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

At over three feet, you’d think the solo coral grouper would be threatening enough. Threatening sure, but a successful lone hunter? Well, not so much, according to National Geographic News Watch:

When hunting alone, groupers only catch their prey about 1 out of every 20 attempts.

So the grouper teams up with the even fiercer moray eel, or the very large Napolean wrasse, to go hunting. The fish are looking for smaller coral reef fishes that hide from their predators under rocks and coral. When the grouper detects the hiding prey, it signals its hunting friend and together they both flush the prey out of hiding.

The cooperation, however, ends there. Whoever gets the prey, eats it whole. There’s no sharing of the spoils. Still, for the grouper, it’s worth the shared hunting, says National Geographic News Watch:

When they have help, the ratio is significantly better—about one out of seven.

What’s most significant about this shared hunting are the signals the grouper makes to its partner during the hunt, say scientists. Researchers studying the fish observed dozens of events where groupers performed upside-down headstands with concurrent head shakes to indicate the presence and location of particular prey to cooperative partners. Their study, published last week in Nature Communications, call the groupers’ signals “referential gestures”. From the abstract:

In humans, referential gestures intentionally draw the attention of a partner to an object of mutual interest, and are considered a key element in language development. Outside humans, referential gestures have only been attributed to great apes and, most recently, ravens.

It’s likely that these gestures have been understudied in non-primate species, say Academy researchers, who point to hunting dogs and even bee dances as potential consideration for referential gestures.

The researchers of the study say that the mental processes underlying these gestures in fish, apes and ravens are unclear and may well vary among these taxa. Their findings point to the fish having developed cognitive skills according to their particular ecological needs.

Whatever the cause, these hunting tactics are pretty extraordinary. Videos of the behaviors can be found here. For more information on the study, visit the University of Cambridge website.

Image: jon hanson/Wikipedia