Part 2 Required Readings Flashcards
Why Ecology Matters, SFE pt4,
What are the two main limiting factors of the geographic distribution of most species of animals and plants?
geography and climate
Changes in historic geographic ranges are now being caused by two main processes:
human introductions and climate change
What is the effect of barriers on dispersal movements?
they prevent dispersal movements, in particular the movement of an individual from its place of birth to a new place for breeding and reproduction
Describe how transplant studies work
Move the organism to a new area. If it survives there and reproduces, you have good evidence that the former distribution was restricted by a lack of dispersal.
Give two examples of deliberate introduction of pest species
- The European Starling (Sturnus Vulgaris) has spread over the entire US and much of Canada within a period of 60 years.
- The cane toad (Rhinella marines) was brought to Australia where it failed to control any insect pests and became a pest itself
If more individuals of a species are introduced….
the species will be more likely to survive and colonise the island.
What are the four major steps of the invasion process? At which step can this process fail?
Transport, establishment, spread, and impact
The invasion process can fail at any of these four steps.
Why may transplants or movements of plants and animals into a new area fail?
- Biological environment may eliminate the newcomer
- Physical-chemical environment may be lethal to the organism and prevent it from reproducing
List the 4 geological processes that may cause changes in distributions for any particular species
- Dispersal limitation: the species is absent because it has not been able to move to an area
- The species does not recognise the habitat as suitable
- Other species prevent colonisation (parasites, predators, pathogens)
- Limiting physical or chemical factors (temperature, water, oxygen, soil, pH)
Describe the simplest model for climactic limitation
geographic ranges for all species should be shifting poleward
How will stream fish react to water temperatures rising?
they will tend to move upstream to stay within their temperature zone
what is the environmental variable most important to organisms?
temperature
what does the latitudinal gradient in temperature arise from?
- the uneven distribution of radiant electromagnetic energy that is blasted at the earth from the sun
- the spherical shape means that the sun’s rays strike the earth at different angles at different latitudes
describe how photon density per unit area of the earth changes as we move towards the poles
it declines because the angle of incidence declines from 90 to 0, eventually reaching a tangent
how does seasonal variation in climate arise?
- the earth’s axis is tilted at about 23.5 off the vertical.
- as it makes its annual revolution, different parts of the earth experience the sun as being directly overhead at noon
at the spring and autumn equinoxes
sun is directly above equator
at the northern hemisphere’s summer solstice
sun is directly over 23.5N
at the northern hemisphere’s winter solstice
sun is directly over 23.5S
the latitudinal lines around the earth at 23.5N and 23.5S are called
Tropic of Cancer and Tropic of Capricorn respectively
solar equator
line of latitude closest to the sun
how does the solar equator change through the year
it oscillates between the two tropic lines, making one cycle per year
tropical region
belt bounded by Tropic of Cancer and Tropic of Capricorn
how does solar light energy transfer so much heat to the earth?
- when lights hit solid surfaces, they are absorbed and reradiated at longer, IR wavelengths
- light is converted to heat
- IR radiation (unlike light) is absorbed by the atmosphere
- solar energy heats the earth’s surface and then the surface heats the air near the surface
what is atmospheric circulation caused by?
solar heating of the bottom of the atmosphere
define atmospheric circulation
the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.
what is the earth’s atmosphere?
a relatively thin layer of gases that is pressed against the earth by gravity
Hadley cells
- equatorial region of earth’s surface heats up the most
- IR radiation from the heated surface in turn heats up the near-surface atmosphere, rendering the air less dense
- this reduction in density (1) causes a meterological low pressure zone (2) impels heated air to rise above the solar equator
- as the air rises, it creates a partial vacuum beneath it, and that suction causes surface air to be drawn toward the solar equator from the N and S
- that new air also heats up and rises
- this sets up a continuous flow
- the air bumps up against the top of the atmosphere, and is then pushed away from solar equator, moving to the south and north.
- as the air rises, it expands more as there is less atmosphere above it to compress it
- expansion of a gas causes it to cool (relationship of temperature drop to altitude gain is described by adiabatic lapse rate)
- cold and heavy air at top of atmosphere sinks, but because it is continually pushed to the north and south, it descends not at the equator, but at 30N nd 30S latitude.
