Albrecht, together with Prof. Dr. Torsten Wappler of the Hessian State Museum in Darmstadt and other Senckenberg researchers, classified a total of 47,064 fossil leaves of 436 plant species from 16 sites in Central Europe, Iceland, and Norway and examined them for feeding traces left by insects. “The fossils we studied cover nearly the entire Cenozoic era, i.e., the period between 66 and two million years before present. Moreover, the fossilized leaves originate from a variety of climates – from subtropical to oceanic to humid continental,” explains Wappler.
The team of researchers examined each well-preserved fossil leaf for signs of feeding by insects. More than one-fifth of the studied leaves revealed corresponding traces. “Based on these data, we can show that food plants were already used by a variety of herbivorous insects in early geological history. Moreover, the detailed evaluation of the feeding traces shows that the shared use of a plant species by different groups of herbivorous insects contributed twice as much to their functional diversity – in terms of their feeding mode – as the species diversity of the food plants themselves,” says Albrecht.
The results thus provide new insights into the origin of insect diversity and show that the co-occurrence of many specialized insect species on the same plant species is the primary factor driving the functional diversity of herbivorous insects, according to the authors. Albrecht adds, “When different insect species share a food plant species, they also have to adapt their diet and feeding mode to avoid direct competition with each other. Over millions of years, this led to the emergence of an incredible diversity of mouthparts, and ultimately species.” The study’s findings are reflected in today’s tropical forests, where most herbivorous insect species specialize on specific plant families, which in turn provide food for a variety of insect species.
“Our study emphasizes that the fossil record can be used to test fundamental theories about the origin of biodiversity. The results of our study are also an important benchmark for identifying the factors that determine the diversity of herbivorous insects in contemporary ecosystems,” concludes Wappler.