community Flashcards
what is community
group of species living in a given area in competiton mutualism or predation
attributes of a community
species number
relative abundance
physical structure
interactions among species
relative abundance
p(i) = n(i)/N
p(i): proportion of individuals of species i
n(i): # of individuals of species i
N: total #of all species
how to examine relative abundance
rank aboundance diagram (rank abundance vs relative abundance)
the longer(more richness) and straighter (greater evenness) the better: more diverse
info on:
species richness (S): number of species
species evenness (E): how equally they are distributed
diversity in a community (not richness) 1 formula
simpsons diversity index (D)
D = sum(p(i)^2)
value between 0 and 1
-> 1 - D : reciprocal
the higher the better
diversity in a community 2 formula
shannon index H
H = -sum(p(i)*ln(p(i))
minimum value : 0 (one species present)
max : ln(S) total # of species present
E = H/Hmax for measure of evenness
dominant species normal?
yes!!
what is important in a forest?
biomass and abundance!
few trees on the ground make not much
many big trees are important
species that has disproportionate impact on community compared to abundance
keystone species
modifies or creates habitats (coral)
elephant destroys trees -> more space for grass -> more food for small herbivores and habitats
removal can have leathal impact for community
flow of food
food chain:
grass to preditor
describes flow of energy from bottom to top
grass -> grasshopper -> sparrow -> hawk
these chains get very complicated very quickly
-> simplification needed
feeding group in food chain
FACHBEGRIFF
trophic levels
lvl1: primary producers 1000pds (phytoplankton)
lvl2: 1st order consumer 100pds (zooplankton)
lvl3: intermediate predators 10pds (grouper)
lvl4: top predator 1pds (shark)
new form of classification
functional types (rather function than taxonomic group) based on: THE ROLE IN THE COMMUNITY response to environment life history charcteristics role within the community
example plants:
shade tolerant and intolerant
physical structure of community
reflect abiotic (light, wind, ect.) and biotic (size, density,…) properties
physical structure of healthy forest?
multiple layers of vegetation
in mediterranian for example no ground layer -> water lack
layers in aquatic communities
FACHBEGRIFF
photic layer
aphotic layer
benthic layer (bottom) can be photic and aphotic
consumer placement in community
they are not restricted to one level.
can move vertically through forest or water (zooplankton)
what is good for community diversity?
environmental heterogeneity
more layers -> more living spaces and food -> more diversity
change in physical and biological structures across landscape
(FACHBEGRIFF)
example
zonation
tree community changes greatly while moving up the mountain
bottom: 17 species top: 3 species
defining communities?
is difficult… mostly a continous drift
vary with objective of study ect…
but dominant species are a good measure
condition for species to survive
there is a min and an optimum
defined by the niche
realized and fundamental niche
bigger or smaller
realized niche can be bigger (mutualism) or smaller (competition)
differences in species tolerance lead to?
FACHBEGRIFF
zonation
shifts in relative abundance
competitive vs. toleration
competitive species:
higher growth rate however not so tolerant
tolerant species moves away from competitive species
competition effects of certain species on community
removal of competitor?
example hare
some species depend on competition with one species, other on comp. with many
can have very different effects (small or large)
the hare only benefits if many preditors die out
competitive effects of a number of interspecific competitors
FACHBEGRIFF
diffuse competition
diffuse interaction -> not that important for the other competitor -> indirect interaction
top-down-control (yellowstone)
wolves eat dears -> deers hide -> less plants eaten -> more birds / less erosion -> better riverbanks -> whole physiological appearance changes
down top control (ocean)
abundance of photoplancton -> fish -> big fish
restore condition in community or ecosystem before human interference
ubranisation ect.