- after descending, air is pulled back toward solar equator
zone of rising, heated air in Hadley cells is known as
intertropical convergence zone (ITCZ)
Hadley cells not only set prevailing winds in motion, but also
affect precipitation:
- air that comes into the ITCZ is humid
- as it rises and cools, much of the water vapour condenses into liquid water clouds and falls as rain, so the equatorial tropical regions are very rainy
- by the time a packet of air has reached the upper atmosphere, it has been wrung dry of most of its moisture
- when that air subsequently descends at the 30N and S latitudes, it comes down as hot, dry, air
- these latitudes chronically experience high-pressure weather systems (=deserts)
describe Ferrell and polar cells
- not as strong or consistent as Hadley cells, but are driven by same processes.
- as the dry air in the Ferrell cells moves across the earth’s surface towards the pole, it also picks up moisture, and finally tends to rise, creating another pair of rainy/snowy low-pressure zones around 60N and 60S
- high-level flows toward the equator close the Ferrell loops; the flows toward the poles set up polar cells (weakest + most diffuse)
why are wind patterns critical influences on organisms?
- they redistribute heat
- they redistribute water (as vapour) from oceans to continents
north wind
blows from north to south
describe the six-cell circulation pattern that imparts northernly and southerly components to prevailing wind directions
- between 0 and 30N, the Hadley cells push air from north to south
- between 30N and 60N, Ferrell cells push air in the opposite direction
- between 60N and the North Pole, the polar cells impart a flow to the south
Prevailing westerlies
- westerlies arise because the air being pushed straight northward by the Ferrell cell is passing over the surface of a spinning sphere
- that action produces a twist of the wind vectors with respect to the earth’s surface (Coriolis effect = pseudo force)
- between 30S and 60S, 30N and 60N
Prevailing easterlies
- between equator and 30N or 30S
- air is moving toward the equator, so air pacers fall behind their apparent target rather than getting ahead
where are prevailing winds strongest?
at the latitudes in the middles of the atmospheric cells, roughly at 15 and 45. here, the air is primarily being pushed horizontally across the earth’s surface, producing consistent winds
where is there little horizontal wind?
at the latitudes where air packets are mainly going upward (0 and 60) or coming down (30)
draw a diagram for wind
Fig. 5 of SFE
define and describe jet streams
another class of wind currents high in the atmosphere - concentrated and narrow westerlies that wander around in irregular fashion.
these blur and transgress the usual boundaries between the cells.
oceanic circulation
massive packets of water produce circulation patterns (currents) in the oceans. They move heat from one place to another and this affects neighbouring land masses; land and sea are not independent systems.
describe how oceans influence nearby land masses by providing thermal inertia
- land masses heat up in summer and cool down in winter much faster than do masses of water.
- in coastal areas, spring arrives more slowly, but summer lingers longer into the autumn
- maritime climates are buffered against temperature extremes
describe the relationship between ocean temperatures and precipitation
- more loading takes place when ocean waters are warm rather than cold
- warm water warms the air
- molecules of liquid water are more able to evaporate into vapour from warmer water and warmer air can retain more water vapour
orogenic precipitation and rain shadows
for a mountain range oriented perpendicular to the prevailing winds, precipitation is greatly enhanced on the windward side and suppressed in the lee.
as air is pushed up the windward side, it is cooled according to the lapse rate equations, causing condensation and precipitation
impact of exposure on vegetation
- in the northern hemisphere, south-facing hillsides face the direct rays of the sun
- north facing slopes are mostly shaded, cooler, and more moist.
- agitation on slopes thus differs
two factors that are most likely to limit the distributions of terrestrial species
temperature and water
why is water important?
- affects concentrations of chemical reactions
- cells and tissues depend on membranes to compartmentalise chemical processes and reactants. proper functioning depends on osmotic balance.
if cells get too dry
concentrations of dissolved salts increase. chemical reactions are slowed and changed
if too much water enters cells,
reactants get diluted and fail to combine as needed
what does it mean for objects to equilibrate?
will tend to reach the same temperature as their environment
thermoconformers
body temperatures more closely track ambient temperatures
endotherms vs ectotherms
Endotherms use internally generated heat to maintain body temperature. Their body temperature tends to stay steady regardless of environment.
