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Feared Negative Effects of Publishing Data: A Rejoinder to Heimer et al

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The Proceedings of the 14 th Symposium of the Northern Wild Sheep and Goat Council contained a 'compilation' by Wayne Heimer of critiques of a paper published by Coltman et al. (2003) in Nature. That 'compilation', published without giving us a chance to respond, refers to a 'sheep management community' including only those who do not agree with Coltman et al. (2003). It attempts to convey the impression that the paper was not based on empirical data and incorrectly claims that environmental effects on horn and body size were ignored. It uses the Boone and Crockett record book to argue that bighorn (Ovis canadensis) rams are increasing in size, ignoring the fact that only large rams make it to the record book and that the number of bighorn sheep has increased substantially over the last few decades. The paper by Geist in the 'compilation' does not critique Coltman et al. (2003). The compilation confuses management regimes at Ram Mountain and elsewhere and provides a data-free defense of the status quo in sheep management. We are confident most sheep managers are interested in our data and will consider their implications .
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RH: Rebuttal to Bienn. Symp. North. Wild Sheep and Goat Counc. 14: 193-209.
Feared Negative Effects of Publishing Data: A Rejoinder to Heimer et
al.
MARCO FESTA-BIANCHET,1 Département de biologie, Université de Sherbrooke,
Sherbrooke, Québec, J1K 2R1, Canada
JON JORGENSON, Alberta Fish & Wildlife Division, Canmore, Alberta, T1W 1P1,
Canada
DAVID COLTMAN, Department of Biological Sciences, University of Alberta,
Edmonton, AB, T6G 2E9, Canada
JOHN T. HOGG, Montana Conservation Science Institute, 5200 Upper Miller Creek
Road, Missoula, MT, 59803 USA
Abstract: The Proceedings of the 14th Symposium of the Northern Wild Sheep and Goat
Council contained a ‘compilation’ by Wayne Heimer of critiques of a paper published by
Coltman et al. (2003) in Nature. That ‘compilation’, published without giving us a chance
to respond, refers to a ‘sheep management community’ including only those who do not
agree with Coltman et al. (2003). It attempts to convey the impression that the paper was
not based on empirical data and incorrectly claims that environmental effects on horn and
body size were ignored. It uses the Boone and Crockett record book to argue that
bighorn (Ovis canadensis) rams are increasing in size, ignoring the fact that only large
rams make it to the record book and that the number of bighorn sheep has increased
substantially over the last few decades. The paper by Geist in the ‘compilation’ does not
critique Coltman et al. (2003). The compilation confuses management regimes at Ram
Mountain and elsewhere and provides a data-free defense of the status quo in sheep
management. We are confident most sheep managers are interested in our data and will
consider their implications
. BIENN. SYMP. NORTH. WILD SHEEP AND GOAT COUNC. 15: 213-219
Key words: Genetics, heritability, horn size, mating system, Ovis canadensis, paternity,
Rocky Mountain bighorn sheep, trophy hunting,
1 Corresponding author e-mail: Marco.Festa-Bianchet@USherbrooke.ca
Most bighorn sheep (Ovis canadensis)
hunting in Alberta involves an unlimited-
entry ‘trophy’ hunt. Any resident can buy
a sheep licence and the harvest is limited
by the availability and accessibility of rams
with horns describing 4/5 curl, reached by
some rams at 4 yr of age and by many at 5
to 6 yr (Festa-Bianchet 1986, Jorgenson et
al. 1993). Although it had long been
assumed that larger-horned rams had
higher fitness (Geist 1971), only recently
data became available on mating success
of bighorn rams (there are no published
data on male mating success of any other
mountain ungulate). Ram reproductive
success was quantified in two populations
in Alberta and one in Montana (Hogg and
Forbes 1997, Coltman et al. 2002). While
results confirm that large-horned males
have high reproductive success, they reveal
a strong interaction with age, so that only
males at the top of the social hierarchy
214
(typically aged 7 yr and older) benefit
substantially from large horns. Other
males rely on alternative mating strategies
whose success is low and appears
independent of horn size. That result
confirms observations that rams employing
alternative tactics rely mostly on speed,
agility, and willingness to take risks, rather
than combat with other rams (Hogg
1984;1988, Hogg and Forbes 1997). A
ram with fast-growing horns will achieve
high reproductive success if it survives to 6
to 7 yr (Coltman et al. 2002), but under
unlimited-entry 4/5-curl regulations it may
be harvested at 4 to 5 yr.
