Final exam lecture vocabulary

Some vocabulary from lectures 10-25 (the ones covered on the final). You can access these in flashcard form on StudyBlue at the following link: http://www.studyblue.com/#flashcard/view/6650316. You'll need to register an account first, but it's pretty nice.

1Lecture 10¶

1.1Embryonic development part one¶

zygote

diploid, union of haploid gametes

embryo

young organism, contained in protective structure

cleavage

cell division in zygote

gastrulation

infolding of embryonic tissue → layers

morula

solid ball of cells, pre-gastrulation

blastula

hollow ball, cells in exterior; pre-gastrulation

gastrula

after infolding begins

blastopore

invagination → mouth (protosome), anus (deuterostome)

archenteron

digestive space (gut cavity)

ectoderm

outer layer → epidermis, nervous tissue

mesoderm

middle layer → internal organs etc

endoderm

inner layer → lining of respiratory, digestive systems

1.2Cnidarians¶

blind gut

digestive (gastrovascular) cavity - one opening

mesoglea

gel, not tissue, structural support in cnidarians

polyp

sessile form of cnidarians, mouth upward

medusa

motile, mouth downward

cnidocytes

cells that produce nematocysts, unique to cnidarians

nematocysts

organelle, coiled tube → prey, releases venom

nerve net

in epidermis and gastrodermis, connected by mesoglea; connected neurons, no brain

planula

free-swimming, bilateral, ciliated larvae

Hydrozoa (class)

polyp dominant - e.g. Hydra

Scyphozoa (class)

jellyfish, medusa dominant, no velum

Anthozoa (class)

corals, anemones etc; polyp - no medusa

velum

shelf under edge of bell, muscular; jellyfish lack this

coral bleaching

zooxanthelle expelled, corals may die

1.3Platyhelminthes¶

platyhelminthes

flatworms, flat like a plat(e)

planarian

specific family; cephalisation, mouth in middle of ventral side

cephalisation

concentration of neurons, senses at anterior

Turbellaria (class)

free-living (the only class)

Monogenea (class)

flukes, parasites on fish gills

Trematoda (class)

flukes, incl. Schistosoma

Cestoda (class)

tapeworms, in vertebrate intestines

fluke

flat body with suckers (body plan)

schistosomiasis

human, snail host; unsanitary water

scolex

head of tapeworm, has suckers and hooks

proglottids

tapeworm hermaphroditic reproductive structures

endo/ectoparasites

inside/outside host body (e.g. on skin)

2Lecture 11¶

2.1Embryonic development part two¶

complete gut

mouth & anus → continuous processing of food, specialisation

crop

store food in certain animals

gizzard

grind food, muscular

rumen

first chamber in herbivore stomach, stores bacteria to break down cellulose

extracellular matrix

assists in mesoderm movement (embyro)

lophotrocozoans

type of protostome, has either lophophore or trocophore or both

lophophore

ciliated feeding/gas exchange structures

trocophore

ciliated free-living larval form

ecdysozoan

type of protostome; must shed external covering periodically

acoelomate

solid (except for the digestive cavity); e.g. flatworms (platyhelminthes)

pseudocoelom

mesoderm lines only the outside of cavity, e.g. roundworms (nematodes)

mesenchyme

unspecialised cells, from germ layers → tissue

coelom

mesoderm lines organs etc too → peritoneum

diploblasts

have only ectoderm and endoderm, no coloem

triploblasts

3 germ layers (ecto, endo, mesoderm), may have a coelom

schizocoely

in protostomes, mesoderm just splits in the middle → coelom

enterocoely

in deuterostomes, mesoderm lines out-pockets of gut → coelom

2.2Nematodes¶

nematodes

roundworms, pseudocoelom, ecysozoan

C. elegans

model organism, species of nematode, used in research

hookworm

type of roundworm, spread through feces → intestine

2.3Annelids¶

annelida

segmented worms, lophotrocozoans

segmentation

evolutionary advance, multiple copies of structures, specialisation

septa

walls separating segments

serial homology

specialisation of similar, repetitive structures

circular and longitudinal muscles

contraction → compression → elongation → movement

Polychaeta (class)

many hairs, marine worms, trocophore larvae, must stay moist

Clitellata (class)

has clitellum, subclasses below

Oligochaeta (subclass)

few hairs, terrestrial, detritivores, aerate soil

Hirudinea (subclass)

leeches, no setae

clitellum

reproductive structure, secretes mucus → cocoon for embryo

3Lecture 12¶

3.1Mollusks¶

aposematic

warning coloration, to warn off predators (might indicate toxicity)

