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

Authors:
  • Wildlife Analysis GmbH, Zurich

Abstract and Figures

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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Over the last two decades, many studies have emphasized the value of natural history collections (NHCs) for ecological and evolutionary research. Furthermore, with the current biodiversity crisis worsening by the day, these specimens offer invaluable insights into past changes, directly helping researchers to understand the current status and to propose apt measures to halt the decline of species and communities. In parallel, the digitization of collections continues being an on-going and pressing endeavor at the global scale. Several achievements are already impressive, with global databases meanwhile offering online access to many millions of specimen data. Unfortunately, especially the use of regional data for regional-scale studies is partly hampered by small- to medium-size natural history museums (NHMs) still awaiting digitalization. But even with completed digitization, many NHC data continue being only available by request. As an incentive for NHMs to more actively and rapidly share their data, in this study we present simple spatio-temporal analyses and visualizations helpful to display NHC data in a research-oriented way. The aim is to allow researchers a rapid online assessment of NHC data for their purposes. To this end, we propose the use – alone and combined – of (i) well-known indices from biodiversity research, (ii) cumulative and/or parametric representations of temporal data, and (iii) Voronoi tessellations and Delaunay triangulations for spatial data. As an illustrative example, we analyze butterfly collection data from a Swiss NHM. With today’s possibilities to quickly set up web applications and with the modest attribute requirements per specimen for our methods, we believe the implementation of these ideas will be affordable and quickly realizable, all the more – to the benefit of research – if NHMs share forces. The ideas and methods will also appeal to global initiatives ultimately aiming at offering access to the majority of NHCs. For the time being, our study may serve as a regional incentive encouraging NHMs to aid researchers generating much-needed knowledge on a rapidly changing natural world.
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Der Nationale Aktionsplan PSM (Bundesrat 2017) hat zum Ziel, das von PSM ausgehende Risiko für Nichtzielorganismen zu reduzieren. Die Amphibien sind eine Organismengruppe, die im aquatischen wie auch im terrestrischen Lebensraum PSM exponiert sein können. Experimentelle Studien haben gezeigt, dass auch zugelassene PSM bei Amphibien Mortalität auslösen können. Hier wurden mathematische Populationsmodelle entwickelt, um die Wirkung von PSM auf einzelne Populationen sowie auf Metapopulationen von Amphibien zu analysieren. Hierbei wurde unter anderem die Effizienz von Massnahmen verglichen, welche die Lebensfähigkeit von Amphibienpopulationen unter PSM-Belastung erhöhen und/oder das von PSM ausgehende Risiko vermindern könnten. Als Modellarten dienen drei Amphibienarten, die von der EFSA als mögliche Schwerpunktarten für die Risikobeurteilung vorgeschlagen wurden: Die Kreuzkröte (Epidalea calamita), der Laubfrosch (Hyla arborea) und der Kammmolch (Triturus cristatus). Das Modell für einzelne Populationen hat gezeigt, dass die drei untersuchten Arten unterschiedlich stark auf von PSM ausgelöste Mortalität reagieren. Bei gleicher Mortalität (z.B. eine proportionale Reduktion einer individuellen Überlebenswahrscheinlichkeit um 10%) wird die Grösse einer Population des Kammmolchs viel stärker reduziert als die Grösse einer Population der Kreuzkröte; der Laubfrosch liegt dazwischen. Weiter wurde untersucht, wie sich eine PSM-Reduktion in gewissen Monaten (z.B. während der Laichzeit) auf die Populationen auswirkt. Dabei zeigte sich, dass die erzielte Wirkung in allen Monaten etwa gleich wäre. Betrachtet man Lebensstadien, die bevorzugt vor PSM geschützt werden sollen (in einer Landschaft, in der PSM appliziert werden), so ist es lohnenswert, speziell die Kaulquappen und die Juvenilen unmittelbar nach der Metamorphose vor PSM-Exposition zu schützen. Beachtet man aber, dass die untersuchten Amphibienarten mehr Zeit an Land als im Gewässer verbringen, so empfehlen sich Massnahmen im Landlebensraum LLR. In allen untersuchten Szenarien wirkt es sich positiv auf die Populationen aus, wenn sie in einem Teil des LLR vor PSM geschützt sind. Auch das Modell für Metapopulationen – einer Gruppe von Populationen, die miteinander durch Austausch von Individuen verbunden sind – wurde unter anderem im Hinblick auf ein Risikomanagement analysiert. Vier Massnahmen wurde genauer betrachtet: (1) Vergrösserung der Metapopulationen durch Bau neuer Gewässer mit zugehörigem LLR; (2) Reduktion