Working at the Charles Darwin Research Station again
Thanks to a research fellowship sponsored by the Schimper Stiftung I was able to go to the Galápagos in February. It was great to continue my work on the Scalesia restoration project in the highlands of Santa Cruz. After intensive work in the invertebrate lab we finished all spider and beetles identifications and counted all other invertebrates caught within the long-term monitoring. This program started in 2014 and invertebrates were caught in 34 plots using pitfall and Malaise traps. First results have been recently published but more detailed analyses will be available soon.
Scalesia pedunculata – an endemic tree in the Galápagos
Argiope spec. – a spider species commonly found in Scalesia trees
Connectivity or area – what drives plant species richness in habitat corridors? has been accepted in Landscape Ecology.
Authors Thiele J, Kellner S, Buchholz S & Schirmel J
In a nutshell, we found out that connectivity is more important for plant species richness in linear landscape elements than area. In particular, the richness of plant species that are dispersal limited and confined to semi-natural habitats benefits from connective networks of linear landscape elements in agricultural landscapes.
My last post belongs to the past by now – anyway, that means that I moved to my outdoor workplace. We are mapping sand lizard populations and sampling pollinators, moths (and recording bats at the same time) and still ground-dwelling arthropods. We also running an experiments to measure seed predation along urban gradients. Hopefully we are able to start another experiment on pollinator visitation rates soon – so long as the weather is co-operating.
Plants, plant traits and ground-dwelling arthropods
Unfortunately, spring was very cold and rainy but however, we ‚bravely‘ started our field work for the BIBS project some weeks ago. Currently, our team is doing the plant diversity assessments and also pitfall traps are exposed. Moreover, we are measuring plant traits to analyse intraspecific trait variations along the urbanisation gradient – we are going to run these analyses for invertebrate taxa and hopefully sand lizard populations as well – wait and see. In addition, some students are observing phenology of plant species at 30 sites – very labour-intensive. Today I emptied our pitfall traps for the first time and I can’t wait to study our samples in the lab.
Urban dry grassland along the highway.
Urban dry grassland along the Heerstraße.
Rural and old grasslands in the Park Klein-Glienicke.
Abstract Urban wastelands are considered to be valuable habitats for biodiversity conservation, but empirical evidence for several poorly investigated taxa such as grasshoppers is still pending – although urgently required for reasonable habitat management and urban planning. For the first time, we analysed grasshopper diversity of urban wastelands at different diversity levels, namely, alpha and functional diversity. In 2014, we selected 24 urban wastelands in the city of Berlin (Germany).
Urban wasteland harbouring a Calliptamus italicus population
We analysed the relationships between local and landscape factors and different measurements of diversity (species richness, Simpson diversity, functional dispersion, functional evenness and functional divergence). We sampled 21 species, which represented about 45% of the entire grasshopper fauna of Berlin and numerous species of conservation interest were present at the investigated sites. Grasshopper diversity was best explained by local factors, with herb cover having a positive effect on alpha and functional diversity. Human impact and accessibility increased the conservation value of urban wasteland sites.
Late successional stages are very important for a high grasshopper diversity in general but early stages are mandatory to promote species of conservation concern. Urban wastelands can be turned into most promising transition zones for city-dwellers that fulfil the needs of conservationists and specialised species at the same time. To achieve this goal we recommend minimum requirements for successful habitat management.
Using resistance distance from circuit theory to model dispersal through habitat corridors has been published in Journal of Plant Ecology.
Authors Thiele J, Buchholz S & Schirmel J
Abstract Resistance distance, based on circuit theory, is a promising metric for modelling effects of landscape configuration on dispersal of organisms and the resulting population and community patterns. The values of resistance distance reflect the likelihood of a random walker to reach from a source to a certain destination in the landscape. Although it has successfully been used to model genetic structures of animal populations, where it most often outperforms other isolation metrics, there are hardly any applications to plants and, in particular, to plant community data. Our aims were to test if resistance distance was a suitable metric for studying dispersal processes of plants in narrow habitat corridors (linear landscape elements). This would be the case, if dispersal processes (seed dispersal and migration) resembled random walks. Further, we compared the model performance of resistance distance against least-cost distance and Euclidean distance. Finally, we tested the suitability of different cost surfaces for calculations of least-cost and resistance distance.
We used data from 50 vegetation plots located on semi-natural linear landscape elements (field margins, ditches, road verges) in eight agricultural landscapes of Northwest Germany. We mapped linear landscape elements, including hedges and tree rows, from aerial images in a Geographic Information System, converted the maps into raster layers, and assigned resistance values to the raster cells, where all cells outside of linear landscape elements received infinite resistance and, thus, represented barriers to dispersal. For all pairs of plots within study areas, we calculated Jaccard similarity assuming that it was a proxy (or correlate) of dispersal events between plots. Further, we calculated resistance distance and least-cost distance of the network of linear landscape elements and Euclidean distance between the plots. We modelled the effects of distance metrics on community similarity using binomial Generalized Linear Mixed Models.
Agricultural landscape of Westphalia
Euclidean distance was clearly the least suitable isolation metrics. Further, we found that resistance distance performed better than least-cost distance at modelling Jaccard similarity. Predictions varied markedly between the two distance metrics suggesting that resistance distance comprises additional information about the landscape beyond spatial distance, such as the possible presence of multiple pathways between plots. Cost surfaces with equal cell-level resistances for all types of linear landscape elements performed better than more complex ones with habitat-specific resistances. We conclude that resistance distance is a highly suitable measure of isolation or, inversely, connectivity for studying dispersal processes of plants within habitat corridors. It is likely also suitable for assessing landscape permeability in other landscape types with areal habitats instead of narrow corridors. Resistance distance holds the potential to improve assessments of isolation (or connectivity) for models of regional population and meta-community dynamics.
On the identity of the Palearctic species of the wolf spider genus Trebacosa (Araneae: Lycosidae) has been published in Zootaxa.
Authors Szűts T, Zalai B, Villepoux O, Buchholz S, Eichardt J, Zhukovets E, Oger P & Szinetár C
Abstract In this paper we propose Trebacosa brunhesi Villepoux, 2007 as a junior synonym of Trebacosa europaea Szinetár & Kancsal, 2007 based on the examination of specimens from all the localities from where those species are known. Illustration of the type species of the genus, Trebacosa marxi (Stone, 1890) and specimens from all known localities of T. europaea are given to show both the inter- and the intraspecific differences of the genus. Scanning electron micrographs were used to illustrate the detailed structure of the female’s genitalia.
The German Society of general and applied Entomology (DGaaE) and the German Scientific Society for Plant Protection and Plant Health (DPG) organised a conference on insect diversity in cities (III. Urbane Pflanzen Conferenz). I contributed a talk on habitat function of urban meadows for wild bees with emphasis on urbanisation effects (see Abstract in German). Due to a very diverse audience with many relevant stakeholders and decision-makers (e.g. scientists, gardeners, landscape planners, landscape architects, authorities and NGOs) it was possible to elaborate this topic from different perspectives. At the end we had very interesting – sometimes controverse – discussions to develop recommendations how to make cities more insect friendly and to comment on the new white book „Grün in der Stadt“ which was recently send out for preview. The official presentation of the white book will be in May 2017.