Mollusca

snails shellfish squid etc, bilateral triploblasts, trocophore larvae (if marine)

mantle

layer covering viscera, secretes CaCO₃ shell

mantle cavity

gills OR lots of blood vessels for terrestrials ("lungs")

radula

located after mouth → tearing and scraping

shell

secreted by mantle, gastropods (nudibranchs) and cephalopods can lack

Polyplacophora (class)

many dorsal plates, ventral gills

Bivalvia (class)

shellfish, hinged shell, siphons, small head, large foot → digging

adductor muscles

clam use → clamp shell shut

incurrent/excurrent

water flows in/out (ref. to siphons usually)

Gastropoda (class)

snails etc, most diverse, 2 tentacle pairs, undergo torsion

torsion

visceral mass rotates 180° (due to different growth rates), separate evolutionary event from coiling

operculum

for snails, → seal off head; else, gill covering

love dart

snails, special mucus → improve fertilisation

cerrata

additional breathing apparatus; nudibranchs can use to store cnidarians' nematocysts

Cephalopoda (class)

squids etc, few tentacles (arms), reduced/no shell

chromatophores

pigmented cells on surface of cephalopods and others → colour change, from neural crest

hemocoel

organs bathed in blood

mantle & siphon

jet propulsion in cephalopods

3.2The nervous system¶

ganglia

concentration of nerve cells

afferent/efferent

going TO/going AWAY FROM

neurons

generate/transmit electrical signals (nerve impulses)

glial cells

support neurons (nutrients, insulate, maintain extracellular environment)

Schwann cells

type of glial cell, insulate axon

axon

branch part of neuron, synapse with neurons/receptors

dendrites

small twig-like part of neuron, interact with other neurons

axon hillock

the centre, integrates signals, initiates action potential

nerve impulse

action potential, quick voltage change across membrane

temporal summation

one neuron stimulated a lot

node of Ranvier

between myelin sections, nerve impulses jump this

myelin

outgrowth of glial cells, wrap around axons

4Lecture 13¶

4.1Arthropods part one¶

Arthropoda

jointed foot, crustaceans insects etc, most diverse

reduced segmentation

some fused, only head, abdomen, thorax (perhaps cephalothorax)

trilobytes

first arthropods, extinct, fossils

antennae

sensory, on head

maxillipeds

hold food, on head

pereiopods

walking, getting food

pleopods

swimming (abdomen)

rigid exoskeleton

chitin, proteins (CaCO₃ - marines), molts

skeletal muscles

need resistor to act on; often antagonistically paired

4.2Muscles¶

saltatory conduction

in vertebrates, action potentials from one node of Ranvier to the next

electrical synapse

mechanical, shorter distance, no neurotransmitters, for reflexes and other quick, simple behaviours

chemical synapse

larger distance, neurotransmitters needed, more common in vertebrates

neurotransmitter

produced by neuron before synaptic cleft; traverse, bind to receptors

sarcomere

contractile unit of muscle cell

actin filament

thin, monomers + tropomyosin + troponin (proteins)

myosin filament

thick (proteins)

contraction

filaments slide past each other (no length change)

fast-twitch fibers

can reach max tension quickly but can't sustain, fatigue quickly

slow-twitch fibers

red muscles, cont. myoglobin, darker, for endurance

myoglobin

binds to O₂ in muscles

skeletal muscles

striated, multinucleated, cylindrical

cardiac muscle

single nucleus (usually), striated, pacemaker cells

smooth muscle

NOT striated (actin & myosin irregularly arranged), involuntary

pacemaker cells

create action potentials independently → heartbeats

5Lecture 14¶

5.1Arthropods part two¶

hormone

chemical messenger substance in endocrine system, in blood

Myriapoda (subphylum)

countless feet, centipedes millipedes

centipedes/millipedes

1 pair / 2 pairs of appendages per segment

Chelicera (subphylum)

fangs, incl. arachnids, no jaws

pedipalps

copulatory organs, pincers in scorpions (for chelicerates)

