Key terms
134 terms- Ecology§54.1
- The study of how organisms relate to one another and to their environments
- Homeostasis§54.1
- Maintenance of a steady-state internal environment despite external variation
- Conformer§54.1
- An organism whose body adopts the temperature, salinity, and other properties of its surroundings
- Endotherm§54.1
- An animal that maintains a constant internal temperature
- Altitude sickness§54.1
- Palpitations, nausea, fatigue, headache, and in severe cases pulmonary edema at high elevation
- Acclimation to altitude§54.1
- Faster breathing, more erythrocytes, easier oxygen unloading, denser mitochondria and myoglobin
- Myoglobin§54.1
- Oxygen-binding muscle protein whose density increases at high elevation
- Glycerol antifreeze§54.1
- Solute some insects add to their blood to avoid freezing in winter
- Norm of reaction§54.1
- The ability of one genotype to produce multiple phenotypes in different environments
- Phenotypic plasticity§54.1
- Nongenetic flexibility of a trait; not all traits are plastic, because flexibility has a cost
- Predator-induced defense§54.1
- Thicker snail shells, Daphnia spines, and thicker tadpole tails triggered by predator scent
- Allen's rule§54.1
- Mammals from colder climates have shorter ears and limbs, reducing heat-losing surface area
- Fog-basking beetle§54.1
- Namib Desert beetle that raises its abdomen on a dune so fog condenses and runs to its mouth
- Spadefoot toad§54.1
- Toad that burrows nearly a meter down for up to nine months with reduced metabolism
- Tibetan altitude mutations§54.1
- Two oxygen-uptake gene mutations at high frequency in highlanders but not lowlanders
- Population§54.2
- A group of individuals of one species occurring together at one place and time
- Population range§54.2
- The area throughout which a population occurs
- Devil's Hole pupfish§54.2
- Fish confined to a single Nevada spring — the smallest range of any vertebrate
- Socorro isopod§54.2
- Crustacean known from a single New Mexico spring system
- Range expansion§54.2
- Growth of a range as climate changes or as populations colonize new suitable areas
- Altitudinal shift§54.2
- Upward movement of cold-adapted species as climate warms, seen in southwestern mountain trees
- Cattle egret§54.2
- African bird that crossed ~3500 km of Atlantic in the late 1800s and spread across the Americas
- Starling introduction§54.2
- 100 birds released in New York City in 1896 that occupied the whole United States by 1980
- Dispersal§54.2
- Movement of individuals, eggs, or seeds to new areas, occasionally founding new populations
- Windblown fruit§54.2
- Seed adapted for long-distance wind transport, as in milkweed and maple
- Adherent fruit§54.2
- Seed with structures that stick to fur or feathers and are carried away
- Fleshy fruit§54.2
- Seed enclosed in edible tissue that passes through a gut and germinates where defecated
- Random spacing§54.2
- Distribution with no strong interactions and no environmental patchiness; uncommon in nature
- Uniform spacing§54.2
- Even distribution, usually produced by competition or territoriality
- Clumped spacing§54.2
- Clustered distribution from patchy resources or social grouping; the most common pattern
- Territory§54.2
- Defended area giving its owner exclusive access to food, water, refuges, or mates
- Creosote bush§54.2
- Desert shrub that releases soil chemicals toxic to its own species, enforcing uniform spacing
- Interior density§54.2
- The tendency for populations to be densest in the range interior and thin toward the edges
- Metapopulation§54.2
- A network of distinct populations that exchange individuals across patchy habitat
- Source population§54.2
- A population in good habitat that maintains itself and exports dispersers
- Sink population§54.2
- A population in poor habitat with negative growth that persists only on immigration
- Source–sink metapopulation§54.2
- Metapopulation in which sources continually bolster sinks
- Colonization rate§54.2
- Rate at which empty suitable patches are recolonized by dispersers
- Extinction rate§54.2
- Rate at which existing local populations wink out; balanced against colonization at equilibrium
- Glanville fritillary§54.2
- Finnish butterfly studied across 1600 meadows: ~200 extinctions vs 114 colonizations per year
- Habitat fragmentation§54.2
- Breaking continuous habitat into patches, which makes metapopulation theory central to conservation
- Population dynamics§54.3
- How a population changes in size through time
- Demography§54.3
- The quantitative study of populations
- Age distribution§54.3
