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Lynx-Hare Cycle Assumptions N 1 and N 2 dependent only on each other predator can find and consume prey at any prey density no Allee effect for predator.

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Presentation on theme: "Lynx-Hare Cycle Assumptions N 1 and N 2 dependent only on each other predator can find and consume prey at any prey density no Allee effect for predator."— Presentation transcript:

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3 Lynx-Hare Cycle Assumptions N 1 and N 2 dependent only on each other predator can find and consume prey at any prey density no Allee effect for predator or prey at low densities

4 Refugium may exist: place for prey to survive without presence of predator e.g., prickly pear cactus introduced to Australia In 1830s for hedge rows, gardens Also resisted drought and had no predators, so spread rapidly and became a nuisance species Cactus moth introduced in 1926, quickly spread and helped control cactus Cactus still present in refugia and expand from them until moth population resurges

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6 jaeger Snowy owlShort-eared owl

7 Response of predatory birds to different densities of the brown lemming near Barrow, Alaska Brown lemming 1 to 5 15 to to 80 (ind per acre) Pomarine jaeger Uncommon, no Breeding pairs 4 Mi 2 Breeding pairs breeding 18 Mi 2 Snowy owl Scarce, no breeding Breeding pairs 0.2 to Breeding pairs 0.2 to 0.5 Mi 2 many 0.5 Mi 2 few nonbreeders nonbreeders Short-eared owl Absent One record Breeding pairs 3-4 Mi 2 Source: Pitelka et al Numerical Response

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9 Lynx-Hare Cycle Explained? Hares still cycle in absence of lynx predators can switch to other prey (e.g., grouse) hare food cycles in quality and edibility do predators just track cycles, not cause them?

10 Charles Krebs: detailed analysis of Lynx-Hare Cycle Disease and parasites? studied parasite loads in hares for years none caused direct mortality Quality of Food? measured winter food abundance hares only eat 20-40% of what’s available food addition experiments showed initial growth response, then decline Predation? marked hares 95% mortality due to predation by lynx, owls, coyotes exclusion showed high survival rate

11 Optimal Foraging Theory developed by MacArthur and Pianka (1966) predicts minimal foraging effort for maximum energy gain minimal effort means lowest search and handling time if food patchy, predators should select best patches, lowest S&H time

12 Predators can be specialists or generalists

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15 Why the world is green: 1.Insects and other herbivores controlled by their predators and parasites Hairston, Slobodkin, and Smith (HSS Model) 2. Not all plants are edible

16 Plant defenses from herbivory: 1. Morphological --thick leaves, thorns, needles 2.Chemical --secondary compounds

17 Secondary Compounds Chemicals produced by plants solely for defense Take considerable energy to produce 1. Nitrogen compounds --derived from amino acids --alkaloids include nicotine, morphine --mostly toxic, bitter tasting 2. Terpenoids --oils and resins --mostly bitter tasting --includes terpetines, solvents 3. Phenolics --tannins that hinder digestion --used in dyes, tanning, inks

18 Ethnobiology: study of anthropology and biology, how humans, past and present, used or use plant and animal resources in their culture Allelopathy: plants use of secondary compounds for defense against competition from other plants --can affect growth and development of other plants around them Corn plants: use terpenoids to attract a parasitic wasp, lays eggs in caterpillar feeding on plant

19 Herbivore response to plants: 1. Morphological --teeth, gut 2.Behavioral --detoxify secondary compounds

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22 Hindgut fermentation Foregut fermentation enlarged cecum enlarged stomach

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24 Behavioral responses: 1. Eat clay to detoxify compounds --primates, parrots 2.Coprophagy -- rabbits

25 A specialized diet on plants is not without costs: 1.Red tree vole, eats only conifer needles --high in tannins, thick cellulose --slow metabolism, growth 2.Lynx-hare cycle --browsing by hares stimulates plants to produce secondary compounds --food becomes less digestible --hare numbers decline --populations cycle without predator

26 Wolves in Yellowstone NP First released in 1995

27 Increase in ungulate predation also impacted grasslands and herbivory

28 Ungulate Impacts -- pronghorns declined from 600 in late 80s to 240 by bison, 2800 to one elk herd 19,000 to 12,000

29 Result: lighter grazing effects and shift in ungulate feeding behavior Frank (Oikos, 2008)

30 Avoiding Predation cryptic and warning coloration Batesian mimicry Müllerian mimicry

31 katydid walking stick Cryptic coloration

32 Biston betularia

33 Warning coloration

34 coral snakeking snake Red on yellow, harm a fellow Red on black, friend of jack

35 Batesian Mimicry Monarch Viceroy

36 Batesian Müllerian

37 Heliconius butterflies and eggs on Passion flowers Mimicry in Plants

38 Predators can be specialists or generalists

39 Specialist versus generalist relates to optimal foraging theory as well -- generalist flowers with small nectar rewards usually are common species -- specialist flowers with large nectar rewards usually are rare species -- a specialist predator seeks out rarer plants with large rewards rather than waste time getting small rewards from abundant plants -- ensures pollination of rare plant


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