ess: chapter 2 - ecosystems and ecology

population size

population size

depends on:

• natality

• mortality

• migration

niche

which abiotic and biotic factors a species responds to; leads to less competition

limiting factors

factors that slow down growth of population

carrying capacity

maximum amount of species in an area because of limiting factors

population dynamics

study of factors that cause population size changes (S and J curves)

abiotic

non-living

biotic

living

fundamental niche

potentially occupied by species

realised niche

portion of fundamental niche actually occupied by species

interspecific competition

competition between different species eg. over resources. tends to lead to sharing resources

parasitism

organism benefits from another organism without killing it

mutualism

relationships between two species in which both benefit and none suffer

S curve

start with exponential growth, at first no limiting factors but above carrying capacity growth rate slows gradually into a final constant size

J curve

show a ‘boom and bust’ pattern, grows exponentially, then collapses, population exceeds carrying capacity for a long time (overshoot)

respiration

glucose + oxygen → CO2 + water

photosynthesis

CO2 + water → glucose + oxygen

food chain

flow of energy from one organism to the next, but realistically food web

trophic level

position that an organism occupies in a food chain

primary producers (PP)

green plants, make their own food from solar energy. provide energy requirements of all other trophic levels, habitat for other organisms, supply nutrients to the soil, bind the soil

primary consumers (PC)

herbivores, consume PP, keep each other in check through negative feedback loops, disperse seeds

secondary consumers (SC)

carnivores and omnivores, consume lower levels

tertiary consumers (TC)

carnivores and omnivores, consume lower levels

decomposers

bacteria and fungi, obtain energy from dead organisms

detritivores

snails, slugs, maggots, vultures, derive energy from dead organisms or parts from an organism

pyramid of biomass

pros:

• takes account of size of organisms

cons

• have to kill organisms

• seasonal variation

• some animals have bone or shell (affects weight)

pyramid of productivity

pros

• shows energy over time (rates of production)

• compare ecosystems easily

• never an inverted pyramid

cons

• collecting data is difficult (bc over time)

• many species feed at more than one trophic level, affects results

pyramid of numbers

pros

• quick overview

• compare numbers in different seasons

cons

• no account taken to size of organisms

ecological pyramids

graphical models of quantitative differences between amounts of living material stored at each tropic level of a food chain

trophic efficiency

90% of energy lost between one trophic level to the next, due to 2nd law of thermodynamics. hence top carnivores vulnerable

productivity

conversion of energy into biomass over given period of time

gross productivity (GP)

total gain of energy or biomass

net productivity (NP)

GP minus respiration

gross primary productivity (GPP)

total gain of energy or biomass from green plants

net primary productivity (NPP)

total gain of energy or biomass from green plants after respiration

net secondary productivity (NSP)

total gain in energy or biomass by consumers after respiration

gross secondary productivity (GSP)

total energy or biomass taken up by consumers;

food eaten - fecal losses

carbon cycle

storages

• soil

• biomass

• oceans

• atmosphere

nitrogen cycle

storages

• organisms

• soil

• fossil fuels

• atmosphere

• water

flows

• nitrogen fixation

• nitrification

• denitrification

• feeding

• excretion

• death and decomposition

nitrogen fixation

atmospheric nitrogen is made available to plants through fixation, creating ammonium ions in these ways:

1. nitrogen-fixing bacteria in soil

2. nitrogen-fixing bacteria in root nodules of Rhizobium

3. cyanobacteria in soil or water

4. lightning

5. industrial Haber process used to make fertilisers

nitrification

nitrifying bacteria in soil, converting ammonium to nitrites. some convert nitrites to nitrates, and it can be absorbed by plant roots

denitrification

denitrifying bacteria in anaerobic conditions reverse nitrification process; the nitrogen gas escapes into atmosphere

assimilation

once living organisms have taken in nitrogen, they build it into more complex molecules

maximum sustainable yield (MSY)

largest crop/catch that can be taken from stock without depleting it

biome

collection of ecosystems with similar climatic conditions

types of biomes

• aquatic - freshwater and marine

• deserts

• forests

• grassland

• tundra

biosphere

part of earth inhabited by organisms

biome shift

caused by climate change;

• toward poles where it is cooler

• higher up mountains where it is cooler

• toward equator where it is wetter

succession

how an ecosystem changes in time

zonation

how an ecosystem changes along an environmental gradient, due to

• temperature (decreasing w altitude and latitude)

• precipitation (along mountains)

• solar insolation (higher in higher altitudes, eg)

• soil type

• interactions between species

primary succession

on bare ground, where soil formation starts process

secondary succession

where soil already is formed but vegetation has been removed

climax community

reached at the end of succession

human impact on succession

in agriculture, by deforestation, grazing, controlled burning

K and r-strategists

describe approaches of different species when getting their genes to next generation

• K-strategist:

  • small number of offspring

  • lot of energy in parental care

  • usually close to carrying capacity (hence name)

• r-strategist:

  • use lot of energy in production of many eggs

  • no energy in raising children

  • reproduce quickly

  • may exceed carrying capacity, then population crash

Lincoln index

capture, mark, release and recapture, getting two samples, using formula N = (n₁ x n₂) / m₂ where m is number of marked animals in second sample

Simpson diversity index

D = (N(N-1)) / (sigma(n)(n-1))

where N = total number of organisms of all species found, n = number of individuals of particular species