G.I.Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.

PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THEPARTI

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2.1.2.3. SUPERTOLERANCE to PLANT PESTS

2.1.2.3.1. Supertolerance to herbivores

2.1.2.3.1.1. Compensation of losses in seed and seedling stages

An operation of CESPPs 2.1.2.3. is based on the fact that seed production of plants is extremely redundant. It is much greater than the possibility of their progeny to survive to the age of maturity. In fact, P.S. Pogrebnyak (1968, pp.310-312) has cited a number of scholars, who show the annual values of seed yield of dominants in forest ecosystems. In coniferous tree species, the average values equal roughly 25 million of viable seeds per hectare at the good yield. Hence, over one forest generation (200 years in coniferous species), at beginning of yielding in 20 years and at the good yield every fourth season, a hectare of forest can produce above a billion of seeds.

Approximately 90% of seeds of the spruce, the fir or the larch are eaten by vertebrate consumers on the soil surface during winter (Vladyshevsky, 1984). Because in the beginning the period of seed producing, density of forest trees composes approximately a thousand per hectare, it is need for regeneration of this area only 1/10.000 part of the seed yield, which has not been consumed by herbivores in tree crowns and the soil surface.

The number of seedlings in the first season after good year usually reaches of several hundreds of thousands per hectare. If a forest cover continues to be closed, in several years only a few seedlings survive – 1/100.000 part of a one-year progeny. Further, the most part of them is condemned to perish even at a lack of PPs dying due to competition with older trees. However, a minute surviving part of the progeny is accumulated during a number of decades and ensures the shift of an old generation of dominants with a new generation. Thus, the consuming by PPs of most part of seeds of dominants and their juvenile regrowth does not exert any effect on character of an ecosystem.

This picture is true on condition that the presence of limitations for activity of consumers of seeds and juvenile plants. The limitations are posed by natural enemies of herbivores. The importance of the enemies gets obvious if consider the situation where their activity is suppressed by human interference.

A part of acorns yield in the English oak is destroyed commonly by the weevil Balanus glandium Marsch. as well as the moths Carpocapsa splendana Hb. and C. amplana Hb. It was showed that in undisturbed by humans ecosystems, losses of acorns due to these species spread on less part of yield, whereas at disturbances connected with grazing (a lack of undergrowth and grass cover, the trampled down soil) the losses grew to values, when it was difficult to gather seeds for forest regeneration. Z.S.Golovyanko (1950), who discovered this fact, supposed that the high damage due to these pests was a result of low activity of their natural enemies in disturbed oak forests.

Now, the establishing of forest stands by sowing of acorns becomes a difficult problem, because they are eaten by numerous rodents and wild boars. High density of these animals is explained by providing them with additional food (in areas of intensive agriculture) and suppression of their predators by people.

In the conditions, where predators of game animals are wiped out (hunting husbandry, and some reserves) and multiplication of these animals is not regulated, it is common a heavy damage of forest regeneration by them. In this respect, particular bad management and ecological illiteracy are characteristic for the Soviet and Post-Soviet societies. Their literature abounds in reports about such cases.

Thus, it is the grounds to state that to be effective as CESPPs, 2.1.2.3.1. "Supertolerance to herbivores" should cooperate with 2.2.2.2. "Natural enemies of vertebrate herbivores."

Here are further examples of operation of CESPPs A.2.1.2.3.1.1. "Compensation of losses in seed and seedling stages." It is well known in the apple-trees. The losses up to 90% of the ovaries due to consumption by the apple blossom weevil, Anthonomus pomorum L. does not decrease yield of apples; in the conditions of the absence of this insect, the same part of the ovaries would fall away (V.A.Grodsky, pers. comm.).

In fact, in an apple-tree, even at control of pest insects, a yearly fall of ovaries is common in the range of 25,000 – 32,000, whereas the apple yield is 1,500 – 3,000 fruits. Hence, 93-94% of the ovaries are redundant. A tree has no resources to provide most part of the ovaries with nutrients. When soil fertilizers are applied and weeds are controlled, value of the fall decreases, and fruit yield becomes greater (Anonim, 2004).

