Unit 8 apbio ecology

Ecology

The study of how adaptations of species help them survive and reproduce in the context of interactions with other species and the nonliving world

Individual

The smallest and most fundamental unit in the ecological hierarchy; the first level that can live on its own in the environment

Population

A group of individuals of the same species within a given area; the level at which evolutionary changes occur

Community

A collection of populations in a given area that interact with each other (e.g., predators eating prey, pollinators fertilizing flowers)

Ecosystem

Multiple communities combined with the nonliving physical and chemical environment (sunlight, water, temperature); focuses on movement of energy and matter

Biosphere

The highest ecological level; includes ALL ecosystems on Earth; focuses on movement of matter and energy via air/water currents and long-distance migration

Law of Conservation of Matter

Matter is not created or destroyed, but can change form; allows us to track elements cycling through ecosystems

Law of Conservation of Energy

Energy cannot be created or destroyed, but can be converted into different forms; governs energy flow through all ecological levels

Kinesis

Random movement in response to unfavorable stimuli (e.g., bacteria moving randomly in overly warm or salty water until conditions improve)

Taxis

Directional movement toward or away from a specific stimulus (e.g., gazelle walking toward grass or running from a predator)

Phototropism

Plant growth toward a light source; caused by auxins accumulating on the shady side of the stem, causing those cells to elongate and the stem to bend toward light

Auxins

Plant hormones found in stem tips that cause cell elongation; responsible for phototropism; build up on shady side of stem when light is uneven

Photoperiod

The number of sunlit hours in a day; used by plants and animals to time reproduction, migration, and hormonal changes

Long-day Plants

Plants that only flower in summer when days are longest (e.g., potatoes, spinach)

Short-day Plants

Plants that only flower in winter when days are shortest (e.g., poinsettia, Christmas cactus)

Day-neutral Plants

Plants whose flowering is not affected by day length (e.g., tomatoes, corn)

How Plants Measure Day Length

Photoreceptors in leaves cause protein accumulation during daylight; the protein degrades at night; long-day plants flower when daily protein accumulation surpasses a threshold

Photoperiod in Animals

Migrating birds use photoperiod to know when to fly north/south; white-tailed deer breed in fall and give birth in spring when food is abundant

Navigation in Homing Pigeons

Use star patterns at night and an internal magnetic compass to navigate home from hundreds of km away; attaching magnets to their heads disrupts this ability

Melatonin

Hormone released by the pineal gland in darkness; causes nocturnal animals to become active and diurnal animals to sleep

Circadian Clock

An approximately 24-hour internal clock regulated by clock genes that turn on and off in feedback loops; found in animals, plants, fungi, and bacteria; continues even in 24-hour darkness

Pineal Gland

Brain structure that releases melatonin in response to darkness; regulated by retinal light detection or skull photosensitive cells in some fish and reptiles

Communication (ecological definition)

A transfer of information between two individuals; involves a sender and a receiver

Visual Communication

Signals detected by sight (e.g., male cardinal's red feathers signal maleness and diet quality; antlers on deer; courtship dances)

Auditory Communication

Signals detected by sound (e.g., rattlesnake rattle warns predators; bird/frog mating calls; vervet monkey alarm calls)

Vervet Monkey Alarm Calls

Uses one call for aerial predators like hawks and a different call for ground predators like leopards and snakes; triggers different escape behaviors in receivers

Chemical Communication

Signals transmitted via chemicals (e.g., female dogs/cats releasing chemicals when in heat; ant food trails; fish releasing alarm chemicals when attacked; territory marking)

Goldenrod Chemical Defense

When attacked by beetles, goldenrod leaves release airborne chemicals; neighboring plants detect this and begin producing anti-herbivore chemicals preemptively

Titan Arum (Corpse Flower)

Releases chemicals that smell like rotting flesh to attract flies needed for pollination; example of chemical communication in plants

Tactile Communication

Communication through touch/vibration (e.g., spider web vibrations from prey; white-lipped frog's body vibrations through ground to attract females; leaf-feeding insects vibrating leaves)

Electrical Communication

Rare; some fish like the brown ghost knifefish send weak electrical signals through water to communicate sex and identity

Innate Behaviors

Behaviors performed without prior experience; largely genetically determined; very similar among individuals of the same species (e.g., bird courtship displays performed perfectly even in isolation)

Learned Behaviors

Behaviors where genes provide the capacity but individual experience shapes the expression; improves fitness through environmental experience

Habituation

Learning to ignore a stimulus over time (e.g., crows initially scared by scarecrow but return after learning it poses no real threat)

Operant Conditioning

Learning through reward or punishment (e.g., rats sample tiny amounts of new food; avoid it if it makes them sick; eat more next time if it does not)

Imitation (Learning)

