Outbreaks
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Outbreaks. An outbreak is the abrupt and massive increase in population size of animals and plants. Schistocera gregaria outbreak 2013 in Egypt. Barbosa et al. 2012. Coccinella septempunctata outbreak 2011 in Northern Germany. Lemmus lemmus.

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Outbreaks

Outbreaks

An outbreak is the abrupt and massive increase in population size of animals and plants.

Schistoceragregaria outbreak 2013 in Egypt


Outbreaks

Barbosa et al. 2012


Outbreaks

Coccinellaseptempunctataoutbreak 2011 in Northern Germany


Outbreaks

Lemmus lemmus

Lemming outbreaks are triggered by winter breeds and by changes in survival that cause additional breeds

Ims et al. (2011) ProcNatlAcadSci USA. 108: 1970–1974.

Korpimaeki et al. 2004, Bioscience 54: 1071-1079.


Outbreaks

Spruce budwormChoristoneurafumiferana

Camerariaohridella


Outbreaks

Jellyfish blooms in Eastern Asian seas

Nemopilema nomurai

Causes for Nemopilemablooms are increased water temperatues, over fishing, polluted waters, and saltier waters, dead zones, and redirected ocean currents.

Blooms are made by anthropogenic factors


Outbreaks

The Rocky Mountain locust (Melanoplusspretus) ranged through the western half of the USA and part of Canada until the end of the 19th century.

It was a typical prairy species.

The last living species was seen in 1902.

During the last half of the Nineteens century it had several mass outbreaks and constant high population sizes.

Probably the species died out by prairy irrigation of settlers.

Extinction was humancaused.


Outbreaks

Mast years in plants as a special form of gradation

Many trees have more or less regulalry mast years (Oak, Beech, castan, but also fruit trees. Mast years occur in cycles of five to ten years.

2013 was in Poland a mast year for apples.

A chronogram of oak masts in the Southern Apalachian

(Speer 2001, http://web.utk.edu/~grissino/downloads/James%20Speer%20dissertation.pdf)


Outbreaks

Common ecological characteristics (life history trades) of outbreak species

  • Phytophages (rarely paraisoids or predators)

  • r strategists

  • High reproductive output

  • Short reproduction times

  • Multiple annual breeds

  • High dispersal rates

  • Regulated by predators

  • Polyphages

Data from Koricheva et al. 2012, InsectOutbreaksRevisited

Theseare not sufficientconditions for anoutbreakspecies!


Outbreaks

Causes for defoliation by herbivore insect outbreaks (Mattson et al. 1991)

  • Defoliation severity increases directly with homogeneity of the forest composition.

  • Defoliation severity increases with the average amount of exposure of the individual tree crowns.

  • Defoliation severity increases, though not necessarily linearly, with tree age.

  • Defoliation severity increases with warm, dry weather during the growing season.

  • Defoliation severity increases with the folivore's predilection for polyphagy.

  • The effects of defoliation on tree vigor are cumulative and not linear.


Outbreaks

Classification of outbreak species

Population

Average outbreaks of herbivores last 2 to 4 years, outbreak duration rarely exceeds 10 years.


Outbreaks

Sustained eruptions

Cyclic eruptions

Larch Tortrix (Zeiraphera griseana)

Bark beetles (Scolytidae)

Pulse eruptions

Gypsy moth Lymantria dispar

The gypsy moth develops on over 300 differed tree species including gymnosperms and angiosperms


Outbreaks

Temporalpattern of outbreaks

Populationsize

Time

Upper population limit

Starvation and diseasereducepopulations

Predatorscontrolpopulations

Populationsize

Habitat conditionsamplifypopulationgrowth

Outbreaklevel

Time


Outbreaks

Mechanisms of outbreaks

  • Environmental factors

  • Favourable weather conditions

  • New resources

  • Threshold effects

Intensive modelling showed that the direct impact of environmental conditions is generally much too small to explain the magnitude of outbreaks.

Outbreaks are caused by ecolgical factors that amplify reproduction rates.

A high increase is population size is linked to a high reproductive output.

Any factor combination that increasesr might be an amplifier for outbreaks.

