population size and ecosystems Flashcards
how are ecosystems dynamic?
- intensity of energy flowing through varies
- biological cycles vary mineral availability
- habitats change as succession occurs
- species arrive and leave
what determines population size?
- birth rate (hatching, binary fission)
- death rate
- immigration
- emigration
fugitive species
- poor at competition
- rely on large scale reproduction and dispersal
- invade new environments rapidly
e.g. algae colonising bare rock
equilibrium species
- control population by competition in a stable habitat
- sigmoid (s-shaped) curve of growth = one-step growth curve
e.g. bacteria in fresh nutrient solution
lag phase
- period of slow growth, adaption or preparation for growth
- cells adjust to new conditions
- intense metabolic activity for enzyme synthesis
- the time to reach sexual maturity, find a mate and gestate young in sexually reproducing organisms
log/exponential phase
- numbers increase, more individuals available for reproduction
- no factor limiting growth
- bacterial population doubles per unit time
- cell numbers increase logarithmically
stationary phase
- birth rate = death rate
- maximum population, fluctuates around carrying capacity in response to environmental changes
death phase
- factors that slow population growth become more significant
- negative gradient
environmental resistance
environmental factors that slow population growth
environmental resistance examples
- food availability
- overcrowding (not enough space or nesting sites)
- competition
- accumulation of toxic waste
biotic
a part of the environment of an organism that is living
biotic factors examples
- predation
- parasitism, disease (infection spreads rapidly)
- competition for other species for nesting sites and food
abiotic
a part of the environment of an organism that is non-living
abiotic factors examples
- temperature
- light intensity
- oxygen availability
predator prey relationships
- negative feedback
- abundance of prey limits the number of predators that can survive, and the number of predators controls the number of prey
- e.g. snowshoe hare and lynx
density dependent factors
environmental factors that affect a greater proportion of the population if the population is denser
- biotic factors (disease)
e.g. parasites are transmitted more efficiently so a larger number are effected
e.g. higher prey density = predators encounter more prey = more prey eaten
density independent factors
abiotic factors (suddenly change) in the environment that don’t depend on population density
same effect regardless of population size
e.g. flood, fire
carrying capacity
the maximum number around which a population fluctuates in a given environment.
around a set point
why are physical features in a habitat described first?
physical features (soil type, temp) determine the number and types of plants
animals present depend on the types of plants
abundance
the number of individuals in a species in a given area or volume
a measure of how many individuals exist in a habitat
measuring animal abundance
- capture-mark-recapture for moving organisms, using lincoln index
- kick sampling in a stream and counting invertebrates. unreliable if misidentified, escaped or miss the net
capture mark recapture assumptions
- few/no deaths or births
- no immigration or emigration
- marked individuals redistribute themselves evenly among the population
- all organisms have equal chance of capture/recapture
- marking method is not toxic / doesn’t make more conspicuous to predation
- marking is not lost
measuring plant abundance
- quadrat. calculate mean no. individuals in known area to find density
- estimate % cover with individuals hard to recognise
- estimate % frequency
distribution
the area or volume of which the organisms of a species are found