Final Flashcards
What is nutrition mutualisms?
Two species exchange nutrients, or one species is rewarded in some way for improving the nutritional status of another
What are some examples of nutrition mutualisms?
- mycorrhizae and N2 fixing bacteria
- Corals- symbiosis with zooxanthellae
- deep sea tube worms
Mutualism will only arise if
pw(sm) + qw(um) > w(nm)
- w(nm): fitness of individuals in a nonmutualistic population
- p: proportion of successful mutualists (W(sm))
- q: proportion of unsuccessful mutualists (w(um))
The major exploitative interactions include
predation, herbivory, and parasitism
Key predator adaptations affect the ___, ___, and ___ of prey.
detection, capture, consumption
Mutualisms generally evolve to facilitate
reproduction, energy/nutrient acquisition, or protection from exploitative interactions
Mutualisms can be
obligate or facultative; specialized or general
What is an ecological community?
a group of interacting species that co-occur in a particular place
What parameters describe communities?
- composition: what species are present?
- structure: how do those species interact with each other?
What is direct filtering determined by?
environmental tolerances of the species
What is indirect filtering mediated by?
interactions with other species that are subject to filtering
What do neutral models of community composition assume?
- communities are random combos of species physiologically able to live in the same place
- two mechanisms determine species membership in communities- dispersal in ecological time and speciation in evolutionary time
- if communities are altered, they do not necessarily recover the same community structure
What do niche-based models of community composition assume?
- biological interactions (ex: competition) shape (and are shaping) the niches of coexisting species and so determine community composition
- “ghost of competition past” may give the appearance of competition not being important in the current community (i.e. that niches are already well separated or even randomly distributed) via competitive exclusion and character displacement some time in the past
Under a neutral model of community structure
species associate at random
In a neutral model
the niches are arranged at random, so that some niches are very similar, and others very different
In a niche-based model
the niches are over- or hyper-dispersed in niche space
Which is more likely: competitive hierarchy or competitive networks?
competitive networks
Coexistence is possible by ___ the niche
subdividing
Coexistence is also possible is resources are ___ and OVERALL niche overlap is ___
abundant; small
What are some ways to pack species into diverse communities?
- increase overlap: possible if resources (k) are large enough and overlap does not exceed some threshold
- decrease niche breadth: a.k.a. become more specialized
- can happen via character displacement
- extend range along resource axis: a.k.a exploiting resources not used by other species
- can happen via character displacement/directional selection
Environmental filtering and competition have ___ effects on community composition
opposing
If environmental filtering dominates over competition,
phylogenetic clustering is more likely
-closely related groups will have similar traits and so pass through environmental filter together
If competition dominates over environmental filtering,
phylogenetic over- dispersion is more likely
-only phylogenetically and therefore ecologically different species are found within guilds in the community
What is community heritability?
the proportion of the variation in a characteristic of the community (such as herbivore diversity) that is explained by genetic variation in the population of a particular species (e.g. plants)
How does community heritability affect community structure?
via “community genetics”
What is facilitation?
a process in which the presence of one species INCREASES the probability that another occurs in the community, usually by mediating competition
How does mutualism operate like facilitation?
lessens the effects of competitive interactions
What are keystone predators?
eat other competitively dominant predators, thus allowing coexistence of a diverse community
What is apparent competition?
two similar species are negatively impacted by the action of a shared predator or herbivore
-good example of an indirect interaction between two species (one that is mediated via another species)
Any process that increases the resource base or decreases the degree to which a resource is limiting will ___ the impact of competition
reduce
Where is competition most important?
at equilibrium
Disturbances may affect
limiting resources
Disturbances can temporarily ___ the resource base
increase
Disturbance can delay the process of
competitive exclusion
The first determinant of species presence or absence in a community is
whether or not it can survive the physical conditions (environmental filtering)
Neutral models of community structure posit that communities are
random assemblages of species that can tolerate the abiotic conditions
What are key determinants of the community composition in neutral models?
dispersal and environmental filtering
Communities structured by competition are affected by both
competitive exclusion and character displacement
Competition in a community leads to
- increased niche overlap
- decreased niche breadth
- increase in the range of resources used
The effect of competition on community structure can be modified by other interactions, such as
- predation
- facilitation
- apparent competition
If resources are not limiting, the role of competition in structuring the community is
reduced
How does disturbance reduce the effect of competition?
by increasing the levels of important resources
Disturbances initiate changes in community structure via
removal of individuals
What is succession?
the sequence of changes in a community following a disturbance
What is a successional stage called?
a seral stage
What do serial stages form together?
sere
What axes are disturbances characterized along?
