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Explaining the coexistence of species in mosaic cushion heath


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Methorst, G 2013 , 'Explaining the coexistence of species in mosaic cushion heath', PhD thesis, University of Tasmania.

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Cushion plants can occur in two-dimensional mosaics of species, which have
been shown to be stable in their proportions of species, but unstable in their
patterns (Gibson and Kirkpatrick 1992). Possible causes of this state of
quasi-stability were explored for a cushion mosaic composed of four principal
species, Pferygopappus lawrencii, Abrotanella forsteroides, Dracophyllum
minimum and Oreobolus pumilio at Mount Field National Park, Tasmania. An
area of a cushion mosaic was selected, the topography measured,
temperature readings taken under different synoptic conditions and the ability
of the two most common species, Pferygopappus lawrencii and Abrotanella
forsteroides to repel moisture measured. Slope, aspect and radiation input in
clear sky conditions were calculated for the 418 grid points at which
topography and temperature were measured and the species noted. The
differences between species in their distributions at the study site were
related to slope, aspect, elevation, clear sky radiation input and temperature
adjusted for radiation and slope. Chi-squared was used to determine the
significance of differences between species for misting and droplet
treatments. O. pumilio was associated with steep slopes and lower radiation
inputs. P. lawrencii was at lower elevations than A. forsteroides. Water
beaded on the surface of P. lawrencii at a higher rate than on A. forsteroides,
regardless of drop size. Temperature alone was found to be a poor indicator
of species occurrence. Species switched their temperature rankings in
different weather conditions. To conclude, the data most closely fit a model of
temporal environmental fluctuations with continuous competition. Differential cushion growth appears to lead to variation in topography and therefore
differences in interception of radiation. This negative feedback mechanism
may be contributing to the perpetuation of coexistence.

Item Type: Thesis - PhD
Authors/Creators:Methorst, G
Keywords: alpine, mosaic, cushion, co-existence
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