Ecology, Species Interactions, and Evolution

Vocabulary practice flashcards covering mutualism-parasitism continua, community ecology concepts, species interactions, mechanisms of succession, and principles of evolutionary genetics.

Carrying Capacity ($K$)

The maximum population size of a species, or the maximum biomass of an organism, that can be sustained by its environment.

Equilibrium (Population Ecology)

The state in which a population size or biomass does not change over time, occurring when change in host biomass ($\Delta\text{host biomass} = 0$) and change in partner biomass ($\Delta\text{fungal biomass} = 0$) both equal zero.

Exploitation (Species Interaction)

A pairwise interaction ($+/-$) in which the fitness of one organism is reduced at the expense of another.

Mutualism

A pairwise species interaction ($+/+$) in which both interacting organisms benefit from the relationship.

Plant–Mycorrhizal Association

A widespread belowground association found in approximately $90\%$ of plant species where plants provide sugars and fats to fungi in exchange for soil nutrients such as nitrogen and phosphorus.

Mutualism–Parasitism Continuum

The conceptual model showing that ecological interactions can shift depending on net cost-benefit balances; for example, mycorrhizal associations become mutualistic when benefits exceed costs ($H > K$) and parasitic when costs to the plant outweigh benefits ($H < K$).

Fungal Necromass

Dead fungal biomass that persists in the soil, acting as a major global reservoir for sequestered carbon.

Ecology

The scientific study of the interactions of living organisms with their biotic and abiotic environment, and the effects of those interactions on the distribution and abundance of organisms.

Community

Groups of populations of different species living together in the same location.

Community Ecology

The study of interactions between species in ecological communities.

Facilitation

An ecological interaction between species in which at least one species benefits and no species is harmed ($0/+$ or $+/+$).

Facultative Mutualism

A mutualistic interaction that is beneficial to the participating organisms but not strictly necessary for the survival of either species.

Obligate Mutualism

A mutualistic interaction that is strictly necessary for the survival and reproduction of one or both species.

Commensalism

A species interaction in which one organism benefits while the other organism experiences neither benefit nor harm ($0/+$).

Consumption

An ecological interaction ($+/-$) that involves the ingestion of all or part of another organism, categorized into predation, parasitism, and herbivory.

Competition

An interaction between species ($-/-$) brought about by shared requirements for a resource that is present in limited supply.

Exploitation Competition

A competitive interaction mediated indirectly by the mutual use and depletion of a shared resource.

Interference Competition

A direct competitive interaction characterized by antagonistic encounters between organisms.

Apparent Competition

An indirect negative interaction between two prey species that resembles competition, caused by a shared predator whose population increases when either prey becomes more abundant.

Indirect Effect

The effect of one species on another species mediated via one or more intermediate species.

Biodiversity

A contraction of biological diversity defined as the variety of life at all levels of biological organization, including ecosystem, species, genetic, and molecular diversity.

Biodiversity Hotspot

A biogeographic region that covers only $2.3\%$ of Earth's land surface but contains $42\%$ of terrestrial vertebrate species and $50\%$ of plant species.

Species Richness ($S$)

The total number of distinct species present in an ecological community.

Species Evenness ($J$)

The distribution of abundance across different species within an ecological community, bounded between $0 < J < 1$.

Shannon Diversity Index ($H'$)

A mathematical index that combines species richness ($S$) and evenness ($J$) to quantify community diversity, where $0 < H' < \ln(S)$.

Disturbance

Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment.

Succession

The directional change in species composition over time within an ecological community in response to disturbance or stress.

Primary Succession

Successional change that occurs in newly exposed areas devoid of pre-existing life and organic soil following catastrophic disturbance.

Secondary Succession

Successional change that occurs after non-catastrophic disturbances in habitats where some living organisms and soil remain.

Grime's CSR Strategy Theory

A plant life-history classification model based on three strategies: Competitive ($C$) plants adapted to low stress and low disturbance, Stress-tolerant ($S$) plants adapted to high stress and low disturbance, and Ruderal ($R$) plants adapted to high disturbance and low stress.