Ectotherms depend mainly on external heat sources, and their body temperature changes with the temperature of the environment.
distinguish between conduction and convection
- conduction is the direct transfer of heat between two bodies that are in contact
- convection is the heat transfer that is facilitated by a moving fluid, typically air or water
how does radiative heat transfer differ from all other types of heat transfer?
they involve molecules bumping into each other and transmitting their kinetic energy
role of fur/feathers
to trap air and prevent convective flow. within the layer of insulation, a temperature gradient is set up and maintained; temperatures are cold near the outside of the fur, but warm next to the skin
how do birds keep warm?
they can lift their outer contour feathers away from their body, creating a dead-air space underneath that is filled by down feathers. these block convective air flow
how do mammals in cold environments usually keep warm?
depend on a thick layer of subcutaneous blubber which serves as insulation and long-term food energy storage
countercurrent circulation
- direct contact between arteries that send warm blood and the veins that bring cooled blood
- heat exchange can occur
- cooled returning venous blood captures warmth before it can be lost to the environment
- because the blood flows are going in opposite directions, there is a continuous temperature gradient between the two vessels
describe biochemical specialisations of photosynthetic pathways
- C3 and C4 pathways. atmospheric CO2 is incorporated into a 3C or 4C molecule.
- CAM. plants keep most of stomata closed in sun and only open at night
what are the cons of C3 and C4?
- not efficient in water use
- enzyme that captures the carbon also captures oxygen, which causes wasteful photorespiration at high temperatures
laminar flow
- airflow is unimpeded so a stratified pattern builds up
- happens when surface is smooth, without bumps or ridges
- one cm above leaf surface, air is going at normal speed
- much closer to leaf’s surface the air forms a boundary layer that is virtually stagnant.
why is stagnant air next to a leave not desirable?
- dead air depleted of CO2 and enriched in oxygen
- heat up cos convective evaporative cooling is reduced
turbulent flow
if the leave surface has enough irregularities, the boundary layer is broken up and freshened by eddy currents and vortices
microphylly
tiny leaves
desert annual plants
compressed life cycle in which the seeds germinate right after heavy rains start, they grow, flower, set seed, and die, all in around 2 months. plants temporally evade desert conditions.
from the standpoint of population growth, the most important differences among individuals are
sex and age
age structured models of population growth
- divide the population into a convenient number of different age classes, each of which has different prospects of death and reproduction
- keep track of females only - only ones who reproduce
in life tables for humans, each age class is typically chosen to be
5 years long
first age class is denoted by
subscript 0
total population size =
sum of nx values over all ages x
set of nx values is called
the age structure of the population at the time we are looking
survivorship schedule
= age-specific risks of mortality
lx =
survivorship at age x = probability that an individual is still alive at age x
3 things that are necessarily true about lx values
- range from 0 to 1 (probabilities)
- l0 = 1 (newborns are necessarily alive at birth)
- lx values must always get smaller as x increases (probability of being alive always declines with age)
describe 3 types of survivorship curves on logarithmic scales
type I = convex curves (low early mortality rate) = eg humans
type II = straight lines
type III = concave curve (much early death) = plants
bx
the average number of daughters produced by a female in her xth year of life
can bx exceed 1?
yes; not a probability
b0 is typically
0
- new organisms need to pass through a period of resource acquisition and growth after birth before they are capable of giving birth themselves
key elements of fecundity schedules
- total number of offspring produced
- waiting period before reproduction
why do simple age-structured models lack density dependence?
we treat both fecundity and survivorship schedules as constants
net reproductive rate/replacement rate
R0 = Σlxbx
if R0= 1
each female exactly replaces herself, and the population size will remain constant
if R0>1
population will increase geometrically without limit
if R0<1
population slides toward extinction
generation time
age of a mother at the time she produces her average daughter
T = Σxlxbx/Σlxbx = Σxlxbx/R0
key tradeoffs
- production of offspring is affected by a size-number trade-off
- early vs late reproduction: organisms that reproduce earlier do not have as long a period to accumulate resources, so they can’t make as many offspring as those others who wait longer to start
- cost of reproduction
producing offspring is costly to parents in two ways:
- parental survival can be reduced (bx schedule affecting lx schedule)
- parental resources for reproduction can be depleted, meaning subsequent offspring production is delayed and diminished (high bx early in life reduces bx late in life)
why should a newborn, with all her life ahead of her, have a lower future value than a somewhat older female, who has only part of her life ahead of her?
