All things Meio with a specific focus on Chile


This glossary contains definitions of ecological, genetic and taxonomic terms and words that may be useful to meiobenthologists. These definitions have been scavenged from the literature, and will be added to over time, references are supplied at the bottom of the page.


α-Diversity: quantifies local diversity, usually species richness or the effective number of species.

β-Diversity: quantifies the dissimilarity or turnover between locations in terms of composition. Can be pairwise between locations, global (average dissimilarity across the region), or reflect the distinctiveness of a location compared to all others in the region.

γ-Diversity: quantifies the total diversity across locations for an entire area of interest, which could be at a regional or global scale depending on the study.


Abiotic facilitation: facilitation that is mediated through changes in the abiotic environment (e.g., vapor pressure deficit, soil porosity, soil moisture, or nutrient enrichment).

Acclimation: the physiological adjustment of an organism to a new long-term stable state following a change in conditions in an experiment.

Accuracy: the degree to which a measurement on an object comes close to the true value of the object. (see precision).

Additive design: an experimental design used to study competition between a target or focal species of interest and its competitors. In an additive design, the density of the target species is kept constant and the different treatments represent different numbers of competitors.

Aerobic scope: the relationship between maximum metabolic rate in fully aerobic conditions (i.e., without the contribution of anaerobic metabolic processes) and minimum maintenance metabolic rate, often termed basal or standard metabolic rate. Aerobic scope is usually quoted as a factorial ratio, e.g., maximum aerobic metabolic rate is three times basal metabolic rate and the aerobic scope is thus 3. Most animals have aerobic scopes in the range of 3–10.

Aesthetasc: a simple, tubular, thin walled, sensory filament found on the antennules (and rarely on the mouthparts).

Akaike’s information criterion (AIC): a measure of explanatory power of a statistical model that accounts for the number of parameters in the model. When comparing among multiple models for the same phenomenon (the models must share at least some parameters), the model with the lowest value of Akaike’s information criterion is considered to be the best model.

Ala (alae): longitudinal cuticle ridge or thickening forming a wing like extension. Also a wing like extension of the spicule.

Allobasis: a compound segment resulting from the fusion of the basis and proximal endopod segment.

Amphid: paired lateral sense organ situated on or just posterior to the head.

Amplicon: a piece of DNA or RNA that is the product of natural or artificial (i.e., PCR) replication.

Ancient DNA (aDNA): DNA isolated from old specimens or from various environments in the absence of obvious fossilized remains of organisms. Such DNA is usually considered to be of low quality, and requires special techniques and sterile conditions for extraction and amplification.

Ancient RNA (aRNA): RNA isolated from fossilized organisms (viruses, seeds, mammals). It is much less well studied and understood than aDNA.

Annulation: conspicuous transverse cuticle striation.

Annule: the transverse section between striae.

Antennae: the second pair of cephalic appendages.

Antennules: the first pair of cephalic appendages.

Apomorphy: A derived character or character state.

Apophysis (apophyses): (Nematoda) a separate process off the main structure, especially off the gubernaculum.

(Harpacticoida) an elongate process formed from an outgrowth of a segment or by modification of an armature element.

Approximate Bayesian computation: a simulation-based approach to create approximate likelihoods for model selection and parameter estimation of complex models, possibly with multiple data sources.

Arcuate: bow-shaped.

Area of occurrence (AOO): the geographic area that is occupied by a species, often defined as the number of occupied grid cells.

Armature: the spines and setae present on a segment or appendage.

Arrhenius relationship: a mathematical relationship to describe the effect of temperature on chemical reactions first proposed by Svante Arrhenius in 1889. It has been used widely in biology to describe temperature effects on biochemical reactions and physiological processes.

Arthrite: a praecoxal endite on the maxillule bearing spines and setae around its distal margin.

Arthropodial membrane: the flexible membrane connecting body somites or limb segments.

Assimilation efficiency: proportion of ingested material that is broken down by digestive enzymes to fuel the organism’s metabolic processes. Unassimilated material is egested.

Autapomorphy: a derived character or character state (apomorphy) that is restricted to a single terminal taxon in a data set.

Axiom: an established (mathematical) principle that is universally accepted, self-evidently true, and has no need of a formal proof.


BACI Contrast: a commonly used term for BACI average change. Given by subtracting the before–after difference of the control group from the before–after difference of the intervention group.

BACI Paired Series (BACIPS): methods that discuss BACI time-series analysis with multiple paired groups, typically considering average change.

Baseoendopod: the basal segment of the fith leg resulting from the fusion of the basis and endopod.

Basis: the distal segment of the protopod.

Bayesian inference: One of three major frameworks for statistical analysis. It is often called inverse probability. Bayesian inference is used to estimate the probability of a statistical hypothesis given (conditional on) the data at hand. The result of Bayesian inference is a new (or posterior) probability distribution.

Bayesian information criterion (BIC): a method to compare the posterior probability distributions of two alternative models when prior probability distributions are uninformative. It discounts the Bayes’ factor by the number of parameters in each of the models. As with Akaike’s information criterion, the model with the lowest Bayesian information criterion is considered the best model.

Before after (BA): a method of analysis that estimates the counterfactual by comparing values from before to after the intervention.

Before After Control Intervention (BACI): a method of analysis that estimates the counterfactual by comparing the change from before to after between control and intervention groups.

Bernoulli trial: an experiment that has only two possible results, such as present/absent, dead/alive. A Bernoulli trial results in a Bernoulli random variable.

Biodiversity facets: categories of biodiversity that describe relevant taxonomic or ecological information to support biodiversity evaluation, and that apply to and can be (relatively) easily measured for all or most taxa. Examples include taxonomic diversity, phylogenetic diversity, genetic diversity, trait/functional diversity, and network diversity.

Biodiversity models: statistical or process-based models that are used to make inferences and predictions about the effect of the environment on biodiversity, accounting for ecological processes explicitly or implicitly. Biodiversity can be represented in units ranging from individuals to entire communities, and additionally represent attributes of those taxa (e.g., abundances, functional traits, phylogenetic position, threat).

Biogeography: the study of the distribution of species and ecosystems in geographic space and through geological time.

Biomonitoring: biological monitoring, or biomonitoring, uses biological responses to evaluate change, caused by pollution, climate, human management and conservation, species invasions and disease.

Biotic interactions: changes in the growth rate of one species that are caused by another species.

Biotic facilitation: facilitation that results from the activity of a higher order trophic interaction (e.g., bacterial, rhizobial, or arbuscular mycorrhizal fungal communities).

Bonferroni method: an adjustment of the critical value, α, at which the null hypothesis is to be rejected. It is used when multiple comparisons are made, and is calculated as the nominal α, (usually equal to 0.05) divided by the number of comparisons.

