Announcements 1 Dr Weis has agreed to adjust

Announcements: 1. Dr. Weis has agreed to adjust the midterm marks so that the class average will be 65%. 2. Please answer problem set questions 19 to 30 for lab next week. 3. There will be a quiz next week on lab 4 (Host-Parasite interactions) 4. I will be away next Tuesday (November 6 th). Dr. Weis will give the lecture November 6 th. I’ll return to lecture November 8 th.

Camouflage or Crypsis: enables prey to avoid detection - often mistaken for inedible objects or missed. Orthoptera: walking stick http: //www. ivyhall. district 96. k 12. il. us/4 th/kkhp/1 insects/walkingstkpix. html

Warning Colouration • Some prey are brightly coloured rather than cryptic • Bright colours are often associated with distastefulness • Hypothesis is that warning colouration is more easily learned by predators. If the predator aviods the colour, prey doesn’t get attacked.

Mimicry is the resemblance of one organism (mimic) to another (model) such that these two organisms are confused by a third organism (receiver). • model and mimic are not usually taxonomically related. • molecular mimicry, pathogenic organism (or a parasite) mimics a molecule of the host so that it escapes recognition as foreign

English Naturalist: Henry Walter Bates (1852) BATESIAN MIMICRY occurs when a harmless organisms copies (mimics) the warning colouration of a “poisonous”organism Monarch butterfly is distasteful (toxic) to birds Viceroy is not distasteful, but has similar colouration to Monarch

Effect of monarch butterfly toxins Photo by Lincoln Brower

Monarch larva feeds on poisonous milkweeds & retain the plant poison in their tissues Toxic A. tuberosa, butterfly milkweed Non-toxic Asclepias syriaca common milkweed http: //www. wfnirvana. com/prairie/ascltube. html

Other examples of Batesian Mimicry • Coral snakes (toxins) vs. harmless milk snakes & king snakes with similar coloured banding. Conant & Collins 1991)

Mimic must be rarer than model. If mimic becomes too abundant, predator may learn that bright colours are tasty.

Acoustic Batesian Mimic: hissing call of ground-nesting burrowing owls resemble rattlesnakes. • Prairies of Canada • Burrows in abandoned prairie dog holes • Endangered species Photo by Greg Lasley

MÜLLERIAN MIMICRY • German zoology, Fritz Müller (1878) proposed an explanation to Bates’ paradox (many unrelated butterfly species were all inedible) • A single pattern of warning adopted by several unpalatable species, so that each participant is both model & mimic. • Avoidance learning by predator becomes more efficient such that a predator needs only to be exposed to a single species to avoid all of them.

Common Wasp Vespula vulgaris Hornet Moth Sesia apiformis Wasp Beetle Clytus arietis Hoverfly Syrphus ribesii. www. bombus. freeserve. co. uk/mimicry. htm

Parasite (+/-): an organism that lives in or on another organism, deriving benefits from it. Parasites often reduce the fitness of the host, but do not generally kill it. GLFC

Parasites may alter the behaviour of their host Players: 1. Parasite: Acanthocephala, Plagiorhynchus cylindraceus - 3 mm 2. Intermediate host: Isopod, Armadillidium vulgare - 8 mm! 3. Final host: Starling, Phlagiorhynchus cylindricus Infected isopod leaves shelter & moves to open areas where is is more likely seen by birds. Moore 1984 Sci. Am. 250: 108 -15 cited in Molles (2002, Fig. 14. 2)

How do predators respond to changes in the availability or abundance of prey? 1. Numerical Response 2. Functional Response

Solomon (1949) and Holling (1959) identified 2 sources of numerical responses. • Reproduction • Immigration Number of Predators Number of Prey

Birds often show a numerical response. Clutch size of short-eared owls varies from 4 -7 eggs, depending on food resources in a given year. • Nocturnal & diurnal • Eats small mammals inland & birds in aquatic habitats Asio flammeus www. owlpages. com/species/asio/flammeus/shorteared 2. html

Numerical Response: Immigration Bay-breasted warbler: characteristic warbler of spruce forest in eastern Canada in summer. Dendroica castanea Numbers vary from year to year - increase quickly during population explosions of the spruce budworm or other forest pests. http: //www. petersononline. com/birds/month/bbwa/index. html

Functional Response: a change in predator feeding rate with an increase in prey density C. S. Holling’s classic studies on functional response by small mammals feeding on pine sawfly. The response is determined by the predator’s feeding behaviour.

Predators: 1. Short-tail shrew 2. Deer mouse 3. Common or American water shrew Prey: sawfly (Hymenoptera) • single generation per year (egg, larva, pupa, adult) • ovipositor of female is SAW-like: inserts eggs into plant host (pine needles) in autumn • larva bore into stems & overwinter • in June, larva drops to ground & burrows (cocoon) • adults emerge to lay eggs in September

Experiment: background information • 3 months during the summer, the forest floor is covered with sawfly cocoons (103 to 106 cocoons/acre). • Each of the 3 predators opens the cocoon in a characteristic manner so the ecologist can tall instances of predation for each species. • Calculate the prey density by sampling the forest floor • Calculate the densities of the predators set LIVE traps to mark & recapture animals

http: //www. tapirback. com/ugglan/grahnab-ugglan. html

Estimate Population Size in the Field No = number at time zero. Mo = animals marked at time zero. C 1 = number captured at time 1. R 1 = number recaptured at time 1 M o = R 1 No C 1 No = M o x C 1 R 1

Functional response of each predator was unique Short-tail shrew 300 # of coccons 200 eaten per day 100 Deermouse Common shrew 200 400 600 800 1000 Prey density of cocoons (103 per acre)

Type I Functional Response: Prey eaten per predator Prey Density • Short tail shrew increased its consumption more quickly than other 2 species. • Increase response at low prey densities • Very typical of zooplankton filter feeders

Type II Functional Response Number of prey eaten by predator Eventually search time becomes trivial & handling time takes up an increasing % of time Prey Density … A VERY COMMON RESPONSE

Predation of dreissenids by the round goby Ray & Corkum (1997)

Type III Functional Response Seen in vertebrates & some invertebrates B A Prey eaten by predator -ignores prey; develops search image Strong prey preference S -shaped curve “predator switching” Prey Density

• Tinbergen said switching was a result of “search image formation” by predator on prey • The search image consists of a SIGNAL that the predator receives from the prey.

% of mayflies in diet lower than expected % of mayflies in diet higher than expected Predator: Notonecta Prey: Isopods Mayflies Lawton et al. 1974 Ricklefs 2001 Fig. 18. 13

But, variation in prey availability does not always lead to switching (see text Fig. 18. 4)

In summary. . . Predator consumes a constant proportion of prey Predator rate declines …satiation Low hunting or search image