Hurricane Katrina

1
Disturbance Ecological Succession
Hurricane Katrina Aug. 29, 2005
Image from http//earthobservatory.nasa.gov/Newsro
om/NewImages/Images/katrina_goe_2005241_lrg.jpg
2
Disturbance Ecological Succession
Succession directional change in community
composition at a site (as opposed to simple
fluctuations), initiated by natural
or anthropogenic disturbance, or the creation of
a new site Some biologists restrict the
definition to directional replacement of species
after disturbance
Disturbance a discrete event that damages or
kills residents on a site either catastrophic
or non-catastrophic (Platt Connell 2003)
Photo of W. J. Platt at Camp Whispering Pines, LA
from K. Harms photo of J. H. Connell from UCSB
3
Disturbance Ecological Succession
Catastrophic disturbance a disturbance that
kills all residents of all species on a site
i.e., creates a blank slate (Platt Connell
2003)
Mt. St. Helens, Washington, U.S.A. May 18, 1980
Photo of Mt. St. Helens from Wikipedia
4
Disturbance Ecological Succession
Non-catastrophic disturbance a disturbance that
falls short of wiping out all organisms from a
site i.e., leaves residual organisms or
biological legacies (Platt Connell 2003)
Luquillo Experimental Forest, Puerto Rico just
after 1989 Hurricane Hugo
Yellowstone Natl. Park, U.S.A. just after 1988
fires
Photo of Yellowstone in 1988 from Wikipedia
Photo of Luquillo Forest, Puerto Rico in 1989
from http//pr.water.usgs.gov/public/webb/hurrican
e_hugo.html
5
Disturbance Ecological Succession
Primary Succession succession that occurs after
the creation of a blank slate, either through
catastrophic disturbance or de novo creation of
a new site
Anak Krakatau, Indonesia appeared above water
1930
Mt. St. Helens, Washington, U.S.A. May 18, 1980
Photo of Mt. St. Helens in 1980 from Wikipedia
Photo of Anak Krakatau from http//amazingindones
ia.net/2008/06/mount-krakatoa-the-wrath-of-earth
6
Disturbance Ecological Succession
Secondary Succession succession that occurs
after non-catastrophic disturbance (including
old fields)
Luquillo Experimental Forest, Puerto Rico just
after 1989 Hurricane Hugo
Yellowstone Natl. Park, U.S.A. just after 1988
fires
Photo of Yellowstone in 1988 from Wikipedia
Photo of Luquillo Forest, Puero Rico in 1989
from http//pr.water.usgs.gov/public/webb/hurrican
e_hugo.html
7
Disturbance Ecological Succession
Henry David Thoreau (1859) is often credited with
coining succession as applied to directional
changes in plant communities
Thoreau made many remarkable observations at a
time when many still believed in such phenomena
as spontaneous generation Though I do not
believe that a plant will spring up where no
seed has been, I have great faith in a seed.
Convince me that you have a seed there, and I
am prepared to expect wonders.
Photo of Thoreau from Wikipedia
8
Disturbance Ecological Succession
A brief history of observations and ideas H.
Cowles (1899) stressed the dynamic nature of
plant societies (phytosociology)
Examined species composition of Lake Michigan
sand dunes concluded that the dunes were older
further inland, i.e., formed a chronosequence
from which temporal change could be inferred
(space-for-time substitution) Believed that
succession tended toward a stable equilibrium
that was never (or at least rarely) reached
Photo of Cowles from http//oz.plymouth.edu/lts/e
cology/ecohistory/cowles.html photo of Lake
Michigan sand dune from http//ebeltz.net/folio/cf
ol-5.html
9
Disturbance Ecological Succession
A brief history of observations and ideas F.