Inhibition (Mechanism of Succession)

A mechanism in which early colonizers occupy space and prevent any subsequent species from colonizing until the established individuals die.

Tolerance (Mechanism of Succession)

A mechanism in which late-successional species establish because they are superior competitors capable of tolerating resource levels reduced by early species.

Primary Producer

An autotrophic organism, typically photosynthetic, that occupies the base trophic level of an ecosystem and supports all other trophic levels.

Detritivore

A consumer organism that derives energy by breaking down nonliving organic matter and detritus from all trophic levels.

Trophic Level

The discrete position or feeding stage an organism occupies within a food chain or food web.

Food Web

A complex network representation of the interconnected feeding pathways and energy flows among populations within a community.

Top-Down Control

Regulation of an ecosystem in which predator populations act as the primary determinant of organism abundances at lower trophic levels.

Bottom-Up Control

Regulation of an ecosystem in which abiotic nutrients and primary productivity dictate the community structure and energy flow to higher trophic levels.

Trophic Cascade

An ecological phenomenon in which predators suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation or herbivory.

Keystone Species

A species that exerts a community-wide effect that is disproportionately large relative to its abundance or biomass.

Artificial Selection

The deliberate selective breeding of domesticated plants and animals by humans to promote desirable inherited phenotypic traits.

Three Assertions of Natural Selection

The foundational requirements for evolution by natural selection: (1) individuals vary in phenotype, (2) offspring resemble their parents due to genotype, and (3) survival and reproduction are selective.

Law of Segregation

Mendel's principle stating that each individual possesses two allele copies for a gene, and these separate during gamete formation so that each gamete carries only one randomly selected allele.

Law of Independent Assortment

Mendel's principle stating that separate genes for independent traits are passed into gametes independently of one another.

Critical Thermal Minimum ($CT_{\min}$)

The lower temperature threshold below which an animal loses coordinated muscle function and becomes stunned or immobilized.

Natural Selection

The evolutionary process by which traits become more or less common in a population over time due to the effects of inherited characteristics on reproductive success.

Genotype

The specific genetic makeup of an organism, represented by the pair of alleles present at a particular gene locus.

Phenotype

The suite of observable morphological, physiological, and behavioral traits that characterize an organism.

Allele

One of two or more alternative versions or sequences of a specific gene located at a particular locus.

Locus

The specific physical location of a gene on a chromosome or DNA sequence.

Additive Dominance (Incomplete Dominance)

A pattern of inheritance in which the heterozygous phenotype displays an intermediate product dosage directly between the two homozygotes ($aa = \text{no product}$, $Aa = 1\times\text{ product}$, $AA = 2\times\text{ product}$).

Overdominance

A form of genetic dominance in which the heterozygous genotype ($Aa$) confers a greater phenotypic value or fitness than either homozygous genotype ($aa$ or $AA$).

Codominance

An inheritance pattern in which both alleles code for distinct functional products, resulting in a heterozygote that displays phenotypic attributes of both alleles simultaneously.

Epistasis

A genetic interaction where the activity or expression of one gene influences, masks, or modifies the expression of another independent gene.

Pleiotropy

A genetic scenario in which a single gene or mutation simultaneously influences multiple distinct, phenotypic traits.

Disruptive Selection

A mode of natural selection that eliminates phenotypes near the population average and favors individuals at both phenotypic extremes.

Stabilizing Selection

A mode of natural selection that reduces phenotypic extremes and favors intermediate or average phenotypes within a population.

Directional Selection

A mode of natural selection that consistently favors individuals at one extreme of a phenotypic distribution, shifting the average trait value in one direction.

Evolution

A change in heritable characteristics or allele frequencies in a population over successive generations.

Hardy-Weinberg Principle

The principle stating that, in the absence of evolutionary influences such as natural selection, drift, migration, or mutation, allele frequencies in a population will remain constant from generation to generation.

Hardy-Weinberg Equilibrium

The mathematical null model describing a non-evolving population where genotype frequencies remain stable and satisfy the equation $p^2 + 2pq + q^2 = 1$.