biology 4

Ecosystems - a species occupies a niche, goverened by adaptations to abiotic and biotic factors

Community - all the species of a habitat

Population - all the organisms of one species in a habitat

birth rate = (no births per year/pop in same year) x 1000

death rate = (no deaths per year/pop in same year) x 1000

% pop growth rate = (pop change / pop at start) x 100

immigration - individuals joining a pop

emmigration - individuals leaving a pop

life expectancy - the average life expectancy is that age at which 50% of the individuals in a particular pop are still alive

increasing population - birth rates > death rates

decreasing population - birth rates < death rates

stable population - death rate = birth rate - no change in pop size

pop growth = (B+I) - (D+E)

random sampling 

• quadrats - consider size of quadrat, number of sample needed & position of each quadrat
• transects - abundance & distribution of a species
• quantative data

abundance

• percentage cover - estimate the area within a quadrat that a species covers
• frequency - the likelihood of a species occuring in a quadrat

mark-release-recapture

• estimated pop size = (total in 1st sample x total in 2nd sample)/no marked in 2nd
• no immigration/emmigration
• few births/deaths
• mark not rubbed off

predation

• one organism consumed by another
• predator-prey relationships: predator eats prey & decreases no of prey. more competiton for fewer prey. predator pop decreases. fewer predators = fewer prey eaten. prey pop increases. predator pop increases.

interspecific competition - individuals of DIFFERENT species

intraspecific competition - individuals of SAME species

abiotic factors

• temperature - enzymes & optimum
• light - energy source for ecosystems
• pH - affects enzyme activiy
• water & humidity - affects transpiration in plants

inheritance

• genotype: genetic constitution of an organism
• phenotype: observable characteristics
• gene: a section of DNA that determines a single characteristic. exists in 2 or more forms
• allele: one of the different forms of a gene. only one can occur

speciation

• the evolution of a new species from an existing species
• geographical isolation: physical barrier prevents 2 pops breeding with each other, conditions in 1 area change, mutations arise & are passed down generations. LONG period of time new species evolves, & is unable to produce fertile offspring with original species

sex linkage

• controlled by recessive alleles
• on X or Y chromosome

Multiple alleles

• only 2 can be present in an individual
• more than 2 alleles for a gene

codominance

• two alleles are dominant
• both expressed in phenotype

stabilising

• environmental conditions remain same
• phenotype closest to mean favoured
• eliminates extremes

directional

• if environmental conditions change phenotypes needed to survive will change
• phenotypes at extremes are favoured

p + q = 1

p2 + 2pq + q2 = 1

• used to predict the frequencies of the alleles of a particular gene in a population
• predicts that the proportion of dominant & recessive alleles remain the same for each generation 

can only be used if:

• population is large
• no mutations
• population is isolated
• no selection
• mating is random

energy transfer

• photosynthesis: main route that energy enters the ecosystem
• energy transferred through trophic levels
• energy transfer = (energy available after / energy available before) x 100

Pyramids

• numbers - no account of size, may not be pyramid shape/ may be inverted, maybe impossible to represent on same scale
• biomass - gm-2, only organisms at a particular time are shown, total mass of the plants/animals at a particular place
• energy - most accurate, energy stored in organisms, difficult & complex

Pest control

• pest = organism that competes with humans for food - may be a danger to health
• effective pesticide should: be specific, biodegrade, be cost effective, not accumulate
• biological control: pests don't develop resistance, control organism may become a pest, doesn't work quickly (time lag), controls the pest - doesn't eradicate it, reproduces itself, specific
• chemical pesticides: pests develop genetic resistance - new pesticides need to be developed, must be reapplied at intervals - expensive, always has some effect on non-target species
• integrated pest-control systems: removal of pests mechanically-time, using biological control, pesticides as last resort.
• pests & productivity - monoculture crop allows rapid spread, pests create a limiting factor, photosynthesis reduces. ∆ productivity decreases.

intensive rearing

• reduce energy losses: feeding controlled, predators excluded, selective breeding, hormones used to increase growth, animals confined, movement reduced - less energy lost in muscle contraction, temperature controlled - reduced heat losses

agricultural ecosystems

• energy input: food for workers, fossil fuels for machinery 
• natural ecosystem only input is sun & productivity is low
• agricultural: productivity increased - reducing effect of limiting factors - reducing competition

net productivity = gross productivity - respiratory losses

net productivity: kJm-2year-1, area of ground covered by leaves of crop, efficiency of photosynthesis

primary              pioneer species

barren land->primary colonisers->secondary->tertiary--shrub land->climax

hostile, instable

community less hostile, more stable & higher biodiversity

secondary(faster): land altered due to fire/disease/grazing/agriculture -               re-colonisation to climax community

• non-living environment becomes less hostile
• a greater number and variety of habitats
• increased biodiversity
• more complex food webs
• increased biomass

• management of Earths natural resources
• managing succession & preventing next stage
• why? - ethical(some species here before humans) -economic -cultural & aesthetic(habitats & organisms enrich our lives

natural/organic

• dead & decaying remains
• animal waste

artificial/inorganic

• mined from rocks & deposits
• converted into different forms
• blended together to form appropriate balance for particular crop

leaching

nutrients removed from soil

rain water dissolves nitrates & carries them beyond reach of roots

find way to watercourse

little nitrate in lakes & rivers = limiting factor

nitrate conc increases, not limiting factor, plant & algae grow on surface & absorb light

no light to lower depth 

light limiting factor for deeper plants, plants die

lack of dead plants not limiting factor so saprobiotic microorganisms grow

increased demand for oxygen - conc decreases - limiting factor - aerobic organisms die

less competition for anaerobic organisms - populations increase

anaerobic organisms decomposed - more nitrates released

consequences

• extinction of organisms
• rise in sea level
• higher temp & less rainfall = failure of crops
• greater rainfall & intense storms = life cycles & pop of insects alters
• methane produced by decomposers