Communities and Ecosystems – Vocabulary Flashcards
Ecosystem Terminology: Definitions and Scales
Ecosystem: all living (biotic) and nonliving (abiotic) components in a particular area and their interactions, with energy and nutrient flows linking everything (air, water, minerals, rocks, soil, etc.).
The ecosystem concept includes the environment and its processes, not just the organisms themselves.
Biosphere: the global sum of all ecosystems; the entire Earth’s living layer.
Community: all the living organisms (populations of different species) in a particular area or habitat, within an ecosystem; it excludes abiotic components.
Population: a group of individuals of the same species living and interbreeding in a defined geographic area.
Note on usage: these terms are related but not interchangeable; they refer to different levels of organization.
Food Chains vs. Food Webs; Descriptiveness of Relationships
Food chain: a single, linear sequence showing the flow of energy from one organism to the next; limited because it captures only a subset of interactions.
Food web: a network of many interacting feeding relationships; more descriptive of the actual complexity in ecosystems because most species interact with multiple others.
Example construction (step-by-step):
Start with a photosynthesizer (plant) at the base (grass/wheat).
Primary consumer: a herbivore (rabbit) eats the plant.
Secondary consumer: a predator (fox) eats the rabbit; other predators (bear, hawk) can also eat the predator or herbivores.
Additional interactions: insects eat plants; a snake eats rodents; a hawk may eat birds or mice; birds prey on insects.
Seasonal variation: interactions shift with seasons (e.g., insect availability vs seed/berry availability for songbirds).
Conclusion: food webs depict the complex, interconnected energy flow; food chains are useful for tracking a specific energy path but are simplistic.
Trophic Levels and Energy Transfer
Primary producers (First trophic level): photosynthesizers that create sugars from CO₂ and water using light energy (plants, algae, cyanobacteria).
Primary consumers (Second trophic level): organisms that eat primary producers (herbivores).
Secondary consumers (Third trophic level): organisms that eat primary consumers (carnivores/omnivores).
Tertiary or higher-level consumers (Fourth/Fifth trophic level): organisms that eat secondary consumers (top carnivores).
Decomposers: break down dead organic matter and recycle nutrients.
Typically, ecosystems do not exceed the fifth trophic level due to energy losses at each transfer.
Energy transfer efficiency: only about 10% of the energy at one trophic level is stored and becomes available to the next level; the rest is lost as heat or waste.
Expressed as: ext{Energy transfer efficiency} \approx 0.10, so E{n+1} = 0.10 \times En.
Implication: energy diminishes rapidly up the chain, requiring a large base of primary producers to support top predators.
Example illustrating the 10% rule:
Grass biomass = 1000 units; a herbivore (rabbit) stores ~10% of that energy: E_{rabbit} = 0.10 \times 1000 = 100{units}.
A predator (fox) feeding on rabbits stores ~10% of the rabbit’s energy: E_{fox} = 0.10 \times 100 = 10{units}.
Apex predators typically require large territories to access enough energy from primary production due to the 10% transfer rule.
Humans: dietary roles vary by what they consume:
When eating plants (fries/salad), humans are at or below primary/secondary consumer levels depending on diet.
Eating livestock places humans higher up (secondary/tertiary) depending on the prey’s position in the chain.
Oceanic high-trophic foods (e.g., tuna) place humans at fourth/fifth levels.
Overall, humans are not producers; they rely on producers and/or other consumers for energy.
Implication for human populations: moving toward plant-based or lower-level consumer diets is energetically more efficient for feeding large populations.
Primary Production and Biodiversity in Biomes
Primary production is the rate at which energy is captured by photosynthesizers; it influences the number and abundance of higher trophic levels.
Biomes with high primary production tend to support greater biodiversity and biomass.
Examples highlighted:
Coral reefs: high primary production, high biodiversity.
Tropical rainforests: extremely high biodiversity supported by abundant primary producers.
Estuaries: high photosynthetic activity in shallow, productive environments that support fisheries and many species.
Biomass concept: total mass of organic material in living organisms within an ecosystem; deserts have lower biomass than tropical forests due to fewer organisms.
Tie-in: primary producers enable the energy flow that supports all other trophic levels; biodiversity often correlates with the amount of primary production.
