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Wildlife Society Bulletin 2002, 30(2):634–643Peer edited
Genetic consequences of hunting: what do we know
and what should we do?
Richard B. Harris, William A. Wall, and Fred W. Allendorf
AbstractPossible evolutionary consequences of sport hunting have received relatively little con-
sideration by wildlife managers. We reviewed the literature on genetic implications of
sport hunting of terrestrial vertebrates and recommend research directions to address cur-
rent uncertainties. Four potential effects can be ascribed to sport hunting: 1) it may alter
the rate of gene flow among neighboring demes, 2) it may alter the rate of genetic drift
through its effect on genetically effective population size, 3) it may decrease fitness by
deliberately culling individuals with traits deemed undesirable by hunters or managers,
and 4) it may inadvertently decrease fitness by selectively removing individuals with traits
desired by hunters. Which, if any, of these effects are serious concerns depends on the
nature and intensity of harvest as well as the demographic characteristics and breeding
system of the species at issue. Undesirable genetic consequences from hunting have
been documented in only a few cases, and we see no urgency. However, studies specif-
ically investigating these issues have been rare, and such consequences require careful
analysis and long time periods to detect. Existing information is sufficient to suggest that
hunting regimes producing sex- and age-specific mortality patterns similar to those occur-
ring naturally, or which maintain demographic structures conducive to natural breeding
patterns, will have fewer long-term evolutionary consequences than those producing
highly uncharacteristic mortality patterns.
Key wordsalleles, effective population size, evolution, gene flow, genetics, heterozygosity, hunting,
selection
Commentary
Wildlife managers have historically placed great
emphasis on demographic issues and relatively lit-
tle on how hunting influences genetic characteris-
tics or the evolution of populations (Rhodes and
Smith 1992). However, speaking as hunters as well
as biologists, we value hunting as an experience of
the wild, which in our view is linked inextricably to
the forces of natural selection that have produced
our native species. Few hunters would find interest
or fulfillment in stalking animals housed in a zoo;
similarly, we believe our descendents deserve
opportunities to interact with species shaped prin-
cipally by their native environments, rather than
artificially molded in adaptation to human desires.
In our opinion, integrity of a wild species’ gene
pool deserves respect similar to that accorded to
maintenance of its natural habitat.
Unlike in fisheries, however (e.g., Sutherland
1990, Stokes et al. 1993, Law 2000), North American
game managers have paid little attention to the
Commentary • Harris et al.635
long-term effects hunting may have on the genetic
makeup of game species. This is surprising because
sport hunting alters population density, sex ratio, and
age distribution (Wall 1989, Ginsberg and Milner-
Gulland 1994, Solberg et al. 2000), all of which
potentially influence the genetics of populations.
We addressed four questions relating to common
sport hunting practices and their long-term genetic
consequences: 1) Can hunting alter natural patterns
of gene flow among demes? 2) Can hunting lower
genetic variation, through increasing genetic drift
caused by reduction of effective population size?
3) Can deliberate selection against traits viewed as
undesirable by hunters or managers reduce fitness?
and 4) Can unintentional selection pressures, usual-
ly arising from management based on demographic
criteria alone, have unintended consequences? We
reviewed the existing literature to examine these
questions, and provide some interpretations and
suggest areas where further research is needed.
Hunting and gene flow
Genetic procedures recently described genetic
differentiation within populations that appear mor-
phologically uniform. Localized genetic differentia-
tion has been documented for many hunted
species, including pronghorn antelope (Antilo-
capra americana, Lee et al. 1989), mouflon (Ovis
gmelini, Petit et al. 1997), red deer (Cervus ela-
phus, Strandgaard and Simonsen 1993), red fox
(Vulpes vulpes, Frati et al. 1998), ring-necked pheas-
ants (Phasianus colchicus, Warner et al. 1988,
Robertson et al. 1993), and bobwhite quail (Colinus
virginianus,Nedbal et al. 1997). In white-tailed
deer (Odocoileus virginianus), considerable differ-
entiation exists among neighboring subpopulations
on a genetic level (Sheffield et al. 1985, Scribner et al.
