The bee and the turtle: a fable from Yasuní National Park

Wandering Yasuni National through the Park forests (YNP) and in along the the Ecuadorian rivers of i ational Park (YNP) in the Ecuadorian Amazon is probably every naturalist's dream. A few years ago, we made that dream a reality (Figure 1). As ecologists with a broad interest in many theoretical and applied aspects of this discipline, we wanted to go to YNP to find inspiration for new ideas about the structure and function of a variety of organisms and their interactions. For many taxa especially insects and other arthropods, which constitute the main model organisms of our research one can see more species in a day's walk in YNP than during a lifetime spent in temperate zones. YNP has the highest density of tree, mammal, amphibian, and insect species ever recorded on the planet (Bass et al. 2010). The numbers are staggering. In an area equal to that of about 34 football fields (25 hectares), one can find over 1 100 species of trees more than in the whole of the US and Canada combined. Comparisons with similar plots in other tropical forests worldwide reveal that YNP has the highest density of tree diversity of any place on Earth. As for fauna, 185 amphibian and reptile species have been found in just a few hectares of the park, which also shelters half of all the mammal species that inhabit the Amazon Basin. As many as 35 000 insect species are estimated to exist within a 3 -kilometer radius of a central point in YNP, which is about 40% of the total number of species described for all of North America (see Dangles et al. [2010] and references therein). YNP was therefore the perfect place to stumble onto exciting interactions, behaviors, and ecological mysteries. For us, as ecologists, it was a scientifically rejuvenating trip. One of us even took his teenage kids, who did not want to miss out on the chance to experience a real jungle firsthand. Our journey began early on a chilly morning in Quito, the capital of Ecuador. A 30-minute flight took us over icecapped volcanoes and pristine Andean jungles, and onwards to the small town of Coca, at the edge of the Amazon forest. The temperature was 20°C and the high humidity left our skin sticky to the touch. Our trip continued by canoe down the sediment-rich waters of the Napo River, the largest river in the Ecuadorian section of the Amazon Basin. From the entrance to YNP, we paddled up several blackwater creeks and reached the base camp of the Anangu indigenous community in the evening, accompanied by the rhythmic flashes of hundreds of fireflies. Many YNP visitors take home treasured memories of seeing a rare harpy eagle in the dense canopy, a jaguar sitting on a river bank, or a giant otter fishing for piranha in the river. We had the privilege of seeing a family of the critically endangered giant otter (only a handful of which remain in the park), but our most memorable experience was, in fact, observing a bee (Centris sp) flying around a turtle ( Podocnemis unifilis). The Bee and the Turtle may sound like a fable by Jean de La Fontaine, but the scene we were fortunate enough to witness and photograph appears to be the first documentation of tear-feeding behavior by solitary bees on river turtles (Figure 2). We spent more than an hour observing this unexpected interaction between the two species, first spotted by the restless teenagers. We watched the scene with the same wonder that characterized our first natural history discoveries as children, while at the same time our adult selves were trying to decipher this behavior in the context of ecological concepts, like optimal foraging and species coexistence. It was only once we were back at home with our books and computers that we learned that tear-feeding behavior is quite well documented. Sodium is an essential nutrient for the survival and reproduction of living organisms: it helps maintain blood volume, regulates the balance of water in cells, and keeps nerves functioning properly. Although plentiful in the oceans, this element is in short supply on land, particularly in plants, which is why many terrestrial herbivores crave salt. Many species of insects, including several types of butterflies and moths, frequently visit moist ground and the excrement and carcasses of animals to obtain the dissolved nutrients they contain. Some of these insects specialize in tear-feeding (ie feeding on placid animals like deer, crocodiles, and even sleeping birds) that cannot readily swat them away. Local scarcity of