Ecology Final

What is primary production, GPP, and NPP?

Primary production: overall process of carbon fixation

GPP: total rate of carbon fixation by producers

NPP: available fixed carbon after accounting for carbon used in respiration

• fixed carbon: organic carbon

• fixed nitrogen: inorganic

What controls productivity in terrestrial systems?

• Temperature + moisture

• Actual evapotranspiration (AET): amount of moisture evaporated in a system over time

• nutrient availability only matters locally

• **for map questions:

  • flatlands > mtns (if all else same)

  • closer to equator with less rain > temperature zone w/ more rain

What controls productivity in aquatic systems?

Nutrients!!!!!

How are nutrients brought up from the aphotic zone?

Coastal upwelling: winds blow water away from shore; forces cooler, nutrient-rich up from the aphotic zone.

Equatorial swelling: winds blow away from equator

Seasonal overturn: when surface water reaches 4C (max density) and sinks to the bottom

Wind-blown nutrients: soil blown into water

What is stratification?

clear layering of water driven by differences in density (primarily driven by temp. differences)

• commonly near equator → never reaches 4C → low NPP

What are the Tropics?

btwn 23.5 N + S; highest latitudes that receive perpendicular sunlight once per year

Why is it rainy in Tropics/Equator? +what is coriolis effect?

hot air rises more → as it rises, it cools → condenses into clouds → hot, dry air drops back down at 30

• Coriolis effect makes winds (and other moving objects) appear to curve or move at an angle (deflected) rather than straight north or south because of Earth's rotation, causing rightward deflection in the Northern Hemisphere and leftward in the Southern Hemisphere, creating curved global wind patterns and spinning storms. 

What are the three cells?

• Hadley cell (0-30) - air rises at 0, hits tropopause

• Ferrell cell (30-60) - influenced by other cells, air rises at 60, drops at 30

• Polar cell (60-90) - air rises at 60, drops at 90

El Nino/La Nina

El Nino: easterlies are weaker than usual; warmer water “sloshes” back eastward; coastal/equatorial upwelling stops

La Nina: stronger trade winds; cooler SST + more nutrients

Describe the N-cycle.

1. Nitrogen gas (N₂) in the atmosphere is fixed into ammonium (NH₄⁺) by nitrogen-fixing bacteria. ✅

2. Ammonium is converted into nitrite (NO₂⁻), and nitrite is converted into nitrate (NO₃⁻) by nitrifying bacteria. ✅

3. Nitrate is converted back into nitrogen gas (N₂) by denitrifying bacteria. ✅

• Mineralized nitrogen (NH₄⁺ and NO₃⁻) is readily available for uptake by plants and microbes. ✅

• Mineralization is the conversion of organic nitrogen into inorganic nitrogen (NH₄⁺) by microbes. ✅

• Immobilization is the conversion of inorganic nitrogen (NH₄⁺ or NO₃⁻) into organic nitrogen in microbial biomass.

Describe the P-cycle.

• Phosphate (PO₄³⁻) is released from rocks and minerals by weathering.

• Plants and microbes take up phosphate and incorporate it into organic molecules.

• Phosphorus moves through the food web as animals consume plants and other organisms.

• Microbial decomposition mineralizes organic phosphorus back to inorganic phosphate.

• Some phosphate is immobilized in microbial biomass temporarily.

• Phosphate can be lost from soil to water or sediments, eventually returning to rocks over long time scales.

Describe Walker-Syers Model.

• Young soils:

  • Most P is still in primary minerals (like apatite) in the rock.

  • Only a small fraction is non-occluded, so available P is limited despite high total P.

• Intermediate soils:

  • Weathering of primary minerals releases P.

  • Enough time has passed for P to become non-occluded and available, but not so long that it has been heavily leached.

  • Result: available P peaks at this stage.

• Old soils:

  • Most primary minerals are gone.

  • P is largely occluded in Fe/Al minerals or lost to leaching.

  • Available P declines, even though total P may still be present.

Evolution + Natural Selection (def, diff)

Evolution: changes in gene frequency in a population

Natural Selection: differential reproductive success based on phenotypic variation

Correct this misconception: Natural selection promotes the good of the species

Natural selection acts on individuals, not species. Traits are favored if they increase an individual’s reproductive success, even if they harm others.