1997). It appears that local differences in white-
tailed deer are maintained by philopatry among
females, but subpopulations are prevented from
becoming too subdivided by male dispersal
(Mathews and Porter 1993, Purdue et al. 2000; see
Cronin et al. 1991 for similar findings in mule deer,
O. hemionus). If males become rare through hunt-
ing, one concern is that the existing level of gene
flow may be reduced further, strengthening popula-
tion differentiation at the expense of genetic vari-
ability within localized demes (Ellsworth et al. 1994).
Conversely, for species that are naturally
philopatric or territorial, local genetic adaptations
might be lost if gene flow among demes is
increased due to the alteration of social structure
caused by hunting. Kurt et al. (1993) examined
populations of European roe deer (Capreolus
capreolus) living in both forested and open habi-
tats. In forest habitats, male roe deer were territo-
rial, controlled access to a number of females, and
variance of reproductive success among males was
high. In open habitats, males were more migratory,
a larger proportion of adult males succeeded in
breeding, and genetic mixing within populations
was greater. These differences evidently reflected
adaptive responses to the variability of environ-
mental resources, and were maintained locally by
low levels of gene flow. However, under high hunt-
ing rates, gene flow between the 2 social systems
increased, and this differentiation began to break
down.
Similarly, among territorial greywing francolin
(Francolinus africanus), Little et al. (1993) found
no difference in heterozygosity (H, the percentage
of loci that are heterozygous in an average individ-
ual) between hunted and unhunted populations,
but higher levels of inbreeding in unhunted popu-
lations. They concluded that any reduction in H
caused by lower population size was compensated
by greater gene flow within the hunted population.
The net effect on Hwas neutral (i.e., higher migra-
tion rates were balanced by fewer potential
migrants), but hunting clearly had contributed to a
breakdown in the usual territorial structure.
Frati et al. (2000) interpreted lower genetic vari-
ability among unhunted populations than hunted
populations of red fox in Europe as reflecting
changes in fox social structure following the loss of
larger predators. Historically, with the presence of
wolves (Canis lupus), leopards (Panthera pardus),
and lynx (Lynx lynx, L. pardinus), fox social struc-
ture was flexible and outbreeding common. They
suggested that hunting, by increasing turnover and
decreasing inbreeding, could partially mimic the
effects of predation pressure under which foxes
had evolved.
Hogg (2000) found that mid-ranking male
bighorn sheep (Ovis canadensis) from an unhunt-
ed population made temporary migrations during
rut to an adjacent hunted population. These rams
faced less competition for mates from the relatively
few high-ranking males in the hunted population
and enhanced their breeding opportunities by mov-
ing. Here, gene flow from one deme to another was
again increased, but in this case the probable deter-
minant was not hunting per sebut rather the
abrupt contrast in density of older, larger-horned
males between adjacent demes.
636Wildlife Society Bulletin 2002, 30(2):634–643
The available evidence suggested to us that alter-
ations in naturally occurring patterns of gene flow
would seem possible from any type of hunt; some
level of social disruption must accompany any
removal of individuals. We found this troublesome
only when locally adapted gene complexes were
compromised by hunting-induced gene flow,
where gene flow would otherwise be discouraged
by social behaviors. As the red fox example sug-
gested, a hunting-induced increase of gene flow
among adjacent demes may help mitigate other
man-made reductions of gene flow.
Hunting and genetic drift
Genetic drift is the random change in gene fre-
quencies caused by sampling (via sexual reproduc-
tion) from a finite population. Genetic drift occurs
in all populations, but its effects become pro-
nounced only if effective population size (N
e
) is
small. N
e
is the number of individuals in an ideal
population expected to lose genetic variation at the
same rate as the census population (N) (Wright
1969, Harris and Allendorf 1989). With small N
e
, H
is expected to decline, rare alleles are expected to
be lost, and alleles may become fixed regardless of
their effect on fitness.
