All Key Terms

Ecological Community

A group of interacting species living in the same place at the same time, linked by shared environment and species interactions.

Community Ecology

The branch of ecology that examines how species interactions and the abiotic environment shape biodiversity and community structure.

Trophic Interactions

Feeding relationships among species (e.g., predator–prey, herbivory) that determine energy flow and community organization.

Keystone species

A species whose effect on community structure is disproportionately large relative to its abundance.

Succession

Directional change in community composition and structure over time following disturbance or habitat formation.

Primary Succession

Succession beginning on previously lifeless substrates (e.g., rock, lava, glacial till), where soil and nutrients must first accumulate.

Secondary Succession

Succession occurring after a disturbance that leaves soil and some organisms or seeds intact, resulting in faster recovery.

Climax Community

A theoretical stable end-stage of succession characterized by a persistent community until disrupted by disturbance.

Biogeography

Study of how species and communities are distributed across space and time, and the processes shaping those patterns.

Species Richness

The total number of species present in a community; a basic measure of biodiversity.

Dispersal

Movement of individuals or propagules from one location to another, influencing colonization, gene flow, and community assembly.

Vicariance

Geographic separation of populations by a physical barrier (e.g., mountains, landmass fragmentation), often leading to speciation.

Disturbance

A discrete event that kills or removes organisms and alters resource availability, often initiating succession.

Community Structure

The composition and relative abundances of species within a community, including diversity and trophic relationships.

Bottom-up Control

When the availability of resources (nutrients, primary production) regulates the abundance and diversity of higher trophic levels.

Top-down Control

When consumers at higher trophic levels (e.g., predators) regulate the structure and abundance of lower trophic levels.

adaptation

heritable trait that increases fitness under specific environmental conditions

acclimation

reversible physiological adjustment to environmental change within an individual’s lifetime

phenotype

observable traits of an organism, influenced by genotype and environment

genotype

genetic makeup of an organism at one or more loci

fitness

relative reproductive success of a genotype or phenotype

natural selection

differential survival and reproduction due to heritable trat variation

directional selection

selection that favors one extreme of a trait distribution

stabilizing selection

selection that favors intermediate trait values, reducing variance

disruptive selection

selection that favors extreme trait values over intermediates

heritability

proportion of phenotypic variance attributable to genetic variance

tradeoff

constraints where improving one trait reduces performance in another

life history

schedule of growth, reproduction, and survival across an organisim’s life

semelparity

single, often large, reproductive event in a lifetime. often results in death for the parent immediately after

iteroparity

multiple reproductive events over a lifetime

age at maturity

age when an organism first reproduces

fecundity

number of offspring produced per reproductive event

parity

number of reproductive episodes across a lifetime

longevitiy

typical lifespan under natural conditions

resource allocation

distribution of energy among growth, maintenance, and reproduction

r and k selection

historical framework contrasting high reproduction vs efficiency near carrying capacity

Population

Group of individuals of the same species in a defined area.

Abundance

Number of individuals in a population.

Density

Number of individuals per unit area or volume.

Geometric growth

Discrete-time population growth with constant λ each time step.

Exponential growth

Continuous-time growth at constant per-capita rate r.

Intrinsic rate of increase

Per-capita instantaneous growth rate of a population.

Finite rate of increase

Growth multiplier per time step.

Logistic growth

Growth limited by carrying capacity.

Carrying capacity

Maximum sustainable population size in given environment.

Density dependence

Demographic rates change with population density.

Density independence

Demographic rates unaffected by population density.

Demographic stochasticity

Random variation in births and deaths among individuals.

Environmental stochasticity

Random environmental variation affecting population growth rates.

Life table

Tabulation of age-specific survival and reproduction.

Survivorship curve

Graph of survivorship by age (Type I-III)

Cohort

Group of individuals born in the same time period.

Generation time

Average age of parents when offspring are born.

Net reproductive rate

Average number of daughters per female across life.

Metapopulation

Set of local populations connected by dispersal.

Source-sink dynamics

High equality patches export individuals; low-quality patches depend on immigrants.

Rescue effect

Immigration prevents local extinction.

Dispersal

Movement of individuals from birthplace or among populations.

Competition

Negative interaction where species share limiting resources.

Exploitative competition

Indirect competition via resource depletion.

Interference competition

Direct antagonistic interactions over resources.

Apparent competition

Two species negatively affect each other via shared enemy.

Competitive exclusion

Two species competing for identical resource cannot stably coexist.

Niche (fundamental)

Abiotic and biotic conditions a species could occupy without interactions.

Niche (realized)

Conditions actually occupied given biotic interactions.

Resource partitioning

Differential use of resources reduces competition.

Predation

One organism consumes another (prey).

Functional response

Change in predator consumption rate with prey density (Type I-III).

Numerical response

Change in predator abundance with prey density.

Handling time

Time required to pursue

Refugia

Places/times where prey experience reduced predation risk.

Parasitism

One organism lives on/in host

Macroparasite

Parasite with multiple life stages and variable parasite load (e.g.

Microparasite

Parasite that multiplies within host (e.g.

Virulence

Degree of harm a parasite causes to its host.

Host resistance

Ability to prevent or clear infection.

Host tolerance

Ability to reduce fitness costs of a given infection.

Mutualism

Interaction where both partners benefit.

Obligate mutualism

Partners cannot survive or reproduce without each other.

Facultative mutualism

Partners benefit but can persist alone.

Symbiosis

Close, often long-term interaction between different species.

Cheating

Partner gains benefit without reciprocating in mutualism.

alpha diversity

the richness within a single habitat

beta diversity

the difference or species turnover between habitats

gamma diversity

the total richness across a larger region