Global Biodiversity and Island Biogeography

Vocabulary practice flashcards covering global biodiversity gradients, community stability hypotheses, global biomass distribution, and the equilibrium and tripartite theories of island biogeography.

Niche Breadth ($w$)

The standard deviation of resource use by a species along a continuous resource spectrum in competition theory.

Resource Separation ($d$)

The distance between two species in their average resource use along a continuous resource spectrum in competition theory.

Full Coexistence Criterion ($d/w > 3$)

The mathematical condition under competition theory where the distance between two species' mean resource use ($d$) is greater than three times niche breadth ($w$), allowing stable coexistence.

Competitive Exclusion Criterion ($d/w < 1$)

The mathematical condition under competition theory where niche separation ($d$) is less than niche breadth ($w$), resulting in extensive resource overlap and preventing coexistence.

Spatial Heterogeneity Theory

An explanation for global species richness proposing that structurally more complex environments provide a higher variety of microhabitats and ecological niches, supporting higher species diversity.

Architectural Rating

A quantitative measurement of structural and physical complexity in plants (demonstrated using Opuntia prickly pear) that correlates positively with insect species richness for the same photosynthetic area.

Environmental Age Theory

An explanation for global species richness suggesting that unglaciated tropical regions are biologically older and have had uninterrupted time to accumulate species, whereas temperate regions have suffered repeated glaciations.

Cordilleran Ice Sheet

The continental glacier that covered much of western Canada and parts of Alaska during the Glacial Maxima approximately $15{,}000$ years ago.

Pollen Influx Diagram

A paleoecological graph derived from sediment cores (such as a 3-meter core from a lake in the Yukon Territory) that quantifies pollen accumulation rates in grains per square centimeter per year over time.

Scale-Dependent Richness Drivers

The ecological concept that the primary drivers of species richness vary by scale: continents are governed by primary productivity and environmental age; regions by productivity, age, and spatial heterogeneity; and local communities by competition, predation, and spatial heterogeneity.

Diversity-Stability Hypothesis

A hypothesis proposed by Charles Elton stating that species-rich communities possess higher ecological resilience and a greater capacity to return to a pre-disturbance state.

Rivet Hypothesis

A hypothesis proposed by Paul and Anne Ehrlich analogizing species in an ecosystem to rivets in an airplane wing, where the loss of each species gradually weakens stability until a critical threshold causes abrupt ecosystem collapse.

Redundancy Hypothesis (Passenger Hypothesis)

A hypothesis proposed by Brian Walker proposing that ecosystem stability is maintained primarily by a few keystone or dominant species functioning as the "pilot," while most other species function as ecologically redundant "passengers."

Idiosyncratic Hypothesis

A hypothesis proposed by John Lawton proposing that ecosystem stability and function change unpredictably as species richness varies because individual species have complex, highly variable roles.

Terrestrial Biomass Pool

The largest planetary biomass reservoir, comprising approximately $86\%$ ($\approx 470\text{ Gt C}$) of all living global biomass, dominated almost entirely by plants ($\approx 100\%$ terrestrial).

Deep Subsurface Biomass Pool

The subterranean living biomass reservoir accounting for approximately $13\%$ ($\approx 70\text{ Gt C}$) of global biomass, which contains $89\%$ of Earth's bacterial biomass and $90\%$ of archaeal biomass.

Marine Biomass Pool

The oceanic living biomass reservoir accounting for approximately $1\%$ ($\approx 6\text{ Gt C}$) of total planetary biomass, while harboring approximately $78\%$ of global animal biomass.

Species-Area Relationship ($S = cA^z$)

The empirical power-law equation relating species richness ($S$) to geographic area ($A$), where $c$ is a taxon-specific constant and $z$ represents the slope on a log-log plot.

$z$-Slope (Mainland vs. Islands)

The slope of the species-area relationship, which typically ranges from $0.10\text{--}0.16$ across arbitrary mainland areas, increases to $0.18\text{--}0.37$ on oceanic islands, and reaches up to $0.72$ in isolated habitat islands like caves.

Equilibrium Model of Island Biogeography

MacArthur and Wilson's theoretical model stating that island species richness reaches a dynamic equilibrium ($S_0$) determined by the balance between immigration rate and extinction rate.

Distance Effect (Island Biogeography)

The principle that islands located closer to a mainland source pool experience higher colonization and immigration rates, resulting in a higher equilibrium number of species than distant islands.

Area Effect (Island Biogeography)

The principle that larger islands sustain larger populations with lower risk of extinction, resulting in a higher equilibrium number of species than smaller islands.

Species Turnover

The ongoing process at biogeographic equilibrium where species identity in a community continuously changes through recurrent local extinctions and immigrations while total richness remains stable.

Ecological Disharmony

The non-representative taxonomic composition of island biotas relative to mainland sources, driven by differing dispersal capabilities and the frequent absence of predators on small islands.

Inbreeding Depression on Islands

The loss of heterozygosity and fitness reduction that accelerates extinction in small island populations, particularly severe when effective population sizes fall to $N \le 15$.

Krakatau Plant Succession Pattern

The post-eruption botanical colonization sequence on Krakatau, initiated predominantly by wind dispersal, followed over successive decades by increasing proportions of animal- or bird-dispersed and water-dispersed seeds.

Mangrove Defaunation Experiment

A field test of MacArthur and Wilson's equilibrium theory conducted by Simberloff and Wilson, in which small mangrove islands were enclosed under plastic scaffolding and fumigated to observe arthropod re-colonization.

Tripartite Model of Island Biogeography

An extended biogeographical framework that incorporates in situ speciation alongside immigration and extinction over geological time to explain island richness and endemism across gradients of area and isolation.

Island Biodiversity Paradox

The macroecological phenomenon reviewed by Matthews and Triantis (2021) wherein islands occupy only $3.5\%$ of global land surface yet support roughly $15\text{--}20\%$ of terrestrial species and over $25\%$ of human languages.

Food Web Connectance ($C$)

A structural measure of community complexity defined as the ratio of actual trophic links ($L$) to the maximum possible links ($N$), expressed as $C = \frac{L}{N}$, where $N = \frac{n(n-1)}{2}$ for a community of $n$ species.