Correct this misconception: Differences in reproductive success are the outcome of natural selection

Differences in relative reproductive success are the cause of natural selection, not the outcome. Natural selection occurs because individuals differ in how many offspring they produce, even when population size is stable.

What evidence needs to be present for ongoing evolution to be occurring?

• phenotypic variation

• phenotype matches selection pressure

• phenotype is heritable

• differential reproductive success

• change in gene frequency

What is the comparative method, and how are phylogenetically independent contrasts used?

• Comparative method: Compares traits across species while accounting for shared ancestry; effective sample size = number of independent evolutionary events.

• Phylogenetically independent contrasts (PICs): Differences in trait values calculated at each independent evolutionary event + average all to find contrasts

  • more evolutionary events = more independent appearances of the trait with the same environment

How does exstrinsic mortality affect trade-offs?

High extrinsic mortality favors early reproduction and greater allocation to current reproduction, often at the cost of growth, survival, or offspring size. Low extrinsic mortality allows investment in survival and delayed reproduction.

r-selection vs k-selection

• r-selected: early reproduction, many small offspring, little care, unstable environment.

• K-selected: late reproduction, few large offspring, high care, stable environment.

How does population density influence life-history trade-offs?

High density favors fewer, larger offspring with more investment per offspring due to competition, while low density favors many, smaller offspring with less investment.

Applied vs Basic research questions?

Applied: addresses specific, current real-world problems for practical solutions

Basic: curiosity; to expand general knowledge

Mark-recapture (for estimating population size)?

• capture, mark, and release Nm individuals

• return, capture Nc2 individuals; note # of individuals who were already marked (=Nr)

• Pm = proportion of 2nd capture that were marked (Nr/Nc2)

• Nt= Nm/Pm

mark-recapture (to estimate survival rate)

• capture + mark

• at least two recaptures

• Assumptions/limitations: individual could still be alive just not spotted; mark doesnt affect survival; closed population; marking doesnt affect behavior

Life-tables (variables, Ro, use, assumptions)

• Ro = sum(lxmx) = net. reproductive rate = # of female offspring per female per generation

  • if Ro = 1; pop = stable

• lx = proportion of surviving to age X

• mx = avg # of female offpsring per female

• Assumptions

  • all individuals are identical

  • closed population

  • Age-specific survival and fecundity are constant over time (constant environment)

  • do not account for overlapping generations!!

Generation time (formula, why its important)

T = sum(xlxmx)/Ro

• avg. amount of time between birth of female and her daughter

• more indicative of population trends in unstable environments; if T is short, then there is more chance for adaptation

Life-stage transition models + population matrices

Life-stage transition models:

• boxes w/ size/stages + arrows between stages (growth, survival, reproduction)

• better when demographic characteristics like survival and reproduction are more dependent on an individual's biological stage, size, or condition than on its chronological age

• allows individuals to stay in same stage

Population matrices:

• predict how populations change over time (lambda)

• column → row (arrow from = column; arrow to = row)

*Assumptions: individuals in each stage are identical, closed population, no density-dependence

***remember that survival rate at each stage = both the arrow moving from it + the arrow repeating that stage

How do you determine which stage transition has the greatest effect on lambda?

1. Sensitvity: vary transitions by fixed increments

2. Elasticity: vary transitions by fixed proportions

• neither of these take into account whether the tested increment is biologically possible

1. Life-simulation analysis: vary transitions to the extent of variability observed in the population

   1. -create many random projection matrices w/ observed values; then plot them w/ the trait on the x-axis and lambda on y-axis; look for trends

Exponential population growth.

• r = per-capita rate of increase

• rmax = rate of increase w/ no limitations (potential)

• dn/dt = rmaxN or Nt=Noe^rt

• **DO NOT ACCOUNT FOR DENSITY!!!!!!

Logistic population growth

dn/dt = rmaxN(K-N/K)

• As N→ K, numerator gets smaller, making fraction smaller; lower dn/dt

• As N decreases, numerator gets larger, making fraction larger; higher dn/dt

• Not always accurate: if N is too low, there are not enough mates for population to be growing

Assumptions: closed population, constant environment, resources are limiting, individuals have identical effects on resources

Exploitation/harvesting of wild populations (MSY, graphical representation, assumptions)

• Max. sustainable yield: max # of individuals that can be harvested continuously without reducing the long-term population size

• Graphical representation:

  • N on x-axis, dn/dt on y-axis. Mark K on x-axis, mark H on y-axis, find the dn/dt where H + current N are.

