Download Effects of Urbanization on the North American Cougar

Effects of Urbanization on the North American Cougar
Emily Wilkinson
Envs 190A
May 2016
Table of Contents
Abstract ...……………………………………………………………………………...…………3
Introduction
History……………………………….…………………………………….…..…….……4
Ecology………………………………………..…………………………….…..………...4
Stressors
Habitat Fragmentation……………………..…………………………………….……….6
Wildfire…………………..………………………...……………………………...………9
Rodenticides……………………………………………………....……………….………9
Threats to humans………………………………………………………….…….………10
Mitigation Efforts
Wildlife Crossings………………………………………….…………..……...…………11
Rodenticide Awareness……………………………….………………..…..………….…13
Wildfire Management…………………………….………………..………….....….……14
Policy…………………………………...…………………………...…………...………15
Conclusions and Recommendations……………………………..…………………………….15
Appendix…………………………..……………….……...………………………………...…..18
Sources Cited……………………………..……………….……...………………………….….21
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Abstract
North American Cougars (Puma concolor) are generalist predators that thrive in the wild
but, more recently, are survivors in the shadow of human development. As large predators,
cougars are perceived as game to hunters as well as a threat to humans, livestock, and companion
animals. When the American West underwent abrupt growth during the 19th century Gold Rush,
new settlers over-hunted wildlife, exploited watersheds, and declined cougars population. Today
roads, agriculture, housing developments, and increased wildfires all infringe on cougars’
traditional habitat, with effects including decreased genetic diversity, inability to disperse,
increased demand for depredation permits, increased vehicular strikes to wildlife, and non-target
rodenticide poisoning. In California, these carnivores are considered a recently protected species,
however further protections are needed to protect and preserve the cougars best interests as well
as the ecological biodiversity of the state.
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Introduction
History
Cougars native to the United States have been negatively affected by humans since the
mid-1850s. In the 19th century, westward expansion enabled settlers to immigrate to California.
Eventually gold was discovered at Sutter’s Mill, and the rate of human settlement increased from
92,594 to 379,994 in just 10 years (U.S. Census Bureau), along with profiteering from
California’s resources. For reasons of safety, cougars were shot on sight by miners, as well as
sheep herders to prevent loss of livestock. Deer populations declined due to the added demand
for their meat for food and hide for clothing. A repercussion from a depressed deer population
were cougars suffering from starvation (Beesley 2004). Mammals historically affected by human
settlement were cougars with reduced populations, the California grizzly extinction, and the state
eradication of the grey wolf. Since then, steps have been taken to protect cougars with the
California Wildlife Protection Act of 1990, which prohibit the hunting of cougars (UC Hastings
1996).
Ecology
Cougars fill a key niche as an apex predator in California. Through top-down controls,
cougars allow for increased abundance of mesopredators and plant species. When cougars prey
on herbivores, they decrease the chance of herbivore overpopulation that could potentially over
consume plants without predator regulation (Calcagno et al. 2011). Mesopredators are mid-sized
mammalian carnivores such as skunks, raccoons, and bobcats. Cougars positively influence
mesopredator behavior and abundance through outcompeting large carnivores such as coyotes
that prey on mesopredators (Wang et al. 2015). Cougars allow for increased biodiversity of
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plants and animals in their ecosystems through apex predator controls (Wang et al. 2015).
Biodiversity is measured by the sum of total species including plants and animals. The
importance of biodiversity in ecosystems goes beyond aesthetic and cultural appreciation.
Biodiversity serves as a tool for human economy, life-sustaining processes, agricultural
protection, material for bioengineering, flood control, and climate variation. To say that
biodiversity lacks value would be a serious misstatement and without cougars, the biodiversity in
certain regions of California may be at stake. A fundamental understanding in ecology is that the
smaller the island, the less species richness or biodiversity. Larger habitats allow for increased
species abundance with more niches fulfilled, so with smaller islands the chance of species
extinction is higher (Schlotterbeck 2003). Cougars are increasingly forced to live in smaller
fragmented habitats, along with other flora and fauna of the state. These lessened areas can be
compared to small islands because of the advancement of artificial borders causing
fragmentation, which leads to disconnectivity. Connectivity is the largest issue that faces the
future of cougar survival because it leads to a lowered genetic diversity in fragmented
populations due to increasing anthropogenic borders (Schlotterbeck 2003, Galetti and Dirzo
2013).
