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Title: Demography and life history of the Eurasian beaver castor fiber
Author: Campbell, Ruairidh D.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2009
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Abstract:
Long-term studies of animal life histories and demography have been key in advancing our understanding of the processed that shape behaviour and population dynamics of species. The Eurasian beaver Castor fiber is a good species in which to study these processes, as it is long-lived, social and territorial. The species is also important to general conservation biology due to its key stone effects on wetland and riparian habitat. In this thesis, I use a 12 year capture-mark-recapture program on a beaver population in Telemark, southern Norway, in conjunction with behavioural, habitat and climate observations to examine life history strategies, demography and territoriality. I examined growth rates of juveniles and showed, for the first time, that beavers exhibit compensatory growth for body size. Juvenile beavers that were smaller than same-age peers managed to narrow the gap in size by trading-off gain in body condition against gain in size. Examining the effects of body size and condition on survival and dominance, I find for the first time evidence that larger, though not heavier for their size, individuals are more likely to obtain dominant breeding positions. Medium size individuals and those with medium body condition suffer less mortality. The largest of the medium sized animals go on to obtain breeding positions within the population. Thus compensatory size growth in beavers has evolved because selection acts through dominance to increase size, but this size increase is stabilised through selection on survival. Examining the effects of age on fecundity I show, for the first time, that after an initial increase to 4 – 6 years (minimum age), beavers exhibit reproductive senescence. I also show for the first time that, apart from exhibiting higher fecundity, females in higher quality territories begin reproductive senescence later. I argue that this supports the disposable soma hypothesis of senescence and not the antagonistic genetic pleiotropy hypothesis. I furthermore examine trade-offs in offspring quantity versus quality and show that this trade-off only exists in younger (<7 years minimum age) mothers, indicating support for both the experience and the terminal investment hypotheses. Investigating the effects of weather on body weight and fecundity I show that that rainfall negatively affected both fecundity and body weight. Examine tree growth-rings, I was able to establish that close to water level (<0.5m) high rainfall suppresses tree growth. Thus higher rainfall can reduce forage availability near water. I also found that cold winters reduced the body weight in young (<2 year old) beavers and rapid phenological advancement associated with warm spring temperatures reduced adult body weight, confirming previous studies on other species. Exploring the effects of weather variability on recruitment and survival, I show that high seasonal amplitude in air temperature and low short-term temperature variability led to an increase in recruitment and low variability in rainfall combined with low short-term temperature variability increased survival. Overall, weather variability may have a greater influence on vital rates in this beaver population than absolute weather conditions. Investigating territoriality and the propensity of offspring to remain within the natal group, I show that a repacking of territories due to mortality and group fission has reduced a previous imbalance in territory quality. After repacking, territories were more clearly configured around the dispersion of resources. Philopatric tendencies are greater in territories with more resources but their presence results in greater resource depletion.
Supervisor: Macdonald, David; Rosell, Frank Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.670008  DOI: Not available
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