Healthy ecosystems often rely on secret agents. Not spies, but organisms that might not seem to have an obvious connection to a natural community. We reported on this earlier in the week when we described the influence of toucans on the evolution of palm trees in the Brazilian rainforest. Now, two other recent studies make these hidden, yet important, connections more apparent.

With coral reef ecosystems around the world under threat from climate change, coral bleaching and ocean acidification, Australian researchers are looking for resourceful ways to save these communities. Reporting in Nature Communications this week, a team led by Joseph Maina from Macquarie University determined that a coral reef off the coast of Madagascar could benefit from a healthy forest on the mainland.

It’s not obvious, but the scientists discovered that improving land-use management strategies, such as controlling sediment pollution caused by deforestation and soil erosion, are crucial to reef survival.

“Curbing sediment pollution to coral reefs is one of the major recommendations to buy time for corals to survive ocean warming and bleaching events in the future,” says co-author Jens Zinke of the University of Western Australia. “Our results clearly show that land-use management is the most important policy action needed to prevent further damage and preserve the reef ecosystem.”

In another study, published last week in PLoS Biology, researchers examined the role of species in a variety of ecosystems—from coral reefs to tropical forests to alpine meadows—in terms of their abundance. David Mouillot of the University of Montpellier 2 and his colleagues found that it is primarily the rare species, rather than the more common ones, that have distinct traits involved in unique ecological functions. As biodiversity declines, these unique features are particularly vulnerable to extinction because rare species are likely to disappear first.

Biodiverse environments are characterized by many rare species. These rare species contribute to the taxonomic richness of the area, but their functional importance in ecosystems is largely unknown. It is often assumed that they fulfill the same ecological roles as those of common species but have less impact because of their low abundance, but the work of Mouillot and his team shows that, in fact, the opposite may be true.

Examples of such functional species include the giant moray (Gymnothorax javanicus), a predatory fish that hunts at night in the labyrinths of coral reefs; the pyramidal saxifrage (Saxifraga cotyledon), an alpine plant that is an important resource for pollinators; and Pouteria maxima, a huge tree in the rainforest of Guyana, which is particularly resilient to fire and drought. Not only are these species rare, but they have few functional equivalents among the more common species in their respective ecosystems.

“Our results suggest that the loss of these species could heavily impact upon the functioning of their ecosystems,” says Mouillot. “This calls into question many current conservation strategies.” The authors argue that the preservation of biodiversity as a whole—not just the most common species—appears to be crucial for the resilience of ecosystems.

Image: David Mouillot/PLoS Biology

In ecosystems, every organism plays a part. From the smallest microbe to the fiercest predator to the tallest tree, each species contributes to making its community healthy. But this role isn’t always obvious.

Take the colorful toucan and the palm tree Euterpe edulis in the Brazilian rainforest. Scientists have long understood that the palm’s seeds are dispersed by not only the large birds, but smaller birds, too. The birds eat the seeds, fly-off and poop—spreading the palm seeds far and wide.

But the past 100 years have seen many changes in the rainforest. Since the 1800s, the forest has become more and more fragmented, mostly due to agricultural development such as the planting of coffee and sugar cane. By creating this patchwork of forest and farmland, humans have affected the rainforest in many ways.

According to a new study in the journal Science, the numbers of toucans have declined in the forest patches, and the palm trees in those areas have responded by producing much smaller seeds.

These palms generally produce different-sized seeds. Different sized-birds with different-sized beaks distribute the seeds evenly. But with the toucan and other large birds, such as large cotingas, absent from the ecosystem, only the small-seeded palm trees are reproducing. The birds are basically changing the evolutionary trajectory of these trees.

Researchers, led by Mauro Galetti from the Universidade Estadual Paulista in São Paulo, Brazil, collected more than 9,000 seeds from 22 different palm populations and used a combination of statistics, genetics, and evolutionary models to determine that forest fragmentation displaced many toucans. They also considered the influence many environmental factors, such as climate, soil fertility, and forest cover, but none could account for the change in palm seed size over the years in the fragmented forests.

For palm tree seeds, size matters. “Small seeds are more vulnerable to desiccation and cannot withstand projected climate change,” explains Galetti. The rainforest is projected to be drier as the climate warms, and the smaller seeds are less equipped than larger seeds for survival in these conditions.

See, every organism plays an important part.

“Unfortunately, the effect we document in our work is probably not an isolated case,” says Galetti. “The pervasive, fast-paced extirpation of large vertebrates in their natural habitats is very likely causing unprecedented changes in the evolutionary trajectories of many tropical species.”

Image: Lindolfo Souto

10 years

102 researchers from 21 countries

129,000 specimens

25,000 species in a 6,000-hectare forest

…yielding an estimate of 6 million arthropod species on our planet.

Ready for the details behind the numbers?

In 2003 and 2004, a large team of scientists (see numbers above) led by the Smithsonian Tropical Research Institute on an endeavor called Project IBISCA-Panama, scoured Panama’s San Lorenzo rainforest for arthropods (which includes insects, spiders, and millipedes).

They sampled the forest from top to bottom from a construction crane, inflatable platforms, and balloons, climbing ropes through forest layers as well as crawling along the forest floor to sift soil and trap arthropods.

They then spent the next eight years identifying the 129,000 specimens collected within twelve 20-by-20 meter squares. They determined that within those specimens, there were over 6,000 species of arthropods. Using various models the team extrapolated the total number of arthropod species to 25,000 residing in the 6,000-hectare forest.

The research is published in the current edition of Science.

According to Science Now,

The study is the most extensive survey of insects, spiders, and their relatives ever undertaken and should help researchers get a better understanding of what factors influence biodiversity.

“This is a high number as it implies that for every species of vascular plant, bird or mammal in this forest, you will find 20, 83, and 312 species of arthropods, respectively,” explains lead author Yves Basset.

“If we are interested in conserving the diversity of life on Earth, we should start thinking about how best to conserve arthropods,” adds Tomas Roslin, one of 35 co-authors.

“Another exciting finding was that the diversity of both herbivorous and non-herbivorous arthropods could be accurately predicted from the diversity of plants,” says Basset.

“By focusing conservation efforts on floristically diverse sites, we may save a large fraction of arthropods under the same umbrella. Further, this strengthens past ideas that we should really be basing estimates of global species richness on the number of plant species,” stresses Roslin.

For some amazing images of these arthropods and the collection process, please visit National Geographic.

Image: Thomas Martin, Jean-Philippe Sobczak, and Hendrik Dietz, T.U. Munich