Community Ecology, Energy Flow, and Biodiversity Loss

Comprehensive vocabulary flashcards covering community ecology, diversity indices, ecosystem energy dynamics, nutrient cycles, and the mechanisms and drivers of global biodiversity loss.

Community

A group of potentially interacting species occurring together in space and time, essentially representing a collection of populations.

Guild

A group of species that exploit the same class of environmental resources in a similar way (for example, hollow-nesting animals such as Leadbeater's possums, owls, and crimson rosellas).

Functional group

A set of species that provide the same ecological function or respond to environmental disturbance in the same manner (for example, legumes that fix atmospheric nitrogen via root nodule bacteria).

Forb

A herbaceous, small flowering plant that lacks woody stems and is distinct from grasses.

Crown cover

The proportion of light blocked by the tree canopy, determined by the density of and gaps between clusters of leaves.

Trophic level

The feeding position of an organism within a food chain or ecological food web (such as primary producer, primary consumer, or secondary consumer).

Species richness ($S$)

The total count of distinct biological species present within a specified ecological community or sample.

Evenness

A measure of how equally total abundance or individual organisms are distributed among the various species present in a community.

Shannon diversity ($H$)

A diversity index combining species richness and evenness, defined by the formula $H = -\sum p_i \ln(p_i)$, which increases with higher species richness and greater evenness.

Shannon evenness ($J$)

A standardized measure indicating how close Shannon diversity is to its theoretical maximum for a given richness, calculated as $J = \frac{H}{\ln(S)}$ on a scale from $0$ to $1$.

Entropy (Information Theory)

A mathematical measure of uncertainty or flatness of a probability distribution formulated by Claude Shannon (1948), which underpins the Shannon diversity index.

Functional diversity

The range and variety of biological traits and ecological functions performed by co-occurring species within a community (such as variations in root depths accessing different soil strata).

Functional redundancy

The co-occurrence of multiple species that execute comparable ecological roles, ensuring community processes persist if a single species is lost.

Averaging effect

The principle that summing multiple independent, fluctuating population trajectories dampens overall community biomass variability, analogous to averaging large numbers of coin flips.

Stability (Tilman)

The temporal persistence of community biomass, mathematically quantified as the mean biomass divided by its standard deviation ($\frac{\text{mean}}{\text{SD}}$) over time.

Ecosystem

An ecological community of interacting organisms together with the abiotic physical and chemical environment through which energy and nutrients flow.

Net primary production (NPP)

The total amount of organic plant biomass generated per unit area per year after subtracting losses from autotrophic cellular respiration.

Consumption efficiency

The proportion of total available biomass present at one trophic level that is actually ingested by consumer organisms at the next trophic level.

Assimilation efficiency

The proportion of consumed food biomass that is absorbed and digested across the gut wall into the consumer's body rather than egested as feces or urine.

Production efficiency

The proportion of assimilated energy that is incorporated into new secondary consumer biomass through physiological growth and reproduction.

Mass-specific metabolic rate

The rate of metabolic energy expenditure per unit of body mass, which scales inversely with body size due to lower surface-area-to-volume ratios in larger mammals.

Upwelling

The upward vertical movement of deep, cold, nutrient-rich oceanic water to the surface, fueling elevated rates of marine net primary production.

Inverted biomass pyramid

A trophic biomass structure characteristic of open oceans where a small standing stock of rapidly dividing phytoplankton supports an overarching, larger consumer biomass.

Bottom-up control

The regulation of community trophic abundance driven primarily by physical resource availability and net primary production ($\text{NPP}$) at the base of the food chain.

Top-down control

The regulation of ecological community structure driven by predation and consumer pressure exerted from higher trophic levels downward.

Trophic cascade

An indirect ecological interaction where apex consumer manipulations propagate down through food chains, causing alternating positive and negative abundance shifts across successive trophic tiers.

Food web

An interconnected network of complex feeding pathways and polyphagous interactions linking diverse producers, omnivores, and predators within a natural ecosystem.

Decomposition

The biological breakdown of dead organic matter, detritus, and waste products by microbial agents, notably heterotrophic fungi and bacteria.

Mineralisation

The biogeochemical transformation of organically bound elements into bioavailable inorganic compounds, enabling plant re-uptake.

Nitrogen fixation

The conversion of inert atmospheric nitrogen gas ($N_2$) into bioavailable ammonium ($NH_4^+$) mediated by specialized diazotrophic bacteria or atmospheric lightning.

Nitrification

The microbial oxidation process that converts ammonium into nitrite and subsequently into nitrate ($NH_4^+ \rightarrow NO_2^- \rightarrow NO_3^-$), the primary nitrogen form absorbed by plants.

Eutrophication

Excessive nutrient enrichment (typically phosphorus or nitrogen) of an aquatic habitat causing dense algal proliferation, microbial oxygen depletion upon senescence, and biodiversity declines.

Acid rain

Atmospheric precipitation acidified by dissolved sulfur and nitrogen oxides emitted during fossil fuel combustion, which strips critical nutrients such as calcium from soils.

Biodiversity

The variability and aggregate richness of biological life spanning multiple hierarchical scales, from genetic variation within populations to species and complex ecological biomes.

Megadiverse nation

One of a select group of $17$ countries recognized internationally for harboring a disproportionately large share of global species richness and endemic biota.

Endemism

The geographic restriction of a biological taxon exclusively to a specific defined geographic location or habitat, occurring nowhere else in the wild.

Biodiversity hotspot

A biologically rich geographic region hosting exceptional numbers of endemic species while simultaneously facing severe habitat destruction and environmental endangerment.

Extinction vortex

A self-reinforcing downward spiral where small population size, demographic stochasticity, inbreeding depression, and genetic drift synergistically accelerate a population toward extinction.

Inbreeding depression

The reduction in biological fitness, fertility, and survival rates observed in offspring produced by matings between closely related individuals within diminished populations.

Genetic drift

The stochastic fluctuation and loss of allele frequencies across generations due to sampling error, which erodes genetic variation and adaptive flexibility in small populations.

Demographic stochasticity

Random, chance-driven fluctuations in individual birth and death rates that exert disproportionately severe extinction threats upon numerically small populations.

Environmental stochasticity

Unpredictable external abiotic variations, weather extremes, and natural catastrophes (such as wildland fires and floods) that simultaneously impact entire ecological populations.

Background extinction rate

The baseline, long-term rate of species turnover and natural extinction documented in the Earth's geological fossil record outside of mass extinction events.

Mass extinction

A discrete geological interval defined by catastrophic, rapid global declines in biodiversity occurring at rates orders of magnitude above baseline background extinction levels.

Anthropocene

The contemporary geological epoch distinguished by profound, pervasive anthropogenic dominance over planetary ecosystems, climates, and biogeochemical cycles.

Evil sextet

The six primary anthropogenic drivers fueling modern global biodiversity declines: habitat loss and fragmentation, invasive species, overexploitation, co-extinction, infectious disease, and climate change.

Co-extinction

The loss or extinction of an affiliated species directly brought about by the extinction of an organism upon which it is obligately reliant (such as a host, specialized pollinator, or sole prey).

Mesopredator release

The rapid demographic expansion and behavioral release of mid-ranked predatory species following the extirpation or population suppression of a dominating apex predator.

Living Planet Index

A biological monitoring index tracking relative changes in monitored vertebrate population abundances across the globe since the benchmark year of $1970$.

IPBES

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, an international scientific body providing objective assessments regarding global biodiversity health and ecosystem functions.