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Eastern
wolf (Canis Lycaon) photographed at Brule Lake
in Algonquin Provincial Park. Photograph
by Michael Runtz.
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Abstract
"Despite ethical arguments against lethal
control of wildlife populations, culling is routinely used for the management
of predators, invasive or pest species, and infectious diseases. Here,we demonstrate that culling
ofwildlife can have unforeseen impacts that can be detrimental to future
conservation efforts. Specifically, we analyzed genetic data from eastern
wolves (Canis lycaon) sampled in Algonquin Provincial Park (APP), Ontario,
Canada from 1964 to 2007. Research culls in 1964 and 1965 killed the majority
of wolves within a study region of APP, accounting for approximately 36% of the
park’s wolf population at a time when coyotes were colonizing the region. The
culls were followed by a significant decrease in an eastern wolf mitochondrial
DNA (mtDNA) haplotype (C1) in the Park’s wolf population, as well as an
increase in coyote mitochondrial and nuclear DNA. The introgression of
nuclearDNA from coyotes, however, appears to have been curtailed by legislation
that extended wolf protection outside park boundaries in 2001, although eastern
wolf mtDNA haplotype C1 continued to decline and is now rare within the park population.
We conclude that the wolf culls transformed the genetic composition of this
unique eastern wolf population by facilitating coyote introgression. These results
demonstrate that intense localized harvest of a seemingly abundant species can
lead to unexpected hybridization events that encumber future conservation efforts.
Ultimately, researchers need to contemplate not only the ethics of research methods,
but also that future implications may be obscured by gaps in our current scientific
understanding."
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| Map of Ontario, Canada. Dark gray area is Algonquin ProvincialPark (APP) where samples were collected for this study over a 43-year period. Other samples used in this study include gray wolf–eastern wolf hybrid animals from northeastern Ontario (NEON; checkered oval) and coyote–eastern wolf hybrid animals from south of APP Park along the Frontenac Axis (FRAX; gray oval). |
Introduction
"[…] In recent years, the impact of human-caused
mortality on the genetic composition of populations has received much attention
because exploitation fosters evolutionary alterations that may increase the
risk of extinction, induce rapid evolution of life-history traits, increase
hybridization, and impact behavioral dynamics in kin-based social groups. There
is little doubt that intense harvest, especially over long time periods,
results in genetic alterations that can be detrimental to populations and
ecosystems. […] Molecular genetic monitoring of populations over time is a
powerful approach to facilitate an understanding of genetic changes in
populations impacted by harvesting, particularly for small populations of
threatened species. Interpreting genetic
data within the context of demographic history is also critical to accurately
explain genetic change. Wolves across North America have been subjected to
intense eradication efforts that have limited their genetic variability and
evolutionary potential, promoted coyote (C. latrans) expansion eastward, and
increased coyote hybridization with eastern wolves (C. lycaon) and red wolves
(C. rufus). [..] Unlike gray wolves in the west, eastern wolves readily
hybridize with coyotes, and it has been suggested that high mortality of APP
wolves could lead to gene swamping by coyotes that are ill-suited to occupy the
niche of an apex predator and exert substantial top–down limitation of large
ungulate prey species (i.e., deer and moose) due to their small size. If
intense harvesting of eastern wolves in APP results in increased hybridization
with neighboring coyote populations, trophic interactions may be decoupled or
otherwise altered. There has also been some suggestion that disruption to pack
social structure associated with harvest pressure and breeder loss could
increase eastern wolf hybridization with coyotes when harvest occurs during breeding
season.
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Assumed model
of population and demographic history for eastern wolves and coyotes in eastern
North America.
