Red Deer Research on the Isle of Rum
Research
Findings
Home Page The Deer Year History of Deer Research on Rum Kilmory Research Project
Meet the Deer Research Findings Publication List People
There has been
continuous research into the ecology and behaviour of red deer in the
12km2
North Block of Rum by members of Cambridge University since 1972 and
research
on genetics in the same population by staff from Edinburgh and
Cambridge since
1982. The work uses long-term records of
individually recognisable red deer to answer a wide range of questions
in three
main areas of organismal biology:
behavioural ecology and life-history evolution; population
dynamics and
demography; and evolutionary genetics.
A brief summary
of the principal findings of our research in each of these three areas
is
provided below. A full
list
of publications from research on the Kilmory red deer
project and information on researchers
involved in the project are
also available at the links above. Links to the relevant original
published paper (in PDF format) are provided throughout the summary
below in square brackets.
Key Areas of Research:
1. Population dynamics & demography
2. Behavioural ecology
3. Evolutionary genetics
Understanding the roles of density-dependent and density-independent effects on population dynamics is one of the central aims of population ecology. Through close monitoring of individual deer resident to the Kilmory study area over three and a half decades we have developed our understanding of the effects of population density and climate on survival, reproduction and dispersal in wild mammals. Our findings also have implications for deer management policy.
2. Behavioural ecology
Linking behaviour to reproductive success in wild populations can be challenging, but is vital if we are to understand how such behaviour evolved. Our long-term data on individual deer allow us to measure individual reproductive success (Figures 4 & 5) in the wild. Our work has shed new light on the trade-offs underlying reproductive behaviour in wild animals, in particular the different reproductive strategies of stags and hinds, and parental investment in sons and daughters.
3. Evolutionary Genetics
Most genetic studies of evolutionary processes are conducted inside the laboratory, and our understanding of how evolution occurs over relatively short time scales in wild populations is still limited. We conduct genetic analysis of the Kilmory study population, using tissue samples collected from the deer. In combination with the long-term data on individual life histories this has allowed us to undertake rare tests of evolutionary theory in the wild. Our genetic research has focused on: determining paternities and building pedigrees; inbreeding and fitness and quantitative genetics.
A brief summary
of the principal findings of our research in each of these three areas
is
provided below. A full
list
of publications from research on the Kilmory red deer
project and information on researchers
involved in the project are
also available at the links above. Links to the relevant original
published paper (in PDF format) are provided throughout the summary
below in square brackets.Key Areas of Research:
1. Population dynamics & demography
2. Behavioural ecology
3. Evolutionary genetics
Understanding the roles of density-dependent and density-independent effects on population dynamics is one of the central aims of population ecology. Through close monitoring of individual deer resident to the Kilmory study area over three and a half decades we have developed our understanding of the effects of population density and climate on survival, reproduction and dispersal in wild mammals. Our findings also have implications for deer management policy.
| Effects of
Population Density
and Climate The number of As the number of hinds in the study area increased from 1972, breeding success and juvenile survival fell leading to the stabilisation of female population size during the 1980s. Key demographic consequences of the increase in population size we have documented include an increase in the averag age at which females began breeding, a decline in female annual fecundity amongst milk hinds (females that bred in the previous year), and a decline in the survival of calves and yearlings (Figure 2) [Clutton-Brock et al. 1985; Clutton Brock & Coulson 2002] As hind numbers rose in the North Block, the number of resident males has fallen and the adult sex ratio has become increasingly male-biased . The decline in the number of resident males has been related to a reduction in the proportion of male calves born as density increases [Kruuk et al. 1999b], a decrease in the survival of male calves relative to female calves and an increase in male emigration and a reduction in male immigration [Clutton-Brock et al. 1997; Clutton-Brock et al. 2002]. Although population size has not increased since the mid-1980s the demographic and spatial structure of the population is continuing to change with important consequences for population dynamics [Coulson et al. 2004]. Our detailed records of the dynamics of the Kilmory population has also allowed us to examine the effects of variation in climatic conditions on reproduction and survival and the extent to which they interact with population density [Albon et al. 1987]. Our work has shown that high rainfall in autumn and spring reduce adult survival whilst low spring temperatures reduce the birth weight of calves and increase calf mortality. As in many long-lived vertebrates, environmental conditions experienced by individuals in early life also have long-term consequences on reproductive success, generating marked differences in reproductive performance between cohorts of individuals. In particular, cohorts of females born in cold springs experience greatly reduced reproductive success throughhout their lives [Albon et al. 1987], although the effects of spring temperature on birth weight decline at high population density (Figure 3) [Nussey et al. 2005]. Stags born in cold springs also have a reduced probability of surviving their frist few years of life [Rose et al. 1998]. Implications for Management of Deer Our work provides little evidence to suggest that selective culling is likely to have an important impact on phenotypic quality. In particular, it provides little support for selective culling of yeld hinds (since the same mothers tend to rear or lose calves in successive years) and shows that, although older hinds show reduced fecundity, their calves show relatively high rates of survival. Conversely, it is clear that high population density has adverse effects on the growth and survival of males and commonly increases rates of male emigration. As a result, management policies that allow hind numbers to increase until they are regulated by natural processes are likely to lead to reductions in the number and quality of resident stags [Clutton-Brock & Lonergan, 1994; Clutton-Brock et al., 2002]. |
 Figure 1: The number of
adult female deer resident to the North Block of Rum in each year of
study (males: open triangles; females: filled circles). The number of
females has increased and then stabilised, while male numbers have
declined slowly.
