ib ess topic 2

ecosystem

made up of organisms and physical environment and interactions between living and non-living components within them

population density

average number of individuals in a stated area

what factors affect population size?

1) natality (birth rate)
2) mortality (death rate)
3) migration (immigration and emigration)

niche

particular set of abiotic + biotic conditions and resources to which an organism or population responds

fundamental niche

full range of conditions and resources in which a species could survive and reproduce

realized niche

the actual conditions and resources in which a species exists due to biotic interactions

biotic factors

living components of ecosystem -- organisms, interactions, waste -- that (in)directly affect another organism

1) every relationship that organism may have
2) where it lives
3) how it responds to resources available
4) how it alters these biotic factors

abiotic factors

non-living physical factors that influence organisms and ecosystem -- eg temperature, sunlight, pH, salinity, pollutants

1) how much space there is
2) availability of light water, etc

can two species inhabit the same ecological niche in the same space at the same time?

no; if many species live together, they must have slightly different needs and responses so they are not in the same niche

ex: lions and cheetahs both live in the African savannah, but hunt different prey -- lions take down zebras and buffalos, cheetahs take down gazelles and impalas

limiting factors

prevent a community, population, or organism growing larger; will slow population growth as it approaches the carrying capacity of the system

ex: phosphate in limited supply in aquatic systems; low temp in tundra, freezing the soil and limiting water availability to plants

population dynamics

the study of the factors that cause changes to population sizes

what interactions fall under biotic factors?

predation, herbivory, parasitism, mutualism, disease, competition

all interactions result in one species having an effect on the population dynamics of the others and on the carrying capacity of the others' environment`

competition

two conditions applied jointly

1) all organisms in any ecosystem have some effect on every other organism in that ecosystem
2) any resource in any ecosystem exists only in limited supply

intraspecific competition

between members of the same species

what is true when numbers of a population are small?

there is little real competition between individuals for resources

provided numbers not too small for individuals to find mates, population growth will be high

what happens as the population grows?

as the population grows, the competition between individuals for resources grows until carrying capacity of the ecosystem is reached

stronger individuals claim larger share of resources

what are some strategies species employ when dealing with intraspecific competition?

being territorial, eg deer -- individual/pair holds area and fends off rivals

individuals most successful reproductively holds biggest territory, hence access to more resources, more successful at breeding

what is the effect of intraspecific competition on population numbers?

intraspecific competition tends to stabilize population numbers

how is intraspecific competition displayed on a graph?

it produces a logistic growth curve, which is s-shaped

interspecific competition

individuals of different species could be competing for the same resource

what could result from interspecific competition?

1) interspecific competition may result in a balance where both species share the resource
2) other outcome is that one species may totally out-compete the other (known as competitive exclusion)

competitive exclusion

one species may totally out-compete the other

ex: garden overrun by weeds; number of weed species coexist together, but original domestic plants have been totally excluded

predation

when one animal, the predator, eats another animal, the prey/consumption of one organism by another

ex: lions eating zebras, wolves eating moose

not only animals eat other animals -- some plants (insectivorous plants) consume insects and other small animals

ex: canadian lynx and snowshoe hare

herbivory

an animal (herbivore) eating a green plant

herbivores can be large or small

how do plants respond to herbivory?

some plants have defense mechanisms

ex: thorns/spines, stinging mechanism, toxic chemicals

parasitism

a relationship between two species in which one species (the parasite) lives in or on another (the host), gaining food from it

do parasites kill their host?

no -- not beneficial for them, but high parasite population densities can lead to the host's death

ex: vampires bats and intestinal worms

mutualism

relation between two+ species in which all benefit and none suffer; example of symbiosis

what are the types of symbiosis?

1) parasitism
2) commensalism: one partner is helped and the other is not significantly harmed
2ex) fern growing half-way up a tree trunk
3) mutualism

what is a prime example of mutualism?

lichen: close association of fungus underneath and algae on top

fungus benefits by obtaining sugars from algae
algae benefits from minerals + water fungus absorbs and passes on to the algae

exponential/geometric growth

no limiting factors slowing growth

s-curves

1) starts with exponential growth -- no limiting factors affect the growth at first
2) above a certain population size, growth rate slows down gradually, resulting in population of constant size

carrying capacity

in s-curve, where numbers stabilize -- maximum number of load of individuals that an environment can carry/support

environmental resistance

area between exponential growth curve and s-curve

j-curve

see a boom and bust pattern
1) population grows exponentially
2) suddenly collapse (diebacks)

often, population exceeds carrying capacity on long-term or continuing basis before the collapse (overshoot)

note: long-term basis as carrying capacity can be exceeded in the short term (human race right now)

what does the j-curve not show?

the gradual slow down of population growth with increasing population size

what is j-curve typical of?

microbes, invertebrates, fish, small mammals

community

group of populations living and interacting with each other in a common habitat

ecosystem

community and physical environment it interacts with

respiration

breaking down food, often in form of glucose, to release energy used in living processes

what are the living processes?