Crustaceans (subphylum)

shrimps Daphnia crabs barnacles etc, compose zooplankton

plankton

cannot outswim currents (zoo = heterotrophic, phyto = autotrophic)

Hexapoda (subphylum)

insects etc, 3 body parts

book lungs/gills

thin, like pages, in arachnids, internal/external

spermatophores

waterproof sperm packets, males pick up and transfer to female

ephippia

thick shell to protect eggs

diapause

delay in development due to environment

5.2Metamorphosis¶

instar

insect stage between molts

complete metamorphosis

huge change, e.g. caterpillar → butterfly

incomplete/gradual metamorphosis

no resting stage, e.g. nymph → adult

paracrines

act on neighbouring cells (quasi-hormones?), not in blood usually

autocrines

act on self

PTTH

neurohormone → prothoraric gland → produces ecdysone

ecdysone

secreted into the blood, targets epidermis → molting, stops production of PTTH

juvenile hormone

determines the instar stage; quantity decreases over time; cessation → pupation

pupation

→ pupa, eventually adult; no juvenile hormone

anti-diuretic hormone

hypothalamus → pituitary → conserve water

oxytocin

contract uterus, release milk from mammary glands

tropic hormones

act on other endocrine glands

insulin

binds to receptors → increase blood glucose uptake

diabetes I

juvenile, not enough insulin produced → insulin shots

diabetes II

target cells unresponsive to insulin, associated with obesity, diet & exercise

calcitonin

hormone when calcium blood concentration too high; increases calcium uptake, osteoblasts

PTH

hormone when calcium blood concentration too low; retains calcium in kidney, osteoclasts, converts vitamin D → calcitriol

osteoclasts/blasts

breakdown/building of bone

calcitriol

hormonally active form of vitamin D → digestive system absorbs more calcium

6Lecture 15¶

6.1Echinoderms¶

Echinodermata

marine, benthic, pentaradial, secrete test

water vascular system

for gas exchange, moving feet etc

madreporite

pores to enter water vascular system, aboral

ampoules

off radial canals in arms

podia

tube feet, locomotion/feeding/respiration/sensory

Crinoidea (class)

sea lilies, feather stars

Ophiuroidea (class)

brittle/basket stars ... fractals

Echinoidea (class)

sea urchins, sand dollars, have pedicellariae

Hoiothuroidea (class)

sea cucumbers, extended body

Asteroidea (class)

starfish, predatory, mobile

pedicellariae

pincers, defense and cleaning

extended body

between radial and bilateral, respire through anus

commensal

one benefits, one unaffected

6.2Chordates¶

chordates

notochord, dorsal hollow nerve cord, post-anal tail

notochord

rigid, flexible, rod of cells, vacuoles filled with water, found in chordate embryos

pharyngeal gill slits

in ancestors and embryo (at least) for chordates

neurulation

embyronic formation of nervous system

neural tube

from thickening of ectoderm → brain in anterior end

myomeres

segmented muscles

Cephalochordates (subphylum)

lancelets, little fish-like things

Urochordates

tunicates, big sessile adult - basket, vertebrate sister group

7Lecture 16¶

7.1Features unique to chordates¶

pouches

embryonic gill slits (pharyngeal) in humans → middle ear

post-anal tail

resorbed in humans, vertebrates fuse → coccyx

gill arches

bars between gill slits, bone/cartilage

gill rakers

trap particles, prevent consumption

arteries → arterioles

away from heart → capillaries

venules → veins

back to heart

ventricle & auricle

two chambers of heart in fish

sinous venous

veins → heart

bulbus conus arteriosis

→ arteries → body

7.2Fish¶

axial skeleton

skull, rib cage, vertebral column

appendicular skeleton

pectoral/pelvic girdles, fore/hind limbs (optional)

Agnatha (superclass)

jawless fish, lamprey/hagfish

Placoderms

early jawed fish, extinct

Hagfish

no vertebral column, retain notochord

Lamprey

complete braincase, cartilaginous vertebrae

Chondrichthyes (class)

cartilaginous fish

sharks, skates, rays

skates

2 lobes on pelvic fins

rays

1 lobe on pelvic fins

paired fins

for propulsion, pelvic/pectoral

lateral undulation

alternate contraction of myomeres → swimming

oviparous

lay eggs

ovoviviparous

embryo in female, but there is yolk sac (resorbed)

viviparous

retain embryo, fed by placenta/secretions

Osteichthyes (superclass)

bony fish, including ray-finned fish

swim bladder

gas-regulated by gland → neutral buoyancy

pheromones

chemicals to signal to conspecifics (same species)

