Ecology midterm #2

Patterns of resource partitioning(3 types)

• habitat and microhabitat

• time

• size and morphology

Why resource partitioning by size and habitat more favorable than resource partitioning by time?

Habitat and size partitioning is an exchange of one type of positive energy gain for a different positive energy gain, whereas by time is an exchange for a positive gain and no gain.

What type of animal favors resource partitioning by time and why?

Predators in order to follow the activity levels of a preferred prey

Null Model to test for resource partitioning

***

Complimentary test for resource partitioning

Compare two resource dimensions. Would expect that high overlap in one resource dimension would predict a difference in the second dimension.(i.e. size, habitat). No high overlap in two dimensions.

Character Displacement test for resource partitioning

Compare species in isolation and in overlap and note that species more alike where the appear separately compared to where they overlap. Specialize more in overlap. Those of the species similar to competing species tend to do worse.

Field experiment test for resource partitioning

place species together and in isolation and look for impacts on survival and reproduction, compare effect to degree of similarity in resources.

Niche

total conditions under which an individual/population lives and replaces itself.

Limiting similarity

how similar 2 species can be and still coexist(not drive each other to extinction)

limiting similarity equation(effect of species 2 on species 1)

a₁₂=(sum(P₁h_i)(P₂h_i))/(sum((P₁h_i)²))

limiting similarity equation(effect of species 1 on species 2)

a₂₁=(sum(P₁h_i)(P₂h_i))/(sum((P₂h_i)²))

d in utilization curves

distance between peaks

w in utilization curves

½ of width between curves

limiting similarity equation for utilization curves

1= d/w

Factors that increase room/space for species to invade a system of resident species

1. More specialization of resident species

2. Looking a more/multiple resource dimensions 

3. If many competing species exist, than no species can reach critical density to eliminate each other, because of lowered carrying capacity, more room

Specialists

Use a narrower range of resources within utilization curve(skinnier curves, lower w)

Generalists

Use a broader range of resources within utilization curve(wider curves, higher w)

Coevolution

two species constantly evolving in relation to each other

Mutualism

interaction between to species that benefit each species, but can range into parasitism

Two types of mutualism and define

1. Falculative: relationship not specifically necessary to the survival of either species.

2. Obligatory: species entirely dependent on each other for survival( fig & fig wasps)

Why obligatory mutualism evolve???

***y

y in a host parasite model

number of infected individuals

x in host parasite models

number of susceptible individuals

z in host parasite models

number of recovered individuals/individuals with assumed immunity

D in host parasite models

Death rate of infected

y* in host parasite models

recovery rate from infection

Overall model equation of change in host population in presence of parasite

dN/dt = rN - Dy

beta(B) in host parasite models and range

transmission coefficient(chance that and xy interaction results in transmission) range 0 to 1

Reproductive rate of infection

R(x)=Bx/(D+y*)

• IF R(x)<1, pathogen wont spread

• IF R(x)>1, pathogen will spread

Threshold value of infection meaning and equation

Threshold value of infection is the minimum number of susceptibles in the host population needed for infection to spread.  

x=(D+y*)/B

Methods of containing infection

• lower the number of susceptibles within the population( lower x to be below (D+y*)/B

• reduce the transmission rate B

implication of immunization based on R(x) values

the higher R(x) of a disease in a population, the greater rate of immunity neccessary to acheive herd immunity.

Two types of competition and define

1. Exploitative competition: individual deprive each other of some resource such as food

2. Interference: interactions between. individuals affect survival, reproduction and population growth

competition coefficient

(interspecific effect x effect of species 1 on 2)/(intraspecific competition x effect of species 1 on 1)

How do populations grow in absence of each other?

When competing population is a zero grow to their own carrying capacity K

competition isocline meaning

the isocline represents all conditions where the population is not growing.

Population growth trend below isocline

Positive growth

Population growth trend above isocline

negative population decline

4 outcomes of competition

1. Species 1 reaches critical density (K2/ α21) at which species 2 is inhibited, and species 2 goes extinct 

2. Species 2 reaches critical density (K1/ α12) at which species 1 is inhibited, and species 1 goes extinct.

3. Both species reach the critical density that inhibits the other, and one or the other goes extinct (unstable equilibrium)

4. Both species reach their carrying capacities before they reach the critical density that inhibits the other, and they coexist (stable equilibrium)

Takeaways of competition experiments

• differences in resource use outcome of competition

• coexistence only possible w/o total overlap

Field experiment test for mutualism

Go out and observe to positive and negative(cost benefit) analysis of different interactions. Experiment with species in isolation and

Field experiment test for competition

combine species and note for decline

Proportion of H vaccinated for no pathogen spread

p=1-(1/R(x))

Equation for when pathogen stop spread

Bxy=y(D+y*)

Factors favoring specialization

1. flowering season is short and lifetime of pollinator is short relative to lifetime of flower, specialization may be favored

2. Pollinator/host only needs to interact with one member of the complementary species

3. From plant’s point of view, specialization on a single pollinator (or kind of pollinator, e.g., bird or bee) might reduce pollen interference between different species of plant

4. Removal of nectar reward by less-preferred pollinator may discourage preferred pollinator

When to expect specialization and generalization

1. Expect specialization when pollinator is reliable -e.g., short arctic seasons -stable tropical regions

2. Expect generalization in unpredictable environments e.g., temperate regions with migratory pollinators

How competition influence evolution?