Bootstrap: in statistics, the bootstrap is a randomisation (or Monte Carlo) procedure by which the observations in a dataset are resampled with replacement from the original dataset, and the resampled dataset is then used to recalculate the test statistic of interest. This is repeated a large number of times (usually 1000-10000 or more). The test statistic computed from the original dataset is then compared with the distribution of the test statistic resulting from repeatedly pulling up the data by its own bootstraps in order to provide an exact P-value.

Box-Cox transformation: a family of power transformations defined by the formula Y* = (Yλ-1)/λ (for λ0) and Y* = ln(Y) (for λ=0). The value of λ that results in the closest fit to a normal distribution is used in the final data transformation.

Buccal cavity: the most anterior portion of the alimentary canal between the oral opening and the beginning of the oesophagus, sometimes containing teeth or manibles.

Bursa (bursae): wing like extension of the cuticle surrounding the cloaca.


Cardia: muscular structure at the posterior end of the oesophagus connecting to and often within the anterior part of the intestine.

Categorical variable: characteristics that are classified into two or mre distinct groups.

Caudal: belonging to the tail.

Causal inference: the statistical process of concluding that an observed association is due to causation not correlation.

Central Limit Theorem: the mathematical result that allows the use of parametric statistics on data that are not normally distributed. The Central Limit Theorem shows that any random variable can be transformed to a normal random variable.

Cephalic: belong to the head.

Cervical: belonging to the neck, which extends from the base of the head to half way along the oesophagus.

Chirocer: the condition of the male antennule with the genticulation located between one very swollen, thich walled segment and the apical segment.

Cladistics: a method of classification that groups taxa hierarchically into nested sets and conventionally represents these relationships as a cladogram.

Cladogram: a branching diagram specifying hierarchical relationships among taxa based upon homologies (synapomorphies). A cladogram includes no connotation of ancestry and has no implied time axis.

Clavate: club-shaped.

Collinearity: the correlation between two predictor variables.

Community: an assemblage of species that co-occur in a location at a given time.

Community assembly: process by which species arrive, establish, persist, increase, or decrease in abundance over time, and go extinct within and across environmental gradients.

Competitive ability: the ability of an individual of one species to reduce the availability of contested resources to an individual from another species, and to tolerate or avoid reduction in contested resource availability by an individual from another species.

Competition coefficient (α): the per capita effect of a competitor species on the population growth rate of a focal species.

Complementarity: in conservation planning, complementarity quantifies the difference between locations in terms of species or features represented within them (two locations are fully complementary if their pairwise β-diversity is equal to 1). By contrast, in ecology, two species are complementary if they fill different roles in an ecosystem or use resources differently.

Components of fitness: measures of individual performance including survival, growth, and reproduction; also referred to as vital rates. The integration of fitness components yields an estimate of total fitness and integration of vital rates yields an estimate of population growth rate.

Confounded: the consequence of a measured variable being associated with another variable that may have not been measured or controlled for.

Contingency: a nonrepeatable response to an event, whereby the outcome is dependent in part on the evolutionary history of the impacted organisms as manifested by the structure of ecosystems and populations at the time of the event and, as such, responses to the same pressure will likely be different in the future; evolutionary changes with long-term historical impacts that are the result of chance survivorship as opposed to the result of strong selective pressures.

Continuous variable: characteristics that are measured using integer or real numbers.

Control intervention (CI): a method of analysis that estimates the counterfactual by comparing values between control and intervention groups.

Controlled or Comparative Interrupted Time Series Analysis: The term used in some disciplines to refer to models that calculate BACI trend and immediate change.

Convergence: independent evolution of a derived character state between taxa from different ancestral traits.

Concerted evolutionary responses among distantly related groups in response to an external stimulus; the historical evolutionary signal of preferential loss or survivorship due to a widespread selective pressure. This definition is similar to the traditional phylogenetic definition, which refers to the phenomenon of functionally similar characteristics that evolved independently and, therefore, are shared among distantly related groups, but applied more generally to both ecological and evolutionary traits.

Convex hull: smallest convex volume that contains a set of points. In trait-based ecology, it is used to quantify the functional volume occupied by a species or community, as well as β-FD and its decomposition into nestedness and turnover components. Convex hulls are sensitive to outliers and do not detect gaps in the occupation of functional space.

Coprolite: fossilized feces.

Corpus gelatum: gelatinous substance filling the cavity of the amphid.

Counterfactual: what would have occurred in the absence of an intervention.

Cryptic genetic variation: genetic variation that normally has little or no effect on phenotypic variation except under atypical conditions.

Cuticle: outer covering of the body which also lines the buccal cavity, oesophagus lumen, vagina and rectum; consisting of several distinct layers.


Dark biodiversity: portion of the regional species pool that is absent from the local community. In other words, the species present at a regional scale that can potentially colonize the local community but are absent from it. This concept provides valuable information for conservation applications and for improving knowledge of community assembly processes.

Demanian system: complex seminal receptacle (sperm store) found in females of the family Oncholaimidae.

Demographic heterogeneity: demographic heterogeneity refers to interindividual differences in demographic parameters.

Demographic stochasticity: the process behind variations in the realized fates of individuals under specified values of demographic parameters. This concerns all the demographic parameters underlying longitudinal trajectories: survival, reproduction, or transition probability among reproductive states. In age-structured populations, or in populations where survival probability does not vary with age, demographic stochasticity creates a distribution of longevities.

Demographic trade-offs: negative correlations between two or more vital rates.

Density dependence: when population growth or specific demographic rates (e.g., mortality, fecundity) are regulated by the density of the population.

Dependent variable: in a statement of cause and effect, the response variable, or the affected object for which one is trying to determine the cause.

Desmen: conspicuous tyre-like transverse rings around the bodies of desmoscolecids, composed of secretions containing foreign bodies such as grains of sand.

Didelphic: having two ovaries.

Dioecious: having separate males and females.

Diorchic: having two testes.

Disparity: the morphological or phenotypic difference between taxa.

Dispersal: permanent movement away from an origin and long-term settlement at a new location.

Disruptive selection: natural selection that favors extreme values of a trait over intermediate values, also known as diversifying selection.

Disturbance: a force or process that causes a response in the biodiversity and/or ecosystem function (e.g., a reduction in species biomass, abundance, or ability to carry out functions).

Diversification rate: the net rate of production of new lineages (i.e., the difference between origination and extinction rate). It usually applies to species (i.e., speciation minus extinction rate) but can be equally applied to higher or lower taxonomic levels.

DNA barcoding: sequencing of an agreed DNA fragment or fragments of the genome of an organism that can then be compared with the corresponding DNA fragments sequenced in other organisms for species identification purposes.

Double-stranded RNA (dsRNA): RNA with two complementary strands, similar to DNA but with the replacement of thymine by uracil. dsRNA can trigger gene silencing in eukaryotes by a process known as RNA interference (RNAi).

