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Exploitative wildlife management as a selective pressure for the life-history evolution of large mammals

12.
Exploitative Wildlife Management as a
Selective Pressure for Life-History
Evolution of Large Mammals
Marco Festa-Bianchet
This chapter explores the usefulness of behavioral ecology when sport hunt-
ing is either a component or the major objective of a wildlife management
strategy. I examine the potential selective effects of different management
practices, and argue that wildlife managers’ ignorance of those effects could
have long-term negative ecological and economic consequences. Knowledge
of the selective pressures caused by sport harvest could help define harvest-
ing programs that avoid or reduce artificial changes in the genetic makeup of
harvested populations. I will assume that the main goal of sport hunting is to
provide recreational opportunities, not to maximize meat production or the
number of animals killed. Within that framework, I suggest that minimizing
the impact of sport hunting on the evolution of the hunted species should be
a major preoccupation of wildlife managers.
Until recently, most wildlife management was concerned with numbers of
animals within a hunted population, and their relationships with their habi-
tat. Hunting regulations and harvest quotas are typically based on popula-
tion goals. Managers either seek to harvest enough animals to prevent some
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type of habitat or health degradation (such as allowing forest regeneration or
decreasing the risk of epizootics), or to avoid overharvesting and thereby
maintain the ability to harvest the population in the future or to increase
long-term yield (Caughley and Sinclair 1994). Consequently, much manage-
ment-oriented research has focused on population dynamics, particularly
questions of density-dependence and of time lags in population and habitat
responses, or on the relationships between herbivores and predators (Fryxell
et al. 1991, Clutton-Brock and Lonergan 1994, Messier 1994, Solberg et al.
1999). Hunting regulations often direct the harvest to particular sex/age cat-
egories, depending on the harvest or population goals (Kokko, Lindström,
and Ranta 2001). For example, male-only harvest is used in cases where fe-
male harvests are expected to decrease the population below the manage-
ment goal. Adult male and young-of-the-year harvests are often used when
populations are at the desired density, and finally all sex/age classes, includ-
ing adult females, are taken where either the population would grow rapidly
in the absence of harvests, or a reduction in density is desired.
In North America, little attention has been paid to the potential selective
effects of sport hunting (Harris, Wall, and Allendorf 2002). In parts of Eu-
rope, on the contrary, there is a rich tradition of “selective” hunting, some-
times with painstakingly detailed hunting regulations that direct the harvest
to particular sex/age classes or even to particular phenotypes. Some of these
practices include the selective removal of individuals that appear weak, or
with “undesirable” antler or horn shape and size. In some cases, the apparent
intent of selective harvests is to decrease intraspecific competition and main-
tain future recruitment by removing those individuals that are least likely to
survive. In other cases, however, the goal of selective harvest is indeed to se-
lect, by favoring certain phenotypes over others. There is evidence that Euro-
pean harvest practices can affect the genetic variability of hunted popula-
tions, at least for red deer (Cervus elaphus) (Hartl et al. 1995, 1991) and foxes
(Vulpes vulpes) (Frati, Lovari, and Hartl 2000).
In North America, hunting rules are not as detailed as some European
regulations, but often go beyond specifying the sex of the animals that can be
harvested. For example, a minimum horn size is often set for male prong-
horn (Antilocapra americana), mountain goat (Oreamnos americanus), and
mountain sheep (Ovis spp.), and a minimum number of antler points for
cervids.
In addition to legal requirements, hunters’ preferences affect the type of
animals they are more likely to harvest. Hunters may avoid shooting females
accompanied by young (Solberg et al. 2000). Given a choice, most hunters
will take the largest individual, or the one with the largest horns or antlers.
Because in many populations of ungulates sport hunting is the principal
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cause of death for adult animals (Langvatn and Loison 1999), it is reasonable
to suppose that nonrandom hunting mortality may have a selective effect.
Recent studies of wild ungulates have shown strong heritabilities for mor-
phological traits such as body size, and varying levels of heritability for life-
history traits, particularly those affecting female fertility (Hewison 1997;
Réale, Festa-Bianchet, and Jorgenson 1999; Kruuk et al. 2000). Hunting-in-
duced mortality of nonlactating females may select for increased investment
in reproduction by generating an artificial positive correlation between re-
productive effort and survival, whereas hunter selection for large-horned
males could lead to either a selective advantage for small-horned males or se-
lection for an earlier investment in rutting activities (Heimer, Watson, and
Smith 1984).
Trophy hunting is well developed in many parts of the world and is a
major economic activity. There is considerable interest in the use of sport
hunting as part of a conservation strategy. Trophy hunting of ungulates is
particularly appealing from a conservation viewpoint because a very large in-
come can be generated from the harvest of a small number of animals (Lewis
and Alpert 1997). Consider for example the markhor (Capra falconeri), an
endangered species. Like many other ungulates in Asia, it is threatened by
poaching and habitat destruction (Shackleton 1997). Trophy hunters will pay
several tens of thousands of dollars to kill a mature male. That money could
be used for conservation and could show the value of habitat protection to
the local population. At the same time, the demographic impact of removing
a few mature males is minor. Indeed, although the markhor is listed in Ap-
pendix I of the Convention on International Trade of Endangered Species
(CITES), a program in Pakistan for limited trophy hunting of this species is
supported by the World Conservation Union (IUCN) Caprinae Specialist
Group.
There are two questions related to the potential selective effects of trophy
hunting. First, what is the effect of increasing the mortality of males with a
trait (large horns or antlers) that is favored by sexual selection and is likely
correlated with individual reproductive success? Second, if trophy hunting
selects for smaller horns or antlers, then it will decrease the availability of
large-horned or large-antlered males over the long term. Therefore, what
management strategies may ensure that trophy hunting can be sustained,
particularly given the direct relationship between the expected trophy size
and the amount of money hunters are willing to pay?
There are many possible selective effects of sport hunting upon the
hunted species. For example, about half of the adult mortality of snow geese
(Anser caerulescens) in North America is due to hunting (Gauthier et al.
2001), and there are untested speculations that wild geese have evolved (or
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CHAPTER 12—Exploitative Wildlife Management for Life History Evolution
learned and then culturally transmitted) behaviors to avoid sport hunters.
Sport fishing has been suggested to select for “smarter” fish (Miller 1957),
more adept at avoiding anglers’ lures. I will consider two specific cases where
sport hunting may have a selective effect on large mammals: changes in re-
productive strategy caused by high hunting-induced adult mortality, and
changes of horn and antler morphology caused by trophy hunting. The evi-
dence for or against a selective effect of sport hunting is limited because this
problem has apparently attracted little attention from either wildlife man-
agers or behavioral ecologists (Law 2001). Rather than review all the available
evidence, therefore, my goal is to point out that artificial selection through
sport hunting can be a serious ecological, economic, and ethical problem,
and therefore research is urgently required to determine the extent to which
it may occur.
Sport Harvest and Life-History Evolution
For many species of ungulates, hunting, legal or otherwise, is the most com-
mon cause of adult mortality. In areas where large predators have been elim-
inated, hunting and road accidents account for almost all adult mortality
(McCorquodale 1999, Ballard et al. 2000). In Europe, outside protected areas,
hunting probably accounts for most mortality of adult chamois (Rupicapra
rupicapra and R. pyrenaica), roe deer (Capreolus capreolus), wild boar (Sus
scrofa), moose (Alces alces) and red deer. In North America, the same could
be said for white-tailed deer (Odocoileus virginianus), mule deer (O.
hemionus), pronghorn antelope, male bighorn (Ovis canadensis) and Dall
sheep (O. dalli), and some populations of moose, wapiti, and black bear
(Ursus americanus). Modern wildlife management can claim a numerical
success: many hunted species are much more abundant now than they have
been for several centuries. In these populations, high density coexists with
high levels of hunter harvest, a situation made possible by past restraint in
harvests, controls over poaching, good habitat, and absence or near-absence
of predation on adults. Artificial feeding is also partly responsible for high
ungulate densities, particularly in central Europe.
