Internal biological clocks with a ~24-hour cycle. Regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus. Affect sleep-wake cycles, hormone release, body temperature, metabolism. Entrained (synchronized) by light-dark cycles. Examples: sleep cycles, melatonin secretion, plant leaf movements. Disruption causes jet lag, shift work disorders
The physiological response to the length of day (photoperiod). Many organisms use day length as a cue for seasonal behaviors: flowering in plants (photoperiodism -> long-day/short-day plants), bird migration, animal reproduction cycles, dormancy. Involves phytochrome (plants) and melatonin pathways. Allows organisms to anticipate seasonal changes
Taxis: directed movement toward or away from a stimulus (directional). Examples: phototaxis (moths toward light, earthworms away), chemotaxis (bacteria toward nutrients), thermotaxis. Kinesis: undirected movement in response to a stimulus; speed/turning rate changes with conditions but no fixed direction. Both allow organisms to respond to environmental gradients
The position an organism occupies in a food chain/web. Producers (autotrophs) -> Primary consumers (herbivores) -> Secondary consumers (carnivores/omnivores) -> Tertiary consumers (top predators) -> Decomposers/detritivores. Each level loses ~90% of energy as heat (10% rule); only ~10% is passed to the next level. Limits the number of trophic levels (~4-5 typically)
Only about 10% of the energy available at one trophic level is transferred to the next. The remaining ~90% is used for: cellular respiration (metabolism), growth and reproduction (biomass that dies without being eaten), waste products, heat. Explains why food chains are short and why there are fewer apex predators. Energy pyramids are always upright
Producers (autotrophs): organisms that produce their own organic compounds from inorganic sources. Use photosynthesis (plants, algae) or chemosynthesis (some bacteria). Form the base of all food chains. Consumers (heterotrophs): organisms that obtain energy by eating other organisms. Include herbivores, carnivores, omnivores, detritivores
A food chain is a linear sequence of organisms showing who eats whom. A food web is an interconnected network of food chains showing all feeding relationships in an ecosystem. Food webs are more realistic because most organisms feed at multiple trophic levels. Energy flows directionally through food chains/webs; chemicals cycle
Diagrams showing the trophic structure of an ecosystem. Three types: (1) Pyramid of energy (always upright, most energy at base). (2) Pyramid of biomass (may be upright or inverted; e.g., inverted in aquatic ecosystems where phytoplankton reproduce rapidly). (3) Pyramid of numbers (may be inverted; e.g., many insects per tree). All demonstrate the 10% energy transfer rule
Population growth without limiting factors. Model: dN/dt = rN (r = intrinsic rate of increase). Graph: J-shaped curve. Only occurs when: unlimited resources, no competition, no predation, ideal conditions. Occurs: introduced species in new environments (early growth), bacterial colonies on fresh medium. r-strategists: species that use exponential growth
Population growth that slows as carrying capacity (K) is approached. Model: dN/dt = rN[(K-N)/K]. Graph: S-shaped (sigmoid) curve. Phase 1: exponential growth. Phase 2: growth slows as resources become limited. Phase 3: population stabilizes near K. When N > K: negative growth (population exceeds carrying capacity -> die-off). Most real populations follow logistic growth
The maximum population size that an environment can sustain indefinitely. Determined by: food supply, water, habitat space, disease, predation, other limiting factors. Denoted K in the logistic growth model. Not a fixed number - changes with environmental conditions (seasonal variation, climate change, habitat changes). Logistic growth oscillates around K
Limiting factors whose effect increases as population density increases. Examples: competition for resources, predation, disease (parasites spread faster at high density), accumulation of waste. More individuals -> more competition -> higher mortality, lower birth rates -> population declines. An important self-regulating mechanism
Limiting factors that affect population size regardless of density. Examples: natural disasters (fires, floods, hurricanes), extreme weather (drought, frost), pollution, habitat destruction, climate change. A population at any density can be devastated by these factors. Largely responsible for the exponential growth phase when species colonize new areas