- size
- intensity
- frequency
Primary succession follows a disturbance that is
so severe that the new conditions are nearly abiotic
What is an important characteristic of primary succession?
soil is lost or destroyed
When does secondary succession occur?
When the disturbance isn’t as severe as primary succession, such that functional soil (and its seed bank) remains intact)
What are some examples of primary succession?
glaciers, volcanic eruptions
What are some examples of secondary succession?
windthrow, fires
Effect of crown fire
- Variation in impact: high-intense crown fire to cool ground fire
- Delayed mortality: no
- Mode of recovery: dispersal
- Recovery rate: rapid
- Plant species dominance: changes in herbaceous species; not trees
- Regional diversity: increases
- Local diversity: initially decreases
Effect of a hurricane
- Variation in impact: low (within boundaries of storm; higher at distance from eye)
- Delayed mortality: yes
- Mode of recovery: resprouting + seeds
- Recovery rate: very rapid
- Plant species dominance: shifts due to pulse of early successional species
- Regional diversity: increases
- Local diversity: little change
Effect of a volcano
- Variation in impact: highly variable as function of distance from blast zone
- Delayed mortality: no
- Mode of recovery: dispersal
- Recovery rate: slow but variable
- Plant species dominance: shifts with succession
- Regional diversity: increases
- Local diversity: initially decreases
What is resistance?
the degree to which the community withstands disturbance
What is resilience?
the speed with which a community can recover from disturbance
-depends on nature of disturbance and traits of organisms, which interact over evolutionary time
What are two examples of chronosequences?
Hawaii and the Lake Michigan dunes
What is a climax community?
- the final stage of succession
- the community that replaces itself and that cannot be invaded by other species
What does the Clementsian paradigm state?
disturbance is infrequent; stability of the climax is the norm
T or F? It has been shown that disturbance, rather than stability, is the norm
T
What is a disclimax?
a successional stage that persists due to recurrent disturbance
What does a Gleasonian paradigm state?
- instead of a highly regulated, predictable pattern of vegetation, community composition is dependent on chance events
- the random occurrence of disturbance events
- the chance events associated with colonization and individual successional sequences
- communities rarely reach equilibrium
- Rejection of simple, fixed chronosequences and focus on the spatial rather than temporal dynamics of plant communities
- Succession is complex, unpredictable, and site specific
What does patch dynamics describe?
a spatial mosaic of areas at different stages of probabilistic succession
What are some environmental effects of disturbance?
- increased light availability
- loss/gain of nutrients or interruption of nutrient cycles
- succession itself: the biotic community in flux as succession proceeds
When does the facilitation model of succession apply?
if the disturbance produces a physical environment in which colonization and survival are especially difficult
-pioneer species facilitate colonization by later successional species
The inhibition model is driven by
the ability of species to colonize the disturbed site and then resist invasion by other species
The tolerance model states that
species replacement only occurs when new species are more tolerant of the newly changed conditions and replace earlier species
What is an example of the inhibition model?
colonization following disturbance of the rocky intertidal zone (in this env, space is the limiting factor)
- the green alga, Ulva spp., is an early colonist that inhibits invasion by the red algae common later in succession
- if Ulva is experimentally removed, red algae quickly colonize
What’s the difference between primary and secondary succession?
primary: occurs following disturbances that revert the ecosystem to abiotic conditions
secondary: follows less severe disturbances
Disturbances vary according to
intensity, spatial scale, and frequency
Although many intense, widespread disturbances are relatively rare, most communities are affected by
frequent disturbance of some kind
Communities are typically a mosaic of
recently disturbed and undisturbed sites
___ and ___ characterize community responses
resistance; resilience
When time since disturbance changes linearly over space,
a chronosequence develops
What is a chronosequence?
a set of communities in different stages of succession as a function of distance from the disturbance
In primary succession, pioneer species must be able to
tolerate harsh abiotic conditions
Why is secondary succession generally more rapid than primary succession?
because the soil is relatively intact and the physical conditions are more conducive to plant growth
The final, self-perpetuating stage of succession is
the climax community
The theory of patch dynamics characterizes communities on the basis of
size, isolation, and successional status of patches within the habitat
Resource conditions change as a result of
disturbance
Plants that colonize early in succession are adapted to exploit
the high-light conditions and thrive in often low-nutrient conditions
Plants that occur later in succession are
more efficient in their use of light but cannot grow as fast when light is abundant
Some early successional species are
fugitive species; their habitat disappears as succession proceeds, making population persistence dependent on dispersal to newly disturbed sites
Three key mechanisms of successional change are described by
the tolerance, facilitation, and inhibition models
How do we define species diversity?