DEMOGRAPHIC EFFECTS OF HUNTING
What are the demographic characteristics of a hunted population, and how
do they differ from those of ungulate populations limited by food availability
or by predators? There are two major effects of hunting: an age distribution
heavily skewed toward younger animals, and a sex ratio biased in favor of fe-
males (Squibb 1985, Ginsberg and Milner-Gulland 1994, Laurian et al. 2000).
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PART IIIWildlife Management
These effects can be extreme: posthunt sex ratios of less than 5 males per 100
females have been reported for elk (Noyes et al. 1996).
Few studies have measured the survival of marked individuals in sport-
hunted populations of ungulates. In a population of red deer in Norway, nat-
ural survival of stags from weaning to 5.5 years of age was 56%, but was re-
duced to 5% by hunting; in the same population and over the same age
interval, survival of females was reduced from 59% to 32% (Langvatn and
Loison 1999). In a trophy-hunted population of bighorn sheep in Alberta,
natural survival of rams from 4 to 8 years was 58%, but actual survival was
reduced to 27% by sport hunting. Because that population was partially pro-
tected by a wildlife sanctuary where most rams spent most of the hunting
season (Festa-Bianchet 1989), it is likely that in other hunted populations
survival to 8 years would be even lower. In one population in Alaska, 10 of 23
mature Dall rams were shot within 2 years of marking, an average harvest-
induced yearly mortality of about 25% (Heimer, Watson, and Smith 1984).
In a population of Norwegian moose, about 15% of adult females were shot
each year, in addition to the 2.5% yearly natural mortality (Stubsjøen et al.
2000). Therefore, fewer than 50% of yearling female moose would survive to
5 years in hunted populations, compared to about 90% in unhunted popula-
tions. Data on survival of marked individuals from other hunted populations
are scarce, but it is reasonable to suspect that in many heavily hunted species,
fewer than 5 to 10% of yearling males and perhaps fewer than 15 to 20% of
yearling females survive to 5 years. In unhunted populations the correspon-
ding figures would be about 50 to 60% for males and 60 to 70% for females
(Loison et al. 1999a, Gaillard et al. 2000). Because almost all studies of
marked individuals report that adult survival of ungulates is not density-
dependent, natural survival should not be lower in unhunted than in hunted
populations (Gaillard et al. 2000).
SPORT HUNTING AS A SELECTIVE PRESSURE FOR
REPRODUCTIVE STRATEGY
Sport hunting causes high mortality of prime-aged adults, whereas most nat-
ural mortality affects young of the year and senescent individuals (Gaillard
1998, Gaillard et al. 2000). Life-history strategy and demography are linked:
early comparative approaches to life-history evolution suggested trade-offs
between, for example, age of first reproduction and longevity (Harvey and
Zammuto 1985), or litter size and juvenile survival (Promislow and Harvey
1990). Over the long term, however, those trade-off are inevitable: a species
where first reproduction occurs late in life and average lifespan is short will go
extinct and therefore will not be around for biologists to study. If adult
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CHAPTER 12—Exploitative Wildlife Management for Life History Evolution
mortality is high, either fecundity or juvenile survival must be high, or extinc-
tion will follow. Conversely, if adult mortality is low, either fecundity or juve-
nile survival will decrease because populations cannot increase indefinitely.
If ungulates evolved with low adult mortality, what are the possible conse-
quences of high adult mortality through hunting? The most likely conse-
quence is an increase in reproductive investment by young adults. In ungu-
lates, strong iteroparity and small litter size select for low maternal
investment to avoid compromising the female’s survival and future chances
to reproduce, particularly when combined with high and temporally variable
juvenile mortality, much of which is independent of the amount of maternal
care (Festa-Bianchet and Jorgenson 1998). Indeed, interspecific comparisons
show that the survival of prime-aged females (before senescence) in un-
hunted populations is high and varies little, regardless of the causes of mor-
tality (disease, predation, starvation, weather) (Gaillard et al. 1998b, Gaillard
et al. 2000). A female with a 92 to 96% yearly survival probability should not
increase her current maternal investment to a point where it may affect her
viability, given that her offspring faces a much lower and widely varying
probability of surviving to 1 year, and then a yearling survival that is typically
lower than adult survival (Gaillard et al. 2000).
In heavily hunted populations, however, female survival is greatly dimin-
ished, independently of current reproductive effort. In addition, a dependent
offspring may increase survival, as hunters are often reluctant to kill lactating
females (Solberg et al. 2000). Hunting regulations for alpine chamois in
many jurisdictions prohibit the killing of lactating females. Similar regula-
tions protect members of grizzly (Ursus arctos) and black bear family groups
in much of North America. In Alberta, there is a high proportion of 2-year-
old ewes among the harvest of “nontrophy” bighorn sheep. Two-year-old
ewes often do not produce lambs, and hunters may select ewes without
lambs (W. D. Wishart, 1982, pers. comm.). In hunted populations, therefore,
there could be selection for increased maternal expenditure. In species like
chamois and bighorn sheep that are usually hunted in open areas, selection
against females without dependent offspring is likely stronger than for forest-
dwelling species such as white-tailed or roe deer, where hunters have fewer
opportunities to evaluate female reproductive status before they shoot.
When populations are kept below carrying capacity through hunting, fe-
male reproductive performance is enhanced: age of primiparity decreases,
whereas fecundity, juvenile survival, and litter size usually increase (Swenson
1985; Jorgenson, Festa-Bianchet, and Wishart 1993; Jorgenson et al. 1993;
Swihart et al. 1998). Over the short to medium term, these effects can largely
be explained by density-dependent mechanisms: observational and experi-
mental studies of ungulates show that female reproduction, particularly age
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PART IIIWildlife Management
of primiparity, is very sensitive to resource availability (Langvatn et al. 1996).
An additional, potentially confusing variable is the modified age distribution,
which in hunted populations is typically heavily skewed toward younger and
more productive age classes. This latter effect, however, should be weak: re-
productive senescence in female ungulates occurs at an age reached by a very
small proportion of females even in unhunted populations (Benton, Grant,
and Clutton-Brock 1995; Bérubé, Festa-Bianchet, and Jorgenson 1999). Age
differences between hunted and unhunted populations, however, are very
likely to cause differences in mortality because survival senescence typically
sets in several years before reproductive senescence (Benton, Grant, and
Clutton-Brock 1995; Loison et al. 1999a). Therefore one may expect greater
natural (i.e., unhunted) female survival in hunted than in unhunted popula-
tions, simply because in hunted populations there are few if any females
older than 8 to 10 years.
