Population Dynamics

Unit 3 (November 2026)

What is Life History?

the survivorship & reproductive pattern of individuals in a population

What does life history include?

• age when an organism is sexually mature'

• how often it reproduces

• how many offspring it has

Does life history vary?

Yes, it varies between species and it favours evolutionary fitness

what is Fecundity?

• average # of offspring produced by a female over her lifetime

• also represents output of energy

Fecundity example: Salmon

Female salmon produce all their egg quota at once, then die.
(High fecundity)

Fecundity example: Annual plants

annual plants only live for a year, reproduce once, then die
(High fecundity)

Fecundity example: Songbirds & Elephants

survive their 1st reproductive vent, and go on to have more offspring

(Low fecundity)

Fecundity example: Perennial Plants

survive for many years & reproduce each year
(Low fecundity)

animals that reproduce and die, often have large numbers of offspring. This is ______ fecundity.

High

animals that survive often care for their young for many years. this is ______ fecundity

Low

Numbers of offspring tends to be ____________ related to the amnt of care that parents provide

inversely

What is something that affects fecundity?

affected by age at which organism becomes sexually mature

what is survivorship?

proportion of organisms that live to a given age within a population

How many types of survivorship are there?

3

Whats type III of survivorship? What is an example?

• most individuals die as juveniles (often before they are born)

• Large # of offspring are produced to compensate

ex. Salmon, oyster

what is type I of survivorship? What is an example?

• opposite of type III

• high rate of juvenile survival

• individuals live long after their young are born

• Young are well cared for

ex. Humans

what is type II of survivorship? What is an example?

• between I and II

• risk of mortality is constant within the organisms life time

ex. squirrel

What is population distribution?

the density of a population

What affects population distribution?

• distribution of resources (ex. water, food)

• interaction between members of population (wether they’re pos or neg)

What are the 3 distribution patterns

• clumped distribution

• uniform distribution

• random distribution

What is clumped distribution?

• resources

• interactions between members

individuals gathered in groups

• resources:

  • working in groups to catch prey

  • gathered near water sources

  • clumped plants

• interactions between members

  • POSITIVE

  • highly socialized

  • co-operative feeding

  • minimization of chances being caught by predator (strength in #s)

Examples of species w clumped distribution?

• meerkats

• wolves

• schools of fish

• whales

• elephants

• humans

• lions

What is uniform distribution?

• resources

• interactions between members

evenly distributed

• resources:

  • distributed evenly but scarce

• interaction between members:

  • NEGATIVE

  • territorial or competition for resources

Examples of species w uniform distribution?

• penguins

• wolverines

• cacti

• wild gerbils

• tigers

• sage

What is random distribution?

• resources

• interactions between members

random, no pattern

• resources:

  • plentiful + evenly distributed

• Interaction between members:

  • NEUTRAL

  • no need for defence or sharing of resources

  • (dispersal of seeds thru wind)

examples of species w random distribution?

• thistle

• oysters

• dandelions

What does N stand for?

Population SIZEWh

What is population size?

# of individuals of same species living in a specific geographic area

Whats does “Dp” stand for?

population density

What is population density?

# of individuals per unit of volume or area

What are the 3 population sampling techniques?

• transects

• quadrats

• Mark-replace

Transects

• samples taken from long rectangular line of a certain length

• starting pts determined randomly

• researchers walk along line, counting individuals of a certain distance away from line

Quadrats

• area of specific size used (ex. 1m squared)

• best for SESSILE (non moving organisms, like plants)

• # of individuals within boundary counted

Formula for quadrants:
Dp=N/A
what do the letter stand for?

N = sum of individuals

A= area

Mark-recapture

• tracks, nests, burrows, scats used to estimate #s

• sometimes populations are caught, tagged + releases. Later, traps are set again, and scientists compare portions of marked to unmarked animals.

Mark recapture formula:
N= (M x n)/m

what do letters stand for?

M = #s originally marked

n = total in recapture

m =.marked individuals in recapture0

examples of animals w high fecundity

• salmon - produces all eggs at once, then dies

• annual plants - live for a year, then die

examples of low fecundity

• songbirds + elephants - survive their first reproductive event and go on to have more offspring

• perennial plants - survive for many years & reproduce each year

Does fecundity also depend on what age an animal reaches sexually maturity?

yes. (ex. bunnies mature at 3 months, while elephants mature at 12 years.)

abiotic

non-living

biotic

living

Density-Independant factors

• define

• examples

are abiotic events that affect population growth regardless of the population density

• natural disasters

• severe weather + climate

• human made disruptions (pollution, oil spills, pesticide applications, etc.)

