A conceptual model is a visual summary with an accompanying explanation of the basic features of an ecosystem under study that explain a person’s thinking about a phenomenon. It is thus drawn from the perspective of the student. It is both a simplification of a complex system and an expression of the modeler’s understanding. Since it emphasizes what the student knows at a point in time, and is not necessarily right or wrong, it is a representation of the student-scientist’s thinking about how the ecosystem functions.
The qualitative model describes the important components of an ecosystem and the linkages between these components. It is a simplification of a complex system. By synthesizing current scientific information, making field observations and conducting experiments, and using professional judgment, it is possible to design a simple qualitative model that can make a reasonably accurate prediction.
By combining features of conceptual modeling and qualitative modeling, we can shows students a way to think about indirect effects and feedback loops, as well as representing the student-scientist’s thinking about how the ecosystem functions at different points in time .
The human brain cannot keep track of an array of complex interactions all at one time, but it can easily understand individual interactions one at a time. By adding components to a model one at a time, we develop an ability to consider the whole system together, not just one interaction at a time.
Why are qualitative models useful in ecology?
Modeling has become an important tool in the study and management of ecological systems. An ecological system or process often cannot be directly manipulated in a field test. Modeling can be used to understand ecosystem functioning, by allowing us to visualize how species are influenced by each other and by abiotic conditions, and to make predictions on how ecosystems might change in response to human activities.
Models can be used to generate hypotheses. Models allow detailed predictions to be made about the ultimate effects of disturbances to the system. Qualitative models are typically drawn as diagrams that describe the relationships between components in an ecological community. A component is any variable such as a given species, or the temperature of the water in a stream. Components are connected with links that represent the type of ecological interaction, the flow of material, or a causal effect of one component on another, such as predation. Any combination of two or more components that have direct and indirect effects on one another is termed a “system.” The overall effect of any input from one component on another (direct and indirect) is observed and can be calculated. Aspects of this analysis can indicate the stability of the system calculated qualitatively (positive, negative, or none) rather than quantitative (exact numerical). Feedback loops, positive and negative links are all multiplied into an overall effect. The analysis can also determine if any of the components might increase or decrease following a simulated disturbance.
Students create their own models illustrating ecosystem interactions. These models can both be used in helping shape their research projects and also reflectively for assessment of how students thinking about ecosystems can change.