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A quantitative framework to guide restoration of butterfly communities in fragmented landscapes

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1. Recent studies have unveiled drastic declines in the diversity and numbers of insects worldwide, unfolding over the last decades. These results have brought insects to the forefront of conservation attention, ranging from mitigation actions planned by dedicated conservation agencies to efforts undertaken by the general public. Further, the conservation focus has necessarily shifted from single (highly endangered) species to multi-species plans, but such a shift can become a daunting task when dealing with several dozens of species. In the last two decades powerful methods have emerged to describe and analyze populations inhabiting fragmented landscapes that are the dominating landscape type in most highly industrialized countries. Moreover, especially studies of butterfly species have enabled deep metapopulation insights, in theory and practice. 2. The quantitative framework I present consists of two connected components. The first aims at mapping a butterfly species list onto habitat patches in a landscape to be restored, uncovering the structure of the butterfly-specific metapopulations. This mapping relies mainly on larval host plant species and the vegetation types they inhabit, but it can accommodate additional resources that ultimately foster the species’ presence. Further, the mapping produces additional data that can conveniently be analyzed using methods from network theory, yielding ancillary insights for restoration planning. Subsequently, the second component aims at analyzing the metapopulations guided by metapopulation theory, to quantify the effect of available restoration actions on ecological and genetic aspects. The weighted, summarized results at the community level are now amenable to decision analysis that ultimately allows selecting the most effective and efficient strategies in a rational way, based on project objectives, strategies, and constraints. I hope the presented framework – as a whole or parts of it – may help inform and guide butterfly restoration projects.
| Changes in butterfly species richness in the Swiss canton of Thurgau over a century. Panel (a) shows the number of butterfly species (species richness) by family (see legend panel b, except «all»), for the years 1913, 1985, and 2018. Panel (b) shows the same data as in panel (a), but as proportions of the respective species richness in 1913. Additionally, the overall changes are shown («all», legend): the number of species declined from 100 in 1913 (100%), to 76 in 1985 (76%), and finally to 72 in 2018 (72%). The connecting lines in panels (a-b) are intended as a visual aid, they should not be interpreted as linear trends over time. Panel (c) summarizes the number of species in 2018 that either was absent in 1985 or disappeared since then. «disappeared»: these species were either only present in 1985, but not in 1913 (x = 1 year), or present in both years (x = 2 years); «(re-)appeared»: these species were either present in 1913, but not in 1985 (x = 1 year), or absent in both years (x = 2 years). Panel (d) shows the species list in 2018 in terms of the red list categories (n = 72). Panel (e) shows the current red list categories of species that disappeared between 1985 and 2018 (n = 18), while panel (f) shows the current red list categories of species that (re-)appeared between 1985 and 2018 (n = 14); cf. panel (c). NA: no RL status, LC: least concern, NT: near threatened, VU: vulnerable, EN: endangered, CR: critically endangered. See section S1 (Supplementary material) for additional information. [Figure from: Bozzuto C (2020): «A quantitative framework to guide restoration of butterfly communities in fragmented landscapes». Technical Report Wildlife Analysis GmbH, Zurich, Switzerland. DOI: 10.13140/RG.2.2.28616.14080]
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... One reason is that NHCs offer the unique opportunity to study long periods of time, e.g. a century or more, thus potentially allowing to study phenomena before massive anthropogenic effects started taking a considerable toll on nature (e.g. Bakker et al., 2020;Bozzuto, 2020;Laussmann et al., 2021;Lister, 2011;Shaffer et al., 1998;Theng et al., 2020). ...
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