Dispersion flight

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As dispersion flight (from the Latin. Dispergere = spread, scatter) refers to the Entomology ( Entomology ) the individual propagation flight active insects from their development Habitat out. Flights only within an action area , for example to search for food or to flee from predators, are therefore not dispersion flights . Dispersion corresponds to the population-biological and ecological consequences of the migration behavior of the individual insect.

The main purpose of the dispersion is to colonize new habitats. The ability to disperse is essential for the survival of populations and species, especially when changing habitats. If dispersion takes place in habitats already populated by the species, one consequence is the networking of different habitats and populations through gene exchange.

Dispersion flight: an optimization problem

In principle, a newly hatched or developed winged insect has two possible behaviors: It can remain in its development habitat, look for food and reproduction partners here and ultimately produce offspring here, or it can leave the habitat in search of new habitats. The advantages of staying are: It is probably in a favorable habitat (which was at least cheap enough to enable it to develop individually), it saves the expenses and costs of dispersion flight, such as energy for flight activity, and in some cases it can even To do without energetically expensive organs, such as wings and flight muscles, and instead invest the energy saved in his offspring. There is also no risk of perishing after landing in a completely unsuitable habitat. However, these advantages are offset by weighty disadvantages. If the habitat changes in a direction unfavorable for the species concerned, it will perish with it. Since almost all habitats have a limited lifespan, this increases the likelihood of extinction . In addition, there may be numerous conspecifics in the original habitat and therefore intense competition , while a newly created habitat may still be uninhabited and thus enable a much faster, possibly explosive reproduction. Dispersion flights are behaviors that have an effect on average individual fitness via the factors mentioned . In this way they are either promoted or suppressed by evolution , and under certain circumstances a genetically determined balance is established in its tendency to disperse. Numerous insect species have evolved phases in their individual life cycle in which obligatory dispersion flights are undertaken regardless of the favor or disadvantage of the habitat currently being inhabited. Others have special morphs that are optimized for dispersion, for example short-winged and long-winged shapes, so that only a part of the population performs dispersion flights.

Migration syndrome

Successful dispersion flights require coordinated adaptations in morphology and behavior, which can only guarantee success if they work together. One speaks here of an evolutionary syndrome . This includes

  • long wings . If, within a species, fully winged individuals appear alongside those with wholly or partially reduced wings, only the fully winged individuals are capable of dispersion flights. One speaks of dimorphism of wing development and calls the long-winged macropter, the short-winged brachypter. Instead of the wings, it is only possible to lose the muscles that drive them. The genetic basis of dimorphism is different, in many cases, e.g. B. in numerous beetle species, a single allele with Mendelian inheritance can cause the dimorphism, whereby the one for the short-winged morph is usually dominant . In addition, dispersing individuals are often somewhat larger than stationary individuals.
  • Hormone levels. In many insect species there is a connection between juvenile hormone and dispersion flights, with the stationary individuals having a higher level of the hormone.
  • Growth rate. Particularly large and particularly well-nourished individuals of a species with high reserves of substances are more widespread than small forms.
  • Tendency to fly. In some species, even with the same wing length, there are individuals with genetically determined different inclinations at the beginning and duration of flight behavior.
  • Age. In many species it can be observed that only young individuals perform dispersion flights before the start of the reproductive period. In some species, such as the winged morphs of the aphid Aphis fabae , no reproduction begins unless it has been preceded by a dispersion flight.

Direction and duration of flight

Insects, especially small-sized species, are barely able to cover long distances with only muscle-powered flight. The Reynolds number when flying in air depends on the body size. Air is increasingly becoming a tough medium for small organisms , so that the effectiveness of muscle-driven flight decreases more and more. This makes transport by convection , especially wind , more and more important. This has an important consequence for the flight behavior: the individual insect is not able to maintain a flight direction against the wind direction. In order to be able to control the flight direction, it is dependent on optimizing the time of departure. This includes reactions to odor stimuli (e.g. secondary plant substances of a host plant in herbivorous insects) and reaction to light intensity with flight, preferably during the day or at night. Flying insects can initiate landing attempts after optical stimuli, for example in response to the silhouette of trees against the horizon. By taking advantage of these mechanisms, even wind-drifted species can under certain circumstances gain a great deal of control over their direction of propagation. Since small insects tend to drift passively with the wind, they can cover enormous distances, especially if they are blown up to great heights by thermal convection. Some editors speak of "aerial plankton" (also: aeroplankton) , in analogy to plankton in waters. Especially smaller insect species are constantly in large numbers at heights of z. Sometimes several hundred meters high, and also over the open ocean. Small herbivorous insects such as aphids can also colonize very isolated host plants.

Investigation of dispersion flights

Because of the great importance that dispersion flights have on the biology, possibly even on the survival, of species, ecologists are very interested in finding out which species make such flights and to what extent. Various methods are available for this

  • Marking individuals with recapture (with measurement of the distance traveled)
  • Transmitting insect individuals and telemetry . Due to the weight of the transmitter, only possible with large insect species.
  • Analysis of the settlement pattern of isolated habitats, especially short-lived ones , for example the settlement of individual very old trees by deadwood colonists.
  • Analysis of genetic similarity between distant populations.
  • Direct catching of flying individuals, for example in window traps , or triggering of flight behavior, for example by an oncoming current.

In the case of habitat specialists, evidence of individuals away from suitable habitats is sometimes sufficient. The dispersion flight of insect species with aquatic larvae such as mayflies and caddis flies can be measured by their distance to the water. A Canadian study showed that the frequency of detection decreases more than exponentially with distance to the water, more so for small than for large species.

Dispersion in vertebrates

A similar process, the dispersal of birds (aves), is commonly known as dismigration .

Individual evidence

  1. ^ A b Hugh Dingle: The evolution of migratory syndromes in insects. In: Ian Woiwood, DR Reynolds, CD Thomas (editors): Insect Movement: Mechanisms and Consequences: Proceedings of the Royal Entomological Society's 20th Symposium. CABI, 2001 ISBN 0851997813 . Definition on p. 160.
  2. a b Derek A. Roff & Daphne J. Fairbairn (2007): The Evolution and Genetics of Migration in Insects. BioScience Vol. 57 No. 2: 155-164.
  3. Derek A. Roff (1986): The evolution of wing dimorphism in insects. Evolution 40 (5): 1009-1020.
  4. ^ Steve G. Compton: Sailing with the wind: dispersal by small flying insects. In: Ian Woiwood, DR Reynolds, CD Thomas (editors): Insect Movement: Mechanisms and Consequences: Proceedings of the Royal Entomological Society's 20th Symposium. CABI, 2001 ISBN 0851997813
  5. Jason W. Chapman, Don R. Reynolds, Henrik Mouritsen, Jane K. Hill, Joe R. Riley, Duncan Sivell, Alan D. Smith, Ian P. Woiwod (2008): Wind Selection and Drift Compensation Optimize Migratory Pathways in a High-flying moth. Current Biology 18: 514-518.
  6. JW Chapman, DR Reynolds, AD Smith, ET Smith, IP Woiwod (2004): An aerial netting study of insects migrating at high altitude over England. Bulletin of Entomological Research 94: 123-136.
  7. Thomas Ranius (2006): Measuring dispersal of saproxylic insects - a key characteristics for their conservation. Population Ecology 48: 177-188.
  8. Zsolt E. Kovatz, Jan JH Cibrowski, Lyndia D. Corkum (1996): Inland dispersal of adult aquatic insects. Freshwater Biology 36: 265-276.