Biodiversity and ecosystem health: a Hawaiian Islands case study | Khan Academy

When you think of islands, you might think of pristine beaches and palm trees gently swaying along with a warm breeze. Sounds like paradise! As a scientist, islands are my kind of place for research.

Islands are very beautiful, and they also have a lot of biodiversity. Biodiversity can be described as the variety of species in an ecosystem. Now, some ecosystems have higher biodiversity than others, but all ecosystems have a variety of species that interact in specific ways with one another.

Islands have such a variety of species that they're often called biodiversity hot spots. They're home to so many diverse species, much more so than the continents. There are nearly half a million islands around the world, but they only make up about five percent of the earth's land area. Yet, islands are home to 20 percent of the world's plant species and 15 percent of all mammal, bird, and amphibian species.

Many of these island species can only be found on one island or within a group of islands. For example, you can only find the 'eevee', a honeycreeper bird species, in the main Hawaiian Islands in the North Pacific Ocean. The 'eevee' are important pollinator species for Hawaiian plants, including the opelu and ohia.

Pollination is an essential part of plant reproduction, allowing plants to produce their fruits and seeds. While the 'eevee' feeds on the sweet nectar of these plants, this bird also helps to support the next generation of opelu and ohia. These and other types of interactions are happening all the time between species in an ecosystem.

You can think of biodiversity as a sort of safety net, with each species as a knot and the ropes between knots as their interactions. The diversity of species and their interactions hold the net together, allowing the ecosystem to function. Plus, the relationships between species are often unique.

For example, the 'eevee' has a special curved bill, and it's evolved to feed on the nectar of very specific flowers that are similarly curved, like the opelu. Now, even though the 'eevee' is highly adapted to its environment, if something happens to the opelu or ohia and these plants start to decline, it can spell disaster for the 'eevee'.

When an ecosystem changes so much that a species can no longer survive, that species may become extinct or die out, causing biodiversity to decrease. Unfortunately, many of Hawaii's honeycreepers and overall biodiversity have been lost through extinction. In the past, there were at least 20 other species of honeycreeper found across Hawaii, but many of them have become extinct over time.

If we return to our analogy of biodiversity as a safety net, whenever a species goes extinct, it's like a knot becomes undone, and parts of the net start to fall apart. A decrease in biodiversity is often a result of human activities, which is especially clear in the Hawaiian Islands.

In the last few hundred years, agriculture, grazing, logging, and development have taken almost half of Hawaii's forest cover and, along with it, a big part of its biodiversity. Humans have also brought non-native animals like rats and feral pigs to Hawaii, which have changed or destroyed native habitats. Plus, new diseases and climate change have led to the extinction of many Hawaiian species.

When an ecosystem loses biodiversity, it doesn't function as well. If ohia starts to disappear from Hawaiian forests, it's not just the 'eevee' that loses an important food source, but the entire ecosystem is affected. In fact, scientists often look at how complete an ecosystem's biodiversity is in order to measure the ecosystem's health.

The safety net of biodiversity is supported by having lots of different species, which allows the ecosystem to cope with natural disasters like drought, storms, and disease. With more biodiversity, ecosystems are stronger and more resilient, so they can recover quickly. But with less biodiversity, ecosystems become more vulnerable.

I've told you a lot about how Hawaii is losing biodiversity; however, there is cause for some hope. The nene, or Hawaiian goose, nearly went extinct. There were less than 30 birds in the wild 50 years ago. Now, thanks to lots of conservation work to improve the habitat for this species, there are over 3,000 nene throughout the islands.

We humans are part of Earth's biodiversity too. We are components of the ecosystems we touch, so if we have the power to hurt these ecosystems, we have the power to protect and heal them too.

Aloha!