The topic of this study is to explore the Swedish landscape composition and its effect on butterflies at different spatial scales. Using data from an ongoing national monitoring program of butterflies in Sweden, the study raised several questions to be addressed which are: (1) How do matrix composition influence the occurrence of butterfly species in semi-natural grasslands? Can different land cover types in the landscape (semi-natural grasslands, arable land, forests, and water surfaces) explain the occurrence of butterfly species in semi-natural grasslands? (2) At which spatial scale do butterflies respond to different matrix types surrounding the semi-natural grasslands? (3) Can life history traits explain the spatial scale of response?
Though habitat area and isolation have been shown to have strong effects on the local biodiversity, a substantial body of research also shows that species abundance and composition in remaining habitat patches are strongly affected by the surrounding matrix. Other species differences have been “attributed to life history traits, e.g. species with low reproduction, low dispersal ability and specialist host plant requirements have been shown to be most sensitive to habitat loss (Bergman at el, 2018).”
They used generalized linear model for each land cover matrix types which are, arable land, semi-natural grassland, forest, and water surfaces to estimate the odds of finding a specific species in a site based on the proportion of each land cover type. The generalized linear model is a simple yet effective method for this study particularly because it allows us to understand whether land matrix have a strong positive or negative effect on species richness across different spatial scales reflected by the median z score. This was shown in the result which for example, they found a significant positive correlation between the amount of semi-natural grasslands and the amount of arable land at the scale of 631 m and higher (highest Pearson’s r = 0.49, p = 0.0002 at the 40 km scale).
In addition, there was also a small negative correlation between the amount of semi-natural grasslands and the amount of forest cover at the smaller to medium scales (from 100 m to * 3 km). Thus, the significance of the relationship is a strong evidence to support the main argument which is whether landscape matrix affects richness in butterflies.
Overall, I am definitely convinced that there is validity to the author’s main argument. The charts contained in the study clearly depict the clear relationship between the landscape matrix and species richness using median z score at different scales. I would rate this paper 8 out of 10. The reason is because the authors successfully answered the three study questions they raised and the entire study was easy to understand and follow. I did not give it a perfect score simply because I believe there are other factors that explains species richness. For instance, some butterflies may simply be specialists that thrives in a particular landscape type, while other butterflies can be generalists, which the study did not account for this.
Source:
Bergman, K.-O., Dániel-Ferreira, J., Milberg, P., Öckinger, E., & Westerberg, L. (2018). Butterflies in Swedish grasslands benefit from forest and respond to landscape composition at different spatial scales. Landscape Ecology, 33(12), 2189–2204. https://doi.org/10.1007/s10980-018-0732-y