• N will move towards K unless H is greater than current dN/dt.

• Risky to harvest at Hmsy: population size and growth estimates may be inaccurate, environmental changes can reduce growth, and MSY occurs at intermediate N, leaving little buffer against overharvesting

Define the different types of interactions (herbivory, predation, parasitism, mututalism, competition)

• Herbivory: consume plants (primary consumers)

• Predation: one organims hunts, kills, and eats another

• Parasitism: one organims benefits at the expense of another by utilizing its resources

• Mutualism: both organisms benefit

• Competition: one organism limits another access to resources

Resource (exploitation) competition

one organism uses a resource before another one can

Interference competition

direct competition; one organism actively prevents another from accessing a resource

Symmetric vs Asymmetric competition

Symmetric: both organisms have an equal effect on each other, proportionate to each of their body sizes

Asymmetric: both organisms are not equally effected by competition, effect is disproportionate to body size

Conclusions from meta-analysis about competition. Why is meta-analysis useful?

• competition is present at varying strengths and in different forms across species

• meta-analysis increases the overall sample size, which enhances the statistical power to detect effects and provides more precise estimates of the effect magnitude

  • looking at mutliple species increases ability to generalize _ can help identify similar factors that lead to similar competition

Lotka-Volterra model + competition coefficient

• calculates change in pop. size when accountinf for intraspecific + interspecific competition

• competition coefficient (𝛼12) quantifies the impact of one individual of species 2 on the growth of species 1, expressed in terms of how many individuals of species 1 it's equivalent to

• *if asked to find α_{12 —-find N2 and N1 in terms of K1; set equal to 0}

• ASSUMPTIONS: no interspecific competition outside of species 2, all individuals of species 2 are identical (all individuals have the same effect on resources)

Competitive exclusion principle

• if two species occupy the same niches, on must be excluded

Define niche segregation.

competing species in a community adapt to use different resources or habitats

Species sorting + community assembly?

Species sorting: community composition is based on which organisms can disperse to an area, persist in the abiotic conditions, and not be outcompeted.

Community assembly: overall how communities form (dont overthink this one!!)

Why do trade-offs allow multiple plant species to coexist?

Trade-offs prevent any one species from dominating because no plant can be good at all traits. Different species are optimized for different resource conditions (light, water, nutrients), so each becomes the best competitor in some environments but not others. This niche differentiation allows coexistence even though all plants require similar resources.

What is disturbance, succession, faciliation and inhibition?

Disturbance: an event that removes biomass quicker than it can replace itself

Succession: predictable replacement/turnover of species over time

Facilitation: species from earlier stages of succession support success of future species

Inhibition: species from earlier stages of succession make it more difficult for later species to establish

What is neutral theory?

Communities are made from random dispersal events. (not niche/exclusion). variation observed in communities is due to random chance alone .

What are null models? How to use for neutral theory vs competitive exclusion principle?

• Used to test if observed patterns in a community are due to random chance.

  • Null hypothesis: species differences arise randomly (neutral theory).

  • Method: measure a trait, calculate observed differences, randomize trait values many times, and compare observed to random distribution.

  • Interpretation:

    • Observed > random → pattern likely deterministic (niche, competition)

    • Observed ≈ random → pattern could arise by chance (neutral processes)

How do humans impact nutrient cycles?

• Eutrophication: nutrient enrichment; excess nutrients (N+P) in water bodies cause excessive algal growth; as algae dies, O2 is depleted (decomposition); causes dead zones (fish need O2 for cell. resp.)

• Decreased nutrient retnetion

  • increased runoff + leaching from agriculture, deforestation, urbanization

What are the most limiting nutrients in different systems (ocean, land, freshwater)?

N: ocean + land

P: freshwater

What is decomposition?

Decomposition: breakdown of organic material that releases CO2 + nutrients

• Decomposers + detritivores

• Detritivores (like earthworms) ingest dead matter and break it down internally and mechanically, while Decomposers (like fungi and bacteria) secrete enzymes externally to chemically digest and absorb nutrients from dead organic matter

What controls the rate of decomposition?

