population size and ecosystems Flashcards
define ecology
study of the ecosystem
define ecosystem
a definable area with its own community of organisms and physical environment, all interacting as a relatively self sustaining unit
define community
all the populations of all the species that live together in a particular ecosystem
define habitat
the part of an ecosystem in which particular organisms live
define population
all the interbreeding organism of one species living in a particular habitat at the same time
define environment
term used for surroundings. term for the external conditions affecting the existence of organisms
define biotic factor
effects of the activities of living organisms on other organisms e.g. food availability
define abiotic factors
non living, physical conditions in an ecosystem e.g. temp,light,soil
define niche
how it feeds and where it lives
the role that each species plays in an ecosystem
what is the carrying capacity
as a population increases it begins to experience environmental resistance as space and resources are reduced and so competition increases
population stabilised at a level which ecologists call the carrying capacity
what is the lag phase
little or no pop growth. period of adaptation for preparation for breeding
what is the log phase
exponential growth. a period of no constraint on pop growth with adequate supplies
what is the linear phase
a decelerating phase when growth rates become limited
what is the stationary phase
the population size is maintained at a constant level
what are some factors affecting population
- immigration
- emigration
- variation in birth or death rate
- sudden physical or chemical environment change
when will a population increase
when birth and immigrants > death and emigrants
what are density dependant factors
factors that increase as the size of population increases = biotic factors
what are density independent factors
unrelated to the size of the population = abiotic factor
describe a brine shrimp ecosystem
algae - for photosynthesis brine shrimp - for respiration competition for space competition for resources mineral in sand reproduction competition for a mate
what does a food chain show
how energy is transferred from one living organism to another
what is a trophic level
the level at which an organism feeds
what is energy transfer measured in
KJ m^-2 year
how is energy lost
lost from each trophic level as heat and some remains stored in dead organisms
what does a pyramid of biomass show
area of bars is proportional to the dry mass of all organisms at the level but different organisms may release difference amounts of energy per unit mass
what is a pyramid of energy
burning the organisms to measure calories and work out heat energy release per unit mass
what is photosynthetic efficiency
measure of the ability of a plant to trap light energy
how can light energy be lost and what %
due to reflection conversion inefficiencies
20-40% exuded into soil to feed the microbes
what is gross primary productivity
the rate at which plants convert light energy into chemical energy
as energy is lost when the plant respires, less energy is available to the primary consumer
the energy remaining is called the net primary productivity (NPP)
how much GPP is lost to respiration
60%
how much GPP is used for growth and respiration (NPP)
40%
what do consumers have a conversion efficiency of
10%
how can energy transfer between each trophic level be calculated
(energy available after transfer)/(energy available before transfer) X 100
why does life require nitrogen
protein and nucleic acids
what is the major reservoir of nitrogen
79% in the air (inert in this form )
how must plants reserve nitrogen and where do they get it from
in a fixed form
nitrate ions (NO3^2-)
ammonia (NH3)
ammonium (NH4+)
where do animals get nitrogen from
plants
they digest absorb and assimilate different forms of nitrogen from their food
what four biological processes participate in the cycling of nitrogen
- nitrogen fixation
- decomposition
- nitrification
- denitrification
what is nitrogen fixation
the nitrogen molecule is inert and uses substantial amounts of energy to break it apart
three processes
-biological fixation by certain microbes
-atmospheric fixation by lightning
-industrial fixation by the haber process
what is biological fixation
-free living bacteria such as AZOTOBACTER
-symbiotic bacteria RHIZOBIUM in root nodules of legumes
contain an enzyme called nitrogenase that converts nitrogen and hydrogen into ammonia -the ammonia is used to make amino acids which the legume can use to make proteins in return for supplying the bacteria with carbs
what is decomposition
the proteins made by plants enter and pass through food webs just as carbs do
at each trophic level their metabolism produces organic nitrogen compounds that return to the environment chiefly in excretions
the final beneficiaries of these materials are microorganisms of decay
they break down the molecules in excretions and dead organisms into ammonia
what is nitrification
ammonia can be taken up directly by plants usually through their roots
most of the ammonia produced by decay is converted into nitrates
1) bacteria of the genus NITROSOMONAS oxidise NH3 to nitrites N02-
OR
2)nitrobacter oxidise the nitrites to nitrates (NO3-)
what is denitrification
reduced nitrates to nitrogen gas, replenishes the atmosphere and closes the nitrogen cycle
bacteria =PSEUDOMONAS live deep in soil and in aquatic sediments where conditions are anaerobic
use nitrates instead of 02 for final electron acceptor
why do we need fertilisers
contain nitrogen nd other mineral ions - obtain from the soil, if farming is intensive then minerals are lost from the soil
nitrogen and mineral ions increase growth and yield
what are the different types of fertilisers
NATURAL - dead and decaying plants
ARTIFICIAL - mined from rocks and blended to give the right mix of nutrients
NPK - nitrogen, phosphorous and potassium
what are the consequences of using fertilisers
reduced species diversity - NPK fertilisers favour the growth of grass and nettle species
leaching - excess nitrogen in soil due to excess fertilisers and causes leaching in rivers
eutrophication - excess fertilisers in lakes cause increase in algae and decreases the amount of sunlight
advantages of organic fertilisers
steady supply go nutrients contain macro and micro nutrients add structure to soil use for disposing farm waste nutrients not readily leached from soil l
disadvantages of organic fertilisers
offensive smells
difficulty spreading
mineral release low
advantages of inorganic fertilisers
nutrients in concentrated form can be in smaller amounts nutrients released rapidly easy to apply clean chemicals lack odour
disadvantages of inorganic fertilisers
readily leached
increased eutrophication
expensive
risk of spreading to other areas
what happens during eutrophication
plants and animals die saprotrophs secrete hydrolytic enzymes enzymes digest organic molecules saprotrophs absorb amino acids and sugars sugars are respired for energy and release co2 into the atmosphere amino acids used for growth excess amino acids are respired carbon is returned to the carbon cycle
what is succession
gradual change in species at a defined location over time
what happens to a community during succession
constantly changing and dynamic unit which passes through a number of stages from its origin to its climax
the transition from one stage to the next is called succession
what is primary succession
plants grow where no plants have grown before
what is secondary succession
plants grow where there has been a previous population. these will have been destroyed
what are pioneer species
the first species to colonise
often opportunistic species which are able to rapidly exploit a sudden new opening in ground plant cover
what is the climax community
the ultimate species to colonise
what is bare rock succession
weathering will start to erode the rock forming crevices and breaking down mineral particles
no plant competition
soil mobile and liable to erosion
what is a sere
the sequence of communities with the different species and structures
what is a xerosere
a sere in a dry environment
what is global warming
he increase of average global temp in excess of the greenhouse gas effect caused by the atmospheres conc of co2
what causes an increase in co2
= burning fossil fuels
=deforestation
what is the greenhouse effect
carbon dioxide, methane, nitrous oxides, cdc’s, ozone and water vapour
allow high energy short wave length solar radiation to pass through earths surface
re-emits lower energy longer wavelength infrared radiation
so the surface warms up
what is global warming caused by
high concentrations of greenhouse gases
consequences of global warming
melting polar ice increased frequency of extreme weather increased forest fires decrease in availability of water world food production may decrease increase in CO2 in oceans will decrease pH which threatens organisms.
