and carbon stable isotopes did not vary significantly 15 between different density treatments. Isotope signatures suggest surface sediment C (to a depth 16 of 1 cm) is not derived predominantly from the trees, but from seagrass adjacent to the site

Shrimp aquaculture as a vehicle for Climate Compatible Development in Sri Lanka. The case of Puttalam Lagoon

At present, aquaculture of black tiger shrimp (Penaeus monodon) in the Puttalam district of Sri Lanka is unsustainable with more than 90% of the former shrimp ponds laying abandoned as a result of shrimp disease and improper management. Between 1992-1998, over 50% of the mangrove cover was removed in order to establish shrimp aquaculture. This severely affected the functioning of coastal ecosystems, reducing their provision of useful services and increasing coastal vulnerability to climate change. Changes in the hydrology and polluted residual matter make the soil unsuitable for other agricultural purposes without costly restoration. The root of the problem was inappropriate management and a focus on short term economic gains. Despite this previous failure, the national development plan, Mahinda Chinthana, now promotes aquaculture as an avenue for development. This will only be possible if aquaculture is regulated in a sustainable and well-managed manner, and does not increase local vulnerability to climate change effects. The current paper discusses the possible costs and benefits in applying the concept of Climate Compatible Development (CCD) to shrimp aquaculture in Puttalam, Sri Lanka. It suggests how the sector can support mitigation of Green House Gas (GHG) emissions and adaptation to climate change effects, whilst stimulating development that will also benefit rural societies. Mechanisms that could enable this change include subsidies, insurance and bank loans which will also facilitate investment by foreign private enterprises and subsequent export. The development of a specific aquaculture policy and master plan would facilitate the process further

Blue carbon solutions in Kenya’s climate actions

Blue carbon ecosystems (mangroves, salt marshes and seagrass meadows) are highly efficient carbon sinks with the potential to make an important contribution to the mitigation of climate change. Conservation and management of Blue Carbon ecosystems and commitments in Kenya are summarised in Table 1 of this brief, along with key stakeholders who need to engage with them. The incorporation of ocean climate actions into Kenya’s updated Nationally Determined Contributions (NDC, 2020) is a significant milestone in climate change intervention measures. Kenya has about 612 km2 and 317 km2 of mangroves and seagrass respectively.UK Natural Environment Research Counci

Ecomuseums as cross-sector partnerships: governance, strategy and leadership

Ecomuseums are attracting increasing attention as means of preserving heritage and also impacting positively on social and economic issues. This paper contrasts ecomuseums with previous forms of cross-sector partnerships. The authors focus on the governance, strategy and leadership of the Flodden 1513 Ecomuseum. The findings have lessons for ecomuseums and other cross-sector partnerships both in and outside the UK