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. Continue.

AXIOM 5. LIFE SYSTEMS OF PLANT PESTS

This Axiom is aimed to outline the regularities that determine compositions of CESPPs, which exert the diverse effects depending on groups (guilds) of herbivores, taxa of them, and the diversity of environmental conditions. Also, it will be outlined the traits of herbivore species that allow them to survive in spite of suppressive effect of ESPPs.

Every taxon of herbivores counteracts with a part of CESPPs operating in its ecosystem, rather than with all the diversity of them. There exists a complex of CESPPs with specific patterns of their effects that counteracts a herbivore taxon. For characterizing of the complex, it has been proposed to use the concept of the life system (LS) of a herbivore species (taxon). The definition of the concept has been done by L.R. Clark et al. (1967, p. 55), as follows: "A part of ecosystem, which determines the existence of particular population is called a life system - and is composed of the subject species and its effective environment... The latter consists of (I) the resources, (II) enemical agencies both biotic and abiotic which oppose the survival and reproduction of individuals of the subject species."

In the context of ESPPs, it should do some specification of the concept of LS. Here, effective environment (EE) is considered as a set of CESPPs and their effects, whereas "subject species" let be a set of the traits of a herbivore taxon that determine its success to overcome EE. The term "species potential" (SP) is proposed for the denomination of these traits as a whole as more exact one than the term "subject species."

EE includes patterns of density-dependence of CESPPs, which compose the following categories:

1. Directly density-dependent, smooth,
2. Directly density-dependent, delayed,
3. Directly density-dependent, spasmodic,
4. Density-independent,
5. Inversely density-dependent.

The pattern (a) "directly density-dependent, smooth" is characterized by such a quotation: "For the production of balance it is essential that a controlling factor should act more severely against an average individual when the density of the animals is high, and less severely, when the density is low" (Nicholson, 1933, cited in H.G. Andrewartha and L.C. Birch, 1973, p. 248). The EE with the directly density-dependent, smooth pattern provides Insignificant or Low densities of herbivores over unlimited time.

When the pattern (b) "directly density-dependent, delayed" takes place, EE enters into operation with a delay, so that herbivores have time to reach the Intermediate value of density. This operation occurs by chance. After that, it begins a decrease of the density to the values Low or Insignificant. The EE with the directly density-dependent, delayed pattern provides a change of the density in time in the range of Insignificant and Intermediate values.

The pattern (c) "directly density-dependent, spasmodic" means that suppression of a herbivore population takes place, when its density reaches the value "High." High density of herbivores cannot be maintained over unlimited time. Therefore, an entering into operation EE, which realizes this pattern, is inevitable. Although depending on circumstances, the pattern can be "early spasmodic" or "lately spasmodic." The EE with this pattern provides changes of the density in the wide range - from High to Insignificant. So that the duration of periods of High density and intervals between them are diverse.

At the pattern (d) "density-independent", it takes place an operation of potent EEs, which are able to provide Zero density of herbivores. CESPPs of such EEs belong to the category 2.1. "Plant resistance to PPs", which operate on vitally important tissues of host-plants, CESPPs 2.2.1.2.1."Natural enemies of invertebrate herbivores, Vertebrate predators", and CESPPs 2.3. "Routine weather suppression" in the W.C. Cook's zone (d). In the W.C. Cook's zone (c), CESPPs 2.3. are less potent. Here, density of herbivore fluctuates in the any value.

The pattern (e) "inversely density-dependent" is opposite to the pattern (a). At growth of herbivore density, activity of some natural enemies gets lower.

The effects of EEs have following characteristics:

1. Longevity, including - Persistent, Common, Spontaneous, and Temporal,
2. Power, including - Potent, Moderate, Weak,
3. Quality, including - The best, Good, Poor, and Bad.

The characteristic "Longevity" means that the effect of density-dependence is in the following states:

The characteristic "Quality" means evaluation of the effect from standpoint of safety of an ecosystem, and it includes the following subcategories:

1. The best - the pattern provides absolute protection of dominants, or promotes the turnover of substances by destruction of biomass of the category D-III,
2. Good - the pattern allows only insignificant decrease of increment of dominants or the same losses of yielding,
3. Poor - the effect allows appreciable mortality of dominants and significant losses of yielding,
4. Bad - the effect allows heavy mortality of dominants that leads to change of a character of an ecosystem or heavy losses of yielding.

The Quality of the effect of EEs results into management implications of the regularities. When the effect is evaluated as The best or Good, the human control measures need not, whereas when it is expected as Poor or Bad, the measures are necessary.

The density-independent pattern is Potent, if CESPPs operating in a given ecosystem always preclude inhabiting of a resident population of herbivores and decrease an immigrating populations of them to the level Zero density. The effects of the pattern are Persistent and The best.