(FACHBEGRIFF)
RESTORING ECOLOGY
reintroducting species
restoring habitats
reestablishing communities
reestablish native species on degraded cropland
destroying present bushes
reseeding and replanting native species
burning the site every two or 3 yearrs
after 80 years community is back:)
bad example of reestablishing
solution?
fear of woodland -> bad for waterbirds:
big herbivores introduced to eat seed and small trees -> population grew fast and had nothing to eat anymore -> they all starved after harsh winter
a cooridor to island to allow migration and release stress if necessary
also no preditors
if a predator suppresses abundance of herbivore and favours plant growth (example)
trophic cascade (influence on further trophic levels) top down or down top
important to know for restauration:
feeding habits, processes in communities, species interaction, regulation processes
steps on abandoned cropland
grass -> bushes -> small pines -> canopy of trees -> big trees (maples)
temporal change in a community structure
FACHBEGRIFF
SUCCESSION
big ass trees
decidous or evergreen hardwoods
need shadow to grow
a point in time in evolution of community
sequence of communities seen in succession
(FACHBEGRIFF)
seral stage (some times years or decades)
some stages can be missed or altered
sere
succession example in rocky algal community
waves overturn rock (nat. disturbance) -> cleared surfaces -> new species colonized as there were before
pioneer species characteristics
FACHBEGRIFF
early successional species
- high growth rate
- small size
- high rate of dispersal -> rapid colonialzatio
- high rate of per capita population growth
late species characteristics
FACHBEGRIFF
late successional species
- longer lifespans
- larger size
- lower rates of dispersal
- low rates of per capita growth
new hampshire tree succession
decidous trees died in lack of shade
herbaceous species started to dominate
they provided shade and big trees came back
community occupies new place
primary succession (algal rock, lava fields, newly exposed glacial till)
community occupies an arleady occupied space
secondary succession (new hampshire)
a series of sites within an area that are at different successional stages
(FACHBEGRIFF)
chronosequence
primary succession example (glacier)
glacier exposes new surface -> shade intolerant species like alder and cottonwood colonize -> then late successional plants like spruce and hemlock replace early ones
three primary plant strategies
evolution through succession
R (ruderal):
rapid colonization, resources allocated to reproduction, wide dispersal
C (competitive):
need abundant ressources, mainly allocated to growth,
S (stress):
stress-tolerant, ressources allocated to maintenance, habitats with limited ressources
with time:
R -> C -> S
when trigger for secondary succession -> R colonize quickly, can use all types of ressources -> biomass increases -> competition occurs -> competitive C plants dominante -> on the long run S plants dominate as resistant to all sorts of stress
ecological vs physiological charac. of early and late successional plants
light and water availabilty vs. seed dispersal, storage and germination
compete for light or nutrients
light: carbon allocation in leaves and stems
nutrients: carbin allocation in roots
environmental change as result of activities of organisms
FACHBEGRIFF
AUTOGENIC
light gradient through forest
environmental change as result of physical change of space
FACHBEGRIFF
ALLOGENIC
temperature change
diversity over succession
peaks at the transition from early to late successional species and stabilizes in the end at a lower level
influence of growth rate on diversity
if faster -> less diversity
if slower -> process of coexisting is longer (late and early)
cuts in succession through disturbance
if frequent disturbances -> no late successional species arrive -> never high diversity
if intermediate disturbances -> high diversity as succession enters transition stage
if no disturbances -> forests get old and in late stages low diversity
animals ect in succession
depend on stages of succession:
grassland species: meadow mouse, grasshopper sparrow
shrubland species: squirrel, deer
forest animals: fox, ..
influence of abiotic environ. changes on succession
fluctuation occur annualy (temp. and precipitation)
these dont influence pattern of secondary succession to much
but large timescale changes (climate change) are likely to influence -> change that occur at intervals in the timespan of organsims life
(FACHBEGRIFF)
study of distribution & abundance of ancient organisms
Paleoecology
sources for information of paleoecology
fossils: bones, insect exoscelets, plant impression and pollen grains
human influence on community dynamics
when americans colonized 1600s -> dominance by forests
- > forests cleared for agriculture
- > now reforestation (secondary succession) -> all forests are very young
tilmans hypothesis of succession
in beginnig, light availability high and nitrogen low
in end, light availability low and nitrogen high
this leads to change in succession
