Community and Population Ecology

Comprehensive practice flashcards in vocabulary style covering community ecology gradients, diversity metrics, ecological interactions, food webs, disturbances, metapopulations, human demography, and population monitoring methods across Lectures 4, 5, and 6.

Humboldt's Mountain Principle

The ecological observation that as one climbs a mountain, biological communities change along the elevational gradient in the same sequence as when traveling from the equator toward the poles.

Mount Chimborazo

An equatorial Andean volcano studied by Alexander von Humboldt to illustrate the altitudinal zonation of plant communities, featured in his classic 'Tableau Physique'.

Moret et al. (2019) Resurvey

A modern resurvey of Mount Chimborazo revisiting Humboldt's 'Tableau Physique' after 200 years to document how vegetation zones have shifted upslope under climate warming.

Ecological Gradient

A gradual spatial change in abiotic or biotic factors (such as temperature, moisture, or elevation) that drives changes in community composition and diversity.

Five Types of Ecological Gradients

The major environmental axes identified as shaping community differences: latitude, elevation, rainfall, area, and isolation.

Species Richness

The total number of different species present in a defined ecological community or sample.

Relative Abundance

The proportional representation of individuals of each species relative to the total number of individuals in a community, reflecting species evenness.

Community 1 (Relative Abundance)

A hypothetical four-species community exhibiting perfect evenness, where species A, B, C, and D each represent $25\%$ of all individuals.

Community 2 (Relative Abundance)

A hypothetical four-species community with low evenness dominated by species A ($80\%$), with species D at $10\%$ and species B and C at $5\%$ each.

Shannon Diversity Index ($H$)

A mathematical index quantifying community diversity by combining species richness and evenness, calculated as $H = -\sum (p \times \ln(p))$, where $p$ is the proportion of individuals of each species.

Shannon Diversity Calculation of Community 1

The diversity value calculated for four equally abundant species ($p = 0.25$ each): $H = -[4 \times (0.25 \times \ln(0.25))] = 1.39$.

Shannon Diversity Calculation of Community 2

The diversity value calculated for an uneven four-species community ($p_A=0.80$, $p_B=0.05$, $p_C=0.05$, $p_D=0.10$), resulting in $H = 0.71$.

Species Accumulation Curve

A graph tracking the cumulative number of unique species discovered as sampling effort (such as survey walks, quadrats, or visits) increases.

Detectability of Rare Species

The sampling reality that species with very small population sizes are easily missed during surveys and dictate the total sampling effort required to inventory a community.

Survey Effort in Even vs. Skewed Communities

The principle illustrated by two 1,000-individual sites: recording $95\%$ of species requires approximately 8 surveys at an even site (20 species) but 262 surveys at a skewed site (15 species).

Alpha Diversity ($\alpha$)

The local species diversity measured as the number of different species coexisting within a single specific habitat patch or site.

Beta Diversity ($\beta$)

The extent of species turnover or difference in species composition when comparing one habitat patch or site to another across a landscape.

Gamma Diversity ($\gamma$)

The overall regional species diversity representing the total pool of species found across an entire geographic landscape or region.

Environmental DNA (eDNA)

Traces of cellular DNA extracted from water or soil samples that allow researchers to detect cryptic, rare, or microscopic organisms without direct physical observation.

Latitudinal Diversity Gradient of Bird Species

The macroecological pattern where global avian species richness increases sharply toward the equator, reaching peaks of up to 532 species in the Neotropics.

History and Climate Stability Hypothesis

The explanation for high tropical diversity proposing that tropical environments have remained warm and stable for longer evolutionary periods, while temperate and polar zones were repeatedly scraped clean by glaciations.

Energy and Water Hypothesis

The explanation proposing that species richness rises directly with available solar energy and precipitation, which fuel high primary productivity and support more species.

Actual Evapotranspiration (AET)

The total volume of water evaporated from soil and transpired by vegetation, which depends on both warmth and rainfall and correlates strongly with broad-scale species richness.

Janzen-Connell Hypothesis

The hypothesis proposing that host-specific seed predators, herbivores, and pathogens congregate near parent trees, driving higher seedling mortality nearby and creating enemy-free space for rare species.

Negative Frequency-Dependence

An ecological mechanism where a species experiences lower seedling survival or recruitment as its local seed abundance rises, preventing any single species from dominating a community.

Bagchi et al. (2014) Experiment

A rainforest field experiment that sprayed plots with water, insecticide, or fungicide to prove that fungal pathogens and insect herbivores drive negative density-dependent seedling survival.

