ecosystems
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127 Terms
temp
pH
light intensity + wavelength
availability of water
CO2 conc.
O2 availability (aquatic)
salinity
wave action
aspect (north, south etc )
feeding by other organisms
competition for (food,territory etc)
adaptation
disease
more plants means more animals
constant conditions so not extreme up and downs
temp is very up and down
features - easily worked and warmed
drainage - water passes through rapidly causing leaching of minerals
features - heavy, hard to work and warm
drainage - easily waterlogged, no mineral leaching
features - heavier than sand, easier to work and warm than clay
drainage - less prone to waterlogging and leaching
\- amount of shade
\- changes in climate
\- distance from sun
\- area
\- time of year
animals depend on plants for food + shelter
\- distance from body of water
\- climate (rain)
\- rate of evaporation
plants need water for structure and transport mechanisms
\- flow of water (faster has more O2)
\- particle size (in soil)
no O2 = no plants and animals
how does wind and currents affect organism distribution
wind increases water loss from the body and cooling
high winds can damage or even destroy habitats making it difficult for organisms to live there
currents can be strong so organisms living there have to be strong swimmers or can attach to a surface
what is intraspecific competition
competitions between organisms of different species
what is interspecific competition
competition between organisms of the same species
what are biotic factors that affect the distribution and abundance of organisms
- competition for a mate
- competition for territory
- disease/parasites
- predation
how does predation affect distribution of animals
influences the abundance of organisms in an ecosystem
pop. sizes of predators and prey fluctuates with the size of one influencing the size of another
they are expected to show a regular cycle where the pop. of predators is out of phase with the pop. of the prey
how does grazing affect distribution of plants
animals eat plants = less of them in an area
how does finding a mate affect distribution of animals
vital for reproduction
likelihood of finding a mate will determine the organisms which are found in a habitat
how does territory affect distribution of animals
territory is an area held and defended by a animal
they have different functions depending on what animal but it is often used to ensure an animal has sufficient resources to raise young
how does competition for light, space and water affect distribution of plants
need to compete for resources for photosynthesis and space to grow
how does parasitism and disease affect distribution of animals
parasites and disease will weaken animals which means they may not reproduce or hunt well so are more likely to get caught
parasites and disease will be spread more rapidly when there is a high pop. density
how does parasitism and disease affect distribution of plants
disease will weaken plants = less likely to grow and reproduce
what is a density dependent factor
wjhere the size of a pop. affects the mortality rate + pop. growth
these factors tend to limit the abundance of a species
always biotic
e.g. competition for food and space
what is a density independent factor
where the pop. size has no affect on morality rate
there factors tend to limit the distribution of a species
usually abiotic
e.g. temp. drop, introduction of toxins
what is abundance
the no. of organisms relative to the numbers of other organisms in the same habitat
what is distribution
where a species is found in the environment + how it is arranged
patterns are either: random, uniform or clumped
what is random distribution
typical of species in which individuals do not interact strongly
usually plentiful resource
what is uniform distribution
typical of species in which individuals compete for a scarce environmental resource
territories may be very large
what is clumped distribution
may show a patchy distribution of resources
most common, seen in herds where there are specific resources
what are 2 ways of assessing abundance and distribution
quadrats ( or point frame quadrats)
line or belt transects
ACFOR scale
discuss quadrats
can be open or gridded
a no. of reading taken to get a mean abundance or distribution
open is to measure the no. of organisms
gridded to measure % cover
limitations = area you can sample, decisions must be made about whether to include organisms partly covered by the quadrat , randomness about sampling area
discuss point quadrats
used to measure % cover
horizontal bar with set intervals where a pin is dropped. the species that touch the pin are recorded
limitations = tricky to set up, can easily lose parts
discuss ACFOR scale
it is a way of measuring abundance
A= abundant
C= common
F = frequent
O= occasional
R = rare
limitations = subjective, no set definitions to each term, species can be easily rated on how obvious they are rather than how abundant they are
discuss transects
transects are used to investigate whether the distribution of an organism is affected by an abiotic factor
line transect - stretch 2 tapes across 2 points, record the species that touches the tape
belt transect - lay 2 tapes and observe the ground between them
random sampling
diff. between 2 areas/methods or estimate abundance in an area
systematic sampling
look at effect of abiotic factor which changes along a gradient/transect on distribution
what is the spearman’s rank correlation coefficient and when would you use it
statistical tool used to test whether 2 variables are significantly correlated
use if looking for a correlation between 2 thing in one area (if carrying out a transect)
how are the results of a spearman’s rank interpreted
+1 indicates a perfect positive correlation
-1 indicates perfect negative correlation
0 indicates no correlation
what is a student t test
statistical test used that allows you to judge whether any diff. in the means of 2 sets of data is statistically significant
use if looking for a difference between 2 areas (if carrying out random sampling)
how are the results of a student t test interpreted
t value calculated is compared to critical value in table for a particular p value chosen
if t value is greater than the critical value, the difference is statistically significant
how do light traps work
they are used at night - flying insects are attracted to the light, they are then trapped
limitation of light traps
- don’t know where they have come from - useful for abundance but not good for distribution
- only night flying animals
how does mark, release, recapture work
trap some animals, mark them, release them
go back later and re-capture
count how many are marked = more unmarked means bigger pop.