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[…] Although wolves in APP, Ontario Canada (Fig. 2) are amorphologically
and genetically differentiated group of approximately 200–300 eastern wolves
that share a common evolutionary lineage with coyotes and red wolves, prior to
the year 2000, they were thought to be a gray wolf subspecies (C. lupus lycaon)
that at the time was abundant across Ontario. Within the park, wolves have
survived a long history of control efforts dating back to the park’s
establishment in 1893. […]Although wolf harvest in the first half of the 20th
century presumably impacted the population size and altered the original
genetic makeup of wolves within the park, the timing of the research culls in
the mid-1960s is important because it occurred at a time when coyotes were
becoming well established in the area. Prior to the 1960s, introgression from
coyotes may have occurred, but was likely limited because the first coyote
confirmed in southern Ontario was recorded in Thedford, Lambton County in
1919 and densities near APP would have
been relatively low until the beginning of the 1960s when coyote populations expanded
rapidly north, east, and south in response to new habitat made available
through land clearing and wolf extirpation. […] To explore the long-term impacts
that wildlife culls can have on conservation, we analyzed genetic data acquired
from eastern wolf samples collected in APP over a 43-year period (1964–2007),
and interpreted genetic changes within the context of wolf and coyote
demographic history in and around APP. Ultimately, this research demonstrates
that although intense localized killing of an apparently abundant species may
seem innocuous under the accepted scientific framework of the time, it may have
lasting, and unforeseen, conservation implications. […]
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Number of Canis clusters inferred from six
autosomal microsatellites. Top figure shows mean log probability of the data (dashed
line) and the second-order change of the likelihood function ([1]K)
(solid line) as a means of inferring the number of clusters in the data. Arrows
indicate “population” divisions, APP = Algonquin Provincial Park. At K = 2, the
major division between Old World evolved animals (gray wolves) and New World evolved
animals (eastern wolves and coyotes) occurs. At K = 3, eastern coyotes separate
and APP animals from all three time periods cluster together. K = 4 hints at a
division within Algonquin animals, but this division is difficult to interpret
biologically and should be treated with caution. Overall, K = 3 is the most
likely number of clusters.
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Simulations
Coalescent simulations generate the genomes of
individuals, moving backwards in time, under a defined demographic scenario
with the assumption that the coalescent process for neutral markers will be
determined by the population and demographic history. Using coalescent simulations,
one can determine the distribution of genetic summary statistics under a given
demographic scenario and determine if the observed data fall within or outside
of the expected distribution. […]
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Proportional
representation of wolves in APP in the three different time periods assigned in
Structure as (A) Algonquin Provincial Park (APP; Q ≥ 0.8 to APP); (B)
influenced by hybridization with eastern coyotes from Frontenac Axis (APP-FRAX;
0.8 ≥ Q ≥ 0.2 to FRAX); (C) strongly assigned to FRAX (FRAX; Q ≥ 0.8 to FRAX);
(D) influenced by hybridization with gray wolf–eastern wolf hybrids from
northeastern Ontario (APP-NEON; 0.8 ≥ Q ≥ 0.2 to NEON); (E) assigned with Q ≥
0.2 to all three populations (APP-NEON-FRAX). HH64–65 = Historic Harvested
samples collected between 1964 and 1965; CH87–99 = Contemporary Harvested
samples collected between 1987 and 1999; CP = Contemporary Protected sampled
collected between 2002 and 2007.
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Discussion
[…] Killing of wolves during the mid-1960s in
APP appears to have influenced the genetic composition of the Park’s wolf population.
Although researchers at the time could not have predicted these outcomes, it
seems likely that extensive culling of wolves prompted the few remaining wolves
in the Park to mate with individuals from the expanding coyote population. The
subsequent decline of an eastern wolf mtDNA haplotype and introgression of
coyote mitochondrial and nuclear DNA correlates well with the demographic
history of the two species, and coalescent simulations suggest these outcomes
were unlikely in the absence of harvest pressure. […]
[…] Above all, our results demonstrate that
intense localized harvesting of species thought to be numerous and widespread can
have unexpected outcomes that threaten conservation of species and naturally
functioning ecosystems. The advanced molecular genetic techniques now used for
studying wildlife populations were unheard of in the 1960s and no one could have
predicted the impacts that such an experimental design could have on a
population. Although the research methods used in the 1960s would fail to meet
current ethical guidelines, targeted culling is still common practice for
managing wildlife under various scenarios. For example, lethal control of gray
wolves (C. lupus) is currently used to increase the size of ungulate
populations in Alaska, USA, and in Alberta, Canada where both total wolf
harvest and areas of intense harvest (>45 wolves/1000 km2) have increased over
the past 22 years. Similarly, lethal methods are routinely used for coyote
control, with intense “spatially clumped” harvest suggested as more effective
than random removal across a broad spatial scale. Coyotes are generally
regarded as vermin, and wolves are often perceived as a major threat to ungulate
populations; both of these view points were similarly applied toward wolves in
APP prior to 1965.
Our results suggest the potential for
ecological assumptions to be incomplete and that culling and other seemingly harmless,
invasive methods, even when applied to abundant “pest” species, may have
unexpected, lasting conservation implications. Whether for the purpose of game
species management, protection of endemics, population size estimates, or
collecting basic ecological knowledge, exploring nonlethal alternatives could
minimize unanticipated impacts to animal populations and thus reduce the burden
on wildlife managers. By following guidelines and principles of ecological ethics
as outlined by a growing number of scientists, sampling methods are less likely
to result in unanticipated negative impacts. In this way, we can avoid leaving
behind a legacy of complications for future conservation biologists and
wildlife managers.
