In this illustration, we will simulate extinctions of hosts, to show how the package can be extended by using the core functions described in the "Interface" section. Simply put, the goal of this example is to write a function to randomly remove one host species, remove all parasite species that end up not connected to a host, and measuring the effect of these extinctions on the remaining network. Rather than measuring the network structure in the function, we will return an array of networks to be manipulated later:

```
using EcologicalNetworks
using Plots
using Plots.PlotMeasures
using Statistics
```

```
function extinctions(N::T) where {T <: AbstractBipartiteNetwork}
# We start by making a copy of the network to extinguish
Y = [copy(N)]
# While there is at least one species remaining...
while richness(last(Y)) > 1
# We remove one species randomly
remain = sample(species(last(Y); dims=2), richness(last(Y); dims=2)-1, replace=false)
# Remaining species
R = last(Y)[:,remain]
simplify!(R)
# Then add the simplified network (without the extinct species) to our collection
push!(Y, copy(R))
end
return Y
end
```

`extinctions (generic function with 1 method)`

One classical analysis is to remove host species, and count the richness of parasite species, to measure their robustness to host extinctions – this is usually done with multiple scenarios for order of extinction, but we will focus on the random order here. Even though `EcologicalNetworks`

has a built-in function for richness, we can write a small wrapper around it:

```
function parasite_richness(N::T) where {T<:BinaryNetwork}
return richness(N; dims=1)
end
```

`parasite_richness (generic function with 1 method)`

Writing multiple functions that take a single argument allows to chain them in a very expressive way: for example, measuring the richness on all timesteps in a simulation is `N |> extinctions .|> parasite_richness`

, or alternatively, `parasite_richness.(extinctions(N))`

. In @fig:extinctions, we illustrate the output of this analysis on 100 simulations (average and standard deviation) for one of the networks.

```
N = convert(BinaryNetwork, web_of_life("A_HP_050"))
X = Float64[]
Y = Float64[]
for i in 1:200
timeseries = extinctions(N)
path_l = parasite_richness.(timeseries)./richness(N; dims=1)
prop_r = 1.0.-richness.(timeseries; dims=2)./richness(N; dims=2)
append!(X, prop_r)
append!(Y, path_l)
end
x = sort(unique(X))
y = zeros(Float64, length(x))
sy = zeros(Float64, length(x))
for (i, tx) in enumerate(x)
y[i] = mean(Y[X.==tx])
sy[i] = std(Y[X.==tx])
end
pl = plot(x, y, ribbon=sy, c=:black, fill=(:lightgrey), lw=2, ls=:dash, leg=false, margin = 10mm, grid=false, frame=:origin, xlim=(0,1), ylim=(0,1))
xaxis!(pl, "Proportion of hosts removed")
```