Spider diversity and ecology in native tussock grasslands of the South Island, New Zealand

Abstract

Tussock grasslands have been the subject of relatively extensive botanical research as they are considered ecologically distinctive and economically important. However, comparatively little is known about the invertebrate fauna of tussock grasslands, and more particularly, almost nothing is known about the spider fauna. The aim of this thesis is to evaluate methods for studying spiders in tussock grasslands, and to answer some questions about their ecological interactions with vegetation and the effects of fire on tussock grassland spider communities. The selection of appropriate sampling methods is crucial for the success of ecological studies. An evaluation of spider sampling methods in tussock grassland identifies pitfall traps as the most effective and efficient. The physical characteristics of tussocks limit the efficiency of some sampling techniques, such as suction sampling. Methods that target the lowest layers of vegetation, such as pitfall traps, should be used for the study of spider community in tussock grasslands, although other methods, such as foliage beating, may also be considered to collect unique species. Molecular methods and analyses have the potential to add value to ecological data and help answer ecological questions. Mitochondrial DNA analyses are used for gender matching, and discrimination and identification of undescribed species. The results of this study show that analytical methods, such as GMYC, developed for DNA identification or taxonomy, may not always be congruent with morphological information and may require data from other sources. Nevertheless, the use of DNA data should be considered in ecological studies as they can provide crucial supplementary information for specimen identification, preventing incorrect conclusions. Little is known about the factors that drive spider diversity in tussock grasslands. Environmental factors, such as soil moisture, affect vegetation structure in tussock ecosystems, which in turn determine spider assemblages. Gradients in vegetation are matched by spider assemblages, with the family Orsolobidae favouring areas with marshland vegetation, and aerial-web builders, such as Linyphiidae, preferring shrubby vegetation. Species of the genus Anoteropsis (Lycosidae), identified as potential indicators of the structure of the vegetation, are recommended to be included in monitoring programs for conservation management. The effects of fire on spider communities are assessed through a long-term experiment with burnt and unburnt plots spanning years before and after a fire. Spider diversity decreases drastically after the fire and remains low for four years. Although the overall trend is a decrease in the abundance of most spider families, Linyphiidae shows a large increase in the years following the fire, which is explained by their ability to disperse and colonise new habitats. An increase in the number of exotic species, particularly Diplocephalus cristatus, is behind this trend, showing the importance of addressing the question of the effects of disturbances on native and exotic species in New Zealand ecosystems, and the dangers that they pose to native biodiversity. This thesis contributes significantly to the understanding of spider communities in one of the most important native ecosystems in New Zealand, providing fundamental methodological information for future studies and unveiling some of the key drivers of spider diversity.spiders, tussock grasslands, sampling methods, DNA identification, DNA taxonomy, diversity patterns, habitat requirements, vegetation structure, community structure, fire, exotic species, conservation management