Sarcopterygians (class)

clade that contains coelacanths, lungfish, and all tetrapods

Coelacanths

skeleton of cartilage (bony fish ancestor)

Lungfish

swim bladder vascularised → breathes air (also has gills); tetrapod sister group

8Lecture 17¶

8.1The rise to land¶

Ichthyostega

early tetrapod, used nostrils to breathe air

Eusthenopteron

lobe-finned, first humerus, radius

transitional forms

rare in fossil record, few species

Tiktaalik

fishapod, transitional form

3-chambered heart

mixing of blood (no septum in ventricle), present in amphibians

8.2The respiratory system¶

ATP

produced when glucose + O₂ → CO₂ + H₂O + ATP

tracheae

have cartilaginous rings to prevent collapse, strength

alveoli

microscopic 1-cell thick air sacs, high surface area for gas exchange

emphysema

alveoli destroyed by inflammation (smoking)

asthma

smooth muscles constrict trachea, bronchi

negative pressure breathing

air goes in because cavity expands → pressure goes down

positive pressure breathing

amphibians; force air into lungs, open glottis

glottis

separates mouth and lungs in amphibians

buccal cavity

mouth (amphibians)

8.3Amphibians¶

Amphibians

first tetrapods, depend on water at some life stage, no scales

neoteny

no true metamorphosis (some amphibians)

paedometamorphosis

e.g. salamanders; larvae → sexual maturity

obligate neoteny

never morphs

facultative neoteny

waits until environmental conditions are right

Salamanders (order)

mostly internal fertilisation

Frogs (order)

includes toads; males = loud courtship calls

Caecilians (order)

lost appendages, look like worms lol

R-strategy

lots of kids, no care (not covered in course just interesting)

K-strategy

few kids, lots of Kare (^)

Marsupial frog

fertilised egg on female's back

Darwin's frog

vocal sac brooder

Gastric brooding frog

female swallows egg, no feeding or HCl production

chytrid

fungal infection, affects amphibians

9Lecture 18¶

9.1The amniotic egg¶

birds

evolved from dinosaurs so they are technically reptiles, but classically we separate the two

non-avian reptiles

truly terrestrial, develop/reproduce on land etc

amniotic egg

extra-embyronic membranes, may have shell

therian

eggs non-shelled, mammalian subclass

albumen

egg white, watery; protection, some nutrients

chorion

gas exchange structure, inside albumen, surrounds others

amnion

wraps around embryo, protects (membranous sac)

allantois

near embryo, gas exchange, stores water

yolk sac

near embryo, holds nutrients

uric acid

non-toxic N-based waste product, held in egg

9.2Excretion¶

excretory system

control volume/concentration/content of extracellular fluids

osmoconformer

extracellular fluids same concentration as environment

osmoregulator

extracellular fluids different concentration than environment

ammonia

NH₃ polar, dissolves in water, toxic, often converted → uric acid/urea

urea

less toxic, less water needed for disposal

protonephridia

flame cells, tubules - excretory organ in flatworms

flame cells

cilia flickering like a '''flame'''

metanephridia

in many invertebrates, like kidneys

nephrostome → nephridiopore

disposal of waste, part of the above

malpighian tubes

filamentous, off midgut - insects

kidneys

2 → one is redundant; filter blood → urine

nephron

functional unit of kidneys

Glomerulus

ball of capillaries

Bowman's capsule

tubule structures, water leaks here

Loop of Henle

strong concentration gradient → further concentrate urine

kidney failure

→ salt/water retention → possible poisoning

dialysis

blood passes over membranes in solutions, filters out bad things etc

9.3Reptile diversity¶

Testudines (order)

turtles (including tortoises = land)

dorsal shell

on turtles; expansion of ribs

Lepidosaurs (superorder)

squamata, tuataras etc

Squamata (order)

lizards, snakes (lost limbs lol)

Tuataras

like lizards, but have a third eye

Archosaurs (group)

crocodilians, dinosaurs and modern birds

Crocodilians (order)

crocodiles, alligators, aimans, gharials

Crocodile/alligator

V-shaped/U-shaped snout (top jaws larger)

