Rare and unique ecological communities will be lost if oceanic islands aren't adequately considered in a global conservation plan, a new study has found. Although islands tend to harbor fewer species than continental lands of similar size, plants and animals found on islands often live only there, making protection of their isolated habitats our sole chance to preserve them.
Many conservation strategies focus on regions with the greatest biodiversity, measured by counting the number of different plants and animals. "Normally you want to focus on the most diverse places to protect a maximum number of species," said Holger Kreft, a post-doctoral fellow at the University of California, San Diego and one of the two main authors of the study, "but you also want to focus on unique species which occur nowhere else."
Biodiversity and rarity of plants. The map with its 90 regions shows both in a combined index. It reveals that oceanic islands are particularly valuable. Among the mainland areas with the highest values are tropical mountains and regions with a Mediterranean climate. (Credit: Image courtesy of University of California - San Diego)To capture that uniqueness, Kreft and colleagues at the University of Bonn, UC San Diego and the University of Applied Sciences Eberswalde used a measure of biodiversity that weights rare species more than widespread ones. They carved the terrestrial realm into 90 biogeographic regions, calculated biodiversity for each, then compared island and continental ecosystems. By this measure, island populations of plants and vertebrate animals are eight to nine times as rich.
The southwest Pacific island of New Caledonia stands out as the most unique with animals like the kagu, a bird with no close relatives found only in the forested highlands that is in danger of extinction, and plants like Amborella, a small understory shrub unlike any other flowering plant that is thought to be the lone survivor of an ancient lineage.
Fragments of continents that have broken free to become islands like Madagascar and New Caledonia often serve as a final refuge for evolutionary relicts like these. The source of diversity is different on younger archipelagos formed by volcanoes such as the Canary Islands, the Galápagos and Hawaii which offered pristine environments where early colonizers branched out into multiple related new species to fill empty environmental niches. The new measure doesn't distinguish between the two sources of uniqueness, which may merit different conservation strategies.
Although islands account for less than four percent of the Earth's land area, they harbor nearly a quarter of the world's plants, more than 70,000 species that don't occur on the mainlands. Vertebrate land animals – birds, amphibians, reptiles and mammals – broadly follow this same pattern.
"Islands are important and should be part of any global conservation strategy," Kreft said. "Such a strategy wouldn't make any sense if you didn't include the islands."
Threats to biodiversity may also rise faster for islands than for mainlands, the team reports. Scenarios based on a measure of human impact projected to the year 2100 warn that life on islands will be more drastically affected than mainland populations.
"That threat is expected to accelerate particularly rapidly on islands where access to remaining undeveloped lands is comparatively easy" said Gerold Kier, project leader at the University of Bonn and lead author of the study. Expanding farmlands, deforestation, and other changes in how people use land are among the alterations expected to cause the greatest damage.
The researchers also considered future challenges posed by climate change and report mixed impacts. Rising sea levels will swamp low-lying areas and smaller islands, but the ocean itself is expected to moderate island climates by buffering temperature changes. "Although disruptions to island ecosystems are expected to be less severe than on the continents, climate change remains one of the main threats to the biodiversity of the Earth," Kier said. "If we cannot slow it down significantly, protected areas will not be much help."
"We now have new and important data in our hands, but still have no simple solutions for nature conservation," Kreft said. "In particular, we need to answer the question how protected areas with their flora and fauna can complement each other in the best way. The part played by ecosystems, for example their ability to take up the green-house gas carbon dioxide, should be increasingly taken into account."
Co-authors included Tien Ming Lee and Walter Jetz of UC San Diego; Pierre Ibisch and Christoph Nowicki of the University of Applied Sciences Eberswalde; and Jens Mutke and Wilhelm Barthlott of the University of Bonn.
The Academy of Sciences and Literature Mainz, the Wilhelm Lauer Foundation, and the German Federal Ministry of Education and Research funded the research. Holger Kreft holds a Feodor-Lynen Fellowship from the Alexander von Humboldt Foundation.
