Libmonster ID: BY-1596
Author(s) of the publication: Alexei SEVERTSOV, Anna SHUBKINA

by Alexei SEVERTSOV, Dr. Sc. (Biol.), Biological Department of the Moscow State University named after M. Lomonosov, Anna SHUBKINA, Cand. Sc. (Biol.), Institute of Problems of the Ecology and Evolution named after A. Severtsov

Why this or that animal falls prey to predator? The observations in natural environment show that it is rather difficult to estimate reasons why the particular animal becomes the prey. Predators are unable to catch any animal suitable for them in size, not each potential object is available. Consequently, there exists, as specialists say, the "selective removal", which means the natural selection, accomplished by predators.

WHO IS LUCKIER THAN A CHEETAH?

Field studies are associated with numerous challenges. Besides, classical field methods are rather inefficient. The first problem for the scientists is estimation of the predator's hunting success. In other words, you should know an exact number of pursuits and their results. Normally, such observations are carried out in winter by tracking in snow, i.e., by way of studying attacks by traces left by the animal. It is a labor-intensive and arduous task, since predators are able to run some tens of kilometers daily, including places difficult of access, while a biologist needs to count all attempts to catch the prey to get reliable biological data. In addition, winter is the hard time for herbivorous animals, when they can become totally helpless. That's why, there is a probability of incorrect interpretation of real elimination reasons. Often it is impossible to use technical devices-predators could be afraid of snowtractors following their

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tracks: active observations may affect their behavior and spatial distribution. Therefore, assessment of hunt success is usually rough. It has been established that efficient pursuits occasionally reach 50 percent of the total number of attempts. For instance, a cheetah-the fastest of big predators-succeeds only in 25-26 percent of all attempts. A team hunting organized by wolves and African wild dogs is considered most productive: they catch the prey in 40-46 percent of all attempts. But, before the start of the chase, wild predators watch probable victims and often cut off the hunt. It is considered that wild Can-ids assess chances before chasing a potential victim.

The second problem is that it is extremely difficult, if ever possible in wild nature, to assess reasons that make this or that animal a victim. First, predators eat the prey, and then come vultures, the remains are decomposed in destructive food chains. That is why selectivity in terms of classical field studies is assessed only in rough figures.

There is a number of wide-spread approaches to studies of remains of dead animals. The general state (conditions) is assessed proceeding from the share of bone marrow fat in tubular bones of dead animals-they are preserved better. If the part is down to 50 percent, this means the starving animal is without subcutaneous and abdominal fat. Due to this method, scientists established that spotted hyenas catch gnu antelopes mainly with a low fat index, but not those which are about to die

There are data evidencing that wild predators selectively remove the youngest and oldest animals, as well as animals in a poor state (in bad conditions, injured, sick, behaving inadequately, etc.). These facts confirm selectivity, but fail to elucidate neither its degree nor mechanisms which determine the accessibility of the potential prey. To determine the degree of selectivity, it is necessary to examine not remains, but the fresh prey, which is hardly possible in wild nature.

THE WILD PREDATOR MODEL-WINDHOUNDS

To get the opportunity to study characteristics of the prey and repeated play of the process of search, pursuit, attack and capture, we elaborated the model of wild Canids hunt. Windhounds (sighthounds) were used as the predator. They are the unique group of domestic dogs capable of game capture without human assistance and without weapons. It is commonly believed that these very fast dogs hold down animals which they descry (get sight of) in the field or steppe. In such a way, windhounds simulate the hunt in hijacking ("driving away")-the chase-form typical of wolves, jackals, cheetahs, hyenas, and other terrestrial predators. The model has a number of advantages. First, pursuit is in the open space, which facilitates observations. Secondly, irrespective of different groups of windhounds (breeds, genetic groups), there is

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a commonly accepted system to describe their "work" adopted for field studies. Finally, the researcher gets the whole bag (prey body), not only its remains. It is true that the model has its shortcomings: centuries-old selection of windhounds was aimed to select the dogs pursuing any game without preliminary assessment of expediency of hunt.

Windhounds are used to hunt hares and foxes, wolves and jackals, small and medium antelopes. Hence, windhounds are able to run a little bit faster. Special high-frequency GPS recording units were designed to study how the speed affects hunt success and quantitatively describe behavior of chasers. Devices were fixed on dog collars during field trainings and trials in chase with free-living European hare. With the help of second-by-second registration of coordinates was determined location, speed and direction of movement of conventional predators and their victims. It was established that the speed of pursuit depends on many factors: the relief and microrelief, soil and vegetation properties, weather, etc. Sometimes predators and prey fail to gain maximal speed due to natural conditions. GPS recording data enabled scientists to identify a number of important factors.

The speed of windhounds, which is higher than that of European hares, is not so high as it may seem. It varies from 7.43 to 16.9 m/s, i.e. does not exceed 17 m/s. This complies with the data obtained at English greyhound racings and indicators on thoroughbred racehorses and cheetahs established by similar methods.

