Lecture 21. Species Interactions

Competition interaction

Negative effect & negative effect (-/-)

Consumer-Resource interaction (Predator/Prey)

Positive effect & negative effect (+/-)

Mutualism interaction

Positive effect & positive effect (+/+)

Commensalism interaction

No effect & positive effect (0/+)

Amensalism interaction

No effect & negative effect (0/-)

Interference competition

Competing individuals interact directly - fighting, stealing, & combat among individuals to obtain resources

Exploitative competition - indirect competition

Individuals or populations depress one another through use of shared resource

Apparent competition - indirect competition

Both competing species preyed upon by same predator

Predation

Species interaction in which one species (predator) eats the other species (prey)

Crests & troughs

High & low points due to population cycling - neither population reaches carrying capacity

Foraging

Seeking & obtaining food

Optimal foraging model

Selection favors traits that maximize surplus energy gained per unit time from foraging

Profitability of prey formula

(energy gain - cost of capture) / (search time + capture time)

Costs of foraging

Risk of predation, energy expended searching for & capturing or processing food

Optimal foraging model example

Foraging oystercatchers choose mussels that are larger than average available mussel but don’t concentrate on the very largest mussels

Balancing risk of predation with food availability example

Risk of predation has greater effect on mule deer foraging than food availability (mule deer & mountain lions)

Foraging behavior - cooperative group hunting in Harris’s Hawks

Cooperative hunting allows Harris’s Hawks to catch large prey (e.g., rabbits)

Herbivory

Species interaction in which an animal eats part of a plant

Defenses against predation

Weapons, speed, chemical defenses, mimicry, etc.

Physical defenses against herbivory

Thorns, trichomes, etc.

Chemical defense against herbivory

Toxic plants

Mimicry as a defense against predators example

Viceroy butterfly mimics color pattern of poisonous Monarch butterfly

Mullerian mimicry

Two or more well-defended species with similar predators mimic each other’s honest warning signals to their mutual benefit

Mullerian mimicry example

Yellow & black coloration of bees & wasps

Batesian mimicry

Harmless species imitates warning signals of harmful or unpalatable species - directed at predator of both species

Batesian mimicry example

Yellow & black flies, many butterflies, king snakes

Parasitism, mutualism, & commensalism are classified as…

Symbioses

Symbiosis

Long-term ecological relationship between two different species that live together in direct & intimate contact

Parasitism

Species interaction in which species (parasite) feeds on cell contents, tissues, or body fluids of another species (host)

Mistletoe

Hemiparasitic plant that grows on other plants

Brood parasitism

Behavioral parasitism involving 2 bird species - host parent cares for parasite chick often to detriment of its own chicks

Mutualism

Species interaction in which both species benefit

Mutualism has 3 levels

Termite gut has protozoa, protozoa have bacterial endosymbionts, bacterial endosymbionts produce enzyme cellulase - breaks down cellulose

Lichen

Mutualistic relationship between fungus & photosynthetic organism

Commensalism

Symbiotic relationship in which 1 species benefits, while other neither benefits nor is harmed

Amensalism

Species interaction in which 1 species is harmed, while other neither benefits nor is harmed

Ecological facilitation

Species interactions that benefit at least one of the participants & cause harm to neither

Nurse plants

Protect seedlings from harsh environmental conditionsN

Nurse plants create microhabitats protected from:

Sun & extreme temps, wind, moisture loss, herbivory

Nurse log

Fallen tree that facilitates growth of seedlings of other plants as it decays