Dynamic range model (DRM): a statistical model to predict the range dynamics of species based on environment–demography relationships and parameters of spatial population dynamics that are jointly estimated from observational data.


Eco-evolutionary dynamics: mutual feedback between evolutionary and ecological processes occurring on similar timescales.

Eco-evolutionary processes: the interplay of ecological and evolutionary processes that violate the assumption that timescales of ecological and evolutionary processes can be separated; ecological processes affect evolution and vice versa.

Ecological generalisation: the ability to use a variety of a given resource type; for example, ecological generalists could breed in a variety of land-cover types, have a broad diet, or tolerate a broad range of soil types.

Ecological hierarchy: a nested biological hierarchy of organization through which energy flow occurs, ranging from enzymes through to cells, organisms, populations, communities, and the biosphere.

Ecological limits: a limit to the number of individuals and/or taxa that can coexist within an ecosystem due to abiotic settings and biotic interactions such as competition for limited resources.

Ecological modeling: an abstract, usually mathematical, representation of an ecological system (ranging in scale from an individual population, to a community, or even an entire biome), which is studied to better understand the real system.

Ecological processes: interactions between individuals of the same or different species driving the dynamics of populations, communities, and ecosystems within an ecological timescale, typically within a few generations of the focal organisms.

Ecological traits: characteristics of organisms that have bearing on the interaction between those organisms and the biotic and abiotic environment around them (e.g., trophic level, reproductive and/or life-history traits, and mobility). Ecological traits may also be emergent at the population or species level (e.g., geographic range size or abundance). Some morphological traits may be used as proxies for ecological traits.

Ecosystem function: combinations of biological, geochemical, and physical processes that take place or occur within an ecosystem. Ecosystem functions are the processes that underpin ecosystem services.

Ecosystem services: the benefits and values that humans gain from ecosystems.

Ectotherm: any animal whose body temperature is predominantly controlled by the external environmental conditions. These animals do not produce enough heat in their normal functioning to significantly alter their temperature. These animals are commonly called ‘cold blooded’, and they account for over 98.5% of animal species on Earth.

Effective population size (Ne): the hypothetical number of inbreeding individuals of a given census population if mating is random (Wright–Fisher population); all individuals are equally likely to mate, and their number is constant over time. It loses or gains genetic variation at the same rate as the actual census population.

Emigration: first range-shift process in which an individual embarks on a journey (movement) outside its natal location.

Endite: a medially-directed projection arising from the protopodal segments of an appendage.

Endopod: the inner ramus of an appendage.

Endopsammic: the habit of burrowing into sediment.

Energy flux model: a model that quantifies relationships between biodiversity and the flow of energy through ecosystems.

Environmental carrying capacity (ECC) of a community: refers to the number of individuals that a population of a single species can sustain in a given environment.

Environmental DNA (eDNA): refers to traces of DNA released by organisms into their environment. eDNA can be collected not only from environmental samples (water, soil, or air) as extracellular DNA but also as cellular DNA (fragments of tissue, gametes) recently released into the environment.

Environmental filtering: the differential establishment, persistence, or performance of a species determined by that species’ ability to tolerate a given set of abiotic conditions.

Environmental RNA (eRNA): refers to RNAs released by organisms into their surrounding environment. The term can be used to refer strictly to RNA extracted from the environment (in cellular, vesicular, or free form) in the absence of progenitor organisms. The term eRNA is used inadvertently in the metabarcoding literature to refer to RNA extracted from bulk, unsorted biological material (e.g., bulk zooplankton samples or bulk benthic samples of micro- or macroinvertebrates).

Environmental RNA interference (eRNAi): refers to sequence-specific gene silencing that crosses cellular boundaries when organisms encounter environmental dsRNA.

Environmental transcriptomics: also known as metatranscriptomics, the term often refers to sequencing mRNA from a bulk sample of microbes generating the community gene expression. The term is also used to refer strictly to gene expression profiling based on eRNA collected in the absence of organisms, a non-invasive approach that could apply to both eukaryotes and prokaryotes, and span all trophic levels.

Epimeron (epimera): the lateral projection of a tergite of the free prosomites.

Epipsammic: the habit of living on or above the sediment surface.

Establishment: range-shift process following movement, in which one or more individuals reproduce and found a self-sustaining population.

Evolutionary Fauna: a set of higher-level taxonomic groups that exhibit shared diversification histories, recognized by similar distributions in geological time.

Evolutionary processes: any processes leading to genetic changes in populations, driving lineage divergence and persistence within an evolutionary time scale, typically spanning many generations.

Evolutionarily stable strategies: strategies in a given environment that cannot be invaded by an alternative strategies.

Exite: a lateral projection on the outer margin of protopodal segments of an appendage.

Exons: parts of a gene that become part of the mature mRNA; can contain untranslated regions and coding sequences that are translated into amino acids.

Exopod: the outer ramus of an appendage.

Expression profiling: measuring the activity of all genes present in a particular sample (cell, tissue, or whole organism), providing information on their function.

Extent of occurrence (EOO): the area within the outer limits of the geographic distribution of a species.

Extracellular vesicles (EVs): cell-derived membranous structures containing lipids, proteins, sugars, and nucleic acids, particularly RNAs. Cells from all domains of life produce EVs that are involved in multiple processes of cell-to-cell communication as well as interspecific signaling. EVs may also offer protection to RNA against extracellular enzymes.

Extrinsic hypothesis: a statistical model for which the parameters are estimated from sources other than the data.


Facilitation: occurs when an increase in the density of species b increases the performance of species a.

Factorial design: an analysis of variance design that includes all levels of the treatments (or factors) of interest.

Factorial scope: the capacity to raise the rate of a biological process above normal minimum maintenance levels. This capacity is reported as the ratio of the maximum over the minimum rate.

Fenestra (fenestrae): rounded area or window, at the anterior end of the cephalic incision, which often accommodates the base of cephalic seta.

Filiform: shaped like a thread.

Fitness: growth rate of a population, genotype, or phenotype. Many studies focus on population growth rate as a measure of the fitness of a population.

Fitness landscape: conceptual or mathematical representation of individual or population-level fitness as a function of one or more phenotypic traits or genes.

Fixation index (FST): a measure of population subdivision that indicates the proportion of heterozygosity found between populations relative to the amount within populations.

Focal ensemble: species that might influence the range limit of the species under investigation.

Focal species: a species whose range limit is under investigation.

Food web: a system of interconnected feeding relationships or food chains.

Food web model or ecosystem model: a mathematical representation of how energy or biomass flows from primary producers to primary consumers and then to secondary consumers and higher predators.

Fovea: cavity in the amphid.

Frequentist inference: an approach to statistical inference in which probabilities of observations are estimated from functions that assume an infinite number of trials.