Relevant questions were whether N
eof hunted
populations might be small enough for drift to be a
legitimate concern, and whether hunting regimes
further reduce it. Concern about small N
ewas
expressed for introduced herds of bighorn sheep
(Fitzsimmons et al. 1997) and upland birds (Little et
al. 1993). Ryman et al. (1981) simulated moose
(Alces alces) and white-tailed deer populations, cal-
culating N
e
based on various approximations from
demographic statistics. They found that N
ewas
likely to be much lower than N, even in a popula-
tion exposed to no selective hunting. N
e
/Nratios
were additionally reduced under most hunting sce-
narios simulated. Although reductions in N
e
/N
under hunting were not large, Ryman et al. (1981)
did not simulate hunts featuring extreme selection
for males. They found N
e
/Nratios as low as 0.2 (i.e.,
a population of 100 would experience genetic drift
at the rate of an ideal population of 20), but point-
ed out that extreme selectivity for males in the hunt
could further reduce this ratio.
Harris and Allendorf (1989) varied hunting
regimes for hypothetical grizzly bear (Ursus arctos)
populations, finding relationships between the type
of hunt and N
e
. In some cases, N
e
/Nincreased from
the nonhunted situation, because reproductive suc-
cess among males became more equitable.
However, in hunting scenarios where the number
of males became limiting, N
e
/Ndeclined from its
unhunted level.
Wall (1989) examined demographics and het-
erozygosity of white-tailed deer populations in
Texas exposed to hunts with differing selectivities.
Although he was unable to estimate variation in
reproductive success, an important determinant in
N
e(Harris and Allendorf 1989), Wall (1989) com-
pared “maximum N
e
” among populations based on
the demographic parameters and assuming no dif-
ferences in variance of reproductive success.
Variable hunting strategies had profound effects on
N
e
/N. However, because those hunting regimes
reducing N
e
/Noften were designed to keep Nhigh,
N
e
generally varied less than did N
e
/N. For exam-
ple, populations exposed to buck-only harvest had
low N
e
/N(because few bucks dominated breed-
ing), but high N
e
(because census population size
remained high, being primarily a female popula-
tion). In contrast, hunting regimes with a relatively
high female harvest (and more equitable sex ratios)
had the highest N
e
/Nratios, but lower N
e
(because
the total population was lower). His sampling of
genetic attributes suggested, however, that genetic
drift (as documented by H) was a substantial con-
cern only in the smallest, most isolated population.
Concerns about low N
e
have been appropriately
focused on small or declining populations
(Allendorf and Ryman 2002) rather than on the
larger populations typically subjected to sport
hunting. Managers of sport hunts should be mind-
ful, however, of the potential for undesirable genet-
ic consequences of low N
ewhere high harvest
rates produce severely skewed sex ratios. Sex ratios
of about 1 adult male:10 adult females were docu-
mented for elk (Cervus elaphus, Leptich and Zager
1991, Noyes et al. 1996) and mule deer (Scribner et
al. 1991), and are probably common in other
species where males are selectively hunted. We
agree with Scribner et al. (1991) that large popula-
tion size substantially reduces the concern about
genetic drift. Nevertheless, smaller breeding
groups of related individuals may occur within larg-
er populations because of strong site fidelity by
females (Scribner et al. 1991). Therefore, highly
skewed sex ratios may increase the frequency of
inbreeding even in the presence of little popula-
tion-wide genetic drift. Most managers of ungulate
populations attempt to prevent adult sex ratios
from reaching such extremes in order to maintain
normal breeding behavior. We believe that loss of
Commentary • Harris et al.637
genetic variability, even if nested within a larger
population, is another reason to avoid highly
skewed sex ratios.
