Population size and ecosystems

What are 4 factors controlling population size?

varying intensity of energy flowing through the ecosystem, mineral availability varied by biological cycles, succession changing habitats over time, new species arrive and some species become absent

What is the number of individuals in a population determined by? (4)

birth rate, death rate, immigration, emigration

Population

an interbreeding group of organisms of the same species occupying a particular habitat

Birth rate (2)

reproductive capacity of a population, number of new individuals derived from reproduction per unit time

Immigration

permanent movement of individuals into a population of the same species

Equilibrium species

species that control their population by competition rather than by reproduction and dispersal

Emigration

the movement of individuals out of a population of the same species or specific habitat

Trophic level

position of organism in a food chain

Fugitive species

species that control their population by having a large capacity for reproduction and dispersal to increase their numbers

What are the 4 phases of an equilibrium species one-step growth curve?

lag phase, exponential/log phase, stationary phase, death phase

What occurs during the lag phase? (2)

first population does not increase, then a period of slow growth

What happens in this period of slow growth related to bacteria? (3)

it is a period of adaptation or preparation for growth with intense metabolic activity, enzyme synthesis, DNA replication

What is this lag phase related specifically to sexually reproducing organisms like rabbits? (2)

it represents the time to meet sexual maturity, find a mate and gestate their young

What occurs during the exponential phase as long as their is no limiting factor for growth?

more individuals become available for reproduction

What occurs during the exponential phase for bacteria?

bacterial cells divide at a constant rate and population doubles per unit time

Why is the exponential phase also known as the log phase?

because the cell number increases logarithmically

Why can’t the rate of increase be maintained indefinitely? (4)

environmental resistance, like less food available, concentration of waste products becomes more and more toxic, not enough space or nesting sites

Why does the gradient of the graph eventually decrease during the exponential/log phase?

the population size still increases but at a slower rate

What are 4 examples of factors that limit the growth of bacteria in a flask?

available food, overcrowding, competition, accumulation of toxic waste

What should you refer to the ‘birth rate’ as when talking about microorganisms?

cell reproduction

What are biotic factors that limit population increase in less artificial situations like rabbits on an island? (3)

predation, parasitism and disease, competition for nesting sites and food

How does parasitism and disease become more of a threat as population size increases e.g. for rabbits on an island?

increased population density allows infection to spread more rapidly

What are 2 abiotic factors that limit population size?

temperature, light intensity

What occurs during the stationary phase? (2)

the birth rate of the population is equal to the death rate of the population, the population fluctuates around the carrying capacity in response to environmental changes

What environmental changes cause these fluctuations around the carrying capacity in the stationary phase? (2)

food availability, number of predators

What occurs during the death phase? (3)

factors that slow population growth at the end of the log phase become more significant, so population size decreases until the death rate is greater than the birth rate, the graph now has a negative gradient

When and how would you calculate population increase from a graph? (3)

when a population increase is very large, a log10 scale is used, each mark on the scale is 10 x the previous mark

What is environmental resistance?

environmental resistance refers to environmental factors that slow down population growth

Biotic (2)

a part of the environment of an organism that is living, e.g. pathogens and predators

Abiotic (2)

a part of the environment of an organism that is non-living, e.g. air temperature, oxygen availability

Carrying capacity

the maximum number around which a population fluctuates in a given environment

Saprobionts (2)

mostly bacteria and fungi, microorganisms that breakdown dead and waste organic matter to obtain nutrients

How do you calculate the rate of growth in the exponential phase?

(number of bacteria at day 9 - number of bacteria at day 4) / 9 - 4, CANNOT read actual numbers at day 9 and 4, use antilog of the number on the scale

How do you find the antilog on the calculator when log is not a whole number?

press shift log

What are density-dependent factors? (2)

factors that affect a higher proportion of the population when their distribution is denser, biotic factors

What are density-independent factors? (2)

the effect of abiotic factors in the environment, their effect is the same regardless of population size

What are some examples of density-dependent factors/biotic factors? (4)

disease, parasitism, depletion of food supply, higher prey density

What are some examples of density-independent factors/abiotic factors? (2)

flood, fire

How are the numbers in a population regulated by negative feedback if population rises above the set-point?

a density-dependent factor increase mortality or reduces breeding to such an extent that the population declines

How are the numbers in a population regulated by negative feedback if population falls below the set-point?

environmental resistance is temporarily relieved so that the population rises again