Characterizing larval breeding sites: physical characteristics
PCA analysis summarizing the 11 physical variables in La Lopé showed
that the four larval breeding site groups (two habitats × Ae.
aegypti present/absent) overlap extensively in the plane described by
the first two principal components, which together account for 38% of
the total variance (Figure 2a). However, forest and peridomestic sites
appeared to differ slightly. In support of that, MRPP tests found a
significant multivariate difference between habitats when including bothAe. aegypti present and absent sites (p = 0.001). Such
between-habitat different was less significant when examining onlyAe. aegypti present sites (p = 0.316), possibly due to the small
sample size (only five samples in the forest Ae. aegypti present
group). Ae. aegypti present and absent sites did not differ
significantly (all sites regardless of habitats: p = 0.311, within
forest sites: p = 1, within peridomestic sites: p = 1). The axis that
differentiated forest and peridomestic larval breeding sites roughly
aligned with the vectors of a few environmental variables, including
ambient temperature and humidity, canopy coverage, container opening
height, and water pH (Figure 2a). These variables also generally had
high variable important ranks in the random forest
analysis (Figure S2a), reflecting
their difference between habitats.
In Rabai (Figure 2b, PCA summarizing 16 physical variables), similarly,
forest and peridomestic sites were modestly but significantly different
in their physical characteristics (MRPP, p = 0.001). The differentiation
between forest and domestic larval breeding sites was more apparent,
while peridomestic and domestic sites shared similar conditions.Ae. aegypti present and absent sites in the forest did not show a
strong difference. Consistent with PCA, MRPP found significant
multivariate differences in most comparisons (p = 0.001), except between
forest sites with Ae. aegypti present vs. absent (p = 0.157) and
between domestic vs. peridomestic sites (p = 0.192 for all sites and p =
0.147 for Ae. aegypti present sites only). Forest and domestic
breeding sites were separated primarily on the first PC, explained by
container size (e.g., diameter, circumference, etc.), water volume, and
water pH (Figure 2b). Domestic sites tended to be larger, contained more
water and had higher pH (i.e., more alkaline). These variables were also
identified as most influential in distinguishing habitats in the random
forest analysis. In addition, canopy coverage, a measure of shading,
also showed a high rank in variable importance in comparisons between
habitats (Figure S2b). This is not surprising as domestic containers
were under roof and peridomestic containers were exposed outdoor, while
forest tree holes were partially shaded by the canopy.