BIOL204-M3

Where do species live

where they can survive and reproduce

Ecological niche

range of conditions that a species can tolerate and the range of resources it can use

Abiotic factors

temperature, precipitation, light availability, salinity, soil composition, flooding frequency

Biotic factors

competition, predation, parasitism, mutualism, dispersal ability

What can species do if they’re outside of the limits of their ecological niche?

they can migrate away or go extinct

Fitness trade-off

evolutionary compromise made between 2 traits that cannot be optimized simultaneously

Why can’t species survive in all types of environments?

fitness trade-off

What does each species have regarding tolerance?

a minimum, optimal, and maximum tolerance

Realized vs. Fundamental niche

realized: actual range considering other biotic factors

fundamental: potential range; where they could exist based on abiotic factors but biotic factors are preventing them from occupying that space

Dispersal

movement of individuals from their place of origin to the location where they can live and breed as adults

• a factor that determines geographical distribution of species

Palm tree Ex. (abiotic & biotic factors / past & present)

Biogeography

how species are distributed and why they’re distributed the way they are

What do the 6 biogeographic regions correspond to?

the 6 major tectonic plates

What do tectonic plates differ in?

• endemism: organism or species that only exists in one place

• species composition

• evolutionary history

What happens when tectonic plates separate?

populations become isolated and speciation occurs

What happens when tectonic plates collide?

dispersal is possible and interchange occurs (mixing of species)

Pangaea + Characteristics

Supercontinent

• no major oceanic barriers leading to broad terrestrial dispersal

• lots of shared lineages

What happened to Pangaea and what did it cause?

Broke up into Laurasia (north) and Gondwana (south)

• initiated massive vicarious events (gene flow restricted)

What did Gondwanan fragmentation cause?

• ocean barriers formed

• isolation increased

• independent evolutionary trajectories emerged

Factors that determine geographical distribution of a given clade

1. Ancestral ecological niche of the clade (what they occupied historically, sets limits)

2. Geographical starting point for dispersal (sets where they can disperse to)

3. Limitations of dispersal imposed by abiotic conditions and other species (can’t just go anywhere Ex. predators)

4. Opportunities for niche evolution that are afforded to individual species by their geographical location (you can only go to a niche space that exists where you are)

5. Amount of time since origin of the clade during which niche evolution and dispersal could occur

Beringia

land-bridge connecting Asia and North America

• humans first entered NA using this land bridge allowing lots of dispersal

The Great American Biotic Interchange/ Isthmus of Panama + consequences

land-bridge connecting North and South America

suddenly groups of mammals were able to disperse into new areas between north america and south america

• a lot of marsupials went extinct because placental animals outcompeted them

• marsupials into north and placentals moving into south

• modern marsupial distribution reflects ancient plate connections, later continental collisions, and competitive interactions

What do modern species distributions reflect?

• present abiotic and biotic conditions

• historical plate movement

• continental fragmentation

• landbridge formation

• mountain building

• climate shifts driven by tectonics

Historical tectonic drivers of species distribution

• where continents used to be

• which land masses were connected

• who was separated

• how long the isolation lasted

How do biotic/ abiotic factors define/ constrain a species ecological niche?

they determine what an organism can tolerate, the niche is defined by where they survive and reproduce best and is constrained by not being able to tolerate or optimize the abiotic/ biotic factors present elsewhere

How did continental drift shape dispersal, isolation, and speciation?

when continents were one (Pangaea) there was lots of dispersal, when continents drifted there was more isolation, less speciation due to less geographical barriers when Pangaea and more speciation when drift occured

How did land-bridge formation shape dispersal, isolation, and speciation?

more dispersal due to being able to move between continents, less isolation, less speciation

How did supercontinent break-up shape dispersal, isolation, and speciation?

less dispersal, more isolation, more speciation

How did mountain building shape dispersal, isolation, and speciation?

less dispersal, more isolation, more speciation

Major events to know

• breakup of Pangaea + Laurasia and Gondwana

• gondwana fragmentation

• isthmus of panama/ great american biotic interchange

• beringia

5 tenants of biogeography + extremes of each on distribution/ dispersal

ancestral ecological niche, geographic starting point, dispersal limitations, opportunities for niche evolution, and time

What defines a species ecological niche and defines its geographical distribution?

abiotic & biotic factors

How does Pangea and Gondwanan fragmentation reflect modern biogeographic patterns?

Where are species richest?

where they originated

Opportunities for niche evolution

you can only go occupy niches that are available to you

• where you are geographically

• what environments are available there

• what competitors/predators are there

Past abiotic & biotic factors

Abiotic: continental drift, tectonic drivers

Biotic: past organism interactions like predation parasitism competition, human land-use influence, diseases

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

Population dynamics

changes in populations through time and space

Why do real populations often deviate from growth models?

in real life, populations can crash, overshoot, and resource depletion can occur

What does it mean when a population crashes?

when a population suddenly goes extinct or decreases significantly due to overshooting carrying capacity and resource overexploitation, leaving not enough resources for everyone

Is carrying capacity static or dynamic?

it is dynamic, it can increase or decrease

Reindeer population crash Ex.

What does it mean for a population to cycle?

a population increases and decreases in a sometimes predictable, recurring pattern over time

What is population overshoot?

when a population exceeds its environment's carrying capacity, consuming resources faster than they can be replenished, leading to resource depletion

Hare Lynx Ex. for population cycles

Ecological mechanisms producing population cycles

Bottom-up control (food limitation): population growth is controlled by availability of resources like food and nutrients

Top-down control (predation): consumers/ predators regulate prey populations

Interaction: both food limitation and predation are acting together and combined affect is stronger than either one alone

What is a metapopulation?

a population of populations connected by dispersal

Metapopulation charactersitics

• habitat fragmentation increases metapopulation structure

• little populations more likely to go extinct Ex. if a disaster occurs

• dispersal restores populations that have gone extinct

Density dependent processes

factors whose effects on population growth increase as population density increases Ex. disease, competition, predation

Density independent processes

affect population growth irrespective of size of populations Ex. climate, weather, disasters

Factors increasing persistence of populations in metapopulations

1. large population size

2. larger habitat patches

3. proximity to other populations

4. higher genetic diversity

Metapopulation butterfly Ex. + Implications

• preserve large habitats

• maintain connectivity

• protect empty habitats as well

What model organizes human population growth?

population pyramids which show human population distribution by age and sex

Top heavy/ even pyramids

• low birthrates

• high survivorship

• aging population—high life expectancy

• slow growth—fewer young people

Bottom heavy pyramids

• number of children being born is higher than number of people existing in older age classes (more young people than old people)

• high birth rates

• population will grow rapidly because the many young people will soon reach reproductive age

Population momentum

continued growth after fertility declines caused by number of young individuals reaching reproductive age

Interpret Lynx-Hare graph

Interpret population pyramid

How age structure and momentum influence population growth

individuals in younger age classes will have the chance to become reproductively mature so more young individuals increases growth while more old individuals slows growth—population momentum will be high with more young individuals

Community

all of the populations of different species that interact in a certain area

+, -, 0 meaning

fitness benefit, fitness cost, neutral affect on fitness

Types of interactions

commensalism, competition, consumption, mutualism

Commensalism

when one species benefits but the other species is unaffected (+/0)

• very conditional