Nowhere to Hide: Tigers Threatened by Human Destruction of Ground cover

The elimination of ground-level vegetation is bringing another of the world’s tiger subspecies to the brink of extinction, according to Virginia Tech and World Wildlife Fund researchers.

The Sumatran tiger, native to Indonesia, could be the fourth type of tiger to disappear from the wild. This is due, in part, because of deforestation and the loss of thick groundcover, also known as understory cover, said Sunarto, lead scientist on a study that is the first to systematically investigate the use of both forests and plantation areas for tiger habitat.

Although tiger’s prefer forest to plantation areas, the study found that the most important factor was that availability of thick ground-level vegetation which apparently serves as an environmental necessity for tiger habitat, regardless of location.

“As ambush hunters, tigers would find it hard to capture their prey without adequate understory cover,” said Sunarto, who earned his doctorate at Virginia Tech and now is a tiger expert for the World Wildlife Fund-Indonesia (WWF-Indonesia). “The lack of cover also leaves tigers vulnerable to persecution by humans, who generally perceive them as dangerous.”

Within forest areas, tigers also strongly prefer sites that have low levels of human disturbance as indicated by their preference for areas closer to forest centers and farther from human activity centers such as bodies of water and areas bordering plantations and towns.

Tigers occupy only around 7 percent of their historic range. Estimates place the current wild tiger populations at as few as 3,200 tigers, including only about 400 Sumatran tigers, which are listed as critically endangered on the International Union for Conservation of Nature Red List of Threatened Species.

“These study results indicate that to thrive, tigers depend on the existence of large contiguous forest blocks,” said study co-author Marcella Kelly, an associate professor in Virginia Tech’s Department of Fish and Wildlife Conservation and Sunarto’s graduate advisor.

The Indonesian government has set aside many areas and national parks for the conservation of endangered species but about 70 percent of tiger habitat in Sumatra, an island in western Indonesia, remains outside these protected areas. The preservation of such habitats, which requires support from government, landowners, and concession holders, is critical for conservation of the species, the study authors emphasize.

A recently published Indonesian presidential decree on land use in Sumatra points out the importance of building wildlife corridors between critical areas, where commitments from concession owners are key to successful implementation.

“Even with current legal protection for the species, tigers are not doing well in many places, especially those outside protected areas,” Sunarto said. “As long as forest conversion continues, tigers will require active protection or they will quickly disappear from our planet.”

The study concludes that in order to protect tigers, it is critical to stop clearing Indonesia’s remaining natural forests for plantations. With adjustments in management practices on existing plantations to include more understory and riparian forest corridors, tigers could use a mosaic of forest patches across fragmented landscapes.

“We hope that plantation managers and concession owners can use the recommendations of this report to apply best management practices to further protect Sumatran tigers from extinction,” said Anwar Purwoto, director of the Forest, Freshwater, and Species Program at WWF¬Indonesia.

“Ensuring that tigers are able to roam freely in natural forests and restored habitat is crucial to their survival,” said co-author Sybille Klenzendorf, head of WWF’s species program, who earned her master’s and doctorate degrees in wildlife science from Virginia Tech. “This study is a reminder of just how important it is for us to protect the natural forests that tigers and other animals rely on.”

The report was published in the Public Library of Science’s online journal PLoS ONE on Jan. 23, and was a collaboration between the university and WWF, with support from the Indonesian Ministry of Forestry.

Over fishing Threatens the Survival of Seabirds

From gannets to seagulls, puffins to penguins, all seabirds suffer the same drop in birth rates when the supply of fish drops to less than a third of maximum capacity. That’s the result from an international study on the relationships between predators and prey in seven ecosystems around the world, published in the magazine Science and coordinated by Philippe Cury, an IRD researcher. Based on nearly 450 cumulative years of observation, the research team compared the growth in fish supplies and the reproductive patterns of 14 species of coastal birds. These birds mainly feed on sardines, anchovies, herring and prawns, all of which are victims of over fishing. Below the critical level of one third of the fish biomass, the birds — and the stability of the entire ecosystem — come under threat.

These studies also provide a reference level for the sustainable management of fisheries, so as to safeguard the bird population, which is often imperilled, and so as to maintain the healthiness of marine environments.

From the Arctic to Antarctica and from the Atlantic to the Pacific, when the supply of fish is reduced, seabirds stop reproducing. Previous studies had uncovered the relationships between the availability of food to birds and their reproductive rates, but this new international study (1) has just made a monumental discovery. Coordinated by Philippe Cury, an IRD researcher, and published in the journal Science, the study identifies the level of a critical supply of fish below which the stability of the bird population is endangered.

A third’s the limit

Gannets, terns, puffins, seagulls and penguins: taking all the species together, if fish supplies drop below a third of their maximum size, then the number of baby birds born drops precipitously. Everywhere in the world. Once the amount of their prey falls below sufficiency, the seabirds fail to reproduce (2). Yet above this level, their reproduction rate doesn’t increase. Abundance in the food supply didn’t produce the expected result as other factors limit reproduction, such as the fact that nesting areas fill up quickly.

By demonstrating such a singular phenomenon, these studies validated empirically — i.e. from data rather than from models — that ecosystems, over the long term, obey similar laws. Until these studies were carried out, the basic principle of living ecologies remained theoretical. Now, for the first time, scientists have achieved a model of predator and prey behaviour based on actual observation in marine environments.

Almost 450 years of data

The research team compared almost 450 years’ worth of data from all over the world to see how the supply of fish correlated with the reproduction of seabirds. To do so, the scientists concentrated on 14 species of birds in seven ecosystems around the globe. The species selected feed mainly on sardines, anchovies, herrings and other small coastline fish that fishermen regularly catch and whose populations are under pressure. Each of the ecosystems was studied for periods ranging from 15 to 40 years; and the study showed that it generally takes 13 years of data to form an accurate notion of what the maximum fish supply is in a given ecosystem.

This is the first time that so much data on the relationships between predators and prey have been brought together over such a long period of time. The scientists stressed cooperation between specialists from the north and the south made it possible to bring together such a vast quantity of information. Scores of research specialists have devoted countless years, sometimes their whole career, to these studies.

Over fishing can kill ecosystems

This study makes it plain that over fishing endangers the survival of higher-level predators such as birds. In fact, they are in direct competition with human fishermen: both groups consume about 80 million tonnes of fish per year. Small bait which are used to make meal and oils in fish farming — such as sardines, anchovies, herring, smelt and capelin — make up 30 % of today’s catch worldwide. As global demand rises, these findings make it possible, at last, to achieve a standard against which to measure the sustainable management of fish, so as to sustain populations of seabirds, over the long term.

Seabird populations are one of the best ways to judge the health of marine ecosystems — which the European Commission, for instance, wants to be able to monitor — and are one of the easiest measurement barometers to use. These bird species are among the most endangered, owing to the lack of food but also to climate change and the destruction of coastal habitats where, once again, they are in competition with humans for space along the water’s edge.

In order to understand the dynamics of ecosystems, it is essential to determine the key relationships between predators and prey. International authorities today have few tools by which to gauge and restrict fishing. The limit of one third of the fish population set forth by this study may not be a hard number in all cases, but it can certainly serve as a guideline for fishery management policies.