Fully crossed: a multiple-factor analysis of variance design in which all levels of two or more treatments are tested at the same time in a single experiment.

Functional distinctiveness (or trait distinctiveness): local-scale characteristics of a species (or an organism) having traits dissimilar from those of other species (organisms) in the community. A metric of functional distinctiveness assesses whether a species (or an organism) is more or less functionally close to the rest of the community.

Functional divergence: the degree to which the abundance in functional trait space of the organisms composing an ecological unit is distributed toward the extremes of its functional volume.

Functional diversity (FD): the diversity of functional forms in a species set (or community) measured by a variety of metrics that use dendrograms or representations in multidimensional space.

Functional evenness: regularity in the distribution of the abundance in functional trait space of the organisms composing an ecological unit.

Functional group: a grouping of species that share combinations of biological traits that affect ecosystem function in similar ways. Note that this concept could also apply to resource use traits, and depending on the context, grouping species by traits that are associated with their resource use behaviour might be more appropriate for assessing their role in the community or ecosystem.

Functional niche: region of the functional space containing all the trait combinations displayed by the individuals of a species. Existing FD approaches based on functional niches, such as the convex hull, consider functional niches as uniform features, ignoring the fact that some trait values within the functional niche of a species are more likely than others.

Functional rarity (or trait rarity): feature of a species (or an organism) that integrates both functional distinctiveness and taxonomic scarcity at the local scale, or both functional uniqueness and taxonomic restrictedness at the regional scale. Functionally rare species are ecological outliers. They possess the highest functional rarity value in the community (local scale) or in the regional pool (regional scale).

Functional redundancy: a simplified view of functional redundancy is that high species richness within a functional group [i.e., species that share the same functional (biological) traits] can compensate for some level of species loss to maintain ecosystem function.

Functional richness: amount of functional space occupied by the organisms in an ecological unit.

Functional traits: morphological, physiological, or phenological attributes of species that impact fitness indirectly through their effects on individual survival, growth, and reproduction.

Biological traits of a species that influence the way the species effects ecosystem function.

Functional uniqueness (or trait uniqueness): regional-scale feature of a species (or an organism) possessing unique traits, in other words traits that are not shared by any other species in the regional pool. A metric of functional uniqueness assesses the extent to which a species (or an organism) has no functional equivalent in the regional pool.

Fundamental niche: the environmental conditions and availability of resources where a species can maintain a viable population. In the presence of competitors, the species is further restricted to its realized niche.

Fusiform: shaped like a spindle, tapering at both ends.


Gene flow: movement of genes from one population to another. In population genetics theory, gene flow is represented by migration rate (m) – the proportion of individuals in a focal population that are immigrants.

Genealogical hierarchy: a nested biological hierarchy of organization through which historical information flow occurs, ranging from codons through to genes, organisms, demes, species, and monophyletic taxa.

Genetic accommodation: a mechanism of evolution wherein a phenotype, generated by either a mutation or environmental change, is refined into an adaptive phenotype through selection driving quantitative genetic changes. Accommodation can also promote either increased or decreased environmental sensitivity of the focal phenotype; when environmentally induced phenotypes lose environmental sensitivity, they undergo ‘genetic assimilation’.

Genetic assimilation: an extreme form of ‘genetic accommodation’ that occurs when selection causes environmentally induced (i.e., plastic) phenotypes to lose their environmental sensitivity over evolutionary time.

Genetic drift: change in gene frequencies over time owing to random differences in the survival and fecundity of individuals, as well as to binomial sampling of alleles during meiosis.

Genetic rescue: increase in population growth of small populations following immigration, resulting from the reduction of genetic load caused by inbreeding depression.

Genome skimming: shallow sequencing of total genomic DNA of an organism.

Genticulate: knee-shaped.

Ghost ranges: the inferred temporal occurrence of a lineage for which there is no direct record implied from the occurrence of a longer-ranging sister taxon. Given that ghost ranges are informed by minimum divergence times from sister taxa, they only extend points of origin backwards in time and cannot alter the inferred timing of extinction. Ghost ranges are one type of adjustment made to stratigraphic or temporal ranges to account or correct for stratigraphic uncertainty, incompleteness, or inconsistency.

Gnathobase: an endite of the mandibular coxa bearing distally the toothed cutting edge.

Gonochoristic: having the sexes separate, producing distinct males and females.

Growth rate: the difference between the birth and death rate of a population over the time interval of interest. We assume that growth rates are typically measured on a percapita basis.

Gubernaculum: a cuticularised guiding piece lying dorsal to the spicules in the cloaca.


Haphazard: assignment of individuals or populations to treatment groups that is not truly random.

Haplocer: the condition of the male antennule where the middle segments are only slightly modified and there are a number of segments distal to these.

Hard selection: natural selection that removes from the population individuals whose phenotype does not attain a particular threshold, independently of population density or genotype/phenotype frequency. Hard selection can result in additional mortality, and can therefore depress population size.

Heat Shock Protein (HSP): a member of a family of proteins that are produced in response to a wide range of stresses by the vast majority of organisms investigated to date. They were first identified as a response to experimental temperature insult in the 1960’s, but are now known to be produced in response to a wide range of stresses including, physical cellular damage, dehydration, UV exposure, hypoxia and salinity in marine species.

Heat Shock Response (HSR): a response by an organism to a thermal challenge that involves the production of, or an increase in the production of, Heat Shock proteins.

Heteroscedastic: the property of a dataset such that the residual variances of all treatment groups are unequal.

High-throughput sequencing: the simultaneous sequencing of millions of DNA fragments.

Homology: similarity due to shared ancestry. Opposed to analogous characters, homologous characters can be compared across organisms to infer, for example, phylogenetic relatedness or species boundaries.

Homoplasy: a character that specifies a different and overlapping group of taka from another character.

Any character that is not a synapomorphy.

Homoscedastic: the property of a dataset such that the residual variances of all treatments groups are equal.

Hyaline frill: the transparent membrane on the posterior margin of the somite or segment covering the arthrodial membrane.

Hypothesis: a testable assertion of cause and effect.

Hypothetico-deductive method: the scientific method championed by Karl Popper. Like induction, the hypothetico-deductive method begins with an individual observation. The observation could be predicted by many hypotheses, each of which provides additional predictions. The predictions are tested one by one, and alternative hypotheses are eliminated until only one remains. Practitioners of the hypothetico-deductive method do not ever confirm hypotheses; they only reject them, or fail to reject them. When textbooks refer to “the scientific method”, they are usually refering to the hypothetico-deductive method.


Impact evaluation: determining how an intervention has causally affected outcomes (examples of outcomes in ecology include population counts, body mass, or rate of habitat loss).

