Community Ecology Exam Flashcards
Succession
A gradual change in plant and animal communities in an area following disturbance
- the disturbance can be small or large, there are a removal of few to many individuals or a creation of an entirely new habitat
pioneer community
organisms that colonize area immediately following disturbance
primary succession
newly exposed substrates and not significantly modified by organisms
ex. glacier retreat, lava flows, sediment deposition (river/stream outflow)
secondary succesion
following disturbance that does not destroy soil
ex. fire, flood, abandoned agriculture land
what occurred in the greenbelt corridor?
plant community responded to flooding and drought
- species richness declined after flood and drought occurred over years, then increased past original and declined slightly and stabalized
climax community
late successional community that remains stable until disrupted by disturbance
disclimax community
maintained only through continual disturbances
ex. grazing, drought, fires, flood (centrifugal organization)
community structure and ecosystem process may change in a predictable manner or not ending in one of few to many _________ ________
alternative states
does disturbance impact all communities equally?
no
stability
the tendancy to resist or recover from disturbance
what was Sousas definition of disturbance?
Discrete, punctuated, killing, displacement, or damaging of one or more individuals (or colonies) that directly or indirectly creates an opportunity for new individuals (or colonies) to be established.
what was white and pickets definition of disturbance?
Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment
what are some spatial and temporal considerations for for disturbance?
- disturbance to bryophyte on a rock near a stream may occur at spatial and temporal scales irrelevant to surrounding forest communities
- a disturbance for one species may be inconsequential to another
- the nature of a disturbance may be environment specific
biotic vs abiotic disturbance:
biotic - disease and predation
abiotic - fire, hurricane, flood, wind, ice storm
intermediate disturbance hypothesis (Connell)?
proposed disturbance is a prevalent feature that influences community diversity
- proposed high diversity consequences of continually changing conditions
- predicted intermediate levels of disturbance promote higher diversity
if disturbance is too frequent and intense only _______ species will be present
pioneer, can complete life cycle between disturbance
if disturbance is too infrequent or minor only _____ species will be present
climax
- most effective competitors
as frequency and intensity increases there is a shift from in species composition from ________ to _______
competitors to colonizers
competitive exclusion
At intermediate levels of disturbance there is sufficient time for competitors to establish but not enough to outcompete early colonizers
what was Sousas study on disturbance ands diversity in intertidal zones?
- studied effects of disturbance on diversity of algae and invertebrates growing on boulders in the intertidal zone
- Disturbance comes mostly from wave action during winter storms.
– Predicted level of disturbance depends on boulder size. Classified boulders into three disturbance levels based on size and force required to move - most boulders subject to high disturbance had one species
- modal number of species on boulders subject to low disturbance was two
- most number of species was highest 4 on boulders subject to intermediate disturbance, boulders that experiences to intermediate rates of disturbance supported more species
one of the most important and ubiquitous sources of disturbance in grasslands is ________ _________
burrowing mammals
describe disturbance of paradise dogs
- creates distinctive patches of vegetation, the areas around the mounds support communities distinct from surrounding grassland
- species diversity highest at intermediate levels of prairie dog disturbance
- grass diversity decreases
intermediate disturbance allows persistence of species that are good _________ and species that are good ________
colonizers and competitors
stability
absence of change
stability can arise from ______ and _________
resistance of resilience
resistance
Ability to maintain structure and/or function in face of potential disturbance
resilience
ability to recover from disturbance
the greater the change the lower the ______
resistance
the faster the recovery the greater the _______
resilience
describe the park grass expierment
- To study effect of fertilizer treatments on yield and structure of hay meadow community
- Silvertown (1987) investigated ecosystem stability
- no new species since 1862* Stability on large scale
- without fertilizing grasses dominated throughout the period
- fertilizing with phosphorus, potassium, sodium, and magnesium increased the proportions of legumes and other species
- fertilizing with nitrogens, phosphorus,, potassium, sodium, and magnesium greatly increased the proportions of other species and produced moderate increases in legumes
- the proportion of major species groups appear very stable over time
- But analysis at level of species, shows large turnover in species within each species group
- Broad taxonomic groupings remain relatively stable but individual species show various responses
stability is _______ dependent
scale
sycamore creek was an example of ________ succession (describe)
primary
- typical desert drainage system, with low to
intermittent flow for most of the year, but periodically subject to flash floods after major storms - Rock scour and sediment deposition can totally remove algae and invertebrates
what was the study with valet in sycamore creek Arizona?