 Figure 2: Percentage of
deer dying withing first two years of life plotted against number of
female deer in the study area (1971-1982, males: filled circles,
unbroken line; females: open circles, broken line). Both sexes showed
increasing juvenile mortality with increased density, but males were
more strongly affected than females (from Clutton-Brock et al. 1985).
 Figure 3: Average annual
birth weight of calves increased in warm springs early in the study
period (left, blue squares and line). The effects of spring temperature
have declined at high density (right inset, black squares and line).
|
2. Behavioural ecology
Linking behaviour to reproductive success in wild populations can be challenging, but is vital if we are to understand how such behaviour evolved. Our long-term data on individual deer allow us to measure individual reproductive success (Figures 4 & 5) in the wild. Our work has shed new light on the trade-offs underlying reproductive behaviour in wild animals, in particular the different reproductive strategies of stags and hinds, and parental investment in sons and daughters.
| Reproductive
strategies in
stags Males are chased out of rutting groups by harem-holding stags when they are around eighteen months old though they commonly return to their mother’s group until the following rut. Between the ages of two and three they typically join stag groups in areas peripheral to those used by the main concentrations of hinds, where vegetation is longer but of lower nutritional quality [Clutton-Brock et al., 1982]. Stags leave their natal area more commonly than hinds and sometimes move to winter ranges several miles or more away from the area where they are born. Well grown stags are more likely to disperse than smaller individuals and emigration increases with population size whilst rates of male immigration are low where density is high [Clutton-Brock et al., 2002]. Each rut, male groups fragment as stags move off to their traditional rutting areas and collect and defend harems of hinds. Individual differences in harem size and mating success are large [Pemberton et al., 1992]. Stags rarely hold substantial harems or show high mating success until they are six or seven years old and seldom maintain their position after they are eleven (Figure 4). Individual differences in reproductive success in males depend principally on variation in fighting ability [Clutton-Brock et al. 1979]. Fighting is dangerous and stags use roaring displays to assess rivals, only fighting when they have a reasonable chance of winning.
Parental Investment in sons &
daughters The reproductive success of stags
is correlated to their body size which is, in turn, related to their
size as
juveniles as well as to their birth weight [Kruuk et
al. 1999a]. Stag calves are
born heavier
than hind calves and grow more rapidly, imposing greater demands on
their
mother’s resources. As a result, hinds
that have reared male calves are more likely to die in the following
winter
than hinds that have reared female calves and, if they survive, are
less likely
to breed successfully the next year [Clutton-Brock et al. 1981] – though the additional
costs of raising sons are restricted to
smaller, lower ranking females [Gomendio et al. 1990]. As a result of
the
increased costs of raising males, only larger more dominant females are
likely
to rear successful sons and the breeding success of stags increases
more rapidly with the size and rank of their mothers than does the
breeding
success of hinds [Clutton-Brock et al. 1984b]. One result of
these differences is that the
sons of dominant hinds are more successful than their daughters – while
the
daughters of subordinates are more successful than their sons [Clutton-Brock
et al. 1986]. Under these
conditions, dominant
females might be expected to produce more sons than daughters while the
situation should be reversed in subordinates. Examination
of the sex ratio of calves produced by hinds over their
lifespan shows that, as predicted, the proportion of male calves born
increases
with the mother’s rank. However, this
effect disappears when population density is
high
and is
replaced by a general tendency for the proportion of males born to
decline with
increasing population density – probably as a result of increased
mortality of
males in utero [Kruuk et
al. 1999b]. |
 Figure
4: Average breeding success (number of calves sired) of stags
changes with age. Young and older stags do poorly, with the peak in
breeding performance between 9-11 years of age.