Hunting and deliberate selection
Many European wildlife managers have tradition-
ally attempted to alter antler or horn characteristics
of artiodactyls by selectively culling those consid-
ered inferior (Webb 1960, Taber 1961, Hartl 1991,
Sforzi and Lovari 2000). Culling of yearling white-
tailed deer with poor antler development was also
suggested in the southeast United States (Harmel
1983, Cook 1984, Newsome 1984, but see Lukefahr
and Jacobson 1998). Although such management
might be seen as a partial correction to practices
where only the largest animals are taken, it is not
without risks. By selecting for one particular trait
of perceived value to humans, we believe it likely
that management simultaneously (if inadvertently)
selects against other traits potentially of adaptive
significance for the species (Voipio 1950, Klein et
al. 1992). In particular, relatively rare alleles that
might be important in a long-term evolutionary per-
spective are vulnerable to loss when such selection
for other traits takes place.
Research on red deer in Europe provided com-
pelling evidence that deliberate selection could
have unintended consequences. In France, Hartl et
al. (1991, 1995) found that alleles at loci Idh-2, Me-
1, and Acp-1were associated with body and antler
size in red deer. Deliberate culling of yearling bulls
with undesirable antler characteristics rapidly
increased the frequency of an allele (Idh-2
125
) pos-
itively correlated with number of antler points.
Importantly, Pemberton et al. (1988) found that
juvenile survival among juvenile female red deer in
Scotland heterozygous at this same Idh-2locus was
higher than among homozygous individuals. Thus,
by selectively removing males with small antlers
and thus reducing the frequency of the alternate
allele at Idh-2, it appeared that French hunters may
have also unwittingly selected for poor juvenile sur-
vival (Hartl 1991). In general, when one phenotyp-
ic trait is maximized other traits are inevitably (and
probably unknowingly) affected because life-histo-
ry strategies inevitably involve trade-offs among
various fitness components related to demographic
equilibrium (Pemberton et al. 1991). Thus, human
attempts to “improve” hunted species through
selective culling seem certain to produce unfore-
seen consequences. Similarly, releasing penned
deer bred specifically for antler growth (Cook
1984) into the wild (to produce large “super
bucks”) seems to us careless disregard for this fun-
damental concept.
Hunting and unintentional selection
North American managers have often down-
played possible genetic consequence of selective
hunting, focusing instead on maximizing yield
either of total animals or of trophy males. However,
harvest regimes that are focused on removing large
males risk producing inadvertent directional selec-
tion against the very characteristics (usually large
antlers or horns in artiodactyls) that hunters desire.
We distinguished the effects that selective hunting
may have on genetic diversity generally (as indicat-
ed by H) from those leading to loss of specific alle-
les.
Selective hunting and H
His often (albeit not universally) thought to be
related to fitness in natural populations (Allendorf
and Leary 1986, Britten 1996, Coltman et al. 1999).
In white-tailed deer, studies have reported positive
correlations between Hand twinning (Johns et al.
1977, Chesser and Smith 1987), fetal growth
(Cothran et al. 1983), body weight (Smith et al.
1982), body size (Chesser and Smith 1987), and
antler size (Scribner et al. 1989). The last-named
authors considered it likely that higher Hresulted
in higher metabolic efficiency, and thus decreased
maintenance-energy requirements, leading to larger
antlers. Fitzsimmons et al. (1995) found slightly
greater yearly horn growth among >
6-year-old
bighorn sheep rams that were heterozygous at >
2
loci than among those heterozygous at a zero or
one locus.
However, other studies have found no correla-
tions between Hand body mass or number of
antler points in white-tailed deer (Sheffield et al.
1985) and red deer (Hartl et al. 1991). Chesser and
Smith (1987) reported negative as well as positive
correlations between Hand components of repro-
duction related to fitness. Further, the relationships
involving antler or horn growth observed by
Scribner et al. (1989) and Fitzsimmons et al. (1995)
occurred only for older age-classes. Because the
majority of antler and horn growth occurred in
younger classes (for which no correlation with H
was found), the total amount of variation attributa-
ble to Hclass was low. Antler and horn growth also
are known to respond to environmental factors
(and the largest single determinant of size usually is
638Wildlife Society Bulletin 2002, 30(2):634–643
age class), so it is difficult to distinguish the effects
of Hon horn or antler size.
