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Biodiversity III: Extinction is Forever

10/27/2015

Life has been on Earth for 3.5 billion years. But most of the familiar multicellular life related to modern plants and animals are 550 million years old. While we think there are currently close to 10 million species on our planet, over 5 billion species have existed but are now extinct. There are 99% more species that have died than are currently alive. When a species becomes extinct it is gone forever and no longer contributes to the maintenance of important ecosystem services including food webs. A mass extinction is when many species go extinct and entire ecosystems collapse.

So why do so many creatures go extinct? There is always a slow rate of extinction due to random events. The majority of species died during 5 mass extinction events that happened millions of years ago. The most recent event was 65 million years ago when dinosaurs were killed by an asteroid impact. This extinction probably killed 75% of the species that were on the planet. 200 million years ago an extinction event killed 50% of the living creatures and was caused by massive volcanic eruptions that produced toxic dust that blocked sunlight. The largest extinctions event on the planet was 252 million years ago and it caused more than 96% of marine and 70% of terrestrial species to go extinct. It is thought that high CO2 concentrations in the atmosphere caused widespread climate shift and increased ocean acidification enough to completely devastate food webs. The oldest known mass extinction event was 440 million years ago and also saw a huge reduction in species (60%, at that time there were no land species). This extinction event was caused by global cooling and a large-scale sea level drop. Common among all of these mass extinction events is that natural disasters caused a shift in the world’s climate. The species that exist on the planet are adapted to their current climate, species go extinct when climate changes.

Currently the rates of extinction are much greater than normal. There is evidence that we are in the middle of the 6th mass extinction. Huge numbers of amphibian species are dying due to warmer temperatures and a fungal disease. More than half of Hawaiian birds have gone extinct due to habitat loss and a disease related to malaria. An entire group of 18 predatory bird species similar to a small ostrich went extinct in South America. The list goes on and on.

So many salmon have been caught and their rivers dammed up that many species are close to extinction. We created the Endangered Species Act (ESA) to protect species that are on the brink of extinction, but this legal mechanism does not fix habitat degradation, the root cause of extinction. For instance we built hundreds of dams in the Pacific Northwest during the 40’s for cheep electricity, to control flooding and for water security. We built way more dams than we needed and now these dams are blocking ancient spawning grounds of endangered salmon. Restoring essential habitat for these fish is critical to avoid their extinction. Many people don’t want to pay to remove dams, they say it is just not worth the money. This type of short sighted outlook will continue our current rapid pace of extinctions, which could be slowed by the restoration of land and ocean habitats.

But some people think that modern technology will save us from a mass extinction. You may have heard recent reports that we can use DNA to bring extinct animals back to life. Technically this is amazing, we can insert DNA in a cell and make it replicate itself to produce a living creature that has some of the genetic code of an ancient creature. This is basically cloning (remember dolly the sheep) but with DNA from a different species. Really a pretty major technical achievement, but fundamentally it does not help us, we need species that contribute to the larger complexity that makes the ecosystems we currently rely on for survival. We might be able to make a franken-creature that contains ancient DNA but we need healthy modern ecosystems, not to recreate ancient ecosystems.

So now we have caught ourselves in a pickle, we have created a changing climate that is causing mass extinctions! We are at a turning point in our history, if we wish to survive we must maintain ecosystem functions. We need clean air and water for survival, if we want to live on this planet we need the plants and animals that we have now. This life is what makes our planet habitable, makes it beautiful and richly complex. It would be a shame to cause a modern mass extinction that changes life as we know it. We need to actively protect the life on this planet to ensure that humans can continue to survive here.

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Biodiversity II: Why Save Diversity?

10/18/2015

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Scientists talk about how much life there is on the planet but why do we care? What is so important about having different species? If there are so many species what difference does it make if we let a few disappear?

