Final Exam Class 5 Flashcards
community structue
describes the composition of communities
what are the components of community structure
number of species
abundance of species
interactions among species
biotic and abiotic factors
species richness describes
the number of species in a community
species diversity accounts for
number of species and abundance
frederick Clements argues
communities are stable and the result of extensive biotic interactions and coevolution
(clements) after disturbance species in an area should reach
climax community which is stable and predictable
henry gleason argues
comunities are dynamic and are the result of historical chance and abiotic factors
(gleason) unpredictiable
communities are ephermeral
how did gleason and clements test their theories?
experimental ponds were built and allowed species to establish themselves over 1 year
which theory (clements or gleason) was correct?
both Gleason and clements (different species colonized different ponds therefore communities are unpredictable, but most of the species occurred in all 12 ponds)
what is a keystone species?
have a disproportionately large effect on their surrounding ecosystem relative to its own abundance
what is a dominant species
can have strong effect just due to high abundance and biomass
what is an example of a keystone species
sea otters, starfish
- starfish preys on mollusks and mussles which it competes for space, so when you remove the starfish the mussels just take over which throws the species abundances out of whack
the presence of a keystone species can limit
one species from dominating and promoting community diversity
their removal can change communities
all communities face
disturbances
what is a disturbance
anything that changes the community structure
what influences the diversity and ability of organisms adapt to changes?
frequency, duration, and predictablility or disturbances
whar are the diffeerent types of predictivablity
daily : tides
seasonal : winter snow monsoons
aseasonal:froughts, forest fires
millennial: volcanoes and earthquakes
what is successsion?
the pattern of recovery
-bare rock to lichen moss to annual herb to perennial herb to scrub to forest (climax community)
what is primary succession?
when a disurbance removes all organisms in an area and the soil
-caused by glaciers or volcanoes (takes hundreds of years)
-pioneer species to intermediate species to climax community
the sequence of succession depends on
the species involved
their interactions
environmental circumstances
disturbance frequency
early species tent o be
r selected (weeds)
later species tend to be
k selected
early species interact with subsequent species 3 different ways
facilitaiton
toerace
inhibition
facilitation
makes conditions avorable for new species
tolerace
does not positively ornegatively affect new species
inhibition
prevents the establishment of a new species
exampes of facilitation
protection from the win
increase soil moisture
increase available nutrients and organic matter
examples of inhibition
limit sunlight
compete for nutrients
allelochemicals to inhibit growth
what is secondary succession?
occurs when a disturbance remove’s some but not all organisms in an area
secodary sucession is caused by
fires r storms and recovery can take only a hundred or so years
- can be important to regulate environments and communities
many communities are adapted to
specific disturbance regimes and altering these regimes may negatively impact community structure
in the early 1910’s
the us forest service began supressing natural forest fires
this reduced frequency of secondary succession that was important for communities adapted to periodic disturbances
