Smaller islands host shorter food chains

Nov 22, 2013
Figure legend: The diversity of herbivore species (here: moths and butterflies) generally decreases with decreasing island size. From the smallest islands, the topmost links in the food chain (i.e. the predators feeding on the herbivores) may simply fall off. The picture shows a tenth of the herbivores encountered by the scientists. Credit: Pekka Malinen

That smaller islands will typically sustain fewer species than large ones is a widespread pattern in nature. Now a team of researchers shows that smaller area will mean not only fewer species, but also shorter food chains. This implies that plant and animal communities on small islands may work differently from those on large ones.

Top predators the first to go

Working across a set of 20 islands off the Finnish coast, a group of Finnish scientists found that a disproportionate number of small islands were lacking the highest levels of the food chain. The results are freshly online in the journal Ecography.

"Ecologists have known for decades that less area means fewer ", explains Tomas Roslin, who spearheaded the current analyses. "What we show is that the decrease in species richness with decreasing area gets steeper when you climb up the food chain. That means that when you move towards smaller island size, you run out of top predators before you run out of intermediate predators, and that you lose the last plant-eaters before you lose the last plant."

The study comes with broad implications for a world shattered by human activities. "While we worked on a set of real islands, you can probably think of habitat fragments as 'islands' in a broader sense", says Tomas. "What our results then mean is that if we keep splitting natural habitats into smaller and smaller pieces, we may not only lose a lot of species from the resultant fragments, but also change the structure and functioning of local food webs."

Knowing your species the key to insights

To explore the effects of island size, the research team focused on islands spanning a hundred-fold range in area. On each of these islands, the team took samples of local food chains consisting of four levels: plants, predators feeding on the herbivores, and top predators feeding on the predators themselves.

Among predators, the researchers targeted a specific group, i.e. . "To test ideas about length, you really cannot deal with raw counts of species – instead, you need to know which species form actual feeding chains" says Gergely Várkonyi, an international expert on wasps involved in the project.

"Among the wasps encountered on these islands, we were able to pick out the species truly dependent on the lepidopteran herbivores. As we see it, knowing not just what the species are but what they do in their lives is the key to sensible ecology", emphasizes Gergely.

Hundreds of species examined

"What is unique about our study is that we were able to look at patterns at the level of large species pools across the islands", explains Marko Nieminen, who spent three long summers boating around the islands, sampling insects by light and bait traps.

"Where other people have looked at effects of island size on restricted numbers of species or restricted levels in food chains, we did the full thing across four levels", he specifies. "Overall, we dealt with 200 species of plants, 415 species of lepidopteran herbivores, 42 species of parasitic wasps attacking herbivores and 7 species of wasps attacking parasitic wasps."

Deliberately keeping things simple

"In choosing the islands, we deliberately went for a simple system" says Marko. "Our islands were essentially smallish pieces of rocks with some forest and heathland on them. Historically, they all rose from the sea just some millennia ago, after being submerged and scraped clean of life by the last ice age. This similarity in structure and history allowed us to look at effects of island size, without having to worry about other differences among ."

Maintaining interactions may be trickier than maintaining species

All three authors worry about the message laid plain by the study: "What this really suggests is that to save ecological interactions, we may need to conserve much larger areas than for just maintaining e.g. plant diversity. If we keep splitting habitats into ever-smaller pieces, then we will be losing upper links from food chains, and important control functions along with them."

Explore further: Introducing species to change ecosystems is a balancing act

More information: Roslin, T., Várkonyi, G., Koponen, M., Vikberg, V., & Nieminen, M. 2013. Species–area relationships across four trophic levels – decreasing island size truncates food chains. Ecography DOI: 10.1111/j.1600-0587.2013.00218.x

add to favorites email to friend print save as pdf

Related Stories

French islands under threat from rising sea levels

Sep 18, 2013

By the year 2100, global warming will have caused sea levels to rise by 1 to 3 meters. This will strongly affect islands, their flora, fauna and inhabitants. A team of researchers from the Ecologie, systématique et évolution ...

Why closely related species do not eat the same things

Jun 24, 2013

Closely related species consume the same resources less often than more remotely related species. In fact, it is the competition for resources, and not their kinship, which determines the food sources of ...

Scientist urges us to 'embrace new invaders'

Oct 04, 2013

A University of York scientist claims that invasive species such as Himalayan balsam and rhododendron should be welcomed to Britain rather than reviled. At least, they should not be hated simply because they ...

Recommended for you

Plants with dormant seeds give rise to more species

Apr 18, 2014

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Scientists tether lionfish to Cayman reefs

Apr 18, 2014

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.