In addition to the ecological effects due to lowered intraspecific competi-
tion, I suggest that heavy harvest may select for a life-history strategy that is
normally disadvantaged in natural populations. Consider a set of genes
whose phenotypic expression led to females that invested heavily in early re-
production, leading to early primiparity and an increase in offspring survival
at the expense of maternal survival. In a naturally regulated population of
ungulates, that genotype would be selected against because longevity is the
greatest determinant of lifetime reproductive success for females (Clutton-
Brock 1988, Bérubé, Festa-Bianchet, and Jorgenson 1999). If very few females
survive more than two to four hunting seasons, however, a reproductive
strategy leading to greater reproductive success early in life would be favored
even if it had a negative effect on lifespan. If the average lifespan including
natural and hunting mortality is 5 years, a gene that decreased natural lifes-
pan from 10 to 6 years would not be selected against. Selection for high ma-
ternal investment would be strengthened by hunter preference for females
without dependent offspring. This scenario is not dissimilar to what may be
expected in other ungulate populations under artificial selection, such as do-
mestic sheep, cows, or goats. Domestic ungulates have a shortened life ex-
pectancy compared to their wild counterparts, possibly because of artificial
selection for increased reproduction (or milk production) early in life.
We readily accept that many traits of domestic animals are the result of ar-
tificial selection, and some life-history traits of wild animals could also be af-
fected by artificial selection. With sport hunting, most adult mortality is
human-caused and human predation is not random with respect to repro-
ductive status or morphology. Obviously, a major methodological challenge
in studying the selective effects of hunting is to separate the environmental
effects due to lowered intraspecific competition and the genetic effects due to
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CHAPTER 12—Exploitative Wildlife Management for Life History Evolution
selection for a less iteroparous reproductive strategy. A modeling exercise
(Benton, Grant, and Clutton-Brock 1995) suggested that the reproductive
strategy of red deer hinds that were hunted until a few generations before the
study may be suboptimal, possibly because it was shaped by culling that for
many generations resulted in a high level of adult mortality. Researchers have
recently expressed concern that the life-history strategies of moose in heavily
harvested populations in Sweden may be affected by hunting-induced mor-
tality, which may select for high reproductive effort in early life and lead to
premature senescence (Ericsson and Wallin 2001, Ericsson et al. 2001).
My review concerns large herbivores (and possibly some bear popula-
tions) that are subject to intense sport hunting, but a similar line of reason-
ing could apply to large carnivores that are the target of both sport hunting
and trapping (or even predator control programs): for example studies of
wolves (Canis lupus) outside protected areas report very high levels of
human-caused mortality (Potvin et al. 1992).
The potential selective effects of harvesting have preoccupied some fish-
eries scientists for a long time (Miller 1957). Heavy fishing pressure may have
not only a demographic effect on fish populations but also a selective effect
(Kirkpatrick 1993, Policansky 1993, Reznick 1993, Rochet et al. 2000). Fish-
ing disproportionately increases mortality of adult fish, and nets with mesh
sizes allowing the escape of some of the smaller individuals further select
against large fish (Law 2001). A logical outcome of these selective pressures is
an earlier age of maturity, as reported by a number of studies (Rijnsdorp
1993, Rowell 1993, Rochet 1998). It is often problematic to partition envi-
ronmental and genetic effects: early reproduction could occur in the absence
of selection simply because resources may be more abundant in heavily har-
vested populations (Rochet et al. 2000).
High predation on adult guppies (Poecilia reticulata) is associated with
earlier maturation, higher reproductive effort, and more and smaller off-
spring compared to populations where predation is mainly on juveniles. Dif-
ferences in life-history strategies are heritable. Translocation experiments to
areas where predation was mostly on juveniles led to life-history changes in
11 years (30–60 generations) (Reznick, Bryga, and Endler 1990), providing
experimental evidence that life-history traits respond quickly to strong selec-
tive pressures. Fisheries scientists are interested in the possible evolutionary
impacts of fishing upon fish populations that are exploited either commer-
cially or for sport fishing. Because most of these populations are very diffi-
cult to study, however, the evidence for genetic changes consists mostly of
phenotypic measurements on exploited stocks and controlled experiments in
short-lived species that are not exploited (Reznick, Bryga, and Endler 1990;
Reznick 1993). A more direct approach is possible with exploited ungulates,
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where individual-level information on morphology, life-history, and geno-
type can be obtained. Different ungulate hunting regimes in adjacent areas
offer great potential to compare life-history differences associated with dif-
ferences in age-specific mortality.
Trophy Hunting and Selective Pressures
on Horns and Antlers
Trophy hunting has a competitive component. Complex scoring formulae
measure various aspects of an animal’s horns, antlers, or skull, and records
are kept by a number of organizations. Trophy scores are strongly correlated
with size, therefore most trophy hunters seek adult males with large horns or
antlers. Trophy hunting is big business: hunters are willing to pay very large
sums in the hope of harvesting a “record book” trophy. Guides and outfitters
typically advertise the trophy scores of animals shot by their clients, and
areas reputed for producing large trophies attract much greater revenues
than areas where males have smaller horns or antlers. For example, consider
the bids received by the Foundation for North American Wild Sheep during
its auctions of special permits for bighorn sheep (Erickson 1988). These per-
mits are offered by some American states and Canadian provinces to the
highest bidder, and typically sell for tens to hundreds of thousands of dollars
that should then be used for conservation, research, or wildlife management
activities. Recent auction results reveal that, although most jurisdictions ob-
tain bids for special permits of between $20,000 and $60,000, those with a
reputation for producing large rams (Alberta, Montana, Arizona) regularly
receive up to 10 times as much, with bids topping $400,000 (http://www.
fnaws.org/page1.html). Some hunters are willing to pay great sums of money
to obtain a few extra centimeters of horn, and the availability of large trophy
males can play a strong role in the economics of a wildlife management
program.
By definition, the trophy hunter selects according to morphological crite-
ria. For most bovids, the criterion is simply horn size, for cervids the number
of tines, antler symmetry and branching pattern can affect a trophy’s score.
Given that a proportion of the variability in horn and antler size is geneti-
cally determined (Fitzsimmon, Buskirk, and Smith 1995; Hartl et al. 1995;
Lukefahr and Jacobson 1998; Moorcroft et al. 1996), trophy hunting may cre-
ate the somewhat paradoxical situation of selecting against the preferred
phenotype. It is therefore surprising that wildlife managers, especially in
North America, have paid so little attention to the genetic effects of trophy
hunting (Harris, Wall, and Allendorf 2002).
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ECOLOGICAL VARIABLES AND ARTIFICIAL SELECTION
The strength of artificial selection caused by trophy hunting will depend
upon ecological variables and harvest regulations. Obviously, a high level of
harvest of trophy-class males should have a stronger selective effect than a
low level of harvest. Harvest regulations based on a simple morphological
criterion, without a limit on the number of permits issued, are likely to have
a stronger selective effect than management regimes that limit the number of
males harvested within each age class or morphological grouping. The tim-
ing of the hunt in relation to the reproductive cycle will also affect the selec-
tive pressure caused by trophy hunting: a pre-rut hunt will have a stronger
effect than a post-rut hunt. The pattern of age-specific horn growth may also
play a strong role. For example, species like chamois, mountain goat, and roe
deer have a relatively rapid horn or antler growth: mountain goats and
chamois achieve over 90% of their horn growth by 3 years of age (Côté,
Festa-Bianchet, and Smith 1998). In these species, males become desirable
trophies at a relatively young age, and therefore large-horned individuals risk
being killed before contributing to future generations. The horns of ibex
(Capra ibex), on the other hand, grow substantially up to about 10 to 12
years, and ibex may reproduce actively for several years before being selected
by trophy hunters (Toïgo, Gaillard, and Michallet 1999). Bighorn sheep are
somewhat intermediate; the horns of 6-year-old rams are about 90% of the
length they will attain by 9 or 10 years (Jorgenson, Festa-Bianchet, and
Wishart 1998). The mating system will also affect the strength of artificial se-
lection for small horns or antlers caused by trophy hunters: where alternative
mating tactics account for a substantial proportion of paternities (Hogg and
Forbes 1997), selection is likely weaker than where paternities are monopo-
lized by a few highly successful males (Apollonio, Festa-Bianchet, and Mari
1989).
