BLeaflet | Issues 1 - 7

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What is a keystone species? Predators, ecosystem engineers and mutualists are the three types of keystone species. They are organisms that help to maintain balance and diversity in a complex ecosystem. Keystone species enable other species to survive, occupying a key role in the ecosystem they are part of and without them, their ecosystem would be dramatically different or could cease to exist. A keystone species can be an animal, plant or microorganism. For example, coral is instrumental in creating diverse reef ecosystems. Another example would be the sea otter. Sea otters eat sea urchins which prevents them from overbreeding. Kelp forests, which sustain a variety of other species, would be severely depleted without the sea otter since sea urchins feed on kelp. Beavers are considered “ecosystem engineers” and are a keystone species responsible for maintaining or producing distinct habitats by removing dead trees along riverbanks and creating dams that divert water creating wetland habitats. Bees and flowers are considered an example of mutualistic relationships. Flowers provide bees with food, and bees provide flowering plants with the means to reproduce.

POLAR BEARS: Keystone Species

As you may well know, polar bears are the largest bears in the world, considered the largest terrestrial carnivores on earth and are the Arctic’s top predator. Ursus maritimus (literally translated as “Sea Bear”) spend most of their lives in and around the ocean, predominantly on sea ice. Over half of a polar bear’s life is spent actively hunting for food, consisting almost entirely of seal species. Polar bears are currently listed as vulnerable to extinction by the International Union for Conservation of Nature (IUCN). It is estimated that there are approximately 26,000 polar bears living in the wild (predominantly across countries that border the Arctic Ocean), however, polar bear populations may rapidly decline soon. An assessment involving sea ice and sub-population data, along with computer simulation and statistical models conducted by the IUCN revealed that populations could decrease more than 30% by 2050, with loss of sea ice as a leading culprit. So why are potential polar bear population declines worth noting? Polar bears are considered a keystone species for the Arctic ecosystem. A keystone species

is a species that helps define the health of an entire ecosystem, and generally consists of animals with a significant influence on food webs. A large decline in Ursus maritimus populations may initiate a top-down trophic cascade, similar to that of the removal of gray wolves in Yellowstone National Park. In the late 19th century, the U.S. government designated land for Yellowstone National Park and hundreds of wolves roamed the park feeding on herds of bison and elk. Government agencies worked to eradicate wolves in the park area out of fear of impacts to elk, bison, and livestock. With no apex predator, elk populations rapidly increased, quickly leading to overgrazing of grasses, sedges, and reeds which ultimately yielded drastic changes in species populations and the ecosystem. It created intense pressure on the animals dependent on plant life such as fish, beavers and birds. Wolves also indirectly feed eagles, coyotes, and bears who scavenge leftover carcasses. The wolves’ story provides a warning of the potential impact of a significant decline in polar bear populations across the entire Arctic ecosystem and to ecosystems and food sources beyond.

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