The interrelations in LS of a herbivore taxon might be expressed with the abbreviations and conventional signs as the following:

LS (a herbivore taxon) = SP ↔ EE (1CESPPs + 2 CESPPs + ... +  n CESPPs), the dependence of the suppressive effect on species density, Longevity, Power, and Quality,
where ↔ is a sign of counteraction.

Hence, LS should be a formula, rather than a story.

Due to limited author's knowledge, a detailed characteristic of LS will be done only for not numerous groups of herbivores. Therefore, these propositions should be considered as a scheme for classification of LS or as a demonstration of a principle to do it with the hope to take interest of readers to develop further attempts.

As to the classification of EEs, it is proposing the following factors, which determine the composition of EEs:

5.1. Life strategy of a herbivore species,

5.2. The level of ESPPs,

5.3. The Cook's zone of the range of a herbivore species,

5.4. Special cases, which determined by local environmental conditions.

5.1. Grouping of herbivores within the category 5.1. is determined by their interactions with host-plant resistance - CESPPs 2.1. "Plant resistance to PPs", and self-protection against CESPPs 2.2. "Natural enemies."

The available information allows give characteristic of the set forth below groups by means considering of LSs of pest insect species, which represent these groups:

5.1.1. Defoliators.

5.1.1.1. Defoliators of deciduous tree species.

5.1.1.1.1. Openly-feeding defoliators of tree species.

5.1.1.1.1.1. The gypsy moth, Porthetria dispar L. (the spring-summer guild).

5.1.1.1.1.2. The little gypsy moth, Parocneria detrita Esp (the fall-spring guild).

5.1.1.1.2. Bud-mining and web-making defoliators (the early-spring guild).

5.1.1.1.2.1.The green oak moth, Tortrix viridana L.

5.1.1.1.2.2.The winter moth, Operophthera brumata L.

5.1.1.1.3. Web-worms of deciduous tree species.

5.1.1.1.3.1. The apple ermine moth, Hyponomeuta malinellus Zell.

5.1.1.2. Defoliators of the larch.

5.1.1.2.1. Bud-mining and web-making defoliators of the larch.

5.1.1.2.1.1. The larch bud moth, Zeiraphera diniana Hb.

5.1.1.2.2. Openly-feeding defoliators of the larch.

5.1.1.2.2.1. The Siberian pine moth, Dendrolimus sibiricus Tschetv.

5.1.1.3. Defoliators of evergreen coniferous tree species.

5.1.1.3.1. Openly-feeding defoliators of evergreen coniferous tree species.

5.1.1.3.1.1. The Siberian pine moth, Dendrolimus sibiricus Tschetv.

5.1.1.3.1.2. The European pine moth, Dendrolimus pini L

5.1.1.3.1.3. The pine beauty moth, Panolis flammea Schiff.

5.1.1.3.1.4. The pine looper, Bupalus piniarius L

5.1.1.3.1.5.The European pine sawfly Neodiprion sertifer Geoffr.

5.1.1.3.1.6. The nun moth, Porthetria monacha L.

5.1.1.3.1.7. The gypsy moth, Porthetria dispar L.

5.1.1.3.2. Bud-mining and web-making defoliators of evergreen coniferous tree species.

5.1.1.3.2.1. The spruce budworm, Choristoneura fumiferana Clem

5.1.2. Bark beetles.

5.2. includes three subcategories, which are presented by 3.1. "Proper control", 3.2. "Lag control", and 3.3. "Late control."

5.3. includes four zones according to W.C. Cook (1929), namely:

1. Normal abundance,
2. Occasional abundance,
3. Possible abundance,
4. Possible occurrence.

Every W.C. Cook's zone is characterized by presence of ecosystems with specific categories of the level of ESPPs. The zones and the levels determine the patterns of density-dependence, which characteristic for CESPPs operating in a given ecosystem, as follows:

1. Normal abundance. The prevalence of the level ESPPs 3.3. "Late control." The late control where EEs in D - I, D - II, and D - III operate mainly in the directly density-dependent, spasmodic pattern. Some CESPPs operate in the inversely density-dependent pattern (avian predators of insect herbivores) but their role in restoring of ESPPs is insignificant.
2. Occasional abundance. Ecosystems with all the levels of ESPPs occur here. On the level 3.1. "Proper control", EEs in D - I, and D - II operate in the directly density-dependent, smooth pattern. On the level 3.2. "Lag control", the pattern is directly density-dependent, delayed. On the level 3.3. "Late control", the pattern is directly density-dependent, spasmodic.
3. Possible abundance. There exist ecosystems with the levels ESPPs 3.1."Proper control" and 3.2."Lag control." In 3.1. "Proper control", the pattern is directly density-dependent, smooth. In 3.2."Lag control", the pattern is directly density-dependent, delayed.
4. Possible occurrence. Here, it is known ecosystems with the only level of ESPPs - 3.1. "Proper control", the pattern is density-independent.

