NetLogo User Community Models

(back to the NetLogo User Community Models)

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## WHAT IS IT?

"The model is essentially a dynamic version of MacArthur's "broken stick" hypothesis, and is based on a nonequilibrium interpretation of community organization. Suppose that forests are saturated with trees, each of which individually controls a unit of canopy space in the forest and resists invasion by other trees until it is damaged or killed. Let the forest be saturated when it has K individual trees, regardless of species. Now suppose that the forest is disturbed by a wind storm landslide, or the like, and some trees are killed. Let D trees be killed, and assume that this mortality is randomly distributed across species, with the expectation that the losses of each species are strictly proportional to its current relative abundance. Next let D new trees grow up, exactly replacing the D "vacancies" in the canopy created by the disturbance, so that the community is restored to its predisturbance saturation until the next disturbance comes along. Let the expected proportion of the replacement trees contributed by each species be given by the proportional abundance of the species in the community after the disturbance. Finally, repeat this cycle of disturbance and resaturation over and over again. In the absence of immigration of new species into the community, or of the recolonization of species formerly present but lost through local extinction, this simple stochastic model leads in the long run to complete dominance by one species. in the short run, however, the model leads to lognormal relative abundance patterns, and to geometric patterns in the intermediate run. The magnitude of the disturbance mortality, D, relative to community size, K, controls the rate at which the species diversity is reduced by local extinction: the larger D is relative to K, the shorter the time until extinction of any given species, and the faster the relative abundance patterns assume an approximately geometric distribution. (Hubbell, 1979)"
## HOW IT WORKS

(what rules the agents use to create the overall behavior of the model)

## HOW TO USE IT

(how to use the model, including a description of each of the items in the Interface tab)

## THINGS TO NOTICE

(suggested things for the user to notice while running the model)

## THINGS TO TRY

(suggested things for the user to try to do (move sliders, switches, etc.) with the model)

## EXTENDING THE MODEL

(suggested things to add or change in the Code tab to make the model more complicated, detailed, accurate, etc.)

## NETLOGO FEATURES

(interesting or unusual features of NetLogo that the model uses, particularly in the Code tab; or where workarounds were needed for missing features)

## RELATED MODELS

Hubbell, S. P. (1979). Tree Dispersion, Abundance, and Diversity in a Tropical Dry Forest: That tropical trees are clumped, not spaced, alters conceptions of the organization and dynamics. _Science_, **203**(4387), 1299–1309.

Hubbell, S. P. (1997). A unified theory of biogeography and relative species abundance and its application to tropical rain forests and coral reefs. _Coral Reefs_ **16**:S9–S21.

Hubbell, S. P. (2001). _The Unified Neutral Theory of Biodiversity and Biogeography_. Princeton, NJ: Princeton University Press.

## CREDITS AND REFERENCES

* Punchi-Manage, R. (2023k). NetLogo Hubbell's (1979) Neutral Model. http://netlogo/models/Hubbell-1979-Neutral-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.