Ornithischians

beaked, herbivorous dinosaurs

Sauropods

long-neck dino

Theropods

T-rexes etc → birds

10Lecture 19¶

10.1Birds¶

Aves (class)

birds, highly evolved reptiles, bipedal, 3 hind toes

Lesser snow geese

population explosion → overforaging of arctic tundra

Archaeopteryx

"ancient wings", transitional form, first bird, Jurassic

Galapagos finches

beaks → niches, adapted to diet

endotherms

generate heat through inefficiency in energy transformation (metabolic processes)

ectotherms

absorb external heat

heterotherms

characteristics of both, e.g. bears (hiberation), flying insects

insect muscles

must be 34° to fly, so they shiver

counter-current heat exchangers

in pelagic fish, blood → muscles to warm them

hypothalamus

negative feedback → thermoregulation

parabronchi

branch off bronchi → air sacs

tidal respiration

e.g. mammals, not unidirectional; like a tide

feathers

insulation, flight, sensory, line nests; keratin (derived from scales)

convergent evolution

common environment/need, not ancestor (not homologous)

spoiler

maintain laminar flow over wing

alula

feathers on first digit → control

hovering

hummingbirds, rotate shoulder joint 180°

dynamic

oceanic birds, dive into wind, go up

static soaring

jump off cliffs, soar on updrafts (e.g. turkey vultures)

soaring

lift without flapping - updrafts, thermals

ground-up theory

bipedal runner, one day decided to fly (supported by partridge chicks)

tree-down theory

arboreal ancestor → gliding between trees; supported by fossil with feathers on legs

11Lecture 20¶

11.1Mammals¶

Mammalia (class)

hair, sweat/mammary glands, 4-chambered heart, 225 mya

skull morphology

number, placement of temporal fenestrae (holes) → muscle attachment

anapsid

only eyehole (turtles)

synapsid

including therapsids, mammals; one extra hole, bottom

euryapsid

extinct marine reptiles; one extra hole, top

diapsid

2 holes, birds and dinosaurs

therapsid

early synapsid, mammalian ancestor, legs beneath body

heterodonty

teeth specialised for different functions

middle ear

3 bones, hammer stirrup anvil, derived from jaw

Ambulocetus

whale ancestor (cetaceans)

Smilodon

sabre-toothed cat, hunted to extinction probably

Megatherium

giant ground sloth, also hunted?

11.2Reproduction¶

reciprocal hermaphroditism

each fertilises the other

sequential hermaphroditism

change change gender, common in fish

hermaphroditic mammals

e.g. beluga in St. Laurence (both gametes), possibly due to pollutants

pseudohermaphrodite

e.g. spotted hyena, female has enlarged clitoris → pseudopenis

sexual dimorphism

sexes look different ...

rodents

incisors constantly growing; largest group of mammals

Prototherians

mammalian group; includes platypi; shelled eggs

Monotremes (order)

only extant order of Prototherians; platypi, basically

Marsupials

some placental, kangaroos etc; viviparous

Eutherians

placental, viviparous, no pouch/shell; with Marsupials = therians

placenta

extra-embryonic membranes + uterus lining (endometrium), nutrients, maintained by hormones

oviduct

where fertilisation occurs

zona pellucida

glycoprotein membrane, ensures same-species fertilisation

cumulus

surrounds the above, like a cloud ☁ ☁ ☁

acrosomal reaction

head of sperm (acrosome) has enzymes to digest zona

trophoblast

outer layer of blastocyst → part of placenta

chorion

secretes hormones, has villi to attach to uterus

allantois

becomes blood vessels, umbilical arteries

umbilical cord

2 arteries, deoxygenated blood → mother; 1 vein, oxygenated blood → fetus

water breaking

fetus emerging from amniotic sac

hCG

Human chorionic gonadotropin, hormone, presence of it in urine measured by pregnancy tests

12Lecture 21¶

12.1Primates¶

Prosimians

in order "primates", arboreal, lemurs etc, large eyes (noctural)

Anthropoids

other primates; tarsiers, monkeys, apes

Tarsiers

tiny primates, completely carnivorous (insects); large tarsus bones (feet)

New World monkeys

Americas, have prehensile tail (grasping)