MRS GREN

m - movement
r - respiration
s - sensitivity
g - growth
r - reproduction
e - excretion
n - nutrition

what are the two types of respiration?

aerobic - oxygen
anaerobic - no oxygen

aerobic respiration

energy released and used
waste products are carbon dioxide and water

c6h12o6 + 6o2 --> energy + 12h2o + 6co2

what kind of energy is produced in respiration?

heat energy -- dissipated into the environment

increases entropy of the system while organism maintains relatively high level of organization (low entropy)

photosynthesis

green plants convert light energy into chemical energy

compensation point

rates of two processes equal (no net release of oxygen or co2)

neither adding biomass or using it up to stay alive -- maintaining itself

food chain

flow of energy from one organism to the next

shows the feeding relationships between species in an ecosystem

what do the arrows connecting the species indicate?

the direction of transfer of biomass and energy

trophic levels

feeding levels of organisms

usually start with primary producer (plant) and end with carnivore at top of chain (a top carnivore)

what are the two classifications of the way organisms obtain energy?

producers and consumers

producers

1) autotrophs (green plants): make food from carbon dioxide and water using sunlight energy
2) chemosynthetic organisms: make food from simple compounds (ammonia, hydrogen sulphide, methane), do not require sunlight, often bacteria found in deep oceans

consumers

also called heterotrophs

feed on autotrophs/heterotrophs to obtain energy (herbivores, carnivores, omnivores, detritivores, decomposers)

what is the hierarchy of feeding?

food chain

visual representations of feeding relationships between one organism and another

ecological pyramids

graphical models of quantitative differences between amounts of living material stored at each trophic level of a food chain; usually measured for given area and time

benefits of ecological pyramids

1) allow easy examination of energy transfers and losses
2) give idea of what feeds on what and what organisms exist at different trophic levels
3) help to demonstrate that ecosystems are systems in balance

types of ecological pyramids

1) pyramids of numbers
2) pyramids of biomass
3) pyramids of productivity

pyramid of numbers

number of organisms at each trophic level in food chain at one time (standing crop)

units: number/unit area

what is the trend of pyramid of numbers?

length of each bar gives measure of relative numbers

most pyramids are broad at base and have many individuals in producer level, but some may have single large plant, a tree as producer, so base is one individual that supports many consumers

advantages of pyramid of numbers

1) simple, easy method of giving an overview
2) good at comparing changes in population numbers with time or season

disadvantages of pyramid of numbers

1) all organisms included regardless of size -- pyramid based on oak tree would be inverted
2) does not allow for juveniles or immature forms
3) numbers can be too great to represent accurately

pyramid of biomass

contains biomass at each trophic level

units: mass per unit area (eg g*m^-2)

biomass

quantity of dry, organic material in an organism, population, trophic level, or ecosystem

what is the trend of the pyramid of biomass?

most likely to be a pyramid shape with some exceptions

ex: oceanic ecosystems where producers are phytoplankton (reproduce fast but present only in small amounts)

advantage of pyramid of biomass

overcomes problems of pyramids of numbers

disadvantages of pyramid of biomass

1) only uses samples from populations, so impossible to measure exactly
2) organisms must be killed to measure dry mass
3) time of year affects the result
4) energy content not represented

what is true about both pyramids of numbers and biomass?

they are snapshots at one time and place, meaning that the pyramids vary with season and year

pyramid of productivity

shows the rate of flow of energy or biomass through each trophic level

shows energy or biomass being generated and available as food to the next trophic level during a fixed period of time

units: energy or mass per unit area per period of time (J*m^-2*yr^-1)

how is the pyramid of productivity different from the other two?

show the flow of energy OVER TIME

what is always true about pyramids of productivity?

