Predation & Herbivory
Photo of acorns & weevil grub from http://www.insectimages.org/browse/detail.cfm?imgnum=0014201
Exploitation (+/- or antagonistic interaction)
Predators (active foragers, ambush predators, sit-and-wait predators, etc.)
generally kill and consume prey
Photo of ants dismembering a cicada from Wikimedia Commons
Exploitation (+/- or antagonistic interaction)
Herbivores (browsers, grazers, phloem suckers, seed predators, etc.)
eat tissues or fluids of plants or algae;
often quite specialized (w.r.t. species & plant part)
Photo of leaf-miner damage to a leaf from Wikimedia Commons
Exploitation (+/- or antagonistic interaction)
Parasites (internal [endoparasite], external [ectoparasite], etc.)
consume tissues or fluids of theirs hosts,
generally without killing them
Photo of human head louse from Wikimedia Commons
Exploitation (+/- or antagonistic interaction)
Parasitoids
Insects that lay an egg or eggs on or in a host (generally an insect or spider);
the larvae eat and usually kill the host
Photo of phorid fly ovipositing (laying eggs) into a honey bee from Wikimedia Commons
Exploitation (+/- or antagonistic interaction)
Pathogens
Parasites that cause disease
(which manifests as pain, dysfunction or death)
Photomicrograph of an Ebola virion (a complete virus particle) from Wikimedia Commons
Prey Switching
Guppies
preferentially eat
whichever prey is
most common
(aquatic tubificid
worms vs. fruit flies)
Cain, Bowman & Hacker (2014), Fig. 13.5, after Murdoch et al. (1975)
Apparent Competition
Robert Holt
H
-
+
P
+
-
P
Solid arrows indicate direct effects,
dotted arrows indicate indirect effects
Original idea from Holt (1977); figure redrawn from Menge (1995) & Morin (1999);
photo of Holt from http://people.biology.ufl.edu/rdholt/
Lotka-Volterra Predator-Prey Models
Prey in the absence of predators:
dN/dt = rN
Prey in the presence of predators:
dN/dt = rN - aNP
where aNP is loss to predators
Losses to predators are proportional to NP (random encounters) and a
(capture efficiency – effect of a single predator on the per capita growth
rate of the prey population)
Large a is exemplified by a baleen whale eating krill, small a by a spider
catching flies in its web
aN is the functional response of the predator (rate of prey capture as a
function of prey abundance); in this case linear, i.e., prey capture increases
at a constant rate as prey density increases
Functional Response Curves
Why might functional responses have these shapes?
Rate of prey capture
Satiation
Host-switching, developing a search image, etc.
Victim
abundance
Prey
abundance
(N)(V)
Figure from Gotelli (2001), after Holling (1959)
Lotka-Volterra Predator-Prey Models
In the model’s simplest form, the predator is specialized on 1 prey
species; in the absence of prey the predator pop. declines exponentially:
dP/dt = -mP
P is the predator pop. size, and m is the per capita mortality rate
Positive population growth occurs when prey are present:
dP/dt = baNP - mP
b is the conversion efficiency – the ability of predators to turn a prey item
into per capita growth
Large b is exemplified by a spider catching flies in its web (or wolves
preying on moose), small b by a baleen whale eating krill
baN reflects the numerical response of the predator population – the per
capita growth rate of the predator pop. as a function of the prey pop.
For the prey (N) population:
dN/dt = rN - aNP
0 = rN - aNP
aNP = rN
aP = r
^ = r/a
P
The prey isocline
Predators (P)
Equilibrium solution:
dN/dt < 0
r/a
dN/dt > 0
^ depends on the ratio of
P
the growth rate of prey to
the capture efficiency of the
predator
Prey (N)
Figure from Gotelli (2001)
dN/dt = 0
Equilibrium solution:
^
N = m/ba
The predator isocline
dP/dt < 0
dP/dt > 0
Predators (P)
For the predator (P) population:
dP/dt = baNP - mP
0 = baNP - mP
baNP = mP
baN = m
^ depends on the ratio of the
N
death rate of predators to the
conversion & conversion
efficiencies of predators
m/ba
Prey (N)
Figure from Gotelli (2001)
The predator and prey
populations cycle because
they reciprocally control one
another’s growth
Predators (P)
Combined graphical solution
in state space:
r/a
m/ba
Prey (N)
Figure from Gotelli (2001)
The predator and prey
populations cycle because
they reciprocally control one
another’s growth
Predators (P)
Combined graphical solution
in state space:
r/a
m/ba
Prey (N)
Prey
Figure from Gotelli (2001)
Huffaker’s mites
Oranges & rubber balls
in experimental arena
Herbivorous mite’s population
increased until addition of a
predatory mite;
predator drove herbivore to
extinction, then itself declined
to extinction
Cain, Bowman & Hacker (2014), Fig. 13.20, after Huffaker (1958)
Huffaker’s mites
Vaseline barriers around oranges created prey refuges;
herbivorous mites could balloon - via silk strands - among oranges;
predators & prey coexisted with coupled, cyclical dynamics
Cain, Bowman & Hacker (2014), Fig. 13.20, after Huffaker (1958)
Adaptations of Prey
Physical defenses
(e.g., large size, rapid or
agile movements, body
armor, spines, etc.)
Toxins
(often accompanied
by aposematic
coloration)
Mimicry
(e.g., crypsis, falseadvertisement, etc.)
Photos of porcupine, lionfish, Draco lizard & snake-mimic caterpillar from Wikimedia Commons
Counter-adaptations of Predators
Detection & preycapture prowess
(e.g., heightened sensory
capabilities, etc.; speed,
agility, fangs, claws, etc.)
Poison
(e.g., venom, etc.)
Photos of owl, cobra & orchid mantis from Wikimedia Commons
Mimicry
(e.g., camouflage, etc.)
Adaptations of Plants
Avoidance
(e.g., masting, etc.)
Tolerance
(e.g., compensation,
etc.)
Defenses
(e.g., structural,
chemical [e.g.,
secondary
compounds],
inducible, etc.)
Photo of acorn mast – http://blog.chron.com/lazygardener/2012/11/of-course-its-raining-acorns-its-a-masting-year;
photos of grazing sheep & raspberry thorns, as well as structure of caffeine, from Wikimedia Commons
Counter-Adaptations of Herbivores
Structural
(e.g., teeth, etc.)
Chemical
(e.g., clay, digestive
enzymes, etc.)
Behavioral
(e.g., consumption of
clay, etc.)
Photos of horse’s teeth from Wikimedia Commons; photo of macaws at clay lick from
http://surbound-birding.blogspot.com/2013/04/macaw-and-parrot-clay-licks-in.html