5.4. includes ecosystems in specific environmental conditions where LSs of herbivore species have characteristics, which differ from those typical for the W.C. Cook's zones. Their subject will be demonstrated by special considerations.

The special cases of EEs are known in the 5.1.1.1.1.1. (5.4.1., 5.4.2., 5.4.3., 5.4.4., and 5.4.5.), in the 5.1.1.3.1. (5.4.6., 5.4.7.), in 5.1.1.3.2. (5.4.8.), and the separate case 5.4.9., namely:

5.1.1.1.1.1. - 5.4.1. Porthetria dispar L., in the reservations,

5.1.1.1.1.1. - 5.4.2. Porthetria dispar L. in isolated plantations in the Semi-desert biome,

5.1.1.1.1.1. - 5.4.3. Porthetria dispar L. on shade trees,

5.1.1.1.1.1. - 5.4.4. Porthetria dispar L. in abandoned fruit orchards,

5.1.1.1.1.1 - 5.4.5. Porthetria dispar L. in North America, including:

5.1.1.1.1.1. - 5.4.5.1. In the generally infested area,

5.1.1.1.1.1. - 5.4.5.2. In the advancing front of the generally infested area and in the island infestations.

5.1.1.3.1.2. - 5.4.6. Dendrolimus pini L. in pine ecosystems with low Antibiosis of host-trees, but with high activity of natural enemies.

5.1.1.3.1. - 5.4.7. Openly-feeding defoliators of evergreen coniferous the species in Scots pine, Pinus silverstris plantations in the Steppe biome.

5.1.1.3.2.1. - 5.4.8. Choristoneura fumiferana Clem. in stands of the black spruce in the Saquenay Region (Quebeck, Canada).

5.4.9. Complex of pest organisms on the winter wheat in the Forest-Steppe biome in Ukraine.

Species potential (SP) is a capacity of a PP taxon to reach in space and time definite level (Zero, Insignificant, Low, Intermediate, High) of density (in herbivores) or to reach definite level of affection of host-plants (in phytopathogens). SP is determined by a group of traits of a PP taxon.

Species traits are a result of adaptation to given environmental conditions, i.e. to ESPPs of a given ecosystem. The more range of environmental conditions where the traits composing SP are able to keep survivorship of a PP taxon to adulthood, the more abundant this PPs in space and time.

For understanding of the character of the conditions where a PP taxon realizes its SP, it is postulated ideas of strategy of survivorship (SS) and its expression. The former characterizes the traits of a PPs, whereas the latter evaluates efficacy of the traits for survivorship in concrete environmental conditions. In other words, expression of a category of SS, used by a PP taxon, is a characteristic of a progress in adaptability of the traits to a given CESPPs.

The difference among PP taxa as to their SP is great among guilds, within a guild, and within a species. A guild includes PP species producing frequent and vast outbreaks, and, on other hand, PPs species, which produce rare outbreaks on a limited area or those continually present as innumerous satellites of mass PP species. The taxa within a species also are different as to capacity to build up outbreaks or epiphytoties.

The guilds of herbivores differ from each other by sets of traits, which allow to state divers strategies of survivorship (SSes) in them. The SS is adaptations of PPs taxa to interact with definite CESPPs or competitors for food.

The level of expression of traits determining SS can be "High", "Moderate", "Weak", and "Zero." The traits exert their effects on the following life cycle stages: eggs, diverse instars of larvae, pupae, and adults.

The level "High" means implies probability of operation of a given SS at all the levels of ESPPs. The level "Moderate" means that a given SS operate at a decreased ESPPs. At last, the presence in SP some category of SS with propriety "Weak" implies a low probability of operation of a given SS in a SP. "Zero" is an absence of SS.

SP of a given herbivore taxa or a group of them might be presented as a formula, where SSes are shown and evaluated of expression of these SSes. If in a formula of SP, a given category of SS is not shown, this means that this category of SS is not characteristic for a taxon, group or guild of herbivores.

An operation of the ideas of SS and its expression, i.e. SP, allows people to know the environmental conditions, where PPs density (affection) to be Zero, Insignificant, Low, Intermediate or High. By showing forte and foible of a herbivore taxon, knowledge of SP promises important management implications. It gives a possibility to evaluate a level of damage exerted by a PP taxon on its host-plants. Also, it allows people to take adequate actions with the aim to suppress a taxon of PPs. In particular, this is prospective at forecast of damage due to invading species of herbivores, which spread their range in a recently invaded area.

It will be made an attempt to spread the concept LS on phytopathogens.