Fungicide Effect on Rainforest Seedlings

The experimental finding from Bagchi et al. (2014) showing that applying fungicide removes negative frequency-dependence, allowing common tree seedlings to escape specialized fungal enemies.

Insecticide Effect on Rainforest Seedlings

The experimental finding from Bagchi et al. (2014) demonstrating that excluding insect herbivores reduces density-dependent seedling mortality in tropical forests.

OCBIL Theory

An ecological and evolutionary framework proposed by Stephen Hopper (2009) to explain high biodiversity and endemism on Old, Climatically Buffered, Infertile Landscapes.

Key Characteristics of OCBILs

Landscapes characterized by deep geological age, an absence of recent glacial disruption, sustained climatic buffering, and extremely poor, weathered, infertile soils.

Global Examples of OCBILs

Global regions embodying OCBIL conditions: Southwest Western Australia, inland Southwest WA, Namaqualand (South Africa), Cape Point (South Africa), and the Venezuela-Brazil border tepuis.

Species-Area Relationship

The biogeographic rule that larger landmasses or islands support more species because larger areas support larger population sizes with lower extinction probabilities.

Island Biogeography Distance Effect

The principle that islands located closer to a mainland source pool exhibit higher colonization rates and maintain higher species richness than more distant, isolated islands.

Simberloff and Wilson (1969) Defaunation Experiment

An experimental defaunation of Florida Keys mangrove islands using fumigation, confirming that islands closer to the mainland were recolonized faster and supported more arthropod species.

Four Explanations for Amazonian Tree Diversity

The combined factors explaining why one hectare of Amazon forest holds more tree species than all of Europe: time (stability), energy and water (warm and wet), enemies (specialized pathogens/insects), and vast contiguous area.

Restoration Ecology

The applied ecological discipline (Campbell Ch. 55) that applies ecological theory to repair, recover, and manage degraded or damaged ecosystems.

Tools of Restoration Ecology

Management techniques including threat removal (fencing, grazing control), structural rebuilding (replanting, adding dead wood), trophic control manipulation, and species reintroductions.

Yellowstone Wolf Reintroduction (1995)

The restoration of grey wolves to Yellowstone National Park 69 years after the last native wolf was killed in 1926, initiating a celebrated top-down trophic cascade.

Yellowstone Ecosystem 'Before' Wolves

An ecosystem state lacking large apex predators, dominated by small predators and overabundant large herbivores (elk), resulting in simplified plant communities and lower songbird diversity.

Yellowstone Ecosystem 'After' Wolves

A restored community characterized by a balanced mix of large and small predators, fewer large herbivores, regenerated woody riparian vegetation, and a diverse songbird community.

Gorongosa National Park

A national park in Mozambique that suffered catastrophic large-mammal population collapse during war, followed by rapid recovery aided by targeted reintroductions.

Atkins et al. (2019) Gorongosa Study

A study demonstrating that the war-induced extirpation of apex carnivores (leopards and wild dogs) released bushbuck from the 'landscape of fear', altering their spatial foraging behavior.

Bushbuck (Tragelaphus scriptus)

A spiral-horned African antelope that shifted its niche from dense woody thickets into open floodplains following large-carnivore extirpation in Gorongosa National Park.

Ecology of Fear

The psychological and behavioral impact of perceived predation risk that drives prey to avoid risky habitats, shaping community structure independently of direct predatory killing.

Mulligans Flat Woodland Sanctuary

An experimental conservation reserve in Canberra, Australia, surrounded by a predator-proof fence designed to exclude feral cats, foxes, and rabbits and restore Box-Gum Grassy Woodland.

Box-Gum Grassy Woodland (BGGW)

A critically endangered Australian ecological woodland community undergoing large-scale experimental restoration at Mulligans Flat and Goorooyarroo Nature Reserves.

Coarse Woody Debris (Dead Wood Experiment)

A habitat restoration experiment at Mulligans Flat adding fallen logs at varying densities to provide shelter and foraging structure for beetles, reptiles, and ground-foraging birds.

Eastern Bettong (Bettongia gaimardi)

A reintroduced marsupial ecosystem engineer at Mulligans Flat that digs thousands of foraging pits per year, aerating soil, trapping seeds, and spreading mycorrhizal fungi.

Ecosystem Engineer

An organism that directly creates, modifies, maintains, or destroys physical habitat structure, profoundly influencing resource availability for other species.