1) they are always pyramid-shaped in healthy ecosystems as they follow the second law of thermodynamics
2) each bar will be about 10% of the lower one (500 --> 50 --> 5)

advantages of pyramids of productivity

1) most accurate system -- shows actual energy transferred and allows for rate of production
2) allows comparison of ecosystems based on relative energy flows
3) pyramids are not inverted
4) energy from solar radiation can be added

disadvantages of pyramids of productivity

1) difficult and complex to collect energy data as rate of biomass production over time is required
2) still problem of assigning a species to a particular trophic level when they may be omnivores

bioaccumulation

concentration of chemical high enough to cause disease/death

biomagnification

when top trophic levels take in so much of chemical that causes disease or death

which trophic level in a food chain is most susceptible to alterations in the environment?

top carnivores -- have limited diet, so change in prey has large effect

population numbers are low because fall in efficiency along a food chain, so ability to withstand negative influences is more limited than species lower in the food chain with larger populations

trophic efficiency

10%

major part of energy used in respiration and lost as heat

less and less energy available after 4 trophic levels

this is why top carnivores are so vulnerable -- only so much energy available (too hard for them to accumulate enough energy to grow to large size and maintain bodies)

solar constant

1400 watts per second

what is the only way for life to convert solar energy into food?

photosynthesis by green plants

productivity

conversion of energy into biomass over a given period of time

rate of growth or biomass increase in plants and animals

measured per unit area per unit time

net productivity (NP)

gain in energy or biomass per unit area per unit time that remains after deductions due to respiration

results from fact all organisms have to respire to stay alive so some of the energy used in staying alive instead of being used to grow

primary productivity

autotrophs base unit of all stored energy in any ecosystem

light energy converted into chemical energy by photosynthesis

gross primary productivity (GPP)

total gain in energy or biomass per unit area per unit time by green plants -- energy fixed by green plants by photosynthesis

plants first organisms in production chain (fix light energy and convert to sugar) so possible to calculate plant's energy uptake by measuring amount of sugar produced

why do we prefer NPP over GPP?

measuring sugar produced extremely difficult as much of it is used up by plants in respiration almost as soon as it is produced

net primary productivity (NPP)

rate at which plants accumulate dry mass

measured in g*m^-2

what happens to the glucose produced in photosynthesis?

1) provides for growth, maintenance, and reproduction with energy being lost as heat during respiration
2) remainder deposited in and around cells as new material represents stored dry mass -- store of energy is potential food for consumers within the ecosystem

equation for NPP

NPP = GPP - R

what is the theoretical max amount of energy available to all animals?

total amount of plant material

what happens to the total amount of plant material?

1) lost from food chains as it dies and decays OR
2) eaten by herbivores, meaning it's removed from primary productivity

how does the amount of biomass produced vary?

1) spatially: some biomes have higher NPP than others
1ex) tropical rainforest vs tundra
2) temporally: many plants have seasonal patterns of productivity linked to changing availability of basic resources (light, water, warmth)

net secondary productivity (NSP)

total gain in energy or biomass per unit area per unit time by consumers after allowing for losses in respiration (also animals, but mainly respiration)

what happens to energy that goes into the herbivore that doesn't make new biomass?

only food that crosses the gut wall of animals is absorbed and used to power life processes (assimilated food energy)
a) some assimilated food energy used in cellular respiration to provide energy for life processes
b) some removed as nitrogenous waste (urine)
c) rest stored in dry mass of new body tissue

some ingested plant material will pass straight through the herbivore and be released as feces -- not absorbed and provides no energy

equation for NSP

NSP = GSP - R

gross secondary productivity (GSP)

total food ingested including food that turns into feces

trophic level - carnivore

1) assimilate 80% of energy in diets
2) egest less than 20%
3) have to chase moving animals so higher energy intake offset by increasing respiration during hunting
4) biomass locked up in prey foods

trophic level - herbivores

1) assimilate 40% of energy in diet
2) egest 60%
3) graze static plants

flows of energy and matter

major biogeochemical cycles (water, carbon, nitrogen, sulfur, phosphorous) characteristics

1) movement of matter, such as nutrients, through an ecosystem is very different from movement of energy
2) energy travels from the sun through food webs and eventually lost as heat
3) nutrients and matter are finite and recycled and reused (via decomposer food chain)
4) organisms die and are decomposed and nutrients are released, eventually becoming parts of living things again, when taken up by plants

where is the carbon stored?

in carbon or carbon dioxide sinks

carbon (dioxide sinks) may be:

1) organic (complex carbon molecules
1a) organisms in the biosphere (plants and animals)
1b) fossilized life forms (fossil fuels)

2) inorganic (simple carbon molecules)
2a) locked up or fixed into solid forms and stored as sedimentary rocks and fossil fuels (stored and locked up for millions of years)
2b) oceans where carbon dissolved or locked up as carbonates in shells of marine organisms
2c) soil
2d) small proportion is carbon dioxide in the atmosphere

carbon cycle

carbon circulates through living and non-living systems in the ecosphere