When evolutionary pressure is applied, favors becoming less similar to competing species 

How predation influence evolution?

1. Prey defenses should match predator foraging tactics

2. Predator foraging tactics should match prey defenses

3. Coevolved matches should be absent where prey and predator do not co-occur

sympatric 

Living together and interacting

allopatric

The physical isolation of the population due to the extrinsic barrier

Sex impact on evolution

sex can act to cause divergence so sexes niche dont overlap, causes flowers to evolve and diverge to match sexes

Energy flow

measure rate at which energy is captured by one group of consumers and passed on to the next

Productivity in energy flow ecology and unit

• the rate at which energy is captured and used by some group of organisms

  • expressed as a rate and as biomass

Primary producers

capture light energy and convert it to tissues that are then available to other consumers

Gross primary productivity

-rate at which primary producers capture radiant energy from the sun via photosynthesis

Net primary productivity

portion of GPP that ends up in producers for tissues and reproduction

Biomass

mass of energy fixed into tissues (physical accumulation of NPP) measured in g/m2

Why communities differ in NPP

1. Life history strategies, some put more work into long term storage.

Conditions that favor high NPP

1. water

2. warmth

3. moderate high rainfall(lots of water)

Trend for productitivity in oceans

high productivity in shallower water where nutrients stay in photosynthetic layer. but aside from that nutrients fall to ocean bottom.

Autotrophs

(green plants or primary producers) -organisms that make their own energy

Heterotrophs

Heterotrophs (herbivores and carnivores; consumers) -organisms that consume other organisms

Detritivores

break down organic matter.

Ecological Efficiencies in food chains

(net production of a level)/net production of level before it

Typical tend for efficiency for predators and herbivores

1) Herbivores/producers < 10%

2) Carnivores/herbivores, top carnivores/carnivores < 15%

Assimilation efficiency

(food digested)/(food consumed)

What determines food chain length

No productivity, not assimilation efficiencies, but determined by disturbance

prey growth equation 

dH/dt= rH -pHP

H and P in predator prey models

• h=prey population

• p=predator population

p in predator prey models

predation efficiency

HP in predator prey models

rate of predator-prey interactions

P^ equation, meaning and implications

• P^= r(intrinsic rate of prey population growth)/p

• # of predators where H prey population does not grow

  • if P<P^, then prey size increasing because not enough predators to manage

  • if P>P^, then prey size decreasing because so many predators

What will happen to equilibrium predator population when predation efficiency increases?

lower P^, because less predators needed to regulate prey pop due to high efficiency

What will happen to equilibrium predator density when rate of prey population growth increases?

higher P^, because prey population growing faster means more predators can exist to forage them

predator growth equation

dP/dt = apHP - dP

a in predator prey models

assimilation efficiency, number of prey needed to make a predator

d in predator growth models

death rate of predators 

r in prey growth model

intrinsic rate of prey increase

H^equation, meaning and implications

• H^= d(death rate of predators)/ap(assimilation and predation efficiencies)

• # of prey where predator population doesn’t change

  • if H<H^, then predator population shrinks due to starvation

  • if H>H^, then predator population grows due to food in excess

Effect of higher assimilation efficiency on H^

lowers H^ because predators need less prey to stay alive per predators.

effect of higher predation efficiency on H^

lowers H^ because predators can hunt prey better, need less prey to get the same number of kills.

effect of higher predator death rate on H^

higher H^ because maintaining predator population more difficult due to higher death rate

Isocline in predator prey model

Line where population growth rate is zero

What is happening to predator population above and below H^

• Above eq. prey density, predators growing

• Below eq. prey density, predators shrinking

What is happening to prey population above and below P^

• Below eq. predator density, prey growing

• Above eq. predator density, prey shrinking

Relation between ellipse size and cycle amplitude

bigger ellipse, bigger cycles

Ellispe size implications

larger ellispe, less stable system. When ellispe touches predator or prey axis, predator or prey go to zero

Cycles and latitudes

Cycles do not occur at lower latitudes because there are more prey species and those predators can switch between them when on

Predator prey cycles

Predator increase, drives prey down, which limits predators, allows prey to increase in size due to low number of predators, excess prey cause predator increase…repeat