Transcript Succession at Glacier Bay

Disturbance and Succession
Intermediate Disturbance Hypothesis
• Disturbance maintains communities in a
"non-equilibrium state" (never reach
equilibrium) and by renewing colonizable
space, disturbance allows the persistence of
species that might otherwise go extinct due
to competitive exclusion. – from Joe Connell
Rocky coast
Intertidal boulder field - California
Waves, boulders and disturbance
Wayne Sousa
Species diversity on intertidal boulders with
different degrees of disturbance – from Sousa
Species diversity on intertidal boulders with
different degrees of disturbance – from Sousa
Boulder size
Small
Medium
Large
turnover
chance
49% / month
9 % /month
0.1%/ month
bare space
most
medium
little
diversity
low - mostly
Ulva
high - several low - mostly
species
Gigartina
Tree fall in Gabon
In an ecosystem, disturbance
1) clears space and interrupts competitive
dominance
2) changes relative abundance of species
3) is a source of spatial and temporal
variability
4) is an agent of natural selection in terms of
life history characteristics
Succession
• Succession is the non-seasonal, directional
and continuous pattern of colonization and
extinction on a site by populations of
species - this definition incorporates a range
of successional sequences that occur over
widely different time scales and have very
different mechanisms.
Types of Succssion
• Primary - succession on a site that has not experienced life
before - extremely severe disturbance may have killed all
life so no seeds or roots or individuals survive - lava flow,
volcanic explosion, glacial retreat, landslides, weathering
of bare rock
• Secondary - succession on a site that may have remnants of
previous life on it - some survivors of the disturbance fire, floods, windstorms, wave battering, severe grazing
• Degradative - succession in which the substrate is decaying
and being exploited by various organisms - succession of
decomposers on carcass, rotting log, etc.
Body Farm – University of
Tennessee
FBI Forensics Class
Facilitation Succession
• Early species change community or
ecosystem in a way that allows later species
to move in and changes the system so that
the early species can no longer survive
there.
Retreat of Muir Glacier
Retreat of Muir Glacier –
1941 – 1950 - 2004
Retreat of Pederson Glacier –
Kenai Fjords NP - 1930-2005
Succession at Glacier Bay
Glacier Bay terminal moraine
Terminal Moraine – Close Up
Early succession – Moss on bare soil
Fireweed at Glacier Bay
Dryas - herbal rose at Glacier Bay
Alder thicket – Glacier Bay
Sitka spruce seedlings
Mature Spruce–Hemlock Forest – Glacier Bay
Tolerance Succession
• All species arrive at start of succession, but
longer lived individuals eventually outlive
short lived species and grow to dominate in
the succession - long lived species can
tolerate shade and competition early in life.
Old Field Succession
Old field succession – bare ground
Old field succession – annual weeds
Old field succession – perennials
Old field succession – pine invasion
Old field succession – hardwood forest
Inhibition Succession
• First species to arrive occupies space and
prevents the settlement of later arriving
species - the first species are replaced only
after they die.
Ulva – above and
Gigartina overgrowing Ulva – right
Typical Succession
• In most successional sequences, all three
mechanisms operate at different times in the
sequence.
Lake Michigan sand dune ecosystem
Marram grass establishment
“Blow-out” in sand dune ecosystem