A measure of species diversity in a community. D = 1 - Sigma(ni/N)2 where ni = number of individuals of species i, N = total individuals. Range: 0 (no diversity) to 1 (maximum diversity). Also expressed as H = -Sigma[(ni/N) × ln(ni/N)] for Shannon index. Higher diversity -> more stable ecosystem
The patterns of species composition and organization in a community. Determined by: species interactions, abiotic factors, disturbance regime, historical factors. Key features: species richness (number of species), relative abundance (evenness), trophic structure, spatial structure (canopy layers, vertical zonation). More diverse communities tend to be more stable
Populations of predators and prey influence each other's numbers cyclically. Classic Lotka-Volterra model: as prey increase -> predators increase -> more predation -> prey decrease -> predators decrease -> prey increase again. Real populations show similar oscillations. Refuge effects, functional responses (type I/II/III), and spatial heterogeneity can stabilize these cycles
Interaction where both species are negatively affected (-/-). Occurs when species compete for the same limited resources (food, water, space, mates). Competitive exclusion principle (Gause): two species competing for exactly the same resources cannot coexist indefinitely - one will outcompete the other. Can be reduced by character displacement (niche differentiation)
Interaction where predator benefits (+) and prey is harmed (-). Controls prey population size and prevents overgrazing/overexploitation. Drives evolution of adaptations in both predators (camo, speed, toxins) and prey (defenses, warning coloration, mimicry). Top-down regulation in food webs. Predator-prey population cycles (Lotka-Volterra equations)
Interaction where parasite benefits (+) and host is harmed (-). Parasites live on (ectoparasites: fleas, ticks) or in (endoparasites: tapeworms, malaria) the host. Often reduces host fitness without immediately killing it. Coevolution: hosts evolve defenses, parasites evolve to overcome them. Parasite load can regulate host populations. Hyperparasitism: parasites of parasites
Interaction where both species benefit (+/+). Very common in nature. Examples: pollinators and plants (bees <-> flowers), mycorrhizal fungi and plant roots, clownfish and anemones, gut bacteria and mammals. Can be obligate (both depend on each other) or facultative (both can survive without the other). Can shift to parasitism under changed conditions
Interaction where one species benefits (+) and the other is unaffected (0). Examples: barnacles on whales (barnacle gets transport and access to food; whale largely unaffected), epiphytes on trees (orchids on tree trunks), cattle egrets following cattle. True commensalism is rare - the host may sometimes be negatively affected
A species that has a disproportionately large impact on community structure and function relative to its abundance. Removal causes cascading effects throughout the ecosystem. Examples: sea otters (control sea urchins -> kelp forest health), bees (pollination), wolves (trophic cascade -> elk behavior -> riverbank vegetation). Not necessarily the most abundant species
Three levels of biodiversity: (1) Genetic diversity: variation in genes within a species (alleles, populations). (2) Species diversity: variety of species in an area (species richness × relative abundance). (3) Ecosystem diversity: variety of habitats, communities, and ecological processes. All three levels are important for ecosystem resilience
The gradual change in species composition of an ecosystem following a disturbance or on newly formed substrate. Primary succession: on bare rock/no soil (e.g., volcanic islands, after glacier retreat). Pioneer species: lichens, mosses -> break down rock -> soil forms. Secondary succession: on disturbed soil with some seed bank remaining (e.g., after fire, farming). Leads toward a climax community
Non-native species introduced by humans (intentionally or accidentally) that establish and spread, causing ecological or economic harm. Traits that promote invasiveness: fast reproduction, broad diet, tolerance of wide environmental conditions, absence of natural enemies. Impact: outcompete native species, alter habitat, spread disease, disrupt ecosystem processes. Management: prevention, early detection, eradication, control
Global changes affecting ecosystems: rising temperatures, ocean acidification, altered precipitation, sea level rise, more extreme weather. Impacts: species range shifts (poleward/upward), altered phenology (timing of migration, flowering), coral bleaching (ocean warming), species extinctions, changes in pathogen distribution. Feedback loops: permafrost thaw -> methane release -> more warming
