Ecology. Stability of ecosystems.

Ebook "STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH"
Gleb I.Vasechko,
Cand.Sc. (Biology)

© Gleb Vasechko, 2005 All rights reserved.
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Created 20.03.2005
Last modification 15.06.2021

PART I. A LIST OF THE AXIOMS. Continuation.

AXIOM 2. THE NATURE of ECOSYSTEM STABILITY to PLANT PESTS and its COMPONENTS. Continuation.

COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY 2.4. PERIODIC (BOTTLE-NECK) SUPPRESSION

This is a mortality or reducing of fecundity under effect of stressors during severe period - a season or a weather situation that occurs more seldom than one time per season. The list of CESPPs 2.4. "Periodic (bottle-neck) suppression" is given in the Table 3.

Table 3. The classification of components of ecosystem stability to plant pests (CESPPs) 2.4. "Periodic (bottle-neck) suppression"

2.4.1. operates as CESPPs suppressing of vertebrate herbivores by means of deficiency of food or water. Such a deficiency occurs in any biome with wide changing of environmental capacity in a definite season (winter or dry summer) - in forest, steppe, savanna, desert, and tundra. In addition, when summer drought is irregular, 2.4.1. operates at recurrence of very dry weather situation. The suppressive effect is realized or by low temperatures in winter or high temperatures and low humidity in summer. In such situations, herbivores need to spend many forces for search for food or basins. In a result, their physiological state gets worse, and they die due to starvation, diseases, and attacks of predators and parasites. The severe period keeps density of herbivores on the level, at which they able to consume a less part of food resource, which exists in a favorable period. Thus, a bottle-neck period occurs to be insuperable for a significant part of herbivore population.

2.4.2. kills a weakened part of a PP population that would survive, if a severe period would absent.

2.4.3. allows host-plants to evade from PPs by means of a completion of vulnerable stages before the main part of PPs gets able to affect host-plants. An interruption of growth of PPs density takes place, because a population enters into inactive state under impact of a severe period. The higher a level of severity of climate of an area, the less the number of generation of PPs per season, the longer of duration of a generation.

The prerequisites of CESPPs 2.4. "Periodic (bottle-neck) suppression" (they are marked by the letter "P") are the following:

2.4.P.1. Keeping of severity of the season of a year, when activity of PPs is suppressed.

2.4.P.2. Common recurrence of suppressive weather situation in an over-year frequency.

THE INTRINSIC CLASS
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY
2.5. EFFECTS of CROWDING - COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS ENTERING into OPERATION at CROWDING of HERBIVORE or PHYTOPATHOGEN POPULATIONS

Diversity of CESPPs of this category enters into operation after that density of a PPs taxon exceeds some threshold. This threshold is a getting of the level of High density. The sense of the term "High density" gets clear at considering of concrete situations. In such situations, the effects, which are excited by individuals pretending on the same food resource, i.e. competitors, become for a taxon the main CESPPs in ESPPs.

The classification of CESPPs 2.5. "Effects of crowding" is given in the Table 4.

Table 4. The classification of components of ecosystem stability to plant pests (CESPPs) 2.5. "Effects of crowding" operating in herbivore populations as a series of effects in a sequence

2.5.1. "Deterioration and/or shortage of food" is a common effect of High density of herbivores, which leads to subsequent effects. The latter are different depending of character of host-plant tissues, which serve as a food of herbivores.

2.5.1.1. "Raising of secondary evasion" operates in defoliators, whose survivorship is determined by coincidence of activity of neonate larvae with proper phase of host-trees. In particular, the larvae need to penetrate into flushing buds.

The delay with bud-bursting induced High density in a previous season results in starvation of them. These is an operation of the effects 2.5.1.1.1. "Delayed bud-bursting (exposition on 2.1.1.2.1.1.1.)" and 2.5.1.1.1.1. "Starvation."

2.5.1.2. "Raising of secondary structural antibiosis." In tree species, which produce protective products (oleoresin), as a response on High density of defoliators in the previous season, it takes place exuding of the oleoresin on surface of the buds, which are objects of attacks of neonate larvae. 2.5.1.2.1. "Exuding of protective substances on a surface of buds or developing of protective barriers in affected tissues " that result in the effect 2.5.1.2.1.1. "Starvation." The effects 2.5.1.1. and 2.5.1.2. cooperate that enhance self-protection of plants. The appearing of protective barriers is known, when feeding of sap-sucking insects.

2.5.1.3. "Raising of secondary physiological (biochemical) antibiosis" resulting in 2.5.1.3.1. "Appearing in endangered tissues of protective substance or increase of their content" and 2.5.1.3.1.1. "Suppression of vitality or mortality" is probable in the cases, when host-plants are protected by weakly expressed Antibiosis.