If mating success is affected by both weapon size and male age, an intense
level of trophy hunting of young males will have a stronger selective effect
than in species where only older males are removed by hunting. For example,
although precise information on male reproductive success is not available,
studies of both chamois and ibex suggest that in unhunted populations most
matings are achieved by males 10 years of age and older (Lovari and
Cosentino 1986; Toïgo, Gaillard, and Michallet 1999). An ibex male may not
achieve “trophy” status until about 10 to 12 years of age, but the horns of a 5-
year-old chamois are not much smaller than those of a 10-year-old. If in a
trophy-hunted population of ibex most matings are done by 10-year-olds
rather than 12-year-olds, there will still be 10 years of time for natural selec-
tion to potentially affect pre-mating male survival. In trophy-hunted popula-
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PART IIIWildlife Management
tions of chamois, on the other hand, most matings may be by males aged 4 to
5 years because few males may survive to older ages, possibly allowing some
reproduction by males that normally would not survive to mating age.
The potential selective strength of trophy hunting is illustrated by fallow
deer (Dama dama), where a single male can mate with 25% of the females
during one rut (Apollonio, Festa-Bianchet, and Mari 1989). If the traits that
favor male reproductive success were the same as those selected by trophy
hunters, a single male shot before the rut could lead to a large difference in
the genetic makeup of fawns born the following year.
Male reproductive success in most ungulates appears to be determined
mainly by an individual’s ability to beat other males. Antler or horn size is,
presumably, only one component of fighting ability: body size and condition
can also play a role, especially if very large weapons suffer a risk of breakage
(Alvarez 1994). Both size and shape of antlers and horns could be modified
by selection to preserve their effectiveness as intraspecific weapons but make
them less attractive as trophies. For example, in most of the Canadian
province of Alberta, hunting regulations specify that only bighorn rams
whose horns describe at least four-fifths of a curl can be shot.
A ram with a large body mass and whose horns were massive but did not
reach the minimum legal size until 6 or 7 years of age would enjoy greater
survival than a ram with fast-growing horns that became “legal” at 4 or 5
years of age (Jorgenson, Festa-Bianchet, and Wishart 1998). In areas with
good hunter access, few rams survive more than one hunting season after be-
coming legal, and in areas with moderate access, about 30 to 40% of legal
rams are shot each year (Festa-Bianchet 1986). A ram that survives the hunt-
ing season will face little competition during the following rut because many
potential competitors will have been shot.It is therefore reasonable to predict
that any genetic trait that retards the age at which a ram’s horn becomes legal
will be strongly selected for. There is considerable interindividual variability
in the age at which rams reach legal status, from as early as 3 years in excep-
tional cases, to never (Jorgenson, Festa-Bianchet, and Wishart 1998). Rams
that reach legal status later in life may have greater lifetime reproductive suc-
cess than those whose horns are legal by 4 or 5 years of age. In addition, re-
cent evidence suggests that horn size only plays an important role in male
mating success after about 7 years of age (Coltman et al. 2002). Rams with
fast-growing horns therefore risk being shot before their large horns give
them a reproductive advantage, compounding the potential selection for
small horns.
Similarly, imagine a wapiti or red deer male with large antlers but with
only a few tines: such an individual would do well in an area where hunting
regulations state a minimum number of tines for harvestable males, or could
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CHAPTER 12—Exploitative Wildlife Management for Life History Evolution
enjoy greater survival under a trophy hunting regime simply because hunters
would “pass him up” in favor of what they may see as a more attractive set of
antlers. Trophy hunting favors a “nontrophy” phenotype by increasing its
survival relative to the population mean, and by removing potential com-
petitors. The harvesting scheme prevalent in parts of Europe, where “unde-
sirable” horn or antler phenotypes are selectively harvested in addition to
trophy-class males, would obviously complicate the situation.
Of course, the preceding scenario does not take into account potential gene
flow among populations subject to different hunting regimes, changes in hunt-
ing regulation or harvest levels, and the strengths of several competing selective
pressures, many of which are likely temporally variable. For example, there
could be a net outflow of genes from protected into hunted areas because
males who survived the hunting season by staying within protected areas
would be in a very good position to compete for estrous females in neighbor-
ing populations where most resident males were shot by hunters (Hogg 2000).
In addition to selection for horn or antler morphology, a high level of tro-
phy hunting may select for greater reproductive effort by young males. Over
the short term, there may be a demographic effect without evolution of novel
mating strategies: if most mature males are removed by hunters, younger
males may take over the role of breeders and possibly suffer higher mortality as
a result, as suggested by Geist (1971) and Heimer, Watson, and Smith (1984).
Over the long term, selection could favor males with high reproductive ef-
fort over their first few years of life, possibly including faster growth, lower fat
reserves, and riskier behavior during the rut. A shortened life expectancy would
weaken selective pressures for less risky behavior that may increase the chance
to survive to breed again. The consequence could be higher nonhunting mor-
tality for young males. Consider the many white-tailed deer, roe deer, chamois,
or moose populations that are subject to very high harvest levels: in these pop-
ulations very few males survive past 2 or 3 years of age. In three management
areas in Oregon, over 90% of wapiti males were killed before 4 years of age
(Biederbeck, Boulay, and Jackson 2001). High hunting mortality of males could
lead to a high selective advantage for those few that survive beyond 4 years
(possibly because they have small horns or antlers, or because their behavior
decreases their chance of being shot), or strong selection for early reproduction.
In either case, sport hunting could lead to evolutionary change.
The Implications for Consumptive Management
Harvest of large mammals through sport hunting can lead to economic
and social benefits that can stimulate conservation. It is therefore impor-
tant that management decisions be based upon the best available informa-
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tion. It is reasonable to suspect that any selective harvest may have evolu-
tionary consequences by altering selective pressures and gene frequencies
compared to naturally regulated populations. There is clearly a need for
more information, particularly about the levels and types of hunting that
may lead to evolutionary change. Sexual selection and possibly female
choice may favor males with large horns or antlers, and partly compensate
for the effects of selective hunting. If the hunting mortality is not very
high, it may be insufficient to change the genetic makeup of future gen-
erations. Immigration from protected areas may reduce the potential for
selection for a “short and fast” reproductive strategy among both sexes. Fi-
nally, harvest schemes that simply stipulate a minimum size or minimum
number of tines required for legal harvest will likely have stronger selective
effects than the more complex harvest strategies prevalent in central
Europe.
Three potential problems should be considered. First, some current har-
vest policies may select for unwanted morphological or life-history attributes
that may lead to loss of economic and recreational opportunities. This would
be the case for selection for small horns or antlers by high levels of trophy
hunting, but also for selection of a reproductive strategy favoring high early
investment in reproduction, if it increased nonhunting mortality of young
adults. Selective hunting may lead to a loss of genetic variability (Hartl et al.
1995), which may negatively affect a population’s ability to survive environ-
mental changes over the long term.