Symbiotic Relationships: Mutualism, Commensalism, Parasitism
Symbiosis: close, long-term interaction between two different species; can be beneficial, neutral, or harmful.
Mutualism: both species benefit; intimate, often prolonged relationship.
Commensalism: one species benefits, the other is neither harmed nor helped.
Parasitism: one species benefits at the expense of the other (host).
Competition (negative for both): two species compete for resources; can be viewed as a form of antagonism, often reducing efficiency for both.
Note: In practice, people often mislabel general interactions as "symbiotic"; the specific categories above are the precise definitions.
Mutualism: Examples
Figs and wasps: wasps pollinate figs while laying eggs inside the fig fruit; both partners benefit—pollination for the fig tree, habitat/reproductive site for the wasps.
Acacia and ants: hollowed plant structures house ants; ants defend the plant from herbivores and competitors in exchange for housing.
Sea anemone and clownfish: clownfish gain a safe habitat within stinging tentacles; anemones receive cleaning and potentially protection via the clownfish’s vigilance and movement.
Cleaner shrimp and fish: cleaner shrimp feed on parasites/debris from client fish, improving host health while the shrimp gain food.
Commensalism: Examples
Snails and hermit crabs: discarded shells used by hermit crabs for protection; snails are largely unaffected.
Remora and sharks: remoras gain a free ride and scraps of food, while sharks are largely indifferent to their presence.
Parasitism and Disease; Behavior-modifying Parasites
Parasitism examples:
Sea lamprey: external parasite with teeth that attach to fish, harmful to hosts; an invasive species in the Great Lakes.
Ticks: external parasites that can transmit diseases such as Lyme disease; climate change may influence spread.
Internal parasites (e.g., heartworms in dogs/cats).
Disease dynamics: disease spread is governed by host abundance, host accessibility, transmission rate, and host lifespan. Key factors:
Host lifespan length influences how long a parasite can persist on a host.
Transmission rate and host abundance interact to shape outbreak potential.
Lyme disease: early treatment with antibiotics is effective; late-stage infection can form biofilms that are antibiotic resistant, complicating treatment.
Parasites and behavior: some parasites alter host behavior to enhance transmission or survival, illustrating complex host–parasite interactions.
Biocontrol: using parasitic organisms to manage pest populations (biological control).
Coevolution: Reciprocal Adaptation Between Interacting Species
Coevolution: reciprocal evolutionary changes between interacting species (e.g., herbivores and plants; predator and prey).
Monarch butterfly and milkweed:
Monarch caterpillars specialize on milkweed that contains cardiac glycosides (cardenolides).
Monarchs sequester these toxins in their bodies, making themselves unpalatable to predators and providing chemical defense.
Milkweed evolved cardiac glycosides; monarchs evolved sequestration to tolerate and reuse the chemical defense.
Moths and bats (predator–prey coevolution):
Bats use echolocation to detect prey at night; some moths have tympanal organs and can hear bat echolocation.
Responses include wing-foiling (freeze) or jamming echolocation signals; some bats adapt by hunting over water where moths’ wing-foiling is less effective.
This ongoing arms race leads to diverse adaptations on both sides.
Additional example: plant defenses and herbivory (capsaicin in peppers deters many herbivores but attracts certain seed-dispersers such as birds that lack teeth and can disperse seeds without being harmed, while humans selectively breed for spicy varieties).
Predator–Prey and Plant–Herbivore Interactions; Defenses
Herbivory and plant defenses:
Plants evolve structural defenses: spines, thorns, prickles; thicker cuticles; waxy coatings.
Plants evolve chemical defenses: toxins (e.g., cardiac glycosides, capsaicin, cyanogenic glycosides) to deter herbivores.
Seeds often protected chemically or structurally; capsaicin concentrates in seeds to deter mammalian browsers while allowing birds (which lack teeth) to disperse seeds.
Predator–prey dynamics:
Predators regulate prey populations; prey develop varied defenses (camouflage, chemical defenses, mimicry, warning coloration).
Some insects exhibit aposematic coloration to warn predators; color patterns often converge among toxic species (e.g., monarchs and other toxic insects).
Plant–insect interactions include mutualistic pollination and herbivory; plants may tolerate some herbivory if fitness is maintained by pollination.
