Pregunta: Access the following model of sheep, wolves and grass. This type of model is known as individual-based model (IBM) or agent-based model because the presence of each organism is considered explicitly. This contrasts with other models we saw in class where organisms are represented by their frequency relative to the total number of organisms in the

Access the following model of sheep, wolves and grass. This type of model is known as individual$-$based model $($IBM$)$ or agent$-$based model because the presence of each organism is considered explicitly. This contrasts with other models we saw in class where organisms are represented by their frequency relative to the total number of organisms in the environment.

IBMs are useful for studying food webs or food webs.

$1$

In the top left $($Settings$)$ activate $4$th Order Runge$-$Kutta in "Simulation algorithm". In the right side panel you can change the initial number of organisms of each species. Press the blue "Simulate" button to run an iteration of the simulation.

Study the four graphs that appear. I recommend setting the playback to $2$x$.$ Note that in this model spatial effects are considered, the wolf eats the sheep if they are in the same place at the same time. The same thing happens for the sheep and the grass. The movement of organisms is random. Graph $1$ and $3$ are the spatial representations of this community. Graphs $2$ and $4$ are the abundances of the species, the type of graph we have seen in class.

$($a$)$ Look at the diagram. Describe the three trophic levels present in this network and mention

Which species occupies which level.

$($b$)$ Run the simulation with the following cases and explain what happens in the community

based on the information provided by the graphs:

$•$ Press refresh on the page and use the model's default values $(50,5,50).$ Run the simulation $3$ times. What do you observe? What are the similarities and differences between the three simulations?

$•$ Start the simulation without wolves $(50,0,50).$ What do you expect to happen? Run the simulation. What happened to the grass and sheep population?

$•$ Repeat the previous simulation $4$ times and record the final abundance of the grass in a table. Calculate the average.

$•$ Now run the simulation with $2$ wolves initially $(50,2,50).$ What do you expect to happen to the sheep and grass population? Comment on what you observed

run the simulation.

$•$ Repeat the previous simulation $4$ times and record the final abundance of the grass in a table. Calculate the average.

$•$ Compare the community average with and without wolves. Explain this difference by mentioning the concept of "keystone species" and "overgrazing".Problema $2$: Red tr$ó$fica o food webs $(35$ pts$)$

Accesa el siguiente modelo de ovejas, lobos y grama. Este tipo de modelo se conoce como

individual$-$based model $($IBM$)$ o agent$-$based model porque se considera la presencia de cada

organismo expl$í$citamente$.$ Esto contrasta con otros modelos que vimos en clase donde los

organismos se representan por su frecuencia relativa al total de organismos en el ambiente.

Los IBMs son $ú$tiles para estudiar redes tr$ó$ficas o food webs.

En la parte superior izquierda $($Settings$)$ activa $4$th Order Runge$-$Kutta en "Simulation

algorithm". En el panel del lado derecho puedes cambiar la cantidad inicial de organismos de

cada especie. Presiona el bot$ó$n azul "Simulate" para correr una iteraci$ó$n de la simulaci$ó$n$.$

Estudia la cuatro gr$á$ficas que salen. Recomiendo poner el playback en $2x.$ Nota que en este

modelo se consideran efectos espaciales, el lobo se come a la oveja si estan en el mismo sitio al

mismo tiempo. Lo mismo ocurre para la oveja y la grama. El movimiento de los organismos

es aleatorio. La gr$á$fica $1$ y $3$ son las representaciones espaciales de est$á$ comunidad. La

gr$á$fica $2$ y $4$ son las abudancias de las especies, el tipo de gr$á$fica que hemos visto en clase.

$($a$)$ Observa el diagrama. Describe los tres niveles tr$ó$ficos presentes en est$á$ red y menciona

c$ú$al especie ocupa cual nivel.

$($b$)$ Corre la simulaci$ó$n con los siguientes casos y explica lo que ocurre en la comunidad

bas$á$ndote en la informaci$ó$n provista por las gr$á$ficas:

Oprime refresh en la p$á$gina y usa los valores default del modelo $(50,5,50).$ Corre

la simulaci$ó$n $3$ veces. $¿$Qu$é$ observas? $¿$Cu$á$les son las similitudes y diferencias

entre las tres simulaciones?

Inicia la simulaci$ó$n sin lobos $(50,0,50).¿$Qu$é$ esperas que pase? Corre la simu$-$

laci$ó$n$.¿$Que ocurri$ó$ con la poblaci$ó$n de grama y de ovejas?

Repite la simulaci$ó$n anterior $4$ veces y anota en una tabla la abundancia final de

la grama. Calcula el promedio.

Ahora corre la simulaci$ó$n con $2$ lobos inicialmente $(50,2,50).¿$Qu$é$ esperas que

ocurra con la poblaci$ó$n de ovejas y grama? Comenta en lo que observaste al

correr la simulaci$ó$n$.$

Repite la simulaci$ó$n anterior $4$ veces y anota en una tabla la abundancia final de

la grama. Calcula el promedio.

Compara el promedio de la comunidad con y sin lobos. Explica est$á$ diferencia

mencionando el concepto de "keystone species" y "overgrazing".