Transcript Type I Functional Response

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 6th).
Dr. Weis will give the lecture November 6th.
I’ll return to lecture November 8th.
Camouflage or Crypsis: enables prey to avoid detection
- often mistaken for inedible objects or missed.
Orthoptera: walking stick
http://www.ivyhall.district96.k12.il.us/4th/kkhp/1insects/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 - 3mm
2. Intermediate host: Isopod, Armadillidium vulgare - 8mm!
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/shorteared2.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.
C1 = number captured at time 1.
R1 = number recaptured at time 1
Mo = R1
No
C1
No
=
Mo x C1
R1
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