Clements (1916, 1928) radical, superorganism
view of communities species interact to promote
a directed pattern of community development
through seral stages, ending in a climax
community
H. Gleason (1926, 1939) individualistic view
of succession in which every species is a law
unto itself Our modern population-biology view
derives primarily from Gleasons conceptual
model, even though Clementsian ideas of
deterministic progression through seral to climax
stages dominated ecological theory well into the
20th century (see Connell Slatyer 1977)
Photos from http//oz.plymouth.edu/lts/ecology/ec
ohistory/history.html
10
Disturbance Ecological Succession
A brief history of observations and ideas F.
Egler (1954) made distinctions between primary
succession (relay floristics, in which
initially there is no vegetation) vs. secondary
succession (following non-catastrophic
disturbance of existing vegetation)
Egler thought secondary successional patterns
were driven by propagules present when the
disturbance occurs (initial floristic
composition hypothesis) In addition, he thought
that changes in species abundances reflected
differences in longevity of species
11
Disturbance Ecological Succession
A brief history of observations and ideas Four
classic papers demonstrate the maturation of
thought concerning the nature of trade-offs
colonization history within Gleasons
individualistic framework
Horn MacArthur (1972) mathematical models of
competition among fugitive species in a harlequin
environment
Drury Nisbet (1973) verbal models of
succession driven by differences in dispersal
competitive ability, growth survival
Platt (1975) empirical demonstration of
mechanisms of coexistence of fugitive species on
badger-mound disturbances
Bormann Likens (1979) introduced the
shifting-mosaic steady-state concept
within-patch non-equilibrial dynamics average to
an equilibrium pattern at the scale of many such
patches taken together
12
Disturbance Ecological Succession
A brief history of observations and
ideas Connell Slatyer (1977) Reacted
against an emphasis on life-history strategies
competition alone recognized a variety of
species interactions that could impact succession
Three models of succession 1. Facilitation
Early species enhance the establishment of later
species (if it occurs, it is perhaps most likely
in primary succession)
2. Tolerance Early species have no effect on
later species
3. Inhibition Early species actively inhibit
later species
13
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence One of the worlds most rapid and
extensive glacial retreats in modern times (so
far) eliminated 2500 km2 of ice in 200 yr,
exposing large expanses of nutrient-poor boulder
till to biotic colonization
Photo of Glacier Bay National Park, Alaska from
Wikipedia
14
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence Classical view of Glacier Bay
succession based on 50 yr of research, which
employed the simple chronosequence assumption
- Mosses - Mountain Avens (Dryas)
shallow-rooted herbs - Willows (Salix)
first prostrate, then shrubby species -
Alder (Alnus crispus) after 50 yr forms thickets
to 10 m - Sitka Spruce (Picea sitchensis)
invade alder thickets - Hemlock (Tsuga
heterophylla) establish last
Succession is driven by N-fixation (Dryas
Alnus) Alnus acidifies the soil, allowing
Picea invasion Accumulation of soil carbon
through succession improves soil texture
and water retention, ultimately allowing invasion
by Tsuga
15
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence Fastie (1995) Reconstructed
patterns of stand development at several sites
within the chronosequence intensively analyzed
tree-rings
Figure from Fastie (1995)
16
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence Fastie (1995) Identified 3
alternative pathways of compositional change (not
a single chronosequence of events)
1. Sites deglaciated prior to 1840 were
colonized early by Picea Tsuga
2. Sites deglaciated since 1840 were the only
sites colonized early by N-fixing Alnus
3. Sites deglaciated since 1900 were the only
sites dominated relatively early by black
cottonwood (Populus trichocarpa)
17
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence Oldest sites Dryas ? Picea
Tsuga Intermediate sites Dryas ? Alnus ?
Picea Youngest sites Dryas ? Alnus ? Populus ?
Picea
What accounts for these among-site differences in
composition?
