Ecology Exam 2

Trophic Species Interaction

species interactions that involves feeding (ex. carnivory, herbivory, parasitism)

Non-trophic species interaction

species interaction that does not involve feeding (ex. competition, facilitation)

Symbiosis

a positive or negative interaction in which one species lives in close physical or physiological contact with other species.

Mutualism species impacts

positive for both

Commensalism species impacts

both species neutrally

Species impacts from Carnivory/ Herbivory/ Parasitism (predation)

Positive for one species, negative for the other

Competition species effects

negative for both species

Amensalism species effects

Negative for one species, neutral for the other.

Predation

trophic interaction where an individual from one species (predator) kills and/or consumes individuals (or parts of) of another species (prey)

Carnivory:

predator and prey are both animals

Herbivory

predator (herbivore) is an animal and prey is plant or algae

Parasitism

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

• may not kill the host (harm, but not lethal)

• parasites can be pathogens that cause disease in hosts

Competition

non-trophic interactions in which two or more species overlap in the use of at least some of the same required limiting resources.

Interspecific competition

competition between different species

Intraspecific competition

competition between members of the same species

Interspecific competition impacts

negatively effects growth, reproduction, and/or survival of each competitor

Interspecific competition limiting resources

food, water, space, territory sites, nutrients, sunlight, etc.

Positive Interactions = facilitations:

trophic or non-trophic interaction in which at least one species benefits and none are harmed.

Mutualisms:

both species benefit

obligate mutualism

species are highly dependent on one another, interaction is required for survival of both.

Some symbioses are -

mutualisms

commensalism:

one species benefits and the other is not affected

• many ways for one species to improve the conditions for the commensal organism

Amensalisms:

one species is harmed and the other is not affected

Are Amensalisms trophic or non-tropic

non-tropic

Amensalism example

elephant stepping on an animal burrow

Do herbivores normally kill their prey (plants)?

often not immediately

In carnivory prey do what to avoid predators?

move away or try to hide

Do animal or plant tissues have higher nutritional content

animal

Which organic compound is essential for animal diets

nitrogen

Do animal or plant tissues have higher N content?

animal

Animal dietary preferences are dependent on

search time and handling time

Search time

time it takes predator to search and find prey

Handling time

time it takes to subdue and consume prey

If search time is high, predators should have more - diet

generalist

If search time is low (even if handling time is high), predators (herbivores) can have - diets

specialist

Prey preferences

in carnivores, consuming species at a higher proportion than you would expect based on the species’ availability

Prey switch

when carnivores specialize on most abundant prey and then switch as prey abundance changes.

Which plant part is the most likely for herbivores to specialize on

leaves (most N)

Herbivory impact on plants

consumption of photosynthetic tissue can reduce plant growth, survival, and reproduction

Herbivore specialization on plant species are driven by

insects

predominant herbivore

insects

Herbivores with broad diets

grasshoppers, larger browsers like deer.

Carnivore strategies

move and search, sit and wait

Carnivore adaptations

cheetah speed, snake swallow huge things, spider venom.

Prey adaptations to escape predation

large size, speed, body armor, poisons, colors, mimicry, behavioral changes

Herbivory causes -

evolution

Masting/mass flowering:

some plants produce huge numbers of seeds in some years and almost none in most years

plant compensation

tissue removal stimulates new tissue growth

Plant (or agal) structural defenses

tough leaves, spines, thorns, nettles

Plant (or agal) chemical defenses

secondary compounds that are toxic to some/most herbivores, or volatile compounds used as cues to attract predators of herbivores

Inducible defense

stimulated by herbivory

constitutive defenses

always present

Herbivore counter defenses

digestive enzymes to disarm or tolerate chemical compounds

behavioral responses

often require specialization

may be costly, but provide an advantage (access to an abundant food source)

Snowshoe hares and Canadian lynx populations demonstrate

predator and prey fluctuations in regular cycles

Hare densities drop (years) after peak densities

2-3

Hypothesis that food supply (vegetation) causes hare pop cycles

food is limiting resource at high hare densities

declining hare populations aren’t always food limited

experimental additions of food does not stop the cycles

Hypothesis that food predation causes hare pop cycles

up to 95% of hare deaths from predation (lynx, coyotes, birds of prey)

predation rates higher during the peak and declining phases of cycle than during the increasing phase

why do hare birth rates drop during decline

why do hares sometimes rebound slowly after predator populations drop

Lotka-Volterra model

What type of growth does the lotka-volterra model assume

exponential growth (density-independent) without the predator present

equilibrium isocline = zero growth isocline =

the population size of one species that causes the population of another species to be stable (kept at equilibrium)

zero growth isocline graph

predators > r/a

prey decreases

predators < r/a

prey increase

prey isocline

no change in prey population at P=r/a

without prey present

predators starve and thus decrease exponentially with a mortality rate = m

with prey present

predators are added to the population as a function of the number of prey killed (aNP) and efficiency of predators producing offspring from eating prey (b= reproductive efficiency), minus the predator death rate

Lotka-Volterra equation without prey present

Lotka-Volterra equation with prey present

Predator isocline

no change in predator population

Predator isocline graph

Predator population not changing when

prey < m/ba predators

decrease

prey > m/ba predators

increase

Prey equation

predator equation

Phase plane

c

exception to lotka-volterra model

at intersection of isoclines

Adding prey density-dependence to the model

Cycling of Lotka Volterra model is - to produce in lab experiements

hard

Huffaker lab experiment for lotka-volterra model

• conducted lab experiments with a prey mite (six-spotted mite; herbivore), using oranges as experimental food habitats for the prey.

• Prey increased in abundance

• Predatory mite was introduced; prey and then predator went extinct

Huffaker’s initial experimental results

predator and prey went extinct

huffaker’s more complicated experiment results

predator prey fluctuations observable

Krebs field experiment on predator prey cycles

Testing effects of food, predation and their interaction on hare population cycles

• Seven 1km 2 blocks of forests in Canadian wilderness

• 3 blocks: controls

• 2 blocks: food added for hares (+Food)

• 1 block: predators excluded with electric fence (-Predators)

• 1 block: predators excluded and food added (+Food/-Predators)

• Measured density and survival of hares for 8 years!

Krebs field experiment results

• removing predators doubled hare density

• adding food tripled hare density

• removing predators and adding food increased hare density 11-fold

Parasites

species that live in or on other organisms (hosts) feeding off their tissues or fluids and having a negative effect on those species

how much of species on earth are parasites

50%

pathogens

parasite that cause diseases

parasites often do not

immediately kill the host

macroparasites

large species. Examples: worms, arthropods

microparasites

microscopic species. Examples: viruses, bacteria, fungi

Parasite facts

• Most species are attacked by more than

one parasite (including parasites)

• Many parasites are specialized to particular

host species

• Many parasites are specialized to live on or

eat certain parts of a host’s body

• Many parasites have complex life cycles

involving two or three host species

Many parasites have - host species and - life cycles

2-3, complex

vertical parasite transmission

parent to offspring

horizontal parasite transmission

between individuals other than parent to offspring

ectoparasites

live on outer surface of its host

ectoparasite examples

plants that grow on and obtain water/food from other plants; many

fungal parasites; insects like fleas, lice, and ticks

endoparasites

lives inside the body of their host, either within the

alimentary canal or in tissues or cells

endoparasites examples

tapeworm robs host of nutrients; bacteria that live in tissues and cells

of animals; bacterial pathogens that infect plant tissues