Ecology, Lyme Disease, and Homeostasis

Host

Organism that harbors or provides resources for a parasite or pathogen.

Vector

Organism (usually an arthropod) transmitting a pathogen between hosts without causing disease itself.

Deer tick scientific name

Ixodes scapularis

Deer tick classification

Arachnid, not an insect (part of the spider family).

Lyme disease pathogen

Borrelia burgdorferi, a spirochete bacterium.

Classic Lyme symptom

Bull's-eye shaped rash at the site of the tick bite.

Common intermediate host of the deer tick

White-footed deer mouse (Peromyscus leucopus).

Zoonotic disease (zoonosis)

A disease that can be transmitted from animals to humans.

Why Lyme disease is zoonotic

Pathogen cycles among animal hosts and transmits to humans incidentally via tick bites.

Tick larvae feeding behavior

Stay low in leaf litter and feed on small hosts like mice.

Tick nymph feeding behavior

Feed a few inches above ground, biting larger animals or humans.

Tick adult feeding behavior

Requires a larger host (e.g., deer) to feed and reproduce.

Organism (level of organization)

A single individual living thing.

Population

Group of individuals of the same species in an area, capable of interbreeding.

Community

All populations of different species living and interacting in a given area.

Ecosystem

A biological community plus its interacting abiotic (nonliving) environment.

Biosphere

The sum of all ecosystems on Earth; the global zone of life.

Biotic vs. Abiotic

Biotic components are living; abiotic components are nonliving elements like temperature and humidity.

Characteristics of living things

Made of cells, metabolize, contain genetic material, reproduce, and populations evolve.

Climate

Long-term, predictable atmospheric conditions of a region over large geographic/time scales.

Weather

Short-term, day-to-day conditions of the atmosphere.

Biome

Large-scale community defined by climate and characteristic plant/animal life.

Examples of biomes

Temperate forest, tropical rainforest, desert, tundra, taiga, savanna, grassland, freshwater, marine.

Greenhouse effect

Greenhouse gases trap heat in the atmosphere, warming the planet.

Evidence for climate change

Ice core historical CO₂/temperature data and Keeling Curve atmospheric CO₂ rises.

Common greenhouse gases and sources

CO₂ (burning fossil fuels) and methane (agriculture, livestock, landfills).

Impacts of climate change

Glacier retreat, sea level rise, intense wildfires, and shifting disease vector ranges.

Population density

Number of individuals per unit area.

Body size vs. population density

Inverse relationship: larger species have lower densities due to limited resources.

Clumped distribution

Individuals grouped together in patches (e.g., elephant herds).

Uniform distribution

Individuals evenly spaced, often due to territoriality (e.g., penguins).

Random distribution

No predictable spacing pattern (e.g., wind-dispersed dandelion seeds).

Survivorship curve Type I

Low mortality early/mid-life, sharp rise late in life (e.g., humans).

Survivorship curve Type II

Roughly constant mortality rate across all age groups (e.g., birds).

Survivorship curve Type III

High early mortality, low mortality for survivors (e.g., oysters).

r-selected species

Produce many offspring with little parental care; associated with Type III survivorship.

K-selected species

Produce few offspring with high parental investment; associated with Type I survivorship.

r (in growth equations)

Intrinsic per-capita growth rate (birth rate minus death rate).

K (in growth equations)

Carrying capacity: maximum population size an environment can sustainably support.

N (in growth equations)

Current population size.

Exponential growth equation

dN/dt = rN; constant growth rate producing a J-shaped curve under unlimited resources.

Logistic growth equation

dN/dt = rN(K-N)/K; growth slows as N approaches K, creating an S-shaped curve.

Population growth when N is less than K

(K-N)/K is positive, causing the population size to grow.

Population growth when N equals K

(K-N)/K equals zero, leaving the population size stable.

Population growth when N is greater than K

(K-N)/K is negative, causing the population size to shrink.

Effect of a high vs. low r

Higher r drives faster population growth; lower r results in slower growth.

Commensalism

Symbiosis where one species benefits and the other is unaffected.

Mutualism

Symbiosis where both participating species benefit.

Parasitism

Symbiosis where the parasite benefits at the expense of the host.

Competitive exclusion principle

Two species competing for identical limited resources cannot coexist indefinitely.

Invasive species

Non-native species introduced into an ecosystem that spreads aggressively, outcompeting native species.

Predator-prey population dynamics

Predator and prey population sizes fluctuate together, with predator changes lagging behind prey.

Fox/coyote/mouse effect on Lyme disease

Coyotes exclude red foxes, increasing mouse populations, tick numbers, and Lyme risk.

Effect of acorn abundance on Lyme risk

Abundant acorns boost mouse populations, supporting more ticks and increasing Lyme risk.

Homeostasis

Maintenance of a stable internal environment despite external changes.

Negative feedback

Response counteracting initial change to return a system toward its set point.

Positive feedback

Response amplifying initial change, driving the system further from set point.

Feedforward information

Anticipatory change to a system's set point prior to expected conditions.

Ectotherm

Organism whose body temperature is regulated mainly by external heat sources.

Endotherm

Organism generating and regulating its own body heat internally through metabolism.

Conduction vs. Convection

Conduction transfers heat between directly contacting objects; convection transfers heat via fluid/air movement.

Evaporation (heat exchange)

Heat loss caused by water evaporating from a surface (e.g., sweating).

Nonshivering thermogenesis

Heat production occurring in brown adipose tissue rather than through muscle shivering.

Brown fat and UCP1

UCP1 uncouples respiration from ATP synthesis, releasing cellular energy as heat.

Surface area to volume ratio and heat

Higher ratio increases heat loss; lower ratio helps conserve body heat.