With flying colors: New study assesses how different land-use types relate to butterfly diversity

The very hungry caterpillar needs food and shelter – and depending on its life-history traits, its requirements can be either decidedly specific or just as generic as the children’s book illustrates: A new study by Wurz et al. (2022) draws off this vast diversity and uses butterflies as a model taxon to assess effects of land-use change on biodiversity in Madagascar. Butterflies demonstrate a complex life cycle, often with host plant specialization during the larval stages, and may respond differently to habitat changes. The higher their habitat specialization, the more likely they are to face extinction when confronted with land-use changes. In Madagascar, landscapes are highly fragmented due to forest areas being turned into agricultural land. Here, agroforestry is advocated as a profitable and biodiversity-friendly land-use choice, allowing possible habitats for a variety of butterfly species.

Wurz et al. assess butterfly assemblages in woody land-use types (forest fragments, forest-derived vanilla agroforests, fallow-derived vanilla agroforests, woody fallows), open land-use types (herbaceous fallows, rice paddies) and old-growth forests. They differentiate between forest-derived and fallow-derived vanilla agroforests, as the land-use history affects the biodiversity value. In their research, Wurz et al. determine butterfly species richness, species composition in the different land-use types, and the land-use types’ importance for the butterflies to shed a light on how habitat dependency of endemic, forest and open-land species is making an impact in human-modified landscapes.

The study was conducted in ten villages covering seven land-use types and two old-growth forests in North-eastern Madagascar. In total, 80 circle plots with a radius of 25m were sampled: 70 plots across the villages and ten in the old-growth forests. Butterflies were caught with bait trapping and time-standardized netting between August and December 2018. In total, 2643 individuals of 88 butterfly species of six families and 49 genera are recorded. Among these, 65 endemic, 42 open-land and 46 forest (43 of these among the endemic) butterfly species could be identified. Species are considered ‘associated’ with a land-use type if they occurred there with > 50% of their relative abundance and ‘exclusive’ to a land-use type if they only occurred in one of the seven types.

Results indicate overall species richness and endemic species richness as comparable across all land-use types. Notably, many endemic butterflies occur in open land-use types as well, emphasizing the need to conserve both forest and open land-use types. Contrastingly, species composition differs between land-use types. Particularly old-growth forests exhibit an unparalleled species composition in comparison to the agricultural system, exposing deforestation and landscape homogenization as a significant threat to the species pool. Interestingly, forest species are found to persist in the woody land-use types. Wurz et al. stress that the forest dependency of Malagasy butterflies has been overestimated and that further investigation on how butterflies use agricultural habitats is needed. This would make an update of the habitat categorization system necessary to ensure effective butterfly conservation. Additionally, Wurz et al. recommend maintaining existing forest-derived vanilla agroforests, but not changing further forest fragments. Forest-derived vanilla agroforests exhibit a high number of species and therefore a high conservation value, but a different species composition compared to forest fragments.

Species richness of overall (a), endemic (b), forest (c), and open-land (d) species sensu Lees et al. (2003) across land-use types in
north-eastern Madagascar. Non-shared letters indicate significant differences between pairs of land-use types based on pairwise Tukey’s honest significance tests (p < 0.05). The line inside the boxplot represents the median. The lower and upper boundaries of the boxplot show the 25th–75th percentiles of the observational data, respectively. The lower and upper whisker represents the scores outside 50% of data scores. Icons created by Made, Linseed Studio and Shashank Singh from the Noun Project (Wurz et al. 2022)

Finally, implementing fallow-derived vanilla agroforests would provide conservation and habitat rehabilitation opportunities, as they present no difference in species richness of any type of species in comparison to woody fallows, but higher numbers of endemic and forest species in comparison to herbaceous fallows which are richer in open-land species. The study of Wurz et al. accentuates the need of preserving the diversity of small-scale land-use types, as they each sustain different butterfly assemblages. 

First hand experience for children at the “School Garden New Generation” in Sambava, Madagascar (source: Gallery – School Garden NEW GENERATION (wordpress.com) )

Related to this study, Wurz also works at the “School Garden New Generation”, a project in Northeastern Madagascar designed to encourage environmentally conscious actions and provide nature-based opportunities for children aged 6-12. That way, children cannot only read about the very hungry caterpillar but learn about it and its endemic Malagasy companions first-hand. Check out the School Garden project here for details of their work.

To read more about the study, feel free to check out the paper by Wurz et al. (2022) here.

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