Chap 2.1, 2.2, 2.3 Community Structure Vocabulary

Vocabulary flashcards covering key terms, mathematical formulas, physical stratification, and ecological concepts from the Community Structure lecture notes.

Species richness

The total number of species present in a given area, which does not take into account species evenness.

Relative abundance

The proportion of all individuals sampled in a community that belong to a given species, calculated as $p_i = \frac{n_i}{N}$.

Ranked-abundance diagram

A graph displaying species relative abundance ordered from greatest to least, where a flatter slope indicates greater species evenness.

Diversity index

A summary value quantifying community structure that takes into account both species richness and species evenness.

Simpson's index ($D$)

The probability that two randomly collected individuals from a community will belong to the same species, calculated as $D = \sum \left(\frac{n_i}{N}\right)^2$.

Simpson's index of diversity

A diversity measure calculated as $1 - D$, where higher values indicate higher community diversity.

Simpson's reciprocal diversity index

A diversity measure calculated as $\frac{1}{D}$, producing values greater than $1$ where larger numbers indicate higher diversity.

Shannon Index of Diversity ($H$)

A diversity metric calculated as $H = -\sum P_i \cdot \ln(P_i)$ or $H = -1 \cdot \sum P_i \cdot \log_2(P_i)$, where higher values represent greater diversity.

Dominant species

Species that predominate within a community, often by controlling limited resources and excluding other species.

Simpson Dominance Index

A measure ranging from $0$ to $1$ calculated as $\text{Dominance} = \left[\sum n_i(n_i - 1)\right] \div \left[N(N - 1)\right]$, where $1$ indicates complete dominance by a single taxon.

Importance value

A measure of the degree of influence a species has on a community, calculated as $\text{relative density} + \text{relative dominance} + \text{relative frequency}$.

Density

In community ecology, the ratio calculated as $\frac{\text{number of individuals}}{\text{area sampled}}$.

Relative density

The density of a given species expressed as a percentage of total density, calculated as $\frac{\text{density for a species}}{\text{total density for all species}} \times 100$.

Areal dominance

A physical coverage measure calculated as $\frac{\text{total of basal area or areal coverage values}}{\text{area sampled}}$.

Relative dominance

The proportional dominance of a single species relative to all species, calculated as $\frac{\text{dominance for a species}}{\text{total dominance for all species}} \times 100$.

Frequency

In sample plot methodology, the ratio calculated as $\frac{\text{number of plots in which species occurs}}{\text{total number of plots sampled}}$.

Relative frequency

The frequency of a single species relative to overall species occurrences, calculated as $\frac{\text{frequency value for a species}}{\text{total of frequency values for all species}} \times 100$.

Keystone species

A species that has a disproportionate impact on community structure relative to its abundance, often acting as a top predator.

Trophic level

A specific feeding position or level occupied by a group of organisms in a food web.

Primary consumers

Organisms in a food web that consume primary producers (autotrophs) and are typically herbivores.

Omnivore

An organism in a food web that feeds across multiple trophic levels.

Guild

A group of organisms within a trophic level that exploit common, shared resources.

Functional type

A collection of species that share a common response to environmental conditions, such as shade-tolerant understory plants.

Canopy

The uppermost stratum in a forest community, serving as the main site of energy capture.

Understory trees

A forest stratum consisting of tall shrubs and short trees (such as dogwood) adapted to shade.

Epilimnion

The warm, upper layer of freely circulating water in a stratified lake system.

Thermocline

The middle layer of a stratified body of water (metalimnion) characterized by a steep temperature gradient.

Hypolimnion

The cold, dark, lower layer of a stratified lake that has low oxygen levels due to decomposition.

Photic zone

The upper illuminated region of an aquatic ecosystem where light is sufficient for photosynthesis.

Benthic zone

The bottom sediment or substrate layer of an aquatic system where organic decomposition occurs.

Littoral zone

The shallow shore zone of a lake where emerged, floating, and submerged aquatic plants grow.

Zonation

Spatial change in biological community structure and physical environment across an environmental gradient.

Organic concept of communities

Frederick Clements' view that species co-occur in distinct, co-evolved clusters or associations along environmental gradients.

Individualistic or continuum concept

H.A. Gleason's view that coexisting species reflect individual overlapping tolerance ranges rather than co-evolved clusters.

Sorensen's coefficient of community ($CC$)

An index measuring species overlap between two communities calculated as $CC = \frac{2c}{s_1 + s_2}$, which does not account for species abundance.