Résultat de la recherche
Soil properties and plant species can predict population size and potential introduction sites of the endangered orchid Cypripedium calceolus
Background and Aims To counteract the ongoing worldwide biodiversity loss, conservation actions are required to re-establish populations of threatened species. Two key factors predominantly involved in finding the most suitable habitats for endangered plant species are the surrounding plant community composition and the physicochemical parameters of the soil rooting zone. However, such factors are likely to be context- and species-dependent, so it remains unclear to what extent they influence the performance of target species. Methods We studied large and small Swiss populations of the endangered orchid Cypripedium calceolus. We measured functional traits related to C. calceolus plant and population performance (clonal patch area, plant height, number, of leaf, stems, flowers and fruits), realized vegetation surveys, soil profile analyses, and tested for relationships between plant traits and the surrounding vegetation structure or soil physicochemical parameters. Results Large populations contained bigger patches with more stems and leaves, and produced more flower per individual than small populations. Neither vegetation alliances nor soil classes per se could predict C. calceolus functional traits and population size. However, functional traits explaining population performance and size were related to specific soil parameters (soil organic matter content, pH and phosphorus), in addition to a combination of presence-absence of plant indicator species, relating to ecotones between forests and clearings. Conclusion We show that even for species that can grow across a wide range of vegetation groups both indicator species and specific soil parameters can be used to assess the most favourable sites to implement (re)-introduction actions.
Detecting preservation and reintroduction sitesfor endangered plant species using a two-step modelingand field approach
To withstand the surge of species loss worldwide, (re)introduction of endan-gered plant species has become an increasingly common technique in conser-vation biology. Successful (re)introduction plans, however, require identifyingsites that provide the optimal ecological conditions for the target species tothrive. In this study, we propose a two-step approach to identify appropriate(re)introduction sites. The first step involves modeling the niche and distribu-tion of the species with bioclimatic and topographical predictors, both at conti-nental and at national scales. The second step consists of refining thesebioclimatic predictions by analyzing stationary ecological parameters, such assoil conditions, and relating them to population-level fitness values. We dem-onstrate this methodology using Swiss populations of the lady's slipper orchid(Cypripedium calceolusL., Orchidaceae), for which conservation plans haveexisted for years but have generally been unfruitful. Our workflow identifiedsites for future (re)introductions based on the species requirements for mid-to-sunny light conditions and specific soil physico-chemical properties, such asbasic to neutral pH and low soil organic matter content. Our findings showthat by combining wide-scale bioclimatic modeling with fine scale field mea-surements it is possible to carefully identify the ecological requirements of atarget species for successful (re)introductions.
From fundamental questions to practical conservation actions: a study of the ecological niche (soil and vegetation), the pollination system, population genetics, population demography and mycorrhizal associations of "Cypripedium calceolus" (Orchidaceae)
The current epoch, the Anthropocene, is witnessing a generalized and rapid extinction of species worldwide. As the causes of such extinctions, often related to global change drivers (e.g., habitat destruction, pollution, climate change), might not be hampered immediately, conservation actions should focus on preserving, restoring and regenerating the disappearing species through concrete action plans. Rare and endangered plant species, for instance, can be preserved by reintroducing seedlings in the same habitat, or introducing them into yet unoccupied habitats to generate novel populations. While this approach holds several good promises, it often generates mixed results, likely due to the fact that the current or novel habitat do not actually offer the optimal conditions for the target species to grow and thrive. With this thesis, we have tackled the problem of how to better characterize the ecological requirements of an endangered plant species in order to increase the success rate of future (re)introduction actions and to develop more efficient and targeted conservation measures. By focusing on the iconic and endangered orchid species Cypripedium calceolus (Lady’s Slipper) as a model species, we have taken a broad-range perspective, including both geomatics and field work to study the links between multiple ecological factors (soil properties, climate, association with local vegetation and health of 34 C. calceolus populations across Switzerland). In the first chapter, we propose a two-step approach to identify (re)introductions sites for endangered plant species using C. calceolus as a model species. The first step involves modelling its niche and its distribution with bioclimatic and topographical predictors. The second step consists in refining these bioclimatic predictions by analysing stationary ecological factors, such as edaphic conditions, and relating them to populations-level fitness values. The first results show that climatic predictions alone were not precise enough, but nevertheless could highlight a likely decline of the species range during the next 50 years due to predicted climate warming. Moreover, when incorporating topographical layers for the modelling approach at the regional scale, we show that the species is more likely to occur near forest edges. Finally, by analysing in situ soil factors, we show that soil organic matter, cation-exchange capacity and pH correlated most strongly with C. calceolus population fitness variables as described by multivariate function trait space. We thus advocate for the combination of modelling tools with fine scale on-site ecological surveys to identify suitable reintroduction sites for this, and potentially other, endangered plant species. In the second chapter, we aimed to determine the relationships between the performance of C. calceolus populations and soil and vegetation factors, to improve this species conservation and but also to advance the theoretical underpinning of which facets of an ecosystem most influence this species fitness. By studying C. calceolus functional traits of 34 sites across Switzerland, we found that large (>20 individuals) populations of C. calceolus displayed a specific assemblage of measurable characteristics that discriminate them from small (<10 individuals) populations, indicating that it is possible to assess the health of a population of a rare plant species by measuring a specific set of traits. While we could not direct predict population health status from vegetation (phytosociological alliances) and soil types, we show that a unique combination of companion plants and several edaphic variables, such as soil organic matter (SOM), CaCO3, pH, and P could be used to potentially assess the optimal sites to implement (re)-introduction actions for this emblematic and patrimonial orchid species. In the third chapter, we addressed the pollination ecology of C. calceolus by studying the links between plant vegetative and floral traits and local pollinator biodiversity. Moreover, we studied potential variation at the population level of how plants attract their pollinators and subsequently how this variation relates to the overall reproductive effort of C. calceolus individuals. We found that small C. calceolus populations occur in less diverse sites, both in terms of surrounding plants and insects. However, while plants from larger populations were physically larger and produced more flowers per capita, they produce the same number of seeds per capita (i.e., seed set) as small populations. This occurred despite the lower pollinator diversity present at the small population sites, meaning that plants from small populations must compensate by providing a stronger attraction to pollinators. Indeed, we discovered that floral volatile organic compounds are produced in higher quantity from the flowers of plants from small populations, suggesting that small populations compensate for low pollinator diversity by producing a stronger floral scent. Two additional perspective chapters deal with the genetic structure of the Swiss C. calceolus populations and their association with mycorrhizal fungi. While these data opens new interesting venues, these topics merits further investigations in the future. In summary, our results do not only increase the fundamental knowledge about C. calceolus biology and ecology but also allow to establish concrete conservation measures and to select more appropriate translocation sites. Moreover, this thesis emphasizes the complexity of orchid ecology and supports the use of integrated research and practical protection measures for this family of plants, and likely others. In a context of global climatic changes and due to the fragility of orchid ecological needs, this kind of approach is more relevant than ever. From a broader perspective, the method we developed is transposable to other plant taxa. Therefore, we advocate for the use of comprehensive methodologies based on multiple aspects of plant biology and ecology, as presented here, to study and protect a broad range rare and endangered plants.