Imputation model: a model that estimates values for missing datapoints in biodiversity datasets (e.g., trait values for a particular taxa).

Independent variable: in a statement of cause and effect, the predictor variable, or the object that is postulated to be the cause of the observed effect.

Indicative traits: characteristics of a species related to environmental tolerance, habitat specialisation, geographical boundaries, or spatial distribution. These traits can be measured at the individual or population level and, therefore, are not life-history traits in the strict sense.

Individual growth rate: rate of expansion or contraction in size of an individual organism over time.

Intercoxal sclerite: the ventral plate connecting the protopods of each member of a pair of swimming legs.

Intervention: an event that disturbs a system. The event could be intentional, accidental, or natural, for instance the designation of a protected area, an oil spill, or a wildfire.

Intrinsic growth rate: population growth rate at low density, in the absence of either intraspecific density-dependent effects or interspecific competition.

Intrinsic hypothesis: a statistical model for which the parameters are estimated from the data themselves.

Intrinsic rate of increase: the rate of population growth in the absence of density-dependent forces (such as competition).

Introns: transcribed non-coding parts of a gene that are removed by RNA splicing during mRNA maturation.

Invasion growth rates: population growth rate of the focal species at low density when growing with competing species that are at their stochastic equilibrium abundances.

Irreplaceability: the extent to which a location or species is distinct from all others (opposite of redundancy). For example, a location where an endemic species occurs is irreplaceable; an irreplaceable species has a unique position in its community (in terms of function or interactions, i.e., distinctive) or in the phylogeny.

Isthmus: a narrow section of the oesophagus.


Jackknife: in statistics, the jackknife is a randomization (or Monte Carlo) procedure by which one observation is deleted from the dataset, and then the test statistic is recomputed. This is repeated as many times as there are observations. The test statistic computed from the original dataset is then compared with the distribution oftest statistics resulting from the repeated application of the jackknife to provide an exact P-value.


Kurtosis: a measure of how clumped or dispersed a distribution is relative to its center.


Labrum: a posteroventrally directed outgrowth of the antennary somite froming the anterior border of the oral opening.

Latent traits: conceptual constructs used when the observed outcome of interest, for example, alive at age a, is assumed to depend on unmeasurable individual traits: such as, the individual survival probability.

Latitudinal Diversity Gradient (LDG): the increase in species diversity from the poles to the equator.

Leptokurtic: a probability distribution is said to be leptokurtic if it has relatively few values in the center of its distribution and relatively fat tails. The kurtosis of a leptokurtic distribution is greater than 0.

Life-history traits: morphological, physiological, or phenological characteristics measurable at the individual level that have an effect on individual performance.

Loxometaneme: metaneme arranged at an angle to the longitudinal body axis.


Macroecology: the subfield of ecology that deals with the study of relationships between organisms and their environment at large spatial scales to characterize or explain statistical patterns of productivity, abundance, distribution, and diversity.

Macroecological model (MEM): a biodiversity model that uses a top-down approach to model α- or β-diversity directly instead of modeling the distributions of the component taxa.

Macroevolution: the study of broad evolutionary trends across geological time; evolutionary patterns associated with the birth, death, and persistence of species and clades.

Manipulative experiment: an experiment in which the investigator deliberately applies one or more treatments to a sample population or populations, and then observes the outcome of the treatment.

Markov process: a sequence of random (state) variables indexed by time with serial dependence in the outcomes. The state of the process at t + 1 depends only the recent past state(s).

Mechanistic macroecology: the study of mechanisms describing how individual organisms interact with their biotic and abiotic environments, and how these mechanisms scale up to result in macroecological patterns, including the LDG and other secondary biodiversity patterns.

Mechanistic model: mechanistic models may vary in complexity and detail, but in the context of the LDG, such a model should at a minimum specify the mechanisms by which the processes of selection, dispersal, ecological drift, and speciation operate on individuals, populations, or species.

Mesopsammic: the habit of occupying the intersticies between sediment particles.

Metabarcoding: a DNA-based identification method involving the extraction of multiple species from a mass collection of specimens (bulk samples) or from complex and possibly degraded samples of eDNA. The metabarcoding approach is also known as amplicon sequencing and is applied frequently to microbial communities, but can be also applied efficiently to meio- and megafauna.

Metabolic Cold Adaptation (MCA): the hypothesis that cold blooded animal species living at low temperature should have elevated metabolic rates to overcome the problems of performing activity at low temperature.

Metagenomics: the study of communities sampled directly from their environment by examining the genomic compositions of all organisms rather than examining the genomes of separate species.

Metaneme: filamentous stretch receptors found in the lateral epidermal region.

MicroRNA (miRNA): small noncoding RNA with a role in gene silencing. Such molecules can be surprisingly stable owing to their ability to bind to proteins and subcellular compartments.

Midden: concentrations of waste (e. g., shells, urine, feces) produced by humans or other animals.

Monodelphic: having one ovary.

Monophyly: a group is diagnosed as monophyletic by the discovery of homologies (synapomorphies). Also known as a clade.

A group that includes the most recent common ancestor plus all and only all of its descendents.

Monorchic: having one testis.

Monte Carlo analysis: one of three major frameworks for statistical analysis. It uses Monte Carlo methods to estimate P values.

Monte Carlo methods: statistical methods that rely on randomising or reshuffling the data, often using bootstrap or jackknife methods. The result of a Monte Carlo analysis is an exact probability value for the data, given the statistical null hypothesis.

Morphological disparity: net morphological differences, usually within a group of organisms sharing a common ancestor; may be assessed within the clade, geographic region, and/or interval of time.

Morphospace: a multidimensional space defined by a set of morphological descriptors, such as morphometric or character data. The positioning of taxa relative to one another in the morphospace reflects their degree of morphological similarity. Morphospace analysis comprises the description of the relative distribution of subsets of taxa that may grouped by taxonomic, ecological, spatial, or temporal association, and how that distribution relates to other groups, often in the context of the original morphological descriptors.

Most recent common ancestor (MRCA): the last ancestor genetically shared by a group of individuals.

Mucroniform process: a projection formed by the elongation of part of the integument of a segment.

Multicopy gene: gene that was duplicated at least once within the history of the respective lineage (i.e., gene copies carried by organisms of the lineage).


Natural experiment: a comparison among two or more groups that have not been manipulated in any way by the investigator; instead, the design relies on natural variation among groups. Natural experiments ideally compare groups that are identical in all ways, except for the single causitive factor that is of interest. Although natural experiments can be analysed with many of the same statistics as manipulative experiments, the resulting inferences may be weaker because of uncontrolled confounding variables.

Nested design: any analysis of variance design for which there is subsampling within replicates.

