School of Botany - Theses
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ItemRestoration of a native grassland inhabited by Synemon plana (Lepidoptera)( 1997)Synemon plana is a diurnal moth belonging to the family Castniidae in the largest insect order Lepidoptera. The habitat is typically an open-woodland or grassland. In 1995 Synemon plana was listed as endangered under the Victorian Flora and Fauna Guarantee Act 1988. This thesis investigated the habitat of Synemon plana, including the germination requirements of the host plant (Danthonia), the size of the population at Mount Piper, Broadford, Victoria and the percentage cover of Danthonia preferred by Synemon plana. Fourteen sites were investigated and sites inhabited by Synemon plana and two historical locations (sites that once supported populations of S. plana) were compared. Floristic and soil surveys showed that the habitat of S. plana was a native grassland dominated by Danthonia, in particular, D. carphoides, D. auriculata, D. setacea, and D. eriantha. The percentage cover of Danthonia at all sites inhabited by S. plana was greater than 40%. While soil chemistry was variable among sites, the concentration of available P was low (less than 14 µg/g) in all sites inhabited by S. plana. The concentration of available P and the percentage cover of weeds at the two historical locations (Flowerdale and Tallarook) were significantly greater than those at the current locations. To determine the effects of weeds on the growth of Danthonia in soils to which P has been added, Danthonia eriantha and Lolium perenne were grown together and on their own in pots. The growth of Danthonia was significantly reduced when grown with L. perenne. Whilst the growth of L. perenne increased with increasing concentrations of P, the growth of Danthonia grown on its own was not significantly different when P was added. Therefore, L. perenne was at a competitive advantage when grown in soils to which P was added whilst the growth of D. eriantha was unaffected. The percentage cover of weeds was greater in soils with greater concentration of available P. Thus in soils to which P has been added, weeds reduce the growth of Danthonia and hence result in the loss of habitat for S. plana. A number of techniques aimed at increasing the cover of Danthonia eriantha in the field at Mount Piper was trialed over twelve months. The greatest increase in the cover of Danthonia was achieved when seedlings were planted in the field and weeds were removed. Although scattering caryopsides on the surface of the soil and removing weeds increased the cover of Danthonia eriantha, a large number of caryopsides was required due to the low number of viable seeds and low germination in the field. The population size at Mount Piper was investigated over two consecutive years. Mark-Release-Recapture methods to determine absolute population size were trialed. However, capturing and marking individuals affected their behaviour and of the 22 individuals captured using this method, 14 died. A new methodology, less detrimental to individuals was employed using tents to determine absolute population size. Tents were erected over quadrats with different percentage covers of Danthonia and moths were captured as they emerged. Eleven individuals (6 males and 5 females) were caught in tents with greater than 40% cover of Danthonia. Transect methods to determine relative population size were also investigated over two seasons. The total number of individuals counted over the 1995/96 and 1996/97 flight season was 311 and 183. The variability in the number of S. plana observed along the transect route during 1995/96 and 1996/96 was probably due to the high rainfall during August to December in 1996 which increased the mortality of the larva in the soil and hence reduced the number of S. plana emerging. All but three individuals were males and therefore the transect technique overwhelmingly selects for males. Assuming a 1: 1 sex ratio then the adult population is estimated to be between 300 and 700 individuals occupying an area of 1500 m2. There was a good relationship between the rate of emergence within the tents and the number of individuals observed using the transect method. The use of tents therefore provided an indication of population size, showed that the sex ratio of Synemon plana was 1: 1 and that the cover of Danthonia preferred by the moth was greater than 40%. To restore the habitat of Synemon plana, and hence to maintain a viable population, the cover of Danthonia must be increased to greater than 40% covering an area greater than 1500 m2 . Seedlings should be planted in autumn and weeds removed. Competition from weeds must be eliminated to increase the percentage cover of Danthonia in the field.