Speaking of English racehorses, the gallop speed varies from 7 to 20 m/s, while cheetahs in the nature usually run at a speed of 10-18 m/s and almost never reach 26 m/s. Diversity of natural conditions affects the changes of pursuit speed of windhounds every several seconds: even a flat surface of a wheat field has areas of different thickness and density, various height vegetation types, micro- and micro depressions and elevations.

Windhounds pursue European hare for a distance from 389 to 2,674 m, which is much more, as compared with a cheetah (average distance is 173 m, maximal distance-559 m). No doubt, such criteria as speed, duration and distance of pursuit are important, however this is not the whole story-the capture takes place in different speed ranges, at different distances and duration of pursuits.

Windhounds often detect hares before they become visible (get up to run away, start moving), i.e. can smell them. This was proved during field observations and data fixed by GPS recording units-active search may start long (tens of seconds) before the hare flashes.

Sometimes windhounds stop pursuit after a number of approaches to the prey, i.e. irrespective of marked superiority in speed. In other cases they pursue a hare for a kilometer or more and then catch it, though not always.

стр. 13

In other words, in the process of pursuing dogs assess its prospects, albeit incorrectly.

It must be emphasized that ethical restrictions are an integral element of our experiments. Field tests were carried out in the late autumn-early winter to eliminate any risks of poor health of wild animals due to hunger or other adverse factors. In this period there are no young animals, pregnant females, etc. We carried out tests in the regions where the state of prey species was characterized as safe, i.e. withdrawal of animals for studies would not have a negative effect on the well-being of populations. For comparison we used animals killed by local hunters within the same period and in the same areas.

SELECTIVITY OF CHOICE

The highest selectivity of windhounds hunt was established while studying saiga chase as early as in the 1980s. This was a starting point to initiate interaction between a predator and a prey on the individual level.

For 2 field seasons in Kalmykia (in the period of abundance of saiga antelope in the region) scientists studied the animals which were pursued by the windhounds. All in all, they caught 38 animals. Concurrently, employees of the State Hunting Supervision Service shot allegedly 40 sick saigas. Each of these 78 animals were subjected to complete pathologoanatomical examination by veterinary surgeons who took part in the expeditions. It turned out that all antelopes caught by windhounds were far from being healthy. As for the shot animals, the share of sick ones was much less-only 33 percent. Thus, the dogs were very precise in choosing sick animals, unlike human specialists. Most pathologies found in saigas were visceral (heart, leaver, lungs, etc.) disorders. We should point out that such abnormalities cannot be identified by remains of the victims caught by wolves and other predators (first of all they eat internal organs).

In the course of 30 seasons, we were studying hunting of windhounds for European hares in steppe regions, comparing animals caught by dogs and shot by local hunters. Outwardly and by average weight, the hares were almost identical, all differences were revealed only in the course of pathologoanatomical studies, when we compared conditions by the state of adipose capsules of kidneys (kidney fat index). Finally, it was found out that the hares caught by windhounds were in a worse condition than the animals shot by the hunters.

The microbiological research enabling to measure the stress level not connected with the moment of capture turned out to be rather promising. The quantity of microflora on the surface of noses of the hares caught by windhounds was higher than in the shot animals. According to the results of immobilization stress tests (hares were put into narrow cages for 3 days), the hares had almost the same number of microorganisms as the hares caught by the dogs. This means that windhounds catch animals existing in a long stress.

The predator shows itself as the very strict breeder-it eliminates the animals with different health disorders. In addition, high selectivity of actions of predators combines with low efficiency of hunting.

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HUNTING SUCCESS

Speaking of saiga hunting, on average 27 percent of windhound pursuits were successful. As for hare hunting, the number of successful chases was from 0 to 70 percent, depending on the day and season. During trials-dogs were let out in groups of 2-3 at least 25 m away from a victim-the hunting success made up 12 percent of the number of pursuits (596 windhounds caught 35 hares in 282 attempts). This complies with the results obtained in the UK, when the fastest dogs (greyhounds) caught 15 percent of hares released from the cages. The hunt of domestic dogs is less successful as compared with wild animals, but their hunt success also varies, depending on the season and prey species. In case of exact registration of all hunts made by wild animals, the result would not be so high. Let's remind you that only 26 percent out of 367 pursuits were successful for cheetahs.

The choice of prey is affected by a number of factors: for example, when hunting for rodents, a feathered predator attacks an animal differing from the majority. Possibly some of the victims have distinctive parameters of movement choosing a wrong strategy to escape, or perhaps are late to get away from the predator, etc. But such animals amount is insufficient to feed predators-at least in autumn, in the period of tests. Observers were able to predict capture of saigas only in 5 cases out of 210 documented pursuits (2 percent). As for the hares, humans are not able to make reliable predictions. This means that visually distinguished signs, as a rule, are not enough to say exactly whether the animal will be caught or not.

