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Biodiversity conservation is one of the important ecosystem services that has been negatively impacted by anthropogenic activities. Natural forests (NF) harbor some of the highest species diversity around the world. However, deforestation and degradation have resulted in reduced forest land cover and loss of diversity. Homegarden agroforestry (AF) systems have been proven to be an intermediary for biodiversity conservation. In this study, we evaluate the effectiveness of home garden AF practices to conserve tree species diversity in Bangladesh and compare them with tree species diversity in NF. A total of nine locations were selected for this synthesis from published literature which comprised of five AF sites and four NFs. Shannon-Weiner Diversity Index (H) was similar for home-garden AF (3.50) and NF (2.99), with no statistical difference between them. Based on non-metric multi-dimensional scaling (NMDS) ordination analysis, the AF and NF plots showed distinct separation. However, Bray-Curtis dissimilarity index ranged from 0.95 to 0.70 indicating nearly no overlap in species composition to significant overlap between AF and NF. Based on our results, we conclude that AF can serve as an important ecological tool in conserving tree species diversity, particularly on landscapes where NF fragments represent only a small fraction of the total land area. Creating and maintaining AF habitats in such human dominated landscapes should be part of the biodiversity conservation strategy.

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This study presents an overview of the existence and effects of six heavy metals, chromium (Cr), lead (Pb), cadmium (Cd), mercury (Hg), manganese (Mn), and aluminum (Al), in tannery effluents released to the Buriganga River in Dhaka, Bangladesh. The pollutants were found in three different sources, such as effluents from tanneries, contaminated river water and three species of fish-climbing perch (Anabas testudineus), spotted snakehead (Channa punctata), and Black tilapia (Oreochromis mossambicus) caught from the river. Tannery effluents, water, and fish samples were collected from three different factories, five sample stations, and three different harvesting points, respectively. Effluents from all three factories contained significant amounts of heavy metals, especially Cr (374.19 ppm in average), whereas lesser amounts were found in the tissues of the three fish species studied. The trends in tissue elemental concentrations of fish were Cr > Pb > Al > Hg > Mn > Cd. In most cases (Cr, Cd, Mn, and Al), heavy metal concentrations were found to be greater in climbing perch than in Black tilapia and spotted snakehead. Although the river water contained high concentrations of harmful heavy metals, the fish species under study had concentrations well below the permissible Food and Agriculture Organization/World Health Organization levels for those metals and seemed to be safe for human consumption.

In the discourse about the development of farmed animal production (terrestrial livestock production and aquaculture) in the tropics, two important food system outcomes emerge: (1) to supply animal-sourced food (ASF) at a level that suffices healthy future diets, including for poor people, and (2) to contribute to climate change mitigation and minimize pollution with nitrogen and phosphorus. Livestock production and aquaculture contribute to food security directly by increasing producers’ food diversity and availability, but also that of urban consumers, and indirectly through income generation and increased farm resilience. Recently, circularity has come to the fore as an integrated approach to food system development. Circularity has four cornerstones: (1) food crops have highest priority (which implies no food-feed competition), (2) avoid losses, (3) recycle waste and (4) use animals to unlock biomass that humans cannot eat. In this review, the role of farmed animals in circular food systems in the tropics is presented in four case studies and the impacts of circularity on food security and environmental impact mitigation are discussed. The cases are ruminants in grazing systems in West Africa and in Colombia, fish in pond aquaculture in general, and land-limited dairy production in Indonesia. Additionally, options for novel protein sources for use in livestock and fish feeding are presented. It is concluded that farmed animals are important in circular food systems because of their use of land unsuited for crop production, their upgrading of crop residues, and their supply of manure to crop production. Nevertheless, the increasing demand for ASF puts pressure on important characteristics of circularity, such as minimizing food-feed competition, maximization of use of waste streams in feed, and the value of manure for fertilization. Hence, in line with conclusions for Western countries, maximum circularity and sustainability of food systems can only be achieved by optimizing the population size of animals. Thus, a sustainable contribution of ASF production to global food security is complex and in not only a technical matter or outcome of an economic process balancing supply and demand. It requires governance for which public, private, and social actors need to partner.

Globally pond aquaculture is the predominant fish/shrimp farming system. Roughly 70% of the farmed fish and shrimps are produced in semi-intensive ponds where feed is a major nutrient supplier but where also natural food contributes to the productivity. Current knowledge on fish nutrition is based on studies where natural food is absent or available at a minimum level. When a complete feed, formulated on the basis of the above nutritional studies, is applied as supplementary feed in a pond where also natural food is available, much of the nutrients are not retained in the fish and the efficiency goes down. The aim of this research was to generate knowledge on how dietary macro-nutrients (with a focus on dietary carbohydrates) determine fish growth directly and indirectly (via natural food) in ponds. In a pond, the carbon to nitrogen (C:N) ratio in the system determines the productivity of natural food. The hypothesis underlying the current PhD research was that lowering the scarce and expensive macronutrients (e.g. protein and fat) in the feed would be compensated by an increased contribution of natural food as a result of a higher C:N input into the system, and thus not leading to lower fish yields. We conducted four experiments to test this hypothesis and have observed that lowering the dietary protein to energy ratio in the feed increased fish production at the pond level, mainly because of an indirect effect of the diet by enhancing the natural food in the pond. The type of non-protein dietary energy (lipid or carbohydrate) did not affect fish performance, not directly as feed nor indirectly via influencing the natural food web of the pond. However, the type of dietary non-starch polysaccharides (NSP) influenced natural food production and ultimately fish growth. Fish performance was better with slowly degradable NSPs in the feed. In all our studies we have noticed that feeding level increased fish production but also increased FCR. We have also observed that fish production increased with increasing stocking density (within the tested levels). Culture intensity (feeding level and stocking density) did not interact with the influence of the dietary macro-nutrient composition (i.e. P:E ratio) on pond productivity which means that enhancement of the natural food web through diets is possible even with increasing culture intensity. So, in ponds with a functional natural food web, the optimal macronutrient composition of supplementary feeds for tilapia differs from the optimal composition as recommended by NRC (1993, 2011) for tilapia. This may be related to the fact that the NRC recommendations were developed without the presence of natural food, and that the effect of the latter may be related to a possible enhancement of its production due to the extra nutrient input in the ecosystem via the waste of the fish (fertilizing effect). However, when monitoring the food web in the ponds, we have barely noticed differences among the treatments. This calls for improved methods to quantify the contribution of natural f...