Poaching of African elephants (Loxodonta africana) for the illegal ivory
trade may select for tusklessness (Jachmann, Berry, and Imae 1995). Second,
artificial “adaptive” changes in hunted populations may compromise their
long-term ability to persist. A cessation of hunting may have unpredictable
consequences for a population that has undergone adaptations to a high level
of hunting mortality: both evolutionary and demographic effects should be
considered when hunting is stopped because of changes in land designation.
Artificial selection is not necessarily reversible (Law 2001). Third, there are
ethical concerns: should hunting shape evolution? Much of the nonhunting
public and many hunters dislike the competitive nature of scoring trophies.
The competitive aspect of trophy hunting spurs a negative reaction by many
people that accept or even support other forms of sport hunting. As public
attitudes change, the conservation of ungulates will increasingly require the
support of people with little interest in hunting. I suggest that the best out-
come for both hunting and conservation would be a decreased emphasis on
trophy scores, and more emphasis on the enjoyment of hunting, independ-
ent of the particular attributes (sex, age, horn size) of the animals that are
harvested.
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Conclusions and Recommendations
The ideas I have put forth in this chapter, if correct, justify changes in several
sport hunting practices. If these ideas are incorrect, however, changes in
wildlife management would not be required and could have a negative effect.
It is therefore important to test these ideas, ideally through long-term studies
conducted in cooperation with researchers, wildlife management agencies,
and sport hunting groups. Wildlife management agencies can do the re-
quired experiments by manipulating hunting regulations. For example, an
experimental change in the definition of legal ram was approved in Alberta
partly to test the effects of different management schemes on bighorn ram
survival and harvest. Changes in regulations, however, require the support of
the hunting public. Future research should combine the analysis of genotype
frequencies, morphology, and life-history attributes in populations subject to
different levels of hunting or to different harvest regimes.
An alternative to experimental manipulation of hunting regulations
would to better exploit available information. There are vast repositories of
data on morphology, sex, and age of harvested animals, in computers and file
drawers of wildlife management agencies all over Europe and North Amer-
ica. Additional information on morphological measurements (or trophy
scores) is available from private organizations and individuals, including
records and actual specimens (stuffed heads) from several decades ago. This
information could be used to investigate hypotheses about the selective ef-
fects of sport hunting, or to form the basis of future research programs.
There are several recent examples of how long-term information gleaned
from wildlife management agencies can provide very valuable scientific con-
tributions (Loison, Gaillard, and Jullien 1996; Post et al. 1999; Schneider and
Wasel 2000).
The diversity of wildlife management schemes in different areas, including
different sex/age restrictions, could also be used to test specific hypotheses.
The main difficulty will be teasing apart environmental and genetic effects: a
high level of harvest that reduces population density will almost certainly
lead to a phenotypic response, but it may or may not also select particular
genotypes. The most powerful test of these hypotheses will be a long-term
study of the survival and reproduction of a large sample of marked individu-
als. Long-term studies of marked large mammals are rare, and very few have
been done in hunted populations (Festa-Bianchet 1989; Jorgenson, Festa-
Bianchet, and Wishart 1993; Langvatn and Loison 1999), partly because re-
searchers are reluctant to invest time and money for marking animals that
may be shot within a few months or years. As a result, much of the informa-
tion on the evolutionary ecology of wild ungulates comes from populations
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that are either unhunted or very lightly hunted (Byers 1997; Clutton-Brock,
Rose, and Guinness 1997; Festa-Bianchet, Gaillard, and Jorgenson 1998;
Gaillard et al. 1998a), and little is known about the evolutionary effects of
sport hunting. Because of the high cost of marking and monitoring pro-
grams, and because a long-term study in a hunted population would be un-
able to consider many questions of theoretical interest, there is a need for
government agencies to become involved. The long-term monitoring pro-
gram of polar bears (Ursus maritimus) in Canada (Messier, Taylor, and Ram-
say 1992; Derocher and Stirling 1998) is an excellent example of a successful
study supported by government agencies.
The effects of gene flow in and out of protected areas is an area of research
that holds particular promise and particular urgency, for both its practical
and its theoretical interest. The amount of gene flow among areas subject to
different harvest regimes will likely decrease the selective pressures brought
about by selective hunting. On the other hand, selective hunting may itself
affect the rate and direction of gene flow (Hogg 2000). There are complex
patchworks of protected and exploited ungulate populations that would lend
themselves to a very productive study.
The possibility that life-history strategies of large mammals have been
shaped by hunting also has potential applications for our understanding of
interspecific differences in behavior and reproductive strategies (Benton,
Grant, and Clutton-Brock 1995). Consider two mountain ungulates, the
alpine ibex and the bighorn sheep. The former has been protected from
hunting in most of its range since early in the twentieth century, and is still
protected from legal harvests in both Italy and France. Bighorn sheep, on the
other hand, have been and are heavily hunted for trophies in most of their
range in North America. Ibex males have a very high survival rate until about
11 to 12 years of age (Girard et al. 1999, Toïgo, Gaillard, and Michallet 1997)
and a very gradual pattern of age-specific horn development (Toïgo, Gail-
lard, and Michallet 1999), whereas bighorn rams have low survival at 3 to 8
years of age (Jorgenson et al. 1997, Loison et al. 1999a), rapid horn growth
(Jorgenson, Festa-Bianchet, and Wishart 1998), and subadult adoption of
risky but successful alternative mating strategies (Hogg and Forbes 1997).
These interspecific differences could be due to a wide range of plausible eco-
logical explanations but may also result from selection for greater reproduc-
tive effort at a younger age in bighorn sheep, brought about by high hunting
mortality over the last century. If this is the case, then one may predict higher
natural mortality rates and faster horn growth of ibex in areas where they are
hunted, such as in Switzerland (Giacometti et al. 1997), and higher survival
and slower horn growth (but not smaller asymptotic horn size) of bighorn
rams in protected areas, such as large national parks. Information on genetic
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CHAPTER 12—Exploitative Wildlife Management for Life History Evolution
differences, however, would also be required to test this prediction because
differences in survival could be due to changes in age ratios and therefore in
age-specific rutting behavior (Heimer, Watson, and Smith 1984), and
changes in horn growth would be expected simply from differences in popu-
lation density (Jorgenson, Festa-Bianchet, and Wishart 1998).
A Final Thought: Is Human-Induced Selection
a Modern Phenomenon?
The current extinction crisis caused by human activities is unprecedented,
but there is evidence that humans have had a strong impact on the species
composition of several ecosystems for thousands of years (Kay 1994a, Balm-
ford 1996, Caughley and Gunn 1996), although the exact nature and strength
of historic human impacts are unclear and often controversial (Beck 1996,
Choquenot and Bowman 1998). Nevertheless, it is reasonable to suspect that
changes in density, distribution, and behavior of many species of large mam-
mals have been affected by human hunters for a long time.
Consider the differences in behavior toward humans of brown bears in
Europe and North America. European bears are less aggressive, possibly as a
result of coevolution with humans, who may have selectively killed aggressive
individuals. Similarly, although North American wolves appear unable to
survive outside wilderness areas (Mladenoff, Sickley, and Wydeven 1999), in
parts of Europe wolves coexist with very high human population densities (
Okarma 1993, Meriggi and Lovari 1996). Differences in response to habitat
fragmentation and other human activities also appear to vary according to
the potential for coevolution of humans and other species, measured by the
length of time since recorded human occupancy (Balmford 1996, Martin and
Clobert 1996). Hunting by humans has likely affected adult mortality of
many large mammal species in much of the world for several centuries, pos-
sibly for millennia. If this is the case, then the reverse argument of the one I
have presented may have some merit: the “new” selective pressures may be
those experienced by ungulates in several European and North American na-
tional parks, particularly southern parks without large predators.
