Ecology And Roles In Ecosystem

Because Collembola are found in all habitats, from the coldest to the hottest supporting multicellular life, and from treetops to the deepest soil layers supporting multicellular animals, it is clear that their responses to various abiotic conditions must vary enormously. Humidity is usually the most important factor in determining Collembola distribution. High humidity is seldom a problem for Collembola but desiccation is often serious. Collembola resist desiccation by moving into microenvironments of high humidity (under stones or into deeper soil layers) and/or limiting activity to nights and by morphological adaptations (such as cuticular thickening, ornamentation, and scales). Some species, as already discussed, change form radically and cease feeding, while others go into anhydrobiosis. Many species lay eggs that are much more resistant to drying and they survive desiccation in this stage, often accompanying this with short postembryonic life cycles.

Collembolans have vastly different temperature tolerances and preferences, ranging from a species of Sminthurides found in volcanic vents with temperatures as high as 48°C to an Antarctic species shown to survive temperatures below -30°C. Survival (and activity) in low temperatures has been studied extensively. Some Collembola are primarily inhabitants of glaciers and ice fields and others are dominant members of the arthropod faunas of high latitudes. Winter-active Collembola in temperate climates often build up large numbers under snow and on suitable warm days pour out onto the snow in vast numbers as snow fleas. Extreme cold tolerance always involves supercooling with the accumulation of cryoprotective substances.

Oxygen requirements of Collembola also vary enormously. The greatest tolerances discovered are in the Antarctic Cryptopygus antarcticus, which has a 30% survival rate after 30 days in pure nitrogen atmosphere. In many Collembola, respiration when submerged is via air films surrounding the animals as a result of their hydrophobic cuticle, but this apparently not necessary in all forms. In many forms the eggs are more resistant to immersion than in other stages.

Collembola, even in uniform soils, are never randomly distributed, but show strong clumping because of pheromones or local food abundance or simply as a result of limited dispersion after founding events and subsequent population growth.

Competition between Collembola species in cultures has in at least a few instances shown that there is no evidence for competitive exclusion, even under long-term clearly competitive conditions. In addition it has been shown that interactions between two species can be either positive or negative depending upon the nature of the interaction (airborne allomones, substrate-transmitted allomones, or direct contact).

While most soil- and litter-inhabiting Collembola feed primarily on decaying vegetation and fungi (and appear to be general feeders), experimental studies have shown that, given a choice, they may be very selective as to both the decay state and nature of the vegetation and the species of fungi. A number of Collembola are occasionally or primarily (and in a few species exclusively) carnivores, different species feeding on a variety of organisms, ranging from rotifers to other Collembola. Probably the most commonly eaten prey is nematodes. Vegetation-inhabiting Collembola eat primarily unicellular algae, pollen, and soft parts of vegetation and fungal spores. Many Collembola are coprophagic, feeding largely on arthropod feces. Some littoral species appear to feed largely on diatoms or unicellular algae, and forms with piercing—sucking mouthparts feed largely on fungal hyphae juices. Thus their primary role in the environment is that of reducer; however, another major role is that of prey. The ability to jump is the major defense mechanism of Collembola; however, many Poduromorpha, particularly those with the furcula short or absent, have body fluids that are repellent to predators, and they may release these by reflex bleeding when attacked. Most carnivorous soil organisms feed on Collembola, and many beetles, ants, and wasps are specialized for feeding on them.

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