Niche: Fundamental and Realized Niche
Niche: the role and position a species has in its environment; what it actively does (resources it uses, actions it performs).
Fundamental niche: the full range of environmental conditions and resources a species could theoretically use given its traits.
Realized niche: the actual set of resources and conditions the species uses in the presence of competitors and other ecological constraints.
Examples:
A bird that is omnivorous might theoretically eat seeds, berries, and insects (fundamental); in a heavily competed environment it may primarily eat insects and berries (realized).
Plants might have deep tap roots and shallow roots in their fundamental potential; under competition, some may invest more in specific root depths (realized) to reduce competition.
Invasions: when humans relocate organisms, their realized niche can shift dramatically, leading to invasive species that disrupt native systems.
Invasive species: nonnative organisms that establish breeding populations and cause ecological, economic, or health harms; their niche may expand in the new environment, often reducing native biodiversity.
Biodiversity: Richness vs Relative Abundance; Role of Predators
Biodiversity components:
Species richness (count of species).
Relative abundance (evenness): how individuals are distributed among species.
A high biodiversity assessment should consider both richness and evenness, not just the raw species count.
Example (forest comparisons):
Forest A and Forest B have the same number of species, but Forest A has even distribution among species; Forest B is conifer-dominated with one or two species making up most of the population. The two systems differ in ecological function and resilience.
Predator role in biodiversity:
Predators can maintain biodiversity by preventing any single prey species from dominating and by controlling disease and population sizes (trophic cascades).
Classic demonstration: sea stars as keystone predators; removing predatory sea stars reduced species richness dramatically due to mussel overgrowth.
Keystone species: disproportionately large effect on community structure relative to their abundance; their removal can trigger trophic cascades and ecosystem collapse.
Example groups often cited as keystone players:
Wolves in Yellowstone: predator presence controls herbivore populations, ecosystem structure, and landscape processes; wolf removal led to trophic cascades affecting vegetation and rivers; reintroduction aided ecosystem recovery.
Sharks: apex predators in marine systems that promote biodiversity; significant declines in shark populations lead to reduced species diversity and altered community structure.
Beavers: ecosystem engineers; their dam-building creates wetlands, modifies hydrology, and increases habitat diversity.
Sea otters: keystone species in kelp forest ecosystems; by preying on sea urchins, they prevent overgrazing of kelp forests, maintaining habitat for many species.
Disturbance and Ecological Succession
Disturbance: an event that changes community structure (e.g., fires, storms, floods, human disturbances like logging).
Succession: the orderly pattern of species replacement that follows a disturbance.
Primary succession: starts with bare rock; no soil or life remains; slow progression from pioneer species (mosses, lichens) to soil formation, then grasses/annuals, perennials, shrubs, trees; commonly ends in a climax community.
Secondary succession: starts with soil and some seed bank or remnants present; faster progression than primary; typical in abandoned fields or after moderate disturbances.
Fire-based succession and longleaf pine ecosystem (an example of a fire-maintained system):
Longleaf pine ecosystems were historically maintained by regular fire; suppression led to loss of habitat and reduced biodiversity.
Prescribed burning is used to renew vegetation, reduce fuel buildup, and restore ecosystem health.
Longleaf pines: unique growth pattern with a grass stage (rocket stage) during which they invest in rapid growth in a fire-prone environment; needles and bark provide fire resistance; seeds require fire-related cues (scarification and smoke) for germination.
Fire ecology and management:
Fire suppression can lead to fuel buildup, hotter and longer fires, and loss of fire-adapted species.
Restoring fire regimes can sustain open understories, biodiversity, and habitat for species dependent on fire-adapted ecosystems.
Common succession trajectories in temperate zones:
Pioneer grasses and forbs → shrubs → young trees → mature forest; in many Southeastern landscapes, pines often establish early and are later replaced by hardwoods in a climax system.
Human land-use legacy and succession:
Old-field succession is a common trajectory in abandoned agricultural land, progressing from grasses to pines to hardwoods over time.
Longleaf Pine Ecosystem: Fire, Growth, and Conservation
Fire-adapted traits in longleaf pines:
Grass stage (early growth) protects the cambial tissue from fire; needles later emerge to form a protective canopy.