2.5.1.3. "Raising of secondary physiological (biochemical) antibiosis" gives another effect 2.5.1.3.2. "Deficiency in endangered tissues of nutrients and/or increase of worthless stuff." This is a common result of exhaust of resources in host-plants due to heavy consumption of their assimilative tissues by herbivores at High density. The effects on herbivores are 2.5.1.3.2.1. "Weakening due to bad feeding" and 2.5.1.3.2.2. "Decrease of body weight and fecundity."

2.5.1.4. "Emigration in the adult stage in advance of food deterioration and/or exhaust" is known in the taxa of herbivores, which have had evolutionary experience to reach often High density. They leave plots, where resources of host-plants are exhausted and density of natural enemies increased. Although such traits promote to maintain High density, a part of emigrated herbivores dies due to the effect 2.5.1.4.1. "Mortality due to diverse factors." Among them, high percentage of a population dies due to accidents.

2.5.1.5. "Migration in the larval stage with leaving of shelters in some species" is known in the taxa having less evolutionary experience to reach High density. The migration results in the effect 2.5.1.5.1. "Mortality due to divers factors." In so doing, value of the mortality is large. It induced by predators, parasites, starvation, and accidents.

2.5.1.6. "Wounding of insect herbivores at contacts" is common as a means of decrease of High density in insects, which in larval stage inhabit a closed space. The best example of an operation of the sequence of the effects 2.5.1.6., 2.5.1.6.1. "Weakening", and 2.5.1.6.1.1. "Mortality due to natural enemies" is offered by the bark beetles; the effects lead to decrease of amount of a population.

2.5.1.7. "Cannibalism" is common again in species of insect herbivores spending larval stage in a closed space. The final effect of cannibalism is 2.5.1.7.1. "Direct mortality."

2.5.1.8. "Diapausation" is a means to evade from suppression by natural enemies, whose activity increased in the conditions of High density. The following effect is 2.5.1.8.1. "Mortality under effect of natural enemies." In a result, the density gets lower, but the decrease is less than that at absence of diapausation. Another effect of 2.5.1.8. "Diapausation" is 2.5.1.8.2. "Disappearing of defoliators on the period, which provides a reprieve for restoring of vitality of dominants." This means that host-plants obtain a reprieve, which gives them a possibility to restore vitality after defoliation.

2.5.1.9. "Wounding at aggressive territorial behavior" operates as a means of decrease of density in hoofed animals. Tournament among males leads to the effect 2.5.1.6.1. "Weakening." Although fighting animals as a rule do not die, they loss vigor and get victims of predators, so that it takes place the effect 2.5.1.6.1.1. "Mortality due to natural enemies." In some species of insect herbivores, in particular in armored beetles, this effect operates also.

2.5.1.10. "Decrease of body weight at shortage of food and/or forced feeding by inadequate food " with the final effect 2.5.1.10.1. Decrease of fecundity and increase of mortality due to weather stress" is common in all the species of herbivores, when their density reaches the value "High." In so doing, it takes place a decrease of the density due to low fecundity and mortality of weakened individuals.

2.5.1.11. "Dormancy in vertebrate herbivores" with final effect 2.5.11.1. "Decrease of body weight and fecundity" is known in the ground squirrels. This trait allows these rodents to survive in the period of shortage of food. Because the dormancy results in decrease of fecundity, density of these animals gets lowered, and their forage plants obtain better possibilities for restoring.

2.5.2. "Attraction of predators and parasites, increase of their searching activity." Aggregations of herbivores produce potent stimuli for their parasites and predators. In such aggregation, values of parasitization and predation gets higher comparing with those at sparse distribution of hosts and preys.

2.5.3. "Increase of activity of pathogens and parasites in the specific conditions of high host density." Growth of density of insect hosts provokes an increase of affection of them with their natural enemies. This effect differs from 2.5.2. The effect 2.5.3. induces inevitable decrease of body weight from beginning of an outbreak to its decline. It is coded as 2.5.3.1.

2.5.3.1. is an outer display of ever-increasing accumulation of the inapparent form of infection in bodies within a herbivore population. This is so because in the conditions of rather Low density in the initial phase of an outbreak, the strains of low virulence have the better chance to spread within an insect host population, whereas the strains of high virulence are eliminated, because infested by them hosts die quickly. Therefore, high virulent strains due out being unable to infest sparse insect hosts. The higher density of insect hosts, the heavier affection of populations by the inapparent form of the infection. 2.5.3.1. induces the further effects, which bring contribution in decrease of the density, are the following:

2.5.3.1.1. "Decrease of fecundity."

2.5.3.1.2. "Decrease of participation of females in sex ratio."

2.5.3.1.3. "Mortality due to weather stress and parasites."

2.5.3.1.4. "Mass mortality due to affection by acute form of infection."

