On the ecology and biogeography of alpine tundra arachnids

Abstract

In the course of the discussion about the effects of manmade Climate Change on ecosystems, alpine regions of the earth have become a major focus. Alpine ecosystems are generally considered to be especially sensitive towards environmental changes. Thus, alpine research concentrates on ecosystematic processes along gradients at various scales. Within this setting of gradiental dependency, alpine ecosystem research often makes use of spacetime substitution. However, the research on spatial and temporal ecological patterns is mostly limited to the analysis of vegetation patterns; studies on spatial patterns of zoological species composition are underrepresented. Yet, especially epigeic arachnids show some characteristics which makes them valuable proxies in processoriented ecosystem research: on the one hand arachnids occur in high abundances in alpine habitats, on the other hand they are often described to be sensitive towards diverse abiotic and biotic factors.<br /> This thesis aims to tackle this research gap by investigating spatial and temporal patterns of arachnids in alpine and arctic habitats. Afurther focus lies on the aranchids' adaptation strategies in relation to tangible environmental conditions within their habitats. Of special interest is, whether and to what extent supposedly harsh alpine environmental factors affect the lifehistory and reproductive traits of arachnids at multiple scales. Therefore, a network along a continentality, an elevational and (micro) topographic gradients has been installed. The network consists of pitfall traps and data loggers, recording microclimatic factors. Furthermore, vegetation composition and snow height and distribution were recorded. This multiscale network was implemented at two research areas in Southern Norway: one is situated in the more oceanic part close to Stranda (Møre og Romsdal), while the other site near Vågå (Oppland) is characterized by a rather continental climate.<br /> With regard to the spatial patterns of Araneae, the results of this study, show a pronounced annidation along the elevational as well as the topographic gradient. Surprisingly, the influence of continentality weakens above the treeline in favor of smallscale environmental factors (Chapter 2).<br /> It is generally assumed that body sizes of spider individuals decrease with elevation and the increase of adverse environmental conditions. In this study, this trend could not be verified for the wolf spider <em>Pardosa palustris</em>. In fact, the elevationrelated environmental conditions were superimposed by topographic influences. However, in direct comparison of the two research sites, specimens caught at the more continental site were significantly larger than at the oceanic site. This denotes a rather prolonged life history trait in the continental part Vågå (Chapter 3).<br /> Focussing on the elevational adaptation of reproductive strategies of five wolf spiders of the genus Pardosa with partly differing habitat preferences, no common adaptation patterns along three elevational gradients in the continental research area could be identified. The assumption, that females would with increasing elevation decrease the number of eggs in favor of a larger egg size could not be verified (Chapter 4). <br /> One of the most common epigeic species trapped within this study has been the Opilionid species <em>Mitopus morio</em>. Here, we could show, how macroas well as microclimatic conditions influence the activity pattern of M. morio along different environmental gradients (Chapter 5).<br /> As a result of the great amount of trapped epigeic Artropods, it was possible to describe a new species and its habitat for Fennoscandia: the Oribatid mite <em>Provertex kuhnelti</em> could be confirmed at an alpine ridge in the oceanic research site. With this finding, the distribution of <em>Provertex kuhnelti</em> can now be described as “boreoalpine” (Chapter 6).<br /> In summary it can be stated that in relation to the multiscale approach and the sampling along three environmental gradients this thesis enables for the identification of driving forces for species annidation. Moreover, some of the influences of ecological parameters on lifehistory and reproductive traits could be identified. This thesis underlines the importance of measuring environmental parameters on a fine scale to better understand alpine tundra ecosystems.