The Big Crawling
Who is the real ruler of the tropics: jaguar, tiger, elephant or gorilla? Far from it: it's the insects. Their number is unmanageable, their function in the ecosystem irreplaceable. Now there are first answers as to why they are so species-rich in the rainforest.
Visiting the Green Hell: mighty trunks in the semi-darkness, now and then a tangle of liana, now and then a single mushroom on the ground, maybe colorful orchids and bromeliads on a broken branch. But animals? Where are the animals in this supposedly diverse rainforest habitat? Well, now and then a distant bird call sounds, something moves in the canopy or a toad crosses the path of the inexperienced visitor - not necessarily what is meant by abundance of species.
Perhaps the discoverer just needs to fine-tune his sights and hearing a bit: apart from the penetrating buzzing of the blood-sucking mosquitoes that can't be got rid of, constantly circling around a squadron - there in the light field of a small clearing the glowing one doesn't always flicker again and again Morpho butterfly blue? A tarantula sits on the trunk just passed and hunts camouflaged moths. And nearby is a street of busy leafcutter ants, who tirelessly carry handy bits of leaf into their subterranean realm to feed them to their mushroom allotment gardens - there is chirping and rustling everywhere.
The tropical rainforests may be world-leading in their collection of bird, frog or monkey species, but in reality their reputation as a global center of diversity is based on the myriad people of beetles, butterflies or hymenoptera. What is the reason for this exorbitant diversity of insects, which outshines everything else? Entomologists led by Vojtech Novotny from the University of Branisovska in the Czech Republic have now started this supposedly Sisyphus task and compared the number and species spectrum of leaf-consuming crawlies in a lowland forest in Moravia with those in a lowland rainforest in Papua New Guinea.
A project that is not so easy, since not only a confusing number of insects, but also thousands of tree species colonize the tropics - more woody plants can be found in undisturbed rainforests on one hectare than in the whole of Central Europe. Therefore, the researchers limited themselves to fourteen different plants, from which they hand-picked as many green-eating kerfes as possible - a total of almost 27,000 animals from 850 species with butterfly caterpillars and adult beetles as the dominant elements in each case.
Surprisingly, both areas performed almost equally well in terms of the number of species per unit area and plant: At the equator, at least the herbivorous insects do not divide their respective feeding grounds more finely than at higher latitudes - for example, one species only eats young leaves, the second only leaf tips and the third rather the stems.
For example, a vegetarian kerf in New Guinea uses one host plant on average, but only two in Europe; Bark beetles, or planthoppers, were even choosier in Moravia than their Pacific counterparts. A denser niche packing is therefore ruled out, at least for this group of insects, as a reason for their higher diversity in the tropics.
But then what explains the still largely obscure diversity of insect species in the rainforest, which some experts estimate is in the millions? Novotny's answer is very simple: it increases linearly with the number of plant species. And since not only more tree species grow in the tropics, but also types of plants such as epiphytes or lianas that are practically non-existent in this country, there are more insects there for that reason alone.
As with the vertebrates, the invertebrates also show another characteristic of tropical nature: many species, but only a few individuals. The total number of plant consumers was significantly smaller in Papua New Guinea than in Moravia, where whole legions of caterpillars, beetle larvae and offspring of various hymenoptera attacked the foliage, while in the south only a few adult specimens predominated. No wonder, after all, according to the researchers, the enemy pressure here was 18 times higher than in the temperate lowland forest - ants in particular excelled as vermin eaters.
If you want to see larger animals in the rainforest quickly, you should also look for the vicinity of ants. Because just when the legions of driver ants go on a cleaning tour through the forest, they are always accompanied by a few birds in their vicinity that want to benefit from the frightened and desperately fleeing beetles, scarecrows and butterflies. The nature lover shouldn't just stand directly on the train.