des ungeschützten Anteils der Landschaft (z.B. Verzicht von PSM in Teilen der Landschaft); (3) Reduktion von PSM-Effekten im LLR; (4) Reduktion der PSM-Effekte in Gewässern. Hier zeigte sich, dass die vorteilhafteste Massnahme bezüglich Erhöhung der Lebensfähigkeit einer Metapopulation die Anlage neuer Gewässer (verbunden mit geeignetem LLR) ist. Diese Massnahme wurde von den drei anderen Massnahmen gefolgt, in der erwähnten Reihenfolge. Zusammenfassend zeigen die Resultate beider Modellanalysen, dass Massnahmen in terrestrischen Habitaten zu bevorzugen sind. Beispiele für solche Massnahmen wären, auf lokaler Ebene geschützte Lebensräume zu schaffen bzw. bestehende zu vergrössern, beispielsweise mittels Kleinstrukturen. Regional wäre es vorteilhaft, in Teilen einer von Amphibien bewohnten Landschaft auf den Einsatz von PSM ganz zu verzichten. Alternativ lohnte es sich regional auch, bestehende Metapopulationen durch die Anlage neuer Lebensrauminseln (Gewässer und assoziierter LLR) zu vergrössern. Eine amphibienfreundliche Veränderung der Landschaft könnte somit eine neue gangbare Risikomanagementmassnahme werden, die möglicherweise über bestehende Instrumente wie BFF umsetzbar ist.
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The objective of this work is to describe risk reduction measures for the terrestrial life stages of amphibians that can be recommended independent from the approval of plant protection products (PPP). These measures should be able to reduce the risk of PPP exposure, as well as promote amphibians in agricultural areas and compensate for the negative effects caused by PPP at the population level. In particular, we evaluated existing measures for ecological compensation and PPP risk reduction, and took changes in agricultural practice also into account. With the help of a literature review and a survey of cantonal advisory agencies, we compiled potential risk reduction measures. In addition, existing measures for other organism groups and measures defined by the Federal Council by means of new regulations for the application of PPPs were examined with regard to their effect on amphibians. All measures were evaluated by interviewing experts with regard to their effectiveness for the protection or promotion of amphibians, their feasibility on a farm, as well as their controllability. The impact on production was not quantified as part of this project. A total of 30 measures were considered conceivable in Switzerland. Of these, nine risk reduction measures are proposed for practical application, whereby a forward-looking and constructive cooperation between agriculture and amphibian conservation will be important for their implementation. In part, these measures are already being implemented or promoted, but they can be adapted more specifically for amphibians based on this work; in turn, the measures would benefit other animal groups in addition to amphibians. In principle, the combination of measures can increase their impact.  Workshops for farmers and agricultural advisors: raising awareness forms the basis for the successful implementation of risk reduction measures and promotes the conscious and careful use of plant protection products and thus the protection of amphibians.  No local application of plant protection products on migration routes during the main migration period of amphibians in spring: this measure requires a differentiated consideration depending on the occurrence of the species and the time of migration. The expected impact would be very high, as direct contact of migrating amphibians with pesticides would be avoided. It mainly benefits the most common species (common frog, common toad, alpine newt). A prerequisite for implementation is a good forecasting model for the timing of amphibian migration; furthermore, it would have to be clarified whether the measure would lead to yield losses.  No (or time-limited) application of plant protection products in area B of amphibian breeding sites of national importance: with area B comprising terrestrial habitats adjacent to breeding sites and parts of migration corridors, they are intended to protect populations of rare species and also significant populations of common species. For individual populations, this measure would have a high impact. In sum, only a few breeding sites would be affected. Approximately 10 % of all amphibian breeding sites are included in the inventory of amphibian breeding sites of national importance. Across Switzerland, about 1008 ha of pesticide-relevant crops are cultivated within area B perimeters.  Spatial arrangement of biodiversity promotion areas: the spatial arrangement of biodiversity promotion areas is very important to their protective function and enhancement of terrestrial habitat. Biodiversity promotion areas could, for example, be targeted along migration routes or near breeding sites. Basics provided in this work should simplify the implementation. The measure is considered to be well feasible and effective, but needs a differentiated consideration and good advice.  