Who wins in the beginning?Who wins in the beginning?

Secondary successionSecondary succession• space, light, and nutrients are abundantspace, light, and nutrients are abundant• classic r-selected species (opportunists)classic r-selected species (opportunists)

Primary successionPrimary succession• space and light are abundantspace and light are abundant• nutrients may not benutrients may not be• N-fixing plants are commonN-fixing plants are common

• convert atmospheric Nconvert atmospheric N22 into NH into NH44++

Who wins at the end?Who wins at the end?

• Early succession species are Early succession species are eventually replaced by more eventually replaced by more competitive late succession speciescompetitive late succession species

• Late succession species get Late succession species get established in niches that early established in niches that early succession species can’t use succession species can’t use

How does succession How does succession happen?happen?

FacilitationFacilitation• early succession species alter conditions early succession species alter conditions

to favor the growth of late succession to favor the growth of late succession speciesspecies• N-fixers make soil richerN-fixers make soil richer• dune grass stabilizes sanddune grass stabilizes sand

AccelerationAcceleration• late succession species alter conditions late succession species alter conditions

to favor their own growth and prevent to favor their own growth and prevent the growth of early succession speciesthe growth of early succession species• some plants produce toxic littersome plants produce toxic litter

Succession, Disturbance, and Succession, Disturbance, and DiversityDiversity

• Succession occurs after disturbanceSuccession occurs after disturbance• Over time, many different species Over time, many different species

live in one arealive in one area• Patchy disturbance leads to a “quilt” Patchy disturbance leads to a “quilt”

of different communities across the of different communities across the landscapelandscape

Disturbance Disturbance increasesincreases diversity! diversity!

• An ecosystem experiencing succession An ecosystem experiencing succession becomes more complex over timebecomes more complex over time• more niches are filledmore niches are filled• greater total number of speciesgreater total number of species

• Disturbance interrupts this processDisturbance interrupts this process

Disturbance Disturbance decreasesdecreases diversity! diversity!

Succession, Disturbance, and Succession, Disturbance, and DiversityDiversity

What is the relationship What is the relationship between disturbance and between disturbance and

diversity?diversity?

Disturbance frequency or intensity

Div

ers

ity

What is the relationship What is the relationship between disturbance and between disturbance and

diversity?diversity?

Disturbance frequency or intensity

Div

ers

ity

ab c

AnnouncementsAnnouncements

• The invasive species writing The invasive species writing assignment is due in lecture on assignment is due in lecture on Wednesday, Nov. 10Wednesday, Nov. 10thth

Summary from MondaySummary from Monday

• Success of different species under:Success of different species under:• primary successionprimary succession• secondary successionsecondary succession

• Mechanisms of successionMechanisms of succession• facilitationfacilitation• accelerationacceleration

• Succession, disturbance, and diversitySuccession, disturbance, and diversity• Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis

Populations across the Populations across the landscapelandscape

Metapopulation: sum of multiple Metapopulation: sum of multiple interacting sub-populations interacting sub-populations

sub-population A

sub-population B

sub-population D

sub-population C

Populations across the Populations across the landscapelandscape

Genetic diversity is maintained by Genetic diversity is maintained by exchange of genes between the sub-exchange of genes between the sub-populations populations

sub-population A

sub-population B

sub-population D

sub-population C

Populations across the Populations across the landscapelandscape

Most mating occurs Most mating occurs withinwithin a sub- a sub-populationpopulation

sub-population A

sub-population B

sub-population D

sub-population C

Populations across the Populations across the landscapelandscape

Some habitat patches are better than Some habitat patches are better than others others

hot and dry

most ideal

manypredators

few nesting

sites

Populations across the Populations across the landscapelandscape

Sub-populations can be Sub-populations can be sourcesource populations or populations or sinksink populations populations

hot and dry

manypredators

few nesting

sitesmost ideal

source

sink

sink

sink

Populations across the Populations across the landscapelandscape

In In sourcesource population habitats: population habitats:• living conditions are good, so births meet or exceed living conditions are good, so births meet or exceed

deathsdeaths• competition may be great, forcing some members outcompetition may be great, forcing some members out

hot and dry

manypredators

few nesting

sitesmost ideal

source

sink

sink

sink

Populations across the Populations across the landscapelandscape

locally extinctsource of

recruits

source

sink

If a sub-population goes extinct, it can be If a sub-population goes extinct, it can be revived by recruits from another sub-revived by recruits from another sub-populationpopulation

Population MaintenancePopulation Maintenance

• Important to preserve both source Important to preserve both source and sink habitatsand sink habitats

• Just because animals are found Just because animals are found somewhere doesn’t mean they can somewhere doesn’t mean they can reproduce therereproduce there

Metapopulations over timeMetapopulations over time

How many species will be found in a certain area?

