Biol 104 Exam 3!

periodt.

What factors contribute to a population change?

lack of predators, resources, favorable climate, ability to outcompete nearby species.

how do populations grow in a pattern

by mult

What condition does pop grow under

births > deaths

Exponential growth

occurs in pop w/ continuous reproduction and overlapping generations

example of exp growth

humans!

Equation for exp growth no need to memorize equation but memorize the parts

< insert equation image>

e = constant (2.718)

r = finite rate of inc (exp growth rate), assume it’s constant

t = time

Example of exp growth curve

it’s J-shaped <insert image here>

With exp growth, what happens when r = 0?

Flatline @ 1, aka no change w/ pop growth

With exp growth, what happens when r>0

pop grows (quicker inc in population size over time!)

With exp growth, what happens when r<0

pop dec

Geometric population growth 

You get points that would form a j-shaped curve

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Geo pop growth examples

cicadas and salmon

Exp growth: as pop size inc, pop growth rate…

increases linearly!

<insert image>

Exp growth: as pop size inc,per capita growth rate aka “r”…

stays constant

bc we assume r to be constant in equation

<insert image>

Why can’t populations grow indefinitely?

Bc there’s limited # of atoms in universe

Limits to pop growth (aka regulating factors)

Regulating factors (4 of them)

depletion of food sources

space depletion

inc aggressive interactons

accumulation of waste → slower growth/reduced survivle, reduced fecundity (means fertility) → reduced pop growth!

Logistic growth

<insert equation>

adds the density into account + regulating factors

Breakdown logistic equation

r = finite rate of inc under ideal conditions

N = current pop size

K = carrying capacity

Logistic growth assumption

assume that K is constant

Intrinsic factors contributning to pop size

what is in the pop

births + deaths

dispersal (immigration into/ emigration out of)

Extrinsic forces for pop growth

stuff outside pop influencing it

resources

predators

disease

pop growth rate vs pop size graph

compare to

pop size vs time

<insert lionfish graph>

Negative density dependent factors

reduce pop’s growth rate when pop’s density (and thus size) is large through one of these measures:

• reducing survivval

• reduce reproduction

• reduce growth of individuals 

examples of neg density dep factors (4 of them)

Intraspecific competition (same species)

Interspecific predation (diff species)

disease + parasites

Social behavior (aggression bc species don like being next to each other)

Density dependent factors… (2 things)

change as pop density changes

can regulate populations

Density indep factors

don’t regulate pop size

impact the population no matter its size

Density indep factors examples

environmental factors (hurricanes, droughts,…)

<insert zero pop growth question>

3 and 4 <insert image>

Is carrying capacity constant in the REAL WORLD?

NO! it is variable

K is constant only when birth and death rate curves intersect

when there is variation in birth + death rate, K can vary

<insert image>

In real life, pop’s fluctuatte around equilibrium point (when environment is variable)

yeah, that.

Logsitic growht in nature

pop size inc initially then levels off at a max pop size

<The chart>

<insert answers>

Why do we get sick? (5 reasons)

sick = physically un-well

1. infection by pathogens

2. Novel environments (shift from ancestral environment to modern day, giving allergies)

3. Trade-offs (consider benefits and harm) ex. sickle cell allele is harmful (gives sickle disease) but can have resistance to malaria

4. Evolutionary legacies (we evolved from ancestors that don’t work, we have hip+knee problem)

5. defenses (symptoms of diseases are our immune system’s defense)

Where do new pathogens come from?

animal hosts (zoonotic disease)

due to agricultural society and close contact w/ animals

Different stages of infection

1. agent only in animals (only animal to animal)

2. primary infection (animal to human only)

3. limited outbreak ( few cycles human to humans)

4. long outbreak (lotta human to human transmission)

5. exclusive human agent (only human to human transmission)

What happens over time when there’s only 2 conditions: susceptible and infected

Everyone becomes susceptible, and everyone gets infected

When we have 3 conditions (susceptible, infected, and recovered) what happens over time?

people eventually recover!

SIR and how does isolation affect it?

increases rate of recovery!

SIR model

s = # susceptible indiv

I = # infected indiv

r = # recovered indiv

Beta = transmission rate (rate of encounter between susceptible and infected indiv, how ofter you come across infected person times probability that encounter causes infection)

L = infectious period (length of infection,, expected time it takes to recover, how long are you sick?)

Graph for SIR

White = susceptible pool

Orange = infected

Pink = recovered

susceptible only decreases thru time

pink only increases thru time

Infection is driven by…

contact between S and I indiv, as well as the transmission rate

REcoveryrate

indiv

Recovery of I

TTQ about sir

If you’re just looking at data it’s just the first 2! 

insert image

 5 of them: What assumptions do we make with SIR model?