a newborn must get through the pre-reproductive, resource-acquisition phase of her life before she can start reproducing, and she encounters some risk of during that period
how can we compare the shapes of vx curves of different species or populations?
by converting raw values to relative reproductive values
in species with a tendency to form lasting pair bonds between mates, there should be fairly strong selection for…
males who prefer female mates with high reproductive values. This could produce a tendency for traits associated with the onset of reproductive age to become associated with sexual attractiveness
many mobile animals characteristically undergo
a temporary life-history stage of migration
- juveniles frequently driven out of their natal territories by disputes with their parents, and have to strike out to find territories of their own
- high vx value
semelparity
species genetically programmed to reproduce only once in their lifetimes then die
iteroparity
species that potentially reproduce numerous times
iteroparous plants are usually called
perennials
semelparous plants are also called
monocarpic (making fruits once)
semelparous plants that only live a single season
annuals
biennials
grow vegetatively for one year, then flower and die in their second year
monocarpic perennials
species that live longer than two years before flowering and dying
is iteroparity or semelparity seen as the norm?
iteroparity
why are annuals common among plants?
in highly seasonal deserts with long annual dry periods plants are exposed to extreme water stress
dormancy
- small, fast maturing plant compresses all of its active growth into the brief wet season then produces seeds that spend the dry season in a state of dormancy
- plants don’t have to endure the full harshness of the environment while they are actively growing
weeds
- annuals prominent
- plants adapted for growing in transient habitats that have been disturbed
fugitive species
have to keep discovering new bare patches after being pushed out by taller perennials
similarities between the two classes of annuals - desert annuals and weedy annuals
- adapted to take advantage of brief windows of time during which rapid growth is made possible by milder conditions
- develop long-lasting seed banks in the soil so that a large proportion of the populations is underground at any one time
-adaptations that selectively promote seed germination at the right time
seeds of desert annuals
germinate only after heavy rains have lashed out water-soluble germination inhibitors in the seed coat, guaranteeing the plants start growth when water is available
seeds of weedy annuals
tend to germinate only when they are struck by sunlight. this lets them get started right after there has been sci disturbance that brings some of them to the surface
third set of annuals
many crop plants, including rice, maize, wheat
- annual strategy has been developed through artificial selection by humans
big-bang reproduction
desperate flowering/reproductive effort exhausts the plant and it dies
possible explanation for Big Bang reproduction
animal pollinators of such plants may have been disproportionately attracted to visit the plants with the largest inflorescences
synchrony in flowering
- seed production may be synchronised across a plant population so there are occasional years of high seed production interspersed among more common years of no production
- when a big seed crop comes along, the predator populations become satiated before all the seeds are eaten up
- the predator populations will crash the year when seeds become scarce again
examples of Big Bang reproduction in animals (not very common)
- salmon: begin life in freshwater lakes/rivers, migrate downstream to the sea, grow to adult size in marine waters, then return t their natal river to spawn. transfer so much of tissues into gametes that it dies
- Antechinus (marsupial): males semelparous. at breeding season, when food is scarce, males do into such a frenzy of courting, fending off rivals, and copulating that they deplete their tissues and die of exhaustion
r-selected species or r-strategists
plants with high fecundity, Low survival, short generation times, small but numerous seeds, good dispersal ability, poor competitive ability
K-strategists
opposite to r-strategists
objections to r and K strategist classifications
- some researchers don’t like term strategy as they think it implies some kind of advance planning by the organism
- making up labels from the logistic parameters r and K may be taken to imply that these categories translate to particular values of those variables
C-S-R trichotomy
J. P Grime
- competitive species: mostly correspond to slow K strategists that compete well in crowded conditions
- stress tolerators: tough plants that grow slowly in situations that remain uncrowded because the physical environment is very harsh
- ruderal species: fugitive type weedy species that exploit transient disturbances to grow quickly in unstressful sites that are temporarily uncrowded
deterministic model
parameters that determine births and deaths are treated as constants, which means that the outcome is completely determined by the starting conditions
why have stochastic models generally replaced deterministic models in real world attempts to gauge the risks of extinction?
chance variation will inevitably introduce, and there are some good reasons for including realistic variability if we are trying to make predictions.