- The proportions of a population that are adults, juveniles, and young
- Sex ratio§54.3
- Proportion of males to females; matters most for growth in monogamous species
- Generation time§54.3
- Average interval between the birth of an individual and the birth of its offspring
- Cohort§54.3
- A group of individuals of the same age
- Fecundity rate§54.3
- A cohort's birth rate — offspring produced per standard time period
- Mortality rate§54.3
- Proportion of individuals alive at the start of an interval that die by its end
- Age structure§54.3
- The relative number of individuals in each cohort of a population
- Life table§54.3
- A table tabulating the fate of a cohort from birth to death, interval by interval
- Annual bluegrass§54.3
- Poa annua; the 843-seedling cohort used for the chapter's life table
- Break-even value§54.3
- A total of 1.0 offspring per original cohort member — neither growth nor decline
- Cross-sectional study§54.3
- Substitute for a full cohort study: sample cohorts of different ages in one period
- Survivorship§54.3
- The percentage of an original population that survives to a given age
- Survivorship curve§54.3
- Plot of survivorship against age, drawn on a log axis so constant mortality is a straight line
- Type I survivorship§54.3
- Mortality rises steeply late in life; humans
- Type II survivorship§54.3
- Equal probability of dying at any age, giving a straight line; hydra
- Type III survivorship§54.3
- Huge early mortality, then very low mortality once established; oysters
- Life history§54.4
- The complete life cycle of an organism, built entirely from trade-offs
- Resource allocation§54.4
- Dividing limited resources between current reproduction and future survival and reproduction
- Cost of reproduction§54.4
- Reduction in future reproductive potential caused by current reproductive effort
- Douglas fir cone trade-off§54.4
- More cones now means slower growth and, because cones scale with size, fewer cones later
- Collared flycatcher experiment§54.4
- Adding eggs cut next year's clutch; removing eggs increased it
- Clutch size§54.4
- The number of eggs produced in one breeding event
- Great tit trade-off§54.4
- Nestling size falls as clutch size rises — more mouths, less per mouth
- Side-blotched lizard experiment§54.4
- Removing follicles gave 1–3 larger, better-provisioned eggs instead of 4–5
- Offspring size§54.4
- Investment per offspring; larger offspring survive better, so an intermediate number is optimal
- Lifetime reproductive success§54.4
- Total surviving offspring over a life; the quantity natural selection maximizes
- Semelparity§54.4
- All reproductive resources spent in one large event, after which the organism dies
- Big bang reproduction§54.4
- Nickname for semelparity, exemplified by annual plants, most insects, and Pacific salmon
- Iteroparity§54.4
- Producing offspring several times over many seasons
- Age at first reproduction§54.4
- Trait that correlates with life span — longer-lived species delay reproduction longer
- Delayed reproduction§54.4
- Waiting to breed so juveniles gain experience and grow larger before paying reproductive costs
- Rate of population increase (r)§54.5
- r = (b − d) + (i − e): births minus deaths, corrected for immigration and emigration
- Immigration (i)§54.5
- Rate of movement of individuals into the area
- Emigration (e)§54.5
- Rate of movement of individuals out of the area
- Biotic potential§54.5
- The rate at which a population increases when nothing limits its growth
- Intrinsic rate of natural increase (rᵢ)§54.5
- A population's innate capacity for growth, used in dN/dt = rᵢN
- Exponential growth§54.5
- dN/dt = rᵢN; numbers accelerate even though r stays constant, giving a J-curve
- Population explosion§54.5
- The outcome of unchecked exponential growth
- Carrying capacity (K)§54.5
- The maximum number of individuals the environment can support
- Logistic growth equation§54.5
- dN/dt = rN[(K − N)/K]; rN scaled by the fraction of K still unused
- Sigmoidal growth curve§54.5
- The S-shaped plot of N versus time produced by logistic growth
- Equilibrium population§54.5
- A population expected to sit at or near K most of the time
- Overshoot§54.5
- Exceeding K so that K − N is negative and growth turns negative until N falls back to K
- Fur seal population§54.5
- St. Paul Island, Alaska breeding males — a natural population that fits the logistic curve
- Density-dependent factor§54.6
- A factor whose effect on the population depends on population size
- Density-independent factor§54.6
- A factor such as a natural disaster that acts regardless of population size
- Negative feedback§54.6