Can selection imposed by hunting reduce H?
Fitzsimmons et al. (1995) voiced concerns that
selectively removing the largest rams by hunting
would, perhaps unintentionally, reduce genetic
variability in such populations. Although not specif-
ically designed to examine such a possibility, the
work of Wall (1989) provided some insight.
Despite widely varying hunting regimes (and thus
standing age structures), he found no differences in
H, as measured by allozymes from harvested deer,
among populations examined. If antler quality
were related to H, we might expect hunter-harvest-
ed samples from those hunts featuring the greatest
selectivity for trophies to exhibit higher Hthan
those from less selective hunts.
We found that the evidence for selective removal
of relatively more heterozygous individuals within
natural populations was weak. Perhaps more
importantly, loss of Hcaused by removal of individ-
uals that tend to be heterozygous at specific loci is
a reversible process. That is, even if heterozygotes
were selectively removed, heterozygous progeny
would be regenerated the next generation by mat-
ings between individuals that are homozygous for
different alleles (Mitton 1997). Thus, although pos-
sible deleterious effects from selective removal of
heterozygous individuals bears monitoring, it does
not appear to be a serious problem.
Selective hunting and changes in allele
frequency
A slightly different mechanism may come into
play where hunter selectivity is based on pheno-
typic traits such as horns or antlers. Such hunts
may unintentionally select against those very traits
by reducing the life span (and thus the reproduc-
tive contribution) of individuals carrying specific
alleles. Festa-Bianchet (2002) suggested that heavy
hunting can alter selective pressures of female
artiodactyls from those favoring high survival and
low maternal investment per litter to those favoring
early reproduction and lower survival. We share
with Festa-Bianchet (2002) additional concerns
about long-term genetic consequences of trophy
hunts on phenotypic characteristics of males.
The empirical literature is ambiguous on
whether hunting regimes focused on taking males
with large horns or antlers unintentionally alters
allele frequencies (as evidenced by phenotypic
changes). Dubas and Jezierski (1989) documented
declining antler quality and carcass weight by age
over a 6-year time period in European red deer,
speculating that selective hunting may have played
a part. However, population density also increased
during their study, confounding interpretation
(Clutton-Brock et al. 1982). Ludwig and Hoefs
(1995) discounted hunting as a possible factor in
their finding that Dall sheep (Ovis dalli) in a hunt-
ed population had shorter horns than did those in
the adjacent (unhunted) Kluane National Park
despite similar age distributions (horn circumfer-
ences in the 2 populations did not differ). Solberg
and Sæther (1994) reported no decline in antler
size over a 23-year period of moose harvest. In con-
trast, Shea and Vanderhoof (1999) observed a reduc-
tion in antler size of 2.5-year-old white-tailed deer 5
years after initiation of a hunting regime intended
to increase antler size by prohibiting harvest of
small-antlered bucks. They attributed the unex-
pected reduction to “high-grading” (i.e., selective
killing) of bucks born earlier during their year of
birth. Their data also showed that early birth was
associated with larger antlers, leaving predominant-
ly late-born bucks to survive to 2.5 years. Shea and
Vanderhoof (1999) evidently did not examine the
genetic basis of these changes, but selective hunt-
ing of larger bucks may have changed frequencies
of alleles that contributed to antler size.
In most cases hunters prefer to harvest large
artiodactyls, and horn or antler size is generally cor-
related with male fitness. However, it does not fol-
low that hunting removes relatively more fit indi-
viduals in all cases. Artiodactyl males begin with
small horns or antlers that become progressively
larger with age. Hunters selecting for individuals
with the largest horns or antlers remove primarily
old individuals, not necessarily those with genomes
conducive to producing large secondary sexual
characteristics. Changes in allele frequencies
caused by selective hunting of large males may be
buffered by the genetic contributions of females,
which will have most of the same alleles as males
but are likely to be subject to differing selective
pressures. Finally, other factors may affect vulnera-
bility to hunting independent of hunter selectivity.