From those observations, and noting
that ram horn length has a strong
inheritable component (Coltman et al.
2005), one could predict that rams with
slow-growing horns may be advantaged if
their large-horned competitors were
eliminated by sport hunting. That
prediction led to a test based on
information from pedigrees and calculation
of breeding values for individual rams in
the isolated population of Ram Mountain,
Alberta (Jorgenson et al. 1998). Those
empirical data confirmed artificial
selection favouring small-horned rams
(Coltman et al. 2003). More recent
analyses suggest that systematic removal
of high-quality individuals may lower the
frequency of other fitness-enhancing traits,
and possibly contribute to population
stagnation (Coltman et al. 2005).
Until recently, the potential genetic
effects of selective harvests figured more
prominently in fisheries than in wildlife
literature (Harris et al. 2002, Festa-
Bianchet 2003). In the near future there
should be more data available to assess
what (if any) are the evolutionary impacts
of sport harvest on wildlife.
Critiques of Coltman et al. (2003)
were published in the 2004 Proceedings of
the Northern Wild Sheep and Goat Council
(Heimer 2004) as a ‘compilation’ that
included personal attacks on the authors of
the 2003 paper, who were not given the
opportunity to defend themselves.
The apparent goal of the ‘compilation’
is set in the ‘Compiling author’s note and
comment’, suggesting that the data in
Coltman et al. (2003) should be ignored
and attention should instead be focused on
the ‘radical’ anti-hunting spin given to it
by the ‘tabloid press’. The compilation
appears to focus on two major critiques: It
implies that Coltman et al. (2003) was
based on computer simulations, not real
data, and suggests that environmental
effects were ignored in the analysis. Both
claims are false.
Coltman et al. (2003) analyzed over
1000 horn and body measurements of 200
rams aged 2 to 4 yr and a population
pedigree encompassing over 700
individuals, reaching back to 1971.
Maternal linkages obtained through
behavioural observations were supple-
mented using 20 microsatellite loci to
identify 241 paternities and 31 clusters of
paternal half-sibs, individuals sharing the
same (but unknown) father. Data were
analyzed using accepted statistical methods
widely applied by quantitative geneticists
in the domestic animal literature.
Substantial effort was made to separate
genetic and environmental causes of
variation in horn and body size, again
using accepted statistical methods.
Coltman et al. (2003) specifically
accounted for environmental effects by
including the average mass of yearling
ewes (that has a stronger correlation with
lamb survival and ram horn growth than
population density, presumably because it
accounts directly for changes in resource
availability).
'Breeding value' is the value of a
phenotypic trait predicted to be expressed
by the descendant of a particular
215
individual. Breeding values are based on
the performance of an individual's known
relatives in pedigree. Animal scientists
routinely use these techniques to select
breeders for traits of commercial interest
based on pedigree and performance data.
The first paper in the compilation
series, by Michael and Margaret Frisina,
reports that half of the bighorn rams in the
Boone and Crockett Record Book scoring
more than 200 points were shot between
1987 and 1997, that over half the top 100
rams were killed in the last 20 yr and that a
new ‘world record ram’ was shot in
Alberta in 2000. None of this is surprising.
Many populations of bighorn sheep
restored over the last few decades are
expanding into unused habitat, where rapid
horn growth is expected. There are a lot
more bighorns today than 30 or 40 yr ago.
In populations managed through a draw,
the chances of a ram surviving to grow
large horns presumably are higher than
under unlimited-entry regulations. In
addition to not accounting for the increase
in sheep numbers, the use of a Record
Book as a source of data assumes that
reporting frequency does not change
through time, and that ‘record rams’ are a
random sample. At Ram Mountain, as ram
horns became smaller through a
combination of genetic and environmental
effects, many rams never reached the 4/5-
curl threshold (Jorgenson et al. 1998).
These rams would not appear in records of
shot animals, because it would be illegal to
kill them. Data from harvested rams have
many uses, but also several limitations
(Martinez et al. 2005).
The ‘Alberta record ram’ was taken
during a special hunt from a population
that spends most of the regular hunting
season in areas where hunting is not
allowed. It illustrates the kind of rams that
could be in Alberta if those with fast-
growing horns were not selectively
removed when aged 6 yr and younger.
The Frisinas state that Coltman et al.
