Introductory Ecology, Evolution, and Population Biology: Key Concepts

What are the traits of life?

Cells, energy use/metabolism, growth and development, reproduction, homeostasis, response to the environment, evolution

Why are viruses considered not quite alive?

They have genetic material and evolve, but lack cells and their own metabolism, and can't reproduce without a host.

What is a null hypothesis?

No relationship between the variables being tested.

What is an alternate hypothesis?

Specifies a relationship between the variables being tested.

What is the difference between a predictor variable and a response variable?

Predictor = what is manipulated; response = the effect measured.

Why isn't a hypothesis confirmed by one supporting result?

One result could be chance; results must be replicated and tested repeatedly.

What is ecology?

The study of interactions among organisms and between organisms and their environment.

What is evolution?

Change in the genetic properties of populations that transcends the lifetime of a single individual.

How do ecology and evolution influence each other?

Ecology shapes selection pressures; evolutionary history shapes the traits of the organisms present in an ecosystem.

In the mutualism between coral and algae, how does each partner benefit?

Coral gives the algae protection and structure; algae give the coral sugars from photosynthesis.

What does the coral chlorophyll ratio indicate?

Chlorophyll in heat-stressed corals divided by chlorophyll in control corals; higher ratio = less bleaching.

What is the taxonomic hierarchy from broad to specific?

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

If two species are in the same family, are they necessarily in the same genus?

Might be true (not necessarily).

If two species are in the same family, are they necessarily in the same order or kingdom?

Must be true (higher levels include them).

What are the levels of biodiversity?

Genetic, species, plasticity, higher taxa, functional groups, habitat/ecosystem.

What is species richness?

The total number of species present.

What is species evenness?

How equal the relative abundances of the species are.

Why does evenness matter if a dominant species is lost?

A community dominated by one species loses most of its individuals and function; an even community is more resilient.

What is a species accumulation curve?

Cumulative species found vs cumulative area sampled; once it levels off you've probably sampled enough to capture richness.

Which group has the most described species?

Insects (about 1 million of ~2 million named animal species).

What are hypotheses for why insects are so diverse?

Short generation times; small body size allows specialization on different resources.

What is the latitudinal diversity gradient?

Species richness is highest near the equator and decreases toward the poles.

Why are the tropics more diverse?

Warm, wet, productive, stable climate with low seasonality supports more species and specialization.

What is a biodiversity hotspot?

Region with many endemic species and high habitat loss.

What are endemic species?

Species found only in one particular region.

What is the difference between weather and climate?

Weather = short-term atmospheric conditions; climate = long-term average patterns.

Why doesn't one cold week disprove global warming?

That's weather (short-term); climate refers to long-term averages.

How do greenhouse gases warm the Earth?

They absorb outgoing infrared radiation and re-emit some back toward the surface.

What effect does a more reflective Earth have on the energy budget?

Less incoming solar energy, so less becomes infrared that is trapped.

What causes the seasons?

Earth's axial tilt.

What is the evidence against the idea that 'seasons come from distance to the sun'?

Hemispheres have opposite seasons at the same time.

What is the difference between an equinox and a solstice?

Equinox: axis tilted neither toward nor away, even energy; solstice: axis tilted toward or away from the sun.

What is the rain shadow effect?

Moist air rises on the windward side, cools, holds less water, and rains; descending air on the leeward side warms and is dry.

What is the difference between the windward and leeward sides?

Windward = faces incoming wind, wet; leeward = sheltered side, dry.

What evidence suggests humans caused the CO2 rise?

CO2 far above the past several hundred thousand years, plus a carbon isotope signature matching fossil fuels.

How do greenhouse gases relate to larger wildfires?

More GHGs lead to warming, drier fuels, earlier snowmelt, longer fire season, and larger fires.

What is a non-climate factor affecting wildfire size?

Fuel buildup from fire suppression.

What do the axes of a climatograph represent?

Gray line = temperature (left axis); black bars = precipitation in mm (right axis).

What are the units of precipitation in a climatograph?

Millimeters (not centimeters).

What are three questions for any climatograph?

1) How warm are summers/how cold are winters? 2) How much water in total? 3) When does the water come?

What characterizes a tundra climatograph?

Warmest month below about 10 C, too cold for trees, low precipitation.

What characterizes a boreal forest climatograph?

Long freezing winters, summers warm enough for trees, about 300 mm/yr.

What characterizes a desert climatograph?

Less than about 250 mm/yr precipitation.

What characterizes a temperate grassland climatograph?

Moderate precipitation, seasonal temperatures.

What characterizes a temperate deciduous forest climatograph?

Plenty of precipitation spread through the year, seasonal temperatures.

What characterizes a Mediterranean climatograph?

Mild wet winters, hot dry summers, rain and warmth out of sync, rarely freezing.

What characterizes a tropical rainforest climatograph?

Warm and wet all year with little seasonality.

How can you determine the hemisphere from a climatograph?

Warmest Jun-Aug = Northern; warmest Dec-Feb = Southern.

What is the principle of allocation?

Organisms have limited resources; resources used for one function can't be used for another.