The male reproductive organs in plants, which cannot be used in further vital activity of a tree, are rejected after pollination. Their biomass is rather significant comparing with biomass of a tree as a whole. Nevertheless, trees do not spare these parts. In fact, every spring after completion of blossoming, the soil surface under large trees of the poplars (Populus spp.) becomes covered by poplar catkins. An amount of such a fall out reaches dozens of pounds per large tree.

At advanced interrelations among host-plants and consumers of their seeds, the operation of CESPPs 2.1.2.3.1. "Supertolerance to herbivores" has been developed into a collaboration of the plants with seed-consuming herbivores. In so doing, the latter act as disseminators, while the former supply them by a part of their seed yield for feeding. A great many vertebrate species take part in this phenomenon. Consider some examples concerning coniferous tree species according to information in the book by G.G. Doppelmeyer et al. (1966, pp.352-354).

The main agents are the squirrels, Sciurus spp., the stripped squirrel, Eutamias sibiricus Laxm., and the woodpeckers. The bird Nucifraga caryocatactes L., which prefers seeds (nuts) of Pinus sibirica (Rupr.) Mayr and P.cembrae L. plays a crucial role in dissemination of these species hiding the nuts in the soil within the range of several kilometers at the rate up to thirty-four thousand of the nuts per hectare.

It is pertinent to paid attention on high amount of resource consumption by these herbivores. In seasons with low yield of the nuts, this yield is consumed by vertebrate herbivores completely. In the seasons with the abundant yield, the losses due to these herbivores, mainly the squirrels, are evaluated as equal 75-85%. In other coniferous species, the losses also are high. Moreover, the squirrels inflict serious damage for seed production by means of the "cutting" in winter of spruce terminals, where they eat away "flowers" buds. It might be, the cause of high values of the losses consists in a deficiency of consumers’ predators in present time. In fact, the active predator of this group of herbivores - the sable, Martes zibellina L. was recently on the level of extinction.

A lack of predators leads to heavy damage on the part of herbivores, which in undisturbed ecosystems probably took part in dissemination of plants. This statement might be illustrated by the rodents – serious pests of cereal crops. O.A. Grikun (pers. comm.) has observed in south of Ukraine that rodents collect in a soil nest up to 60 kg of wheat grains of the best quality, and the total losses of the grain are evaluated as equal 2.5 metric tons per hectare.

In above situations, CESPPs 2.1.2.3.1."Supertolerance to herbivores" is effective on condition that a cooperation with 2.1.2.2.1. "Disappearance from herbivores" and 2.2.2.2. "Natural enemies of vertebrate herbivores, Predators."

In deciduous plants, it is seen the trend, when plants collaborating with consumers of seeds take some measures for limitation of seed consumption by them. The case is interrelations of the English oak, Quercus robur L. and the European jay, Garrulus glandarius L. This bird is known as the main agent of dissemination of acorns, and in the same time, it is a consumer of them making no seed stores. How does this contradiction is settled?

It occurred to be, the key role is played by a form and a structure of an acorn’s surface. The slanting form and the smooth elastic surface cause a slipping out of acorns from paws of the jay. Usually, the birds gather several acorns in oak crowns keeping them in their mouths and gullets. Then, they fly to shelters in a forest canopy on the distance up to several kilometers. Here, the birds peck acorns, but a part of them slips out from their paws and falls on the soil surface, where they get out of birds’ vision, and germinate. The protective role of the form and the structure of an acorn surface were described by M.G. Kholodnyi (1941).

This is a case of cooperation of CESPPs 2.1.2.3.1. "Supertolerance to herbivores" with 2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent."

