Temporal specialist

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A temporal specialist (from Latin tempus "time", plural tempora ) is an animal species that specializes in a particular period of activity in relation to the twenty-four hour cycle of day and night that is called circadian . This can be seen as a time niche that enables ecological competitors as well as predators and their prey to coexist in the same habitat .

A distinction is usually made between the following types of activity:

• diurnal species. (diurnal, from Latin diurnus "days, on the day")
• nocturnal species. (nocturnal, from Latin nocturnalis "at night, nocturnal")
• crepuscular species. (rarely crepuscular, from Latin crepusculum "twilight")

You can connect:

• cathemeral types. (from ancient Greek ἡμέρα hemera “day” and the prefix κατά- kata- in the meaning of next to) This expression was coined by the primatologist Ian Tattersall in 1987 for species that have pronounced activity maxima both in the daytime and in the night, but without any relation to it Dawn or dusk.

Ecological reasons and effects

The chronobiological research is usually heavily on the neurological and physiological (eg. As hormonal) Basis of rhythm focused, so answer especially as questions. The reasons for the creation and maintenance of these rhythms, i.e. the why questions, are independent of this. The research on this topic is far less extensive.

Avoidance of competition

The ecological theory predicts that species with a similar way of life in the natural habitat are normally subject to strong interspecific competition , which can lead to the exclusion of one of the species from the habitat. For both species, but especially for species that are inferior to their competitors, there is an evolutionary incentive to nod down the ecological niche in such a way that competition is reduced. The temporal activity period is one of the "niche axes" into which the niche can take place. This is immediately evident in the competition called interference through direct, often aggressive interactions, so you can “avoid” one another. This was shown, for example, at the ecological guild of large and defensive African predators, where the smaller African wild dogs and cheetahs usually avoid the larger lions, leopards and hyenas through daytime activity, because these can only be seen when visibility is better, with bright moonlight, also hunt at night. In the case of competition due to the exploitation of both types of essential resources , such as food, such a mechanism is less understandable. If an inferior species refrains from exploiting a resource at certain times, this should always be disadvantageous for them as long as the profit from the yield would still exceed the costs of search and treatment (this can e.g. be significant with predators, their prey as well Has activity cycles). Temporal niche here is presumably essentially limited to cases in which a resource is continuously being renewed.

Enemy avoidance

More important than avoiding competition in ecological systems is probably the adaptation of the cycle of activity in order to avoid threatening predators (predators). Many diurnal predators are dependent on visual stimuli to locate their prey. For species that are neither poisonous nor defensive, or faster than the predator, a shift in activity in times of low predator activity can significantly increase the survival rate. In the case of the wild rabbit on the Iberian Peninsula , for example, it was made probable that the nocturnal species shifts its activity maximum to dawn and dusk when fewer predators are active.

A possible test of this theory is possible, for example, if a significant predator fails and does not occur in the habitat. So bats are generally nocturnal, especially to avoid birds of prey as predators. On small islands, on which most birds of prey cannot live, there should be an incentive for them to be active during the day. This was actually found in a species of bat on the island of São Tomé . Fish species living in coral reefs also increased their activity times after many of their predators were decimated (by recreational divers with harpoons).

Activity types: distribution in the animal kingdom

Although each individual animal species ultimately has its own cycle of activity, and this often remains surprisingly plastic even within a species, the various types of activity are not evenly distributed across the animal kingdom. Systematic groups ( taxa ) often have similar activity cycles due to their similar way of life. In addition, light or dark-adapted species often have special adaptations , especially regarding their sensory physiology , which make a change difficult. The temperature balance is also often important here, so that species therefore prefer the hot hours of the day or the cooler hours of night. The air humidity is also linked to this; the relative humidity is always higher during the cooler night hours.

It has been noticed for a long time that birds tend to be more diurnal and mammals more often nocturnal; this is especially true for smaller species. The thesis has been popular since the 1970s that mammals are preferably nocturnal because they inherited this characteristic from their evolutionary parent group in the Mesozoic era: According to this, the success of mammals can be explained by the fact that, by opening up the night hours, they can be explained by the superior competition how the predation pressure of the dinosaurs - the direct evolutionary parent group of the birds - were able to evade, above all their warm-bloodedness (homoiothermia) would be due to this. This thesis is supported by the fact that all mammals have lost two of the original four color vision pigments ( iodopsins ) in their eyes (presumably because color vision was less important at night), while these were retained in birds (that mammals still often have three visual pigments , i.e. seeing trichromatically, is due to the fact that one of the pigment genes later doubled and its sensitivity shifted secondarily to different spectral ranges).

