Treatments
We used a fully factorial experiment to investigate the interactive
effects of corridor quality with drought severity and the number of
drought patches across landscape on the persistence of metapopulations.
In the good corridor quality
treatment, corridors had 2ml of water added each week to keep them moist
(Li et al. 2021), whilst in the poor corridor quality treatment no water
was added to the corridors. For each corridor quality treatment (i.e.,
good or poor), we manipulated drought in two different ways: changing
the rate at which the moisture content of patches declined (i.e.,
drought severity), and the number of patches simultaneously experiencing
drought (i.e., number of drought patches). Severe drought was created by
reducing the 2ml of water added to each patch by 0.4ml water per week,
whilst weak drought was simulated by reducing the 2ml by 0.2ml water per
week (Fig. 1b). In addition, a number of patches were also randomly
selected to receive no water at all in any given week, and the number
impact in this was increased through time (the number of drought patches
treatment). The number of patches which did not receive any water was
generated by drawing a number (from 0 to 4) from a binomial distribution
with the probability increasing from 0 to 1 at either 0.2 per week
(i.e., fast increase) or 0.1 per week (i.e., slow increase) (Fig. 1b).
This was done for each replicate landscape, and the location of patches
impacted by this was randomized for each landscape. We also implemented
a constant (control) treatment for each corridor quality group (i.e.,
good or poor) where 2ml water were constantly added to all the patches
each week. This gave us in total two levels of corridor quality (good
vs. poor), two levels of drought severity (severe vs. weak), and two
levels of increase in number of drought patches (fast vs. slow), and one
control group (no change in water through time), with each treatment
combination replicated 6 times for a total of 60 replicates.