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Predation & Herbivory Photo of acorns & weevil grub from

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1 Predation & Herbivory Photo of acorns & weevil grub from

2 Predators (active foragers, ambush predators, sit-and-wait predators, etc.) generally kill and consume prey Exploitation (+/- or antagonistic interaction) Photo of ants dismembering a cicada from Wikimedia Commons

3 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

4 Exploitation (+/- or antagonistic interaction) Parasites (internal [endoparasite], external [ectoparasite], etc.) consume tissues or fluids of their hosts, generally without killing them Photo of human head louse from Wikimedia Commons

5 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

6 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

7 Prey Switching Cain, Bowman & Hacker (2014), Fig. 13.5, after Murdoch et al. (1975) Guppies preferentially eat whichever prey is most common (aquatic tubificid worms vs. fruit flies)

8 P H - 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 Robert Holt Apparent Competition

9 Prey in the absence of predators: dN/dt = rN 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 Prey in the presence of predators: dN/dt = rN - aNP where aNP is loss to predators 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 Lotka-Volterra Predator-Prey Models

10 Satiation Host-switching, developing a search image, etc. Why might functional responses have these shapes? Rate of prey capture Victim abundance (V) Figure from Gotelli (2001), after Holling (1959) Functional Response Curves Prey abundance (N)

11 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. Lotka-Volterra Predator-Prey Models

12 dN/dt > 0 dN/dt < 0 Equilibrium solution: For the prey (N) population: dN/dt = rN - aNP 0 = rN - aNP aNP = rN aP = r P = r/a The prey isocline P depends on the ratio of the growth rate of prey to the capture efficiency of the predator ^ Figure from Gotelli (2001) Prey (N) Predators (P) r/a dN/dt = 0 ^

13 The predator isocline N depends on the ratio of the death rate of predators to the conversion & conversion efficiencies of predators Equilibrium solution: For the predator (P) population: dP/dt = baNP - mP 0 = baNP - mP baNP = mP baN = m N = m/ba dP/dt > 0dP/dt < 0 ^ Figure from Gotelli (2001) Prey (N) Predators (P) ^ m/ba

14 Combined graphical solution in state space: The predator and prey populations cycle because they reciprocally control one another’s growth Figure from Gotelli (2001) Prey (N) Predators (P) m/ba r/a

15 Combined graphical solution in state space: The predator and prey populations cycle because they reciprocally control one another’s growth Figure from Gotelli (2001) Prey (N) Predators (P) m/ba r/a Prey

16 Huffaker’s mites Cain, Bowman & Hacker (2014), Fig , after Huffaker (1958) 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

17 Huffaker’s mites Cain, Bowman & Hacker (2014), Fig , after Huffaker (1958) Vaseline  barriers around oranges created prey refuges; herbivorous mites could balloon - via silk strands - among oranges; predators & prey coexisted with coupled, cyclical dynamics

18 Adaptations of Prey Physical defenses (e.g., large size, rapid or agile movements, body armor, spines, etc.) Poisons / Toxins (often accompanied by aposematic coloration) Mimicry (e.g., crypsis, false- advertisement, etc.) Photos of porcupine, lionfish, Draco lizard & snake-mimic caterpillar from Wikimedia Commons

19 Detection & prey- capture prowess (e.g., heightened sensory capabilities, etc.; speed, agility, fangs, claws, etc.) Poisons / Toxins (e.g., venom, etc.) Mimicry (e.g., camouflage, etc.) Photos of owl, cobra & orchid mantis from Wikimedia Commons Counter-adaptations of Predators

20 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 – photos of grazing sheep & raspberry thorns, as well as structure of caffeine, from Wikimedia Commons Adaptations of Plants

21 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 Counter-Adaptations of Herbivores


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