 Figure 5: Females
begin breeding between 3-5 years of age and with around 75% of females
breeding in a given year after that, and a decline in fecundity amongst
the older females (green squares and line). The survival of
calves also declines markedly mongst older females (red circles and
line).
 Figure
6: The breeding success of offspring increases with mother's
social rank for sons (black circles, unbroken line) but not daughters
(open circles, dotted line). From Clutton-Brock
et al. 1986.
 Figure
7: The proportion of male calves born in the study area has
decreased with increasing population density (from Kruuk et
al. 1999b)
|
3. Evolutionary Genetics
Most genetic studies of evolutionary processes are conducted inside the laboratory, and our understanding of how evolution occurs over relatively short time scales in wild populations is still limited. We conduct genetic analysis of the Kilmory study population, using tissue samples collected from the deer. In combination with the long-term data on individual life histories this has allowed us to undertake rare tests of evolutionary theory in the wild. Our genetic research has focused on: determining paternities and building pedigrees; inbreeding and fitness and quantitative genetics.
Inbreeding & fitness in the wild Evolutionary theory predicts that the negative genetic consequences of inbreeding should depress fitness (‘inbreeding depression’). Evidence from wild vertebrates for either inbreeding depression is scarce because few study systems have sufficiently detailed information on both individual genotype and individual life history to detect it. Microsatellite DNA data collected from the Kilmory deer has revealed that deer that are homozygous at many loci (they have the same two alleles) and hence may be inbred and have lower lifetime reproductive success (Figure 8) [Slate et al. 2000]. The availability of a detailed pedigree for the Kilmory deer population has allowed us to utilise quantitative genetic ‘animal models’ to estimate the additive genetic variance and heritabilities of different life history and morphological traits. The detailed information on individual reproductive performance also allow us to accurately estimate natural selection on different traits. We have shown that, as predicted by evolutionary theory, traits more closely associated with fitness show lower heritability in the Kilmory deer population, although this may be largely due to high levels of environmental variance [Kruuk et al. 2000]. Genetic and pedigree data from Kilmory animals have been used in quantitative trait loci (QTL) mapping analyses to identify genes or chromosomal regions associated with specific traits [Slate et al. 2002]. An important question in evolutionary biology is why heritable traits under directional selection often do not show an evolutionary change as is predicted by theory. Our quantitative genetic analyses also show that natural selection favours males with larger antlers – these males have more offspring – and antler size is heritable (Figure 9), but there is no evidence for a micro-evolutionary change towards larger antler size [Kruuk et al. 2002]. This is probably because the relationship between antler size and fitness is actually determined by environmental rather than genetic factors . We also found that birth weight and birth date are both heritable traits, but selection acts on these traits in a complex and variable manner. This means these two important early life history traits are unlikely to show strong micro-evolutionary responses to selection [Coulson et al. 2003]. Recent work has also revealed that genes that produce fit sons may produce poor quality daughters (Figure 10) [Foerster et al. 2007]. Such sexually antagonistic effects could substantially slow the effects of natural selection, but this is the first time such an effect has been documented in the wild. |
 Figure 8: Lifetime breeding
success (total number of offspring) plotted against increasing
heterozygosity, a molecular measure of inbreeding for males (filled
squares) and females (open squares). More outbred individuals (highest
heterozygosity) have higher fitness and the effect is stronger among
males than females (from Slate et al. 2000).
 Figure 9: The proportion of
total variance in a stag's antler mass explained by different factors.
Antler mass is under genetic control, and has an estimated heritability
of around 20%. Age, conditions in year of growth and other
environmental factors are also important sources of variation in this
trait (from Kruuk et al. 2002).
 Figure 10: The
relationship between the fitness ('pti') of daughters (top) and sons
(bottom) with their father's lifetime fitness. Fathers with high
fitness produce poor quality daughters (from Foerster et
al. 2007). |