Change in # of Change in # of species over time species over time = ImmigrationImmigration – – Local extinctionLocal extinction

Change in # of Change in # of species over time species over time =

SpeciationSpeciation ++ Immigration Immigration

– – ExtinctionExtinction

On an ecological time scale:

On a geological/evolutionary time scale:

Controls on immigrationControls on immigration

Distance to source populationDistance to source population

main

lan

d

Lots of immigration

Little immigration

Controls on immigrationControls on immigration

Distance to source populationDistance to source population

main

lan

d

Lots of immigration

Little immigration

ObstaclesObstacles• MountainsMountains• WaterwaysWaterways

mountains

hills

How do non-native species How do non-native species arrive?arrive?

• AccidentallyAccidentally• seedsseeds• parasitesparasites• unintended cargounintended cargo

• DeliberatelyDeliberately• foodfood• timbertimber• biocontrolbiocontrol

Why study invasive species?Why study invasive species?

• After habitat loss and fragmentation, After habitat loss and fragmentation, the third greatest threat to the third greatest threat to conservation is conservation is invasioninvasion

• economic consequenceseconomic consequences• human health consequenceshuman health consequences

Invasive Species GlossaryInvasive Species Glossary• native:native: an organism that is living in its home an organism that is living in its home

environmentenvironment

• exoticexotic• non-nativenon-native originally from a different location originally from a different location• foreign/alienforeign/alien

• naturalized:naturalized: a non-native that has become a part a non-native that has become a part of its of its new environmentnew environment

• invasive:invasive: a non-native that has spread to become a non-native that has spread to become a a dominant member of its new environmentdominant member of its new environment

• noxious weed:noxious weed: an invasive species of plant that an invasive species of plant that causes causes environmental or economic problemsenvironmental or economic problems

How many invaders are How many invaders are successful?successful?

• PlantsPlants• 10% of introduced species will naturalize10% of introduced species will naturalize• 10% of naturalized species will become 10% of naturalized species will become

weedsweeds• 10% of weeds will become major 10% of weeds will become major

problemsproblems

• AnimalsAnimals• How would the proportions be different?How would the proportions be different?

What makes an invader What makes an invader successful?successful?

• r-strategistsr-strategists• grow quicklygrow quickly• produce many offspringproduce many offspring• short generation timeshort generation time

• good dispersion good dispersion • generalists: highly adaptable to new generalists: highly adaptable to new

conditionsconditions• broad geographic range in native environmentbroad geographic range in native environment• broad dietbroad diet

What makes a community vulnerable What makes a community vulnerable to invasion?to invasion?

• human disturbancehuman disturbance• early successionearly succession• climate similar to native habitatclimate similar to native habitat• absence of predators or pathogens absence of predators or pathogens

• wrong ones for the invaderwrong ones for the invader• no predators or pathogens at all - no predators or pathogens at all -

islandsislands

What do invasive plants do?What do invasive plants do?

Change ecosystem structureChange ecosystem structure

• fire suppressionfire suppression• grassland grassland shrubland shrubland

• grow faster than competing speciesgrow faster than competing species• woodland woodland kudzu-dominated land kudzu-dominated land

• use up limiting resources, such as wateruse up limiting resources, such as water• riparian zone riparian zone desert desert

What do invasive animals What do invasive animals do?do?

*Humans are the most invasive *Humans are the most invasive animal*animal*

Change foodweb structureChange foodweb structure• hyperpredationhyperpredation• drive out native competitorsdrive out native competitors

A case study: kudzuA case study: kudzu

• originally from China and Japanoriginally from China and Japan• introduced to Florida in 1876 as introduced to Florida in 1876 as

forageforage• grows over everything!grows over everything!• competes for lightcompetes for light

A case study: zebra musselsA case study: zebra mussels

• native to Russian lakesnative to Russian lakes• introduced to North America in 1985 introduced to North America in 1985

from bilge of a shipfrom bilge of a ship• after <1 year, can produce after <1 year, can produce

1,000,000 eggs1,000,000 eggs• large colonies clog pipeslarge colonies clog pipes• very efficient filterersvery efficient filterers

• clear waterclear water• eliminate native specieseliminate native species

Zebra mussel range map