Eco - Predation

carnivory

both predator and prey are animals

herbivory

predator is an animal, prey are plants or algae

parasitism

predator (a parasite) lives symbiotically on or in the prey (its hot) and consumes certain tissues

true predator

kills and consumes organism

grazer

live prey, consumes, but does not kill’ many prey per individual grazer

parasite

live prey, consumes, but does not kill; few hosts per individual parasite

parasitoid

live prey, consumes & kills, one host per individual parasitoid

monophagous

feeding on one food type

oligophagous

few types of food

polyphagous

many types of food

how are diet preferences determined?

determined by comparing what is available to be eaten tp what is actually eaten

a predator’s functional response

the relationship between the per capita rate of consumption and the number of prey

a predator’s numerical response

the relationship between consumption of prey and predator reproduction

what are the three ways that predators act

1. forage by moving around in search of prey - e.g., wolves, sharks, hawk

2. remain in one place and attack prey that come within striking distance - e.g., moray eels, some snakes

3. set traps, such as spider webs, or modified leaves of a carnivorous plant

physical features that are adaptations to escape being eaten

• large size (elephants)

• rapid movement (gazelles)

• body armor (snails)

warning coloration (aposematic)

• predators learn not to eat organisms that have toxins

• adaptation to escape being eaten

crypsis

• they prey is camouflaged, or resembles its background

• adaption to escape being eaten

mimicry

• the prey resembles another organism that is toxic or very fierce

• adaptations to escape being eaten

plant defenses

• some produce huge numbers of seeds in some years and hardly any in other years (masting)

• the plants hide (in time) from seed-eating herbivores, then overwhelm them by sheer numbers

effects of herbivory on individual plants: compensation for the effects of herbivory

• herbivory can reduce self shading

• lead tissue can be rebuilt using carbohydrates stored in roots

• alteration of root : shoot distribution of fixed carbon

• increase in photosynthesis per unit of leaf area

effects of herbivory on individual plants: tolerance to grazing (grasses)

• meristem (origin of growth) is located close to ground (ability to regrow)

• aided by grazers as grazers remove species that can not tolerate grazing

effects of herbivory on individual plants: plant defenses

• morphological defense

• low nutritional quality

• chemical defenses (constitutive vs. inducible)

• costs vs. benefits of constant vs inducible defense

effects of herbivory on individual plants: intensity of herbivory

• defoliation (removal of leaves) by herbivores can lead to plant death or can be tolerated

• consumption of seeds or whole seedlings is clear indicator or mortality

• impact on plant not necessarily mortality, but reduced fecundity

• herbivory of pollen and fruit can actually benefit a plant, as this form of mutualism can provide dispersal of pollen or seeds

effects of herbivory on individual plants: interactive effects of herbivory

• herbivores often vector of disease transmission among plants (viral, fungal, bacterial pathogens)

• interaction of herbivory and competition

Lotka - Volterra Model of Predation

dN(prey)/dt = r N(prey) - a N(predator) N(prey)

change in N as a function of births and deaths

change in prey population over time

dN/dt = rN - aNP

N = number of prey

P = number of predators

r = population growth rate

a = capture efficiency

what occurs when P=0 in prey population cycle

the prey population grows exponential

• with predators present (P does not equal 0), the rate of prey capture depends on how frequently they encounter each other (NP) and efficiency of prey capture (a)

change in predator population over time

dP/dt = baNP - mP

N = number of prey

P = number of predators

m = mortality rate

a = capture efficiency

b = efficiency with which prey are converted to predator offspring

what happens if N=0 in predator population cycle?

predator population decreases exponentially at death rate d

• when prey are present (N does not equal 0), individuals are added to the predator population according to the number of prey killed (aNP) and efficiency (b)

what factors can prevent predators from driving prey to extinction

• habitat complexity and limited predator dispersal

• prey switching in predator

• spatial refuges (where predators cannot hunt effectively)

• evolutionary changes in prey populations

findings of the hare study and the lemming study

• food supplies and predator abundance are both important

• stress responses of prey influence cycles

• other predators ‘switch’ to abundant prey

barriers to herbivory

1. structural/physical - thorns, spines, stinging hairs

2. animal associations - many plants form associations with ants; the ants protect the plants from herbivores

3. chemical barriers - 2 major groups

   1. qualitative defenses

      1. very toxic in small amounts

      2. alkaloids (cyanide, nicotine, caffeine)

      3. many of common drugs

      4. “relatively cheap” to produce in terms of biomass

      5. mobile within a plant (transport via phloem)

   2. quantitative defenses

      1. complex polymers and inorganic crystals (siica, cellulose, tannis, polyphenols)

      2. for defense, need large quantities of these polymers

      3. relatively immobile for most plants

what other variables need to be taken into account in the real world when discussing predator and prey populations and relationships?

• crowding of predators and prey (density - dependence)

• variability in the environment

• metapopulations (dispersal)

  • local extinctions

  • local founding of new populations

  • subsequent colonization by predator