Cougars’ population dynamics are influenced heavily by their gender and chance to travel
to other populations. Cougars leave their natal areas before full maturity at approximately 10-33
months old. Male cubs mature later, disperse further distances, require a larger habitat (Sweanor
et al. 2000, Seidensticker et al 1973, and Beier 1995), and remain more independent than
females. Females are usually able to remain nearby their mother’s home range, filling smaller
vacant gaps in territory (Beier 1995). Gene flow improves population genetic diversity and when
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metapopulations are able to disperse to subpopulations, populations benefit from fresh gene
addition and can be more physically fit (Sweanor et al. 2000).
As generalist predators, cougars will make use of what prey is available. The behavioral
plasticity traits in cougars allows them to acclimate to changing conditions. Seasonal differences
such as prey migration are important to consider when studying these predators because cougars
will typically remain in their territory and consume smaller prey until their main prey returns
from seasonal migration (Elbroch et al 2013). Depending on their geographic location, cougars
dietary sources may differ but usually include large vertebrate such as deer or elk. In Northern
California’s Mendocino forest, kills by cougars include black tailed deer followed by other
vertebrates, and it has been found that cougars will even kill black bears that compete with them
for food (Allen et al 2015).
Stressors
Habitat Fragmentation
Habitat fragmentation occurs when a large, general habitat of a species becomes divided
into smaller disconnected populations by impassable borders. Fragmentation can occur naturally
over time with borders drawn by geographic constraints like rivers or deserts, but anthropogenic
borders are becoming more common. Urban areas fragment wildlife habitat through construction
of roads, golf courses, housing, agriculture fields, and shopping centers. Together and
individually, these additions to the land can have serious adverse effects on cougar survival.
Areas such as southern and central California expect large human population growth by 2060
(Dept. of Finance 2013), which means more infrastructure will be added to the land, further
fragmenting cougar habitat. Southern California appears to be the most affected by
fragmentation due to the highest human population settlements and major infrastructure. In
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central California, while cougars have a lower occupancy within exurban areas (Figure 1), they
tend to maintain a presence in areas bordering open habitat (Wang et al 2015). In areas affected
by fragmentation, cougars will use habitat corridors, golf courses, and freeways to disperse,
some of which are more dangerous than others. Cougars that disperse into unfamiliar habitat
avoid city lights, row crops, and orchards (Beier 1995).
A large effect of habitat fragmentation to cougars is death by motorists from roads within
urbanized settings. A study done in southern California by Vickers et al. (2015) confirmed that
the Santa Ana cougar population, which is within a more urbanized setting, has a significantly
higher rate of vehicular strikes versus the Eastern Peninsular Range population. These
populations are divided by highway 15 (Figure 2) and scientists argue that both populations are
threatened due to their less than 60% survival rate, compared to the Santa Monica Mountains
population survival rate of over 70%. Roads also affect cougars by changing their traveling
methods. Cougars in southern California move around more in riparian, chaparral, and scrub
areas over urbanized location, generally avoiding human built features such as paved roads, dirt
roads, and urban vegetation (Dickson et al. 2005).
Agriculture, specifically vineyards in Sonoma County, are known to infringe on cougar
habitat along with their traveling methods. Cougars avoid vineyards and prefer to travel in creek
riparian areas where they can feel secure with concealment provided by trees and vegetation.
There is also a link to increased abundance of cougars in wider riparian zones versus riparian
zones that are diminished and unpreserved surrounding agricultural areas. Along with cougars,
other native mammals are eleven times more likely to be traveling in riparian habitat, making
riparian zones the overall preferred landscape when areas are fragmented by agricultural vines to
produce wine (Figure 3). With native species showing an intolerance towards agriculture, non-
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native species are filling the niche, and have become more predictable inside of vineyards (Hilty
and Merenlender 2004).
Habitat fragmentation also has adverse effects on cougar reproduction along with gender
differences in proximity to anthropogenic settings. Cougars displaying reproductive behavior
require a larger land buffer from human development than cougars not exhibiting reproductive
behavior due to required chemical and auditory communication between potential mates. While
cougars in whole tend to avoid homes, there is a clear gender difference in house avoidance
behavior with males being more likely to avoid houses than females. This can be attributed to the
fact that females with cubs are more likely to be dependent on consistent prey populations found
in human settings, while males have the option to travel further distances and wait for their food
(Wilmers et al 2013). When habitat fragmentation infringes on chemical and auditory signals
between potential mates, they may struggle to find members of the opposite sex due in part to
differing proximity to humans with males further in distance and females closer.
