Remember, a species, such as homo sapiens, can exist in many places. The population is all the...

Understanding Populations

What is a population?Remember, a species, such as homo sapiens, can exist in many places. The population is all the members of the species living in the same place at the same time!

Populations

Note that the word POPULATION refers to the group in general AND the size of the group!!

Populations

DENSITY

NUMBER of individuals PER UNIT AREA (or volume) the number of individual organisms in a space

This is often related to habitat qualityFluctuations in density reflect changes in the local conditions (new parasite, abiotic factors change, etc)

DispersionDispersion is the distribution or arrangement of organisms in the habitat

Most populations are clumped. Why?Resources are not uniformly distributedProtection of the group / Pack living gives some predators greater success Temporary mating or young-rearing groups / seed distribution

Populations are Dynamic

Age structure – Who can add to population?

Pre-reproductive stageReproductive stagePost-reproductive stage

Population Growth

Growth Rate

How fast a population’s size changes over time is called a growth rate.Growth rates can be positive… what would that mean?Growth rates can be negative… what would that mean?Growth rates can be zero… what would that mean?

Lab Time

Moving On?

How do you think MIGRATION affects growth rate?Immigration would ADD to populationEmigration would SUBTRACT from population

Population Growth

Factors affecting Growth

Biotic Potential is the fastest rate at which a population can grow.Limited by reproductive potential, or the maximum number of offspring a member can produceAlso limited by generation time: the average time needed to reach reproductive age.

Compare Biotic PotentialMosquito:- has thousands of kids- able to reproduce in days!- population growth? MONGO!

Elephant:-Has less than 10 offspring - Takes 13 years before able to reproduce- Population growth? Pitiful!

It’s Out Of Control!

Exponential growth occurs in nature only when populations have plenty of food and spaceNo competition or predators can existOften occurs with exotic or invasive species! (why??)

Wascally Wabbits!

Australia’s Mccaw IslandAfter rabbits were introduced…

Where’s Elmer Fudd when you need him??

Population Regulation

What causes exponential growth to be limited?

Limiting ResourceHabitat lossDiseaseDisaster (natural or manmade)CompetitionPredator-Prey relationships

Limiting Resources

The natural resource that inhibits growth is called the LIMITING RESOURCE. Habitat loss can increase potential candidates for thisCompetition, disease, and predation also limit population growth.

Many times, members of a species will carve out TERRITORY to avoid competitionHow do different species mark out territory? Birds? Dogs? Trees?


Habitat Loss is also listed as a means in which growth is inhibitedHow would this affect population growth?It would speed up the use of the limiting resource, increasing death rate.

CARRYING CAPACITY-The theoretical limit that a habitat can support is called the carrying capacity.-What pattern do you see over there ?

A Closer Look - Activity!

Exponentialgrowth

Environmentalresistance

Population stabilizes

Carrying capacity (K)

Bioticpotential

Time (t)

Pop

ula

tion

siz

e (N

)


Beyond resource and habitat limitations, other factors, such as disease and disaster can regulate populationsWe divide all population limiting factors into DENSITY DEPENDENT and DENSITY INDEPENDENT regulation


Density DependentDefinition: deaths occur more quickly when population is crowded.Most limiting factors are density dependent.Example – disease: needs to spread from organism to organism.Example – competition: the more individuals in an area, the less of a resource is available to each.


Density IndependentWhen the cause of death is density INDEPENDENT, a proportion of the population will die, regardless of congestion.Weather and disasters are examples

Let’s Classify Some, shall we?

No Man Is An Island

Species are never alone in an ecosystem.In order to survive, any population must carve out its unique role within the ecosystem – called its NICHE.A niche includes the species’ physical home, the environmental factors necessary for the species’ survival, and all the species’ interaction with other organisms!

Inter Species Relationships

The Way that SPECIES INTERACT can accentuate or inhibit population growth.We’ve discussed these relationships before, but now we’re going to study them in depth

Symbioses: Ways Species Interact

Interaction Species A Species B Description

Competition Harmed Harmed Each species negatively impacts the other

Predation and Parasitism Benefited Harmed Species A feeds on

Species B

Mutualism Benefited Benefited Each species is helpful to the other

Commensalism Benefited UnaffectedSpecies A benefits from species B, Species B is

unaffected

Amensalism Unaffected HarmedSpecies A may benefit

from the death of species B

Symbiosis and CoevolutionA relationship in which two organisms live in close association is called symbiosisUsually, at least one of the organisms benefitsOver time, species in close relationships may coevolve – that is, they evolve adaptations that reduce the harm or improve the benefit of the symbiotic relationshipAs we go through relationships, see if you can spot the coevolutions!

Species Interactions


Competition

Predation

Parasitism

Mutualism

Commensalism

Amensalism

Competition

Competition is a relationship in which different INDIVIDUALS OR POPULATIONS attempt to use the same limited resource.It occurs within and between speciesWhen species compete, we say their niches overlap.

Name the Resource Competition

Indirect Competition

Species can compete even if they never come in contact.Day feeders and nocturnal animals may all use the same water hole – they are indirectly competing.Humans rarely interact with potato bugs, but we’re in competition for potatoes.

Adaptations to Competition

In the course of evolution, adaptations that decrease competition will be advantageous when niches overlap.Niche restriction is when each species uses LESS of the niche than they are capable of using (for example, territory restriction)

Barnacles use only one part of intertidal zone