Biodiversity is critical for life as we know it. Plants produce the oxygen we breath. Bacteria decompose waste. Coral reefs protect islands from eroding into the sea. Many different creatures have roles in keeping the planet clean and giving us important resources. When biology helps people to survive, we call this ecosystem services. These services come in many forms but they rely on the interactions among many different species. Think of these interactions as a chain, each link represents a species. As you break these links the chain breaks. When enough species are gone ecosystems stop functioning, stopping the services they provided for us. Imagine a planet without oxygen…not the easiest place to survive!

Clean water, air these types of services are critical for us but they are also critical for other organisms on the planet. We think of the inter relationships of different species as the threads of a spider web and each species are the connections. We often use this analogy to map out a food web. A food web shows which organisms each other organisms, typically with plants on the bottoms, herbivores above them and predators above the herbivores. As people we eat all of these levels of the food web, plants (like corn, broccoli, etc.), herbivores (cows, deer, etc.) and predators (tuna, etc.). As species go extinct connections on the web are broken and the organisms on higher levels no longer have as much to eat. If enough species from the bottom levels disappear then all of the upper levels collapse causing a cascade of species extinctions. Since we eat many of these organisms we should be actively working to preserve food webs to ensure we can feed people.

Our health and survival is important, and medicines are one of the ways that we stay healthy. Most medicines come from natural sources, this makes sense, for thousands of years native cultures found plants and animals that had medicinal uses. Even now this is still true, approximately 60% of our medicines come from natural sources. We are constantly finding new chemicals from plants that cure a range of problems from headaches (aspirin comes from the bark of a willow tree) to cancer (taxol is currently the most used anticancer medicine and is derived from an evergreen tree). A cone snail like the one in the photo to the right contains a potent pain killer compound. But there are a huge amount of species that we don’t even know about (see the last blog). Many of these land and marine species might contain chemicals that are useful medicines but we have never tested this. We don’t even know the names of these creatures let alone how they might help us survive. This is a real problem, imagine if we let a species go extinct that had the cure to breast cancer. Once the species goes extinct there is no way for us to know what chemicals they contained. This is especially true for marine creatures, we have only been looking for medicines in marine animals for the last 40 years. This corresponds to our ability to scuba dive, before that we were really limited in our ability to find marine creatures. But we have always been able to walk around a forest and eat a plant (there must have been a lot of trial and error in the beginning). Currently there are 3 medicines made from marine animals, but you can imagine this is just the tip of the iceberg.

As our population increases more and more human actions are affecting the ability of different organisms to survive. We don’t often interact with most of the biodiversity that lives on the planet, but there is a huge amount of different creatures on the planet that all have a role to play in their habitats. It is critical that we appreciate diversity not only for its beautiful variety but also for the services that these creatures provide to us. Extinction is the biggest threat to these services because the species that die are gone forever. There have been 5 previous mass extinctions when life on the planet changed dramatically, for instance when the dinosaurs died. Some scientists think that we are in the middle of the 6th mass extinction. We have seen many species go extinct in the last 10,000 years, a relatively rapid rate for species to disappear. We should be very worried, all of the life on the planet helps us to survive so if we are causing a mass extinction we are breaking more links in the chain and disrupting food webs. We need to do everything in our power to stop extinctions and preserve biodiversity. We only live on one planet, and we need to actively preserve the rich biodiversity we have.

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Biodiversity I: How do you count life?

10/13/2015

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Biodiversity is a complicated thing, life comes in many shapes, sizes and forms. We are surrounded by an amazing diversity of plants, animals, fungus, bacteria and other weird microbes. Not only is the array of shapes and sizes dizzying, the variety of ways of getting food is crazy. For instance most consumers eat plants that produce energy from sunlight using photosynthesis. Some marine slugs actually steal chloroplasts from their plant food and harness photosynthesis for themselves. These little green slugs just need sunlight to eat. Imagine if we did this, green people that basked in the sun for food.

Biodiversity is amazing on many levels but we still don’t understand what we have on the planet. How many species are there? The truth is no one knows! Many scientists are interested in cataloging life and putting a name on species. This process is usually done by an expert called a taxonomist. Think of a taxonomist as a librarian, their job is to make sure the book is named appropriately and categorized based on its relationship with other books. A taxonomist names new species, which can be challenging since we want every species to have a unique name.

