Ecological Succession

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Ecological Succession ecological succession -
ecosystem change from an early, immature,
transient stage to a more mature and final
stage (climax community) examples clearcuts
to mature forest, burned prairies to mature
grasslands seral stages a temporary,
distinct stage in succession primary
succession - on sites previously unoccupied
by living organisms lava flows, volcanic
islands secondary succession - on sites where
organisms existed burned or cut areas
structure and function of ecosystem becomes
more complex with each seral stage
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disclimax - system held at a stage below climax
by some disturbance longleaf pine forests, some
prairie areas biologists are interested in
which stages support different organisms some
depend on early stages (quail) some on old-growth
stages (woodpeckers, goshawk) many animals rely
on several stages for food or shelter Niche and
Environment niche - role or function of an
organism in the biotic community includes
trophic level (feeding level), foraging location
(forest, pasture, etc.), where it feeds
(canopy, mid-story, ground, etc.), what it eats
(insects, seed, etc.), what size food it eats
(large or small seeds) habitat - set of
environmental conditions under which
an individual, species, or community exists can
have seasonal habitats
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• environment - habitat of an organism plus all
  surrounding
• conditions (flooding regimes, regular weather
  patterns, etc.)
• microhabitat - small area of intensive use
  within the habitat
• of an organism dead logs for salamanders, nest
  sites for
• birds
• guild - group of organisms that use resources
  in similar
• patterns and often have much niche overlap
  (bottom feeder
• fish, insectivorous birds, grazers on the African
  plains)
• Competition
• occurs when 2 or more organisms living in the
  same area
• try to use the same resource that is in limited
  supply
• 2 types
• interspecific - between 2 or more species
  density
• dependent
• 2. intraspecific - within a species highly
  density dependent

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For interspecific (between 2 or more species)
niche segregation - species can overlap on
several niche dimensions and still not have
competition hawk and owl (same area and food but
different time of day) competitive exclusion
principle (Gauses principle) - no 2 species can
completely occupy the same niche
indefinitely one species will win (outcompete)
and the other perish Examples sunfish partition
food in a pond, theyll feed in different levels
of the water column yellow and
red-winged blackbirds will partition nesting
sites when using the same area of a marsh in
natural, undisturbed systems, interspecific
competition (niche partitioning) has been worked
out by co-evolution problems usually arise when
we introduce exotic species into a system (giant
marine toad, fish from SE U.S. moved to west
coast U.S., many plant problems)
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Gauses paramecium experiment
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Niche partitioning by warblers in a New England
forest
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For intraspecific (within a species) species
sometimes partition habitat by sexual
dimorphism (smaller male hawks take smaller prey
than females) 2 categories 1. exploitative
competition - individuals divide resource
and suffer same ill effects (reduced birth rates,
poor body condition) most fish populations 2.
contest (interference) competition - some
individuals do better than others in obtaining a
resource (dominance, larger body size, faster,
etc.) typical with carnivores Home Range and
Territory home range - the area within which an
individual animal normally travels in its daily
activities geographic range (species range) -
boundary of a species
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individuals change home range seasonally due to
weather, habitat condition, food availability,
and reproductive condition you can identify
seasonal or annual home range useful to know
when an animal needs specific resources Examples
turkeys need nesting, feeding, and
roosting habitat deer in cold regions have
summer grazing lands and wintering grounds in
forested bottoms territory - portion of home
range defended against others of the same or
closely related species deals with
space requirements Examples most large
carnivores defend a hunting area birds use
displays and songs to delineate a nesting
and foraging area during the breeding season
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pack territory - area defended by several
individuals acting as a single unit wolf
packs territories can be seasonal if
individuals must group together during certain
seasons still have individual distance
requirement that they will defend Examples
migrating birds travel as flocks, deer
group together on wintering grounds