- tested hypothesis that ecosystem resilience in Sycamore Creek, Arizona is higher where linkages between surface and subsurface waters increase supply of N
- used piezometers
- Studied two stretches of stream and produced hydraulic maps; both had similar profiles
- nitrate concentrations are highest in upwelling zones
- nitrate concentrations decline through stationary and downwelling zones
- N content was highest where greater linkage of subsurface and surface waters
- Physical pattern of upwelling and downwelling zones remained stable through floods (resistance)
- Increased N in upwelling zones correlated with greater algal biomass increase after disturbance. Rate of algal biomass accumulation a measure of resilience
- Supports idea that hydrologic linkages increase stream resilience
Piezometers
measure flow bewteen surface water and water in flow in sediments
the relationship between diversity and ecosystem function involves :
- Complementarity
- Facilitation
- Sampling effect
insurance hypothesis:
which diversity increases stability due to increased probability of there being some species able to cope with any particular disturbance
diversity ____ a community from the potential consequences of a disturbance or any environmental change
buffers
______ ________ become important within a community under different conditions
different species
what changes during succession?
dominance, evens, diversity, composition
succession is the outcome of _____ ______ including:
ecological processes: dispersal, niche requirements, competition, exploitation, mutualism
describe primary succession at glacier bay
- Late 1700’s, glaciers extended to the ocean outlet of the bay
- By 1880’s, glaciers had retreated by ~40 km; lower bay supported plants and young forests, upper bay did not
- Fossil wood exposed by retreating glaciers
chronoconsequence
a group of communities or ecosystems that represent a range of times since disturbance
what was the study at glacier bay with Reiners?
- 8 sites ranging in age from 10 to 1500yrs post glacier retreat
- Species richness increases with age of site
- Richness increased most rapidly in early stages of succession
- Alaska, the successional process is quite slow
what where the taxa specific responses at glacier bay?
- Mosses, etc. (green bar) reached maximum species richness at ~100 y, remained steady thereafter
- Tall shrubs (red bar) reached maximum species richness at ~100 y, but declined afterwards
- Tree (yellow bar) species richness peaked at ~500 y
- Low shrubs & herbs (purple bar) richness continues to increase
the boreal forest has widespread dynamic diveristy subject to frequent disturbances especially ______
fire
what is the role of fire ?
- removes canopy, increases light penetration
- speeds nutrient cycling
describe the fire tolerant species in the boreal forest
- Aspens sprout from roots; this is a clonal species, with some clumps essentially immortal
- Paper birch can re-sprout as well, although not as robustly as aspen
- Spruce and pine; fire releases seeds from cones; smoke compounds act as germination stimulants
describe secondary succession in the boreal forest
- used forests of progressively older ages (longer times since last major fire event) to develop a forest community chronosequence
- Hardwood deciduous species dominate – aspen, birch, willow, pin cherry
- next forest forest experiences fire in 1916
- Paper birch and aspen in decline
• Balsam fir and white spruce beginning to become more important
• Young firs and spruce are prominent in the understory
“older” forest, experienced fire in 1823:
- Dominant tree species is balsam fir (although many dead stems)
- White cedar beginning to become important
- Birches and aspens much reduced
Oldest forest of all, experienced fire in 1760:
- Dominant forest trees are white cedar, white spruce (although declining) and balsam fir
describe primary succession by Sousa in intertidal zones
- bare surfaces on intertidal boulders to encrusted communities of algae, barnacles and mussels
- pioneer species algae and barnacle
- next colonists, red algae
- if no disturbance, red algae becomes dominant and occupies 60-90% of space
- Colonization is rapid initially, but then levels off
- if not disturbed it exemplifies a dominance controlled community
describe primary succession in sycamore creek
- typical desert drainage system, with low to
intermittent flow for most of the year, but periodically subject to flash floods after major storms - rock scour and sediment deposition can totally remove algae and invertebrates
- recolonization by algae after flood
- 2 days – some diatoms appear mainly bare ground
- 5 days – diatoms over 50% of the streambed
- 13 - 22 days – diatoms over entire streambed
- 35 days – other algae appear, including Cladophora
- 63 days – diatoms, cyanobacteria, Cladophora
- Overall, H’ increased sharply early, levelled off, then started to decline
- recolonization by benthos following flood
- stream is dominated by larvae of a crane fly, Cryptolabis sp.
– diversity remained constant (swamped by presence of Cryptolabis), except during crane fly emergence period - Species richness ranged from 38 to 43
- during August flood, most benthic species had adult aerial stages
– source of recolonization
describe shallow lake succession
- lakes experience succession on 2 time scale
- Over seasons or years, changes in species composition due to disturbance (freezing, flooding, introduction of novel species)
- Lakes also experience succession over geological time scales. Predictable changes in species composition as result of sedimentation.