The predator uses any circumstances to facilitate hunting. As a rule, it eliminates animals with health disorders. This disparity brings up a problem of making difference between available (sick) and unavailable (healthy) animals. In theory there are only two mechanisms enabling to determine availability of the prey in advance remotely: visual and olfactory. The latter implies changes of smell of attacked sick animals in comparison with healthy ones. The mechanism of such change was initially registered in laboratory and open air cage animals during tests led by the biologist Acad. Vladimir Sokolov in the early 1990s.

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SIGNIFICANCE OF MICROFLORA

Cavities and surface of a human body and animals are full of numerous microorganisms-mutualists, commensals, pathogens, and simply symbionts, including bacteria and yeast forms. Their number and composition are constantly changing: both diseases and any deterioration of the state of the macroorganism results in an increase of the number of microflora on the body surface in 2-3 days.

The number of microbes is 10 times greater than the number of cells of the macroorganism (established for a human being), while their number and even composition vary depending on the physiological condition of a carrier, for example, in case of fever. This is a result of the universal generalized adaptation syndrome, known as a stress. The microflora in cavities and on the surface of a body is processing and mediating all excretions of animals and man-i.e. the smell of any macroorganism is a result of bacterial processing (which is widely used in perfume and deodorant industry). Odor intensity depends on the number and composition of microorganisms.

According to our field observations, windhounds are attracted both by the smell of caught hares and bacterial imprints from their noses. The experiments showed that the smell of bacteria is sufficient to change the direction and rhythm of their motion-dogs move towards the source of the smell. This smell is a unique modulator of metazoans' behavior. For example, the smell of bacterial population (imprints from the skin surface) from the people suffering from malaria is enough to change the direction of movement of malaria carriers, mosquitoes of Anopheles genus.

Thus, in the course of experiments carried out with participation of windhounds, we determined one of the mechanisms used by the predators to assess accessibility or non-accessibility of a potential victim. No doubt, it is not ideal, since spreading of smell depends on many factors: from meteorological to biotopic conditions, and, of course, from the distance.

WHAT'S HAPPENING IN PREDATOR-PREY INTERACTION?

The welfare level vary among animals and also for each of them for life. These variations determine changes in

стр. 16

Frequency of incidence of hares with a varying number of bacteria caught by windhounds (a), in a stress (b), shot by hunters (c).

Distribution of brown hares with different bacteria amount in three groups

caught = 46*0,1*normal (x; 0,5085; 0,1639)

stress= 18*0,1*normal (x; 0,4111; 0,0618)

shot = 22*0,1*normal (x; 0,1859; 0.0583)

the microflora, therefore microbiota is one of the indicators of the state of metazoans. In their turn, microbiota changes, induced by the state of a host organism, modify individual odor, which enables the predator to identify the available prey. Disorders of different origin become key characteristics of the prey increasing the probability of its capture. It is marked by the body surface microflora change, which affects the animal odor.

Among animals caught by predators predominate those with physiological disorders, i.e. changed or increased microbiota. It implements a mediator function in predator-prey relations. The use of smell increases the selectivity of elimination. In other words, participation of microbiota explains one of the mechanisms of natural selection by predators.

Not only a long-term stress, but also any temporal reduced adaptability can trigger the prey removal (or elimination). Predators have an influence on the number of animals, but do not regulate it. Removing the sick animals, they improve a qualitative composition of populations. High selectivity of elimination means survival of the fittest. The main value of the selection performed by predators is stabilization of the population norm and increase of the number of phenotypes possessing a sense of adaptability to the integral effect of the environment.

We should acknowledge that the predator is in fact a universal breeder. Co-evolution in food-chains will never ensure complete protection of the 1st order consumers (plant-eating) or an absolute success of the 2nd order consumers (predators). Selectively eliminating all and any insufficiently adapted animals, predators act as strict and tough breeders. However, since natural selection is implemented simultaneously according to numerous and diverse features, it is almost inefficient by each of them. At the same time, it is difficult to overestimate its significance for existence of prey-species populations. The only comparison we can offer is a purifying selection at a molecular level through elimination of any harmful mutations. At an individual level, selection carried on by predators stabilizes not separate factors, but an organism in its integrity.

The work is supported by RFFR grant No. 13-04-00179, grants of the RAS Presidium "Biological Diversity", "Biological Resources'', and "The Animate World".


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Alexei SEVERTSOV, Anna SHUBKINA, PREDATOR AS A UNIVERSAL BREEDER // Minsk: Belarusian Electronic Library (BIBLIOTEKA.BY). Updated: 21.11.2021. URL: https://biblioteka.by/m/articles/view/PREDATOR-AS-A-UNIVERSAL-BREEDER (date of access: 04.12.2021).

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