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Polar bear - example of keystone species and apex predator

Updated: Mar 19

Why don't we want polar bears to go extinct?

We don't want to be heartbroken; besides that, polar bears are the apex predator and keystone species in the Arctic and are significant to the ecosystem's health. As a keystone species, the polar bear's health is an indicator of the Arctic ecosystem's well being.

What is a keystone species?

Zoologist Robert T. Paine first introduced the concept of keystone species in 1969. It was defined as "a species that has a disproportionately large effect on its environment relative to its abundance." We understand that all species are important, but some are unequally more critical than others in maintaining the ecosystem's balance, although they are smaller in numbers, total biomass, and productivity.

The keystone species help to maintain the types and numbers of other species in the eco-community. Once the keystone species is removed from the habitat, the ecosystem may dramatically change or collapse.

Scientists identify different categories of how keystone species work to maintain the eco-structure; some of the common types are:

  1. Predators: they prevent the overpopulation of its prey.

  2. Engineers: they build, change, or break down the habitats, to maintain it for themselves and other species.

  3. Mutualists: cooperating with another species in a beneficial way to each other.

  4. Competitors: they compete for resources with other species to maintain eco-balance.

What is an apex predator?

An apex predator is the one on top of the food chain with no natural predator. Apex predators are critical to the ecosystems. They regulate the number of their prey and other small predators in top-down control, influencing disease spread, and maintaining biodiversity.

The removal or addition of apex predators, which leads to a drastic shift of ecosystem structure, is named top-down trophic cascades. Top-down trophic cascades change the prey and predators' relationship down the food webs and lead to a significant change in different species' populations and the ecosystem's nutrient cycle. The effect of shifting in the abundance of species can extend to the food chain's primary producers (autotrophs).

Primary producers turn simple substances such as carbon dioxide and light into complex compounds such as carbon, e.g., plants and algae. The inter-relationships between species in the food webs are complex and vary from habitats to habitats. Apex predators play a different role in maintaining the balance of eco-structure within diverse habitats. Sometimes they suppress the population of herbivores and other times the autotrophs.

Scientists suggested some of the undesirable indirect effects as a consequence of trophic cascade are:

  1. Wildfire: cause primarily due to warm and dry climate. An example shows that manipulating the food chain, possibly reducing the herbivorous population, will increase plants' biomass that fuel wildfires.

  2. Disease: caused mainly by climate change or habitat deterioration. Also, a shift in species, e.g., decreases in the population of fish that prey on mosquito larvae, can be linked with an increase in human malaria.

  3. Change in the physical and chemical composition in the atmosphere, water, and soil: mainly due to industrialization and agriculture. However, disturbing the abundance of primary producers such as algae can affect the atmosphere and sea's carbon dioxide level.

  4. Biodiversity: apex predators maintaining the population of species in the food web in check, thus providing chances for niche species to survive.

What may happen if polar bears disappear or their behavior changes?

  1. The primary food of polar bear ringed seals may become overpopulated, threatening seals' prey, the Arctic cod.

  2. Without enough sea ice for polar bears, they may turn to other food such as Arctic fox or walrus, disturbing their abundance.

  3. Other species that depend on polar bears' kills as a food source may suffer, and they may turn to plants and depleting vegetation that is already scarce in the Arctic.

Arctic food chain including polar bear, ringed seal, Arctic cod, shrimp, algae

We only mentioned a tiny part of the influence between species in the ecosystem. Trophic cascade could also happen from bottom-up or cross-boundary. Scientists are working hard to provide new information about how species interact with each other and the environment. It could be the case that it may take a few generations to observe the impact of a lost species on the planet. There are still many research gaps; however, the urge to protect the vulnerable species is evident. Let's take action now as it could be too late to reverse the situation.

Information from:

J. A. Estes, J. Terborgh, J. S. Brashares, M. E. Power, J. Berger, W. J. Bond, S. R. Carpenter, T. E. Essington, R. D. Holt, J. B. C. Jackson, R. J. Marquis, L. Oksanen, T. Oksanen, R. T. Paine, E. K. Pikitch, W. J. Ripple, S. A. Sandin, M. Scheffer, T. W. Schoener, J. B. Shurin, A. R. E. Sinclair, M. E. Soulé, R. Virtanen, D. A. Wardle, Trophic downgrading of planet Earth. Science 333, 301–306 (2011).

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3 comentarios

The food chain on this link is incorrect. My students noticed that the arrows are pointing in the wrong direction.

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Contestando a

Thank you very much for the comment. We had updated the picture with reverse arrows.

Super thanks!

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Batool Khalil
Batool Khalil
31 ene 2022

Cool resource

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