Another effect of habitat fragmentation is lower genetic diversity due to isolation from
other populations. Dispersal is an important factor in population ecology, and without the ability
to spread DNA to other populations, gene pools become more allele limited. The cougar
population in the Santa Ana Mountains has been studied since the 1980s, and has been noted to
have a population with the lowest genetic diversity in California due to genetic isolation (Figure
4). The Santa Ana population also shows evidence of a population bottleneck which means that
their population diversity is limited. Statistical analysis shows that relatedness in the Santa Ana
population is significantly higher (p = 5.8×10−6) than the population in the eastern Peninsular
Range (Table 1, Ernest et al. 2014). Implications of this data are that there are more cases of
inbreeding among the cougar populations causing genetic relatedness, especially in the Santa
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Ana Mountains. This may be attributed to barriers preventing dispersal and resulting in
fragmentation.
Wildfire
With increased fire events, cougar habitat and prey are negatively affected as the land
burns more frequently, decreasing opportunity for ecological succession. Anthropogenic
practices including habitat fragmentation have led to a catch 22 wildfire problem in California,
which has been attributed to an increase in urbanization and human behavior. On one hand,
wildfire suppression in California has prevented natural ecological disruptions which in turn has
led to plant overgrowth. On the other, an increase in large and more intense fires in part due to
climate change has become a common pattern. Fire suppression increases fuels for these fires,
and many of these fires can be tied to spatial distribution and density of human development,
climate change, and human caused ignitions (Jennings et al 2016). Increased vegetation from fire
suppression impedes cougar movement and ability to hunt while in other areas increased
wildfires as a result of climate change prevents cougar habitat from rebounding.
Rodenticides
Another large threat to cougar survivorship is rodenticide use in urbanized areas.
Carnivores living in California are indirectly exposed to these toxicants through predation of the
targeted rodent. This is an unintended result of residents in households poisoning pests, and also
from farmers in agricultural areas trying to keep out rodents. Cougars that may come across the
poison, or more commonly eat the poisoned rodent suffer from the toxicants in their systems.
Some effects of exposure are mange, mites, anticoagulant toxicity, and death. Anticoagulant
toxicants were found in cougar livers within the Santa Monica Mountains, Simi Hills, and Santa
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Susana Mountains, which are all areas of large human populations. In deceased cougars,
bromadiolone and brodifacoum were present. Cougars found with severe notoedric mange also
had anticoagulants present in their systems. The toxicants found in the livers of cougars are
commonly used for pest control for golf courses, water plants, office parks, and by private
homeowners (Riley et al. 2007).
Threats to humans
With an increasing human population in California, cougar encounters are becoming
more common. In California a total of three verified fatal and twelve verified non-fatal cougar
attacks on humans occurred from 1986 to 2014; more commonly in southern California (CDFW
2016). Public attitudes toward cougars are that they are a danger toward children, the elderly,
companion animals, and livestock (Campbell and Lancaster 2010).
Cougars have been documented to stalk and grab children by their throats, then run off
with them. Seventy percent of fatal attacks on humans have been on children, with British
Columbia, Colorado, California, and Texas having the most events. Cougars will usually strike
the head and neck region first, usually when a young child is unsupervised. Severe and even fatal
injuries include lacerations, clogged vessels leading to stroke, infection, and rabies. Common
attempts to deter an attack are to maintain eye contact, yell, get big, and play dead. The worst
thing to do is to run away because cougars are very fast, and will recognize this as a reaction of
prey (Kadesky et al 1998).
While it is illegal to kill cougars in the state of California, depredation permits are
available to kill cougars that are considered a threat to humans, to livestock, or have caused
damage to property (CDFW 2014). This has been an attempt to combat cougars that infringe on
human comfort, while maintaining their protection status in California.
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Mitigation
Wildlife Crossings
Wildlife crossings and habitat corridors are intended to mitigate animal deaths by
motorists and re-connect populations (Gloyne and Clevenger 2001). With the implementation of
wildlife crossings, connectivity between fragmented populations can be accomplished, which
will boost biodiversity and the possibility for cougars to disperse. Habitat corridors were an idea
by ecologists Wilson and Willis in the 1970s. Since then, many projects have been created
(Thwaites 1998).
Cougar specific wildlife crossings lack scientific studies, therefore it is relevant to look to
other cases. A classic example is the Pygmy possum in Australia. The sexes of this species live
at two different altitudes on a mountain that has been separated by a ski resort road. When male
pygmy possums were ready to migrate, they were unable to due to the road barrier, and then
competed with females for food to which females lost, resulting in a declining female population.
