# 3 Theory and motivation of process modeling

## 3.1 Key questions

- What is a process modeling approach?
- What kinds of questions can process models explore (that other methods cannot)?
- What are the limitations or constraints of process modeling?

## 3.2 Lesson objectives

After this lesson, learners should be able to…

- Describe what defines a process model.
- Evaluate the advantages and limitations of a process modeling approach.
- Generate questions in ecology and evolution that could be addressed using process modeling.
- Understand the unified neutral theory of biodiversity as an example of a well-established process model in ecology.

## 3.3 Lesson outline

Video lectures:

- Theory and motivation of process modeling
- The Unified Neutral Theory of Biodiversity as a process model
- Video on playing neutral theory as a game, and in R

### 3.3.1 (Lecture + discussion) What do we *mean* by process modeling, anyway?

Key points:

- In a process model, we play a “game”, with a set of entities following a system of defined rules, and see how the outcomes of the game vary as we change the rules.
- These models are often nondeterministic and often do not have closed-form, analytical solutions.

### 3.3.2 (Lecture + discussion) What are the applications of process modeling for eco-evo?

Key points:

- A process model offers almost unlimited flexibility for modeling complex, interacting processes.
- Everything depends on the rules we define! So it is very important to understand the rules of the game we are playing.

Discussion/brainstorm:

- What are some possible applications of process modeling in your area of interest?

### 3.3.3 (Lecture + discussion) What are the *constraints* we encounter in a process modeling approach?

Key points:

- Process models are computationally expensive! Modern computing strategies help, but high dimensionality is a serious constraint.
- Issues like model identifiability and correlation != causation. Just because our mechanism produces results that match some data, doesn’t
*necessarily*mean our mechanism is the same mechanism that produced that data. - Process models are themselves nondeterministic, so must be run many times.

### 3.3.4 (Example) The Unified Neutral Theory of Biodiversity

Key points:

- Hubbell’s UNTB is a process model. Simply put, it is a game played with a set of simple rules, with emergent properties that we find interesting.
- For the rest of today, we’ll be using UNTB as an example process model.

### 3.3.5 (Lecture + game of chance) Playing neutral theory

Key points:

- The rules of neutral theory
- We can play neutral theory manually. However, computers would make it considerably faster!