Insect community composition varies between temperate and tropical regions but functional structure remains conserved

Abstract

1. Insect herbivores and their parasitoids make up a large proportion of biodiversity, but studies of their communities rarely involve geographic comparisons. If the community on a host plant varies geographically, insect diversity will be underestimated by ignoring this. In addition, community functional structure may vary geographically due to differential abundance of functional groups. 2. To address these issues, we compared the composition and structure of the fig wasp community associated with Ficus rubiginosa between temperate (Sydney) and tropical (Townsville) regions of eastern Australia. We sampled figs from four sites per region, twice a year for 2 years, resulting in about 14,000 wasps from 11 genera and 19 sub-generic taxa. Since two of these taxa each comprise two cryptic species, we refer to taxonomic diversity below, but this is largely at species level. 3. Taxonomic richness (14) was the same in both regions and nine taxa were shared across regions. However, 10 taxa were found in only one of the two regions, driving a significant difference in the taxonomic composition of the tropical and temperate communities, and increasing overall diversity in the system.4. The wasps belong to five functional groupspollinators, small and large gallers, and small and large parasitoids. In contrast to taxonomic composition and diversity, community functional structure did not differ significantly between regions. 5. Our results highlight that there can be broad latitudinal conservation of functional community structure across regions, despite considerable regional differences in taxonomic composition.

Host insect specificity and interspecific competition drive parasitoid diversification in a plant–insect community

“…Lower host plant specificity of parasitoid fig wasps has also been reported in different geographic regions, such as Asia (Zhou et al, 2012), America (Farache et al, 2018), and Africa (McLeish et al, 2012). Even when low host specificity of parasitoids has been found in some ecological studies, the wasp community structure is still largely conserved (DeGabriel et al, 2022; Deng et al, 2021).…”

“…Parasitoid wasps were collected in the tropical rainforest at Xishuangbanna, China (21 41 0 N, 101 25 0 E) between 2008 and 2018. Parasitoid wasps occupy high trophic levels in the fig-fig wasp community; thus, their population sizes are generally smaller than those of pollinators and most gallers, and some parasitoids are rare species (e.g., DeGabriel et al, 2022). Mature figs were sampled from trees, and the wasps were allowed to emerge in mesh bags at ambient temperature.…”

“…Few studies have compared phylogenies of figs and gallers, but in tune with their antagonistic relationship and lack of vertical transmission (Hayward et al, 2021), there is little support for cospeciation (Wang, Peng, et al, 2019; Weiblen, 2002). Fig‐pollinating wasps and the various lineages of non‐pollinating gallers are all insect herbivores and, as such, are attacked by a range of insect parasitoids (DeGabriel et al, 2022; Kerdelhue et al, 2000; Marussich & Machado, 2007). Existing evidence suggests that these parasitoid fig wasps are also highly host–plant specific (Jousselin et al, 2008), but at least some of them attack insects on more than one Ficus species (Jiang et al, 2006; Marussich & Machado, 2007), and relatively few studies have probed this issue of host plant specificity.…”

“…In this tri‐trophic community, when we consider resource (host) availability, one important difference between pollinators and gallers as hosts is that essentially every fig contains many pollinator offspring, while the offspring of any given galler species are patchier in space and time and, on average, much less numerous in the figs where they do occur. Different galler species may be either common or rare across fig fruits and have high or low numbers of individuals in occupied figs (DeGabriel et al, 2022; Segar et al, 2013). However, in general, from a parasitoid perspective, gallers represent a less abundant and patchier host resource than pollinators (Segar et al, 2013), and this may favor a wider host range for parasitoids of gallers than for parasitoids of pollinators.…”