Nestedness: the component of beta-diversity that reflects differences in alpha-diversity between sites when species assemblages at different sites are nested subsets of one another

Next-generation sequencing (NGS): NGS, or high-throughput sequencing, allows the sequencing of DNA and RNA much more rapidly and cheaply than the prior technology of Sanger sequencing, thus ‘revolutionising’ genomics and molecular biology. It is a catch-all term to describe a number of different sequencing methodologies including Solexa (Illumina), Roche 454, Proton/PGM, PacBio, GridION/ MinION and SOLiD sequencing.

Niche conservatism: the tendency for descendant lineages or species to retain their ancestral niche.

The phenomenon by which species and closely related taxa maintain similar environmental tolerances; inheritance by a daughter species of the niche or part thereof from its parent species.

Novel climate: climate conditions not previously experienced by a given species anywhere in its current range.

Novel interaction: an interaction between species whose distributions did not previously overlap, but then overlap following migration with climate change or after introduction to new biogeographic regions.

Novel trait: broadly, any major developmental innovation; sometimes defined as a body part that is neither homologous to any body part in the ancestral lineage nor serially homologous to any other body part of the same organism; a difficult concept to define.

Nuchal organ: a dorsal, presumably sensory organ found medially on the cephalothorax.

Null hypothesis: the simplest possible hypothesis. In ecology and environmental science, the nul hypothesis is usually that any observed variability in the data can be attributed entirely to randomness or measurement error.


Odontium (odontia): a tooth which is formed in the oesophagus but moves forward to the anterior of the buccal cavity to become functional.

Oesophageal bulb: a muscular swelling at the posterior end of the oesophagus.

Onchium (onchia): a tooth which is formed in the buccal cavity; in some enoplids attached to the mandible.

Ontogeny: the pattern of changing features of an organism as development proceeds from zygote to adult.

Operational taxonomic unit (OTU): a pragmatic definition for a group of closely related individuals. The term OTU is used to refer to clusters of organisms, grouped by their sequence similarity for a specific set of taxonomic marker genes, such as the 16S or 18S rRNA genes.

Orthogonal: in a multifactor analysis of variance, the property that all treatment combinations are represented. In multiple regression design, the property that all values of one predictor variable are found in combination with each value of another predictor variable.

Orthologs: genes that arose from a single ancestral gene in an organismic group of interest by speciation.

Orthometaneme: metaneme arranged parallel to the body axis.

Osmium: modified intestinal epithelium connected to the demanian system.

Outliers: unexpectedly large or small data points.


Paleoecology: the study of the fossil record to reconstruct the life habits of past organisms, their association in communities, and their interactions with the biotic and abiotic components of the environments in which they lived.

Parallelism: independent evolution of a character state in different taxa from a similar and shared ancestral trait.

Paralogs: genes that arose in an organismic lineage of interest from an ancestral gene by gene duplication within a genome.

Parametric analysis: one of three major frameworks for statistical analysis. It relies on the requirement that the data are drawn from a random variable with probability distributions difiened by fixed parameters. Also called frequentist analysis or frequentist statistics.

Paraphyly: a group recognised by symplesiomorphies.

A group that remains when one or more components of a monophyletic group are excluded.

A group that includes a most recent common ancestor plus only some of its descendants.

Parsimony: the general scientific criterion for choosing among competing hypotheses that states that we should accept the hypothesis that explains the data most simply and efficiently.

Pattern-driven research: research focusing on the detection of biological patterns in empirical data.

Pattern-oriented modeling: a modeling approach where multiple patterns observed in real systems at different hierarchical levels and scales are used systematically to optimize model complexity and to reduce uncertainty.

Pediger: a somite bearing a pair of periopods.

Peduncle: stem or stalk, often the base for seta.

Pereiopod: a thoracic walking (swimming) leg, usually biramous in harpacticoids (except for the sixth which is very reduced).

Phylogenetic diversity: the evolutionary diversity represented by sets of taxa, where the most common metric (Faith’s phylogenetic diversity) is the branch length of the minimum spanning tree connecting a set of species in a phylogeny (sets of species can be from a single area or multiple areas combined).

Phylogenetic paleoecology: an emerging branch of paleoecology that combines tree-based methodologies with habitat, abundance, and biogeographic data of fossil taxa to study the interplay of historical and environmental processes in shaping the evolution of life.

Phylogenetic tree: an hypothesis of genealogical relationships among a group of taxa with specific connotations of ancestry and an implied time axis.

Phenotypic accommodation: the maintenance of a novel, induced trait or phenotype that is an automatic consequence of multidimensional adaptive physiological, morphological, and/or behavioral plasticity in the face of a developmental change.

Phenotypic plasticity: the ability of an organism to alter its behavior, morphology, and/or physiology in response to changes in environmental conditions; sometimes used synonymously with developmental plasticity.

Pinnate: a spine or seta with a row of setules or spinules on the lateral border.

Plasticity-first hypothesis: a mechanism of adaptive evolution in which environmental perturbation leads, via phenotypic plasticity, to developmental reorganization (via, e. g., altered gene expression) and uncovers ‘cryptic genetic variation’ for, and ultimately production of, a novel developmental variant (i.e., trait) that immediately undergoes ‘phenotypic accommodation’ and is subsequently refined through ‘genetic accommodation’ some definitions include cases in which mutation initiates trait origin.

Platykurtic: a probability distribution is said to be platykurtic if it has relatively many values in the center of the distribution and relatviely skinny tails. The kurtosis of a platykurtic distribution is greater than 0.

Plesiomorphy: an apomorphy of a more inclusive hierarchical level than that being considered.

An ancestral or primitive character or character state.

Plumose: feather like, the condition of a pinnate seta when the pinnules are long and fine.

Polymerase chain reaction (PCR): a method used in molecular biology to copy or replicate a single or a few pieces of DNA over several orders of magnitude of times, producing thousands to millions of copies of a particular DNA sequence.

Polyphenism: environmentally induced alternative phenotypes.

Polyphyly: a group besed on convergent characters.

A group based on homoplastic characters assumed to have been absent in the most recent common ancestor of the group.

A group that does not include the most recent common ancestor of all its members.

Population fitness (λ): finite rate of increase of the population. This can be directly quantified for a single time step as Nt+1/Nt , where ‘N’ is number of individuals and ‘t’ is time. It can also be estimated using population models as the average or asymptotic population growth rate by computing the dominant eigenvalue of the transition matrix.

Post-prandial: following a meal. In the context of biological functions it is any process that is entrained or altered in rate following a meal.

Potential range: the geographic area in which environmental conditions are suitable for a given species, regardless of whether the species is present. Potential range is often calculated using SDMs.

Praecoxa: the proximal segment of the protopod of an appendage.

Precloacal supplements: in males, additional copulatory organs usually situated ventrally or subventrally anterior to the cloaca and often appearing to have a secretory function.

Predator–prey mass ratio (PPMR): the ratio of the average mass of an individual predator to that of its prey.

