[PART 2] Population Ecology Population Characteristics, Dynamics, Growth, and Life History

Distribution

What is the distribution pattern of the population

_________________ - spacing of individuals in a population

- reflects the characteristics of the species or its environment; resource availability

Patterns of Population Distribution

• CLUMPED - resources are patchy

• RANDOM - unpredictable distribution no strong interaction

• UNIFORM - evenly spaced, reflects competition

Patterns of Population Distribution

• ______________ - resources are patchy

• ______________ - unpredictable distribution no strong interaction

• ______________ - evenly spaced, reflects competition

Population growth

DEMOGRAPHY

__________________ - is the increase in number of individuals

______________ - statistical study of population changes over time

• birth

• death

• immigration

• emigration

What is the formula for growth rate (r)?

BIOTIC POTENTIAL

It is the maximum growth rate, which a population could achieve in unlimited environment

BIOTIC POTENTIAL

_________________ - the capacity of a species to reproduce under ideal environmental conditions (sufficient food supply, no predators, and absence of disease)

BIOTIC POTENTIAL

___________________ - determined by the quantity of offspring produced, the frequency with which they reproduce, and size of each offspring

• varies depending on the species

• age

• frequency

• number of offspring

BIOTIC POTENTIAL is determined by:

• typical reproductive _____

• general ____________ of reproductively available time or cycle

• _______________ after birth that lives to their respective reproductive age

• offspring; once

• pregnancies; lifetime

BIOTIC POTENTIAL is determined by:

• total number of ____________ that are born at _______

• total number of ____________ in the entire _________ of an organism

Exponential growth

exponentially

A population will grow _____________ for as long as the resources necessary for survival and reproduction remains unlimited.

Type of Exponential Population Growth

_______________

• organisms of a species reproduce at a constant rate

• population starts with slow growth and then into steep, rapid growth with no limit

N_t = N₀e^rt

Type of Exponential Population Growth

What is the formula for population size within an exponential pop. growth?

Type of Exponential Population Growth - Exponential growth

Example: Initial population of bacteria in a petri dish was 25, with a constant growth rate of 5. What is the population size after 2 days?

Geometric growth

Type of Exponential Population Growth

Individuals are added to the population in pulses

Geometric growth

Type of Exponential Population Growth

Exhibited by species that follow a breeding season such that growth peaks and then decline till the next season (e.g., birds, insects)

Type of Exponential Population Growth - Geometric growth

What is the formula for the growth rate with a geometric growth pop.

Type of Exponential Population Growth - Geometric growth

Example: Initial population of 100 birds, and after one breeding season you end up with 30 deaths and 50 births. What is the growth rate (λ)?

ENVIRONMENTAL RESISTANCE

any condition/factor that inhibits the increase in population size

ENVIRONMENTAL RESISTANCE

• is the environmental pressure which limit a population’s inherent capacity for growth

• may be abiotic or biotic

ENVIRONMENTAL RESISTANCE

generally measured as the difference between the biotic potential of a population and the actual rate of increase as observed under laboratory or field conditions

Density-dependent

Limiting factors (population regulation) - Density-dependent or Density-independent?

resource availability (food, water, space/shelter)

Density-dependent

Limiting factors (population regulation) - Density-dependent or Density-independent?

accumulation of toxic wastes

Density-dependent

Limiting factors (population regulation) - Density-dependent or Density-independent?

diseases (infectious)

Density-dependent

Limiting factors (population regulation) - Density-dependent or Density-independent?

predation

Density-dependent

Limiting factors (population regulation) - Density-dependent or Density-independent?

competition

Density-independent

Limiting factors (population regulation) - Density-dependent or Density-independent?

severe storms and flooding

Density-independent

Limiting factors (population regulation) - Density-dependent or Density-independent?

sudden unpredictable severe cold spells

Density-independent

Limiting factors (population regulation) - Density-dependent or Density-independent?

earthquakes

Density-independent

Limiting factors (population regulation) - Density-dependent or Density-independent?

volcanic eruption

Density-independent

Limiting factors (population regulation) - Density-dependent or Density-independent?

fires

• N < K - r = positive - pop. growth: increase

• N > K - r = negative - pop. growth: decrease

• N = K - r = 0 - pop. growth: stop

Life history

Growth potential of a population is related to the life history of the species

_________________ is the series of changes undergone by an organism during its lifetime; varies tremendously among species

Life history

_________________ patterns evolve by natural selection, and they represent an "optimization" of tradeoffs between growth, survival, and reproduction.

• Fecundity (number of offsprings)

• Relative size of offspring

• Age at reproductive maturity

• Parental care
  

• High adult survival, late reproductive maturity, few large offsprings (e.g., mammals)

• Low adult survival, early reproductive maturity, high reproductive effort (e.g., fish)

What are the factors or characteristics of life history strategies?

• ______________________

• ______________________

• ______________________

• ______________________

LIFE HISTORY (Reproductive) STRATEGIES → reproduction

• _______ adult survival, _______ reproductive maturity, few _______ offsprings (e.g., mammals)

• _______ adult survival, _______ reproductive maturity, _______ reproductive effort (e.g., fish)

r-selected (r - reproduction)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Many small offsprings

• Little or no parental care and protection of offsprings

• Most offsprings die before reaching reproductive maturity

r-selected (r - reproduction)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Small adults

• Adapted to unstable climate & environmental conditions

• High population growth rate

r-selected (r - reproduction)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Population size fluctuates wildly above & below carrying capacity

• Generalized niche

• Low ability to compete

• Early successional species

K-selected (K – carrying capacity)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Few but large offsprings

• Typically develops inside mother

• Parental care or cooperative breeding/brooding and protection of offspring

K-selected (K – carrying capacity)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Most offsprings survive to reproductive age