• recovered can’t get reinfected

• Everyone gets infected in same rate, beta don’t change (pathogen don’t become more infectious)

• infected individuals are instantly infectious

• no deaths (only recovery is possible)

• no birth (individuals added to susceptible pool)

Which rate (infection or recovery) gets affected with

• masks

• social distance

• vax

  • testing + isolation

• masks + social distance decrease transmission rate (beta) in different ways

• vax = increases recovery rate (L)

• Testing + isolation = less people in contact with sick people means that beta decreases

Herd immunity

the proportion of vaccinated people is high enough to ensure that each infected peorson infects less than one susceptible person 

immunization slows spread of disease inc herd immunity 

if # of people in community w/ vax decreases, chance of disease outbreak….

inc!

“There’s always going to be a bigger fish”

Why is this a false statement

limited amnt of energy in ecosystem, so it can support only some organisms

all the energy available In one level ain’t available in the next

Trophic efficiency

the production of a trophic level relativ e to the one below it

Between each level you lose energy!

Keystone species 

small pop, big impact

have large effects on community despite lower abundance bc of strong interactions

Dominant species

large amnt of them

have a large effect on identity and diversity of other species in community bc of abundance/large biomass

What should you look at when differentiating keystone and dom speices?

look @ biomass and total impact!

<graph slide 19>

Different types of competition (3)

Direct: Predation, Competition

• between 2 species, include trophic+nontrophic interaction

Indirect: can be positive or negative

• when relation between 2 species is mediated by a third species

Competition

A and B wanting same resources competing with eachother

predation

C hates on A, B gets food

Indirect

It’s literally what it sounds like <cba triangle>

Species composition

types of species in community

Interactions of multiple species (2)

Density mediated indirect interactions (DMII)

Density mediated indirect interactions (DMII)

change in density due to pos or neg interactions

<get diagram>

Trophic cascade

One species indirectly affects other species at diff levels in the food chain

rate of consumption by predator affects lower trophic levels (ex wolves positively affecting growth of grass)

Top down vs bottom up

Top down: predator keeps the population in check

Bottom down: depletion of resources (water, sunlight, food…) keeps the pop in check

Can you have more than one type of relationship between species?

yes!

ex. the pisasters and chitons: direct neg (eats the chiton) and indirect positive (eats competition, limpets)

pls review pisaster + yellowstone case study!

do it. pls. 10/27 slides.

Biogeography

Island

an area of suitable habitat surrounded by inhospitable “matrix”

“Island” biogeography

studies factors that affect species richeness in isolated communities

The island problem <>

Highest to lowest A (d or c) (d or c) B

Islands: the larger the area, the (more/less) the species

more!

Why do we expect larger islands to have more species?

(C)

• higher habitat diversity

• larger pop size, lower extinction rates

• Larger island DOES NOT ALWAYS mean closer to mainland!

Why is there effect on isolation (distance from mainland) for birds but not ferns?

Dispersal barriers more signaificant for birds

• ferms propogated by wind blown 

• birds are energy limited (ex. blown off couse duirng storm and migration)

island near continental source may have (higher/lower) immigration rates

higher

Theory of island biogeography

assumption: species richness

immigration

highest when no species present

extinction

highest when no species is present

Equilibrium theory of island biogeography

lowest extinction when no species present

highest when we have all species present

graph <>

Immigration rate

no. of species arriving to island over time highest when island is unoccupied

extinction rate

no. of species that go extinct on island over time highest where species # is at max

smaller islands have (high/low extinction)

high

lose species, how to get back to equilibrium

increase immigration

inc in immigration relates with… (how to get back to equilibrium, think graph)

inc in extinction

small/large island impacts…

extinction rates

small island = higher extinction

near/far island impacts…

immigration rates

draw that graph

DRAAW IT NOW

<> graph

NOT GIVEN ON EXAM

Island b is… <insert image>

answer B

Which island has higher rate of turnover?

<insert image>

D!

Which axis do you look at to determine turnover rate

y

Theory of island biogeography: (Near or far) island has high species number?

near island!

Why aren’t lions and tigers and bears found everywhere?

continents move over long periods of time due to TECTONIC activity!

Wallace Line 

What formed the biogeography

Divergent evolution on isolated landmasses…

leads to regional differences in species composition

Species diversity tends to be (higher/lower) near poles, and (higher/lower) near equators

highest diversity near equator, and lower diversity near poles

Latitudinal gradients

the biogeographic pattern of more species near equator/tropics

Not all species follow this trend (ex. penguins)

Why are there more species in tropics/ equator area? 

more sunlight, stable temp @ equator, large land mass near equator, no glaciers here during ice ages

Evolutionary rates hypothesis

Tropics have more species than temprate zones, bc evolution occurs @ a faster rate.

Bc warmer temp (meaning organisms have shorter generation time) , also resources play a role!. 

<insert graph here>

history hypothesis

There was an event in time where the temperate zones couldn’t hold species at all (the ice age was the event)

Tropics have been able to accumulate species @ all times

<insert graph here>

Ecological Limits hypothesis

Resources are a limiting factor, tropics have more resources and can have more species than temperate zones

<insert graph here>