Outbreaks

1. Outbreaks An outbreak is the abrupt and massive increase in population size of animals and plants. Schistoceragregaria outbreak 2013 in Egypt

2. Barbosa et al. 2012

3. Coccinellaseptempunctataoutbreak 2011 in Northern Germany

4. 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.

5. Spruce budwormChoristoneurafumiferana Camerariaohridella

6. 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

7. 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.

8. 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)

9. 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!

10. 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.

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

12. 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

13. Temporalpattern of outbreaks Populationsize Time Upper population limit Starvation and diseasereducepopulations Predatorscontrolpopulations Populationsize Habitat conditionsamplifypopulationgrowth Outbreaklevel Time

14. 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

15. 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

16. 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)

17. 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

18. 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

19. 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

20. 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

21. 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

22. Outbreaks collapse usually due to one of the following mechanisms: • Destruction of resources • Natural enemies • Unfavorable weather

23. 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

24. 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

25. 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 ?

26. Do outbreaksharmecologicalsystems? ? In terms of economy: yes. In terms of ecosystemfunctiong: probably no Outbreakslead to higherresourceturnover. Post-outbreaksystemsincrease in speciesrichness. Outbreakmightlead to evolutionayinnovations. Leptinotarsadecemlineata