Rare island species 'undervalued'
BBC News 12 May 09;
Rare species on islands are at risk of being lost forever because they have been generally overlooked by current conservation models, a study suggests.
Although islands had less diversity of species compared to mainland sites, a greater proportion were unique to the remote habitats, researchers concluded.
Yet the impact of human activities was relatively greater on islands because space was at a premium, they added.
The findings appear in the Proceedings of the National Academy of Sciences.
The team from Germany and the US wrote: "Islands are well-known centres of range-restricted species and thus high levels of endemism.
"However, they are also acknowledged for their lower species richness compared to mainland areas," they added.
"Hence, an index combining both endemism and species richness can provide insight into the question of relative conservation value of islands and mainlands."
But to date, the team observed, no study had focused on the differences between mainland areas and islands.
While some islands, such as the Galapagos archipelago and Madagascar, were well known for their biodiversity richness, the team said the habitat's biological value had not been quantified.
"Normally, you want to focus on the most diverse places to protect a maximum number of species," said co-author Holger Kreft, a post-doctoral fellow from the University of California, San Diego.
"But you also want to focus on unique species that occur nowhere else."
To understand the level of endemic species found in particular areas, the team used a measure of biodiversity that weighted rare species more heavily than widespread ones.
When they calculated the level of weighted biodiversity, they then compared island ecosystems with continental habitats.
Using this measurement, the team found that islands' populations of flora and fauna were eight to nine times as rich.
The team observed: "Island floras and faunas are usually recognised to maintain a high degree of endemism because of their geographic isolation and the limited interchange with neighbouring mainland or island biota."
"Islands are important and should be part of any global conservation strategy," Dr Kreft added.
"Such a strategy wouldn't make any sense if you didn't include the islands."
The team also noted that islands were at the centre of "past and imminent species extinctions, stressing even more the need for information on both biodiversity and specific threats in this part of the world".
Lead author Gerold Kier, project leader at the University of Bonn, warned that threats to islands' biodiversity were likely to rise more sharply in the coming decades.
"That threat is expected to accelerate particularly rapidly on islands where access to remaining undeveloped lands is comparatively easy," he explained.
As a result, expanding farmlands, deforestation and other changes in how human populations use land were likely to be more stark than on the mainlands.
"We now have new and important data in our hands," said Dr Kreft, "but still have no simple solution for nature conservation."
Invest in islands to save most species
Emma Young, New Scientist 16 May 09;
LOOKING for a sound investment to combat the biodiversity crisis? Spend your cash on an island. It turns out they are about nine times as valuable as an equally large piece of mainland. So says the first worldwide analysis of the importance of different regions for maintaining global biodiversity.
While it is common knowledge that islands generally house ahigh number of species that live only in that location, the total diversity of life on most islands is relatively low compared with mainland areas. As a result, their importance for conservation efforts hasn't been clear, says a team from the Universities of Bonn and Eberswalde, Germany, and the University of California, San Diego.
To settle this question, they calculated a new combined index which takes into account both the number of unique species in a given region and the total number of different species living there. This "endemism richness" scale measures how much a given area of land contributes to global biodiversity. The team evaluated the endemism richness of plants and vertebrate land animals for 90 regions covering most of the Earth's surface. They discovered that values for islands were 9.5 times higher for plants and 8.1 times higher for vertebrates, compared with similarly sized regions of mainland (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0810306106). Tropical islands scored highest, with New Caledonia topping the list.
"The results should lead to an increased investment in conservation on tropical island biodiversity hotspots," says Thomas Brooks, head of Conservation Priorities and Responses at Conservation International's Center for Applied Biodiversity Science in Arlington, Virginia.
To some extent, this is already happening. For example, the Critical Ecosystem Partnership Fund, run partly by Conservation International, is in the process of preparing a multimillion dollar investment in the Caribbean islands.
Increased investment in islands should be doubly worthwhile because they are likely to lose more habitat from human impact this century than mainland regions, say the researchers.