Hysteresis in Tasmanian Kelp Restoration

The ecological barrier where removing sea urchins alone fails to bring back overgrazed giant kelp forests because the degraded urchin barrens represent a resilient alternative stable state.

Interspecific Competition ($- / -$)

An ecological interaction occurring between individuals of different species where both suffer reduced fitness, survival, or reproduction due to reliance on shared limiting resources.

Competitive Exclusion Principle

The ecological rule proposing that two species competing for the exact same limiting resources cannot coexist indefinitely; the species with even a slight competitive edge will exclude the other.

Gause's Paramecium Experiment

Classic laboratory competition experiments showing that Paramecium aurelia drives Paramecium caudatum to extinction when grown together in a shared culture medium.

Connell's Barnacle Experiment

A seminal marine field experiment demonstrating that interspecific competition from Balanus restricts Chthamalus to the high intertidal zone, despite Chthamalus being able to survive lower down.

Fundamental vs. Realized Niche

The theoretical range of environmental conditions under which a species could survive without competitors, compared to the actual, narrower niche space it occupies in the presence of competitors.

Predation, Herbivory, and Parasitism ($+ / -$)

Antagonistic ecological interactions where one organism derives nutritional benefit ($+$, survival/fecundity) while the host, prey, or plant suffers a fitness cost ($-$).

Mutualism ($+ / +$)

An interspecific interaction in which both interacting species experience net fitness, survival, or reproductive benefits.

Commensalism ($+ / 0$)

An ecological relationship where one species benefits while the other species is neither helped nor harmed by the interaction.

Tree Hollow Commensalism

An Australian woodland commensal interaction where birds and arboreal marsupials gain vital nesting cavities from mature eucalypts without measurably impacting the trees.

Eastern Spinebill (Acanthorhynchus tenuirostris)

A nectar-feeding Australian honeyeater whose long, decurved bill represents an evolutionary adaptation shaped by mutualisms with tubular flowers and competition for nectar.

Adaptive Radiation of Caribbean Anolis Lizards

The rapid evolutionary diversification of Anolis lizards across the Greater Antilles into specialized ecomorphs adapted to specific structural microhabitats on trees and shrubs.

Ecomorph

A group of species with similar morphology and behavior adapted to a shared structural habitat type, regardless of their phylogenetic relatedness.

Crown-Giant Anole Ecomorph

An anole ecomorph living in the high tree canopy, characterized by an exceptionally large body size and robust jaws.

Trunk-Crown Anole Ecomorph

An anole ecomorph occupying the upper trunk and canopy, possessing enlarged subdigital toe pads for adhering to smooth leaves.

Trunk Anole Ecomorph

An anole ecomorph living on vertical tree trunks, characterized by a dorsoventrally flattened body that minimizes shadow and clings close to tree bark.

Trunk-Ground Anole Ecomorph

An anole ecomorph residing on lower tree trunks and the ground, equipped with long hind legs built for rapid sprinting and jumping.

Twig Anole Ecomorph

An anole ecomorph adapted to narrow twigs and branches, possessing very short limbs and moving slowly and deliberately.

Grass-Bush Anole Ecomorph

An anole ecomorph living in grasses and low bushes, characterized by a slender body and an exceptionally long tail for balance.

Convergent Evolution in Caribbean Anoles

The independent evolution of matching ecomorph body plans on Cuba, Hispaniola, Jamaica, and Puerto Rico, where species on each island are more closely related to each other than to matching ecomorphs elsewhere.

Sympatry

The condition where two or more species or populations inhabit the same geographic area and encounter one another regularly.

Allopatry

The condition where populations or closely related species live in physically separate, non-overlapping geographic ranges.

Character Displacement in Anolis Perch Heights

The behavioral divergence observed by Stroud et al. (2024) where sympatric brown anoles (A. sagrei) perch significantly lower ($33\%$ on ground) and crested anoles (A. cristatellus) perch significantly higher compared to when living in allopatry.

Character Displacement

The evolutionary divergence of morphological, physiological, or behavioral traits in sympatric populations of competing species to reduce interspecific competition.

Natural Selection Mechanism in Character Displacement

The process whereby individuals with traits overlapping a competitor suffer reduced resource access and lower fitness, favoring individuals with divergent traits that experience less competition.

Character Displacement in Australian Dasyurids

Morphological divergence documented by Jones (1997) where body size and canine dimensions in carnivorous quolls and relatives diverge in sympatry to partition prey sizes.