Learning a behavior by observing others perform it (e.g., one bird in Britain learned to pierce foil milk bottle caps for cream; behavior spread rapidly across multiple bird species)

Imprinting

Young animals fix on the first animal they see as their parent; critical for knowing who to follow for food and protection; can misfire if a human is the first thing seen

Cooperative Behavior

Behaviors that improve another individual's fitness; benefits include more eyes for food and predators, group defense, and cooperative hunting

Muskox Defense

Adults form an outward-facing circle with horns out to protect vulnerable young calves in the center; example of cooperative defense

Honeybee Eusociality

One queen lays all eggs; diploid eggs become daughter workers; haploid eggs become sons that leave to fertilize other queens; workers build hive, collect nectar and pollen, raise offspring

K-selected Species

Species with slow reproduction that remain near carrying capacity; large mammals, Type I survivorship; e.g., elephants take 13 years to mature and have 1 offspring every 2-4 years

r-selected Species

Species with rapid reproduction and large population fluctuations; Type III survivorship; e.g., frogs lay hundreds of eggs with ~95% mortality before adulthood; house mice mature at 6 weeks and breed every 5 weeks producing ~12 offspring

Thermoregulation

The process by which an organism controls its body temperature

Endotherm

Organism that regulates body temperature internally (e.g., mammals, birds); uses negative feedback loops via hypothalamus; higher metabolic rate; can live in wide range of environments but must eat frequently

Ectotherm

Organism whose body temperature is strongly influenced by the external environment (e.g., reptiles, amphibians, insects, most plants); lower metabolic rate; can go long periods without eating; more limited in habitat range

Skunk Cabbage

A plant that uses mitochondria to generate metabolic heat up to 10 degrees C above air temperature; emerges in early spring even through snow; attracts fly pollinators before competing plants emerge

Behavioral Thermoregulation in Ectotherms

Ectotherms adjust body temperature through behavior: basking in sun to warm up, seeking shade to cool down, pressing against warm or cool rocks; improves movement, predation, digestion, and fitness

Hypothalamus

Brain structure that acts as the body's thermostat; sends signals to initiate shivering, vasoconstriction, vasodilation, and panting in response to temperature changes

Vasoconstriction

Narrowing of arteries in limbs to reduce blood flow and heat loss; used by endotherms in cold environments

Vasodilation

Widening of blood vessels in limbs to increase blood flow and release excess heat; used in hot environments by both endotherms and ectotherms

Metabolic Rate

The number of calories an organism burns over time while at rest; higher in endotherms than ectotherms; higher in larger animals in total, but lower per kg in larger animals

Why Large Animals Have Lower Metabolic Rate Per Kg

As body size increases, volume grows faster than surface area; larger animals lose heat more slowly relative to their mass, so they need less energy per kg to maintain temperature

Autotrophs (Producers)

Organisms that obtain energy via photosynthesis or chemosynthesis (e.g., plants, algae, chemosynthetic bacteria); base of all food chains

Heterotrophs (Consumers)

Organisms that obtain energy by consuming other organisms; break down carbohydrates, lipids, and proteins via catabolism

Primary Consumers

Herbivores that eat producers (e.g., zebras eating grass)

Secondary Consumers

Carnivores that eat primary consumers (e.g., lions eating zebras)

Tertiary Consumers

Carnivores that eat secondary consumers (e.g., bald eagles eating fish that eat herbivores)

Chemosynthesis

Process used by specialized bacteria in sunless environments like deep-sea hydrothermal vents; converts energy from hydrogen sulfide bonds plus CO2 and H2O into sugars; basis of deep-sea food webs

Trophic Levels

Successive levels in a food chain organized by how organisms obtain energy; producers then primary, secondary, and tertiary consumers

Ecological Efficiency

The percentage of energy transferred from one trophic level to the next; typically ~10% with a range of 5-20%; only 1% of producer energy reaches secondary consumers

Why Ecological Efficiency Is Low

Not all organisms are consumable (e.g., thorns); not all consumed organisms are fully digestible; energy transformation is never 100% per second law of thermodynamics; much energy used for body maintenance and heat generation

Food Web

A realistic depiction of energy and matter flow among many species in a community; includes omnivores, scavengers, detritivores, and decomposers

Scavengers

Consumers of dead animals (e.g., condors)

Detritivores

Organisms that break dead organic matter and waste into smaller particles (e.g., earthworms)

Decomposers

Organisms such as fungi and bacteria that convert dead organic matter into molecules and elements that producers can recycle

Carbon Cycle

The movement of carbon between pools in air, water, land, and organisms via 7 key processes: photosynthesis, cellular respiration, decomposition, exchange, sedimentation, burial, and extraction plus combustion

Sedimentation (Carbon Cycle)

Dissolved CO2 in water combines with calcium ions to form CaCO3 which precipitates and forms limestone and dolomite on ocean floor; creates a massive long-term carbon pool

