The remains of red deer (Cervus elaphus) increase the number of arthropods (including non-scavengers) and plant biomass, even in those communities where there are enough nutrients without corpses, writes in PLoS ONE. The effect of the presence of carcasses is manifested even when their decomposition is almost complete.
In densely populated Europe, carrion has become a rarity. After death, farm animals must be removed, their corpses must be destroyed. An exception is made only in cases where the remains can serve as food for rare scavengers - for example, vultures. However, local residents, as a rule, are against corpses lying near them. Animals that have been hunted can also be left at the place of death, but in practice almost no one does this.
Meanwhile, decaying remains are one of the most important sources of organic and mineral substances for many species in any natural community. Detritophages (those who feed on the flesh of the dead or the waste products of living organisms) convert various elements into a form more accessible to other organisms. This indirectly increases the mass of those who are able to feed on this site, as well as the diversity of species in the community.
Roel van Klink of the German Center for Integrated Biodiversity Research (iDiv) and his colleagues investigated how the presence of large carrion affects the biodiversity of one of the oldest European nature reserves, Ostvardersplasse. Its area is 56 square kilometers, of which 36 are swamps. It is located below sea level and is fenced off from it by a dam.
The main large herbivores of the Ostvardersplasse are Heck bulls (a breed of domestic cow), Polish konics (a breed of domestic horses) and red deer. Large predators are absent there, so the number of ungulates is regulated by the amount of food in the cold season and sometimes by humans (they shoot those who definitely will not survive the winter). The corpses of bulls and horse bunks are disposed of after death (although it is not necessary to do this specifically in Ostvardersplass, but this is done due to the reaction of the population), but deer are often not.
In 2013, scientists determined the number of species of various arthropods and the size of plant biomass on the lands of Ostvardersplass near and far from deer carcasses. All ungulates whose remains were studied in this study died in February and March, when food was least available. In that year, 1,296 deer died, traps for arthropods were set only around five corpses and at five control sites at a distance of at least 25 meters from these corpses. The authors explained such a modest number of experimental sites by the fact that in a few months they expected to catch so many individuals of arthropods that they should be enough for statistical processing of the data.
The traps were installed at the end of April, three for each site. The content of the traps was assessed once a week and it was noted which species of arthropods were encountered there. Scientists also determined the density of vegetation at control and experimental sites. At the beginning of the observations, it did not differ: the average height of the grass cover was 5 centimeters, the ungulates ate last year's grass, and the new one had not yet had time to noticeably grow. At the end of August, biologists collected samples of arthropods and plants directly from the remains of deer (by that time they were almost completely decomposed) and from the ground within a radius of 50 centimeters from them. After that, the observations were stopped.
The influence fell on the number of arthropods one month (top line) and five months (bottom line) after its appearance.
As expected, the number of detritivorous arthropods in the plots with deer remains was higher (P <0.01) one and five months after the start of observations than in the control plots. In addition, at the end of August, more carnivorous and herbivorous arthropods were also found in the carcasses of ungulates (in both cases, P <0.05). This appears to be a delayed effect of the presence of a fall.
The place where the corpse of the deer lay, about five months after the death of the animal, is covered with lush vegetation. It is mainly curly thistle and medicinal thistle.
By the end of the observation period, the plant biomass was five times higher on the plots with corpses than on the control plots. Many species were invisible because of tall specimens of curly thistle (Carduus crispus), but besides it, on the deer remains, the medicinal walker (Sisymbrium officinale), plantain (Plantago major) and others grew. Interestingly, the ratio of carbon to nitrogen atoms in them was lower than in the same plants from the control plots, which indicates their greater nutritional value.
The authors emphasize that the soils of Ostvardersplasse are themselves rich in nutrients, and therefore it is unusual that carrion there promotes an increase in plant biomass and the number of arthropods, especially after decomposition. They suggest that larger carcasses have a more noticeable effect than smaller ones. Scientists believe that if legal and unspoken prohibitions on leaving fell in this reserve and other similar places can be circumvented, the diversity of arthropods will benefit from this.
The decomposition of bodies is studied not only by ecologists, but also by criminologists - albeit from a different angle. They find out how human remains change after death under the influence of various factors. The first "body farm" in Europe appeared in the Netherlands. She, like other similar sites, provokes public protests.