PopulationsPopulations

What influences how What influences how populations flourish or populations flourish or

die out? die out?

Biotic PotentialBiotic PotentialThe maximum number of offspring that a species could reproduce in a life time, if resources were unlimited.

Biotic Potential is determined by:

1. Birth potential: max # of offspring per birth 2. Capacity for survival: # of offspring that reach reproductive age 3. Procreation: # of times a species reproduces each year 4. Length of reproductive life: # of years species

can reproduce

Limiting FactorsLimiting FactorsA limiting factor is any factor that places an upper limit A limiting factor is any factor that places an upper limit on the size of a populationon the size of a population

Limiting factors can be biotic or abioticLimiting factors can be biotic or abiotic

Human influences often act as limiting factorsHuman influences often act as limiting factors

What are the limiting factors that might affect a What are the limiting factors that might affect a population of penguins? How about a suburban human population of penguins? How about a suburban human population?population?

Tolerance RangeTolerance RangeThe abiotic conditions within which a species can surviveThe abiotic conditions within which a species can survive

Species can be successful over a range of Species can be successful over a range of

abiotic conditionsabiotic conditions

A population will become stressed and die out if A population will become stressed and die out if conditions exceed their tolerance limitsconditions exceed their tolerance limits

See Figure 1, Nelson, p. 52See Figure 1, Nelson, p. 52

CactiCacti Waterlillies BunchberriesWaterlillies Bunchberriesabiotic abiotic

conditionsconditions

that keep that keep

species species

withinwithin

tolerance tolerance

rangerange

abiotic conditionsabiotic conditions

that put species that put species

outside of toleranceoutside of tolerance

rangerange

Tolerance RangeTolerance Range

- long periods ofDrought-full exposureto sun

- long periods of rain (rootscannot survive damp conditions-low light availability

Use Figure 2, p. 53 (Nelson) to fill in the following chart

- water levels minimize exposureof roots to air-full exposureto sun

- if water level dropsexposing roots to air-low light availability

- shade

- too much light

Carrying CapacityCarrying CapacityThe population remains within the limits that the environment can supportThe population remains within the limits that the environment can support

This is the largest population size of a species that an ecosystem can This is the largest population size of a species that an ecosystem can support or sustainsupport or sustain

There are several factors that can influence the Carrying Capacity of a There are several factors that can influence the Carrying Capacity of a species:species:

food (think also food chains, webs)food (think also food chains, webs)

waterwater

sheltershelter

spacespace

climateclimate

susceptibility to diseasesusceptibility to disease

predationpredation

competition for many of the abovecompetition for many of the above

Carrying CapacityCarrying CapacityCarrying capacity can be altered through natural or human Carrying capacity can be altered through natural or human

Think-Pair-Share:Think-Pair-Share: Consider a species we Consider a species we

have discussed or you know about from your previous have discussed or you know about from your previous

personal experience. How was the carrying capacity of this species personal experience. How was the carrying capacity of this species

affected by either a natural or human action? (can be positive or negative)affected by either a natural or human action? (can be positive or negative)

Example 1Example 1: Irrigation systems in African deserts increases the carrying : Irrigation systems in African deserts increases the carrying

capacity of organisms living in a desert ecosystem (increased water capacity of organisms living in a desert ecosystem (increased water

availability)availability)

Example 2Example 2: the removal of wolves by human hunters will increase the : the removal of wolves by human hunters will increase the

carrying capacity of moose in this ecosystem (more space, less predators)carrying capacity of moose in this ecosystem (more space, less predators)

Example 3Example 3: clear-cutting trees will decrease the carrying capacity of : clear-cutting trees will decrease the carrying capacity of

certain bird species that rely on these trees for habitat and to maintain certain bird species that rely on these trees for habitat and to maintain

their neststheir nests

Population DensityPopulation DensityIs the number of organisms living in a given spaceIs the number of organisms living in a given space

Use a diagram to show a high population density Use a diagram to show a high population density

vs. low population density and provide a specific real vs. low population density and provide a specific real example in natureexample in nature

