If large carnivores go extinct, must the ecosystem collapse?

Either because of their large size or because humans are at the top of the food chain, we pay more attention to large carnivores that are also higher up the food chain. As a result, we subconsciously believe that large carnivores are more important in the ecosystem than small, herbivorous animals. One cannot help but wonder if the ecological balance will be upset if large carnivores become extinct, and if the ecosystem will eventually become irreparable and collapse.

I. Substitutable among species at the same trophic level

Ecosystems are in dynamic balance through energy flow, material cycling, and information transfer between organisms and organisms, and between organisms and the inorganic environment. At the same time, an ecosystem can maintain its stability, and it is generally believed that the more complex its food web, the stronger its ability to recover itself.

In a more stable ecosystem, the extinction of a species can be replaced by other species with similar characteristics. For example, in a grassland ecosystem, when a large carnivore cheetah becomes extinct, the number of herbivores gazelle will increase sharply for a short time and the amount of grass will decrease sharply; if there is another carnivore (such as wolf) besides cheetah, then once the cheetah becomes extinct, the wolf will increase its predation pressure on the deer If there is another predator besides cheetahs (e.g. wolves), then once cheetahs are extinct, wolves will increase their predation pressure on deer without causing the deer population to grow too large, thus potentially preventing ecosystem collapse.

Wolves and cheetahs hunting (Photo credit: veer gallery)

Wolves and cheetahs can be at the same trophic level in the food web, and different species at the same trophic level have the same "role", so when cheetahs go extinct, they can be "replaced" by wolves. In detail, different species at the same trophic level can perform the same level of material cycling, energy flow, and information transfer functions in the ecosystem.

Back to the initial assumption, if we can find other things that can replace large carnivores in the ecosystem to accomplish the same degree of material circulation, energy flow, and information transfer, or if the extinction of large carnivores will not destroy the ecological balance by affecting these three functions, then we think the ecosystem will not collapse due to the extinction of large carnivores.

Second, it can be replaced in the process of energy flow

Therefore, as far as energy flow is concerned, energy flow is unidirectional and can only flow from the first trophic level to the second trophic level, and then to each trophic level in turn, which is irreversible and cannot flow circularly; energy decreases step by step in the flow process, and the transfer efficiency between two adjacent trophic levels is about 10% to 20%.

Therefore, very little energy is obtained by large carnivores, and most of the energy is still concentrated at the bottom of the species, i.e., between green plants and herbivores. In other words, even if large carnivores become extinct one after another, the process of energy flow is almost unaffected. Large carnivores can be replaced in the process of energy flow.

Almost all of the energy on Earth comes from the sun (image source: veer gallery)

At the same time, the material cycle of an ecosystem refers to the fact that elements such as C, H, O, N and P, which make up living organisms, are constantly undergoing a cyclic process from the inorganic environment to the biome and then to the inorganic environment. For example, carbon enters biomes from the inorganic environment mainly in the form of carbon dioxide by photosynthesis of green plants, and then is transferred between organisms in food chains and food webs, and finally enters the atmosphere from biomes by respiration of organisms or decomposition of decomposers.

If large carnivores become extinct one after another, only the respiration of organisms will be affected to a certain extent (for example, if cheetahs in grassland ecosystems become extinct, the number of gazelles will increase, resulting in a corresponding increase in respiration), but the decomposition of decomposers will have little effect, so the material cycle of ecosystems is unaffected, and large carnivores can be replaced in the material cycle.

Material cycle (Photo source: panorama.com)

Third, little impact on ecosystem information transfer

Finally, as far as information transfer is concerned, the information transfer pattern of the ecosystem will change after the extinction of large carnivores, but the overall effect will not be too great, because without the predators, there is no way to transfer the physical and behavioral information of the predators to the herbivores, and the alertness of the herbivores will decrease, but the decrease in alertness will not threaten their survival. The extinction of large carnivores will not collapse the ecosystem even if it affects the information transfer between organisms.

Predation is only one of the factors limiting the number of other animals, such as herbivores, that might be feared to proliferate. Predation is only one of the exogenous factors that limit the growth of animal populations. Exogenous factors include disease, parasitism, natural disasters, food limitation, etc. Endogenous factors include domain behavior, endocrine regulation, etc., which do not change in a short period due to the sudden disappearance of predators, and all of these factors limit the growth of other species.

Dead deer (Photo credit: veer gallery)

In summary, from the point of view of "collapse", even if all large carnivores are extinct, the ecosystem will not completely collapse, and the bacteria can make the ecology restore to a completely unrecognizable shape again after a long evolution. Even if all plants and animals are gone, bacteria can continue to maintain the Earth's biosphere active, and "large carnivore extinction" does not cause many animals to become extinct, as the number of food herbivores can also be controlled by pathogens, parasites, and people.