Bivariate stochastic modeling of functional response with natural mortality

A correction due to Abbott (1925) is the standard method of dealing with control mortality in insect bioassay to estimate the mortality of an insect conditional on control mortality not having occurred. In this article a bivariate stochastic process for overall mortality is developed in which natural mortality and predation are jointly modeled to take account of the competing-risks associated with prey loss. The total mortality estimate from this model is essentially identical with that from more classical modeling. However, when predation loss is estimated in the absence of control mortality the results are somewhat different, with the estimate from the bivariate model being lower than that from using Abbott’s formula in conjunction with the classical model. It is argued that overdispersion in observed mortality data corresponds to correlated outcomes (death or survival) for the prey initially present, while Abbott’s correction relies implicitly on independence

Chasing the Dream: A Systems Modelling Approach to Biological Control

Abstract Sustainable production with reduced reliance on pesticides places some big demands on the effectiveness of biological control of pest and disease problems within horticultural production systems. There is currently a need to integrate and synthesise knowledge from all aspects of the production system to determine the most effective strategies for biological control of pests and disease. For this a systems-based modelling approach is appropriate, due to the inclusive nature of this approach and its focus on understanding processes and their interactions. The development of a systems approach for biological control in horticulture is incredibly daunting due to the huge diversity of crops, pests, natural enemies and production practices in horticulture. New and up-and-coming sensor and production technologies combined with new modelling approaches have however, great potential to either simplify the system to a manageable level or provide a common framework for modelling that will greatly enhance the ability to take a systems approach to coping with reduced pesticides. Current models are primarily oriented towards enhancing the understanding of a system and its processes, however, often with limited focus on producing practically useful outcomes. For the future, there will be a need to translate research models into practically useful tools, through the simplification of the research models, so that there is rapid transfer of knowledge and understanding from researchers to growers

Scoping the strengths and weaknesses of different auction and PES mechanisms for Countryside Stewardship

This is the final version. Available from Defra (Department for Environment, Food and Rural Affairs) via the link in this recordThe majority of farmers in England currently receive a fixed fee for managing their land under an agrienvironment scheme (Environmental Stewardship), which is based on an estimate of the typical income forgone by participating. The aim of this research is to explore alternative mechanisms for allocating agri-environment contracts with a view to achieving a more cost-efficient and effective use of funds. The focus is on reverse auctions, whereby farmers opt into a bidding process, offering to manage their land under prescribed management options at a price that more closely reflects their cost of doing so. The researchers have used a combination of laboratory experiments, simulation modelling and farmer workshops to consider the opportunity for efficiency gains, aspects of auction design and farmer responses to auctions. A secondary objective of the work is to explore opportunities for the private sector to engage in agrienvironment actions by leveraging match-funding where there are common goals and mutual benefits for private firms and society. This has entailed a review of the payment for ecosystem services (PES) literature and consultations with a number of relevant private firms. A particular focus for the latter has been the water companies, as they have already established some initiatives on PES around improving water quality