Sedimentation
deposition of suspended matter onto lake bottom
shallow lakes and ponds are ______ in the long term
ephemeral
in shallow lakes and ponds rates of decomposition < __________ or inputs from erosion > _____
sedimentation, outputs
what is the chronoconsequence?
A series of communities or ecosystems representing a range of ages or times since disturbance
- Glacier Bay “sequence of ages” represented by sites of different ages since glacial retreat – but limited to a relatively short time frame (at most ~1,500y)
what are some ecosystem changes during succession?
- Include increases in biomass, primary production, respiration, and nutrient retention.
- Communities alter ecosystem properties
-Time alone might influence ecosystem through
processes such as weathering of bedrock.
describe the soil structure and depth (ecosystem changes) at glacier bay
Top-most: the O horizon, also called the LFH horizon
Next: the A horizon (importance of invertebrates and leaching)
Next: the B horizon (a depositional zone)
Finally: the C horizon
Note roots extending down through the horizons (root exudates are important)
- 60-70 y old: soil depth increased, with some organic material & litter
- 200-225 y old: fairly deep soil, all horizons well represented
- overall soil increased in both quantity depth and
complexity - Organic content & moisture increased with site age and soil depth & complexity
what are the 4 soil properties at glacier bay?
- organic content
- moisture
- bulk density
- phosphorus
describe Chapins study at glacier bay
- studied 4 sites of different ages at Glacier Bay, Alaska.
Observed changes in soil. - Observed changes in organic content, moisture,
phosphorus, and bulk density - reveals that physical and biological systems are inseperable
describe chronoconsequence on the Hawaiian islands
- Limits to 1° production: nitrogen early & phosphorus late in the successional sequence
- First organic matter accumulates – over 1st 150,000
- Total N also increases as organic matter increases
- Organic matter & total N were lower at Molokai, a little higher again on Kauia
- Total phosphorus did not vary with soil age – but weatherable phosphorus was depleted by 20,000 y & refractory phosphorus had increased to a plateau
- Rates of nitrogen and phosphorus loss were different
- For N: 1st 2,000 y, N is retained, but then is lost at progressively higher rates, due to leaching to the groundwater
- For P: with age, ecosystems retain more phosphorus, but in refractory form; rates of loss are high early on, but decrease later
what was the Hubbard brook site?
forests of nutrient loss and retention
- Clear cut catchment
- 3 years of suppression of regrowth
- recovery period
- deforestation experiment showed that succession can reduce loss of plant nutrients caused by disturbance
- once succession was allowed plant biomass increased
- Export of calcium, potassium and nitrate decreased, but only nitrate loss decreased to control levels
- Primary production increased
- Nutrient pools had been depleted prior to vegetation regrowth (losses peaked before herbicide treatment ended)
what is the model of recovery (Bormann and likens) ?
- according to the biomasss accumulation model disturbing a forest and ecosystem will induce a series of distinct recovery phases
1. reorganization
2. aggradation (biomass increase)
3. transition (biomass decline)
4. steady state (consistent biomass)
what is the key prediction of BAM (biomass accumulation model)?
Achievement of a steady state in biomass
in streams there is a early rapid _______ of biomass indicated by ________ _ levelling off after 30 days
accumulation, chlorophyl a
in streams oxygen has a rapid ______ followed by a slower ____ followed by _______ ____
increase, increase, levelling off
in streams invertebrate respiration has a ______ _____ to a ______
gradual increase, plateau
described the nitrogen dynamics in streams
- Upwelling zones and downwelling zones ; compared dissolved inorganic N content
- Retention of N in the reaches peaked ~30 days into the succession
- By ~90 days, N is exported – suggesting biomass loss
what are the mechanisms driving succession? (2 models)
- eggless and floristics model- offered as a synthesis and clarification of the monoclimax individalistic debate
- connell and slayters model- Facilitation, Inhibition & Tolerance
describe floristics (the clementsian model):
- waves of species, each replacing the former because of biotic changes to the environment
- facilitation, lack of overlap, an order to the groups of succeeding species
describe initial floristics:
- Somewhat like the Gleasonian model: considerable overlap amongst species, but different periods of dominance
- many species can potentially establish after a disturbance, but vary when they become abundant
what was the study by Peters in the boreal forest?