Precision: the level of agreement among a set of measurements on the same individual.

Press experiment: a manipulative experiment in which the treatments are applied, and reapplied throughout the duration of the experiment in order to maintain the strength of the treatment.

Primer: a short strand of RNA or DNA that serves as a starting template for DNA replication.

Process-driven research: research focusing on the underlying processes generating observed patterns.

Production: the generation of biomass or energy. Primary production refers to the synthesis of organic compounds from carbon dioxide most often via photosynthesis. Secondary production involves the generation of biomass through consumption of another organism.

Productivity: the rate of production.

Progressive Change BACIPS: a modified form of BACIPS that considers multiple linear and nonlinear responses in the after period. These methods assume a steady state, or no trend, in the before period.

Proliferation: fourth range-shift process in which established populations become more than self-sustaining, producing individuals that in turn disperse and cause further population spread.

Protein folding: the final process in the production of a protein in the cells of an organism. Proteins are synthesised as a chain of amino acids on a ribosome. Protein folding is the process whereby the amino acid chain folds to achieve its three dimensional functional state.

Protopod: the three basal (proximal) segments of an appendage, bearing the exopod and endopod.

Pulse experiment: a manipulative experiment in which treatments are applied only once, and then the treated replicate is allowed to recover from the manipulation.

Punctation: dotted cuticle, formed from tiny raised knobs, rods, or rounded depressions in the cuticle.

Pyriform: pear-shaped.


Q10 : the change in rate of a chemical or biological process produced by a 10ºC change in temperature. If a rate doubles with a 10ºC rise in temperature the Q10 is 2, if it trebles it is 3.

Quasi-experimental: a range of approaches used to estimate the causal impact of an intervention without randomisation.


Randomised block design: an analysis of variance design in which sets of replicates of all treatment levels are placed into a fixed area in space or a fixed point in time ( a block) in order to reduce the variability of unmanipulated conditions.

Range filling: the proportion of its potential range that a species occupies.

Range limit: the boundary between locations where a species is present and locations where a species is absent.

Range shift: expansion of one part of the range margin following colonisation events. Range shift may or may not be accompanied by a contraction in another part of the range margin.

Reaction norm: a graphical representation of the set of phenotypes that a single genotype produces in response to some specific environmental variable(s); individuals show plasticity if their reaction norm is non-horizontal.

Realized niche: the environments where a species is present. This includes dispersal and biotic interactions. The regional realized niche is the same at broad spatial scales (where dispersal from external sources can be ignored).

Recombination: recomposition of the allelic variation across loci during meiosis by random assortment of chromosomes and crossing over.

Regional species pool: set of species present in a region that could potentially colonize a local site or community based on the suitability of local ecological conditions.

Remote sensing: the use of satellite- or aircraft-based sensor technologies to detect and classify objects on Earth, including on the surface and in the atmosphere and oceans, based on propagated signals (e.g., electromagnetic radiation).

Renette cell: the ventral excretory gland, unicellular.

Reniform: shaped like a kidney.

Repeated measures design: a type of ANOVA in which multiple observations are taken on the same individual replicate at different points in time.

Reproductive strategy: the number, timing, and degree of investment in each reproductive event, which are related to demography, fecundity, and speed of life history. Species with an ‘r’ strategy reproduce early, have small body mass, and many offspring per year. Species with a ‘K’ strategy are older at first reproduction, have larger body mass, and fewer offspring.

Resilience: ability of a population or ecosystem to recover to its original state following a disturbance.

Resilience is the capacity to retain ecosystem function despite disturbance and is assessed by functional group diversity.

Resilience attribute: an attribute (or trait) of an individual species, population, or community that increases the resilience of ecosystem functions.

Resilience indicator: a variable that can be used to predict how ecosystem function will respond to change.

Resistance: is an aspect of resilience that is concerned with the ability of species or functions to resist change in the face of disturbance. This is related to both the survival of species, but also the ability of species to continue to carry out its function when under stress.

Resource: an entity that organisms consume and which increases their growth rate.

Resource complementarity: occurs when species have unique and complementary resource requirements that can allow some species to stably coexist; these groups of species can be more productive and capture available resources more comprehensively than any species in monoculture.

Recovery: is an aspect of resilience that is concerned with the ability of species or functions to return to predisturbance levels.

Response diversity: the diversity of species that contribute the same to ecosystem functions but have different responses to disturbance.

Richness: the raw count of taxonomic units, usually species or genera. Typically richness is a property of communities, but the term ‘species richness’ has been used synonymously with taxonomic diversity, for example, the number of species in a genus.

Rostrum: a small plate, projecting from the anterodorsal margin of the cephalic shield between the antennues.

rRNA genes: genes that code structural components of ribosomes. In metazoans, the corresponding genes of the large subunit (60S) are 5S, 5.8S, and 28S, and that of the small subunit (40S) is 18S. These genes are arranged in tandem repeats and present in large numbers.

Ruga (rugae): rib-like thickening of the folded anterior part of the buccal cavity, usually twelve in number.


Saturation: in a saturated community, local richness exhibits a maximal level that depends on ecological or areal constraints or limits.

Scale transition theory: an approach to analyzing differences between local and regional population growth rates, based on the consequences of local interactions, mediated by dispersal among sites, and other processes.

Secondary biodiversity patterns: spatial, temporal, phylogenetic, or trait-based diversity patterns that emerge from the same ecological and evolutionary processes as the LDG.

Selection coefficient: a measure of the reduction in the relative fitness of a given genotype. The selection coefficient takes a value between zero (no reduction in fitness) and one (fitness is zero).

Selection effects: occurs when higher diversity mixtures have a higher statistical probability of including particularly productive species. When those species that are more productive in monoculture are also better competitors in mixture, higher diversity communities can be more productive than lower diversity communities.

Setiform: shaped like a hair or bristle.

Shotgun sequencing: the random sequencing of DNA fragments.

Sideways’ biodiversity models: models that predict the distribution of biodiversity with a combination of bottom-up (i.e., single-taxon predictions) and top-down (i.e., models of the properties of an assemblage or community of taxa) approaches.

Simulation model: a set of rules (usually formulated in a programming language) governing the dynamics of artificial entities that reflect individuals, populations, or communities.

Single-copy gene: gene that is present in a single copy in all genomes of the respective organismic lineage.

Single factor design: an analysis of variance design that manipulates only one variable.

Site (in)fidelity: reflects the likelihood that an individual will embark on a dispersal event to emigrate away from the natal patch. High site fidelity corresponds to a low likelihood of emigration and, thus, low range-shift capacity.

Size spectrum model: a mathematical representation of a food web that groups individuals by their sizes.

Small population effects: factors that make it difficult for small populations to grow and, thus, hinder population establishment. These include Allee effects, genetic drift, and susceptibility to demographic or environmental stochasticity.