Character Displacement in Australian Thornbills

Morphological bill size and shape divergence documented by Coman et al. (2020) among co-occurring Acanthiza thornbill species to partition insect prey.

Sooty Oystercatcher (Haematopus fuliginosus)

A coastal shorebird species where bonded pairs defend rocky tidal outcrops and display pronounced sexual bill dimorphism to minimize food competition during low tide.

Bill Sexual Dimorphism in Sooty Oystercatchers

An ecological trait partition where female sooty oystercatchers have longer 'slicing' bills and males have shorter 'hammering' bills, dividing the food niche between pair members.

Fitness Penalties of Competition vs. Predation

The evolutionary principle that competition reduces individual fecundity and survival, whereas predation eliminates survival and lifetime reproduction entirely ($0\,\text{fitness}$).

Muskoxen Anti-Predator Defense Formation

A collective anti-predator behavioral adaptation where adult muskoxen form an outward-facing defensive horn ring in the snow to protect vulnerable calves from Arctic wolves.

Maxillary Overhang

The slight downward tip of an avian upper beak that overlaps the lower mandible, functioning as an essential grooming tool for controlling ectoparasites.

Clayton et al. (2005) Ectoparasite Experiment

An experimental trimming of the avian maxillary overhang that did not alter feeding rates but caused explosive increases in feather lice, proving its role in parasite defense.

Global Historical Prevalence of Malaria

The spatial extent of malaria infection, which covered approximately $53\%$ of the world's land surface in 1900 before being eradicated across regions to cover $27\%$ by 2002.

Commensalism in Cattle Egrets and Cape Buffalo

An ecological interaction where cattle egrets feed on insects flushed from grass by grazing buffalo, gaining food without affecting the buffalo ($+ / 0$).

Co-evolutionary Arms Race

A recurring evolutionary cycle where adaptations in one interacting species (such as prey defenses or parasite virulence) drive reciprocal counter-adaptations in another species.

Mixed-Species Foraging Flocks

Cooperative foraging groups of different bird species that move together, benefiting from shared vigilance against predators while partitioning vertical foraging strata.

Thornbill Stratum Specialization (Farine & Milburn 2013)

Niche partitioning in mixed flocks where buff-rumped thornbills shift lower when flocking with yellow-rumped thornbills and higher when flocking with striated thornbills.

Interspecific Alarm Call Sharing

An antipredator cooperative benefit in mixed flocks where distinct bird species respond immediately to one another's alarm vocalizations regarding approaching raptors.

Ecological Interaction Network

A graph-based representation of community structure where species are modeled as nodes and their biological interactions (trophic, mutualistic, competitive) are modeled as connecting edges.

Nodes and Edges

The mathematical components of a network: nodes represent distinct individual organisms or species, while edges define the relationships or interactions connecting them.

Food Chain

A linear sequence tracking the transfer of food energy from primary producers through successive consumers and up to top predators.

Trophic Levels

The hierarchical feeding stages in an ecosystem, spanning primary producers, primary consumers, secondary consumers, and apex predators.

Tasmanian Kelp-Urchin-Lobster Food Chain

A marine trophic chain where southern rock lobsters consume long-spined sea urchins, which in turn graze upon primary-producer giant kelp.

Lichen-Reindeer Food Chain

A classic two-level subarctic food chain linking primary producer lichens directly to herbivorous reindeer.

Food Web

A complex, interconnected network of multiple overlapping food chains illustrating the multifaceted feeding relationships across all species in a community.

Keystone Species

A species that exerts disproportionate control over community structure and species diversity relative to its biomass or abundance (e.g., Pisaster sea stars or apex wolves).

Top-Down Control

Regulation of community structure where the abundance, predation, or behavior of higher trophic levels controls the population sizes of organisms at lower trophic levels.

Bottom-Up Control

Regulation of community structure where nutrient availability or primary producer biomass limits the energy available to higher trophic levels.

Australian Desert Boom-and-Bust Dynamics

An ecological pulse system where erratic heavy rainfall triggers rapid desert plant flowering and seeding, initiating bottom-up booms followed by top-down predator crashes.

Desert Booms: Long-Haired Rats and Letter-Winged Kites

A classic Australian arid trophic boom where rainfall flushes vegetation, sparking an irruption of long-haired rats (Rattus villosissimus) that feeds a population surge in predatory letter-winged kites.