Dietary composition
To further explore dietary differences between ginger and native forest,
samples were assessed by sampling event, defining a site using the block
and transect number, rather than the diet of each individual spider.
Incidence and Hellinger-transformed relative read abundances were used
to calculate beta diversity using ASV, and order-level identities. Beta
diversity values were highest between the sites in ginger and sites in
native forest when using incidence data, indicating compositional
differences (Figure 3). Ordination space overlapped between ginger and
native forest sites, most noticeably when using ASVs (Figure 4); using
ASVs, high dietary dissimilarities existed across all sites, both within
habitat types and between habitat types (Figure 3), which resulted in
less clear differentiation. Hellinger transformed read abundance
produced a significant difference between ginger sites and native forest
sites when using ASVs but not when using orders. This is likely because
dietary communities across ginger and native forest sites showed more
similarity at the order level while other sites in ginger habitat were
extremely different. However, using beta diversity calculated from
incidence data, there was a significant difference between ginger and
native forest sites across both ASVs and order (PERMANOVA, p-value
< 0.05; Figure 4b, 4d). This provides interesting implications
for the different ecological patterns detected with and without
abundance information. In our case, a high similarity in a handful of
sites across both habitat types is detected when using relative read
abundances because certain orders are being eaten in similar quantities;
without abundance, rarer orders are having more of an influence.
Another interesting finding is that there is high compositional turnover
in the diets of spiders within ginger habitat when we look at
order-level diversity; this is reflected in the beta-diversity values
(Figure 3) and in the NMDS plots, where the polygon encompassing ginger
sites occupies a larger portion of the ordination space (Figure 4). The
compositional differences in the diets of spiders from ginger sites are
due to the higher diversity of prey consumed, with four orders
(Hemiptera, Lepidoptera, Diptera and Entomobryomorpha) detected most
commonly (Figure 5). The diets of spiders in ginger are not dominated by
any one order, with the most common prey (Hemiptera) detected in the
diet of 43.6% of ginger spiders followed by Lepidoptera in 42.3% of
spiders and Diptera in 37.1% of spiders; the non-consistency of the
diet across spiders in ginger is the cause of increased beta diversity
and wider polygons. In contrast, spiders in native forest are consuming
more similar diets consisting predominantly of Hemiptera, with 72.4% of
spider diets containing Hemiptera. The second most common order,
Lepidoptera, only occurs in 36.2% of spider diets. Spiders in native
forest are not predating Entomobryomorpha (Collembola) or Coleoptera at
the same rate as ginger spiders. In fact, Entomobryomorpha was the
fourth most common prey group in ginger, detected in 27 spiders (34.6%)
while Entomobryomorpha were only detected in 1 spider (1.7%) in native
forest sites (Figure 5).
To further understand diets between native forest and ginger forest, we
examined phylogenetic beta diversity within the most common orders,
Hemiptera and Lepidoptera. Here, we were interested to see if spiders
were eating the same taxa within commonly detected orders. Because of
low BLAST identification, phylogenetic beta diversity using 16s within
orders was used to allow us to detect any finer scale taxonomic
similarity that may exist. We find large overlap between the Hemipteran
and Lepidopteran prey in both native forest and ginger (see S6 in
Supplemental Information). Hemipteran in the family Cicadellidae and
Lepidoptera in the families Geometridae and Hesperiidae were most
detected across both habitats. In native forest, more spiders were
detected consuming family Cicadellidae and family Hesperiidae (See S7 in
Supplemental Information. There were three Hemipteran families and six
Lepidopteran families detected in ginger that are were found in native
forest; however, these were detected in the diets of very few spiders.