ecology p.2

three limits where a species can live(remove one and species is absent)

dispersal, abiotic environment, biotic environment

bottom up control

The amount of resources at the base (nutrients, sunlight) determines plant abundance, which determines herbivore abundance, which determines predator abundance. Adding fertilizer → more plants → more herbivores → more predators.

Top-down control (trophic cascade)

The apex predator controls the system. Remove predators → middle level explodes → bottom level crashes. Add predators → middle level declines → bottom level recovers.

carbon cycle

The organic circulation of carbon from the atmosphere into organisms and back again

nitrogen cycle

the series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition to create "fixed"/usuable forms(ammonia NH3, nitrate NO3-)

natural nitrogen fixation

Specialized bacteria (in soil, or in root nodules of legumes like soybeans and peanuts) convert N₂ to ammonia using the enzyme nitrogenase. This requires a lot of energy.

Haber-Bosch process

Humans figured out how to do industrial nitrogen fixation using high pressure, high temperature, and a catalyst (and huge amounts of fossil fuel energy). This made cheap synthetic fertilizers possible and drove the Green Revolution — massive increases in crop yields in the 20th century that fed billions of people. Humans now provide ~51% of all nitrogen fixation on Earth.

stock (pool)

amount stored in a compartment (units: kg, Pg, etc.); ex. current balance

flux

rate of movement between compartments (units: kg/year); ex. monthly income and spending

residence time

stock ÷ flux (only defined at equilibrium); ex. how long a dollar stays in your acc on average (balance/monthly spending

parasite vs pathogen

Not all parasites are pathogens. both cause disease and are biotic reserviors but pathogen may live in/on a host but parasites do

Janzen-Connell effect

pathogens and herbivores that attack their host more strongly when the host is common cause negative density dependence in the host population. This prevents any one species from dominating and promotes coexistence — potentially explaining why tropical forests can have thousands of tree species.

Biotic homogenization

As urbanization spreads, communities become more similar across regions — generalist and invasive species replace specialist and native species. Beta diversity decreases even as local alpha diversity may remain stable.

portfolio effect;vector and vechile and contact transmission

More diverse communities are more stable and more reliably productive over time. Just like a diversified investment portfolio — if one stock crashes, others compensate. If one species fails in a drought, another might thrive. This means biodiversity itself is an ecosystem service that improves resilience.

Contact transmission

Direct host-to-host contact. Sexual transmission, parent-to-child at birth. Example: Hepatitis B

Vehicle transmission

indirect movement from one host to another Via contaminated water, food, feces, or dust. Example: Giardia in water, Valley fever fungal spores in dust

Vector transmission

Via a third organism that carries the pathogen. Example: Lyme disease (Borrelia bacteria, transmitted by ticks); malaria (Plasmodium parasite, transmitted by mosquitoes)

negative density dependence

In real life, as a population gets larger, individuals compete more for food, space, and mates. Disease spreads faster. Predators pay more attention. Life gets harder. This means the per-capita growth rate DECREASES as N increases

positive density dependence

populations can do BETTER when they're larger. Example: abalone spawn by releasing eggs and sperm into open water. If they're too rare, sperm can't find eggs. So population growth rate INCREASES with density at low N.

density independent factors

A volcano, a drought, or a severe winter can kill individuals regardless of how dense the population is. They cause population fluctuations that don't fit either the exponential or logistic model neatly.

prey evolution defenses:

Physical defenses: Spines, shells, armor, thick skin

Chemical defenses: Toxins, bad taste, venom

Escape: Speed, burrowing, camouflage

Mimicry: Honest mimicry (look like something dangerous, AND actually are dangerous) vs. dishonest mimicry (look dangerous but actually harmless — like a harmless king snake mimicking a venomous coral snake)

Behavioral: Some moths detect bat sonar and drop to the ground; others "jam" the sonar signal

Exploitation competition

Fox and coyote both eat rabbits. If foxes eat more rabbits, fewer rabbits are left for coyotes. The fox indirectly harms the coyote, even though they never directly interact.

Indirect mutualism / trophic cascade

Sharks eat skates; skates eat mussels. Removing sharks → more skates → fewer mussels. Sharks INDIRECTLY harm mussels, even though they never touch one.

basic frameworks

competition, predation, herbivory, parasitism, mutualism, commensalism

fundamental niche

is the full set of conditions where a species COULD maintain a stable population — set by its physiology. It's the niche the species has in a world with no other species.; ex. anything im physically capable of doing

realized niche

where the species ACTUALLY lives — constrained by competition, predation, and other biotic interactions. Usually smaller than the fundamental niche. ex. job I actually get

Lotka-Volterra predator-prey cycles:

When prey are rare, predators don't eat well, so predator populations decline. With fewer predators, prey recover. With lots of prey, predators thrive. With lots of predators, prey decline again. This creates cyclical oscillations, like the famous lynx-snowshoe hare data from Canadian fur trading records.

Spatial refuges:

Huffaker's mite experiments showed that complex environments with patches and barriers allow prey to persist by escaping the predator in space. Even if a predator wipes out prey locally, some prey escape to new patches and recolonize.

richness

number of species ex. 20 trees species in the forest or how many sonfs are on spotify

evenness

how similar their abundances are ex. are all 20 species equally common or does one dominate OR all songs play equally or some dominate

composition

which species are present ex. which tree species dominate

alpha

richness at ONE local site ex. species in a pond or songs in your playlist

beta

difference in composition between sites ex. how different are the 2 ponds

gamma

richness across ALL sites in a region ex. total species in all ponds in california OR all songs on spotify

Island biogeography theory

Larger islands: lower extinction rates (more habitat, more ways to survive) → higher equilibrium richness

Closer islands: higher immigration rates (dispersers more likely to arrive) → higher equilibrium richness

Hadley cells and precipitation:

At the equator, warm air rises. As it rises, it cools, and water vapor condenses and falls as RAIN (tropical rainforests). The now-dry air travels poleward, then DESCENDS at about 30° latitude. Descending air warms and becomes even drier. This creates the mid-latitude deserts (Sahara, Arabian, Australian Outback, Mojave). The air then travels back toward the equator along the surface. At higher latitudes (40-60°), a second cell creates more precipitation.