Population DensityPopulation Density

Density-Density-independent factorsindependent factors

Density-dependent Density-dependent factorsfactors

factors that do not factors that do not depend on the population depend on the population sizesize

weather (storms, cold, weather (storms, cold, drought, floods, early drought, floods, early freezing, heavy snow)freezing, heavy snow)

forest firesforest fires

cometscomets

density-independent density-independent diseases (DDT poisoning)diseases (DDT poisoning)

environmental pollution

factors that do depend factors that do depend on the population sizeon the population size

food availabilityfood availability

space (shelter, territories, space (shelter, territories, denning sites, nest cavities)denning sites, nest cavities)

density-dependent density-dependent diseases (rabies, SARS)diseases (rabies, SARS)

competition competition (intraspecific. vs. (intraspecific. vs. interspecific)interspecific)

affectpopulation size

can lead to species aggressionand/or panic

can lead to extinction

can help populations flourish

Intraspecific vs. InterspecificIntraspecific vs. Interspecific

Intraspecific: when two organisms from the same Intraspecific: when two organisms from the same species are after the same resources or foodspecies are after the same resources or food

THINK/PAIR/SHARE: Give a specific example of intra-THINK/PAIR/SHARE: Give a specific example of intra-specific competition.specific competition.

Interspecific competition: when two organisms from Interspecific competition: when two organisms from different species are after the same resources or fooddifferent species are after the same resources or food

THINK/PAIR/SHARE: Give a specific example of inter-THINK/PAIR/SHARE: Give a specific example of inter-specific competition.specific competition.

Reaching the Carrying CapacityReaching the Carrying Capacity

Exponential Growth

Carrying capacity reached (populationsize has reachedequilibrium or is inbalance)

In the 1800s, the fur trade led to a Drastic decline in the fur seal population

In 1911 a treaty was signed to protect the fur seal population

Humans and Carrying CapacityHumans and Carrying CapacityWhat actions have humans taken to increase the carrying capacity of our species?

- Early on: using fire, making simple tools/weapons- Improvements in public health, education, agriculture,

medicine, technology- Exploiting huge amounts of energy and resources to

run complex, modern societies

What paths might the curve take after this century? Which path do you think is mostlikely? Why?

What next?What next?

Invasive speciesInvasive species

An invasive species is one that can be An invasive species is one that can be either native and non-native that heavily either native and non-native that heavily colonize a particular habitat.colonize a particular habitat.

Natural, wild species can be threatened Natural, wild species can be threatened with extinction.with extinction.

The good ones

Asian Oysters-Asian Oysters- are better are better at filtering out water at filtering out water

pollutants than native pollutants than native oysters.oysters.

Garlic Mustard- introduced as a means of

erosion control

Characteristics of Good InvadersCharacteristics of Good Invaders

High rate of reproduction High rate of reproduction (short generation time)(short generation time)Long-livedLong-livedHigh dispersal ratesHigh dispersal rates (produces a lot of seeds) (produces a lot of seeds)Single-parent reproductionSingle-parent reproduction Tolerant of wide range of conditionsTolerant of wide range of conditionsHabitat generalistHabitat generalistBroad dietBroad diet Opportunistic (aggressive, out competes)Opportunistic (aggressive, out competes)Difficult to control and resistant to eradicationDifficult to control and resistant to eradication

Characteristics of the CommunityCharacteristics of the Community(that make it susceptible to invaders)(that make it susceptible to invaders)

Invading nonindigenous species tend to be more Invading nonindigenous species tend to be more successful when native species do not occupy similar successful when native species do not occupy similar ecological nichesecological nichesSpecies that inhabit disturbed environments and those Species that inhabit disturbed environments and those with a history of close association with humans tend to with a history of close association with humans tend to be successful in invading human-modified habitatsbe successful in invading human-modified habitatsSuccessful invasion is enhanced by similarity in the Successful invasion is enhanced by similarity in the physical environment between the source and target physical environment between the source and target areasareasAbsence of predators on invading speciesAbsence of predators on invading speciesAbsence of native species morphologically (form or Absence of native species morphologically (form or structure) or ecologically similar to the invaderstructure) or ecologically similar to the invader