Nocturnal animals use the visual system to a lesser extent than day animals. As a rule, the olfactory ( night butterflies , most mammals ) and acoustic senses ( crickets , owls , bats ) are far better developed in nocturnal animals .

The Mammals specialized originally referred to a night life, and only some diurnal groups such as the primates developed color vision. Nocturnal animals usually have pronounced camouflage colors that allow them to hide from predators during the rest phase during the day . If they wear a warning color , it is usually black and white (e.g. skunks ).

"Day" and "night animal" are global terms that indicate the period of their preferred activity time. There are also animals that are mainly active during twilight. A good example of this are trout - sight hunters who can barely benefit from the nocturnal insects at dusk.

Small mammals such as field mice , shrews , but also guinea pigs can often not be clearly classified as day or night animals because they have to eat at both halves of the day due to their high energy consumption and / or low calorific food. In these animals, activity is mainly based on the ultradian rhythm . If small mammals are forced to stop their activity either during the day or at night, they have to find methods to save energy ( torpor ) or to eat high-energy food.

It can also be observed that there are temporary shifts in niches when the food supply requires it. For example, bats hunt during the day in spring and autumn when the nights are too cold for a sufficient supply of insects.

Individual evidence

1. ^ Entry type of activity in Lexicon of Neurosciences, www.spektrum.de
2. ^ ^{A b} Noga Kronfeld-Schor & Tamar Dayan (2003): Partitioning of time as an ecological resource. Annual Revue of Ecology, Evolution and Systematics 34: 153-181. doi: 10.1146 / annurev.ecolsys.34.011802.132435
3. ^ Ian Tattersall (1987): Cathemeral Activity in Primates: A Definition. Folia Primatologica 49: 200-202. doi: 10.1159 / 000156323
4. ^ Gabriele Cozzi, Femke Broekhuis, John W. McNutt, Lindsay A. Turnbull, David W. MacDonald, Bernhard Schmid (2012): Fear of the dark or dinner by moonlight? Reduced temporal partitioning among Africa's large carnivores. Ecology 93 (12): 2590-2599. doi: 10.1890 / 12-0017.1
5. ^ TW Schoener: Resource partitioning in ecological communities. Science 185, 1974, pp. 27-38.
6. ^ RH MacArthur & R. Levins: The limiting similarity, convergence and divergence of coexisting species. American Naturalist 101, 1967, pp. 377-385.
7. ↑ Pedro Monterroso, Paulo Celio Alves, Pablo Ferreras (2013): Catch Me If You Can: Diel Activity Patterns of Mammalian Prey and Predators. Ethology 119: 1044-1056. doi: 10.1111 / eth.12156
8. ↑ John R. Speakman: Chiropteran nocturnality. Symposia of the Zoological Society of London 67, 1995, pp. 187-201.
9. ^ Danilo Russo, Guglielmo Maglio, Ana Rainho, Christoph FJ Meyer, Jorge M. Palmeirim (2011): Out of the dark: Diurnal activity in the bat Hipposideros ruber on São Tomé island (West Africa). Mammalian Biology 76: 701-708. doi: 10.1016 / j.mambio.2010.11.007
10. ^ Douglas J. McCauley, Eva Hoffmann, Hillary S. Young, Fiorenza Micheli (2012): Night Shift: Expansion of Temporal Niche Use Following Reductions in Predator Density. PLoS ONE 7 (6): e38871. doi: 10.1371 / journal.pone.0038871
11. ↑ for mammals cf. Laura Smale, Theresa Lee, Antonio A. Nunez (2003): Mammalian Diurnality: Some Facts and Gaps. Journal of Biological Rhrthms 18 (5): 356-366. doi: 10.1177 / 0748730403256651
12. ↑ Menno P. Gerkema, Wayne IL Davies, Russell G. Foster, Michael Menaker, Roelof A. Hut (2013): The nocturnal bottleneck and the evolution of activity patterns in mammals. Proceedings of the Royal Society B 280 (issue 1765) 11 pages. doi: 10.1098 / rspb.2013.0508
13. ^ Alfred W Crompton, C. Richard Taylor, James A. Jagger: Evolution of homeothermy in mammals. Nature 272, 1978, pp. 333-336.
14. ↑ David M. Hunt, Livia S. Carvalho, Jill A. Cowing, Wayne L. Davies (2009): Evolution and spectral tuning of visual pigments in birds and mammals. Philosophical Transactions of the Royal Society B 364: 2941-2955. doi: 10.1098 / rstb.2009.0044