NetLogo User Community Models

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## WHAT IS IT?

Neutral models refer to communities of ecological similar species in which individuals compete with one another and do not describe trophic interactions (Bell, 2001). Here I developed the NetLogo model that used in Bell's (2000) paper. Bell (2000) describes the properties of a very simple neutral model. It represents macro-ecological patterns of a community of functionally identical species. He used the term "neutral" to mean that individuals possess the same properties, regardless of species membership; thus, individuals of different species are indistinguishable (Bell, 2000).

Bell (2000) assumed followings:

1. Species of community terms) is drawn from a external regional pool of _JMS_ species.

2. The community initially consists of _N__i individuals of each species (Bell, 2000).

Bell (2000) assumed the following dynamics in his model.

1. **Immigration:** A single individual is added to the community from each species in the pool with probability _m_.

2. **Birth:** Each individual gives rise to a single offspring with probability _b_.

3. **Death:** Each adult individual dies with probability _d_.

4. **Density regulation:** If the community exceeds its capacity of _K_ individuals, excess individuals are removed at random, each individual having the same probability of being removed, until the community is reduced to exactly _K_ individuals before the next cycle is begun.

**Note:** "It is individuals that are culled, and that all species are treated alike, so that each species is on average culled in proportion to its relative abundance alone. Species do not differ in their sensitivity to density, and there are no implicit or explicit interactions among species (Bell, 2000)".

The model is different from Hubbell's model becaused Bell (2000) used a species pool where each species has equal chance, not individuals, to immigrate.

## HOW IT WORKS

There are two sets of turtles. Trees and meta-species. Trees and meta-trees own property called "species". Patches have a property called "occupied". If a tree or meta-tree occupied the local community then patch is 'occupied'. When a patch is vacant patch is 'unoccupied'. Initial abundances of species are set to N_i.

## HOW TO USE IT

### Sliders

1. **JMS:** Species present in the regional species pool. It is equal to size of the regional pool. _JMS_= _(w1 + 1)_². The JMS slider automatically changes when w1 changes.

2. **w1:** It is used to decides the JMS.

3. **Ni:** Initial abundances of species (all the populations have equal sizes).

4. **initial-local-richness:** This decides the inital species richness of the local community.

5. **JL:** This is the initial local community size. Initial local community size (_JL_) is also a automatically change. Initial abundances of species are set to _Ni_. Therefore, initial abundance of the community is equal to 100 times initial-local-richness.

6. **w2:** This decides the size of the local community, the maximum capacity. (_w2 + 1_)².

7. **m:** It is the rate of immigration of species from the regional pool.

8. **K:** Automatic slider. It is the maximum capacity community can hold. Also called carrying capacity.

9. K = (_w2 + 1_)².

10. **b:** It is the birth rate of individuals.

11. **d:** It is the death rate of individuals.

## THINGS TO NOTICE

The model can then be used to describe the relationship of diversity and abundance to the six parameters of the model: pool size _JMS_ species, size of the initial species populations (N_i individuals), community capacity _K_ individuals, immigration rate _m_ per species per cycle, birth rate _b_, and death rate _d_ per individual per cycle. It can then be determined whether the patterns exhibited by natural populations differ systematically from those generated by a finite stochastic birth-death-immigration process.

### Outputs

1. **Local Community Trees:** Number of trees or meta-trees in the local community

2. **Total dead trees from t = 0 to t = t:** Total number of deaths happened in the local community.

3. **Immigrant-trees from t = 0 to t = t:** Total number of immigrations happened in the local community.

4. **New Births from t = 0 to t = t:** Total number of births happened in the local community.

5. **Local community species richness:** Species richness of the local community.

6. **Number of temporal extinct species in the local community:** Total number of temporal extinctions happened in the local community.

### Plots

1. **Local Community Size:** Abundance of the local community.

2. **Local Community Species Richness:** Number of species in the local community.

3. **Species Abundance Distribution of Local-Community:** Species abundance distribution of the local community.

4. **Relative Species Abundance Distribution:** Relative species abundance distribution of the local community.

## THINGS TO TRY

Change the sliders (_i.e._ b for birth rate, d for death rate, and m for immigration rates, initial-species-richness for initial species richness). Use slider w1 to change the regional species richness (JMS) and slider w2 to chnage the carrying capacity (K)).
See how community species richness and community species abundance vary.

## EXTENDING THE MODEL

## NETLOGO FEATURES

## RELATED MODELS

Bell, G. (2000). The Distribution of Abundance in Neutral Communities. _The American Naturalist_, **155** (5), pp. 606-617.

Bell, G. (2001). Neutral Macroecology. _Science_, **293**(5539), 2413–2418.

## CREDITS AND REFERENCES

* Punchi-Manage, R. (2023e). NetLogo Bell's (2000) Model. http://netlogo/models/Bell-2000-Model.

Please cite the NetLogo software as:

* Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.