Site-specific creation of small structures that can serve as hiding places for amphibians in the terrestrial habitat: these include, for example, wood and stone piles, but also other structural elements such as groups of shrubs and water ditches. These provide suitable habitat for amphibians and are already familiar to farmers. The creation of small structures at field edges, in biodiversity promotion areas or around amphibian breeding sites is considered to be particularly effective and easy to implement. This measure can help to increase the survival of juveniles in particular, which are especially important for the viability of populations.  Integrative water management: climate change requires a reconsideration of agriculture. Retention ponds, for example, can be created to ensure the irrigation of agricultural crops. If these are planned appropriately, they would also create new breeding habitat for amphibians. This is a future-relevant topic with a lot of potential for amphibian protection. The feasibility requires a combined planning of land and water management along with amphibian and nature conservation.  Construction of new amphibian breeding sites: the construction of new breeding waters was judged by herpetologists to be an extremely effective risk reduction measure. While proven methods can be used for the construction of breeding waters, their acceptance by farmers may be low (e.g. because of legislation over the distance requirements of the use of plant protection products near water bodies). Agricultural advisors could play an important role here. Population models show that the establishment of breeding waters is the most effective measure to promote metapopulations of amphibians at the landscape level. Analysis of migration routes between breeding waters provides an overview of where new breeding waters can contribute to population connectivity.  Establish wet rice as a special case of amphibian breeding waters: wet rice fields could substantially support amphibian populations, especially the late breeding species that prefer temporary waters. At the same time, a niche product is produced (Swiss rice), which can be sold at attractive prices directly from the farm. Ecological cultivation of wet rice will be financially supported as a biodiversity promotion area type starting in 2024. This measure is proposed based on new research results (www.nassreis.agroscope.ch); it was not part of the evaluation procedure of the project.  Adapted management in the vicinity of amphibian breeding waters: this refers, for example, to extensive agriculture or the use of drift-reducing nozzles. This was evaluated as a very effective measure, especially since the choice of nozzles does not affect agricultural production and the nozzles are already widely used. Further research contributions from this project provide a scientific basis for the selection of locally adapted measures and their implementation. With models of the dynamics of populations and metapopulations of amphibians, we describe the potential effects of plant protection products and provide information on how amphibian populations respond to risk reduction measures. In this way, measures can be identified that have the greatest effect on amphibian populations. We also analyzed amphibian use of agricultural landscapes on a national scale and show where populations potentially live on agricultural lands where PPPs are used. This work provides baseline information on where and when to best protect which species and life stages and how. For example, based on modeling, protecting tadpoles and especially juveniles (after metamorphosis) appears to have the greatest protective effect on populations. Regionally, the creation of new breeding waters (with suitable terrestrial habitat) represents the most efficient measure. At the local level, small structures in terrestrial habitat or on seasonal migration routes are also considered effective. Risk reduction measures should be selected and implemented on a species-specific basis. For example, in the natterjack toad field study, the toads were observed to use cropland as terrestrial habitat because they prefer open soils. Therefore, biodiversity enhancement areas with open soils would be a promising enhancement measure to promote natterjack toads. Although enhancement programs are often species-specific and species vary in local occurrence, mapping indicates that amphibians are not exceptional in agricultural areas, but are potentially widespread. Highly endangered species, in particular, have a high likelihood of coming into contact with plant protection products, especially on potential migration routes between amphibian breeding sites.
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