College Papers

2.3 simulations were carried out over 100 years,

2.3 The Baseline

The
standard protocol of 1000 simulations were carried out over 100 years, which is
an equivalent to 4-12 orangutan generations, per Ancrenaz et al., (2004), Bruford et
al., (2010) and Singleton et al.,
(2004). All of these papers recommended 1000 simulations for increased accuracy
and used the 100 year time frame although Ancrenaz et al., (2004) did also use a 25 year and 200 year simulation.
These papers all studied the same groups of orangutans allowing results to be
compared to other similar papers.

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Mortality
and reproduction rates were both equally applied across all of the PSU’s and
included El Nino weather events and human conflict, the only parameters that
were specific to each population were carrying capacity from Ancrenaz (2004)
and population numbers which come from Bruford et al., (2004), Ancrenaz et
al., (2010) and Singleton et al.,
(2004). These studies used both ground and helicopter surveying to estimate the
population sizes of all 11 populations. Mortality rates were developed over a
10 year period of observation by Ancrenaz et
al., (2010). Due to the very high density of orangutans in some PSUs
density dependant reproduction was used for all models using the following
formula for density dependence: P(N)=(P(0)-(P(0)-P(K))(N/K)B)N/N+A
the variables of which are shown in table 1.

2.4 Simulations

2.4.1 No intervention

A
baseline simulation was ran both with and without inbreeding depression across
all eleven of the populations to show the state of the populations without any
intervention (Lacy, 1993).

 

2.4.2 Translocations

The
second model tested the translocation of two females from PSU 2 and three
females from both PSU 1 and 5 to the other populations, as these hold the
largest numbers of orangutans. This is has been modelled at every 10, 20 and 50
years to see the effect it has on the genetic diversity of the overall
populations. Females were chosen to be translocated as they are less likely to
genetically dominate a population (Utami et al. 2002).

 

2.4.3 Connectivity

The
third model gradually increased carrying capacity to simulate the effects of
implementing forest corridors to connect each PSU to its nearest neighbouring
population. Connectivity between populations can only take part a long each
side of the river as it is very rare for orangutans to cross (Arora, et al., 2010).
The increase in capacity is dependent on the size of the population area,
distance to nearest population and other factors such as rivers and roads. The
following data set was be used:

PSU1

+0.1%

PSU2

+0.2%

PSU3

+0.8%

PSU4

+0.5%

PSU5

+0.1%

PSU6

+0.8%

PSU7

+0.1%

PSU8

+1%

PSU9

+1.6%

PSU10

+2%

PSU11

+2%

 

2.4.4
Mixed Approach

The
final model uses both translocation of one female every 20 years and the
introduction of corridors between sites used in the connectivity simulations.