Population Ecology Flashcards
Population ecology
Explores how biotic and abiotic factors influence the density distribution size and age structure of populations
Population
A group of individuals of the same species that live in the same area
Density
Number of individuals per unit area or volume (how many units in a given space)
Dispersion
Pattern of spacing among individuals
B.I.D.E. model
Increase/decrease in local density (B.I. = increase, D.E. = decrease)
- birth
- immigration
- deaths
- emigration
3 types of dispersion:
- clumped dispersion
- uniform dispersion
- random dispersion
Clumped dispersion
Individuals aggregate in patches
-things that give rise to clumped dispersion are resource distribution/availability and behavior
Uniform dispersion
Individuals are evenly distributed
-given rise by social interactions (territoriality)
Random dispersion
The position of each individual is independent of other individuals
-given rise by absence of strong attractions or repulsions
Demography
Study of population attributes and how they change over time
- composition of the population (population structure)
- rates that describe population change
Population structure
- sex ratio = number of males:number of females
- age structure = percent of individuals in different age groups in the population
- age groups based on reproductive status (pre-reproductive, reproductive, post-reproductive)
Population structure shapes
- urn-shaped: a few kids, many parents, even more seniors (non-growing or declining population)
- pyramid-shaped: lots of kids, some parents, fewer seniors (rapidly growing population)
- bell-shaped: some kids, more parents, few seniors (slow [non] growing population)
Population rates
- birth rate = number of births/population size
- fecundity/fertility rate = number of offspring per unit time
- death rate = number of deaths/population size
Generation time
Average amount of time between the birth of an individual and the birth of its offspring
Survivorship
Tracks the changes in the number of individuals in a cohort over time
Cohort
Group of individuals born at the same time
3 types of survivorship curves
- type I = low death rates during early and middle life then an increase among older age groups (humans)
- type II = the death rate is constant over the organism’s life span (rodents)
- type III = high death rates for the young then a slower death rate for survivors (oysters)
Rate of increase
- r = per capita birth rate - per capita death rate
- r = b - d
- exponential growth model: dN/dt = rN
- N = number of individuals in the population
- t = time
Exponential growth
Rate of increase (r) determines speed at which population size increases
- when population grows, eventually something will give out (resources, disease, accidents/disasters)
- populations cannot exponentially grow forever
2 controls on population size
- density-independent controls
2. density-dependent controls
Density-independent controls
Not sensitive to size of population
-i.e. disasters, etc.
Density-dependent controls
Sensitive to density of population
- changes as size of population increases
- i.e. competition, disease, predation
Logistic growth
Some populations will increase then level off
-point of population stabilization = carrying capacity (K)
-exponential growth + a “buffering” term that keeps the population at/near carrying capacity (K)
-change in a population over time (dN/dt) =
rN * (K-N)/K
-(K-N)/K describes density-dependent control
