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Community composition, assembly and priority effects in a volcanically disturbed alpine herbfield, Mount Taranaki, New Zealand

The New Zealand alpine flora is highly diverse, having evolved extensively over only c. 2 Ma. Examining how communities assemble and the effects of historical contingency may provide evidence for the mechanisms of rapid diversification of the New Zealand alpine flora. Evolutionary priority effects, in which the sequence of colonisation during community assembly can drive radiation of early arriving clades, has been tested in one South Island alpine community. The results showed genera belonging to older evolutionary lineages were more dominant and diverse in those communities, supporting the presence of priority effects. Mount Taranaki in the North Island is geologically the youngest alpine zone in New Zealand, and supports a depauperate assemblage of alpine species compared to other New Zealand mountains. Mount Taranaki has had approximately 10 moderately sized eruptions in the last 500 years and is separated from other New Zealand alpine regions by 130 km. The present study sought to determine how the vegetation in the alpine herbfield of Mount Taranaki has been affected by various eruptions, and to test if priority effects have influenced those communities. To quantify community composition in the Taranaki alpine herbfield, estimates of percent cover from 55 (2 x 2 m) plots were used to calculate relative species abundance at three sites within an altitudinal range of 1450–1650 m above sea level. Study sites were located at North Egmont, East Egmont and Fantham’s Peak. Multivariate analysis using non-metric multidimensional scaling ordination of relative abundances was used to compare variations in composition between sites and elevations. To test for priority effects, time-calibrated molecular phylogenies of clade divergence (as age estimates) were compared to the relative abundances of genera within the plots using linear regression. The results showed significant variation of species composition between sites, which correlates with the spatial pattern of the AD 1655 Burrell eruption. The eruption was directed toward East Egmont, and the plots there showed considerably lower species diversity compared to the other two sites. In addition, the inconsistency of species distribution between the sites indicated a lack of community convergence, suggesting herbfield vegetation is still in the early ages of assembly following eruptions. The test of priority effects showed no age-related abundance or richness relationships, therefore priority effects are unlikely to be contributing to community assembly in the Taranaki alpine herbfield. Instead, assembly appears to be influenced by the geological age and frequency of eruptions of Mount Taranaki, and its isolation from other alpine systems. This is the first study to determine the effects of volcanic eruptions on the herbfield vegetation of Mount Taranaki, and it is recommended that plots be re-measured in the future to determine how those communities develop. Because no priority effects were evident on Mount Taranaki, further research on a range of older volcanic and non-volcanic alpine systems in the North Island would be valuable. This would further contribute to our understanding of how communities assemble and if and when priority effects become significant.
Type of thesis
Moore, T. G. (2017). Community composition, assembly and priority effects in a volcanically disturbed alpine herbfield, Mount Taranaki, New Zealand (Thesis, Master of Science (Research) (MSc(Research))). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/12023
University of Waikato
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