Predicted longer-term genetic consequences of linear
transport infrastructure on the impacted population.
Figure 1 shows, for each phase of the two disturbance processes (natural
vs linear transport infrastructure), the simulated predicted speed at
which genetic diversity will be lost over the next 30 generations from
genetic drift alone. Together, it illustrates how rapidly the expected
heterozygosity (He) of the small remaining population of
koalas located above the linear transport infrastructure could erode
from genetic drift alone. After five generations, the predicted loss of
expected heterozygosity (He) of the resident koala
population impacted by ‘natural’ mortality events is 4.1% (Dataset 2)
in comparison to 41.38% (Dataset 3above) and 5.75%
(Dataset 3below) for the remaining two subdivided koala
populations located above and below the linear transport infrastructure.
After ten generations, these predictions are 8.99%, 69.9% and 12.48%
respectively.
Predicted effect of
longer-term dispersal post-habitat fragmentation on the genetic
connectivity and genetic diversity of the impacted population.
Forward time dispersal simulations showed the predicted impact of
different dispersal treatments on the genetic connectivity and diversity
of the now subdivided koala populations located above and below the
linear transport infrastructure (Figure 2 and 3, Table S2-S4). Results
from these simulations can be summarised as follow. First, any dispersal
treatments ≤ 6 koalas in each direction (e.i. = ≤ 12 koalas per
generation in total) would require remediation after 10 generations,
given that they would result in Fst greater than 0.05
(Figure 2; e.g. upper 95% CI for 0 koala dispersing treatment = 0.249
and lower 95% CI for 6 koala dispersing treatment = 0.055, Table S2)
and an extensive expected loss in genetic diversity (Figure 3 and
TableS3). After 10 generations, for instance, the He ±
95% confidence interval (CI) of any dispersal treatments ≤ 6 koalas
above (0 koalas dispersing 95% CI = 0.167-0.174; 6 koalas dispersing
95% CI = 0.226-0.231) and below (0 koalas dispersing 95% CI =
0.237-0.241; 6 koalas dispersing 95% CI = 0.245-0.248) were much
smaller and showed no overlap with He of the population
prior to its subdivision (He = 0.271, Dataset 2, Table
1). An increase to 8 dispersing koalas in each direction per generation
(16 koalas in total per generation) would be the minimum required number
of dispersing koalas to maintain Fst below 0.05 (95%
CI-Fst = 0.045-0.049, Table S2) and a zero change in
Shannon’s mutual information (MI) which is weighted more strongly by
rare variants. Genetic diversity, however, would still show a sharp
decline for the koala population located above the linear transport
infrastructure with its He ± 95% confidence interval
(0.229-0.233, TableS3) smaller and not overlapping with
He of the population prior to its subdivision
(He = 0.271, Dataset 2, Table 1). This would still
result in an average loss of more than 15% when compared to the genetic
diversity (He) prior to the population subdivision. An
increase to 16 dispersing koalas in each direction per generation (32
koalas in total per generation) would be best case scenario given that
both genetic connectivity and genetic diversity would remain unchanged.