• AET - postively correlated

  • microbes needs H2O; heat speeds up rate of reactions (but not TOO much H2O, or their is lack of O2)

• quality of carbon

  • Fastest: Glc → Cellulose → Lignin: slowest

• Nutrient content (C:N)

  • have separate card for this :)

• Litter quality (C:N + C quality)

  • determined by nutrient availability and longevity of leaves

  • high nutrient + low longevity = faster decomposition!

How does C:N content affect rate of decomposition + [N] in soil/leaves?

• low N limits decomposition

  • but immobilzation of mineralized N is quicker

• high N increases decompositon rate

  • not limiting so less is immoblized immediately; can be leached or taken up by plants

Why dead leaves have relatively low N?

• as leaves died, N moves away (to shoots/stems + roots)

Why organic Carbon accumulates in some soil?

• slow decomposition rate

  • high altitudes: low O2, low temp

  • moisture (too high or too low)

What is rarefaction?

• Standardizes species richness across communities with unequal sampling effort.

• Steps:

  1. Choose the smallest total sample size among communities.

  2. Randomly take many subsamples:

     • For a single standardized richness comparison: only subsamples of that size.

     • For a rarefaction curve: subsamples of all sizes ≤ the standardized size.

  3. Calculate the average number of species in each subsample.

  4. Plot a rarefaction curve (X = sample size, Y = average species richness).

• Compare richness at the same standardized effort to determine true differences.

α- and β-Diversity & Body Size

1. α-Diversity (local richness)

• Larger-bodied species have larger home ranges.

• To capture the true local richness (α-diversity), the sampling area must be larger.

• Smaller species → small home ranges → small sampling area is sufficient.

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2. β-Diversity (turnover)

• Larger-bodied species can disperse farther.

• Nearby communities are more likely to share the same species, so turnover is lower at small spatial scales.

• To observe meaningful β-diversity patterns, you must sample over larger spatial scales.

• Smaller-bodied species → limited dispersal → higher turnover at finer scales.

Top-Down Regulation & Trophic Cascade

Top-Down Regulation: predators control herbivore population size rather than resources.

Trophic Cascade: effects of predators propagate through lower trophic levels.

• Example: fewer herbivores → less plant damage → plants can invest more in growth and competition rather than defense.

Bottom-up regulation

• Definition: Population sizes are limited by resources at the base of the food web, usually plants or primary producers.

• Mechanism:

  • Scarce or low-quality plants

  • Plants with stronger defense mechanisms
    → fewer herbivores → fewer predators.

• Specialists: more affected because they rely on a narrow set of resources; plant defenses or scarcity strongly impact their populations.

Trophic Level, Body Size, Population Density, & Extinction Risk

• Higher trophic levels → greater energetic limitation → larger home ranges, lower population densities, higher extinction risk

• Body size is not equivalent to trophic level; herbivores and carnivores span wide size ranges

• Home range size often increases with body size and energetic demands

Climate Change & Ecological Communities – Species Responses

1. Extinction

• Species fail to survive under new climate conditions.

• Evidence: fossil record (past climate-driven extinctions), contemporary declines, model forecasts.

• High risk: specialists, low-dispersal species, narrow thermal tolerance.

2. Geographic Range Shifts

• Species move to track suitable climates.

  • Upslope: higher elevations (limited by mountain height).

  • Poleward: higher latitudes (cooler areas).

• Evidence: contemporary (plants, butterflies, birds), fossil record (glacial-interglacial cycles).

3. Evolutionary Adaptation

• Populations genetically adapt to new conditions if heritable variation and strong selection exist.

• Evidence: phenology shifts, thermal tolerance changes in some plants, insects, birds.

• Limitation: slow adaptation in long-lived species or low genetic diversity.

What is ecosystem ecology?study of the cycling of nutrients and the flow of energy through
systems

cycling of nutrients and flow of energy through systems

What is biodiversity, richness, and evenness?

Biodiversity: variety of life

Richness: # of species

Evenness: relative abundance of species

What is Equilibrium Theory of Island Biogeography? + what does it say about isolation + area

• species richness is a dynamic equilibrium btwn colonization + extinction rate

• as island area increases: pop. size increases, species richness increases, extinction decreases

• as island isolation increases: colonization rate decreases, species richness decreases, endemic species increase

What is the ETIB graphical model? Assumptions?

