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Extinction and Survival

When we hear the word extinction, most of us immediately think of dinosaurs and woolly mammoths and cataclysmic events precipitating their extinction. Some of us are also aware of current extinction threats and recent extinctions, but few, if any, of us understand the varying and complex circumstances under which extinction actually happens. It turns out that extinction and species survival are closely linked through species diversity in the ecosystem.

Researchers at UC Santa Barbara are studying these intertwined issues of extinction, survival, and diversity, trying to understand what has happened in the past, what threats species face in the present, and what needs to be done to safeguard the future. In trying to gauge the full impact of anthropogenic effects such as climate change, loss of habitat, and pollution, however, scientists everywhere face a fundamental obstacle: They don’t know how many species exist on Earth, and have only rough estimates of how many of those are vulnerable or endangered.

Even the International Union for Conservation of Nature and Natural Resources (IUCN), producer of the benchmark annual Red List of Threatened Species, acknowledges it has barely scratched the surface. The Red List classifies and categorizes nearly 48,000 species of animals, plants, fungi, and protists. It specifies each species’ distribution, habitat, population, and specific threats, and places each along a risk spectrum ranging from “extinct” to “least concern.” (The list’s title can lead to some erroneous assumptions, since only 36% of the included species are threatened with extinction, and there is insufficient information on 14% of the included species to evaluate their status.)

The IUCN acknowledges that the 12,000 plant species catalogued on the list represent less than 3 percent of all known plants, and fewer than 1,000 of those are properly documented. The Red List includes less than 5 percent of marine species, and has only sketchy coverage of the world’s estimated 8,000 to 9,000 reptiles.

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How many species are there? The IUCN estimates between 5 and 10 million, though other recognized scientific sources put numbers as low as 2 million and as high as 100 million. That huge discrepancy may be explained in part by how far down the microscopic scale you search for species.

Bradley Cardinale, assistant professor in the Department of Ecology, Evolution, and Marine Biology (EEMB) at UCSB, agrees with estimates of 10 million species of mammals, fish, birds, insects, plants, fungi and protozoans, such as amoeba. He also says, however, that if you extend that microscopic kingdom to include bacteria, viruses and other microbes, then the total could easily top 100 million.

Cardinale was lead author of a report which concluded that as plant species go extinct and natural habitats become less productive, humans could well be the ones to suffer most. Co-authors of the report included Marc Cadotte, Ian Carroll and Jerome Weis, all of UCSB.

The study, involving an international group of scientists, mined data from 44 previous research projects around the world simulating plant extinctions. It concluded that a decrease in species diversity will trigger a significant drop in plant biomass in a given ecosystem.

Cardinale and his team said that such a drop could compromise certain benefits plants provide mankind, from essentials like producing oxygen and food, to the provision of fiber and biofuels.

Cardinale is not overly sentimental about endangered “poster-child” species like pandas and polar bears. “Although big, beautiful species can be important for many reasons, the productivity and sustainability of our planet ultimately depends on plants and the microbes that exist symbiotically with them. If we lose these species, we’re in real trouble.”

The plant study quoted what seems a rough rule of thumb among many scientists: as many as half of all species known today could be extinct by the end of this century. Cardinale called that a “best reasonable guess” based largely upon habitat loss and a simple methodology like measuring the number of species in an acre of rain forest and multiplying by the number of such acres being lost each year.

Are we setting ourselves up for huge future extinctions by introducing new species, predators and diseases, or are systems still so under-saturated that they can handle greatly increased biodiversity?

“The human population is exploding—our species now uses more than 50 percent of all available space, food and water on the planet,” he says. “Because of human domination, conservation efforts for most species have been too little, too late. We are in the middle of one of the great mass extinctions in the history of life.”

Steve Gaines, dean of UCSB’s Donald Bren School of Environmental Science and Management, says while the number of species is clearly decreasing on a global scale, within smaller regions the opposite seems to be true, since the introduction of exotic species can greatly outpace the loss of natives.

That was the conclusion of a recent study in which Gaines and Dov Sax—a postdoctoral researcher at UCSB at the time of the study and now an assistant professor of ecology and evolutionary biology at Brown—looked at biodiversity on remote islands.

After combing through centuries of data from places like New Zealand, Lord Howe Island, east of Australia, and Tristan da Cunha—isolated volcanic islands in the South Atlantic—the researchers were shocked at how much regional diversity had increased. Plant species had almost all doubled, with introduced varieties becoming naturalized and few natives going extinct; the number of bird species was about constant; and freshwater fish species had “increased dramatically.”