Since the beginning of naming (the idea that each species gets a unique two part name, a genus and species name was created by Carl Linnaeus in 1753) scientists have been adding more and more species to our library. We currently have named about 1.2 million species. This is pretty impressive, that is a lot of weird bugs. Literally almost a million of these species are insects, which is the most diverse group of animals. But that is just the tip of the iceberg, scientists are discovering many new species every day. Actually we are in the middle of describing all of the organisms on the planet and we probably haven’t even found 10% of them. This is a real problem, how can we hope to understand life if we don’t even know how many species are on the planet.

Most of the named species live in tropical rain forests, making this the most diverse habitat on the planet. The smallish country of Columbia hosts 10% of all the living species in a little more than 400,000 square miles. Coral reefs also hold a huge diversity of creatures, but no insects, so they come in second as the habitat with the most species. However, it is much more challenging to count the number of species underwater. To find creatures on reefs we need to scuba dive, but we are limited by the amount of air we can carry. This limits our time, most scuba tanks last me about an hour, and the most I usually do is four dives in a day, giving me 4-6 hours to look for creatures. This is not even close to the 16 hours (assuming the researchers sleep) that people can spend in a forest.

So what we need is a fast and easy method to quantify how many species are in an underwater habitat without actually being there. This is the topic of a recent paper “DNA barcoding and metabarcoding of standardized samples reveal patterns of marine benthic diversity”. In this paper marine biologist argue that using a standardized habitat is the best way to quantify the number of species in an area. They use autonomous reef monitoring structures (ARMS) as the habitat and these are built to resemble miniature apartment buildings. They have multiple plastic tiles stacked up to be about 10 tiles high, about 2-3 feet tall. If the ARMS are left underwater for 6 months or longer there are a ton of creatures that settle and grow on these plastic tiles. When the ARMS are brought out of the water and it can take a full day to sort all the weird creatures that they find. Then you have to count and put a name on everything you bring up, and preserve it so that the unknown creatures can be identified by taxonomists. Lots of work!!

Taxonomy is changing, now we can use genetics to identify a species, and compare the genetic code of two different individuals to confirm whether they are different species. This type of barcoding a species based on its genetics is how Leray and Knowlton counted the number of species they found in oyster reefs. Sequencing has recently changed enough to allow us to analyze hundreds of samples at the same time, which should revolutionize our ability to detect new species that were previously ignored. This is really exciting, and allowed these scientists to determine that 8% of the species they found matched known species. ONLY 8%!! That means that more than 90% of the species they found have no genetic information in our databases. Some of these creatures could be new to science, or they might already have a name but we just don’t have any genetic data for them. We really don’t understand most of the life on our planet!

The great thing about ARMS is it is a standard method. So we have a standard way of comparing biodiversity across space and time…very cool. The disadvantage of ARMS is it is a standard method, it only represents one type of habitat. For instance these structures only attract species that like to live on plastic tiles. Other creatures that only live in coral will not be found in the ARMS. There is no way for ARMS to capture all of the creatures in an ecosystem. So we still can’t really answer the fundamental question of; how many species are there?

To discover biodiversity we can not replace putting people in the ocean and having them search for life. We also need more taxonomists, because without more experts there is no way for us to name and catalog all of the new species. Using genetic technology we are getting a much better idea of the biodiversity on our planet. Taxonomists continue to name and categorize life, and new technology is giving us a leg up on understanding how many creatures we have. At the same time our ability to catalog life is becoming more pressing as many species are disappearing even before we know what they eat or how they might help people.

Reference:
Leray, M. and Knowlton, N. (2015). DNA barcoding and metabarcoding of standardized samples reveal patterns of marine benthic diversity. Proceedings of the National Academy of Science, USA. 112: 2076-2081.

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Biodiversity III: Extinction is Forever

Biodiversity II: Why Save Diversity?

Biodiversity I: How do you count life?

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