Old World monkeys

Asia, Africa; no prehensile tail

ape

larger brain/body ratio than monkeys, lack tails (so do some monkeys)

gibbons

lesser apes, smaller, arboreal

Orangutans

larger, walk and climb up trees

African apes

gorillas, chimps, hominids

Homo neanderthalis

coexisted with humans, extinct 30,000 ya

Hominids

arose from ardipithicine ancestors (protohominid)

Lucy

australopithecus afarensis, extinct, bipedal, small brain; a relatively complete skeleton

Homo habilis

first evidence of tool use, shorter jaw ... extinct

Homo erectus

first to leave Africa, use fire ... also extinct

Homo sapiens

200,000 ya, larger brains ... STILL EXTANT you might have met one

Homo floriensis

hobbit, extinct due to volcanic eruption?

12.2The mammalian nervous system¶

central nervous system

brain + spinal cord (continuous)

peripheral nervous system

lateral nerves + spinal nerves from spinal cord

forebrain

from telecephalon + diencephalon

telencephalon

cerebrum, limbic system

diencephalon

hypothalamus, thalamus

cerebrum

center of intellect etc, 2 hemispheres separated by corpus callosum

cerebral cortex

top layer, rich in cell bodies

limbic system

amygdala, hippocampus, nucleus accuben; basic drives

nucleus accubens

site of dopamine release

amygdala

controls fear; without, you're fearless

hypothalamus

continuous with pituitary, produce neurohormones, released by pituitary

thalamus

relay station between cerebral cortex, others

midbrain

relay, cerebrum → brainstem

brainstem

pons, midbrain (huh?), medulla oblongata

hindbrain

pons, medulla, cerebellum

pons

breathing along with medulla, messages → cerebrum from nerve cords

medulla oblongata

autonomic functions

cerebellum

smaller than cerebrum, outgrowth of pons; coordination etc

spinal cord

reflexes, protected by vertebrae, meninges

meninges

membranes; cushioning, blood supply

reflex

involuntary neuromuscular action, controlled by spine; after, message → brain informing it

sympathetic

stress, fight or flight (norepinephrine)

parasympathetic

rest & digest (acetycholine)

13Lecture 22¶

13.1Ecosystem ecology¶

ecosystem

chemical/physical properties + organisms

Anthropocene

current geological era ("after" Holocene)

biome

environment of similar climate, vegetation

eutrophication

too many nutrients → algal bloom → algae die, aerobic bacteria to decompose → O₂ down

paleoliminology

study of lake sediments

chronosequence

looking at different sediments with different ages?

14Lecture 23¶

14.1Introduction to evolution¶

evolution

changes in inherited traits of a population over generations

mutation

imperfect replication of gene sequence

genetic drift

random change in allele frequency → fixation of one allele

natural selection

best traits for surviving → next generation

artificial selection

choosing a trait, e.g. breeding, crops

sexual selection

intrasexual (male competition) or intersexual (female choice)

gonopodin

male mosquitofish, aids sneaky copulation; but a hindrance, natural selection wise

15Lecture 24¶

15.1Speciation¶

gene flow

movement of genes across populations, opposes divergence, through migration/interbreeding

neutral allele

no effect on fitness/phenotype, usually only lost due to genetic drift

morphological

definition of a species, based on appearance

cryptic species

a bunch of species that all look the same, e.g. in frogs

biological

definition of a species, due to reproductive isolation

reproductive isolation

can only breed → fertile offspring with each other

phylogenetic species

branch on tree of life

ring species

Siberian greenish warbler, around mountain; reproductive isolation at ends

allopatric/sympatric

different/same area ("country")

speciation

one species, 2+ groups diverge; gene flow must be interrupted

ecological speciation

adaptation to different niches → divergence

polyploidy

offspring has different number of chromosomes

cytoplasmic incompatibility

Wolbachia bacteria, infects beetles, inf. males only reproduce with inf. females

16Lecture 25¶

16.1Ecology¶

ecology

study of interactions between organisms, environment

foraging theory

animals eat to maximise $\frac{\mbox{energy intake}}{\mbox{work done}}$

geophagia

eating dirt, protects against toxins (binds to them)

group selection

group with lots of altruism → more reproductively successful

allee effects

at low population numbers, hard to find mate; growth rate low

trophic cascades

cascading effects in food chain. see: Yellowstone disaster