limitations of mark , release, recapture
could by chance get all the same ones if they live in a small area
can be difficult to catch animals
cannot mark them in a way that will affect their survival
how does tree beating work
net under tree, shake branch, organisms fall off
limits of tree beating
won’t get all the organisms
higher up won’t drop down
animals will hold on , birds will fly away
how does roadkill work
look at no. of dead animals
high no. of roadkill suggests high pop.
limits of roadkill
factor in traffic density
animal intelligence
what are trophic levels
describe the position of an organism in a food chain/web
describes the feeding relationship with other organisms
who proposed the model of a food chain
Charles Elton in 1920
name and describe the trophic levels
producers - make food by photosynthesis e.g plants and algae
primary consumers - organisms that eat producers, herbivores
secondary consumers - animals that feed on herbivores, carnivores
tertiary consumers - animals that feed on carnivores, usually top predators
decomposers - microorganisms that break down remains of animals + plants to return minerals into the environment
what are the issues with a food chain
few animals only eat one thing - a complex food web is more accurate
single food chains are unstable and can be easily disrupted
complex food webs are more stable as there are multiple food sources
how can the ecosystem structure be represented
- pyramid of numbers
- pyramid of biomass
- pyramid of energy
what is a pyramid of numbers
represents the no. of organisms at each trophic level in the food chain
+ easiest to measure
- can be distorted by large organisms
what is a pyramid of biomass
shows the biomass of organisms at each trophic level in the food chain
+ more accurate than no.
- dry mass is very accurate but you have to destroy the material as wet biomass is very inaccurate. need to take a small sample which doesn’t show the whole picture
what is a pyramid of energy
represents the total energy store of the organisms at each trophic level in a food chain
+ most accurate
- hardest to measure, use an outdated definition of energy
how is energy transferred at each trophic level
only a small amount of energy is passed on at each trophic level and some energy is never taken in due to:
some parts of food isn’t eaten
some food is indigestible
plants can’t use all light energy as it is sometimes the wrong wavelength
why is energy lost along a food chain
lost to animals as undigested
exothermic processes which loses energy
some plant material is lost in metabolic waste products
what is Gross Primary Production (GPP) in plants
the rate at which light from the sun catalyses the production of new plant material (energy transferred to primary consumers)
what is Net Primary Productivity (NPP)
the material produced by photosynthesis stored as new plant body material
depends upon abiotic and biotic factors
how do you work out NPP
NPP =GPP - R (respiration)
what is the role of microorganisms in a ecosystem
they recycle nutrients back into the environment
what is the nitrogen cycle
recycling of nitrogen between living things and the environment by the actions of microorganisms
describe the role of microorganisms in the nitrogen cycle
nitrogen-fixing bacteria in soil and roots convert nitrogen gas in air into ammonia
nitrifying bacteria oxidise ammonium compounds into nitrates and nitriles
denitrifying bacteria convert nitrates in soil into nitrogen gas in the air
what is the carbon cycle
series of reactions by which carbon is constantly recycled between living things and the environment
what is a carbon sink
is a reservoir where carbon is removed from the atmosphere and ‘locked up’ in organic and inorganic compounds
what is the statistical analysis paragraph
my calc. value of … is higher/lower than the CV of … at p=0.05 level therefore i can reject/accept H0 and conclude there is/is not a significant difference/correlation between x and y.
i can be 95% sure this diff/correlation did not occur by chance (if reject H0)
there is more than a 5% chance that any diff./correlation shown did occur by chance (if accept H0)
what is succession
the long term changes in the composition of a community eventually leading to the development of a stable community
what is primary succession
occurs when an area previously devoid of life is colonised by communities of organisms
e.g. after the eruption of a volcano which has led to the formation of a rock surface
what is secondary succession
occurs with existing soil that is clear of vegetation
may occur after an event such as a forest fire
what is climax community
the end point of succession, where the community is in equilibrium with the environment and is stable
what is sere
succession from bare ground
what is the serel stage
different communities/stages in a succession
what is an xerosere
succession beginning in dry conditions
what is hydrosere
succession beginning in water
what is plagioclimax
a climax community that is at least in part due to human intervention
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