20.1 Population Growth Flashcards
Population density
The number of organisms in a given are or volume
D= (number of organisms)/ (area)
Three theoretical distribution patterns for populations
Uniform
Random and clumped
What affects population density estimates?
population distribution
Random Distribution (3)+ex
Occurs when resources are very abundant and population members do not have to compete with one another or conversely group together for survival.
Individuals or pairs of organisms are distributed throughout a suitable habitat with no identifiable pattern.
Ex: Individual bull moose or female moose with calves sometimes exhibit a random distribution pattern.
Random distribution in nature is rare.
Clumped distribution (3)+ex
More common
Members of a population are found in close proximity to each other in various groups within their habitats
Most populations, including humans exhibit a clumped pattern of distribution, congregating in an area where food, water of shelter is most abundant.
Ex: Aspens: they reproduce asexually by sprouting new trees from the roots of older trees, they grow in groves, resulting in their clumped pattern of distribution.
Uniform distribution
Individuals are evenly spaced over a defined area
Ex: Artificial populations such as plants growing in orchards or agricultural fields
A population’s size directly depends on
how much and how fast it grows
4 processes that can change the size of a population:
- Births
- Immigration (Movement of individuals into a population) Increase population size
- Deaths
- emigration (movement of individuals out of a population) decrease in population size
Change in population size equation:
Change in population size= (Births+immigration)-(Deaths+emigration)
Discuss immigration and emigration affect on population sizes:
In nature, these processes can result in gene flow between populations, but they often occur in equal amounts or in such low numbers that they are difficult to measure or do not significantly affect the sizes of the populations.
Population explosion: (Ex)
A population increase that grows so rapidly that it spreads before it can be contained
- Invasive species
Population crash
Population decrease so rapidly
Growth Rate (gr)
The change in the number of individuals in a population over a specific time frame
Formula for Growth rate+ its usage
gr= (change in number of individuals)/time
- Used to measure increase or decreases in population size over time
Per capita growth rate (2)
The rate of change per individual
Like cgr, it can be negative if deaths and emigration outnumber births and immigration
Formula for cgr and its usage: (4)
cgr= (Change in number of individuals *final-initial)/ (the original number in the population)
- To compare populations of the same species that are different sizes or live in different habitats
- Multiply by 100 to show the percent the population has grown
- The amount that a population size has changed in relation to its original size
Biotic potential (3)
the highest possible per capita growth rate for a population
the maximum amount of offsprings an individual can produce with unlimited resources
- a population growing at its biotic potential would be expected to grow exponentially
factors that determine a species biotic potential: (4)
- Number of offsprings per reproductive cycle
- the number of offspring that survive long enough to reproduce
- the age of reproductive maturity and the number of times that the individual reproduce in a life span
- the life span of the individual
Exponential growth pattern
a J shaped curve
Logistic growth pattern
- S shaped
If growth is limited by resources such as food, the exponential growth of the population begins to slow as competition for those resources increases. The growth of the population eventually slows nearly to zero as the population reaches the carrying capacity (K) for the environment.
Carrying capacity (K)
The theoretical maximum population size that the environment can sustain over an extended period of time
The number of individuals in a population that can live in a given environment without depleting the resources they need or harming their habitat or themselves.
density dependent factors (3)+ex
biotic
when a population is small and below the carrying capacity of the habitat, density dependent factors do not limit growth
impact increases with the density of the population
-ex: parasite/predators
density independent factors
abiotic
- ex: harsh winter/floods/forest fires
limits growth regardless of the size of density
Environment resistance
prevents population from growing at its biotic potential and determines the carrying capacity of the habitat.