We should be concerned about the potential selective effects of sport
hunting because they may limit the future ability of populations to adapt to
a changing environment, or future opportunities for trophy hunting. There
is also an ethical concern that sport hunting may lead to “artificial” selection.
If we wish to avoid the evolution of “artificial” phenotypes, however, we must
know what is “natural.” Establishing what is “natural” for species whose evo-
lution has been shaped by human predation may be very difficult.
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Summary
Game management is mostly concerned with what determines the size and
sex/age composition of populations of hunted animals. Consequently, prin-
ciples of population dynamics are most often applied to wildlife manage-
ment, including considerations of sex- and age-specific survival and repro-
ductive rates. It is often assumed that sport hunting affects population
dynamics but is not a selective force. For many game species, however, avoid-
ing getting shot is a major selective force because most mortality is due to
human hunters.
The age-specific mortality caused by sport hunting of large mammals is
usually very different from natural mortality. Hunters often kill prime-aged
individuals, which normally have a very high survival rate. Regulations often
specify the sex and the age class of animals to be killed. Hunters may select
prey according to sex, age, reproductive status, or morphology. In much of
Europe, morphology-based harvests favor certain phenotypes, particularly
with regard to antler or horn size. The term selective hunting is somewhat
foreign to North American managers, but it is often used in Europe. In North
America, harvest is directed to certain age classes through morphology-based
definitions of what can be killed, particularly with regard to horn size and
antler points. Principles of evolutionary theory suggest that “selective” har-
vesting may indeed “select,” but not necessarily with the results that man-
agers or society may seek. Intensive hunting may select for precocious matu-
rity and increased reproductive effort, and trophy hunting may select for
small horns or antlers. Long-term management plans must take into account
the potential selective pressures of alternative harvest schemes, as is recog-
nized by some fisheries scientists. Because sport hunting is as much a social
issue as a biological one, changes in wildlife management require changes in
attitudes, particularly in the case of trophy hunting. Relegating the competi-
tive attitude to the past will benefit both hunters and biodiversity.
Acknowledgments
Bill Wishart, Rich Harris, Wayne Heimer, Jon Jorgenson, Val Geist, and Jean-
Michel Gaillard helped me develop the ideas presented here, particularly
when they vigorously disagreed with my opinions. I thank Marco Apollonio,
Steeve Côté and Sandro Lovari for comments on an earlier draft. My research
on ungulate ecology is supported by the Natural Sciences and Engineering
Research Council of Canada, the Fonds pour la Formation de Chercheurs et
l’aide á la Recherche (Québec) and the Université de Sherbrooke.
... Harvesting of wild animal populations serves economic, cultural, and management purposes, but when exerted at a high rate, it can threaten population persistence (Jackson et al., 2001) and induce trait changes in life history, morphology, and behavior (Palkovacs et al., 2018). Human harvest constitutes a unique form of "predation" that fundamentally differs from "natural predation," because harvest mortality is often higher than natural mortality and not always directed toward individuals that are most vulnerable to natural mortality (Allendorf & Hard, 2009;Darimont et al., 2015;Festa-Bianchet, 2003). Because of this, human harvest has emerged as an important driver of trait change in the wild (Darimont et al., 2009;Palumbi, 2001), inducing selective pressures that vary both in strength and in direction, depending on harvest levels and practices, as well as on the phenotypes being targeted (Darimont et al., 2015). ...
... Hunting regulations often aim at directing the harvest toward (or away from) individuals with specific traits within a population to achieve a management goal, for example, to manipulate the population growth rate. As such, hunting regulations can create harvest biases and, intentionally or not, induce selectivity (Bunnefeld et al., 2009;Festa-Bianchet, 2003;Hengeveld & Festa-Bianchet, 2011;Leclerc et al., 2016;Mysterud, 2011). In the case of reproductive traits, such hunting selectivity can affect the fitness pay-off of different female reproductive tactics (Rughetti & Festa-Bianchet, 2014; Van de Walle et al., 2018). ...
Article
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Harvest, through its intensity and regulation, often results in selection on female reproductive traits. Changes in female traits can have demographic consequences, as they are fundamental in shaping population dynamics. It is thus imperative to understand and quantify the demographic consequences of changes in female reproductive traits to better understand and anticipate population trajectories under different harvest intensities and regulations. Here, using a dynamic, frequency‐dependent, population model of the intensively hunted brown bear (Ursus arctos) population in Sweden, we quantify and compare population responses to changes in four reproductive traits susceptible to harvest‐induced selection: litter size, weaning age, age at first reproduction, and annual probability to reproduce. We did so for different hunting quotas and under four possible hunting regulations: (i) no individuals are protected, (ii) mothers but not dependent offspring are protected, (iii) mothers and dependent offspring of the year (cubs) are protected, and (iv) entire family groups are protected (i.e., mothers and dependent offspring of any age). We found that population growth rate declines sharply with increasing hunting quotas. Increases in litter size and the probability to reproduce have the greatest potential to affect population growth rate. Population growth rate increases the most when mothers are protected. Adding protection on offspring (of any age), however, reduces the availability of bears for hunting, which feeds back to increase hunting pressure on the non‐protected categories of individuals, leading to reduced population growth. Finally, we found that changes in reproductive traits can dampen population declines at very high hunting quotas, but only when protecting mothers. Our results illustrate that changes in female reproductive traits may have context‐dependent consequences for demography. Thus, to predict population consequences of harvest‐induced selection in wild populations, it is critical to integrate both hunting intensity and regulation, especially if hunting selectivity targets female reproductive strategies.
... En effet, la survie juvénile est un paramètre démographique qui peut varier de manière importante dans l'espace et dans le temps influençant ainsi fortement la dynamique des populations de chevreuils à court et long-termes Cependant, des études suggèrent que certains comportements pourraient être le résultat de pressions de sélection à long-terme par les humains. Par exemple, la moindre agressivité des ours bruns en Europe par rapport à ceux d'Amérique du Nord, ou encore la plus grande tolérance des loups européens aux activités humaines, pourraient résulter de méthodes de chasse plus agressives en Europe par rapport à l'Amérique du Nord (Festa-Bianchet 2003). Il serait donc nécessaire d'approfondir nos connaissances sur l'impact réel des pressions de sélection par la chasse sur le comportement des populations animales chassées de manière intensive. ...
