Download Week 7 Lecture

Who wins in the beginning?
Secondary succession
• space, light, and nutrients are abundant
• classic r-selected species (opportunists)
Primary succession
• space and light are abundant
• nutrients may not be
• N-fixing plants are common
• convert atmospheric N2 into NH4+
Who wins at the end?
•
Early succession species are eventually
replaced by more competitive late
succession species
•
Late succession species get established in
niches that early succession species can’t
use
How does succession happen?
Facilitation
• early succession species alter conditions to
favor the growth of late succession species
• N-fixers make soil richer
• dune grass stabilizes sand
Acceleration
• late succession species alter conditions to
favor their own growth and prevent the
growth of early succession species
• some plants produce toxic litter
Succession, Disturbance, and Diversity
•
•
•
Succession occurs after disturbance
Over time, many different species live in
one area
Patchy disturbance leads to a “quilt” of
different communities across the
landscape
Disturbance increases diversity!
Succession, Disturbance, and Diversity
•
An ecosystem experiencing succession
becomes more complex over time
more niches are filled
• greater total number of species
•
•
Disturbance interrupts this process
Disturbance decreases diversity!
Diversity
What is the relationship between
disturbance and diversity?
Disturbance frequency or intensity
What is the relationship between
disturbance and diversity?
c
Diversity
a
b
Disturbance frequency or intensity
Announcements
•
The invasive species writing assignment is
due in lecture on Wednesday, Nov. 10th
Summary from Monday
•
Success of different species under:
• primary succession
• secondary succession
•
Mechanisms of succession
• facilitation
• acceleration
•
Succession, disturbance, and diversity
• Intermediate Disturbance Hypothesis
Populations across the landscape
Metapopulation: sum of multiple interacting
sub-populations
sub-population A
sub-population C
sub-population B
sub-population D
Populations across the landscape
Genetic diversity is maintained by exchange
of genes between the sub-populations
sub-population A
sub-population C
sub-population B
sub-population D
Populations across the landscape
Most mating occurs within a sub-population
sub-population A
sub-population C
sub-population B
sub-population D
Populations across the landscape
Some habitat patches are better than others
hot and dry
most ideal
many
predators
few nesting
sites
Populations across the landscape
Sub-populations can be source populations
or sink populations
sink
hot and dry
sink
source
most ideal
many
predators
few nesting
sites
sink
Populations across the landscape
In source population habitats:
•
•
living conditions are good, so births meet or exceed deaths
competition may be great, forcing some members out
sink
sink
hot and dry
source
most ideal
many
predators
few nesting
sites
sink
Populations across the landscape
If a sub-population goes extinct, it can be revived
by recruits from another sub-population
sink
source
source of
recruits
locally
extinct
Population Maintenance
•
•
Important to preserve both source and
sink habitats
Just because animals are found
somewhere doesn’t mean they can
reproduce there
Metapopulations over time
How many species will be found in a certain area?
On an ecological time scale:
Change in # of = Immigration – Local extinction
species over time
On a geological/evolutionary time scale:
Change in # of = Speciation + Immigration
species over time
– Extinction
Controls on immigration
mainland
Distance to source population
Lots of immigration
Little immigration
Controls on immigration
mainland
Distance to source population
Lots of immigration
Little immigration
Obstacles
Mountains
• Waterways
•
mountains
hills
How do non-native species arrive?
• Accidentally
• seeds
• parasites
• unintended cargo
• Deliberately
• food
• timber
• biocontrol
Why study invasive species?
• After habitat loss and fragmentation, the
third greatest threat to conservation is
invasion
• economic consequences
• human health consequences
Invasive Species Glossary
•
native: an organism that is living in its home environment
•
•
•
exotic
non-native
foreign/alien
•
naturalized: a non-native that has become a part of its
new environment
•
invasive: a non-native that has spread to become a
dominant member of its new environment
•
noxious weed: an invasive species of plant that causes
environmental or economic problems
originally from a different location
How many invaders are successful?
• Plants
• 10% of introduced species will naturalize
• 10% of naturalized species will become weeds
• 10% of weeds will become major problems
• Animals
• How would the proportions be different?
What makes an invader successful?
•
r-strategists
• grow quickly
• produce many offspring
• short generation time
good dispersion
• generalists: highly adaptable to new conditions
• broad geographic range in native environment
• broad diet
•
What makes a community vulnerable to
invasion?
•
•
•
•
human disturbance
early succession
climate similar to native habitat
absence of predators or pathogens
• wrong ones for the invader
• no predators or pathogens at all - islands
What do invasive plants do?
Change ecosystem structure
•
fire suppression
• grassland  shrubland
•
grow faster than competing species
• woodland  kudzu-dominated land
•
use up limiting resources, such as water
• riparian zone  desert
What do invasive animals do?
*Humans are the most invasive animal*
Change foodweb structure
• hyperpredation
• drive out native competitors
A case study: kudzu
•
•
•
•
originally from China and Japan
introduced to Florida in 1876 as forage
grows over everything!
competes for light
A case study: zebra mussels
•
•
•
•
•
native to Russian lakes
introduced to North America in 1985 from
bilge of a ship
after <1 year, can produce
1,000,000 eggs
large colonies clog pipes
very efficient filterers
• clear water
• eliminate native species
Zebra mussel range map