- species richness: the number of species
- species evenness: the relative abundance of species
What is alpha diversity?
the species richness of a single community at one site
What is beta diversity?
the change in species composition across several adjacent communities
What is gamma diversity?
the total diversity among a group of different communities on a landscape scale
What is community composition?
the species that are found in a community (a species list)
What is species endemism?
the number of species endemic (i.e. unique) to the region
-a result of evolutionary history, including isolation
What is biodiversity?
the total biological diversity in a community, including species diversity and genetic diversity
Why can describing communities be difficult?
- cryptic species
- complex life cycles
- poor taxonomic understanding
How is species richness typically measured/shown?
lognormal species curves: reveal a common pattern in the structure of most communities
- most species occur at moderate abundance
- few species are very rare or very common
What is the effect of sample size on lognormal species curves?
Preston’s “veil line”
What is the Shannon-Weaver Index of Species Diversity?
H ‘ = −∑^n p(i) ln(pi)
n: number of species in the community
p(i): the frequency of the ith species
What is a Rank-Abundance curve?
a plot of the log proportional abundance of each species as a function of its ranked abundance (most to least abundant)
-the slope of this curve is a measure of species evenness
How are species richness and area related?
S = cA^z S: number of species A: area z: slope of the line (usually lies between 0.2 and 0.35) c: constant
Low species richness is an inherent property of
islands
The number of species on an island is determined by the relationships between
the immigration and extinction rates and the relative size of the species pool
Small and distant islands have ___ species than large and near islands
fewer
The farther the island from mainland, the ___ the probability that a dispersing individual will arrive
lower
Small islands have a ___ extinction rate
higher
What are the processes controlling species diversity at large scales?
- speciation
- extinction
What are the processes controlling species diversity at small scales?
- colonization
- extirpation (of non-endemic species)
- speciation (e.g. on islands)
What does the allopatric speciation model describe?
Situation in which a geographic barrier separates two populations of a species
- reproductive isolating mechanisms arise
- post-mating isolating mechanisms
- pre-matching isolating mechanisms
What is WBI?
wild bird species index
What is WPSI?
waterbird population status index
What is LPI?
a measure of vertebrate diversity
What is RLI?
red list index, a measure of extinctions
What are autotrophs?
organisms that obtain energy (and carbon) from inorganic sources, such as by chemo- or photosynthesis
What are the ultimate biological source of energy for ecosystems?
autotrophs
What is primary production?
the energy that autotrophs acquire (or carbon-fix) from the inorganic environment
What is gross primary production (GPP)?
the total rate of carbon fixed by autotrophs
What is net primary production (NPP)?
the total rate of carbon fixed by autotrophs minus the carbon they respire
(NPP=biomass)
What are heterotrophs?
organisms that obtain energy (and carbon) from organic compounds, generally from other organisms, living or dead
What is secondary production?
the production of biomass by heterotrophs
Chemoautotrophs derive energy from
the oxidation of electron donors in the environment
What are example of electron donors?
hydrogen (H2), hydrogen sulfide (H2S), methane (CH4)
What are examples of electron acceptors?
O2, NO3, SO4
Photoautotrophs derive energy from
sunlight (through photosynthesis)
Both chemoautotrophs and photoautotrophs use energy to fix
CO2 as a source of carbon
What is the energy flow through ecosystems?
3rd consumer (4th TL)
^
2nd consumer (3rd TL)
^
1st consumer (2nd TL)
^
1st producer (1st TL)
^
Solar energy
*TL: trophic level
What is the equation for ingestion efficiency?
E(ingested)/E(available)
What is the equation for assimilation efficiency?
E(assimilated)/E(ingested)
What is the equation for production efficiency?