Thesis
Les populations sauvages sont de plus en plus soumises à d’importantes pressions de prédation en lien avec les activités humaines, qui sont la source de multiples facteurs de stress pour les populations sauvages. Parce qu’il est quasiment impossible pour la plupart des organismes desatisfaire l’ensemble de leurs activités fondamentales (alimentation, reproduction, repos,…) sans encourir un risque de prédation, ils sont souvent confrontés à des compromis. Notamment dans le processus d’alimentation, les animaux doivent faire des compromis entre l’acquisition de ressources de bonnes qualités et l’évitement du risque de prédation ou de dérangement, car les meilleurs ressources sont généralement associées à un risque de prédation plus fort. Une des manière dont les animaux peuvent résoudre ce compromis est par la modification de leurs patrons d’utilisation des habitats. Dans cette thèse nous nous sommes intéressés au système Chevreuil-Homme pour comprendre comment les activités humaines peuvent impacter les patrons d’utilisation et de sélection des différents habitats. La population de chevreuils étudiée évolue dans un paysage fragmenté et fortement anthropisé, représentatif des paysages agricoles modernes. Le suivi depuis plus de 10 ans de cette population, avec plus de 300 animaux capturés et équipés de colliers GPS, nous offre une opportunité unique de mieux comprendre les mécanismes qui sous-tendent les stratégies adoptées par les individus au sein du compromis « risque – acquisition des ressources ».Nous avons ainsi montré que le compromis « risque-acquisition des ressources » affecte différemment les patrons de sélection des habitats en fonction des variations spatio-temporelles dans l’intensité du risque et la disponibilité des ressources. L’ensemble de nos travaux a égalementpermis de mettre en évidence l’impact de facteurs environnementaux, tels que la période de chasse ou le moment de la journée, mais également l’impact de facteurs internes, tels que le statut reproducteur ou la sensibilité au stress des individus (probablement liée à leur personnalité), sur lesstratégies d’utilisation des habitats. Les stratégies d’utilisation des habitats résultent donc d’interactions complexes entre les facteurs externes et internes et peuvent avoir potentiellement des conséquences importantes sur la valeur adaptative des individus et, à terme, sur la dynamiquedes populations. La prise en compte de l’ensemble de ces facteurs, et notamment de la variabilité inter-individuelle dans les stratégies d’utilisation des habitats, devrait permettre d’améliorer les outils de gestion et de conservation des populations d’ongulés sauvages.
... Reproductive value (RV) refers to the expected individual contribution to population growth that varies with age such that the highest RV values correspond to mature adults of middle ages and the lowest ones to juveniles [54]. Thus, size-selective hunting of individuals with the highest RV can cause a lower growth rate in the population by increasing the reproductive investment of young adults [55]. ...
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Full-text available
We examine population trends in light of male harvest data considering the long-time series of population data on northern fur seals at Tyuleniy Island. To answer the question has the way males were harvested influenced the population trajectory, we analyzed the visual harem size and birth rate dynamics of the population, as well as the strategy and intensity of the harvest. We analyzed the dynamics of the sex ratio in the early (1958–1988) period to estimate parameters in the late period (1989–2013) based on the observed number of bulls and pups, while utilizing the distribution of reproductive rates obtained from pelagic sealing. Using a matrix population model for the observed part of the population (i.e., the male population), we analyzed the population growth rate associated with changes in both birth and survival rates considering the stochastic effects. Observations allow us to reject the hypothesis of nonselective harvest. Among the variety of natural and anthropogenic factors that could contribute to the decrease in the birth rate in the population, the effect of selective harvesting seems to be the most realistic.
... Artificial selection (i.e. selection driven by human activities) shapes wild populations through the removal or promotion of certain morphological and behavioural traits (Ciuti et al., 2012;Coltman, 2008;Festa-Bianchet, 2003). Traditional artificial selection studies focus on the impacts associated with harvesting activities, such as hunting and fishing. ...
Article
The artificial selection of traits in wildlife populations through hunting and fishing has been well documented. However, despite their rising popularity, the role that artificial selection may play in non‐extractive wildlife activities, for example, recreational feeding activities, remains unknown. If only a subset of a population takes advantage of human‐wildlife feeding interactions, and if this results in different fitness advantages for these individuals, then artificial selection may be at work. We have tested this hypothesis using a wild fallow deer population living at the edge of a capital city as our model population. In contrast to previous assumptions on the randomness of human‐wildlife feeding interactions, we found that a limited non‐random portion of an entire population is continuously engaging with people. We found that the willingness to beg for food from humans exists on a continuum of inter‐individual repeatable behaviour; which ranges from risk‐taking individuals repeatedly seeking and obtaining food, to shyer individuals avoiding human contact and not receiving food at all, despite all individuals having received equal exposure to human presence from birth and coexisting in the same herds together. Bolder individuals obtain significantly more food directly from humans, resulting in early interception of food offerings and preventing other individuals from obtaining supplemental feeding. Those females that beg consistently also produce significantly heavier fawns (300–500 g heavier), which may provide their offspring with a survival advantage. This indicates that these interactions result in disparity in diet and nutrition across the population, impacting associated physiology and reproduction, and may result in artificial selection of the begging behavioural trait. This is the first time that this consistent variation in behaviour and its potential link to artificial selection has been identified in a wildlife population and reveals new potential effects of human‐wildlife feeding interactions in other species across both terrestrial and aquatic habitats. Human‐wildlife feeding interactions are increasingly popular, yet the role that they may play in the artificial selection of behavioural traits in wildlife populations remains unexplored. This work begins to unravel the complex dynamics and impacts of these interactions, opening up new dimensions for human‐wildlife studies.
... In so doing, a higher proportion of mature individuals can achieve reproduction at the cost of an increased offspring mortality. The high hunting pressure may have increased the advantage of such a risky investment, as individuals counting on a short life expectancy have to exploit every reproductive opportunity to maximize their fitness (Festa-Bianchet 2003). We observed no relationship between the number of culled adult males per female and ovulation and pregnancy temporal Table 1. ...
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Full-text available
On a population-level, individual plasticity in reproductive phenology can provoke either anticipations or delays in the average reproductive timing in response to environmental changes. However, a rigid reliance on photoperiodism can constraint such plastic responses in populations inhabiting temperate latitudes. The regulation of breeding season length may represent a further tool for populations facing changing environments. Nonetheless, this skill was reported only for equatorial, non-photoperiodic populations. Our goal was to evaluate whether species living in temperate regions and relying on photoperiodism to trigger their reproduction may also be able to regulate breeding season length. During 10 years, we collected 2,500 female reproductive traits of a mammal model species (wild boar Sus scrofa) and applied a novel analytical approach to reproductive patterns in order to observe population-level variations of reproductive timing and synchrony under different weather and resources availability conditions. Under favorable conditions, breeding seasons were anticipated and population synchrony increased (i.e., shorter breeding seasons). Conversely, poor conditions induced delayed and less synchronous (i.e., longer) breeding seasons. The potential to regulate breeding season length depending on environmental conditions may entail a high resilience of the population reproductive patterns against environmental changes, as highlighted by the fact that almost all mature females were reproductive every year.
... Changes in reproductive life histories as a consequence of hunting have been documented in several vertebrate taxa. Such studies have shown that reduction in population size due to hunting (even in groups as disparate as teleosts, pinnipeds, and cetaceans) results in a decrease in average age of maturation Lockyer, 1972;Rijnsdorp, 1993;Trippel, 1995;Rochet, 1998;Festa-Bianchet, 2003, Gabriele et al., 2007. Likewise, increased fecundity has been documented in overhunted populations of teleost fish (Bagenal, 1966;Healey, 1978;Horwood and Howlett, 1986;Kelly and Stevenson, 1985), while birthing interval decreases in various iteroparous tetrapod species (Anderson and Burnham, 1976;Swihart et al., 1998;Gosselin et al., 2015). ...