This problem was solved when a rock tunnel was constructed in order to allow for males to pass
the road safely and securely. The female population showed positive results, and increased,
resolving the problem of food competition (Thwaites 1998). While this was an example of a
smaller mammal resolution, the same concepts apply to large mammals affected by roads and the
problem of impassable barriers that cause negative effects. In areas that have major highways
fragmenting cougar dispersal, a similar method of providing safe passage to cougars may be
beneficial to restoring a fractured genetic population.
Perhaps a better, large scale example of wildlife crossings is in Canada, where crossings
are used frequently by ursids. The crossings available are overpasses, underpasses, and open11
span underpasses. The type of crossings utilized by ursids differs between each species, with
black bears using each type due to their generalist behavior, and grizzly bears using larger, wideopen crossings (Sawaya et al 2013). This can be a useful study to a potential wildlife crossing
project for cougars in southern California. When looking at similar species that will be using a
crossing, it it important to build a relevant path that will fit their behavior. While cougars are
generalists and may already use smaller crossings, a large crossing might be beneficial to
cougars as well as other species in their habitat such as prey.
With low connectivity between habitats in northern California due to agricultural
vineyards impeding cougar travel, it is important to look to riparian conservation and restoration
to ensure cougar dispersal in the future. Features such as trees offering cover, and increased
native vegetation that can be food sources to cougar prey in wide riparian corridors, may aide in
cougar dispersal (Hilty and Merenlender 2004). Underpasses and drainage culverts already in
place are being used by mammals to cross roads. While these were intended for purposes such as
flood control, it has been observed that certain carnivorous mammals, including an occasional
cougar, use these to travel and disperse (Ng et al 2004). Road fencing along major highways can
prevent wildlife collisions with motorists; however, fencing increases the barrier effect and
prevents wildlife from dispersing. An analysis of car frequency, wildlife strikes, and animal
avoidance must be looked at to determine whether or not fencing should be constructed (Jaeger
and Fahrig 2004).
Wildlife crossings can be small or large projects and may end up being very costly. With
the risk of building major crossings that may not be utilized by mammals, it is an obvious case to
have construction management plan with biologists and geographers on the best areas to
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implement a structure or put money into restoration in a given location to increase the chance for
the highest connectivity.
There are many different approaches to re-connecting wildlife through the use of models
representing habitat corridors: Least cost path (LCP), least cost corridor (LCC), circuit theory,
and graph theory. LCP and LCC use models to determine the path of least resistance between the
starting point to the destination. They are known as least cost, because to the organism it reflects
the lowest ecological cost of traveling from point A to point B, and rarely ever reflects a straight
course. The difference between the two is “pixilation.” LCP will be one pixel wide, while LCC
may be several pixels wide, reflecting more options for course traveling. These approaches both
have room for features such as resource availability, habitat, expert opinion, and step selections
known as weighting schemes (Figure 5). These models will look different, and vary in size
depending on the species of concern. While it is more likely to have connection within shorter
distances, long distance travel may be needed to restore key populations. Finding least cost paths
can be the economic approach to enticing private and public land participation (Parks et al,
2013).
Graph-theoretic representation using Delaunay triangulation (DT) to determine habitat
connectivity may be the most accurate method to predict where cougars will most likely cross
barriers (Figure 6). By using geographic prediction models, biologists can create most likely
scenarios for crossings related to following auditory mating calls, moving to a new habitat patch
without many suitable patches between, and distance from a home range. These are important to
consider when creating prediction models, because animals responding to different situations
react and travel differently in the moment (Downs and Horner 2012).
Rodenticide Awareness
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Some opportunity for mitigation effort could be increased public awareness of how
rodenticides can contribute to negative health and death of felids (as well as other carnivores). In
areas where cougars are more affected, tighter regulations may be important to protecting their
wellbeing (Riley et al. 2007). With increased awareness about anticoagulants effect on cougars,
encouragement to use alternative replacements must occur. A study by Donlan et al. in 2003
confirmed that alternatives such as diphacinone and cholecalciferol are effective at removing
rodents and not causing secondary poisonings to non-target carnivores. Alternative rodenticides
to anticoagulants lack much research, and anticoagulants are still considered to be the most
effective on the market. Secondary non-target poisoning is a problem for cougars as well as other
carnivores, and future rodenticide research must focus on anticoagulant alternatives to mitigate
non-target species poisoning.
Wildfire Management
While cougars have adapted to natural disturbances, further action is needed to protect
them, and to address increased wildfire incidents along with intensity due to humans (Jennings et
al 2016). Climate change is altering the meteorological and hydrological dynamics of the state of
California and further research is needed to address wildfire mitigation efforts. Increased fires
reduce the ability for cougar habitat to recover, and water shortages have made it hard for
firefighters to combat wildfires. While the present and ongoing drought has exacerbated water
availability, alternative sources to combat fire destruction may include chemicals and dirt. Future
urban construction planning will need to take into account the state’s dilemma, and perhaps not
encourage urban sprawl that infringes on cougar populations nor campfire legality in dry regions
of the state.
