A study was carried out to investigate the effect of different levels of supplementary food on populations of wood mice Apodemus sylvaticus. The objective was to test the hypothesis that population density of wood mice is associated with habitat productivity. An experiment was set-up whereby three different levels of supplementary food in the form of wheat was given to a population of wood mice living in a sand-dune area in North-East Scotland. Using capture-recapture data, the population dynamics and demography of the supplemented populations were compared with a control population with natural levels of food. Supplemented populations had higher peak densities compared to the control population but not in proportion to the level of supplementation. Extra food however did not bring forward the onset of the autumn increase in numbers and populations in summer remained low and depressed. Recruitment was low in all populations and only showed substantial increase in autumn. Recruitment was associated with the level of supplementary food and with sex ratios increasingly biased towards males. Supplemented population had a lower proportion of reproductive females. Food supplementation also did not improve survival over the breeding season. A second supplementary food experiment was carried out using a replicated treatment design. Control populations were compared with populations that received a single level of supplementary food. The experiment was repeated for another year but with treatments exchanged between grids; previously supplemented grids treated as controls and vice versa. The objective of the experiment was to verify that the observed changes in density and dynamics can be attributed to the additional food provided and not to other environmental factors. Supplementation was confined to the breeding season only during both years. The results of the second experiment confirms the positive relationship between food availability and population density. Supplementary food led to higher recruitment of both males and females. However variation in population abundance was positively related to male recruitment only. Using statistical modelling to model survival and recapture parameters, survival rates of supplemented populations appeared to have improved during early summer but were not different from controls during the later period. The third study looked at the effect of food supplementation on ranging and spacing behaviour of wood mice. The objective was to test the hypothesis that supplementing with extra food early in the breeding season would cause existing reproductive females to reduce their range sizes, in so doing giving rise to gaps between previously adjoining territories. The creations of this gaps would allow new females to become recruited and join the breeding population. Comparison between range sizes indicated that supplementation led to a reduction in female home range and core range sizes but not that of males. Supplemented females also had a smaller mean percent core range overlap, suggesting less interaction between neighbouring territorial females at the range boundaries. The spatial distribution of female territories shows that established females decreased their core areas with supplementary food, allowing new females to become established in the area. Since food addition led to a reduction of territory size of resident females and allowed the establishment of new females in the supplemented area, females therefore play a more crucial role than males in limiting numbers during the breeding season. The low population density during the breeding season can be attributed to the spacing behaviour of reproductive females. Increased food availability may increase the number of resident females. However the territorial nature of females means there is an upper limit to the number of females accommodated for a level of food availability. Therefore the lower recruitment and poor survival at all levels of food over the breeding season was due to the failure of new females to establish a home range. At the end of the breeding season in autumn, when females no longer possess territories, recruitment rose to a peak and survival improved considerably.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:592534 |
| Date | January 1997 |
| Creators | Noor, Hafidzi bin Mohd |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602284 |
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