Rainforest transformation reduces parasitoid wasp diversity—Can the enrichment of flowering vegetation alleviate this?

• Published in: Ecological entomology Vol. 49; no. 6; pp. 825 - 836
• Main Authors: Azhar, Azru, Grass, Ingo, Rizali, Akhmad, Pudjianto, Buchori, Damayanti
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-12-2024; Wiley Subscription Services, Inc
• Subjects: Abundance; Asystasia gangetica; Biological control; Biological effects; Community composition; Community structure; Composition effects; Enrichment; Flowering; Flowering plants; Genetic transformation; Land use; Landscape preservation; land‐use change; Monoculture; oil palm; Parasitoids; Plantations; Plants (botany); Population decline; Rainforests; Rubber; Species composition; Species richness; Vegetable oils; Vegetation
• ISSN: 0307-6946; 1365-2311
• DOI: 10.1111/een.13355

In Indonesia, the rapid expansion of oil palm and rubber plantations replaces large areas of tropical rainforest. Rainforest transformation alters the diversity and composition of parasitoid wasp communities, but appropriate management strategies to buffer their decline in rainforest transformation landscapes are not yet developed.
Here, we studied the effects of rainforest conversion to smallholder rubber and oil palm plantations on parasitoid wasp species richness, abundance and species composition. We also conducted a flowering vegetation enrichment experiment using the flowering weed Asystasia gangetica in all land‐uses to investigate potential mitigation effects on parasitoid wasp diversity and composition.
Rainforest transformation to rubber plantations caused a large decrease in species richness (46%) and abundance (59%) of parasitoid wasps. Community structure of parasitoid wasps differed between forest and monoculture habitats with more habitat‐specialised species in forest and a higher proportion of common species in the monoculture.
The experimental flowering vegetation enrichment increased parasitoid wasp species richness by 18% and abundance by 127%. Enrichment also enhanced the presence of unique parasitoid species in plantation and furthermore increased differences in community composition between rainforest and plantations. However, the enrichment experiment was confounded by time, meaning that a multi‐year experiment with targeted controls is necessary for statistically more reliable statements.
Our study shows the effect of rainforest transformation to oil palm and rubber plantations on parasitoid wasp communities. Although providing additional flowering vegetation in plantations seems to potentially mitigate diversity loss, further research is needed to confirm and to investigate the mechanisms how flowering plants alleviate negative effects of rainforest transformation on parasitoid communities. Thereby, efficient conservation strategies for parasitoids wasps and their biological control services can be developed for rapidly changing tropical landscapes.
Rainforest transformation to monoculture plantations reduced species richness and abundance of parasitoid wasps. The study also highlighted the differences in community composition of parasitoid between forest and plantations.
Experimental enrichment with flowering vegetation increased species richness of parasitoid wasps by 18% and abundance by 127%. It also increased unique parasitoid species presence and community composition differences between rainforest and plantations.
Although adding flowering vegetation to plantations may mitigate diversity loss, the experiment was confounded by time. Further studies are needed to confirm how flowering vegetation mitigate rainforest conversion effects on parasitoids.