In the birch, Betula verrucosa Errh., catkins are damaged by the weevils of the genera Apion and Curculio usually with the rate of several percents. A.S. Serebrovsky (1947, pp.93-98), who reported this fact, explain it as a result of parasite activity. However, R.I. Zemkova (1980, pp.14-15) showed that the low damage of catkins is peculiar only for Betula verrucosa, whereas the exotic birch species, which grow near by this species in a botanical garden – B. lutea Michx., B. halii Howell, B. mandshurica Nakai, were damaged by the weevils with much greater rate – up to 50% of catkins. This fact suggests a presence an Antibiosis (2.1.1.2.1.) in Betula verrucosa . On the other hand, the feeding on this species by bugs, which suck a sap from the ovaries, results in high percentage (40-96%) of hollow seeds (Zemkova, 1980, p.15). This is characteristic for a lack of Antibiosis. Nevertheless, due to abundant seed production, no problems arise with regeneration of this species. Here, it takes place an operation 2.1.2.3.1. "Supertolerance to herbivores."

The further step in development of the collaboration of plants with seed-consuming herbivores is the producing of seed-bearing fruits. This trait has signs both 2.1.2.3.1. "Supertolerance to herbivores" and 2.1.1.3.1.3. "Tolerance to herbivores, Indifference to losses of host-plant tissues." Although the plants having such a trait allow to herbivores to consume a significant part of annual increment of their biomass (in seasons with abundant seed yielding, this is the main part of the increment), advantages of this trait are obvious. In this case, it arises a possibility to spread seeds on the unlimited distance and secure a comfortable media for germination of seeds. Probably, evolutionary advantage of this trait consists also in the fact that the herbivores consume a specialized tissue (fruit parenchima), whereas the seeds bearing hereditary information occur in safety. In fruits, CESPPs 2.1.2.3.1. "Supertolerance to herbivores" is important as to insect herbivores, whereas vertebrate ones are actually symbionts of these species.

At last, seed production in a plant species can be so high that an abundant consumer having no own natural enemies is not able to stop further dissemination of this species. An example of such a situation was provided by C.B. Haffaker (1959). The case is consumption of 98.67% seeds of the whin, Ulex europea L. by the seed-consuming weevil, Apion ulicis Forst. in New Zealand. This weevil was introduced in this area for control the exotic species, which had become a weed there. In spite of high percentage of the seed consumption, complete success in further dissemination of the whin was not achieved. This case demonstrates the great potency of CESPPs 2.1.2.3.1. "Supertolerance to herbivores."

2.1.2.3.1. Supertolerance to herbivores

2.1.2.3.1.2. Compensation of losses at competition of plants within a stem stock

An operation of this CESPPs is demonstrated well by the phenomenon of the annual stem fall in dominants of forest ecosystems. This is a minute part of dominants, which die annually being as a rule colonized by stem borers – numerous species of insects of the families Scolytidae, Cerambycidae, Buprestidae, Curculionidae, Siricidae, Cossidae, and Sesiidae. The value of the annual stem fall depends on stocking density of dominants, and it reaches a few percents of their stock.

If stocking density is so low that interactions among trees are absent, the annual stem fall does not appear. Further, the annual stem fall consists moistly of the trees of lower classes of growth. In not too old forest, the diameter of their stems is lower than annual diameter of dominant of their ecosystem. The height of them is also lower that the average. These facts suggest that the annual stem fall is a result of competition of dominants for vital resources. In overmatured forest, senescent trees prevail in the annual stem fall. A demand for the resources increases steadfastly with growth of plants that determines appearing of the annual stem fall year after year.

So that, the losses of trees due to the competition and old age are compensated by the rest of dominants. Stem borers take part in the process of appearing of the annual stem fall. The participation of these herbivores does not endanger ESPPs. Therefore, these events should be considered as an operation of CESPPs 2.1.2.3.1.2. "Compensation of losses at competition of plants within a stem stock."

2.1.2.4. HETEROGENEITY of a STOCK of DOMINANTS
within an ECOSYSTEM

2.1.2.4.1. Hereditary heterogeneity of a stock of host-plants