The 18-month study leaves the question hanging: Are we setting ourselves up for huge future extinctions by introducing new species, predators and diseases, or are systems still so under-saturated that they can handle greatly increased biodiversity?

Associate professor Jonathan Levine (EEMB) brings another dimension to the debate over the importance of diversity with research supporting the long-standing assumption that plants sharing a common habitat use the environment differently. He says a lot of plant species depend on variability, and this adaptation is illustrated when it comes, for example, to a changing climate: some types of seeds may germinate after hot dry weather, others when it’s wet.

According to Levine, this variable response to variable conditions has an overall moderating effect—meaning biomass remains more stable than it might otherwise—while underlining the value of plant diversity and complementary co-existence. His latest paper on this topic, published recently by Nature, uses empirical and mathematical techniques to prove the inherent stability of species diversity.

Levine says the research also supports the notion that as a species is pushed to low numbers, it actually gains some advantage because there is less competition in its particular niche. While that may not be enough to save a species from extinction, it does help the recovery of plants that become very rare; conversely, when plants become very common and begin to exhaust their particular niche resource, growth rate and measurable “quality” factors will decline.

With the clock ticking, UCSB biologists are trying to determine how best to prioritize plant conservation efforts. Another recent report, co-authored by Cardinale, assistant professor Todd Oakley (EEMB) and postdoctoral associate Marc Cadotte, made the case for giving priority to the most genetically differentiated species.

The researchers drew from about 40 studies of global grasslands, looking at the diversity of plants in each community and how productive they were in terms of biomass. “Biomass is one measure of the efficiency of ecosystems,” says Oakley. “Ecosystem efficiency is critical for everything from balancing levels of carbon dioxide and oxygen in the atmosphere to a smoothly running food chain.”

The team reconstructed the evolutionary history among 177 flowering plants by comparing their genetic makeup. “Previously people just counted the number of species in a community,” says Oakley. “We looked at the evolutionary relationships.” What they found was that some species are more critical than others in preserving the functions and productivity of ecosystems, and that the critical species tend to be plants that are genetically distinct or unique in the ecosystem.

Extinction issues are uppermost for marine scientists as well as their colleagues on land. Ben Halpern, a research project coordinator at UCSB’s National Center for Ecological Analysis and Synthesis (NCEAS), led a four-year study to map human impact on the world’s marine ecosystems. The study, which had 19 co-authors and involved dozens more worldwide contributors, created a practical tool for measuring and managing the health of oceans everywhere.

“When undertaking this global study, two things became clear,” says Halpern. “First, no spot on the planet is untouched by human activities—there is no truly pristine ocean left. Second, we found more than 40 percent of the oceans have been heavily impacted—that is they are 50 percent degraded or worse. People think the oceans are in good shape, but this was a sobering result.”

Researchers measured numerous threats caused by human activity including pollution from land and ships, the introduction of alien species, destructive fishing practices, oil and gas exploration, and the changing climate. Despite that daunting list, Halpern remains optimistic. “Oceans are remarkably resilient, and we know they can recover if given the chance. If we can reduce other stresses, we can make the ocean more capable of dealing with climate change.”

Halpern says while dozens of species have become extinct locally, perhaps only 20 to 30 marine species are known to have been completely lost during human history. Now he hopes this new tool for mapping, measuring and managing the ocean can help avoid further losses.

The model has already been used to study the California Current, which runs the length of the West Coast, and coral reefs in the Northwestern Hawaiian Islands. Right now Halpern’s focus is off Massachusetts, with similar research off New York next.

NCEAS researcher Kim Selkoe was co-author of a report by an international team of ecologists and economists showing how loss of biodiversity is “profoundly reducing” the ocean’s ability to remain healthy and productive. Selkoe says this trend is threatening services the ocean provides to mankind—everything from seafood, tourism, and recreational and cultural activities, to the absorption of our waste.

To assess the effects of marine degradation, researchers examined 50 years of catch data from different parts of the world. It showed that the greater the biodiversity, the more stable and productive the fisheries. Using sediment cores, archival records and other data covering the past 1,000 years, they also studied lost biodiversity, such as fish and waterfowl, in wetlands and estuaries of more than a dozen areas around the world.

“A century ago people thought it was impossible to overfish a species,” Selkoe says. “We’re now close to overfishing more than one-third of the world’s fisheries. We’re on the cusp of causing irreparable loss,” she cautions.