(2003) was not based on empirical data
and that it did not account for
environmental effects, two claims refuted
above. They also claim our analyses did
not account for the genetic contribution of
mothers, yet Coltman et al. (2003) states
that 709 maternities were used in
pedigrees. The Frisinas provide a spirited
defense of hunting, but we have no idea of
what led them to suggest that our paper
criticized successful sheep conservation
programs.
Eric Rominger’s paper, labeled a ‘call
to academic accountability’, does not allow
for the possibility that both genetic and
environmental factors may affect horn
growth. Festa-Bianchet et al. (2004)
ascribed over two-thirds of the variance in
body mass and annulus circumference to
changes in resource availability and age.
We stand by that result. Age and resource
availability are important in determining
horn size, but that does not imply that
genotype has no role to play. As density
on Ram Mountain declined, horn size of
rams declined (Fig. 1, see also Fig. 2 in
Coltman et al. 2003). Horn growth rates
remained low despite the very low density
of recent years. That is why instead of
population density we accounted for yearly
changes in resource availability by the
average mass of yearling ewes in June.
Rominger’s paper suggests that traits
must be all-genetic or all-environmental.
Our analysis partitioned environmental
from genetic variance because both are
important. We have now released sheep
from an unselected population onto Ram
Mountain and will monitor the growth of
descendants with varying admixtures of
‘local’ and ‘immigrant’ genes. The
importance of genetic rescue of stagnating,
isolated populations was illustrated by an
216
25
50
75
100
HORN LENGTH OR NUMBER OF EWES
1975 1979 1983 1987 1991 1995 1999 2003
YEAR
EWES
HORN LENGTH
The paper by Heimer and Lee includes
offensive language and personal
accusations. It claims that Coltman et al.
(2003) compromised wild sheep
conservation because it may be used as
fuel for anti-hunting campaigns in the U.S.
The result of this could be the loss of
conservation funding coming from hunters
and hunting organizations. Instead, we
suggest that hunters and managers are
interested in ensuring that trophy hunting
regimes are sustainable. In many hunted
deer, moose, reindeer, chamois, wild boar,
pronghorn, black bear or sheep (adult
males only in most cases) populations,
most of which are managed sustainably,
most adults die by getting shot (Festa-
Bianchet 2003). Avoiding harvest could
be a very strong selective pressure.
Figure 1. Average horn length of 4-yr-old
bighorn sheep rams and number of ewes at
Ram Mountain, Alberta, 1975 to 2003. Ram
horn length continued to decrease after the
number of ewes declined in 1995-2003.
elegant experiment in Montana (Hogg et
al. 2006).
We find no need to issue an
Errata/Corrigendum. Eric Rominger owes
us an apology.
The paper by Val Geist is not a
critique of our 2003 paper. Geist doubts
that the decline in horn size is permanent
but otherwise agrees with our conclusions.
We don’t know if the decline is permanent,
but recent experimental work in fish
suggests that overcoming the effects of
artificial selection may be difficult (Walsh
et al. 2006). Ram Mountain is an isolated
population and some alleles present at the
beginning of our study have now been lost
(D. Coltman, unpublished data). There can
be no evolution without genetic variability.
After pointing out environmental effects
on horn and antler growth (with which we
are in agreement), Geist lists earlier
examples of artificial selection on antler
shape. In writing, Val Geist confirmed
that he does not disagree with our 2003
paper. Why then is his paper in this
‘compilation’?
The same paragraph states that what
we reported is not new because
‘Reproductive success was quantitatively
linked with dominance three decades ago’.
The supporting citation is Geist (1971),
which does not have data on paternity.
Again, the interactions between domin-
ance, horn growth, age, and mating
strategy revealed by recent research (Hogg
1984;1988, Hogg and Forbes 1997,
Coltman et al. 2002, Pelletier 2005,
Pelletier and Festa-Bianchet 2006, Pelletier
et al. 2006) are ignored. The relationship
between either dominance or horn size and
mating success is not linear.
Without citing a source, the next
statement claims that only 3 to 10% of
available rams are harvested in Alaska.
Clearly, the lower the harvest rate, the
lower the potential for artificial selective
effects. What is meant by ‘available rams’
is important here. Most rams are not
‘available’ because they are not legal. The
key question is what proportion of legal
rams are taken. In the Yukon, with curl
217
regulations similar to those in Alaska,
approximately 37% of registered rams are
shot the year they become legal, and about
72% within one year of reaching legal size
(J. Carey, Yukon Environment, pers.
comm.). That does not mean that the
yearly harvest rate is 37% because it does
not account for natural mortality, but it
implies that the 3 to 10% figure may be an
underestimate. Genetic consequences were
observed at Ram Mountain with a harvest
rate of ~35% of legal rams (Festa-Bianchet
1986) or about 5 to 8% of all rams.