Thed discrete Pearl - Verhulst model of population growth


Outbreaks

Rain might serve as an amplifier

Schistocera gregaria

Swarming

Swarming

Abundance

Smaller stationary form

Larger gregarious form

Smaller stationary form

Larger gregarious form

Time

Rain

Drought

Rain

Drought

Drought


Outbreaks

Important amplifiers are:

Type II

Type I

Escape from enemies

Type III

Consumption rate

Relative mortality caused by generalist predators of type II or type III functional response decreases with increasing prey density.

The greater is the population density, the faster it grows.

Prey density

N

US state Maine population outbreak

Reproductive output

1924

1996

Prey density

Gypsy moth Lymantria dispar

Data from Williams and Liebhold (1995)


Outbreaks

Lymantria dispar

Low spring predation of small mammals after mast failures cause outbreaks of the gypsy moth winter

Random regional weather conditions

Small mammal population cycles

Mast failures

Time

Physiological oak mast cycles

Time

Time

Time

Mast failures cause breakdown of small mammal population during winter

Time


Outbreaks

Important amplifiers are:

Threshold effects

  • After reaching a certain threshold density population increase becomes positively density dependent and results in an outbreak.

  • Some bark beetles (Scolytidae) might succeed in attacking a healthy tree only when the number of beetles is large.

  • When the density of adults is high, then they cause considerable damage and the tree looses its resistance to developing larvae.

Threshold

Beetle abundance

Tree damage


Outbreaks

Important amplifiers are:

Habitat effects

  • Population of spider mites grow very fast at high temperature.

  • They live on plant leaves where local temperature is lower than the ambient temperature.

  • During the draught, plant transpiration is reduced, and thus, the temperature of leaves increases causing rapid reproduction of spider mites.

Citation

16

90

Tetranychus urticae

Developmental time

Number of eggs

12

70

T. urticae is extremely polyphagous

8

50

15

20

25

30

35

Temperature

Higher temperature increases fecundity and decreases developmental times leading to accelerated pupolation growth


Outbreaks

Drought

IncreasedtemperatureDecreasedhumidity

Plants

IncreasedDecreased

TemperatureGrowth

StressmetabolitesResistance

OsmolytesWatercontent

Sugars

Secondarycompounds

Natural enemies

IncreasedDecreased

-Abundance

Phytophagousinsect

IncreasedDecreased

ResourcesAdultsurvival

Plant utilisationLarvalsurvival

Enemy escape

Growth of symbionts

Rate of reproduction

Outbreak


Outbreaks

Important amplifiers are:

Habitat effects

  • Pine sawflies, Diprion pini, have >50% of their population in a prolonged diapause lasting from one to five years.

  • Drought may cause reactivation of a large proportion of diapausing sawflies.

Diaprion outbreak in Germany was finished by the outbreak of the red backed vole

Diprion pini

Abundance

Clethrionomys glareolus

1964

1965

1966

Time

Turced 1966, Waldhygiene 6: 181-182


Outbreaks

  • Outbreaks collapse usually due to one of the following mechanisms:

  • Destruction of resources

  • Natural enemies

  • Unfavorable weather


Outbreaks

The Clark and Holling (1979) model of insect outbreaks

a is related to the strength of biotic interaction

C. S. Holling 1930-

r is the intrinsic growth rate

Interaction effects

Logistic growth

b is related to the behaviour of the species


Outbreaks

How to derive the model?

Effective search time TS is the difference between total search time T and handling time TH.

Predation P is proportional do prey density N and to effective search time TS.

Holling’s disc equation

Searching time is proportional to prey density

Predator efficacy or pedator rate

The model describes Holling’s type II functional response.

Consumer abundance

Resource abundance


Outbreaks

Monocultures

Do monocultures increase the probability of outbreaks?

Outbreakspeciesareoftenpolyphagous.

Tropicalforestsoften face severeinsectoutbreaks.

The proportion of potentialoutbreakspeciesishigher in tropicalforests.

Monoculturesareoftendevoid of naturalenemies.

Outbreakspeciesasre of opfhigherdensity.

Monoculturesprovide high resourcedensities

?


Outbreaks

Do outbreaksharmecologicalsystems?

?

In terms of economy: yes.

In terms of ecosystemfunctiong: probably no

Outbreakslead to higherresourceturnover.

Post-outbreaksystemsincrease in speciesrichness.

Outbreakmightlead to evolutionayinnovations.

Leptinotarsadecemlineata


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