Flies of the genus Drosophila have been extensively used as model systems to study competition. Experiments using larval crowding in these species have furthered our understanding of competition ecology, stress-adaptation, density-dependent selection and population dynamics. Historically, larval competition has been induced by crowding the larvae in high density cultures, compared to low-density controls. However, recent studies have shown that two larval cultures having the same total eggs per mL food density, with different absolute quantities of eggs and food, can differ greatly in their density-specific fitness functions. Similarly, populations adapted to two types of cultures achieving the same density through different means, can also evolve different traits. Thus, it is clear that there is more to larval crowding than just eggs/food density, which has until now been the benchmark variable for quantifying larval crowding in Drosophila studies. In the current study, we explore the consequences of implementing crowding in different ways, using a three-way factorial experiment with egg number and food volume, cast into different food column heights or cylindrical vials with different diameters. We find that not just the same density, but cultures having the same egg number and food volume combination but experienced in food columns of varying height and diameter can have very different pre-adult survivorship and development times. We further propose a new variable for quantifying larval crowding: effective density, which is the density within the larval feeding band, a volume of food close to the surface, with access to air, wherein a majority of the larvae feed. We show that effective density is a much better predictor of the outcomes of competition than the popularly used total eggs/food density.

This paper proposes the methodology for preparing the Cost Value Stream Map (CVSM) which possesses the advantage of measuring the cost involved and time consumed in the production process stream. A value stream map addresses the value addition process in terms of time domain in a production process. CVSM addresses both the time and cost information simultaneously in a production process. This CVSM method equips the study of the production process in detail and helps to figure out the wastages in the process directly in terms of the cost involved in the production. The cost line added alongside the time line in the modified VSM is a simple tool which can be utilised by lean experts in identifying the wastage in production process in terms of the cost involved. CVSM is prepared by collecting data from company in the prescribed format. All this data thus collected can be consolidated to prepare CVSM. A case study is conducted and a CVSM is prepared in a scaffolding pipe manufacturing unit in Kerala.