Population and ecosystems

What factors affect population size + when will they increase?

• birth + death rate and immigration + emigration

• when birth + immigrants > deaths + emigration

community

all population of 2 or more species living in the same habitat at the same time

define niche

role + position a species has in it's environment

ecosystem

community of living organisms interacting with the abiotic factors that influence them

population

group of interbreeding individuals of same species found in particular habitat at a time

habitat

physical environment where population/community is found

environment

set of external conditions like biotic + abiotic factors that surround organism

carrying capacity

max population size the environment can support

describe the lag phase

• period of slow increase in population

• for bacteria it's for adaptation or prep for growth e.g. yeast cells adjusting + producing digestive enzymes

• for sexually reproducing organisms its time to reach sexual maturity

describe the exponential (log) phase

• rapid reproduction rate

• no limiting factors so rate of cell division is at max = population increases

• good supply of nutrients + waste is in low conc

describe the stationary phase

• birth rate = death rate

• population has reached carrying capacity

• limiting factors like waste accumulation prevent further pop increase

describe the death phase

• factors slowing population growth become significant e.g waste accumulation

• death rate > birth rate

• population decreases

What is different about population growth in natural environment?

• after log phase pop reaches carrying capacity

• pop reached equilibrium (number slightly fluctuates about carrying capacity)

What causes lag phase in sexually + asexually reproducing organisms?

sexu - number of individuals that can reproduce in pop

asexu - amount of nutrients in environment

factors regulating population increase

-density dependant factors (biotic)

-density independent factors (abiotic)

how is population size regulated?

-negative feedback

-if population rises above set point DD factor increases mortality to reduce size

-if population decreases below point environmental resistance is temporarily relieved to allow increase

interspecific competition

competition between individuals of different species

intraspecific competition

competition between individuals of same species