following fire disturbance:
- Many species can get established early on
- Adjacent stands vary in pattern of regeneration
ex. spruce can sometimes establish early (as saplings) in some stands, but in other stands, establishment occurs much later
describe the model by connell and slayter:
- Facillitation
- Involves initial establishment by pioneer species
- Pioneer species modify the environment
- Involves a chain of facilitations and
replacements
- Culminates in a self- perpetuating community which can be replaced only by disturbance - Tolerance
- initial colonizers are not necessarily pioneer species
- activities of early species do not make conditions more favourable for later species, although conditions do become less favourable for themselves
- later colonists are tolerant of the prevailing conditions
- the climax is reached when all tolerant species have colonized
- the system is reset by disturbance
- Inhibition
- initial colonizers could be any species (like tolerance model)
- early colonizers make conditions less suitable for subsequent arrivals
- early colonizers resist invasion by new arrivals
- replacements occur only when early colonists die
- the climax community consists of long-lived, resistant species
- disturbance resets the system
what was Sousas study in intertidal zones on early successional processes?
Hypothesis: early successional species are more vulnerable to biotic & abiotic mortality factors
- 4 controls no removals
- removed middle successional species
- removal plots ulva reinvaded very quickly
- very high densities of late successional species
- more evidence needed for inhibition
in intertidal communities there was physical stress due to exposure including:
combined effects of tide and temperature, therefore ulva was less able to survive afternoon low tides
- Ulva more vulnerable than the various species of red algae (mid or late)
Sousas work consistently points towards the role of __________
inhibition
describe turners intertidal studies (Oregon)
- wave action creates space
- Successional pattern: Ulva (early); red algae (middle, various species); surfgrass, Phyllospadix scouleri (late dominant)
- facilitation hypothesis with respect to the recruitment process
- Surfgrass seeds need presence of macroscopic algae for attachment & germination
Surfgrass becomes dominant following vegetative growth & spread
describe the removal experiments in intertidal communities:
All attached algae cleared from experimental plots in
September; control plots untouched
- control plots contained red algae and removal plots contained brown algae
- Removal experiments, Phyllospadix seed comparisons
- Many (48) seeds in the control plots, all attached to Rhodomela larix
• Few (2) seeds in the removal plots – neither attached to Phaeostrophion – both attached to remnants of original Rhodomela (had resprouted from holdfasts)
- supports conclusion of an obligate facilitation mechanism that allows surfgrass recruitment
probabilities of fire depends on both ____ and ______
climate and forest type
areas dominated by _____ have less fire
aspen
areas dominated by _____ have more fire
spruce
Aspen ____fire, even though its own recruitment is enhanced by fire
resist
Spruce _____ fire, in the short-term, this allows aspen recruitment, but in long-term, it promotes spruce recruitment & establishment
promotes
_____ _____ _____ for the boreal forest, hence, the large areas of mixed-wood forests
alternate stable states
No single factor determines the pattern of succession at Glacier Bay; both ______ and ________ play roles
inhibition, facilitation
keystone species
- Despite lowbiomass and relative abundance exert a strong effect on community strucutre
- a disproportionate effect on their community relative to their abundance and biomass
species that have a significant influence on community structure by virtue of high biomass are _________ species
domia
keystone species can occur at any _______ level within a food web
trophic
ecosystem engineers
species whose activities maintain and/or create new habitat
beavers are _______ _______ and keystone species
ecosystem engineers
describe affects that beavers have on communities:
Beavers cut down trees near stream, forming dams.
- Dams cause flooding, formation of ponds and increased riparian area.
- Beavers build lodges in resulting ponds
what was the study with John fryxell?
Transects to assess plant community structure and beaver activity
- Cut stems: # decreased with distance from water
- Diversity(species richness) peaked at intermediate distances – a function of a mix of species that could re- sprout (tolerant of cutting), those that are good competitors, and species that prefer less water- logged soils
what is the only requirement for keystone status?
that species in question has low biomass and disproportionally high impact on community structure.
describe the relationship between wrasses and cleaner fish
- A reef mutualist, the cleaner wrasse, Labroides dimidiatus
- 1 wrasse can eat up to 1200 parasites per day
- Fish on reefs without wrasses have 4X the parasite load
- Study of 46 reef patches in Red Sea over 4 months; removal or addition of wrasses
- Where wrasses were removed (or naturally disappeared) reef fish richness diminished by 24%
- contrast to 24% increase on patches where wrasses were added experimentally or naturally
describe the role of ants and seed dispersal in south africa
- Native ants disperse 30% of the seeds
- Ants are attracted to the elaiosomes attached to the seeds
- Argentine ants exclude the two native species that are much more likely to move large seeds
- Non-excluded ants species will move seeds, but one species never moves large seeds
- Argentine ants do not disperse or burys eeds
dispersal and burial of seed is critical to ________ of large seeded plants
persistance
where Argentine ants have invaded large seeded plants have suffered _______ _______ ______
greatly diminished recruitment
