Lynx-Hare Cycle Assumptions• N1 and N2 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

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 andexpand from them until moth population resurges

jaeger Snowy owl Short-eared owl

Response of predatory birds to different densities of the brown lemming near Barrow, Alaska  

1951 1952 1953

 Brown lemming 1 to 5 15 to 20 70 to 80 (ind per acre)  Pomarine jaeger Uncommon, no Breeding pairs 4 Mi2 Breeding pairs

breeding 18 Mi2  Snowy owl Scarce, no breeding Breeding pairs 0.2 to Breeding pairs 0.2 to 0.5 Mi2 many 0.5 Mi2 few nonbreeders nonbreeders  Short-eared owl Absent One record Breeding pairs 3-4 Mi2

 

Source: Pitelka et al. 1955.

Numerical Response

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?

Charles Krebs: detailed analysis of Lynx-Hare Cycle

• Disease and parasites? studied parasite loads in hares for yearsnone caused direct mortality

• Quality of Food?measured winter food abundancehares only eat 20-40% of what’s

availablefood addition experiments showed

initial growth response, then decline• Predation?

marked hares95% mortality due to predation by lynx, owls, coyotesexclusion showed high survival

rate

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

Predators can be specialists or generalists

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

Plant defenses from herbivory:

1. Morphological--thick leaves, thorns, needles

2. Chemical--secondary compounds

Secondary CompoundsChemicals produced by plants solely for defenseTake 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

Ethnobiology: study of anthropology and biology,how humans, past and present, used or use plant andanimal resources in their culture

Allelopathy: plants use of secondary compounds fordefense 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

Herbivore response to plants:

1. Morphological--teeth, gut

2. Behavioral--detoxify secondary compounds

Hindgut fermentation

Foregut fermentation

enlarged cecum

enlarged stomach

Behavioral responses:

1. Eat clay to detoxify compounds--primates, parrots

2. Coprophagy-- rabbits

A specialized diet on plants isnot 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

Wolves in Yellowstone NP

www.dailygalaxy.com

First released in 1995

www.ecotourismlogue.com

Increase in ungulate predationalso impacted grasslands and herbivory

Ungulate Impacts

-- pronghorns declined from 600 inlate 80s to 240 by 2001

-- bison, 2800 to 2400

-- one elk herd 19,000 to 12,000

Result: lighter grazing effects and shiftin ungulate feeding behavior

Frank (Oikos, 2008)

Avoiding Predation

• cryptic and warning coloration

• Batesian mimicry

• Müllerian mimicry

katydid

walking stick

Cryptic coloration

Biston betularia

Warning coloration

coral snake king snake

Red on yellow, harm a fellowRed on black, friend of jack

Batesian Mimicry

Monarch Viceroy

Batesian

Müllerian

Heliconius butterflies and eggs onPassion flowers

Mimicry in Plants

Predators can be specialists or generalists

Specialist versus generalist relates to optimalforaging theory as well

-- generalist flowers with small nectar rewards usually are common species

-- specialist flowers with large nectar rewards usuallyare rare species

-- a specialist predator seeks out rarer plants with largerewards rather than waste time getting smallrewards from abundant plants

-- ensures pollination of rare plant