Predation Herbivory Photo of acorns weevil grub from

Predation & Herbivory Photo of acorns & weevil grub from http: //www. insectimages. org/browse/detail. cfm? imgnum=0014201

Pairwise Species Interactions Influence of species A Influence of Species B A - - (negative) 0 (neutral/null) - 0 - B Competition Amensalism - 0 A 0 0 B Amensalism + A A - B + Antagonism (Predation/Parasitism) A 0 B A + (positive) + B Antagonism (Predation/Parasitism) + A B 0 Neutralism (No interaction) Commensalism 0 + A B + Commensalism Redrawn from Abrahamson (1989); Morin (1999, pg. 21) A + Mutualism B

Exploitation (+/- interaction, a. k. a. antagonism) 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 (+/- interaction, a. k. a. antagonism) 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 (+/- interaction, a. k. a. antagonism) 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

Exploitation (+/- interaction, a. k. a. antagonism) 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 (+/- interaction, a. k. a. antagonism) Pathogens Parasites that cause disease (which manifests as pain, dysfunction or death) Photomicrograph of an Ebola virion (a complete virus particle) from Wikimedia Commons

Predator Generally Experiences Net Benefit, but not always! Fire ant latched onto mandible of ant lion, fire ant died, prevented ant lion from building pit, and ant lion starved to death K. Harms’s photo of ant lion pit (Kisatchie Nat’l. Forest, LA); figure from Lucas & Brockman (1981)

Prey Switching Guppies preferentially eat whichever prey is most common (aquatic tubificid worms vs. fruit flies); owing to development of search image or learning to efficiently handle the prey Bowman, Hacker & Cain (2017), Fig. 12. 6, 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: d. N/dt = r. N Prey in the presence of predators: d. N/dt = r. N - a. NP where a. NP 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 a. N 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: d. P/dt = -m. P P is the predator pop. size, and m is the per capita mortality rate Positive population growth occurs when prey are present: d. P/dt = ba. NP - m. P 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 ba. N 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: d. N/dt = r. N - a. NP 0 = r. N - a. NP = r. N a. P = r ^ = r/a P The prey isocline Predators (P) Equilibrium solution: d. N/dt < 0 r/a d. N/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) d. N/dt = 0

Equilibrium solution: ^ N = m/ba The predator isocline d. P/dt < 0 d. P/dt > 0 Predators (P) For the predator (P) population: d. P/dt = ba. NP - m. P 0 = ba. NP - m. P ba. NP = m. P ba. N = m ^ depends on the ratio of the N death rate of predators to the capture and 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 – predator-prey cycles in the lab 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 Bowman, Hacker & Cain (2017), Fig. 12. 15, after Huffaker (1958)

Huffaker’s mites – predator-prey cycles in the lab Vaseline barriers around oranges created prey refuges; herbivorous mites could balloon - via silk strands - among oranges; predators & prey coexisted with coupled, cyclical dynamics Bowman, Hacker & Cain (2017), Fig. 12. 16, after Huffaker (1958)

Population Cycles Top-down vs. bottom-up influences on snowshoe hare abundance Figure from Krebs (2011); photos from Wikimedia Commons

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

Counter-adaptations of Predators Detection & prey-capture prowess (e. g. , heightened sensory capabilities, etc. ; speed, agility, fangs, claws, etc. ) Poisons / Toxins (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