Lecture 6 - Population Ecology

Population ecology -

how the collective life histories of individuals collectively impact the ennvironment.

Population -

a group of individuals of a single species inhabiting a specific area

-interbreeding

Distribution -

geographical range of an organism

• spatial arrangement of individuals in a local population

• BALANCE OF PUSH/PULL

Density -

number of individuals in a population per unit area

-ex: population size/total land area

22 students/classroom

Abundance -

number of individuals of a species present in a particular ecosystem or area

Area based counts:

individuals in a given volume are counted

-SESSILE organisms

-plants, oysters, snails

Distance methods

distance of an individual from a line or point are converted into estimates of abundance

-detection function

-FAST MOVING SPECIES

-rabbits, falcons

Mark-recapture studies -

-subset of individuals captures and marked or tagged, then released and at a later date recaptures and ratio of marked:unmarked individuals is used to estimate population size

-MOBILE ORGANISMS

Geographic range -

entire geographic region over which a species is found

What are the abiotic factors of geographic range?

climate, topography, disturbance

What are the biotic factors of geographic range?

competition, predation, resources, etc.

What is the greatest limit to distribution and abundance?

Habitat sustainability.

Why do creosote bushes have a wider range than saguaro cacti?

because they are more tolerant of arid climates and cold temperatures

Why are saguaro cacti limited so much in their geographic range?

Because they can’t exist where it is ever freezing more than 36 hours.

What species is of least concern and why?

Coyotes because their distribution expanded with CC and human disturbance.

Dispersal and distribution

history of dispersal, (immigration and emigration)

-Polar bears happened to heat to the N pole when Pangea split.

Where species evolved and distribution

limits whre they are now (naturally) found, even when environments are similar.

Resource availibility and distribution

1. space and food is FINITE

   1. competition repels species

2. Attractants

   1. species will follow/cluster

Disturbance frequency

damage that may wipe out individuals

• opens space for others that may be a mediator.

Random pattern of dispersal

all are relatively neutral

don’t help or hurt to be near each other.

Regular pattern of dispersal

uniformly spaced through environment

• usually negative effects if too close to one another

  • antagonistic interactions between individuals or local depletion of resources.

Clumped pattern of dispersal

individuals live in area of high local abundance, separated by areas of low abundance

Seychelles warbler is an example of what?

Clumped populations towards center of island

• because salt spray from ocean was killing the plants they needed as vegitation

Dispersal

can increase/decrease local populations with immigration/emigration

Meta populations

• dispersal leading to group of spatially separated sub populations connected by active exchanges in individuals

Africanized honeybee is an example of what?

rate of population expansions being different by species.

-stopped in S as they were too hot, and N US in 2008 due to winters killing them off.

Climate change has variable effects on what?

the rate populations expand depending on species

Why are populations dynamic?

Because their abundance varies over time

Natality

Birth rate B

Mortalitiy

Death rate D

immigration

individuals going INTO a population I

emigration

individuals LEAVING a population E

What are eurasian collard doves an example of?

Logistical growth and how exponential isn’t realistic long ter

they were estimated to be exponentially growing, but numbers showed they were were 10 years behind.

N =

current population

-the higher this number, the lower the rate of increase

r =

rate of increase

• the closer to k, the slower you can add to the popultion

K =

carrying capacity

Life Tables

sum of how survival and reproduction rates vary with the age of individuals in a population

• used to predict future population trends and develop strategies for population management

Cohort -

individuals born during same time period

-longitudinal tracks actual mortalitiy experience of a specific group born in the same time period

With cohorts

survivorship is DIRECTLY OBSERVED

Age-at-death-observed time table

calculates parameters, with probability of dying and number of deaths

-estimated a cohort’s life table on known stages of death

Static life table

records number of living individuals of each age in a population at a specific time

• sometimes uses age at death data

• estimates cohort life table based on survival of individuals of different ageas during a single time period.

• WE MUST KNOW THE AGES

  • ex: tree tings, dental wear

Survivorship curve

summarized pattern of survival in a population

Type I survivorship

high survivorship - with young and middle age individuals, high mortality rates with older individuals

• humans, sheep, large mammals

Type 2 survivorship

constant rate of mortality and survivorship

• songbirds, turtles, fish

Type 3 survivorship

high mortality rates when young

• ex: insects, plants, marine invertebrates

fecundity

Fecundity in ecology is the measure of an individual's or population's biological capacity to produce offspring,

-u the number of female offspring produced per female over a specific timeframe

What are teds? What are they an example of

TURTLE EXCLUDER DEVICE - example of conservation management, since life tables revealed we needed to focus more on adult protection and not just hatchling protection

Age structure distribution -

the proportions of populations in each age class (interval)

Population momentum -

continuation of population grows as females reach reproductive age

Wide base in an age stucture =

high reproductive potentials and population growth POSITIVE GROWTH

-less developed countries ex: Guatemala

Narrow base in age structures =

low reproductive potentials and low population growth

NEGATIVE GRowTH

-more developed countries ex: Japan

Oak tables showed that

There was a high population of 50 year old individuals, which would go on to replace the older oak trees (positive growth

Rio grande tables showed that

there were very little younger individuals, meaning they weren’t there to replace the older ones, (40-50 years old) and they are unlikely to persist (negative growth)

Human population growth has been

FASTER than exponential in the last 2000 years

Why is human population growth so rapid?

1. agriculture, increased resources

2. modern medicine and lower death rates

   1. expansion all over the globe

Ecological foot print -

estimate of the amount of land required to provide raw materials an individual or population consumes

• fuel, water, shelter, waste disposal

  • NOT equally distributed across the planet

Carbon footprint -

total set of green house gas emissions cause by an individual, event, organization, or product

From 1950-2010 we saw what

population growth occured more in lesser developed countries

• relatively steady

• in more developed countries it was more static

Geometric pattern

J - shaped SET OF POINTS

synchronous repro at discrete time periods - “breeding periods”

To predict geometric population growth BEYOND one period at a time

N _t+1 = 𝜆N _t

pop size at time t!

geometric

𝜆

geometric population growth

t

time frame

exponential over ONE period of time

exponential growth beyond one period of time

Exponential pattern

continuous repro pops change size by constant proportion at each instant time

J-shaped CURVE

dN/dt = rN(1-N/K)

Logistical growth is LOGICAL - and has k to keep things from getting out of hand.

• occurs when increasing rapidly at first, then stabilizes at a carrying capacity.

Carrying capacity - (k)

maximum population size that can be supported indefinitely by the environment