E(in new tissue)/E(assimilated)
What does a food web do?
summarizes the feeding relationships in a community (who eats who)
What is one of the most basic and revealing descriptions of community structure?
food webs
What is omnivory?
feeding at more than one trophic level
What are stable isotopes?
non-radioactive forms of biologically important elements
- carbon (C12 and C13)
- nitrogen (N14 and N15)
The trophic position of an organism can be quantified on the basis of its ___ ratio
N15/N14
- N14 is lost in urine at a higher rate than N15, making higher trophic levels progressively heavier in N15
- ratio of N15/N14 increases up the food chain relatively predictably
The max efficiency of plant photosynthesis is between
4.6 and 6%
What are the most important selective forces on plants?
the combined effects of low CO2, limited water, and high temperature
C4 pathways in plants are favored
at low CO2 and high temperature
What are ecological factors limiting primary production?
-light
-water
-temp
*actual evapotranspiration (AET)- the total amount of water that evaporates and transpires from a region per unit time- correlates with NPP
-nutrients
ALL REPRESENT BOTTOM-UP CONTROL
Nutrients, particularly ___, control phytoplankton biomass in lake ecosystems
phosphorous
The highest rates of NPP are also related to high levels of
nutrient availability
The highest rates of NPP are concentrated on
continental shelves (because of terrestrial run-off) and upwelling zones
In open oceans, primary production is limited by
very low concentrations of nutrients
Vertical mixing (and entrainment of deep nutrient-rich water) is prevented by a permanent ___ in tropical oceans, resulting in the lowest levels of marine primary production
thermocline
What are the three hypotheses about what determines food chain length?
Hypoth 1: ecosystems with higher primary production have longer food chains
-pred 1: food chain length inc with primary prod but not with ecosystem size
Hypoth 2: larger ecosystems have longer food chains
-pred 2: food chain length inc with ecosystem size but not with primary prod
Hypoth 3: production and ecosystem size interact
-pred 3: food chain length inc with both primary prod and ecosystem size
What is was determined by data to be the actual determinant of food chain length?
ecosystem size
What is a food chain?
hierarchical pattern in which energy passes from producers to consumers
What limits the number of trophic levels along food chains?
inevitable energy losses
Each transfer of energy among trophic levels results in
energy lost to higher trophic levels
Ecosystems vary widely in their rate of
primary production
Any factor that limits photosynthesis or plant growth may limit
primary production
Plants face strong selection to increase their acquisition of
light, water, and nutrients
Ecosystems differ in the number of __ __ they contain
trophic levels
Biogeochemical cycles
describe the cyclic movement of nutrients in ecosystems, in which elements and compounds are exchanged among the principal pools (atmosphere, rocks, soil, water, and organisms)
What are the principle pools?
atmosphere, rocks, soil, water, and organisms
Pools are expressed as an
amount per unit area
Pools are linked by
fluxes (rates expressed as amount per unit per unit time)
Biogeochemical cycles are ___ at the global scale
closed
Biogeochemical cycles can operate (and be studied) at any
spatial scale
Why is carbon important?
it’s the primary component of biomolecules that form the basis of life
Why is nitrogen important?
vital for amino and nucleic acids
Why is phosphorous important?
essential for phospholipids, ATP, ATP and nucleic acids
T or F? Nitrogen and phosphorous are available at unlimited quantities
F
The global carbon cycle is driven by
photosynthesis and respiration
Equation for photosynthesis/respiration?
—>photosynthesis
6CO2 + 6H2O C6H12O6 + 6O2
What is the equation for nitrogen fixation?
N2 + 8H+ + 8e- –> 2NH3 + H2
Nitrogen fixation is energetically expensive because
triple bond between atoms must be broken
What are some other pathways in the N cycle?
- microbial and plant uptake
- decay and ammonification
- NH3 –> nitrite –> nitrate
- dentirification
- nitrate –> nitrite –> NO + N2O –> N2
Dentrification
- is anaerobic
- requires an organic C source
- is how N2 is returned to the atmosphere
Phosphorous is an important component of
nucleic acids, cell membranes, and energy conversions
Is there a significant atmospheric pool of phosphorous?
no
Movement of nutrients through ecosystems is
cylic
Biogeochemical cycles are characterized by
- pools or sinks (components of the ecosystem where the nutrients reside)
- fluxes (the pathways of transfer among pools)
Decomposition releases organic nutrients into
the soil or water, where they can be taken up again
