Florian Hartig

Notes on: Statistical inference for stochastic simulation models – theory and application

Abstract: Statistical models are the traditional choice to test scientific theories when observations, processes or boundary conditions are subject to stochasticity. Many important systems in ecology and biology, however, are difficult to capture with statistical models. Stochastic simulation models offer an alternative, but they were hitherto associated with a major disadvantage: their likelihood functions can usually not be calculated explicitly, and thus it is difficult to couple them to well-established statistical theory such as maximum likelihood and Bayesian statistics. A number of new methods, among them Approximate Bayesian Computing and Pattern-Oriented Modelling, bypass this limitation. These methods share three main principles: aggregation of simulated and observed data via summary statistics, likelihood approximation based on the summary statistics, and efficient sampling. We discuss principles as well as advantages and caveats of these methods, and demonstrate their potential for integrating stochastic simulation models into a unified framework for statistical modelling.

Hartig, F., Calabrese, J. M., Reineking, B., Wiegand, T. & Huth, A. (2011): Statistical inference for stochastic simulation models – theory and application. Ecol. Lett. 14, 816-827. [journal] [stats] [pdf]

Post-publication notes

to be added

Background: The idea of my notes on published articles is to provide a platform for discussion and additional information on articles after their publication. I welcome any comments – please use the field below (comments will be moderated). I will sporadically updated this page with personal notes, new results or other interesting articles on the same topic.
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Notes on: Smart spatial incentives for market-based conservation

Abstract: Market-based instruments such as payments, auctions or tradable permits have been proposed as flexible and cost-effective instruments for biodiversity conservation on private lands. Trading the service of conservation requires one to define a metric that determines the extent to which a conserved site adds to the regional conservation objective. Yet, while markets for conservation are widely discussed and increasingly applied, little research has been conducted on explicitly accounting for spatial ecological processes in the trading. In this paper, we use a coupled ecological-economic simulation model to examine how spatial connectivity may be considered in the financial incentives created by a market-based conservation scheme. Land use decisions, driven by changing conservation costs and the conservation market, are simulated by an agent-based model of land users. On top of that, a metapopulation model evaluates the conservational success of the market. We find that optimal spatial incentives for agents correlate with species characteristics such as the dispersal distance, but they also depend on the spatio-temporal distribution of conservation costs. We conclude that a combined analysis of ecological and socio-economic conditions should be applied when designing market instruments to protect biodiversity.

Hartig, F. & Drechsler, M. (2009): Smart spatial incentives for market-based conservation. Biol. Conserv. 142, 779-788. [journal] [preprint] [stats] [pdf]

Post-publication notes

to be added

Background: The idea of my notes on published articles is to provide a platform for discussion and additional information on articles after their publication. I welcome any comments – please use the field below (comments will be moderated). I will sporadically updated this page with personal notes, new results or other interesting articles on the same topic.

Notes on: The time horizon and its role in multiple species conservation planning

Abstract: Survival probability within a certain time horizon T is a common measure of population viability. The choice of T implicitly involves a time preference, similar to economic discounting: Conservation success is evaluated at the time horizon T, while all effects that occur later than T are not considered. Despite the obvious relevance of the time horizon, ecological studies seldom analyze its impact on the evaluation of conservation options. In this paper, we show that, while the choice of T does not change the ranking of conservation options for single species under stationary conditions, it may substantially change conservation decisions for multiple species. We conclude that it is of crucial importance to investigate the sensitivity of model results to the choice of the time horizon or other measures of time preference when prioritizing biodiversity conservation efforts.

Hartig, F. & Drechsler, M. (2008): The time horizon and its role in multiple species conservation planning. Biol. Conserv. 141, 2625-2631. [journal] [preprint] [pdf]

Post-publication notes (will be updated sporadically)

Although this wasn’t our starting point, it soon turned out that this study inherited a lot of ideas from Emily Nicholson et al.’s excellent paper on “Objectives for Multiple-Species Conservation Planning”. Basically, we take a similar multi-species objective functions, and test for sensitivity of optimal conservation actions to a change of the time horizon. Turns out that most of them can be highly sensitive when time horizons are changed within the typical range of 30 to a few hundred years.

I found then, and still think, that this is a quite important and really under-researched topic – imo, already the question of conservation preferences in general is quite underrepresented in the literature, but questions related to time preferences are discussed to an even lesser extent. Unfortunately, this paper hasn’t really changed that, at least judging from the number of citation attracted so far, and I fear that this won’t change much in the future. It was my first paper, and in retrospective I think I presented the subject way to technical for the target audience. I hope a recent paper by Howard B. Wilson et al. that examines the same question will do a better job – I discuss this paper in a recent blog post

Background: The idea of my notes on published articles is to provide a platform for discussion and additional information on articles after their publication. I welcome any comments – please use the field below (comments will be moderated). I will sporadically updated this page with personal notes, new results or other interesting articles on the same topic.