Internal biological clocks with a ~24-hour cycle. Regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus. Affect sleep-wake cycles, hormone release, body temperature, metabolism. Entrained (synchronized) by light-dark cycles. Examples: sleep cycles, melatonin secretion, plant leaf movements. Disruption causes jet lag, shift work disorders
The physiological response to the length of day (photoperiod). Many organisms use day length as a cue for seasonal behaviors: flowering in plants (photoperiodism -> long-day/short-day plants), bird migration, animal reproduction cycles, dormancy. Involves phytochrome (plants) and melatonin pathways. Allows organisms to anticipate seasonal changes
Taxis: directed movement toward or away from a stimulus (directional). Examples: phototaxis (moths toward light, earthworms away), chemotaxis (bacteria toward nutrients), thermotaxis. Kinesis: undirected movement in response to a stimulus; speed/turning rate changes with conditions but no fixed direction. Both allow organisms to respond to environmental gradients
The position an organism occupies in a food chain/web. Producers (autotrophs) -> Primary consumers (herbivores) -> Secondary consumers (carnivores/omnivores) -> Tertiary consumers (top predators) -> Decomposers/detritivores. Each level loses ~90% of energy as heat (10% rule); only ~10% is passed to the next level. Limits the number of trophic levels (~4-5 typically)
Only about 10% of the energy available at one trophic level is transferred to the next. The remaining ~90% is used for: cellular respiration (metabolism), growth and reproduction (biomass that dies without being eaten), waste products, heat. Explains why food chains are short and why there are fewer apex predators. Energy pyramids are always upright
Producers (autotrophs): organisms that produce their own organic compounds from inorganic sources. Use photosynthesis (plants, algae) or chemosynthesis (some bacteria). Form the base of all food chains. Consumers (heterotrophs): organisms that obtain energy by eating other organisms. Include herbivores, carnivores, omnivores, detritivores
A food chain is a linear sequence of organisms showing who eats whom. A food web is an interconnected network of food chains showing all feeding relationships in an ecosystem. Food webs are more realistic because most organisms feed at multiple trophic levels. Energy flows directionally through food chains/webs; chemicals cycle
Diagrams showing the trophic structure of an ecosystem. Three types: (1) Pyramid of energy (always upright, most energy at base). (2) Pyramid of biomass (may be upright or inverted; e.g., inverted in aquatic ecosystems where phytoplankton reproduce rapidly). (3) Pyramid of numbers (may be inverted; e.g., many insects per tree). All demonstrate the 10% energy transfer rule
Population growth without limiting factors. Model: dN/dt = rN (r = intrinsic rate of increase). Graph: J-shaped curve. Only occurs when: unlimited resources, no competition, no predation, ideal conditions. Occurs: introduced species in new environments (early growth), bacterial colonies on fresh medium. r-strategists: species that use exponential growth
Population growth that slows as carrying capacity (K) is approached. Model: dN/dt = rN[(K-N)/K]. Graph: S-shaped (sigmoid) curve. Phase 1: exponential growth. Phase 2: growth slows as resources become limited. Phase 3: population stabilizes near K. When N > K: negative growth (population exceeds carrying capacity -> die-off). Most real populations follow logistic growth
The maximum population size that an environment can sustain indefinitely. Determined by: food supply, water, habitat space, disease, predation, other limiting factors. Denoted K in the logistic growth model. Not a fixed number - changes with environmental conditions (seasonal variation, climate change, habitat changes). Logistic growth oscillates around K
Limiting factors whose effect increases as population density increases. Examples: competition for resources, predation, disease (parasites spread faster at high density), accumulation of waste. More individuals -> more competition -> higher mortality, lower birth rates -> population declines. An important self-regulating mechanism
Limiting factors that affect population size regardless of density. Examples: natural disasters (fires, floods, hurricanes), extreme weather (drought, frost), pollution, habitat destruction, climate change. A population at any density can be devastated by these factors. Largely responsible for the exponential growth phase when species colonize new areas