2.5.3.1.5. "Spontaneous or winter mortality of embryos."

2.5.3.1.6."Abnormal behavior of herbivores in the conditions of high density, which results in mortality of individuals."

2.5.4. "Fluctuations of insect host resistance to pathogens and parasites as well as virulence of pathogens and aggressiveness of parasites." Suppression of herbivore populations by the effects of 2.5.3.1.4. and 2.5.3.1.5. occurred to be so potent that these populations stay on the level Insignificant density over a number of years. During the period of Insignificant density of defoliators their host-plants having advanced Tolerance are able to restore their vitality. Thus, although ESPPs from time to time decreases to the low level, the ecosystems, where these effects operate, exist over unlimited time. These effects are true CESPPs.

The effects of 2.5.3. and 2.5.4. operate simultaneously, and they are pertinent not only invertebrate herbivores, but also vertebrate ones.

2.5.5. "Disturbance in the media of inhabitation" embraces two final effects:

2.5.5.1. Affections by pathogens due to deterioration of sanitary state of the media.

2.5.5.2. Mortality due to appearing of obstructions for further development.

2.5.5.1. arise in a result of accumulation of waste products of vital activity of herbivores.

2.5.5.2. is discomforts of diverse character arising in the conditions of High density.

2.5.6. Exhaust of adequate food.

2.5.6.1. Mortality due to starvation or inadequate food in the same generation or in the next one, decrease of fecundity.

This effect needs no comments.

In the phytopathogens, the effects of CESPPs 2.5. operate similarly to that in the case of herbivores. A high concentration of agents of the phytopathogens in an inoculum results in decrease of their virulence.

Prerequisites of CESPPs 2.5. "Effects of crowding" (they are marked by the letter "P") are the following:

2.5.P.1. Surpassing by PPs density some threshold.

2.5.P.2. State of ecosystems, where it is possible to operate the temporal increase of resistance of herbivores to their pathogens (non-operation of CESPPs 2.5.4.1.) due to microevolutionary process.

THE ANTHROPIC CLASS
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY 2.6. HUMAN CONTROL MEASURES

This is a category of CESPPs operating in the under warship ecosystems (articenoses), where natural CESPPs have been disturbed by human activity, and in the natural ecosystems (biocenoses), which are in danger on the part of PPs affection, whereas the human interest consists in a precluding damage of them by PPs. The people in their practice use both CESPPs operating in nature and artificial measures. The classification of CESPPs 2.6. "Human control measures" is given in the Table 5.

Table 5. The classification of components ecosystem stability to plant pests (CESPPs) 2.6. "Human control measures"

The contents of most part of the subcategories of CESPPs 2.6. is clear from their names. Nevertheless, it is proposed some elucidation.

2.6.1. is the human activity with the aim of effective operation of CESPPs, which are close to those operating in nature.

2.6.1.1. embraces human activity concerned the usage of the plants with traits of "Plant resistance to PPs."

2.6.1.1.1. is a maintenance of ESPPs by means of usage of the plants with natural traits of CESPPs 2.1. "Plant resistance to PPs."

2.6.1.1.2. is a maintenance of ESPPs by means of the usage of the plants with traits of CESPPs 2.1. modified by breeding, i.e. CESPPs A.2.1.

2.6.2. comprises measures invented by people and directed on long-lasting suppression of PPs in a given area.

2.6.2.1. is used, when it needs to destroy invading pests or to eradicate a plant species, which serves an additional host-plant for PPs. In so doing, plants with PPs inhabiting on them and objects, where PPs can be stay, are treated by all the known means.

2.6.2.2. is a releasing of sterilized individuals or application of pheromones after suppression of PPs populations in nature with the aim of eradication of these populations.

2.6.2.3. is a ceasing of growing of a crop, which is affected heavily by PPs in a given area; instead of it, other crops are grown.

2.6.3. embraces measures again invented by people. They are practiced with the aim to exclude the problem of damage due to PPs over one growing season.

2.6.3.1. includes cultural practices, which are directed only on destroying of PPs or combined this aim with other demands of plant growing; some of them are based on CESPPs operating in nature.

2.6.3.2. embraces sanitary measures; this is an activity directed on destruction of plant stuff affected with PPs or a holding of it in the conditions that preclude an affection by PPs.

2.6.3.3. embraces temporary suppressive measures sensu stricta, which include all the kinds of application of pesticides (synthetic, microbial, hormonal, etc.), destruction of PPs by technical or manual ways (traps, direct killing, burning, etc.), inundation an area with natural enemies of PPs, the breach of a sex contacts in herbivores by means of exposition of pheromones.

The prerequisite of efficacy of CESPPs 2.6. "Human control measures" is a proper level of professionalism of persons practicing these measures.