Density-Dependant factors

Biotic events that affect population growth in high density(lots of individuals packed)

• competition for resources'

• predation

• diseases + parasites

• waste accumulation

intraspecific competition

• define

• example

competition within individuals of a species

ex. coyote vs coyote compete for rabbits

interspecific competition

• define

• example

competition within individuals of diff species

ex. coyote vs fox compete for rabbits

Explain predator-prey relationship and what this helps animals reach?

helps reach carrying capacity

carrying capacity

Maximum population a habitat can sustain

Biotic Potential

the highest possible per capita growth rate for a population

factors that affect biotic potential

• # of offspring per reproductive cycle

• # of offspring that survive long enough to reproduce

• age of reproductive maturity

• # of times an individual reproduces in a lifespan

• lifespan of the individuals

Two population growth patterns and what environments there found in?

• exponential growth ( unlimited environments)

• logistic growth (limited environments)

exponential growth pattern

• explanation

• shape

• example

• brief lag phase, followed by steep increase in growth curve.

• ‘J’ shape

• population growing at biotic potential (no predators, unlimited resources, etc.)

• ex. bacteria, small invertebrates, plants - in labs.

whats a limited environment?

resources become limited

(ex. lack of food limits energy for survival)

carrying capacity

max population size that a habitat can sustain over an extended period of time

Logistic growth pattern

• explanation

• shape

• examples

• initially only few individuals so growth is slow

• this leads to period of rapid growth

• which means resources eventually become limited + competition starts : growth slows

• birth rate = death rate

• sigmoidal ‘s’ shaped

ex. any creature w a predator prey relationship

r selected strategies

• define

• how

• examples

used by organisms that lie close to their biotic potential

• short livespans

• mature sexually at young age

• produce large # of offspring

• dont spend much time caring for young

ex. insects, annual plants, algae

k- selected strategies

used by organisms that live close to the carrying capacity of their habitats

• longer lifespans

• sexually mature at older age

• produce fewer offspring

• provide lots of care to young

ex. mammals, birds

Can r vs k selected strategies be relative?

Yes! for example compare rabbits to insects, and then rabbits to humans

why does human population in Canada increase?

• people live longer

• fewer women dying in childbirth

• catastrophic diseases mostly absent

• immigration

4 processes that influence population change

• immigration

• emigration

• birth

• death

calculating change in population size equation

N = B - D
( humans tend to move a lot, so immigration and emigration are equal and therefore discounted)

Population change w immigration and emigration

N = (B+I) - (D+E)

what helps ecologists make management decisions?

rate of population growth

population explosion
+ examples

rapid increase of individuals (like invasive species)

ex. zebra mussels, silver carp, cane toads

population crash (+ example)

many individuals die rapidly (like during extinction)

ex. horseshoe crabs

rate of population growth equation

gr = N/T

growth rate = change in population size (N2-N1) / change in time

when do we measure per-capita growth rate?

when comparing growth rate of 2 populations

(initial population is not taken into account when calculating gr. in the absence of limiting factors, the growth of a larger population will always be greater (more individuals to reproduce))

per capita gr equation

cgr = N/N1 × 100%
per capita growth rate = (change in population size/ initial population size) *100%

Types of defence mechanisms to protect from predators

• thorns

• quills

• toxins

• protective colouration

what are the types of protective coloration?

• camouflage

• color ( as warning signal)

• mimicry

batesian mimicry

when a species has coloration to look like another species that is dangerous to predators

example of a species that uses camouflage

stick insects

example of a species taht uses body coloration

poison dart frog

example of a species that uses bayesian mimicry

scarlet king snake is NOT poisonous but has similar colouring to the POISONOUS Eastern Coral Snake

Symbiosis

an ecological relationship between 2 species living in direct contact (within direct proximity) with each other

types of symbiosis

• parasitism

• mutualism

• commensalism

Example of parasitism ( + how each species’ population is affected)

caterpillar (-) vs wasp larvae (+)

example of mutualism (+ how each species’ population is affected)

acacia tree (+) vs acacia ants (+)

2 examples of commensalism ( + how each species’ population is affected)

Zebra Shark (N) vs Remara Fish (shark sucker) (+)

Manta trays or whale sharks (N) vs cobia (+)