Thesis
Full-text available
The end of the Pleistocene saw the extinction of many large vertebrate species, including mammoths (genus Mammuthus). Despite many decades of work by various researchers, the cause(s) of mammoth extinction are still heavily debated, with climate change and human hunting being the two primary hypothesized agents of extinction. One major problem with identifying the cause of this extinction is the fact that changing climates and movement of human hunters into ecosystems containing mammoths are both broadly associated with the time of extinction, making it difficult to decouple one potential cause from the other using only temporal data. This study bypasses the strictly chronological approach of many previous studies and instead investigates the cause of the end-Pleistocene extinction using information about reproductive life history. The age of first conception and the average time between conceptions are both expected to change predictably and divergently under the hypotheses of climate-driven extinction and hunting-driven extinction, so assessment of changes in these aspects of life history approaching the time of extinction could provide a test for cause of extinction. I use the record of growth within tusk dentin to identify patterns associated with reproductive life history in mammoths. Thin sections and serial isotope analyses document the periodicity of X-ray density features observed in microCT sections of tusks. These attenuation features form annually in both Columbian and woolly mammoths (Mammuthus columbi and Mammuthus primigenius, respectively), but form semiannually in a gomphothere from South America. MicroCT scans of entire tusks are employed to provide a record of multiple decades of growth for ten Siberian woolly mammoths. In eight of these specimens, all of them adult females, we observe a repeated 3- to 6-year-long cyclical pattern of regularly varying growth rate. This pattern was absent in both adult males and juveniles. We interpret this pattern as a record of calving in females, and its onset is observed in several individuals to occur at an age approximating that of sexual maturation in extant elephants. Our dataset shows a minor decrease in age of maturation and average calving interval near the end of the Pleistocene. This is predicted by a hunting-driven model of extinction but is not expected for extinction driven by climate change. This work contributes to our knowledge of the reproductive life history of mammoths, which we argue is key to understanding the cause of their extinction.
... While hunting was included in the analyses, we can only report on whether a species was hunted or not, and not the degree of hunting (particularly from private hunters). Removal of adult animals by hunters can significantly reduce both population size and growth rate (Festa-Bianchet, 2003). Several of the species in this study likely experienced some level of hunting pressure, given that many of these populations were introduced specifically for the purpose of recreational hunting (n = 28), whereas others were subsequently hunted as trophies (Bender et al., 2019;Bradshaw & Brook, 2007;Fuller et al., 2018). ...
Article
Full-text available
When introduced to new ecosystems, species' populations often grow immediately postrelease. Some introduced species, however, maintain a low population size for years or decades before sudden, rapid population growth is observed. Because exponential population growth always starts slowly, it can be difficult to distinguish species experiencing the early phases of slow exponential population growth (inherent lags) from those with actively delayed growth rates (prolonged lags). Introduced ungulates provide an excellent system in which to examine lags, because some introduced ungulate populations have demonstrated rapid population growth immediately postintroduction, while others have not. Using studies from the literature, we investigated which exotic ungulate species and populations (n = 36) showed prolonged population growth lags by comparing the doubling time of real ungulate populations to those predicted from exponential growth models for theoretical populations. Having identified the specific populations that displayed prolonged lags, we examined the impacts of several environmental and biological variables likely to influence the length of lag period. We found that seventeen populations (47%) showed significant prolonged population growth lags. We could not, however, determine the specific factors that contributed to the length of these lag phases, suggesting that these ungulate populations' growth is idiosyncratic and difficult to predict. Introduced species that exhibit delayed growth should be closely monitored by managers, who must be proactive in controlling their growth to minimize the impact such populations may have on their environment.
... For example, increasing anthropogenic stress from contaminants, noise, and conflicts with fisheries may exacerbate fitness costs to beluga whales (SLE). Certain harvesting strategies, such as selecting large size, can result in the evolution of life-history traits, and result in negative impacts on population demography (Festa-Bianchet 2003;Stockwell et al. 2003). Furthermore, contemporary evolution might reduce fitness through interactions between population size and strength of selection making most conservation efforts risky unless they are able to measure and account for changes in fitness (Fernandez and Caballero 2001). ...
Preprint
Identifying phenotypic characteristics of evolutionarily fit individuals provides important insight into the evolutionary processes that cause range shifts with climate warming. Female beluga whales (Delphinapterus leucas) from the Canadian high Arctic (BB) residing in the core region of the species’ geographic range are 14% larger than their conspecifics at the southern periphery in Hudson Bay (HB). We investigated the causal mechanism for this north (core)-south (periphery) difference as it relates to fitness by combining morphometric data with ovarian corpora counted in female reproductive tracts. We found evidence for reproductive senescence in older HB females from the southern peripheral population but not for BB whales. Female beluga whale fitness in the more-northern BB increased faster with age (48% partial variation explained) versus a more gradual slope (25%) in HB. In contrast, body length in HB female beluga accounted for five times more of the total variation in fitness compared to BB whales. We speculate that female HB beluga fitness was more strongly linked with body length due to higher density, as larger body size provides survival advantages during seasonal food limitations. Understanding the evolutionary mechanism of how fitness changes will assist conservation efforts in anticipating and mitigating future challenges to peripheral populations.
... Such undesigned selection is also occurring during domestication, causing changes in morphology, behavior, and physiology in many species (Campbell et al., 2015;He et al., 2014). In yet another analogue, hunting may change the structure of populations through a selection of individuals with certain phenotypic characteristics (Berger et al., 2001;Festa-Bianchet, 2003;Madden & Whiteside, 2014). During the first stages of a biological invasion, human-induced selection acting during uptake and continuation along the invasion pathway was therefore predicted to affect a range of traits (Briski et al., 2018;Carrete et al., 2012;Chapple et al., 2012) ...
Article
Full-text available
Biological invasion is a global problem with large negative impacts on ecosystems and human societies. When a species is introduced, individuals will first have to pass through the invasion stages of uptake and transport, before actual introduction in a non‐native range. Selection is predicted to act during these earliest stages of biological invasion, potentially influencing the invasiveness and/or impact of introduced populations. Despite this potential impact of pre‐introduction selection, empirical tests are virtually lacking. To test the hypothesis of pre‐introduction selection, we followed the fate of individuals during capture, initial acclimation, and captivity in two bird species with several invasive populations originating from the international trade in wild‐caught pets (the weavers Ploceus melanocephalus and Euplectes afer). We confirm that pre‐introduction selection acts on a wide range of physiological, morphological, behavioral and demographic traits (incl. sex, age, size of body/brain/bill, bill shape, body mass, corticosterone levels, and escape behavior); these are all traits which likely affect invasion success. Our study thus comprehensively demonstrates the existence of hitherto ignored selection acting before the actual introduction into non‐native ranges. This could ultimately change the composition and functioning of introduced populations, and therefore warrants greater attention. More knowledge on pre‐introduction selection also might provide novel targets for the management of invasive species, if pre‐introduction filters can be adjusted to change the quality and/or quantity of individuals passing through such that invasion probability and/or impacts are reduced.
Thesis
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Invasive species are a leading cause of biodiversity loss worldwide. Deer have been introduced to environments around the world, and many species have gone on to become invasive. Feral deer potentially compete with native species and livestock, pose risks to vehicles or by acting as vectors of disease, as well as contributing to economic and social losses. Presently there are six free-living deer species in Australia: chital (Axis axis), fallow (Dama dama), hog (Axis porcinus), red (Cervus elaphus), rusa (Rusa timorensis), and sambar (Rusa unicolor). Four chital deer were liberated on Maryvale Station in Northern Queensland in 1886 and since then, the number and range of chital deer has slowly increased. The factors that contributed to both the delayed growth as well as their sudden range and population increase are not known, such as how they select and use habitat as well as the cues that drive their reproduction. Considering the broad economic and environmental impact chital could have on this region, understanding their ecology is critical to developing more effective management and control strategies, as well as predicting where these feral species are likely to spread next.
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