The next section laments that papers
by Heimer in the Northern Wild Sheep and
Goat Council Proceedings are not given
sufficient prominence. We strongly
encourage those interested in sheep
management to read all papers by Heimer
as well as Whitten (2001).
Heimer and Lee argue that because
50% of lambs are not sired by dominant
rams, selection against large horns cannot
occur. Here they miss two points. First,
the 50% of paternities by dominants
typically belong to 2 to 3 rams each year,
while the 50% by subordinates are shared
by 10 or more individuals. That mating
distribution implies a high potential for
rapid selection for the genetic
characteristics of the few highly successful
rams. Second, as recognized by their own
quote: “alternative mating tactics [are] less
dependent on body and weapon size”, horn
size plays a limited role in the reproductive
success of subordinate rams. Therefore,
shooting a 6-yr-old with large horns ends
its life before those horns helped achieve
high mating success.
The final sentence is insulting and
attempts to belittle people who have
devoted a lifetime of effort to
understanding the ecology and conserva-
tion of mountain ungulates.
Where do we go from here?
Ram Mountain is an isolated
population that during our study fluctuated
between 26 and 152 adults. It likely
experienced genetic drift in addition to
artificial selection, and is highly unlikely
to receive immigrants from unhunted
populations. Future research should focus
on other possible genetic effects of trophy
hunting, and on what management
strategies can avoid artificial selection.
Managers should be particularly concerned
about the potential effects of selective
hunting in small populations, including
those recently established. Trophy hunting
of mountain ungulates is a potential
conservation tool for many species,
particularly in Asia, that are threatened by
habitat destruction, exotic disease, and
poaching (Harris and Pletscher 2002). It is
important not to perpetuate management
strategies that select for small horns.
Full-curl regulations may decrease the
selective effect of hunting by allowing
some large-horned rams to survive to an
age where large horns confer a high mating
success. There may be differences in the
determinants of mating success in bighorn
and thinhorn (Ovis dalli) rams, and we do
not know what level of selective harvest is
tolerable before genetic consequences are
generated. We suspect that a limit on the
number of large-horned rams harvested
(either through a draw or simply because
of the inaccessibility of terrain) would
decrease the selective effect of trophy
hunting. Hence the urgent need to quantify
harvest pressure in terms of the proportion
of legal rams taken. We observed a
selective effect with a 35% harvest of legal
rams, therefore we recommend a lower
harvest rate, but currently cannot suggest a
more precise harvest goal. Finally, the
potential role of protected areas as sources
of unselected rams is worthy of
investigation, for two reasons. It may
dampen the selective effects of hunting,
218
and it may lead to one-way gene flow out
of protected areas, possibly decreasing
effective population size inside those areas
(Hogg 2000). There is much more to
mountain ungulate conservation than
trophy hunting. We are confident that
managers will consider the potential
implications of our work.
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Possible 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.
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Conservation science is often interested in predicting the future state of populations living in variable environments. Behavioral ecology is often interested in understanding individual behavior in terms of adaptive strategies for dealing with variable ecological, social, or phenotypic states. To the extent that individual behavior is strategic, predictable in different environments, and has population-level consequences, the study of behavior can advance the predictive goals of conservation. Mating system studies, via data on variation in individual reproductive success, have most frequently been applied to conservation in the estimation of effective population size and prediction of genetic trajectories of single populations. However, mating strategy may also influence dispersal, gene flow, and genetic trajectories at spatial scales involving many populations. Mating competition within populations and dispersal will often have opposing effects on effective population size. Future studies of mating systems might aid conservation (i) in evaluating the genetic effects of mating strategy at different spatial scales, and (ii) by providing, in place of point estimates, descriptions of the way in which variation in lifetime reproductive success and population dispersal pattern change in reaction to environmental variation. Such information may allow conservation science to provide better guidance regarding the appropriate spatial scale of habitat protection and restoration and effective strategies for reserve design and re-design.
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Heimer's conclusions about the effects of horn curl regulations were based on incorrect methods, did not account for differences in resighting probability. Suggests most of Heimer's ideas were based on incorrect analyses and untested assumptions