what do most ecology studies consider?
a subset of the species in a local system, which may be taxonomically defined or functionally defined. Often the restriction goes down to the guild level
organisms share a guild if they have
similar functional niches
in addition to species richness and diversity, community ecologists are interested in
- stability of species composition
- resilience in the face of stress or disturbance
- types of changes that occur through time
- kinds of interactions that link the species
condition for stable co-existence
each species inhibits its own population growth more than it inhibits the growth of the other species’ population
G. F Cause
- investigated competition with various species of Paramecium in lab cultures
- populations tended to behave in ways that resembled predictions of the LV competition models
- certain pairs seemed incapable of coexisting, with one going to deterministic extinction
- others tended to equilibrate
Thomas Park
- worked with two congeneric species of flower beetles
- showed that competitive exclusion was the rule
- varied environmental conditions of containers of flower
- under certain conditions, one species tended to win; in others, the other beetle prevailed
what did Park demonstrate
demonstrated the importance of abiotic conditions in determining the outcome of biotic interactions between species, but also tended to reinforce the idea that it was unlikely for two competing species to coexist
Robert MacArthur
- asked how so many species of insectivorous warblers were able to coexist in their summer breeding habitats of northern coniferous forests
- did time-budget behavioural studies
- the most common warbler species were usually feeding in different zones of the coniferous trees
- they were engaging in finer-scale niche partitioning
why was MacArthur’s study so impactful?
- quantitative; one. could measure similarity in the way that two bird species used their shared habitat. You could compute the degree of niche overlap on a scale of 0-1
- one could argue that those measures of niche overlap should be equivalent to the competition coefficients in the LV model
limiting similarity
maximum amount of niche overlap that would allow two species to coexist
distribution of Anolis lizard species across the islands of the West Indies
- divide up habitats in patterns than reflect functional feeding niches
- behavioural feeding specialisations co-vary with sets of morphological characters that are related to the different mechanical challenges posed by the different substrates used by the different lizards
- which species co-occur on different islands does seem to depend on their foraging niches
what is the reason why the resource-partitioning viewpoint fell from favour?
- factors that tend to make real communities non-equilibrial
- populations are influenced by factors other than competition
Robert Paine
- field experiment in which he continuously removed predatory starfish from the rocky intertidal zone of ocean shores in the Pacific Northwest
- intertidal is submerged at high tide but exposed at low tide
- competition for space is keen
- where Paine removed the starfish, the no of species present dropped over the years surfaces became dominated by a single species of mussel
- in a control area, mussels did not push out the competition. they remained just one component species within a diverse community
explain the results of Paine’s experiments
- mussels were superior competitors for space, capable of pushing out every other species and creating a mussel monoculture unless something restrained them from doing so
- however, the starfish provided exactly that restraint
- Pisaster is specialised for killing them
how do density-dependent, abiotic factors have an impact on competition?
Paine showed that species diversity was lower in calm-water rocky intertidal areas than more violent wave action ones.
when storms blow in, the surf slams floating logs or ice against the rocks, scraping off mussels and other species. the resulting patches of open rock surface serve the same function as the patches opened up by starfish predation
when is the importance of competition diminished?
when species populations are routinely knocked down by other factors (predators, disease, bad weather, physical disturbances)
patches vs matrix areas
patches represent areas that fall within the range of tolerance of the species. matrix areas fall outside the range of tolerance and are effectively death zones
species that have high colonisation potential and low extinction rates will tend to be found in
nearly all patches at equilibrium
source patch
particularly large or suitable patch that maintains a growing subpopulation and serves as a net exporter of dispersing colonists
sink patch
lower quality, incapable of maintaining a subpopulation except through the immigration of colonists from other patches. it is a net importer of dispersers, and if dispersal were cut off, the subpopulation would go extinct
when can a sink patch remain occupied indefinitely?
when it is embedded in a healthy meta population, with source populations nearby
- migrants keep arriving to restock the otherwise doomed subpopulation
metapopulation representations show that
subdivided systems can display properties that homogeneous systems cannot
describe the Earth as a system
- small amount of matter input from meteorites and cosmic dusts
- but is mostly a closed system in which energy propels atoms through biogeochemical cycles
what did the HSS argument say?