For example, DuFour et al. (1993) found that mal-
lards in poorer body condition were more vulnera-
ble to hunting than those in better condition.
Given these complexities and ambiguities, we
believe the simulation model constructed by
Thelen (1991; see also Hundertmark et al. 1993,
1998) currently provides the best indication of
how selective hunting might unintentionally alter
the genetic constitution of big game populations.
Commentary • Harris et al.639
Thelen (1991) assumed that antler characteristics of
elk were polygenic traits, inherited in simple
Mendelian fashion but with no dominance or epis-
tasis. Antler size increased with age, but antler char-
acteristics were also assumed to be an additive func-
tion of multiple loci (i.e. the greater the number of
alleles favorable for large antlers, the larger the
antlers). Heritability, the proportion of variation in
antler size attributable to genotype, varied from 25%
to 75%. Breeding success was controlled by both
age and antler size. Age-specific survival of bulls was
also negatively correlated with antler size (i.e., a sur-
vival cost of carrying heavy antlers was assumed).
Hunting strategies were modeled to reflect various
possible management objectives. Hunting regimes
that specified minimum antler sizes always reduced
the frequency of large antler alleles in modeled pop-
ulations. When heritability of antler traits was mod-
eled as 50%, allele frequencies were altered by
approximately 10–20% after 50 years. When heri-
tability was assumed to be 75%, the 50-year reduc-
tion in favorable allele frequency was on the order
of 20–25%; with heritability of 25%, the 50-year
reduction was about 10% (Figure 1).
By contrast, other hunting regimes had little
effect on the frequency of existing alleles in the
population. A nonrestricted harvest strategy, in
which the sex and age of individuals harvested was
directly proportional to their abundance in the
population, had little effect on allele frequency
after 50 years. The nonrestricted hunting regime
also resulted in relatively high yield overall, but low
yield of trophy males. But a split hunting regime, in
which spike (mostly yearling) and >
5 point (tro-
phy) males were legally taken (but 2–4 point males
protected) resulted simultaneously in moderate
overall harvest, moderate harvest of trophy males,
and little change in large-antler alleles (Figure 1).
It is likely not coincidental the mortality pattern
produced by the split hunting regime resembled
that of an ungulate population experiencing only
nonhunting mortality (high mortality in young age
classes, low among mature animals, high again as
animals senesce). Thelen’s (1991) model suggested
the possibility of achieving a sustainable harvest
(including of trophy males) while avoiding sub-
stantial alterations in allele frequencies, by moder-
ating hunting pressure focused on large males and
simultaneously harvesting young males vulnerable
to natural mortality. Klein et al. (1992) also recom-
mended a split hunting regime as one that would
produce a good compromise between hunter satis-
faction and long-term evolutionary concerns.
Thelen’s results were sensitive to heritability of
antler size (Figure 1). There is little doubt that
antler characteristics are heritable traits (Harmel
1983, Williams et al. 1994, Lukefahr and Jacobson
1998, Wang et al. 1999). However, all studies to date
have estimated heritability under captive condi-
tions, thus the “unexplained” portion of antler vari-
ability (i.e., that remaining after inheritance is
explained) has been low. In the wild, we would
expect age-specific antler size to vary considerably
with nutritional status as well as with genotype
(Brown 1990).
An additional, important factor in such models is
the strength of reproductive advantage enjoyed by
males with desired traits. Conventional wisdom
suggests that males with the largest horns and
antlers have the highest reproductive success
(Solberg and Sæther 1994). But just how much
higher? The rate of loss of alleles affecting horn and
antler size on the population caused by hunter
selection of large males would be higher if males
vulnerable to hunting dominate the breeding, and
lower if smaller males (which would presumably
survive a selective hunt) also make substantial con-
tributions under natural conditions.