What is an example of a trade-off in resource allocation?

Many small offspring or few large ones, since the parent's resources are limited.

What does semelparous mean?

Reproduces once and then dies.

What does iteroparous mean?

Reproduces many times.

When does investing everything in reproduction pay off?

When the chances of reproducing again are low.

What is the root:shoot ratio?

Biomass in roots divided by biomass in shoots.

What happens to the root:shoot ratio in nutrient-poor soil?

Increases (more roots); cost is less light capture/growth above ground.

What happens to the root:shoot ratio in water-stressed plants?

Increases (more resources to roots).

What happens to the root:shoot ratio with extra nitrogen supply?

Decreases (fewer roots needed, more shoots).

What are r-selected traits?

Small, short-lived, fast growth, early reproduction, many small offspring, little parental care.

What are K-selected traits?

Large, long-lived, slow growth, delayed reproduction, few large offspring, high parental care.

How is population size controlled by r vs K?

r-selected: controlled by growth rate; K-selected: controlled by carrying capacity.

What is an ectotherm?

Body temperature controlled mainly by external conditions.

What is an endotherm?

Body temperature controlled mainly by metabolic energy.

Does an ectotherm's body temperature always match its environment?

No, it can move to warmer or cooler spots to regulate.

What is acclimation?

Phenotype change within an individual; short-term and reversible.

What is adaptation?

Genotype change across generations by natural selection; long-term.

What are the criteria to tell acclimation from adaptation?

Time scale, reversibility, whether it is heritable.

What is Bergmann's rule?

Body size is larger in colder habitats.

What is Allen's rule?

Limbs and extremities are shorter in colder habitats.

How does surface area to volume ratio relate to heat?

Larger bodies have a lower SA:V and lose less heat; smaller bodies have a higher SA:V and lose more.

Why is a spherical body better for staying warm?

Less surface area for the same mass, so less heat loss.

What is the trade-off of evaporative cooling?

Increased risk of dehydration.

What is the trade-off of opening stomata?

CO2 uptake for photosynthesis vs water loss.

What is a fundamental niche?

The range of conditions a species could survive and reproduce in, based on its physiology alone.

What is a realized niche?

Where a species actually lives after competition, dispersal, and history.

What happens to the realized niche when a competitor is removed?

It may expand to fill the available space.

What is the difference between abiotic and biotic limits on range?

Abiotic limits include temperature and precipitation (fundamental niche); biotic limits include competition and predators (realized niche).

What is the difference between autotrophs and heterotrophs?

Autotrophs make their own food (photo- or chemoautotrophs); heterotrophs eat others (herbivores, carnivores, detritivores).

What does Liebig's Law of the Minimum state?

Growth is limited by the resource that is scarcest relative to need, not by total resources.

How can you identify the limiting nutrient in an enrichment experiment?

It is the nutrient whose addition causes the largest growth increase relative to the control.

Why don't treatments below the control tell you the limiting nutrient?

Lower growth means it isn't limiting (or is harmful); limiting means adding it boosts growth.

What does overlapping error bars between treatment and control indicate?

You can't conclude a real difference; it could be due to chance.

What does a clear gap between error bars suggest?

The treatments probably differ.

What is optimal foraging theory?

Selection favors foraging decisions that maximize net energy gain per unit time.

How is the profitability of a prey item calculated?

Energy content divided by handling time (E/h).

When should a predator eat small prey?

Only when big prey are rare (when the rate from big prey drops below the small prey's profitability).

Why might a forager skip the most energy-rich food?

Long handling or travel time can make it less profitable per second.

What are rhizobia?

Nitrogen-fixing bacteria in legume root nodules; the plant gives sugar and gets nitrogen.

What are mycorrhizal fungi?

Fungi extending into soil to acquire phosphorus and other nutrients; the plant gives sugar.

What is the trade-off of mutualisms for plants?

Carbon spent on the partner can't be used for roots or leaves; worthwhile in poor soil, less so in rich soil.

What is osmoregulation?

Maintaining the proper balance of water and salt in the body.

What does hypertonic, hypotonic, and isotonic mean?

Hypertonic: higher solute concentration; hypotonic: lower solute concentration; isotonic: equal, relative to another solution.

In marine fish, seawater is ___ and water moves ___ the fish.

Hypertonic; out of.

How do marine fish cope with their environment?

They drink seawater, excrete salt through gills, and make small amounts of concentrated urine.

In freshwater fish, the environment is ___ and water moves ___ the fish.

Hypotonic; into.

How do freshwater fish cope with their environment?

They don't drink, take up salts through gills, and make lots of dilute urine.

What are anadromous fish?

Fish that live in the ocean and migrate to freshwater to reproduce; they must switch osmoregulatory strategy.

What is the exponential growth equation?

Nt = N0 e^(rt).

What is the logistic growth equation?

Nt = K / [1 + ((K - N0)/N0) e^(-rt)].

What is intrinsic rate of increase (r)?

Per-capita births minus deaths per unit time; r>0 indicates growth, 0 indicates stability,

How is doubling time calculated in exponential growth?

Doubling time = ln(2) / r.