Differences are unrelated to soil parent
material
Strong effect of seed source Refugial
Picea stands are concentrated at the mouth
of the bay distance from the nearest seed
source explains 58 of among-site variance
in early Picea recruitment
Younger sites received more of their seed
rain from new communities colonizing
exposed surfaces than from refugial
populations
18
Disturbance Ecological Succession
Primary succession along the Glacier Bay
chronosequence What about facilitation? Successi
on of Alnus to Picea was considered a textbook
example of facilitation in the mid- to-late 20th
century
The real pattern is more complex! Alnus was
absent on older sites, so Picea does not require
it for establishment Alnus may either inhibit
or facilitate seedling establishment of
Picea Chapin et al. (1994) Found net positive
effects of Alnus on Picea on glacial moraines,
but net negative effects on floodplains
19
Disturbance Ecological Succession
Facilitation along cobble beaches of New England
Bruno (2000) Determined mechanisms by which
Spartina alterniflora is a facilitator of
relatively large impact on the community (i.e., a
foundation species - Drayton 1972 keystone
modifier - Bond 1993 ecosystem or keystone
engineer - Jones et al. 1994)
Observations Spartina occurs along the shore
cobble-beach plants occur behind Spartina
Cobble-beach community is absent along breaks
in the Spartina phalanx
Photo by J. Bruno
20
Disturbance Ecological Succession
Facilitation along cobble beaches of New England
Bruno (2000) Question At which life stage(s)
is colonization cobble-beach plants limited to
sites behind Spartina?
Experiment Addition experiments to determine
limiting life stages (seed supply, seed
germination, seedling emergence, seedling
establishment adult survival) for cobble-beach
plants
Results Only seedling emergence establishment
were adversely affected by the absence of Spartina
21
Disturbance Ecological Succession
Facilitation along cobble beaches of New England
Bruno (2000) Question By what mechanism(s)
does Spartina facilitate seedling emergence
establishment of cobble-beach plants?
Experiment Conducted manipulations of water
velocity, substrate stability, herbivory soil
quality in sites lacking Spartina
Results Substrate stability increased seedling
emergence establishment, whereas manipulations
of the other factors had limited influence
22
Disturbance Ecological Succession
Facilitation along cobble beaches of New England
Bruno (2000) Conclusions Spartina
alterniflora acts as a foundation species,
keystone modifier ecosystem engineer) by
stabilizing the substrate, enabling seedlings of
cobble-beach plants to emerge survive
Photo by J. Bruno
23
Disturbance Ecological Succession
Primary succession on Krakatau Anak
Krakatau Explosion of Krakatau (1883) The
loudest explosion ever heard by
humans Created tsunamis that killed
30,000 people on larger
islands mainland The island was
effectively sterilized
Anak Krakatau
Anak Krakatau (Child of Krakatau) appeared out
of the ocean in 1930 has been growing
ever since
First analyses of colonizing vegetation were by
Doctors van Leeuwen (1930s) more recent
expeditions by Robert J. Whittaker
Photo of Anak Krakatau from http//amazingindonesi
a.net/2008/06/mount-krakatoa-the-wrath-of-earth
24
Disturbance Ecological Succession
Primary succession on Krakatau Anak
Krakatau Whittaker (1994) Examined dispersal
characteristics of plant arrivals Nearest
mainland site is Sumatra ( 50 km away) Nearest
island is 21 km away First arrivals (within 4
yr of eruption) were either wind or water
dispersed
Early zoochorous plants were dominated by figs
17 of 24 fig species on the island arrived in the
first 30 yr and are now canopy dominants, which
suggests that bats have been very important
dispersal vectors or mobile links (Old World bats
have gut-retention times up to 12 hr)
25
Disturbance Ecological Succession
Primary succession on Krakatau Anak
Krakatau Whittaker (1994) There are now 124
zoochorous species on Anak Krakatau Doves and
pigeons (gt 4 hr gut retention time) have been
important dispersers subsequent to colonization
of the island by figs (an indirect mechanism of
facilitation by bats operating through
figs?) Many large-seeded species are absent
relative to Sumatra the mainland flora
26
Disturbance Ecological Succession
Primary succession on Krakatau Anak Krakatau
Anak Krakatau Image taken June 11, 2005 from
Ikonos satellite
Image from http//earthobservatory.nasa.gov/Newsro
om/NewImages/Images/krakatau.IKO2005_06_11_lrg.jpg
27
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens May 18, 1980 the north face of the
previously symmetrical mountain collapsed in a
rock-debris avalanche that essentially wiped
clean 60 km2 of forest
Fagan Bishop (2000) Examined the influence of
herbivores on the rate of spread of lupines
(Lupinus lepidus), the sites main colonizing
species
Mt. St. Helens, Washington, U.S.A. May 18, 1980
Photo of Mt. St. Helens from Wikipedia
28
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens Lupines are efficient N-fixers trap
detritus they are often facilitators in
ecological succession Lupines colonized from
remnant populations elsewhere on the volcano
to form patches Spread rapidly initially and
then slowed
Why?