In unhunted red deer, paternity data showed not
only that dominant bulls had greater reproductive
Figure 1. Percent change after 50 years in frequency of alleles
modeled as favorable for large antler formation in elk, under 4
alternative hunting strategies, and assuming antler heritability
of 25%, 50%, and 75%. Under “nonrestricted” hunts, bulls
were killed in the simulated hunt in proportion to their abun-
dance; under “2-” and 4-point minimum” hunts, only bulls
with these antler characteristics were killed; “spike and 5+
points” hunts protected males with 2–4 points from hunting
mortality. Adapted from Thelen (1991).
640Wildlife Society Bulletin 2002, 30(2):634–643
success than did subordinates, but also that their
relative success was even greater than had been
estimated from behavioral data (Pemberton et al.
1992). Younger, smaller, or less dominant bulls did
relatively little breeding. In contrast, paternity data
on bighorn sheep in two intensively studied popu-
lations showed that high-ranking rams, while still
more successful than lower ranking rams, fathered
fewer lambs than would have been estimated from
only observing their success at tending estrous
ewes (Hogg and Forbes 1997). Rams using “uncon-
ventional” courting tactics associated with lower
rank were surprisingly effective in contributing
their genes to subsequent generations. Thus, a vari-
ety of alleles in bighorns may be transmitted to sub-
sequent generations by smaller, younger rams that
would be unaffected by strongly selective hunts.
We suspect that long-term changes in allele fre-
quencies are a common attribute of terrestrial pop-
ulations subjected to strongly selective hunting. It
is difficult to see how it could be otherwise, given
that hunting often constitutes the largest source of
mortality (Festa-Bianchet, 2002). However, because
age and environment exert major influences on
size, mating systems are often flexible, gene flow
among adjacent populations that vary in mortality
patterns may replenish vulnerable alleles, heritabil-
ities of phenotypic traits observable to hunters may
be low, and offtake rates usually are moderated in
the most strongly selective hunts, we expect such
changes to occur gradually and to be undetectable
for many generation lengths.
Research directions
Research into genetic effects of hunting has been
much less common than research into demograph-
ic and behavioral effects of hunting. Several impor-
tant questions remain unanswered: 1) under what
conditions is the alteration of gene flow among
population subdivisions resulting from hunting of
sufficient magnitude to cause problems? 2) does
selective hunting preferentially take more het-
erozygous individuals than would a random hunt,
and if so, does this reduce heterozygosity in the
population? and 3) how much breeding is con-
ducted by subordinate males, and how does that
change under various hunting regimes? Answers to
these questions are likely to vary by species, and
perhaps also geographically.
Now that genetic techniques allow paternity
determination (e.g., Hogg and Forbes 1997, Cronin
et al. 1999), researchers are in a much better posi-
tion to understand male reproductive success, its
correlates, and its variance. Understanding patterns
of male reproductive success has implications for
the survival effects on other age classes of remov-
ing dominant males, influences of removing domi-
nant males on breeding activity of females, and of
the effects of management on genetically effective
population size (N
e
), which, in turn, tells us about
the magnitude of genetic drift. It is most useful to
add paternity studies to populations already under
intensive demographic study, but where these con-
ditions exist, the laboratory expenses usually will
be justified by the insight gained. Where paternity
studies are conducted and phenotypic information
also obtained, the opportunity exists to document
the heritability of secondary male sexual character-
istics of interest to hunters (usually horns or
antlers) under wild conditions. The strength of her-
itability remains a critical, but largely unknown,
piece of the puzzle in considering the long-term
evolutionary consequences of selective hunting in
ungulates (Rèale et al. 1999, Kruuk et al. 2000).
