BIOL204-M3L13

Goals of population ecology

• how population size changes

• why those changes occur

• how populations are distributed in space

Why is population ecology important?

because it links ecology & evolution and is essential for conservation biology, fisheries management, and understanding human population growth

What are the 2 fundamental questions of population ecology?

• Where does a species live?

• How many individuals are there?

What is a species range?

total area over which the species is occurring

What determines range of a species?

abiotic & biotic factors

What is population density and what is it dependent on?

number of individuals per unit area

• varies across a species range

• scale is important

• dependent on resource availability

dispersion patterns

Random: position of each individual is independent of others

• Ex. dispersal of seeds

Clumped: individuals associate/ aggregate in social groups

• Patchy resources, social behaviors (mating, feeding), most common

Uniform: individuals distance themself from each other/ evenly spaced

• due to negative reasons like competition, fighting for territories

Metapopulation

population of populations connected by dispersal

Metapopulation characteristics

• habitat fragmentation increases metapopulation structure

• local extinctions can be offset by recolonizations Ex. butterflies

What do sampling methods depend on?

• mobility of organisms

• habitat type

• spatial scale

What sampling methods are used to count abundance & distribution of sedentary/ sessile organisms?

• quadrats: counting inside rectangular plots

• transects: counting inside lines of known position/ length

and then extrapolate

What sampling methods are used for moving organisms?

Mark-recapture

1. capture and mark individuals

2. release them and allow them to mix with others in the pop.

3. recapture and count marked vs. unmarked individuals

Mark-recapture assumptions

• no immigration or emigration

• no trap avoidance or attraction

• marking does not affect survival

How does population size change through time?

birth, death, immigration, emigration

Age structure

number of individuals in each age class

Generation time

avg. time between a females birth and the birth of her offspring

Life table + limitations

summarizes survivorship and reproduction across an individuals lifetime

• Limitations: data is difficult to get & you need a marked population

Survivorship

proportion of individuals that survive on average to a particular age

Age specific fecundity

avg. number of female offspring produced by a female in each age class

Survivorship curves

• Type I: survivorship is high throughout life and drops dramatically at old age Ex. humans

• Type II: individuals have the same probability of dying in each year of life Ex. vulnerability to predation

• Type III: extremely high death rates early mortality and adults survive after Ex. larvae, insects, plants

Fecundity

number of female offspring produced by a female in a pop.

Fitness trade-off Ex.

fecundity vs. survivorship

Life history

the sequence of significant events—growth, reproduction, and survival and how an individual allocates energy for growth, reproduction, and survival

• traits like survivorship, fecundity, growth rate, lifespan, age of maturity, number of offspring

Life history patterns across species

they vary

• high fecundity: live fast die young, mature early, lots of small offspring

• low fecundity: live longer lives, mature late, large offspring

What is population growth rate and what does it depend on?

change in population size over time

• births, deaths, immigration, emigration

Density independent factors

affect populations regardless of size

• Ex. weather, natural disasters

Density dependent factors

effects that increase with population density

• Ex. competition, disease, predation, waste build-up

What happens to age-specific fecundity with age often?

it increases

Define population

a group of individuals of the same species living in the same place at the same time

Factors that regulate population changes

density dependent & density independent

How does distribution change through time?

influenced by abiotic and biotic factors and can follow clumped, uniform, or random patterns

What does quadrat and transect sampling count?

abundance and distribution of organisms

What is dispersion?

how individuals are spaced within their habitat

Life-history trade-offs

evolutionary compromises where organisms allocate limited energy and resources to one trait (like reproduction) at the expense of another (like survival or growth)

What happens to population size, distribution, and abundance over time?

they change over time

What is abundance?

the total number of individuals of a species or type present in a given area

What is distribution?

the geographic range or spatial arrangement (clumped, random, uniform) of a population

Exponential vs. Logistic growth

Exponential: infinite resources, density independent, constant r

Logistic: finite resources, density dependent, grows and then growth slows as reaching carrying capacity