Figure from Fagan Bishop (2000)
29
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens Fagan Bishop (2000) Ruled out various
alternative explanations for slowed population
growth rates focused on the effect of insect
herbivores, whose colonization lagged behind the
lupines by 10 yr
Experimental test Established plots at the
center of lupine patches (core) and at the edge
of expanding patches (edge) Sprayed half of the
plots with pyrethroid insecticide
30
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens
Much higher incidence of damaging insects at
patch edges
Higher leaf damage at patch edges
Figure from Fagan Bishop (2000)
31
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens
Lower seed production at patch edges
Edge Site
Core Site
Why was there more herbivore activity at the edge?
Densities of predators (e.g., spiders)
parasitoids (e.g., a tachinid fly) were 4x higher
at the core vs. edge Predators may be more
abundant in the core where plant density
productivity are higher
Figure from Fagan Bishop (2000)
32
Disturbance Ecological Succession
Primary succession on the flanks of Mount St.
Helens
Fagan and Bishop (2000) Diffusion model showed
how reduced seed production at the edge affects
rates of lupine spread (assuming no
long-distance, jump-dispersal events)
Figure from Fagan Bishop (2000)
33
Disturbance Ecological Succession
Modeling secondary succession
Horn (1975)
Developed simple Markov models of successional
replacement of temperate-zone tree
species Forest consists of cells, each occupied
by a single tree
Probability of replacing an individual tree with
a new individual of a given species is
calculated from a transition matrix
Example of transition matrix for four species
(GBgrey birch BGblack gum RMred maple
BEbeech) GB BG RM BE GB 0.05 0.36
0.50 0.09 BG 0.01 0.57 0.25 0.17 RM
0 0.14 0.55 0.31 BE 0 0.01
0.03 0.96
Initial composition vector (100, 0, 0, 0)
After 1 time step (5, 36, 50, 9)
Iterate this process plot the changes in
relative abundance
34
Disturbance Ecological Succession
Modeling secondary succession
Horn (1975)
BE
GB
RM BG
Figure from Horn (1975)
35
Disturbance Ecological Succession
One approach for estimating transition
probabilities proportional to the fraction of
each species as saplings beneath adults, e.g., if
5 of saplings beneath GB are GB, then
P(GBGB)0.05
Modeling secondary succession
Horn (1975)
If the same transition matrix is used throughout,
then a stable composition (the dominant
Eigenvector) will result (here dominated by BE)
However, the Markov approach is phenomenological,
so Why do recruitment probabilities vary, i.e.,
what biological traits lead to different
colonization rates relative abundances?
