Monkeys groom in Sanjay Gandhi National Park.Richard T. Nowitz/Corbis

Expanding cities can swallow biodiversity hotspots and other important protected natural areas. The resulting conflicts can prove fatal for both humans and wildlife.

Defining boundaries between human homes and wildlife habitats presents a serious challenge when conservation areas intertwine with cities, Charles Nilon, professor of urban wildlife management at the University of Missouri, told Discovery News. Nilon provided eight examples of places where parks and people cohabitate.

Sanjay Gandi National Park and Mumbai

Mumbai, India's most populous city, sprang up around Sanjay Gandhi National Park's 40 square miles (104 square kilometers). Many squatter settlements fringe the park. These communities often lack proper latrines and running water, so residents may go into the forest to relieve themselves. These trips into the forest can prove deadly. Between 1986 and 2010, leopards caused 92 deaths in the park and its outskirts, according to Mumbaikars for SGNP, a park supporters' organization.

Garbage-eating feral dogs also attract leopards into the settlements around the park, reported the Times of India. The dense population of dogs makes easy prey for the big cats, compared to the park's fleet-footed chital deer.

A giraffe wanders through Nairobi National Park. Mkimemia, Wikimedia Commons

Only 4 miles (7 kilometers) from Nairobi's center, Nairobi National Park hosts the full array of East African wildlife, including elephants, African buffalo, lions, leopards, rhinos, and giraffes.

Electric fences help keep the animals in the park and reduce conflicts with citizens of Nairobi, but can't stop poachers. In August, poachers killed a white rhino in the park, reported the BBC, marking the first poaching incident within the park's boundaries in six years.

Fences may not stop poachers, but they do restrict wildlife movement. Historically, the herds of herbivores in Nairobi National Park migrated to grasslands further south as seasonal rains caused an explosion of green. However, expansion of the city threatens to cut off their migration route.

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Alligators roam through the Everglades National Park. Willisis2, Wikimedia Commons

Everglades National Park forms the southern fifth of a vast wetland ecosystem that runs from Orlando to south of Miami. Over the past century, the area has been under siege by humans.

In 1920, only 30,000 people lived in Miami, according to U.S. Census statistics. By 1950, the population exploded to 250,000. The building boom, along with sugarcane plantations, destroyed fragile Everglades habitats and damaged the wilderness that remained.

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Even the decorative plants and pets brought by the human newcomers proved to be disastrous for the Everglades. For example, Burmese pythons now slither among Australian melaleuca trees there. The invading pythons compete with native alligators for the title of top predator in the Everglades, while dense stands of melaleuca trees out-compete native plants and suck the wetlands dry.

The Miami metropolitan area now holds more than 5.5 million people, according to the U.S. Census. Floridians and wildlife conflict when animals move back into areas devoured by urban sprawl, exemplified by alligators on golf courses (shown here).

Christ the Redeemer statue overlooking Rio de JaneiroMike Theiss/Corbis

The famous statue of Cristo Redentor stands atop a peak in the Tijuca forest in the heart of Rio de Janeiro. Tijuca Forest National Park preserves more than 12.4 square miles (32 square kilometers) of forest from the constantly growing city. The park protects some of the last remnants of Atlantic rainforest in the world.

In the 18th and 19th centuries, Tijuca suffered heavy deforestation by sugar and coffee plantations, which resulted in the destruction of Rio's fresh water supply. In 1861, the Brazilian government tasked Major Manuel Gomes Archer with replanting the area, resulting in the park of today.

Rio will host the World Cup in 2014 and then the Olympics in 2016. Many of the events will be held in Barra da Tijuca, a residential area near the forest. Construction in that residential area raises environmental concerns for some. A study in the journal Sustainability stated that construction of Olympic venues will increase strains on Tijuca Forest's environment.

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A biologist from the National Park Service holds one of the cougar kittens born in 2012.National Park Service

Like Rio and Mumbai, Los Angeles also swallowed a wilderness area. The Santa Monica Mountains National Recreation Area provides a barrier between downtown L.A. and the suburbs of the San Fernando Valley. But the highways and habitats of humans also serve as a barrier to animals trying to migrate into the mountains from the rest of the California wilderness.

An isolated population of mountain lions, also called cougars or pumas, live in the Santa Monica Mountains, according to the National Park Service. The lions of L.A. face threats from poaching, vehicle collisions and competition with each other. Male mountain lions need approximately 200 square miles of territory, so the limited size of the Santa Monica area forces them into deadly competition with each other for space.

The National Park Service currently monitors seven lions in the Santa Monica zone. Last year, two kittens were born in the mountains, but genetic testing suggests the animals in the isolated area may suffer from inbreeding. "Unfortunately, the amount of habitat is not sufficient to support a viable population long-term and when new animals like these are born, especially young males, they run into freeways and development when they try to disperse,” said Seth Riley, a wildlife expert with the National Park Service in a press release.

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Lake Tahoe is America's largest Alpine lake. Ville Miettinen, Wikimedia Commons

The environment around America's largest Alpine lake has been degraded by construction and development to serve the tourist industry. More than two million visitors per year results in serious air pollution around the lake, according to a study in Atmospheric Environment. One air pollutant, road dust, contributes to the increasing murkiness of Lake Tahoe.

Humans completely altered the ecosystem of the lake. As in the Everglades, invasive species re-wrote the role call of animals in the region. In particular, salmon dominated Lake Tahoe after being introduced in 1941. The salmon were brought to the lake from the Pacific Ocean to provide recreational fishing.

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Indiana Dunes National Lakeshore with Chicago skyline in the distance.J. Crocker, Wikimedia Commons

Efforts started in the 1890s to save a portion of Lake Michigan's shore from development. However, by 1966, when Congress officially designated the Indiana Dunes National Lakeshore, as a wildlife preserve, the region had already been logged and polluted by coal power plants and steal mills in nearby Chicago and Gary, Ind.

The National Park Service has worked over the decades to fight invasive species and restore native ecosystems. For example, controlled burns of vegetation help native plants to reestablish themselves. The area now provides habitat for endangered species, such as the Indiana bat (Myotis sodalis), amidst the rust belt decay of Gary, Ind.

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Tina, a rehabilitated loggerhead sea turtle bolts for the open gulf after being released on Clearwater Beach.Jim Damaske/Corbis

Coastal habitats lure both humans and other animals. A National Oceanic and Atmospheric Administration report found that in the contiguous United States, coasts account for only 10 percent of the land area, yet hold 39 percent of the population. The 123.3 million people living along U.S. coastlines put heavy pressure on beach ecosystems and the animals that depend on them.

For example, the lights from coastal cities, such as Pensacola, Fla., disorient sea turtles nesting in the Gulf Islands National Seashore. After nesting, mother turtles use the light of the moon reflecting off the ocean to guide them back to the water, as do their hatchlings. When urban lights overpower the ocean, the turtles go inland and die of dehydration or are killed by dogs, humans, automobiles, or other threats. Dogs, cats and humans also threaten baby turtles.

In the Gulf Islands National Seashore, sea turtle nests are marked and protected by National Park Service workers. After BP's Deepwater Horizon oil disaster, many sea turtle eggs and hatchlings were evacuated to the Atlantic coast of Florida.