BIOB50H3 Chapter L#17: LECTURE #17 reading
LECTURE #17: 356-357, 377-387, 392-395
KILLER ALGAE CASE STUDY: (356-357)
- on the sealfloor of Mediterranean sea grew seaweed called Caulpera taxifolia near an
aquatic musuem doesn’t grow in cold water (grows in Caribbean) Mediterranean is
6*C colder
- asked: why is it growing here, how did it get here, and was it spreading beyond the soft-
sediment habitats near the museum? found: it growing 5km away from the shore near
a fishing location must have been moved by ships
- these seaweeds release a secondary compound that deters fish and invertebrate
herbivores in the tropics (hence killer algae, even though not toxic to humans) it
invaded and dominated marine comm. In the Mediterranean sea
- became very abundant
PG 377-387
CHAPTER 17: CHANGE IN COMMUNITIES
- Mt. St Helens had lots of diversity then it erupted (volcano) created whole new
habitats (some of which were completely devoid of living org)
INTRODUCTION
- Human actions are changing ecosystems
AGENTS OF CHANGE (17.1)
-succession: change in the species composition of communities over time the result of
variety of abiotic and biotic agents of age
Agents of change can be biotic or abiotic
- abiotic factors vary over daily/seasonal/decadal/100k year time-scales and have
implications for community change (eg. Increased temp. and ocean acidification = coral
lose symbiotic algae = coral bleaching = coral death // increased sea level = less sunlight
for plants = replaced
by macroalgae like
seaweed)
-disturbance: an
abiotic event that
physically injured or
kills some indiv. And
creates
opportunities for
other individuals to
grow and reproduce
(though some
ecologists consider events like digging by org. to be disturbances as well)
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-stress: occurs when some abiotic factor reduces
the growth, reproduction, or survival of indiv and
creates opportunities for other indiv. I.e a stress
in the coral reef might be the effect of warmer
water temp. on their growth
-both disturbance and stress play roles in driving
succession
- biotic factors also play role; eg. Coral example:
change might be driven by competition by
platelike coral and branched corals // eg. Can have
coral diseases that can kill species of coral
ecosystem engineers also play role in these
biotic factors
- abiotic and biotic factors interact to produce
change in communities eg. Beavers cause
changes in abiotic conditions that in turn cause
species replacement // eg. Things like the
tide/wind/waves can affect interactions +vely/-
vely thus creating opp. For other species (eg. Sea palms in the rocky interdial zone)
Agents of change vary in their intensity, frequency, and extent
- weak and frequent distance might have more subtle effects/affect a smaller area eg.
Prior to Mt. St Helends erupting, disturbances could have been wind blwing old trees
down the mountain
- these small, frequent disturbances open up patches of resources that can be used by
indiv. Of the same or diff. species a mosaic of disturbed patches can promotes species
diversity in comm. Over time, but may not lead to much successional change
THE BASICS OF SUCCESSION (17.2)
- succession refers to the process by which species composition of a comm. Changes over
time involves colonization and extinction due to abiotic/biotic agents of change
- succession progresses through various stages that include a climax stage: thought to be
a stable end point that exp. Little change until a particularly intense disturbance sends
the community back to an earlier stage
Primary succession and secondary succession differ in their initial stages
-primary succession: involves the colonization of habitats that are devoid of life, either
as a result of a catastrophic disturbance (eg. The pumice plain at Mt. St. Helen) or
because they are newly created habitats (eg. Volcanic rock and island) 1* succession is
very slow b/c the first arrivals (called pioneer species/early successional species) face
extremely inhospitable conditions thus: the first colonizers then tend to be species
that are capable of withstanding great physiological stress and transforming the habitat
in ways that benefit their further growth an expansion
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-secondary succession:
involves the re-
establishment of a
community in which
most, if not all, of the
organisms or organic
constituents have been
destroyed eg.
Fire/hurricanes eg.
Mt. St. Helens had area
called the blowdown
zone where some org. survived and secondary succession took place
The early history of ecology is a study of succession
-Chandler Cowles studies successional sequence of vegetation
in sand dunes on the shore of Lake Michigan dunes are
continually growing a new sand is deposited at the shoreline
Cowles inferred the successional pattern along a dune by
assuming that the plant assemblages farthest from the lake’s
edge were the oldest and that the new ones were near the
lake first stages were dominated by an ecosystem engineer
called American beach grass (it traps sand and can create
hills which provides refuge for plants ont eh leeward side
who can’t tolerate sand burial) Cowles assume dtha the
diff. plant “societies” in diff. positions on a diff. dune rep.
successional stages would allow him to predict how a
com.. would change over time w/o actually waiting for the
pattern to unfold, called space for time substitution
(assumes tha time is the main factor causing comm. To
change and that unique conditions in particular locations are
inconsequential)
-Fredercik clements believed that plant comm. Were like superorganism that worked
together in a mutual effort succession was similar to the development of an org., and
he thought that each comm. Had its own predictable life history and if left undisturbed
would reach an ultimate stable point .. climax community
- Gleason: thought that view a comm. As an org. ignored the response of indiv. Species to
prevailing conditions thought: communities were not the predictable and repeated
result of coordinated interactions among species, but rather the random product of
fluctuating env. Conditions acting on indiv. Species
-Charles Elton: perspective on succession; he believed that organism and the env.
Interact to shape the direction succession will take used Pine forests in England as an
example (succession in the forest depended on moisture of the env; wetter areas
developed into bogs, drier areas into wetlands w/ grasses; eventually all these comm.
Became birch scrub and then diverged into 2 types of forests) thus: only way to
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Document Summary
Killer algae case study: (356-357) on the sealfloor of mediterranean sea grew seaweed called caulpera taxifolia near an aquatic musuem doesn"t grow in cold water (grows in caribbean) mediterranean is. St helens had lots of diversity then it erupted (volcano) created whole new habitats (some of which were completely devoid of living org) Agents of change (17. 1) succession: change in the species composition of communities over time the result of variety of abiotic and biotic agents of age. For other species (eg. sea palms in the rocky interdial zone) Agents of change vary in their intensity, frequency, and extent. Weak and frequent distance might have more subtle effects/affect a smaller area eg. prior to mt. St helends erupting, disturbances could have been wind blwing old trees down the mountain these small, frequent disturbances open up patches of resources that can be used by indiv.