36
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE) The most recent generation of
forest simulation models precursors include
FORET (Shugart West 1977)
Spatially explicit, mechanistic simulation model
developed to predict dynamics of succession for 9
species of northeastern U.S.A. hardwoods Early
occupation by Red Oak (Quercus rubra) Black
Cherry (Prunus serotina) followed by late
dominance by Beech (Fagus grandifolia) Hemlock
(Tsuga canadensis), with Yellow Birch (Betula
alleghaniensis) present in gaps
37
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE) Basics of SORTIE
Spatially explicit model predicting the fate of
every individual tree throughout its life
Individual performance is affected by resource
availability at each trees location (original
SORTIE only included competition for light)
Species-specific functions predict each
individuals growth, mortality, fecundity
dispersal estimated from data collected in the
field
Four sub-models determine the fate of each
individual throughout its life
38
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE) (1) Resource (light) submodel
Calculates light available to an individual based
on its neighborhood the process is analogous to
taking a fisheye photo above each
plant Calculates a projected cylindrical crown
for each individual based on data relating crown
diameter depth to stem diameter Computes
whole-season photosynthetically active radiation
(PAR) for each plant based on the location
identity of neighbors
Figure from Pacala et al. 1996
39
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
(2) Growth sub-model Species-specific
equations predict radial growth from diameter
light availability
Figure from Pacala et al. 1996
40
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
(3) Mortality sub-model Species-specific
equations predict probability of death from an
individuals growth rate over the past 5 yr
Figure from Pacala et al. 1996
41
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
(4) Recruitment sub-model Species-specific
equations predict the number spatial locations
of seedlings based on the sizes of adult trees
Figure from Pacala et al. 1996
42
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
Community-level output From randomly seeded
initial composition Hemlock Beech clearly
dominated after 500 yr
Figure from Pacala et al. 1996
43
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
The mechanistic approach taken in this model
allows one to ask
Which key traits define species performance?
How sensitive are model predictions to parameter
values (and therefore sampling errors in
parameter estimation)?
How would hypothetical species with different
parameter values perform in this community? What
would constitute a superspecies (i.e., one of
J. Silvertowns ecological / evolutionary
demons)?
How many species could potentially coexist,
e.g., gt 50 spp. for gt 10,000 yr?
How would changing abiotic / biotic conditions
affect forest trajectories?
44
Disturbance Ecological Succession
Modeling secondary succession Pacala et al.
(1996 SORTIE)
See Doug Deutschmans on-line visualization of
SORTIE! Link to SORTIE visualization
Baseline without disturbance
Heavy disturbance
Large, circular clear-cut
Figures from Deutschman et al. 1997
45
Disturbance Ecological Succession
Succession may involve changes beyond species
composition
Community and Ecosystem Properties
Diversity often increases throughout
succession Standing-crop biomass often
increases throughout succession Elemental
cycling other biogeochemical processes
e.g., the Hubbard Brook experiments in New
Hampshire, and Peter Vitouseks work in
Hawaii Susceptibility to disturbance may
be a function of time since last disturbance,
e.g., fire and the accumulation of fuel loads
46
Anthropogenic Disturbance Ecological Succession
If all species have evolved in the presence of
disturbance, and thus are in a sense matched to
the recurrence pattern of the perturbation, why
are anthropogenic disturbances often so damaging?
(Paine et al. 1998)
Anthropogenic disturbances often differ from the
natural disturbance regime in timing, frequency,
or intensity
Paine et al. (1998) also argued that more
serious ecological consequences result from
compounded perturbations within the normative
recovery time of the community in question
47
Anthropogenic Disturbance Ecological Succession
A marine example Corals in the
Caribbean Hughes (1994, Science) One-two punch
of overfishing (selective disturbance)
natural mass mortality of dominant urchins
(Diadema) has created a phase-shift from
coral-dominated to macroalgae-dominated
reefs Caribbean coral reefs may never recover!
Photo of macroalgae-dominated reef from
http//news.mongabay.com/2008/0108-hance_coral.htm
l
48
Anthropogenic Disturbance Ecological Succession
A terrestrial example Dipterocarps in southeast
Asia Curran et al. (1999, Science)
One-two punch of logging increased frequency of
El Niño events (due to anthropogenically induced
climate change?) resulted in elimination of
recruitment by dipterocarps in forests of
Borneo! May result in a large-scale
phase-shift away from dipterocarp domination of
the forests dipterocarps are the principal food
of giant squirrels, bearded pigs, several species
of parakeet myriad specialist insects, etc.
Photo of dipterocarp forest from
http//biology.ucsd.edu/news/article_012706.html