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Models in Ecology

A discussion of several papers focused on the role of models in ecology.
by

Stephanie Peacock

on 9 February 2012

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Transcript of Models in Ecology

Why don't we believe the models? "..modeling projects and modeling papers are not generally held to a consistent rigorous set of standards..." John A. Aber Models provide understanding, not belief. "The goal should be not to believe models, but rather to use them to understand the system." Virginia H. Dale An introduction to the practice of ecological modeling. How do models fit into the scientific process? what is the purpose of a model? understanding projections decision making hypothesis testing Underwood (1990) how complex should a model be? identifying gaps in knowledge "The model should strike a balance between incorporating enough detail to capture the necessary ecological structure and processes and being simple enough to be useful in generating hypotheses and organizing one’s thoughts."
-Jackson et al. (2000) All models are wrong; some models are useful. -George Box, statistician Models should follow from specific research questions rather than questions following from models.
-Jackson et al. (2000) How important is it to validate models? Are you a modeler or a field scientist? "Modeling offers exciting possibilities for the exploration of ideas that are not easily pursued through field experimentation or laboratory studies." Can we make management decisions based on models that haven't been validated?
is it okay to build and test models on the same dataset? Leland J. Jackson Wiegand et al. (2003) Using pattern-oriented modeling for revealing hidden information:a key for reconciling ecological theory and application. Thorsten Wiegand, Florian Jeltsch, Ilkka Hanski and Volker Grimm Good practices for sharing ecological models. "...many models lack comprehensive documentation, especially in a format that is easy to use and to understand." A Pragmatic Approach to Modeling for Wildlife Management Supplemental Reading Models in Ecology WHy would you use a model?
Are models required to guide data collection? WHat's the difference between a model, hypothesis and a theory? Theory: a formulation of apparent relationships or underlying principles of certain observed phenomena which has considerable supporting evidence.

Hypothesis: an unproved theory, a basis for further experimentation.

Model: a sylized representation of a particular thing, idea, or condition. Can be qualitative or quantitative. population dynamics when the model doesn't work... What techniques have you come across to deal with this? Are models dangerous? model assumptions
extrapolation garbage in - garbage out what unique challenges Do ecologists face when modelling? model structure, parameterization, validation, sensitivity analysis, prediction professor of Natural Resources at University of New Hampshire
developed simple, validatable computer models of ecosystem function which can be linked to geographic information systems for regional and spatial applications, and extended to examine the impacts of environmental change
h-index of 57 adjunct professor in the Department of Ecology and Evolutionary Biology at the University of Tennessee
landscape design for bioenergy, environmental decision making, land-use change, landscape ecology, and ecological modeling
h-index of 5 professor in the Department of Biological Science at the University of Calgary
stability of aquatic communities and ecosystems, and relationships between sustainable growth and water quality and quantity.
this papaer cited 27 times
H-index = 7 Aber's suggestion were valid, but his emphasis was incorrecty on belief rather than understanding. "The failings he identifies with models and modellers reflect, in part, unrealistic expectations more than a situation that can or should be changed." many ecological theories are not possible to test through experimentation, so models provide the tool
conceptual and quantitative models


"...remember that models are only tools and not reality, and there is no “correct” model." Aber vs. Dale & vanWinkle Why don't we believe the models?

Models provide understanding, not belief.

Mostly a misunderstanding, I believe.

Model interactions: A reply to Aber. How do you know if a model sufficiently represents reality?
How do you know if it's too complex? conceptual quantitative equations
parameters Dale adds to the discussion of how the assumptions and sources of uncertainty of a model
must be recognized
a model cannot be built with incomplete understanding
a model is not worth building if there are gaps in the data
a model cannot be used in any way or form until it has been validated
a model must be as realistic as possible
modeling is for mathematicians - it cannot be unterstood by most managers and field biologists
the primary purpose of building models is to make predictions
modeling is time consuming and expensive. The more multipurpose the model, thebetter the value one is getting for one's investment 'If truth is the measure of a model, then validation is the proof of that truth and the issue of validation
is crucial. However, if a model is constructed as an experiment or viewed as a hypothesis or a problem-
solving tool, then the question of validation is irrelevant. The model is like a logical proposition: it only
reveals the logical consequences of its assumptions.' - Starfield, 1997 Waxman & Gavrilets. 2005. Journal of Evolutionary Biology18: 1139-1154. Reproducibility is a cornerstone of science.
How can we ensure that models and model predictions are reproducible? WHAT IS A MODEL? A model can thus be considered a set of hypotheses about the way a system works given certain assumptions and context.
- Dale and Winkle (1998)

A model is a representation of a particular thing, idea, or condition.
-Jackson et al. (2000)

...an accurate (or faithful) representation of reality.
– Starfield (1997) conceptual mechanistic phenomenological statistical mathematical dynamic deterministic stochastic qualitative simulation What are different types of models?
How do you know which to use? Do you agree? Model Misconceptions Anthony M. Starfield Karin M. Kettenring, Barbara T. Martinez, Anthony M. Starfield, Wayne M. Getz
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