- Rising density lowering reproductive rates or raising mortality rates, or both
- Equilibrium population density§54.6
- The density where the birth-rate and death-rate curves cross
- Song sparrow study§54.6
- Mandarte Island data: young per female falls and juvenile mortality rises as adults increase
- Toxic waste accumulation§54.6
- Density-dependent buildup of harmful metabolic products at high density
- Density-dependent emigration§54.6
- Crowding driving individuals to leave, as in swarming migratory locusts
- Allee effect§54.6
- Density dependence in which growth rate increases with population size — positive feedback
- Positive feedback§54.6
- Amplifying response; illustrated in population ecology by the Allee effect
- Population cycle§54.6
- Repeating increase and decrease rather than settling at an equilibrium size
- Snowshoe hare§54.6
- Lepus americanus; its "10-year" (really 8–11 year) cycle swings numbers 10- to 30-fold
- Canada lynx§54.6
- Lynx canadensis; its abundance cycle tracks the hare cycle but lags slightly behind it
- Krebs experiment§54.6
- Yukon plots showing the hare cycle disappears only when food is added AND predators excluded
- Moth pupae study§54.6
- Four German moth species fluctuating in concert — evidence of density-independent control
- r-selected§54.6
- Adapted to populations far below K: many small offspring, early reproduction, short life, no care
- K-selected§54.6
- Adapted to populations near K: few large offspring, delayed reproduction, long life, parental care
- r–K continuum§54.6
- The reality that most species blend r and K traits rather than being purely one or the other
- Population pyramid§54.7
- Bar graph of numbers in each age class, males left of the axis and females right
- Rectangular pyramid§54.7
- Shape of a stable population, neither growing nor shrinking (Sweden)
- Triangular pyramid§54.7
- Broad-based shape predicting rapid growth as a large young cohort matures (Kenya)
- Inverted pyramid§54.7
- Shape of a shrinking population, usually from sharply declining birth rates
- Fertility rate§54.7
- Offspring per woman; 1.9 in Sweden versus 3.5 in Kenya
- Doubling time§54.7
- Years for a population to double at its current rate — 63 years for the world at 1.1%
- Baby boom§54.7
- The mid-20th-century birth surge visible as a middle-aged bulge in Sweden's pyramid
- Industrial Revolution§54.7
- The 1800s turning point after which the human death rate fell long-term
- Biosphere§54.7
- The world's interacting community of living things
- Ecological footprint§54.7
- Productive land needed to support one person's lifetime standard of living, including CO₂ absorption
- Per capita consumption§54.7
- Resource use per person; the richest 20% consume 86% of resources
- Family planning effect§54.7
- Kenyan programs cut fertility from 8.0 to 3.5 and growth from 4.0% to 2.3% per year
- Pandemic§54.8
- A disease outbreak extending over multiple countries and even continents
- Epidemic§54.8
- A more localized disease outbreak
- Reproduction number (R₀)§54.8
- Average number of new individuals infected by each infected individual
- Zoonotic disease§54.8
- Disease arising when a pathogen moves from one species into another
- Transmission rate§54.8
- How readily a pathogen passes between hosts; the key to disease dynamics
- Superspreader§54.8
- An individual who transmits far more than average — 10% of cases caused 80% of infections
- Herd immunity§54.8
- Enough of the population immune (often ≥70%) that the pathogen stops spreading
- Asymptomatic infection§54.8
- Infection without symptoms; 40–50% of COVID-19 infections
- Chestnut blight§54.8
- Asian fungus introduced in 1904 that destroyed the American chestnut
- Rinderpest§54.8
- Cattle virus that devastated African livestock and wildlife, later eliminated by vaccine
- Myxoma virus§54.8
- Virus that killed >99% of Australian rabbits, then evolved to be less lethal
- Yersinia pestis§54.8
- Bacterium causing bubonic plague, spread by fleas and by contact
- Black Death§54.8
- The worst plague outbreak, killing a third of Europe in the fourteenth century
- Spanish flu§54.8
- Influenza pandemic that killed more than 50 million people in 1918–19
- Delta variant§54.8
- More contagious SARS-CoV-2 variant of 2021 with an estimated R₀ of 6 to 9
- Nipah virus§54.8
- Bat- and pig-borne virus that kills 40%+ of victims but has R₀ ≈ 0.48, so outbreaks stay small
- HA and NA proteins§54.8
- Influenza surface proteins whose mutation lets the virus escape acquired immunity
- Vaccine§54.8
- Route to widespread immunity without infection; eliminated smallpox and rinderpest