• x-axis: species richness; y-axis: colonization + extinction rate (colonization decreases w/ inc. species richness; extinction rate inc. w/ inc. species richness

• Assumptions:

  • distance from mainland determines isolation

  • no speciation, new species only through colonization

  • island area predicts extinction

  • constant environment

Why is isolation effect in ETIB less reliable than area effect?

• dispersal ability varies among species and environments

• Ex: mountains have high richness despite isolation (high spatial heterogeneity)

How does island age impact richness?

1. Young islands: low richness

   1. low colonization rate due to fewer resources/niches

2. Intermediate age: highest richness

   1. high colonization; lots of resources + niches available

3. Old: low richness

   1. high extinction rate as island erodes + resources become more limited

What dictates species richness on continents?

1. Spatial heterogeneity: more niches

2. Climate stability: less extinction, more time to adapt and diversify

3. Energy (NPP)

   1. species -energy theory: more energy means more species

   2. **Not entirely supported: doesnt explain all patterns, likely not only factor

Why is diversity hard to quantify?

• unequal sampling effort!

• species-accumulation curve (x: # of individuals sampled; y: # of species identified)

  • increases then plateaus

• proportions is not a good way to correct for this: relationship btwn effort + species identified is NOT linear!!

• RAREFACTION!!!!!!

Rank-abundance curve

• x: rank (most abundant = 1; least abundant = higher ##)

• y: relative species abundance

• more flat slope = more evenness

• longer slope/line = more richness

What is alpha, beta, and gamma diversity?

Alpha: local, homogenous community

Beta: across mult. communities (species turnover/diff. of species btwn them)

Gamma: across large regions

What is NEE? What does it mean when it is negative/positive?

NEE: Net ecosystem exchange (consumer resp. - NPP)

• indicates direction + magnitude of CO2 exchange btwn land + atmosphere

• negative NEE = more stored carbon than lost (stored in lignin + soil)

What are the direct biological effects of increased CO2 on terrestrial systems?

1. Increased NPP: higher CO₂ can boost photosynthesis and plant growth, but only if nutrients (N, P) are not limiting.

2. C3 vs C4 plants:

   • C3 plants (~90% of species) are better adapted to elevated CO₂ because their photosynthesis is normally limited by CO₂; at low CO₂, O₂ competes with CO₂ for Rubisco.

   • C4 plants: have a CO₂-concentrating mechanism in which CO₂ is first fixed into a 4-carbon compound in mesophyll cells and then delivered to bundle sheath cells for photosynthesis. This allows them to thrive in low CO₂, high temperature, and high light conditions. Because of this mechanism, C4 plants are less responsive to elevated CO₂.

3. Implication: C3 species may increase in growth and potentially richness relative to C4 species under elevated CO₂.

C3 Plants under Elevated CO₂ (+ Rubisco)

1. Rubisco adjustment: C3 plants rely on Rubisco for CO₂ fixation and are normally limited by CO₂ availability.

   • Elevated CO₂ allows Rubisco to operate efficiently → plants decrease Rubisco production.

2. Nitrogen demand: Rubisco contains a lot of nitrogen. Less Rubisco → lower nitrogen requirements.

3. Carbon fixation: More CO₂ available → more carbon is fixed overall, increasing biomass.

4. C:N ratio: Because carbon accumulation outpaces nitrogen, C:N ratio increases.

Key takeaway for C3 plants: They are more responsive to elevated CO₂ than C4 plants because they can increase carbon gain while reducing nitrogen investment in Rubisco.

• more efficient + fix more carbon

• This is an adaptive response that is potentially beneficial for the individual plant's resource optimization but is detrimental to the consumers of those plants

How increased CO2 affects oceans

• ocean acidification:

  • co2 reacts w/ carbonate → bicarbonate

  • inhibits formation of calcium based shells in organisms

Why are no-analog communities sometimes cited as evidence that species sorting and niche segregation are not important in determining community composition?

If species sorting and niche segregation were important, it would be expected that communities would remain similar over time, as coexisting species have adaptations to specific niches that allow them to coexist with each other but not with other species outside of their community. Since no-analog communities exist, this indicates that species can respond to changing conditions differently than species they previously coexisted with. These species disperse to and persist in communities that match their abiotic niche requirements regardless of what species from their previous community do, suggesting that under rapidly changing environmental conditions, species’ niches are influenced more by abiotic factors than by the species they previously coexisted with.