Populations

• Population growth is increased by births and immigration and decreased by emigration and deaths
• Population growth rate = change in population / initial population size
• The population growth curve begins with a lag phase as the microorganisms adjust, then the log phase of exponential growth, followed by the stationary phase as resources are limited, the decline phase occurs due to lack of nutrients and buildup of toxic waste
• In the stationary phase birth rate = death rate
• A logarithmic graph allows for linear graphs which dont run off of the page and allow readable results, representing all points
• Carrying capacity is the maximum population that an environment can sustain
• Carrying capacity is determined by limiting factors such as disease, competition, food and habitat availability and predation
• Limiting factors cause fluctuations in population as species adjust, for example, overpredation of rabbits causes starvation of predators and an increase in rabbit population
• Abiotic factors involved in maintaining an ecosystem include light, temperature, ph and water availability
• Animals can compete for food, water, mates, habitats or space
• Intraspecific competition is between members of the same species
• Interspecific competition is between different species, this wont be for mates
• A species with a competitive advantage will lead to one species outcompeting the other for resources
• Random sampling in a large population removes bias as it is representative
• Reliability is where results can be repeated with similar results
• Validity will occur when control variables dont change and the sample hasnt been affected by more than one independent variable
• Accuracy is determined by using a higher resolution, for example, using smaller intervals on a ruler to find to a greater degree of accuracy
• A line transect will involve any species touching the line to be recorded, this may be less representative as it excludes organisms
• A belt transect can be even or interrupted, quadrats are placed along the line and any species within is recorded
• A species which is less evenly distributed should be recorded with more smaller quadrats than less larger ones
• The greater the number of quadrats taken, the more reliable and representative the results are
• Percentage cover = number of hits or species touched / total number of pins
• Abundance is the number of individuals in a species in a given area, it can be measured with density, frequency, biomass or percentage cover
• Density is the mean number of individuals per unit area
• Frequency as a measurement provides no information about distribution or data or actual numbers of species
• Percentage cover is an estimate of the area in a quadrat covered by a species, however, it can be difficult when organisms overlap one another
• Biomass will reflect the productivity of a site by measuring the energy stored, however, organisms need to be harvested which is time consuming
• Capture recapture is where some organisms of a species are captured, marked, released and then recaptured, the total in the recaptured population that are marked are compared to the unmarked and this represents the proportions in an area
• The mark used in capture recapture should be non removable, shouldnt impact hunting or predation, shouldnt harm the animal or prevent reintegration into the population
• The lincoln index assumes no immigration and few deaths and births, it assumes that the marking is non toxic and wont rub off
• In capture recapture, it is important to allow time for redistribution of animals into the population so the recapture is representitive
• A community is all the plants and animals occupying an area
• A community is constantly changing from its origin to its climax, this is called succession
• In the primary stage of succession, pioneer species such as algae are adapted to survive in a hostile, abiotic environment, eg, extreme pH
• Adaptations of the pioneer species such as algae include wind dispersed seeds, asexual reproduction, photosynthesis and nitrogen fixation
• In stage 2 of succession, the environment changes and soils will emerge from weathered rock, pioneer species die and decompose, providing nutrients and changing the environment for colonisers who will outcompete the pioneer species
• In stage 3 of succession, secondary colonisers will continue to weather rock and increase organic matter, changing the abiotic environment to become more suitable for new species which out compete the secondary colonisers
• In stage 4 of succession, new food sources from new colonising species will cause animals to colonise, conditions become stable, increasing diversity, the climax community is the final stage of succession
• Climax communities are stable and a dominant species is influenced by the climate, eg, tall trees in england
• Succession can be from secondary succession, this is where an existing community has been cleared by fire or farming, leaving soil intact