A measure of species diversity in a community. D = 1 - Sigma(ni/N)2 where ni = number of individuals of species i, N = total individuals. Range: 0 (no diversity) to 1 (maximum diversity). Also expressed as H = -Sigma[(ni/N) × ln(ni/N)] for Shannon index. Higher diversity -> more stable ecosystem
The patterns of species composition and organization in a community. Determined by: species interactions, abiotic factors, disturbance regime, historical factors. Key features: species richness (number of species), relative abundance (evenness), trophic structure, spatial structure (canopy layers, vertical zonation). More diverse communities tend to be more stable
Populations of predators and prey influence each other's numbers cyclically. Classic Lotka-Volterra model: as prey increase -> predators increase -> more predation -> prey decrease -> predators decrease -> prey increase again. Real populations show similar oscillations. Refuge effects, functional responses (type I/II/III), and spatial heterogeneity can stabilize these cycles
Interaction where both species are negatively affected (-/-). Occurs when species compete for the same limited resources (food, water, space, mates). Competitive exclusion principle (Gause): two species competing for exactly the same resources cannot coexist indefinitely - one will outcompete the other. Can be reduced by character displacement (niche differentiation)
Interaction where predator benefits (+) and prey is harmed (-). Controls prey population size and prevents overgrazing/overexploitation. Drives evolution of adaptations in both predators (camo, speed, toxins) and prey (defenses, warning coloration, mimicry). Top-down regulation in food webs. Predator-prey population cycles (Lotka-Volterra equations)
Interaction where parasite benefits (+) and host is harmed (-). Parasites live on (ectoparasites: fleas, ticks) or in (endoparasites: tapeworms, malaria) the host. Often reduces host fitness without immediately killing it. Coevolution: hosts evolve defenses, parasites evolve to overcome them. Parasite load can regulate host populations. Hyperparasitism: parasites of parasites
Interaction where both species benefit (+/+). Very common in nature. Examples: pollinators and plants (bees <-> flowers), mycorrhizal fungi and plant roots, clownfish and anemones, gut bacteria and mammals. Can be obligate (both depend on each other) or facultative (both can survive without the other). Can shift to parasitism under changed conditions
Interaction where one species benefits (+) and the other is unaffected (0). Examples: barnacles on whales (barnacle gets transport and access to food; whale largely unaffected), epiphytes on trees (orchids on tree trunks), cattle egrets following cattle. True commensalism is rare - the host may sometimes be negatively affected
A species that has a disproportionately large impact on community structure and function relative to its abundance. Removal causes cascading effects throughout the ecosystem. Examples: sea otters (control sea urchins -> kelp forest health), bees (pollination), wolves (trophic cascade -> elk behavior -> riverbank vegetation). Not necessarily the most abundant species
Three levels of biodiversity: (1) Genetic diversity: variation in genes within a species (alleles, populations). (2) Species diversity: variety of species in an area (species richness × relative abundance). (3) Ecosystem diversity: variety of habitats, communities, and ecological processes. All three levels are important for ecosystem resilience
The gradual change in species composition of an ecosystem following a disturbance or on newly formed substrate. Primary succession: on bare rock/no soil (e.g., volcanic islands, after glacier retreat). Pioneer species: lichens, mosses -> break down rock -> soil forms. Secondary succession: on disturbed soil with some seed bank remaining (e.g., after fire, farming). Leads toward a climax community
Non-native species introduced by humans (intentionally or accidentally) that establish and spread, causing ecological or economic harm. Traits that promote invasiveness: fast reproduction, broad diet, tolerance of wide environmental conditions, absence of natural enemies. Impact: outcompete native species, alter habitat, spread disease, disrupt ecosystem processes. Management: prevention, early detection, eradication, control
Global changes affecting ecosystems: rising temperatures, ocean acidification, altered precipitation, sea level rise, more extreme weather. Impacts: species range shifts (poleward/upward), altered phenology (timing of migration, flowering), coral bleaching (ocean warming), species extinctions, changes in pathogen distribution. Feedback loops: permafrost thaw -> methane release -> more warming