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Policy
Cougars were fully protected by the state of California from 1972-1986, however in 1986
they were no longer protected by law and classified once more as game for hunters. California
residents were so upset by the news that they sued California Fish and Game (CFG); now known
as California Department of Fish and Wildlife (CDFW). CDFW was sued for being out of
compliance with California Environmental Quality Act (CEQA) in their documents. Proposition
117 passed in 1990 for California, making cougars a specially protected animal, and therefore
illegal to hunt (Koch 1994) without a depredation permit.
The California Environmental Quality Act (CEQA) currently provides ecosystems and
species with habitat protection. When new projects are proposed for instance, environmental
impacts are to be stated and mitigation or project alternatives are to be found if there is no
negative declaration; however, this is not enough. CEQA needs to encourage wildlife corridors
so as to prevent ecosystem decay and promote biodiversity. While there are protected habitats
and land for species to live on, they are unable to connect with outside populations to improve
genetic diversity. Arguments against habitat corridors are: the increased ability for diseases to
spread, wildfire chances are increased, the dispersal of parasites, and high costs. However, while
there is an increased risk of those happening, the benefit to biodiversity would outweigh the
negatives in many biologist’s opinions (Schlotterbeck J. 2003).
Conclusions and Recommendations
Human population growth and increasing urbanization in California will become more
apparent threats to wildlife, specifically the North American Cougar, in the future with increased
15
attacks due to habitat loss and fragmentation. With so many negative effects already inflicted on
cougars from urbanization, it is the responsibility of California residents to implement mitigation
and vote on policy to protect to native wildlife. Cougar populations in southern California have
been studied and determined to be threatened on the basis of their low survival rates (Vickers et
al. 2015). Habitat fragmentation not only threatens connectivity, but decreases genetic diversity
and biodiversity within ecosystems. Ecological structure depends on top down controls just as
much as bottom up controls, and the loss of cougars potential as an apex predator may prove
detrimental to what native life remains in California.
With so much evidence of negative effects to cougars by human infrastructure,
atmospheric pollution causing climate change, and rodenticides secondary effects to non-target
species, further growth in California must acknowledge cougars needs to disperse and reflect
positively on the niche they fill rather than presenting cougars largely as a threat to humans.
While threats to children are very serious and real, proper education and awareness can prevent
many instances of attack. Human developments that divide cougar populations should be advised
that their presence and daily activities including use of rodenticides can have negative effects on
wildlife. Educational signs in cougar habitat for human awareness and safety will increase
knowledge on proper behavior in response to cougar confrontation, minimizing the chance of
attacks. Future conservation plans have potential to orient around urban sprawl and incorporate
corridors while providing cougars with vegetation to hide in to disperse and expand their genetic
diversity.
Requiring state legislation to include habitat corridors as mitigation may prove beneficial
to reduce human and cougar conflict, as well as cougars’ inability to disperse. With specific
areas laid out as conservation for cougar, their future genetic pools can become more diverse
16
while also providing them with a safe passage that is not a person’s backyard, preventing many
instances of conflict. Cost-effective methods can be utilized and increasing the chance that a
corridor will be used is available through geographic technology and biologist’s knowledge.
Positive change can happen in California, and it is up to residents, scientists, engineers, and
politicians to pursue future alternatives that include wildlife’s best interests.
17
Appendix
Figure 1. Map of the Santa Cruz Mountains in central California, with urban developed areas in
dark gray. Highway 17 is the main connection for cars from San Jose to Santa Cruz (Wang et al
2015).
Figure 2. Map of southern California’s mountain ranges, including major highways and cities.
(Vickers et al 2015).
18
Figure 3. Map of a section of Sonoma County in northern California showing riparian habitat
corridors in respect to edge habitat and vineyards (Hilty and Merenlender 2004).
Figure 4. Mean population relatedness of California cougars by geographic region with
confidence intervals in blue. Expected range of unrelatedness in red (Ernest et al 2014).
19
Figure 5. Different connectivity routes based off weighing schemes by percentile (Parks et al,
2013).
Figure 6. A delaunay triangulation (DT) using Graph-theoretic representation of habitat
connectivity (Downs and Horner 2012).
Table 1. Statistic summary on genetic relatedness of California cougars by geographic region
with abbreviations listed below (Ernest et al 2014).
20
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