Ecology Exam 2

Mutualism

Mutually beneficial interaction between individuals of two species (+/+)

Commensalism

Individuals of one species benefit, while individuals of the other species do not benefit and are not harmed (+/0)

Trophic mutualism

A mutualist receives energy or nutrients from its partner (ex: Mycorrhizal fungi & plants - Fungus gets energy in the form of carbohydrates - Plant gets help in taking up limiting nutrients, such as phosphorus)

Service mutualism

Interactions in which one partner performs an ecological service for the other (ex: Pollination, seed dispersal, defense against herbivores/predators/parasites)

Habitat mutualism

One partner provides the other with shelter, a place to live, or favorable habitat (ex: Bluehead Chub nests and associated minnow species)

Examples of cheating in mutualism

Nectar robbers, Deceptive orchids

How do Yucca plants prevent cheating?

Yuccas are able to abort flowers with too many eggs, before the moth larvae hatch

Parasite

obtains nutrition from single or alternate hosts, but usually don’t kill the prey

Endoparasites

Live in the host

Ectoparasite

Live on the host

Examples of parasitism

Induced fruit mimicry in the gliding ant, Epifagus (beech drops) grows on the roots of oak and beech trees, mistletoe takes nutrients from most disciduous trees

Parasitoids

Single prey (host) consumed by one or more young, and the host is always killed

Examples of parasitoids

Wasps in goldenrod plants

Red Queen Hypothesis

For an evolutionarily labile system, change is needed to maintain fitness relative to systems it is co-evolving with. (Advantage of sexual reproduction)

New Zealand Mudsnail Example

They can reproduce both sexually and asexually. Asexual reproduction allows for more efficient reproduction but less defense against parasitsm.

Chemical herbivory defense

Producing noxious or poisonous chemicals to deture consumption from herbivores

Mechanical herbivory defense

Developing structures like thorns to make the plant harder to eat

Nutritional herbivory defense

Growing structures that are less nutritious for herbivores

Tolerance herbivory defnese

Adapted to regrow quickly after being grazed

Chemical Predation defense

Producing chemicals that are noxious or poisonous to predators

Physical predation defense

Creating physical barriers to prevent predation (shells, armor)

Aposematism

Warning colors, sound, or characteristics to alert predators that they are not good for consumption

Crypsis

Was of camoflaging or hiding from predators (colors, shapes)

Mimicry

Looking or sounding like a species predators avoid

Behavioral

Behaving in ways to minimize risk from predation

What is a zero-growth isocline?

When the prey population size at which the change in predator population size is zero, or vice versa.

Assumptions for the Lotka - Volterra model

• No prey density-dependence

• Well-mixed predator and prey populations

• The predator only feeds on the prey species

• The predator is the only significant cause of prey

  mortality

• Handling time for prey = 0

• No immigration or emigration of prey or predators

Numerical response

Predator population size as a function of prey population size

Functional response

Predator consumption rate as a function of prey population size

Type 1 Functional Response

As long as prey density increases, predation rate will increase proportionally. Often drawn without any upper limit

Type 2 Functional Response

As prey density increases, predation rate becomes limited by handling time associated with each prey item

Type 3 Functional Respone

At high prey density, similar to Type II. At low prey densities, predation rate is slow to increase until prey becomes more common, a result of learning to eat a rare prey type or having alternative prey to focus on when this prey is rare.

Fundamental Niche

The complete set of conditions under which an organism can survive and reproduce

Realized Niche

The subset of the fundamental niche describing the conditions, under which an organism actually lives, given limitations created by interactions with other species.

Interspecific competition

Competition for resources between individuals of different species

Intraspecific Competition

Competition for resources between individuals of the same species

Indirect (resource) competition

Consumption of a resource by oneorganism means there is less of that resource available to other organisms

Direct (interference) competition

Individuals interact with each other directly to limit access to resources

Connell’s barnacles experiment

Two different types of barnicles on different parts of tide pools. Testing to see if it is a niche reason or a competition reason for why they are distributed a certain way. Move the barnicles around and see fitness.

“Ghost of competition past”

Competition, acting as an evolutionary force in the past, can explain present-day phenotypes even when no present-day competition exists

Limiting Similarity

If the niche overlap is near 100%, then it results in the competative exclusion of one species

Resource Partitioning

If there is an overlap in niches, then the species who sit in the middle of the overlap will be selected against, until the two species have seperated niches

Character Displacement

Competition causes the phenotypes of competing species to evolve to become more different over time

Unstable equilibrium

both species co-exist until there is a small perturbation, then one or the other goes to extinction

Stable equilibrium

both species co-exist and perturbation does not cause one or the other species to go extinct; rather, they return to their equilibrium pop. abundances

What does αij mean in lotka-voltera

the competitive effect on species i by species j

Zero Growth isocline for population 1

Zero growth isocline for population 2

Species 1 wins

Species 2 wins

Succession

the relatively repeatable change in community composition through time following a disturbance

Disturbances

alter communities by killing organisms, altering resource availability, and changing the physical structure of the environment.

Life-history traits

Differences in physiology & behavior that make each species well suited to grow in particular environments

Facilitation model

colonizing species make the environment more suitable for later arriving species

Inhibition model

colonizing species make the environment less suitable for later arriving species; replacement by death/damage

Tolerance model

colonizing species have little or no effect on the growth of later arriving species (late arrivals tolerate early colonizers); replacement by better competitors

Trophic Cascades

when addition or removal of a top predator affectsmultiple, lower trophic levels in the community

Behavioral trophic cascade

predators affect the behavior of herbivores, with cascading effects on lower trophic levels

Ecosystem engineers

Autogenic - alter resource availability through their own physical structures (forest, coral reef)

Allogenic - alter resource availability by transforming or redistributing parts of the environment (beavers, woodpeckers, gophers)

The Step Model

Both top-down and bottom-up forces can act simultaneously, Producer biomass provides the

foundation for consumer populations

Resistance

the ability to withstand a disturbance

Return time

the time required to return to “equilibrium” after disturbance

Resilience

how closely the post-recovery community resembles the pre-disturbance community

Alturnative stable states

After a major change, it is hard to return to form.

diversity-stability hypothesis

species-rich communities are more stable

Food web theory

communities with higher connectance (i.e., with many species interacting trophically) should be more stable

SIR model

Susceptible to infection, Infected (and capable of transmitting pathogen), Recovered (not capable of transmitting pathogen; may be immune to further infection)

Zoonosis

a disease communicable from animals to humans under natural conditions