Biology subjects

Andersen, D. K.

Publications and source records attributed to Andersen, D. K..

4 recordsLinked to original sources

bioRxiv2024

A slippery slope: assessing the amphibian extinction crisis through the lens of climate refugia

In a time of increasing climate uncertainty, it is ever important to identify and preserve refuges for species, optimizing the effort to cover the largest possible number of clades. Climatic refugia are areas of climatic stability that will remain suitable for species over time under multiple climate change scenarios. Amphibians are important indicators of biodiversity and ecosystem health, in addition to being the most threatened class of vertebrates and can therefore serve as proxies to designate protected areas. In this study, we use ecological modeling to delineate current distributions of all amphibian species with adequate data globally. We then projected these distributions to four climate change scenarios, and four time periods, under two climate models representing low and high climate sensitivity. Climate refugia by species were calculated as the average of all climate change scenarios and time periods and were calculated separately for the two climate models of low and high sensitivity. We additionally extracted areas of current distributions and refugia to geographic regions, Udvardy biomes, and global protected areas. With the high climate sensitivity model (CNRM-CM6-1), 2,959 species would experience a refugia area that is reduced from their current distribution, with 139 species having no refugia area. Under the low climate sensitivity model (MIROC6), 2,864 species would have a reduction in area, with 136 having no refugia. While both climate models yielded similar results in terms of percent change, the MIROC6 model overall had less of a negative impact on species refugia. The results of this study present a somber warning of the amphibian extinction crisis in contrast to some of the recent literature, as well as encouragement for managers to act in order to preserve species and the ecosystems they represent.

ecology↗

bioRxiv2024

Environmental drivers of the decline of the fen orchid, Liparis loeselii

BackgroundLiparis loeselii is a rare and declining orchid species restricted to rich fens in the Northern Hemisphere. Habitat destruction, eutrophication, drainage and scrub encroachment have been suggested as reasons for the decline. However, which factors are most important is not well understood. AimsBased on vegetation and environmental properties from extant, potential and historical L. loeselii sites, we i) developed habitat suitability models from either Ellenberg Indicator Values or field-measured environmental properties, and ii) identified the primary reasons for the observed decline of L. loeselii. ResultsNutrient status was the most important predictor for L. loeselii occurrence, followed by hydrology proxies (Ellenberg reaction and Ellenberg moisture). Vegetation height and Ellenberg light were of minor importance. ConclusionEffect partitioning based on sites, from which L. loeselii has gone locally extinct, pinpointed eutrophication and drainage to be the most likely primary drivers of the species demise. Phosphorus limitation induced by discharge of Calcium-rich groundwater seems to be crucial for L. loeselii to sustain populations in landscapes dominated by intensive agricultural.

ecology↗

bioRxiv2022

High nutrient loads hinder successful restoration of natural habitats in freshwater wetlands

Restoration of natural processes in ecosystems is key to halt the biodiversity crisis. Here, we evaluate 20 different stream-valley wetland restoration projects - mainly rewetting - in a large region in Denmark in terms of successful restoration of natural wetland habitats. We used quadratic discriminant analysis and generalized linear models to compare the projects 80 vegetation plots with >50.000 natural wetland-habitat reference plots and modelled the influence of time, grazing, rewetting and nutrient availability on the study plots probabilities of belonging to such natural habitats and their richness of high-quality habitat indicator species. In our study, the probability of a restored wetland being a natural wetland habitat - almost always an alkaline fen - was generally below 10 %. Also, we only found half as many indicator species in restored wetlands than in reference wetlands and we demonstrated that the number of characteristic alkaline fen species did not deviate from what could be expected under the prevailing nutrient conditions. We found a negative effect of nutrient availability on the number of high-quality habitat indicator species and the lowest probability of plots being natural wetlands in the most nutrient rich plots. The effect of grazing was only positive in the first years after restoration and only in the most nutrient rich plots, while the effect of rewetting sites to their historical hydrological conditions was generally negative. Our findings reveal that unnaturally high nutrient availability is probably the core limiting factor for successful restoration of natural wetlands and their associated plant diversity. Implications for practice- To successfully restore natural and characteristic freshwater wetland habitats focus on recreating natural processes and conditions is needed - Restoring natural hydrology and grazing is not enough, the soil and water must be naturally nutrient poor for successful restoration of these habitats - Restoration of stream-valley wetlands such as alkaline springs and fens is more likely to be successful in spring-dominated landscapes where clean groundwater diffusely exfiltrates the soil

ecology↗

bioRxiv2022

Scrub encroachment promotes biodiversity in wetland restoration under eutrophic conditions

Wetlands are important habitats, often threatened by drainage, eutrophication and suppression of ungulate grazing. In many countries, considerable resources are spent combatting scrub encroachment. Here, we hypothesize that encroachment may benefit biodiversity - especially under eutrophic conditions where asymmetric competition among plants compromises conservation targets. We studied the effects of scrub cover, nutrient levels and soil moisture on richness of vascular plants, bryophytes, soil fungi and microbes in open and overgrown wetlands. We also tested the effect of encroachment, eutrophication and soil moisture on indicators of conservation value (red-listed species, indicator species and uniqueness). Plant and bryophyte species richness peaked at low soil fertility, whereas soil fertility promoted soil microbes. Soil fungi responded negatively to increasing soil moisture. Lidar-derived variables reflecting degree of scrub cover had predominantly positive effects on species richness measures. Conservation value indicators had a negative relationship to soil fertility and a positive to encroachment. For plant indicator species, the negative effect of high nutrient levels was offset by encroachment, supporting our hypothesis of competitive release under shade. The positive effect of soil moisture on indicator species was strong in open habitats only. Nutrient poor mires and meadows host many rare species and require conservation management by grazing and natural hydrology. On former arable lands, where restoration of infertile conditions is unfeasible, we recommend rewilding with opportunities for encroachment towards semi-open willow scrub and swamp forest, with the prospect of high species richness in bryophytes, fungi and soil microbes and competitive release in the herb layer.

ecology↗