• Larger adults

• Lower population growth rate

• Population size is fairly stable and usually close to carrying capacity

K-selected (K – carrying capacity)

Characteristics of r-selected (r - reproduction) or K-selected (K – carrying capacity) strategies

• Common in fairly stable late successional environments where competition for resources is intense

• Specialist niche

• Highly able to compete

r - selection 

Population attribute	r - selection or K - selection
Intrinsic rate of increase, rmax	High
Competitive ability	Not strongly favored
Development	Rapid

r - selection 

Population attribute	r - selection or K - selection
Reproductive maturity	Early
Body size	small
Reproductive events	Single, semelparity

r - selection 

Population attribute	r - selection or K - selection
Offspring (fecundity)	Many, small
Lifespan	Short
Survivorship curve	Type III

r - selection 

Population attribute	r - selection or K - selection
Description of population	ruderals (in plants)

K - selection

Population attribute	r - selection or K - selection
Intrinsic rate of increase, rmax	Low
Competitive ability	Highly favored
Development	Slow

K - selection

Population attribute	r - selection or K - selection
Reproductive maturity	Late
Body size	Large
Reproductive events	Repeated, iteroparity

K - selection

Population attribute	r - selection or K - selection
Offspring (fecundity)	Few, large
Lifespan	Long
Survivorship curve	Type I or II

K - selection

Population attribute	r - selection or K - selection
Description of population	stress-tolerant (in plants)

Semelparous populations

Reproductive strategy - Semelparous or Iteroparous populations?

new generation is produced in a single reproductive event (or over a short interval)

Semelparous populations

Reproductive strategy - Semelparous or Iteroparous populations?

producing young with little or no parental care (e.g., salmon, insects)

Iteroparous population

Reproductive strategy - Semelparous or Iteroparous populations?

new generation is produced over a series of events throughout the reproductive span of the parent.

Iteroparous population

Reproductive strategy - Semelparous or Iteroparous populations?

Parents take care of the few young until they are capable of living on their own (e.g., mammals)

• bigger; space

• fewer

K-selected species are more prone to extinction because:

• Tend to be __________, hence need more ________ to live in

• Tend to have __________ offspring, so populations cannot recover as fast from disturbances such as hunting or fire

• later; long

• small; inbreeding

K-selected species are more prone to extinction because:

• Breed at a ________ age → generation time to grow from small to larger population is ______

• Population size often _________ → pose a high risk of _______________ among individuals

SURVIVORSHIP

• vary from one species to another

• dictated by the environment

• recorded and analyzed using a life table

Life Table

_____________ - shows the survival rate (and mortality rate) of the different life stages or ages of individuals in a population; standardized presentation of age structure of a population

Dynamic/Cohort Life Table

Which type of Life Table?

• follows a cohort population until the last one dies

• short-lived species

Dynamic/Cohort Life Table

Which type of Life Table?

• used to determine age- or stage-specific fecundity and mortality rates, survivorship, and basic reproductive rates

• enables an analysis of their annual variation

Cohort

Life Table

___________ – group of individuals born at the same time of over a short period

Static life table

Which type of Life Table?

• Studies survivorship of long-lived organisms

• Follows fate of members of a population at a given time

Static life table

Which type of Life Table?

• Individuals of the group sampled are of different ages

• Snapshot of survival taken within a population during a short interval of time

Type I

Which type of Survivorship curve?

high survivorship of young, death mostly occurs at maturity;

Type I

Which type of Survivorship curve?

low number of offspring but parental care increases survivorship of young; e.g. large mammals

Type II

Which type of Survivorship curve?

relatively even deaths at all stages of life;

Type II

Which type of Survivorship curve?

few offspring; provide significant parental care; e.g. many bird species

Type III

Which type of Survivorship curve?

High mortality at young age, mortality decreases as individuals mature.

Type III

Which type of Survivorship curve?

Little parental care but compensated by producing numerous offspring at a time. e.g. most insects and marine fishes

AGE (or AGE-SEX) STRUCTURE

• shows the proportion of individuals belonging to different age group

• can reveal population’s growth trends

AGE (or AGE-SEX) STRUCTURE

• used to predict if a population will grow or shrink

• applicable only to iteroparous organisms, not to semelparous organisms

Expanding population

Which type of population based on AGE (or AGE-SEX) STRUCTURE?

• with a higher proportion of younger age individuals, the population will increase

Stable population

Which type of population based on AGE (or AGE-SEX) STRUCTURE?

• with even distribution of ages, the population will remain stable

Declining population

Which type of population based on AGE (or AGE-SEX) STRUCTURE?

• with higher proportion of older age individuals, the population will considerably decline

DISPERSAL

______________ - movement of an individual or multiple individuals away from the population in which they were born to another location, or population, where they will settle and reproduce

Gamete

__________ dispersal - especially common for nonmotile adult individuals, such as plants.

Active Dispersal

Which type of dispersal?

• Movement of an organism from one place to another place through its own ability

• Without assistance

• Common in adult and juvenile animals

Passive Dispersal

Which type of dispersal?

• Dispersion of both plants and animals that cannot move on its own

• plants; some sessile marine invertebrates like sponges and corals

Passive Dispersal

Which type of dispersal?

• use dispersal units called disseminules moved by dispersal agents

Limits To Dispersal

• Environmental factors (e.g., temperature)

• physical barriers (e.g., mountains, rivers, lakes, oceans etc.)

• Anthropogenic barriers (e.g., roads, farming, river dams)

Limits To Dispersal

• _____________________

• _____________________

• _____________________

Ecological corridors

• biological or physical strips connecting areas and allowing movement of species

• facilitate dispersal and reduce risk of extinction of species