- in most terrestrial communities, there is a lot of plant material (primary productivity) that is not consumed by herbivores
- therefore, the second trophic level (herbivores) must not be limited by their food supply, and must instead be limited by their consumers (predators)
criticism of HSS
- perhaps the explanation for the greenness of the world is that not all of those unconsumed leaves are edible
- the arguments only apply to entire trophic levels: perhaps the second trophic level is limited by predation from the third, but that doesn’t mean that all of the species populations in the second level are limited in that way
trophic cascades
measurable, important, indirect relationships between two trophic levels that are mediated through a third level
why are trophic cascades more likely to be found in aquatic systems than terrestrial ones?
because the aqueous habitat lacks barriers to dispersal, the organisms will behave more as populations and less as meta populations.
- terrestrial systems are more heterogeneous and more unruly
if plant defences make life so hard for herbivores, why is herbivory found in so many animals?
herbivory came first and diversification came second
Ehrlich and Raven showed that
evolutionary relationships between plants and the insects that eat them give clear evidence of a coevolutionary interaction that leads to specialisation and speciation
describe how plants/insects evolve specialisation
- after an insect species has developed resistance to a particular compound, it can evolve to specialise on that plan, sometimes even using the compound as a chemical cue to help find the plant, as a feeding stimulant, or as a cue for egg-laying
herbivorous lineages have produced —- species than their carnivorous sister lineages
more
why does the pattern of extreme specialisation not appear in large-bodied herbivores such as mammals?
- can move through habitat and make choices
- can take many different species
- handle toxic chemicals by selecting a mixed diet in which they avoid the worst poisons and take milder toxins in low enough doses to avoid bad effects
- diet generalists so don’t need detoxification pathways for dealing with secondary compounds
glassy-winged sharpshooters
- stab plants with piercing mouthparts and suck the fluid from their vessels
- agricultural menace
Hemiptera
a diverse order that includes bed bugs, assassin bugs, scale insects, and leaf-hoppers, all of which are characterised by stabbing, sucking mouthparts
Buchnera
- aphids feed on phloem sap: deficient in several nutrients, including 10 essential aas
- amino acids flow from Buchnera to host
- Buchnera’s genome retains many of the genes for making the aas
giant tube worms - Riftia pachyptila - Galápagos Islands
- does not eat
- worm’s trophosome (organ) packed with crystals of pure sulphur
- have bacteria in their body, which use sulphur to make energy
- sulphur (sulphides) is source of energy in absence of sunlight. bacteria oxidise chemicals and use liberated energy to fix carbon
- churn out pure sulphur
chemosynthesis
making your own using chemical energy instead of light or solar energy
how does chemosynthesis explain why the worms are mouthless and gutless?
their symbionts provide them with all the food they need
is chemosynthesis restricted to deep water?
no
how do the Olavius worms in Elba’s sediments make a living if they are very low in sulphides?
two symbionts: one big, one small
- small grabs sulphates, which are plentiful in Elba sediments, and converts them into sulphides
- big bacterium then oxidises the sulphides to power chemosynthesis
what did Ruth Ley find
- each mammal has its own distinctive set of gut microbes
- communities clustered into certain groups depending on their owner’s ancestry and diet
- plant-eating herbivores typically have the highest diversity of bacteria
- meat eating carnivores have the lowest
- omnivores in middle
why plant-eating herbivores have the highest diversity of bacteria?
- compared to animal flesh, plant tissues contain more complex carbohydrates such as cellulose, hemicellulose, lignin and resistant starches.
- vertebrates don’t have the molecular chops for breaking these apart; bacteria do
foregut vs hindgut fermenters
foregut: fermentation chambers/microbes sit ahead of stomachs or in first of several chambers
hindgut: chambers sit at end of gut
relationship between microbiomes or foregut fermenters and hindgut fermenters
microbiomes of foregut fermenters are more similar to each other than those of hindgut fermenters, and vice versa
protists and termites
- protists can make up half weight of termite host
- they have enzymes that digest the tough cellulose in the wood that termites eat
macro termites
destroy wood via agriculture
- inside nests, they farm a fungus, which they feed with bits of wooden shrapnel.
- fungus splits cellulose into smaller components, creating a compost that the termites then eat
- inside their guts, bacteria digest the fragments even further
- macro termite queen relies on worker daughters to feed her