Extraction and Combustion

Extraction moves buried fossil fuels to the surface; combustion burns them releasing CO2 similar to cellular respiration; both are human-driven disruptions to the carbon cycle

Human Impact on Carbon Cycle

Burning fossil fuels and deforestation (often with burning) releases vast amounts of CO2 into the atmosphere; disrupts the natural balance where carbon movement among pools was offset by other processes

Population Size (N)

The number of individuals in a given area

Population Density

Number of individuals divided by area size; used to determine crowding, food availability, and set hunting and fishing limits

Geographic Range

The area over which a population is spread; determined by favorable conditions and dispersal ability (e.g., European starling spread from 160 birds in NYC in 1890 to 7 million across all 48 states)

Population Distribution

How clumped individuals are within their range: Random means no pattern; Uniform means evenly spaced like nesting seabirds; Clumped means aggregated like schools of fish or meerkats

Mark-and-Recapture

A technique to estimate population size; mark individuals, release them, recapture a sample, and calculate population size from the ratio of marked to unmarked individuals in the recapture

Sex Ratio

Ratio of males to females in a population; most species are ~50:50; uneven ratios affect how rapidly a population can grow

Age Structure

Distribution of individuals across age categories (pre-reproductive, reproductive, post-reproductive); affects annual offspring production and population growth rate

Population Growth Formula

dN/dt = B minus D; change in population size per unit time equals birth rate minus death rate

Per Capita Growth Rate (r)

r= (dN/dt) divided by N; when r is positive population grows; when r is negative population shrinks; when r equals 0 population is stable

Exponential Growth Model

dN/dt = r_max times N; assumes no constraints on growth; produces J-shaped curve; population grows faster as N increases because more individuals reproduce

r_max

Maximum per capita growth rate; the growth rate when a population faces no resource constraints whatsoever

Logistic Growth Model

dN/dt = r_max times N times ((K minus N) divided by K); incorporates carrying capacity; produces S-shaped curve; growth slows as N approaches K

Carrying Capacity (K)

The maximum number of individuals a given habitat can support; when N equals K, dN/dt equals 0 and population is stable

S-shaped (Logistic) Curve Behavior

When N is much less than K the population grows almost exponentially; growth rate is steepest at N = K/2; growth approaches 0 as N approaches K

Population Overshoot and Die-off

Population temporarily exceeds K (e.g., St. Paul Island reindeer: 25 in 1920 to ~2000 in 1938 to crash of 8 by 1950); occurs when carrying capacity changes seasonally or species cannot respond fast enough

Type I Survivorship Curve

High survival throughout most of life; sharp decline late in life; characteristic of large mammals like humans, deer, and elephants

Type II Survivorship Curve

Steadily declining survival throughout life; characteristic of birds and small mammals like squirrels

Type III Survivorship Curve

Sharp drop in survival early in life; slow decline after; few reach adulthood; characteristic of mosquitoes, amphibians, and dandelions

Species Richness

The number of different species present in a community

Species Evenness

How equally individuals are distributed among species in a community

Simpson's Diversity Index Formula

D = 1 minus the sum of (n/N) squared; where n equals number of organisms of one species and N equals total organisms of all species; higher D means more diverse community

Simpson's Diversity Index Example

Community A (uneven, 5 species, 100 total): D = 0.645; Community B (perfectly even, 5 species, 100 total): D = 0.80; Community C (even, only 3 species, 100 total): D = 0.67

Habitat

The physical setting where a species lives (e.g., eastern cottontail rabbit in eastern North American fields; moose in northern forests)

Fundamental Niche

The full range of abiotic conditions such as temperature, pH, salinity, nutrients, and water under which a species can survive, grow, and reproduce

Realized Niche

The actual conditions where a species lives after accounting for biotic factors like competition and predation; always equal to or smaller than the fundamental niche (e.g., red-winged blackbird pushed to shallow marsh edges by yellow-headed blackbirds)

Range of Tolerance

Each species has an optimal range for each abiotic condition within which it can survive, grow, and reproduce; above or below optimal causes stress; extreme values cause death

Niche Generalist

Species that can live under a wide range of abiotic and biotic conditions and eat many food types (e.g., gray kangaroo)

Niche Specialist

Species that lives in a very narrow range of conditions (e.g., panda eating only bamboo); effective at exploiting one resource but vulnerable if that resource declines

Predation

Interaction in which one species kills and consumes another; can drive cyclic population dynamics

Canada Lynx and Snowshoe Hare Cycle

Populations cycle approximately every 10 years; hare cycles driven by vegetation abundance; lynx cycles driven by hare abundance with a 1-2 year lag; Hudson Bay Company pelt records provided ~100 years of data

Camouflage

Anti-predator adaptation where prey blend into environment (e.g., katydids resembling plant leaves)