Indirect information on possible directional
selection of genomes can also be obtained from
existing data sources (e.g., hunter check-stations)
by careful examination of long-term data sets com-
paring hunting intensity to trends in horn/antler
size by age. Confounding effects, such as popula-
tion density and varying environmental conditions,
will need to be carefully considered. Further labo-
ratory analyses (e.g., using carcasses at hunter
check-stations) correlating the presence of specific
alleles, as well as estimates of H, with male charac-
teristics (coupled with sampling of unhunted indi-
viduals) would further elucidate whether selective
hunting has disruptive effects on Hand allelic
diversity.
Conclusions
We began by expressing concern about the long-
term genetic consequences of hunting, but our
review of the literature suggested little empirical
evidence of such consequences. We have hypothe-
sized a number of characteristics of hunting and
hunted species that may act to mitigate expected
negative effects. However, we found no grounds for
complacency; studies designed to quantify genetic
effects have been rare, and the effects eliciting our
greatest level of concern are subtle and difficult to
detect without long-term monitoring.
We stress that demographic and genetic changes
occur on different time scales. Demographic
Commentary • Harris et al.641
effects are often immediate and easily recognized;
genetic changes occur over evolutionary time
scales of many generations. Thus, although short-
lived actions are unlikely to have genetic effects
over the long term, any genetic changes will be dif-
ficult to detect because of the time scale over
which they occur. For example, it would require
careful study to detect the effects of a hunting man-
agement scheme that decreased mean antler size
by 4% per generation (i.e., 1% reduction/yr in a
species where the mean age of reproduction was 4
years). However, such a rate of change may have
substantial effects over the long term. For example,
this rate of change would reduce mean antler size
by 30% in 50 years.
We urge managers to consider not only the main-
tenance of genetic diversity, but also whether the
primary selective forces influencing adaptations in
hunted populations have become artificial rather
than natural. Where concern is justified, it is pru-
dent to manage hunting such that the age-specific
survival pattern (and thus age-specific breeding
structure) emulates that occurring in the absence
of hunting (Klein et al. 1992, Hundertmark et al.
1993). Such hunting regimes will generally pro-
duce little alteration in allele frequencies, have low
chance of causing extinction of rare alleles, mini-
mize extremely skewed sex ratios (and thus have
less effect on N
e
),and still allow for the hunting
opportunities we cherish.
Acknowledgments. We thank P. Voipio for pro-
viding a copy of his classic monograph on the
genetic effects of game management. M. S. Boyce,
W. J. Sutherland, W. M. Ford, M. A. Cronin, J. T. Hogg,
and 2 anonymous reviewers suggested improve-
ments to earlier versions of this manuscript.
Funding for R. B. Harris during initial portions of
this work was provided by Safari Club
International. We thank J. Hensiek and P. Sandstrom
for translation help, and the staff at the Maureen
and Mike Mansfield Library at the University of
Montana for assistance.
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Address for Richard B. Harris:Wildlife Biology Program, School
of Forestry, University of Montana, Missoula, MT 59812, USA;
e-mail: rharris@montana.com. Address for William A. Wall:
Safari Club International, 441-E Carlisle Dr., Herndon, VA
20170, USA. Address for Fred W. Allendorf: Division of
Biological Sciences, University of Montana, Missoula, MT
59812, USA.
Richard B. (Rich) Harris(photo) is research associate in the
Wildlife Biology Program at the University of Montana, and also
serves as editor of the journal Ursus. He received his Ph.D.
from the University of Montana and later worked as program-
matic biologist for the Montana Department of Natural
Resources and Conservation. His research interests include
enhancing incentives for local people to conserve wildlife in
western China, where he has conducted surveys and worked
with hunting programs since 1988. William A. (Bill) Wallcur-
rently is senior scientist for wildlife conservation for Safari Club
International Foundation. He received his Ph.D. from Stephen
F. Austin State University in Nacogdoches, TX. He currently is
developing conservation hunting programs for argali sheep in
Central Asia. Fred W. Allendorfis professor of biology at the
University of Montana. His primary research interest in the
application of genetic principles to problems in the conserva-
tion and management of natural populations.