Rocket stage: rapid vertical growth before full canopy formation, enabling fast year-to-year growth while remaining adapted to fire.
Fire resistance in mature trees with thick bark and canopy architecture to survive regular burns.
Ecological importance of longleaf pine systems:
High biodiversity and unique understory communities supported by the open canopy and frequent fire.
Habitat for species such as the gopher tortoise, indigo snake, Bachman’s sparrow, and the red-cockaded woodpecker (many endangered species depend on this ecosystem).
Seed activation by fire:
Some seeds require fire to germinate, a process called activation; mechanisms include scarification (seed coat abrasion) and thermal cues; cold stratification and smoke exposure can also influence germination.
Management implications:
Prescribed burns are used to mimic natural fire regimes and maintain open understories, promote regeneration, and protect fire-adapted species.
Fire management helps prevent catastrophic wildfires by reducing fuel loads and maintaining ecosystem health.
Real-World Relevance and Takeaways
Biodiversity assessment: species richness vs relative abundance provide a fuller picture of ecosystem health and function.
Invasive species: human movement and habitat alteration can introduce new species that disrupt native niches, reduce biodiversity, and alter ecosystem processes.
Predator importance: keystone predators (e.g., wolves, sharks) can maintain biodiversity and ecosystem balance through trophic cascades; their removal can lead to ecological collapse in some systems.
Human nutrition and energy budgets: the 10% energy transfer rule explains why lower-trophic-level foods are more efficient for feeding large populations; shifts toward plant-based diets or lower-trophic-level consumption can improve energy efficiency and sustainability.
Parasites and climate: climate change and human activity influence parasite spread (e.g., ticks and Lyme disease; sea lampreys in the Great Lakes), with economic and health implications.
Keystone and disturbance concepts: recognizing keystone species and the role of disturbance and succession helps explain how ecosystems recover after disruption and where conservation priorities should lie (e.g., protecting large carnivores, preserving habitat connectivity).
Fire ecology and habitat restoration: fire regimes are integral to certain ecosystems (e.g., longleaf pine) for maintaining structure, nutrient cycling, and species diversity; restoration often requires reintroducing fire.
Quick Connections to Foundational Ideas
Systems thinking: ecosystems are networks of energy flow, matter cycling, and species interactions; changes in one component ripple through the system.
Evolutionary biology: coevolution explains reciprocal adaptations (plants–herbivores; prey–predator) and drives biodiversity and niche diversification.
Conservation biology: recognizing keystone species, habitat connectivity, and disturbance regimes guides management to sustain ecosystem services and biodiversity.
Key Terms to Memorize
Ecosystem, biosphere, community, population
Food chain, food web, trophic levels, primary producers, primary/secondary/tertiary consumers, decomposers
Energy transfer efficiency: \eta \approx 0.10; E{n+1} = \eta En
Mutualism, commensalism, parasitism; competition (exploitation vs interference)
Niche: fundamental vs realized
Keystone species, trophic cascade
Disturbance, succession (primary vs secondary)
Fire-adapted ecosystems; longleaf pine; rocket stage; grass stage; seed activation by fire
Invasive species; examples: European starling, sea lamprey
Monarch–milkweed coevolution; aposematism; sequestration of cardiac glycosides
Possible Exam Prompts You Should Be Ready To Explain
Distinguish between ecosystem, community, and population with examples.
Compare and contrast a food chain vs a food web; explain why food webs are more descriptive.
Explain the 10% energy transfer rule and illustrate it with a numerical example.
Define a keystone species and provide several examples; describe what a trophic cascade is.
Describe mutualism, commensalism, and parasitism with three examples each from the transcript.
Explain the concepts of fundamental vs realized niche; discuss how invasive species can alter realized niches.
Describe primary vs secondary succession and give a Southeastern example (longleaf pine) including the role of fire.
Discuss how predators influence biodiversity and ecosystem stability, citing Yellowstone wolves and other keystone examples.
Explain monarch butterfly–milkweed coevolution and the role of cardiac glycosides in defense and adaptation.
Outline how climate change and human activity can alter parasite transmission and disease dynamics (ticks/Lyme, sea lamprey in the Great Lakes).