Soft selection: natural selection that eliminates individuals that do not achieve a particular relative value of a given trait. Under soft selection, selective deaths are substituted for non-selective mortality, and it therefore has little effect on population size.

Somite: a “segment” of the body.

Spatial biodiversity models: biodiversity models that are explicitly spatial, and where inferences and predictions are made for biodiversity in particular locations (e.g., planning units or grid cells).

Spatial prioritization: a form of systematic conservation planning (SCP) that selects a set of areas that maximize conservation value given other constraints (e.g., cost, protected areas, feasibility).

Species delimitation: recognition of boundaries between species.

Species distribution model (SDM): a model that predicts the potential geographical distribution of a species based on statistical relationships among observed occurrences or abundances and environmental data.

Species identification: assigning a taxonomic name to a species. Species boundaries must be known in advance.

Species richness: number of species present in a community or area. This concept is equivalent to α-diversity.

Specific Dynamic Action (SDA): the rise in metabolic rate exhibited by an animal following a meal. In most species the maximum rise is in the range of x1–x4 over standard or basal prefeeding metabolic levels.

Spicule (spicules): copulatory organ, usually paired, in the cloaca of the male.

Spinneret: terminal part of the tail with pore of the caudal glands.

Stable isotopes: naturally occurring, non-radioactive atoms of the same element that have different numbers of neutrons. The isotope with fewer neutrons is lighter in mass, which results in faster chemical reaction rates, and may lead to a preference for its uptake by organisms. Comparing ratios of carbon and nitrogen stable isotopes in organismal tissues to ratios in their prey can elucidate the processes that formed these tissues and estimate the organism’s trophic level.

Stasis: retention of the same ancestral character state over an extended period.

Statistical null hypothesis: the formal hypothesis that there is no mathematical relationship between variables, orthe statistical form of the scientific hypothesis that any observed varaibility in the data can be attributed entirely to randomness or measurement error.

Stochastic growth rate: population growth rate including temporal variation in growth rate.

Stoma: mouth

Stratigraphic range: the temporal interval over which a taxon has been sampled from the fossil record. The stratigraphic range is bounded by the oldest (‘first’) and youngest (‘last’) sampled occurrences of specimens, and is an estimate of the true duration of the taxon. First and last occurrences can be assigned absolute ages with varying precision based on the association of radiometric dates with sediments from which that taxon was sampled.

Stria (striae): transverse groove in the cuticle.

Stylet: a long slender spear-like structure in the buccal cavity.

Symplesiomorphy: a synapomorphy of a more inclusive heirarchical level than that being considered.

The occurrence in two or more taxa of a monophyletic group of a plesiomorphic character or character state; that is, one that has been inherited from an ancestor more distant than the most recent common ancestor of the group. Paraphyletic groups result from mistaking symplesiomorphies for synapomorphies.

Synapomorphy: a secondary homology.

An apomorphy that unites two or more taxa into a monophyletic group.

Syncoxa: a compound segment resulting from the fusion of the praecoxa and the coxa.


Tagmosis: the division of the body into functional regions (tagmata).

Taphonomy: the deposition, preservation, transport, etc., of biological materials in the eDNA archive.

Taxonomic diversity: the raw count of taxonomic units, often species but frequently higher taxa, such as genera or families, within a clade, geographical region, and/or interval of time.

Taxonomic marker genes: genes regularly used in taxonomic identification [e.g., cytochrome oxidase (COI), ribosomal RNA (16S, 18S, ITS), ribulose bisphosphate carboxylase (rbcL)].

Taxonomic restrictedness (or species restrictedness): regional-scale characteristics of a species being geographically restricted (e.g., small extent of occurrence or small area of occupancy).

Taxonomic scarcity (or species scarcity): local-scale feature of a species with low relative abundance (in terms of number of individuals or biomass) in the community.

Telemon: cuticularised structures lying either side of the gubernaculum.

Tergite: the dorsal plate of a somite, completely fused to the pleurite forming a pleurotergite.

Time-averaging: a property of fossil assemblages that reflects the degree to which they contain individuals that lived at different times. Time-averaging occurs because rates of population turnover typically exceed rates of net sediment accumulation; time-averaging is increased by low sediment accumulation rates or reworking of sediments. In marine environments, time-averaging is typically in the range of decades or millennia.

Time series model: a statistical model for which time is included explicitly as a predictor variable.

Time-series data: a series of measurements at intervals through time. For example, annual counts of lions in a pride, monthly measures of deforestation in a region, and annual hunting rate of a bird species.

Transfer efficiency: the proportion of resource production converted into consumer production. Transfer efficiency is often calculated as the proportion of production passed from one node to another in a food web.

Tree-based methods: methods applied to studies of ecology and evolution that incorporate trees of hypothesized relationships between taxa.

Trophic level: the position of an individual within a food web based on the number of feeding links between it and the primary producer. Primary producers such as phytoplankton and plants have a trophic level of 1, herbivores have a trophic level of 2, carnivores have a trophic level of at least 3. Non-integer trophic levels result from mixed diets. Detritus is often also assigned a trophic level of 1.

Trophic model: a mathematical representation of a food web that groups individuals by their position in a food chain.

Tropis: hollow tooth-like structure formed by the ventral wall of the cephalic capsule in certain enoplids.

Turnover: the component of beta-diversity that reflects the replacement of species at some sites by different species at other sites

Two-way design: an ANOVA design with two main effects, each of which has two or more treatment levels.

Type I error: falsely rejecting the true statistical null hypothesis. Usually indicated by α.

Type II error: incorrectly accepting a false statistical null hypothesis. Usually indicated by β. Statistical power equals 1-β.


Ubiquitination: ubiquitin is a small protein present in the cells of eukaryotes. Its function is to help regulate the production of proteins in cells. For example, when proteins begin to degrade, or do not fold properly when made and their function is impaired beyond repair ubiquitin is attached to them (called tagging) to signal this state. Those proteins are then identified by the mechanisms in cells that break the proteins down to allow the amino acids to be recycled. This process of tagging with ubiquitin is called ubiquitination or less commonly ubiquitinylation.

Ultra-conserved elements: DNA segments of about 200 base pairs that are highly conserved across a large phylogenetic range. They may be present in non-coding regions or overlap with genes (exons and introns).


Varved sediments: sediments with layers distinguishable at an annual resolution.

Vermiform: shaped like a worm.

Vital rates: rates of birth, death, and growth of individuals, also called demographic rates and components of fitness.


Weighted endemism: the ratio between a species local range of occurrence and its total range. Note: this is different from the definition of endemism; the extent to which a species range is restricted to a particular location.

Whole-genome sequencing: in-depth sequencing of total genomic DNA of an organism.





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